Proceedings of the 15th REHVA HVAC World Congress - CLIMA 2025

Table of Contents

1. New HVAC Components and Systems

   1. Frontmatter

   2. Refrigerant R-454C for the European Heat Pumps Strategy: Efficiency, Safety and Circularity

      Fabrizio Codella, Hans-Dieter Küpper

      Abstract

      European policies are shaping the future of heating in buildings. On the one hand, there are Green Deal Industrial Plans targeting to phase out most stand-alone boilers and decarbonize heating by widely adopting heat pumps; on the other hand, one of the heat pumps’ key components, fluorinated refrigerants, is strictly regulated.

      The use of low GWP (Global Warming Potential) refrigerants is one viable approach for increasing heat pump installation while reducing emissions. This study is particularly focused on R-454C because of its low GWP, favorable safety profile, performance and circularity. Furthermore, R-454C has handling practices that are extremely similar to refrigerants that have been used for decades, making it easier for technicians to accept and use. This HFO refrigerant requires less training effort to grow and convert specialists from other fields.

      It is widely recognized that the effects of direct refrigerant emissions on climate change are significantly less than the indirect impact of energy consumed by the heat pump during its whole lifetime. That is why, in this study, the level of optimization achievable when using R-454C to develop new heat pumps with remarkably high efficiency is investigated. Based on experimental data from a third-party research institute, the benefits of employing optimized R-454C heat pumps to enable European decarbonization of heating strategies, reduce energy consumption, and greenhouse gas emissions, have been assessed.

   3. Holistic Optimisation of a Plus Energy House with Hydrogen Storage

      Mara Magni, Fabian Ochs, Elisa Venturi, William Monteleone, Alice Tosatto, Georgios Dermentzis, Harald Malzer, Daniel Oberschmied

      Abstract

      Within the framework of the European project REN+HOMES, a seven-storey demo multi-apartment building (MAB) will be built in the city centre of Innsbruck (AT) with the goal of demonstrating the possibility and challenges of achieving a positive energy balance. The MAB will be built with a very high envelope quality and MVHR (i.e. Passive House Premium certified) and with shower drain water heat recovery. A very efficient low-temperature heat emission and distribution system combined with a central groundwater heat pump for domestic hot water (DHW) production and space heating allows very low electricity demand, such that on-site PV, partly on the roof and partly on the façade can cover it. Batteries for short-term storage and a hydrogen system for seasonal storage complete the system. Another novelty of this project is that the waste heat of the hydrogen storage will be integrated into the building to cover part of the DHW, increasing the efficiency of the system. Within this work, a holistic analysis of the MAB with 7 storeys, 42 flats and a treated floor area of 2838 m² is performed aiming at optimising the size of the hydrogen system, PV and battery storage also considering different scenarios for the electricity demand of the appliances and control strategies that allows an increase of direct PV self-consumption. The parametric study is performed by means of dynamic simulations in Matlab/Simulink and the results show that the net positive balance can be achieved, but building-level autarky could only be achieved with off-site PV.

   4. Numerical Study of Dynamic Adaptability for Flat-Plate Solar Evaporators Subjected to Transient Radiation Conditions

      Santiago Valencia-Cañola, Federico Méndez, Carlos A. Bustamante

      Abstract

      Sustainable and more efficient thermal technologies can contribute to meeting carbon reduction goals and reduce the electric energy demand around the world. A large part of thermal and refrigeration systems uses heat exchangers to carry out evaporation processes of different working fluids. One of the main advantages of these subsystems is that they can use renewable thermal energy sources such as solar radiation. However, the design of the thermal and refrigeration devices is normally given for specific operating conditions, while the source of solar radiation is variable over time. System high sensitivity to operating conditions leads to the need of real time adaptability to variable energy sources, to maintain their efficiency. In this study, the dynamic performance of a flat-plate solar evaporator with R1234yf as working fluid is assessed by means of a validated two-phase mixture numerical model at typical solar radiation conditions in Ciudad de México (CDMX), México. The behavior of the heat exchanger is assessed in terms of temperature and pressure, and an adaptability mechanism is proposed by varying the inlet mass flow according to the solar energy availability. In consequence, complete evaporation process and admissible outlet pressure range are guaranteed. Results show that the system is stable for a wider operation time range in comparison to the base system. This analysis can contribute to expanding the operating ranges and improving the efficiency of novel thermal systems such as solar ejector refrigerators or direct-expansion solar heat pumps.

   5. Infrared Heating for the Decarbonisation of Existing Buildings - Study on Different Building Types and Interaction with the Electrical Grid

      Joachim Seifert, Andrea Meinzenbach, Lars Schinke, Martin Knorr, Alf Perschk

      Abstract

      Infrared heaters are systems that have not been widely used in the building sector in the past. However, with the EU’s target of decarbonizing the building sector, IR heating systems can represent an interesting technical solution option as a hybrid system in combination with heat pumps. The water-based heating system is used as the basic system and the IR heating system covers the peak load. The following publication presents the results of several studies on this topic and shows the advantages and disadvantages of IR heating.

   6. Numerical Evaluation of the Effect of the Wettability of the Plates on the Performance of Indirect Evaporative Cooling Systems

      Roberta Caruana, Luca Marocco, Stefano De Antonellis, Manfredo Guilizzoni

      Abstract

      Indirect Evaporative Cooling (IEC) systems exploit the latent heat of water vaporization to lower the temperature of an air stream, thus allowing to refrigerate an environment with reduced energy use compared to conventional air conditioning technologies. Several literature papers have shown that it is desirable that the plates of IEC recuperators are as uniformly wet as possible to promote water evaporation and improve the system performance. However, an accurate assessment of how plate wettability affects the effectiveness of IEC heat exchangers is difficult to obtain by means of experiments. As a consequence, in this study, a Computational Fluid Dynamics model, supported by experimental validation and which integrates a lumped parameter model to account for film evaporation, has been employed to estimate the potential impact of the plate wettability on the cooling performance of a cross-flow IEC heat exchanger. Specifically, a wide range of values of the wetting parameters was used as input for the numerical simulations, showing that a reduction of the plate contact angle, namely an increase in the wettability of the plates, improves the system effectiveness, as expected. However, for the analyzed recuperator, there is a flattening of the performance for plate contact angles lower than 50°, probably due to the intrinsic performance limitations of the cross-flow recuperator.

   7. Comfort Evaluation Method for Personal Comfort Systems Considering Latent Heat Losses

      Yuki Uchiyama, Masanari Ukai, Kazuki Aono, Yoriaki Nitta, Kaho Kodama, Chiaki Shimoyama, Hikari Ryuzaki, Momoka Watanabe, Shin-ichi Tanabe

      Abstract

      In recent years, offices have tended to emphasize the comfort of individual office workers. Equivalent temperatures using thermal manikins have been used to assess the performance of PCS. However, the equivalent temperatures do not consider latent heat losses such as respiration, dead heat excretion and perspiration. The performance evaluation of PCS needs to take latent heat loss into account. Therefore, the amount of sensible and latent heat loss during PCS use was analyzed. In addition, a new thermal environment evaluation index called site-specific ET*, which takes latent heat loss into account, was proposed and the cooling effects of each site were verified and analyzed under sitting rest. The results showed that under condition, the site-specific ET*, which considers latent heat losses, showed a greater temperature decrease due to airflow exposure than the equivalent temperature used to assess the performance of conventional PCS, indicating that latent heat losses influence the temperature experienced when using PCS.

   8. Laboratory with Three Different Radiant Systems Cooperation with Heat Pump

      Martin Šimko, Dušan Petráš, Daniel Szabó, Lukáš Živner

      Abstract

      The paper deals with the description of the laboratory of large-scale radiant systems and the experimental measurement of the operation of the air/water heat pump in connection with three large-scale radiant systems in cooling mode. The measurements showed that the average cooling performance of the ceiling radiant system of 28.56 w/m² compared to the wall radiant system of 31.56 W/m² and the floor radiant system of 25.02 W/m² did not reach the highest value, but it was able to ensure the most favorable indoor air temperatures. Radiant systems achieved satisfactory results in the cooling mode in terms of ensuring the average indoor air temperature. The efficiency of the heat pump in the cooling mode indicated by the manufacturer with an EER value of 4.52 was compared with the calculated SPF value of 5.06 during the measured period and it can be concluded that the efficiency of the HP declared by the manufacturer agrees with the calculated efficiency of the HP and even exceeds it.

   9. Ventilation Systems Adaptation to the Increasing Global Carbon Dioxide Concentration and Options for Mitigating the Consequences Over Their Performance

      Ivan Dimchev, Martin Ivanov, Angel Terziev

      Abstract

      The level of carbon dioxide in the outdoor air has risen significantly over the past 50 years by nearly 100 ppm. CO₂ is the most important factor contributing to global warming. If the concentration continues to rise at the same rate, it is expected to reach nearly 500 ppm by 2050. This study aims to analyze the negative consequences over performance of the HVAC systems due to the increased out-door air CO₂ concentration and the possible options for mitigating this effect, since this change will lead to a requirement to increase the air flow rates with which the ventilation systems work in order to maintain the same indoor air quality in the occupied premises. As a result, it is necessary to apply a new approach, both in the design of HVAC systems, and in the maintenance and renovation of existing systems. The current European requirements, on the basis of which numerous standards and regulatory norms of the EU member states have been pre-pared, are nearly 25 years old. Therefore, it is possible that in the near future many buildings will end up with ventilation systems that are not capable of fully performing their function. In the deep renovation, this effect will also have a significant impact. These changes, in addition to the efficiency and energy consumption of the ventilation systems, also increase the investment costs with around 17.4%, as well as there will be the need for larger spaces in the buildings for both equipment and ductwork.

   10. Development of a Metamodel for the Optimization of the Energy Performance of Cold Food Warehouses

       Aleksandr Gevorgian, Giovanni Pernigotto, Andrea Gasparella

       Abstract

       Cold storage is essential in the perishable-goods supply chain, yet its HVAC systems remain highly energy-intensive. This study presents a machine learning (ML) metamodel trained on EnergyPlus simulations and integrated with reinforcement learning (RL) for adaptive, closed-loop control of HVAC–PV–battery interactions. Replacing static sizing methods, the metamodel explores system parameters and identifies optimal insulation levels and PV–battery configurations. It selects 25 south-facing, 10 east-facing, and 15 west-facing PV panels (17.5 kWp total), generating 8,163 kWh/year, and a 16-kWh battery that supports 7,342 kWh/year of solar self-consumption. The framework supports planning-based control over future horizons, maintaining simulation-level accuracy with a 60% reduction in computational time. It maintains optimal indoor conditions within allowed HVAC bounds (temperature: − 0.5–4 ℃, humidity: 75–90%, airflow: 1,000–8,000 m³/h) to prevent beef carcass spoilage and increase renewable energy use. The approach lowers annual HVAC energy consumption by 14% (from 11,591 to 9,968 kWh) and grid reliance by 38% (from 4,249 to 2,626 kWh/year). Using sequential predictions, the RL agent anticipates how present actions affect future energy flows, battery levels, and indoor conditions, supporting proactive control. Unlike reactive or MPC-based methods, this forward-looking framework can handle variability—such as weather shifts or irregular meat loading—improving energy efficiency, preserving food quality, and reducing CO₂ emissions. It offers a scalable and practical solution for real-world cold-storage management.

   11. Renewable Energy and Self-sufficiency in High-Altitude Alpine Historic Farmstead: A Design Workflow for Optimizing Solar and Water Solutions

       Benedetta Colombo, Anna Comi, Elena Lucchi

       Abstract

       The conservation and adaptation of historic buildings in high-altitude environments presents unique challenges, particularly in integrating renewable energy solutions for energy self-sufficiency. The study focuses on the restoration of Monte Fontana Secca and Col de Spadaròt, a 150-hectare alpine farmstead located on the Monte Grappa Massif (Belluno, Italy), and owned by the Fondo per l’Ambiente Italiano ETS (FAI). The site is a typical alpine pasture, without connections to water, electricity, or sewage systems. The intervention aims to revitalize the pasture, reintroduce cattle farming, and restore cheese production. From 2025, the farmstead will open to the public as an educational center dedicated to mountain agriculture and pastoralism, with overnight accommodations. To ensure the site’s energy and water self-sufficiency, the project incorporates local RES and traditional techniques to minimize water and electricity consumption. Active solar systems using copper indium gallium selenide (CIGS) photovoltaic panels are installed on the buildings’ roofs to meet electrical and thermal needs. For water, historical pits (pose) used by herders are restored, and new systems like rainwater harvesting from roofs are implemented. The study outlines the complexity of executing this work at high altitude, detailing the stages of architectural and systems design and construction. The project highlights how combining RES with traditional practices can create low environmental impact and self-sufficient buildings.

   12. Energy Efficiency Evaluation of the Direct Liquid Cooling (DLC) System for High-Density Computing Data Centers

       Jinkyun Cho, Joo Hyun Moon, Sangwoo Byeon, Jikyum Kim

       Abstract

       This study systematically examines direct liquid cooling (DLC) solutions for high-density data centers, leveraging CFD-based simulations for a 2U GPU server and facility-level design analysis for a 30 MW data center. The results highlight how coolant supply temperature (12–50 ℃) and flow rate (0.25–10 LPM) affect cold plate inlet–outlet temperature differences, pressure drop, and GPU stability. Low flow rates reduce pump energy but risk GPU overheating. By integrating CFD findings into ASHRAE S-Class configurations, we show that low supply temperatures (12–18 ℃) necessitate extensive chiller usage, while higher supply temperatures (42–50 ℃) can eliminate chillers but require adequate flow rates for thermal safety. The optimized approach yields a cooling PUE as low as 1.04, underscoring the energy-saving potential of DLC compared to traditional air-cooled systems. These findings provide actionable guidance on balancing coolant parameters to minimize operational costs while safeguarding IT equipment performance. Hence, the approach underscores how carefully selecting TCS supply temperature and flow rate is crucial for ensuring both GPU reliability and cost-effective data center operation, especially in emerging high-density compute environments.

   13. Multi-criteria Analysis of Different Heat Pump Solutions Using Natural Refrigerant Propane for Existing Multi-family Buildings

       Björn Nienborg, Mu Huang, Annette Uhl, Bruno Bavia Bampi, Peter Engelmann

       Abstract

       Heat pumps are a proven solution for the decarbonization of the heat supply, both for space heating and domestic hot water, in individual houses. However, the implementation of heat pump systems in multi-family buildings remains marginal. The main challenges include the lowering system temperatures on the supply side (space heating and domestic hot water) and difficulties in accessing suitable heat sources in densely populated urban areas. This study presents a comparative and multi-criteria analysis of the potentials and constraints of various heat pump solutions using the natural, low Global Warming Potential refrigerant propane (R-290). It evaluates the technical feasibility and user-related aspects such as acoustics and appearance of different heat pump systems implemented in various types of existing multi-family buildings based on real case studies in Germany. After characterizing available heat sources and building demands, the energy performance of the heat pumps systems is examined through simulation. Further aspects such as the investment costs, space requirement and safety requirements due to R-290 flammability are evaluated bases on literature data and expert opinion. The findings highlight the potential of propane-based heat pumps to provide a sustainable and efficient alternative to conventional heating systems but also the complexity of finding solutions under the boundaries of existing buildings. The multi-criteria approach ensures a comprehensive assessment, offering valuable insights for policymakers, engineers, and stakeholders aiming to enhance the sustainability of heat supply in existing multi-family buildings.

   14. Modelling of the Automated Supply Air Temperature Control Through Empirical Graphs

       Marika Eik, Afzaal Ather, Andrea Ferrantelli, Ahmet Kose, Juri Belikov

       Abstract

       Air Handling Units (AHUs) substantially affect the energy demand of buildings. Their operation and energy use depend on several factors, such as indoor or outdoor temperatures and occupant activities; this requires AHUs’ performance optimization through operation data modeling and suitable control algorithms. Given multiple AHUs, if their operation is sufficiently similar, a Federated Learning (FL) model can be constructed, resulting in a global control algorithm. Here, we present the modeling of Automated Supply Air Temperature (ASAT) for three AHUs that serve multiple spaces in a university building. Clustering, Wasserstein distance, and Kullback-Leibler divergence (KLD) methods were used to identify the similarities or differences in the operation of ASAT based on historical data. Clustering and KLD indicated differing AHUs patterns, while the Wasserstein distance showed a high level of similarity. The technical reasons underlying the differences in operational principles were identified and explained. The FL developed in this study was implemented by modifying the regularization parameter, reflecting the similarities between the graph nodes.

   15. Control-Oriented Graph-Based Modelling of Building Energy System: A Conservation-Based Framework for Multi-zone Buildings

       Zeinab Echreshavi, Enrico Sisti, Mohsen Farbood Palangari, Ruggero Carli, Mirco Rampazzo

       Abstract

       Building energy modelling (BEM) plays a critical role in designing sustainable buildings by minimizing energy consumption and associated costs. To ensure accurate and efficient simulations, this study proposes a graph-based modelling (GBM) strategy for multi-zone buildings. By leveraging the graph-based representation, the model captures interactions between various building components, including thermal and structural elements. To enhance model accuracy, a genetic algorithm (GA)-based optimization technique is employed for parameter calibration. The GA iteratively adjusts model parameters to minimize the discrepancy between simulated and measured data of the rooms’ indoor air temperatures. This approach enables the incorporation of additional building details, such as wall temperatures and specific humidity, leading to more realistic simulations. The effectiveness of the proposed methodology is demonstrated through a case study of a five-room building. The calibrated model predicts indoor air temperatures with appropriate accuracy under both heating and cooling conditions, validating its ability to capture the dynamic thermal behavior of the building.

   16. Comparison of Performance, Efficiency and Control Quality of Large Instantaneous Water Heaters for Regenerative Heating Systems

       Peter Pärisch, Maik Kirchner, Sebastian Engelke, Sven Schuba, Jonathan Walter, Carsten Lampe, Raphael Niepelt

       Abstract

       Converting from central storage water heaters to central instantaneous water heaters is a sensible initial measure to improve energy efficiency and potable hot water hygiene in existing large systems (e.g. hotels, apartment blocks). There are performance limits (minimum and maximum output), electric energy consumption, and control quality issues that require an objective testing and assessment procedure. Up to now, there is no standardized test procedure and no transparency in the market, except for capacity. In a research project, the test procedure previously elaborated for small instantaneous water heaters was further developed and applied to 9 large products with a hot water output of up to 100 l/min including circulation pumps. The products are assessed according to key performance indicators. The control quality, also known as comfort, evaluates the control behavior of temperature fluctuations caused by load changes. Most products show a high control quality for heat pump applications with low storage temperatures, but only few products achieve it for solar thermal applications with high storage temperatures. The performance factor indicating ratio of transferred heat with electric energy demand is higher than 500 for all products, ranging up to 1200. The heat transfer capability allows temperature reduction in the storage and increases its stratification, which allows a higher share of renewable heat generators. Here, the products range from A to G.

   17. Utilization of the Energy Potential of Waste Water in the Preparation of Hot Water in a Building

       Lucia Hrnčárová, Jana Peráčková

       Abstract

       The energy crisis is a hot topic in the world today. Society is increasingly concerned with reducing energy consumption in buildings. In addition to saving the environment, the required energy savings are also due to the huge and unexpected rise in energy prices in recent years. In Slovakia, energy savings in general are mainly contributed to by the thermal-technical standard STN 73 0540-2+Z1+Z2 of 2019, which, by tightening the required values of thermal resistance and heat transfer coefficient through building structures, contributes to a significant insulation of building envelopes and a reduction in the need for heating. However, less emphasis is placed on the energy demand for hot water preparation, which is an integral part of any building structure. Huge quantities of waste water are discharged daily into the sewers, the energy of which can be reused through heat transfer. The energy potential of wastewater lies in its temperature. In some cases, wastewater in internal sewer pipes can reach up to 60 ℃.

       By transferring the thermal energy from wastewater that is normally discharged into the sewer, it is possible to make a significant contribution to energy savings, for example in the preparation of hot water. Cold water can take the heat energy and raise its temperature. The article deals with the preparation of hot water using only the thermal energy from wastewater.

   18. Optimization of the Design and Operation of Potable Hot Water Heating in Sports Halls

       Jonathan Walter, Peter Pärisch, Sven Schuba, Maik Kirchner, Miriam Kirsch, Georg Schmitt, Carsten Lampe, Raphael Niepelt

       Abstract

       The heating of potable hot water (PWH) in sports halls often presents significant inefficiencies, particularly due to high heat losses. These losses are exacerbated by the widespread use of hot water storage tanks, which must maintain high temperatures for hygiene reasons. Additionally, the low number of full-load hours complicates the integration of regenerative heat sources, such as bivalent systems for preheating.

       We monitored the heating of potable water in more than 40 sports halls with high temporal resolution over a representative 4-week period. Based on the gathered data, several heating supply options were evaluated to enhance efficiency. The first option is centralized instantaneous water heating (IWH), which allows for more flexible buffer storage and facilitates the integration of renewable heat sources in the preheating stage. The second option is decentralized IWH, which places water heaters closer to the demand points, such as showers, allowing for a more efficient and demand-based control of circulation. The third option involves electric decentralized IWH, which eliminates storage and distribution losses entirely. Design guidelines for these systems are presented.

       The analysis is supported by dynamic simulations in TRNSYS of an exemplary system. Our results indicate that with the integration of a solar thermal system and a smart operating strategy, energy costs could be reduced by up to 78%. These findings contribute valuable insights for improving the energy efficiency and sustainability of PWH systems in sports halls.

   19. Research Regarding Ecological Alternative Refrigerants

       Tarlea Gratiela, Vinceriuc Mioara

       Abstract

       The study on refrigeration systems in this paper was made at the Technical University of Civil Engineering of Bucharest (U.T.C.B) - Colentina Laboratories Complex. The chosen topic is aiming to contribute to the theoretical basis and practical research in terms of development and use of ecological refrigerants.

       The ecological refrigerants proposed in this scientific work are chemicals obtained by mixing in different proportions of various current ecological refrigerants with one or more natural or synthetic substances that have zero values of ozone depletion potential (ODP) and low global warming potential (GWP).

       The results of the simulations from this paper performed with the help of the high-performance program EES (Engineering Equation Solver) for the refrigerants: R 134a, R1234yf, MV3T, MV3TN (mixteres of R 134a, R1234yf) in the case of the air-water heat pump.

       An important objective was the realization of an experimental stand air-water heat pump, designed to determine the performance of the refrigeration system operating with the refrigerant R134a and to find new ecological refrigerants of mixture type MV3T, MV3TN. From the ecological point of view the MV3TN mixture (GWP = 560) is the most advantageous compared to R134a (GWP = 1430).

       The comparative study of these facilities followed the coefficient of performance (COP/EER) and also the TEWI factor (Total Equivalent Warming Impact – in respect with EN 378-1).

   20. Domestic Hot Water Production in Residential Buildings: Energetic Analysis of Different Systems Through Dynamic Simulations

       Hamed Namdar, Eugenia Rossi di Schio, Paolo Valdiserri, Giovanni Semprini

       Abstract

       The energy used for Domestic Hot Water (DHW) production currently accounts for approximately 15–40% of the total energy needed in residential buildings. The present study deals with the energetic optimization of the Domestic Hot Water (DHW) system in a residential building of 10 apartments in Bologna, Italy. Two different systems are analyzed: the first has one centralized tank storage and a circulation loop, and the second has specific decentralized tanks (one for each apartment) with an internal heat exchanger. In both systems, the water is heated by an Electrical Heat Pump (EHP) coupled to a central storage tank. The energy performance analysis of the two DHW models is evaluated by dynamic simulations under different scenarios (for case two) of charging the decentralized storage tanks by circulating pump units. The results allow an evaluation of the DHW consumption profile, temperature variation in both the system’s central storage and (for case two) decentralized tanks and the annual electrical/thermal energy analysis.

   21. Harnessing Waste Heat from Air Conditioning Units with Thermoelectric Generators

       Paul Danca, Corina Babutanu, Florentina Bunea

       Abstract

       In the current political context, characterized by uncertainty regarding access to natural resources, rising electricity and natural gas prices, and legislation mandating the increasing production of energy from renewable sources, the topic of energy efficiency is of growing relevance. Buildings consume approximately 40% of global energy, with more than 40% of that energy being used by heating and cooling systems. Concurrently, global warming is driving an increase in the number of domestic air conditioning system users. These systems, in turn, contribute to rising outdoor temperatures by releasing heat into the atmosphere via the condenser.

       This study presents a method for harnessing the ambient heat extracted by air conditioning system through the use of thermoelectric generators. During the experiments, the temperature difference between the two faces of the generator was maintained at approximately 50 ℃. The power generated by the solution proposed for this temperature difference exceeded 3.2 W, which is negligible compared to the 1,500 W power of the equipment. However, it could be further increased by adding additional thermoelectric generators and the major advantage is that it does not require external energy input.

   22. Cost-Optimal Dimensioning of Run-Around Heat Recovery, EAHP and PV System for a Nordic Hospital Building

       Jiayi Liu, Yuchen Ju, Xiaolei Yuan, Risto Kosonen, Juha Jokisalo, Altti Meriläinen, Antti Kosonen

       Abstract

       Nordic hospital buildings have a significantly ventilation heat loss, primarily due to the continuous operation of high airflow systems and the relatively low effectiveness of run-around heat recovery systems. Integrating exhaust air heat pumps (EAHPs) with run-around heat recovery and PV system has the potential to reduce the ventilation heat loss and save the energy costs. This study evaluates the energy and eco-nomic performance of a hybrid solution combining EAHP, run-around heat recovery, and PV systems in a newly built Finnish hospital. The cost-optimal sizes of the systems are investigated under current commercial energy tariffs. Numeric simulations are conducted by utilizing IDA ICE software and a developed customized EAHP component. Results show that enhanced run-around heat recovery efficiency, reduced EAHP capacity, and expanded PV integration can together lead to notable reductions in total energy use and LCC. The utilization of cost optimal combined EAHP, run-around heat recovery and PV system saves the total energy demand and LCC of the demo building by 29% and 16.6%, respectively.

   23. Performance Characteristics of a Double-Effect Absorption Chiller Driven by Waste Heat from an HT-PEMFC

       Bongsu Choi, Junhyun Cho, Bong Seong Oh, Ho-Sang Ra, Hyung-ki Shin, Jongjae Cho, Beomjoon Lee, Sun Ik Na, Youngbok Lee, Sanghyun Che, Gilbong Lee

       Abstract

       Recently, with the growth in the data industry, huge power consumption and carbon emissions of data center have become a crucial problem. A high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) system with absorption refrigerator can be a solution because it supplies carbon-free electric power and cooling energy by driving the absorption refrigerator with HT-PEMFC waste heat. In this study, the coefficient of performance (COP) of a double-effect absorption refrigerator cycle have been analyzed, depending on the operating conditions of the data center and HT-PEMFC system. The COP of the absorption refrigerator has been obtained via simulations, depending on the cooling water, chilled water, and heat source temperatures. The results show that the higher the chilled water temperature and the lower the cooling water temperature, the higher a COP. In addition, when the heat source temperature is ≥165 ℃ and the cooling water temperature is ≤37 ℃, the COP of ≥1.15 can be obtained regardless of the chilled water temperatures.

   24. Occupant-Centric Interdisciplinary Approach to Obtain Occupants’ Preferences on Comfort Adaptative Behaviours in Office Environments

       Han Li, Rianne Appel-Meulenbroek, Theo Arentze, Pieter-Jan Hoes

       Abstract

       Among the various influential factors that impact building performance, occupant behaviour is considered one of the most important factors. Occupants dynamically interact with various indoor environment control systems, such as thermostats, operable windows and blinds, to perform daily routines and/or to maintain, restore, or improve their comfort and needs in an indoor environment. Conventional survey approaches have offered valuable insights into changes in occupants’ attitudes, behaviours, and the characteristics of sample populations, either over time or at a single point in time. However, studies exploring occupants’ preferences for using various building controls in situations involving multiple types of discomfort (e.g., thermal, visual, or acoustic) remain limited. This study incorporates a discrete choice experiment to obtain occupants’ perspective on building usage. In addition to a conventional survey, it also collects occupants’ choice preferences for energy-related comfort adaptive behaviour in office settings. The experiment design includes four types of influential factors: building characteristics, contextual factors, environmental conditions, and personal attributes. Mixed logit regression is used to reveal the utilities and to generate probability model from the data. The results show that occupant behaviours in office environments are strongly influenced by tasks, location, and expected social interactions, while also demonstrating a cooperative intention among co-workers. This model complements existing occupant behaviour models and agent-based modelling approaches by accounting for multiple behaviours (e.g., window opening and blinds use) and the capability to model both individual and collaborative behaviour.

   25. Heat Pumps Coupled to Air Systems vs. Condensing Radiant Tubes for Industrial Buildings Heating: Energy, Environmental and Economic Analysis of the Most Advantageous Option

       Marco Noro, Francesco Cerboni

       Abstract

       Industrial buildings present specific characteristics that make them different from other types; in particular, they have much greater heights and therefore very high air temperature stratification. Furthermore, air heating systems are recently often coupled to a heat pump (typically air/water or direct expansion type) to comply with the obligations introduced by the European Renewable Energy Directive to get the mandatory renewable quota of 60%. It is worth asking whether, for industrial buildings, it is always advantageous, from an energy, environmental impact, and economic point of view, to opt for a heating system with air units (air heaters or ventilation units) coupled to an air/water heat pump. This article reports on a Trnsys® transient analysis of a typical industrial building modelled in two different climates. The performance of two heating plants, high temperature condensing radiant tubes and heat pump coupled with the air heater system, were compared through dynamic simulation. The results indicate that, when no photovoltaic system is installed, condensing radiant tubes are more advantageous than a heat pump system. The best solution depends on the climate, the characteristics of the building (less or more thermal insulation, which corresponds to existing buildings rather than new ones), and the size of the photovoltaic system eventually installed on the roof.

   26. Thermo-economic Sizing of a Heat-Pump Based Residential HVAC System with Latent Thermal Energy Storage and in Situ Photovoltaic Generation

       Carolina Mira-Hernández, Simone Mancin

       Abstract

       The use of photovoltaic electricity to drive heat pumps in combination with latent thermal energy storage (LTES) is a promising solution for sustainable HVAC. The present study aims to understand the optimal sizing for the components of a sustainable residential HVAC system by considering the total cost of investment and operation. The HVAC system of a detached house in Venice, Italy, is evaluated. The system consists of a heat pump, an LTES and a photovoltaic array. The heat pump can be driven by both the photovoltaic array and the electric grid. The dynamic behavior of the system is evaluated via a numerical model with a rule-based control that aims to maximize the utilization of renewable energy. From model results, the total energy consumption and the fraction of photovoltaic electricity that is self-consumed are determined for each year of operation. The results for the energy flows are incorporated in an economic analysis to estimate the total cost for HVAC during a 20-year lifetime as function of the LTES and heat pump nominal capacity. PV self-sufficiency and self-consumption are found to rapidly increase with LTES capacity up to a value of around 25 kWh. At current commercial prices for LTES of around 200 €/kWh, there is not an economic advantage of including the storage, and the minimum total cost is achieved with zero LTES capacity.

   27. Numerical Analysis of Concrete Thermal Storage with PCMs for Underground Application Integrated with Heat Pump

       Francesca Martelletto, Luca Doretti, Simone Mancin, Claudio Zilio

       Abstract

       A study was conducted on a combined sensible and latent heat storage element using cementitious materials integrated with Phase Change Materials (PCMs). The findings from this study serve as a preliminary basis for conducting experimental tests on an almost-ready rig within the laboratory of the department. Employing the computational fluid dynamics software ANSYS Fluent, a numerical analysis was carried out on the thermal storage elements to simulate the behavior and processes associated with concrete heat exchangers, particularly pile heat exchangers that incorporate PCM. The numerical model examined various temperature profiles and the amount of energy stored within a concrete cylinder containing PCM, which is heated by water at different temperatures flowing through either a smooth or finned metal tube aligned with the axis of the cylinder. This entire system is positioned within a sand volume, simulating the conditions typically found in the soil for geothermal exchange systems. The results of the numerical simulation were consistent with initial expectations and hypotheses: configurations incorporating PCM, with inlet water temperatures of 80 ℃ and 90 ℃, exhibited approximately a 20% increase in stored thermal energy with a 10% PCM addition to the concrete mixture, while a 40% increase was observed with a 20% PCM addition. These findings are encouraging and support further investigation through an experimental campaign with the laboratory rig.

   28. Review of Passive Cooling Strategies for Buildings and Their Effectiveness in Different Climates

       Ernesta Mensah, Francesca Valentini, Nur Cobanoglu, Simone Mancin, Luca Doretti

       Abstract

       Passive cooling strategies are solutions for the regulation of thermal comfort in buildings where mechanical ventilation is not available. There are numerous strategies such as natural ventilation, direct night cooling, controlled thermal phase-changing, evaporative cooling, and shading.

       The existing literature suggests the use of passive design strategies due to their ability to reduce the demand of cooling and heating loads, to construct low-energy buildings. However, in the present time passive design strategies are accepted as a ‘black box’ solution, as there is limited understanding of the available strategies and their change in effectiveness due to the climate in which they are used.

       In this work, different solutions for passive cooling of residential and commercial buildings are presented, accounting for different climate zones. Unique solutions such as vegetation-based walls that use the principles of evapotranspiration and solar shading effect are illustrated.

       More techniques such as external shading, and the use of phase change materials are compiled, analysed, and evaluated in terms of their performance at different climate zones. From the analysis, it emerges that it is necessary to choose a specific strategy considering building design itself, external environmental conditions such as climate, and the elements surrounding the building. The effectiveness of passive cooling strategies is quantifiable but unpredictable for the future. Henceforth, further studies will be necessary due to climate change effects on geographical location, and meteorological data of different regions.

   29. Optimisation of a Heat Pump-Based Heating System Control Logic Through Dynamic Simulations

       Sara Giordani, Rossano Scoccia

       Abstract

       Given the current European objectives related to the challenge of buildings decarbonisation, an important role can be played by heat pump-based heating systems. The paper concerns the optimisation of the heating system control logic of a real case study through dynamic simulations with the goal to improve its overall energy efficiency. The work regards the optimisation of the heating system control strategy through an ad hoc TRNSYS 18 dynamic model. To improve the energy efficiency of the heating system –regulated with a constant heat pump set point– and to achieve better indoor thermal comfort, an optimisation process based on the employment of heating curves is performed. The outcomes are discussed from an energetic, economic, and environmental impact perspective. Three heat pump models are analysed and the results indicate that implementing a heating curve could boost monthly COPs up to 14% and improve SCOP up to 7%. One of the three heat pump models is selected for further analysis changing the weather files used in the simulations. It appears that the future climate may enhance heat pump efficiency due to higher outdoor temperatures. Additionally, using weather files from different areas within the same city, even for the same time period, can result in significantly different outcomes. The economic and environmental analysis, based on electricity consumption, highlights that optimisation with heating curves leads to reductions in costs and CO₂ emissions for the three heat pump models, with percentage decreases of 6.7%, 3.1%, and 2.1% respectively, reflecting varying levels of efficiency improvement.

   30. Optimizing Energy Efficiency in HVAC Systems: A Computational Study of Adaptive Fan Blade Configurations Using Shape-Memory Alloys

       Timo Eichenhardt, Fabian Kosel, Ralph Krause

       Abstract

       In real-world applications of HVAC units, fans are designed to operate close to their optimal working point. However, deviations from the best efficiency point can often result from varying operating requirements. Adapting the fan’s blade geometry to the current load exploits a potential of otherwise lost energy.

       To address this challenge, a research project conducted in collaboration between ILK Dresden and STFI Chemnitz is exploring the use of composite materials with embedded shape-memory alloys for manufacturing adaptive fan blades. These materials enable dynamic adjustments of blade curvature, offering a novel method to improve efficiency under changing operating conditions.

       This study demonstrates the potential for energy savings and efficiency improvements through targeted fan blade adaptations and operational analysis. Using measured operating data over a 79-day period, energy savings of up to 17.3% for individual operating points and approximately 3.3% in total were estimated. The findings highlight the importance of effective blade shape modifications, particularly adjustments to the profile camber angle and stagger angle, which result in trailing edge displacements of 6 mm (just over 1% of the fan diameter). These adaptations are considered achievable through the integration of shape-memory alloys. The results emphasize the potential of adaptive blade geometries to optimize system performance and contribute to more sustainable ventilation solutions.

   31. A Tool for the Optimal Design of Climate Resilient Thermal Energy Networks. Part 2: District Heating and Cooling Network Model

       Giorgio Villa, Adriana Angelotti, Marcello Aprile

       Abstract

       The 5^th generation District Heating and Cooling Systems, comprising a low temperature network and substations equipped with heat pumps to upgrade heat, are the most suitable networks for exploiting low temperature sources and geothermal energy at the urban scale. However, comprehensive modelling tools are lacking. To fill this gap, in the framework of the PNRR project NEST, task 8.5.3, an open-source unique tool to analyze the community energy demand and design the district geothermal system is provided. The tool will address the climatic resilience issue of the network, by considering future energy needs and ground source temperature evolution.

       This paper deals with the incompressible network that connects the central heat pump to substations. Time dependent loads, bidirectional flows, and decentralized pumping system are the main challenges to tackle with the hydraulic network solver. The Todini’s gradient algorithm is implemented providing a linearization of equations within an iterative procedure. Then, temperatures are calculated imposing the energy balance to the network’s components. A case study is analyzed showing the implemented strategies to overcome the numerical challenges and the useful results provided by the tool for the design process and energy evaluation of the network.

   32. Analysis and Forecasting of Energy Consumption of Innovative Heating and Cooling Generation Systems in Existing Healthcare Facilities

       Leonardo Andrea Bisogno Bernardini, Giacomo Salvadori, Umberto Desideri, Silvia D’Agostino

       Abstract

       Italian healthcare facilities are generally obsolete and energy-intensive buildings. It is essential to employ advanced technologies and predictive energy consumption estimates to optimize the use of energy resources, prevent inefficiencies and ensure continuous and high-quality service. This study describes the interventions aimed at energy saving in a group of 13 healthcare facilities managed by the Azienda USL Toscana Nord-Ovest, through the modernization of heat generation and cooling systems and the implementation of an advanced energy management system, within the framework of an Energy Performance Contract. This system is based on a large network of sensors, controllers, servers and a centralized control center, allowing remote and real-time management of energy production and distribution systems. An adaptive data-driven Grey-box model is being developed and is planned for implementation by the University of Pisa to identify the major sources of energy consumption in order to optimize energy performance. The results show a significant reduction in overall thermal and electrical consumption: after just one year, a 40% reduction was recorded compared to previous levels. The improvement interventions and the integrated remote management system have also led to increased environmental sustainability of the facilities, with a 41% reduction in CO2 emissions. The application of a centralized energy control system on large, complex and distributed facilities on such a vast territory represents is unprecedented in Europe. The results demonstrate the potential of this approach for improving energy efficiency and reducing the environmental impact of large-scale healthcare facilities.

   33. AIRsana®: “Specific Device for Sanitizing Air Conditioning Systems”

       Giovanna Serena Michetti, Diego Liberati, Selma Sally Jrhalf

       Abstract

       Air conditioners, unfortunately, are the ideal environments for the proliferation of bacteria, viruses and molds. AIRsana was born from the practical need of the founder who, after years of experience in the air conditioning industry, found a gap in the instrumentation useful for the maintenance and sanitization of the systems. In 2014 he conceived, designed and patented the “Specific device for sanitizing air conditioners”. AIRsana uses an innovative technology with saturated steam at 160/180 ℃ at 6–8 bar pressure, with simultaneous injection and suction flows, which eliminate any contaminant (dirt, dust, bacteria, molds, viruses, etc.) from any type of system, in a completely ecological way, ensuring safety for the operator. AIRsana brings systems back to the energy consumption specifications set by the manufacturer and minimizes interventions due to failures. It eliminates energy wastes, thus also mitigating its environmental impact. In addition, it is suitable for the integration of IOT technologies that allow the provision of predictive maintenance, reducing failures, within a circular economy logic. Currently, the company, consolidated in Lombardy, aims to spread throughout the country. In addition, the collaboration with the National Re-search Council is a harbinger of modeling methodologies and interpretation of data and signals also in relation with health effects of pollution; moreover, it is a potential source of complementary expertise on outdoor pollution. The company invests assiduously in its growth, in view of the sensitivity towards the green economy of 2030.

   34. Comparison of Stratified Tank Modelling Techniques in a District Heating System Evaluated on Accuracy and Computational Load

       Ilya T’Jollyn, Tore Boeykens, Alixe Degelin, Wim Beyne, Michel De Paepe

       Abstract

       The influence of different modelling techniques for stratified tank thermal storage systems is analyzed based on the computational time and simulated energy use of the system, when integrated in a district heating network. The different modelling techniques include a fully-mixed tank and two multi-layer models with four or twenty nodes. A district heating network with 35 individual dwellings is considered. The influence of several boundary conditions is investigated: central and decentral storage systems are compared and the network supply temperature is varied (55 ℃ and 75 ℃). The simulations are performed with the Modelica programming language using the IDEAS and MoSDH library. The results show that the simulated energy use is significantly higher when using a fully-mixed model compared to a multi-node model, due to the inherent simplification of uniform temperature and its effect on the tank heat losses in the fully-mixed model. The computational time increase when switching from a fully-mixed to a multi-layer tank with four layers is negligible in case of central storage, while the required time doubles for decentral storage. Additionally, an increase of 16–18% is found in case of a central storage system with twenty nodes and an eight times increase in case of a decentral storage system with twenty nodes when compared to using the fully-mixed model. Overall, a multi-node tank model with a limited amount of nodes gives the best trade-off between accuracy and computational load, albeit with a large increase in computation time for decentral storage systems.

   35. Applicability Analysis of Thermoelectric Active Condensation Prevention Material in HVAC Systems

       Minseong Kim, Jae-Weon Jeong

       Abstract

       Various attempts have been made to solve the condensation problem by using existing building materials. However, passive condensation prevention material has difficulty responding to indoor dew point temperatures that change depending on the comfort range of occupants. It is difficult to prevent indoor air quality deterioration because of mold and bacteria as condensation occurs repeatedly under certain outdoor air conditions.

       If thermoelectric technology that can immediately respond to a wide range of temperature changes is used in the condensation prevention material, the condensation risk can be eliminated in a building. Accordingly, in this study, it was derived that areas where the indoor wall surface temperature in winter fell below the dew point temperature with operating time. Based on the simulation results, it was analyzed the applicability of active condensation prevention material using thermoelectric module, which can flexibly respond to the condensation risk according to the changes of indoor and outdoor temperature and humidity, in building systems.

       The average daily power consumption of thermoelectric elements per unit area was analyzed as 727.20 Wh/m²/day, 1,249.72 Wh/m²/day, and 1,087.61 Wh/m²/day at the side wall, top and bottom of the front wall. The annual power consumption in one apartment unit was 16.65 kWh/year at the side wall, 28.61 kWh/year at the top of the front wall, and 24.90 kWh/year at the bottom of the front wall. Considering the health of occupants, such as mold and bacteria caused by continued condensation, thermoelectric active condensation prevention material is expected to have excellent economic feasibility.

   36. IAQ Performance of Personalized Ventilation and Chair Fans: Experimental Measurements in a Multi-occupied Living Lab

       Douaa Al-Assaad, Hilde Breesch, Twan van Hooff

       Abstract

       As showcased by multiple field studies, one of the main challenges continuously plaguing the building sector is the need for energy efficient means of improving occupant comfort and productivity. This had led to the emergence of personalized environmental control systems (PECS) – a type of system installed in the vicinity of each occupant and which operating conditions can be individually controlled to satisfy each occupant’s personal environmental comfort needs (acoustic, visual, thermal and IAQ). The aim of this study is to assess through experimental measurements the IAQ performance of personalized ventilation system coupled with chair fans in a mechanically ventilated classroom. Results showed that personalized ventilation improved the breathable air quality of all occupants by 50–66%. PV could improve IAQ in the background by 15–20% except between occupants’ workstations where PV caused a build-up of contaminant originating from exhalation. The addition of chair fans can improve thermal comfort but can cause additional mixing deteriorating IAQ in the breathing zone by 8–15% and in the background by 10–20%. Consequently, additional design considerations should be taken when combining PECS for comfort benefits under relaxed background conditions.

   37. Use of Solid Desiccant Materials in HVAC Dehumidification: Analysis of a Case Study

       Luca Socci, Federica Savelli, Andrea Rocchetti, Martina Lippi, Lorenzo Talluri, Javier Rey-Hernandez

       Abstract

       In this work, the topic of airflow dehumidification in HVAC systems is studied. The work compares three dehumidification methods: traditional dehumidification with low-temperature cooling coils, isoenthalpic dehumidification with desiccant wheels and a novel near-isothermal dehumidification operated by heat and mass exchangers coated with desiccant material. Systems performances have been evaluated using as a case study a gym located in Florence, Italy. An hourly simulation throughout the cooling season has been performed. Results indicate that the coated exchanger system achieves a 70% reduction in cooling power requirements compared to the traditional method, while the desiccant wheel system achieves a 41% reduction. Additionally, the COP (Coefficient of Performance) of the refrigeration device is enhanced in both systems assisted by desiccant material. This comparative analysis highlights the potential of advanced dehumidification technologies to significantly improve HVAC system performance, posing them as interesting options to decarbonise the HVAC sector.

   38. Energy Use and CO2 Emission Reduction Potential of a Stand-Alone PECS Prototype

       Jun Shinoda, Futa Watanabe, Sae Ichinose, Takayoshi Iida, Bjarne W. Olesen, Ongun B. Kazanci

       Abstract

       Personalized environmental control systems (PECS) have the potential to save energy by enabling setpoint relaxation of the heating, cooling, and ventilation systems without compromising comfort. The authors have previously reported on the heating, cooling, and air distribution performance of a stand-alone PECS prototype. The developed prototype, together with additional mockup devices developed and tested to improve the future prototype design, were modelled and assessed in terms of energy use and CO₂ emissions. Annual building energy simulations were conducted with the medium office building model developed by the U.S. Department of Energy. Based on experimental data, characteristic curves for heating and cooling of the PECS and mockup components were derived as a function of the corresponding power use. When PECS was installed, the heating/cooling setpoints and outdoor air intake of the background variable air volume system were relaxed by the maximum performance of PECS in terms of equivalent temperature and ventilation effectiveness, respectively. It was assumed that PECS was always modulated to provide optimal conditions within its available performance. The electrical power use of the corresponding settings was calculated with the characteristic curves and treated as internal heat gain. The current PECS prototype resulted in a 3% energy penalty due to its high standby power, indicating the importance of minimizing unnecessary power use. The combined use of mockups providing more efficient heating through contact and cooling through isothermal air flow resulted in a 13% reduction of energy use and CO₂ emissions, even with the same standby power as the PECS prototype.

   39. Thermodynamic Mapping of a R744 Simple Cycle for HTHPs: Application to a Brewery Process

       Lubna Hajaltoom, Antonio Rossetti, Francesco Fabris, Sergio Marinetti, Enrico Sisti, Mirco Rampazzo, Silvia Minetto

       Abstract

       High Temperature Heat Pumps (HTHPs) are a key technology toward industry decarbonization. Based on the variety of needs and boundaries, significant research efforts are underway to identify the best technical solutions and the most suitable refrigerants. Among natural refrigerants, which offer long-term sustainable options, carbon dioxide (CO₂) offers additional safety benefits. This paper conducts a thermodynamic analysis of a simple CO₂ cycle, exploring its application limits as HTHP working fluid. It presents a map of the maximum Coefficient of Performance (COP), along with its corresponding operating points, as functions of source and sink inlet temperatures and sink temperature lift. The methodology incorporates pinch point analysis for the gas cooling process, enabling precise optimization of CO₂ thermodynamic cycles under varying conditions. The findings serve as preliminary design recommendations to discuss HTHP applicability. The outcomes of this study are applied to the heating processes of a small craft brewery, to quantify the impact of an HTHP as a substitution for gas burners and limiting electric heaters’ contributions, while keeping simplicity in the system layout and complying with safety requirements for indoor installations.

   40. Multi-criteria Decision Support for the Procurement of Retrofit Ventilation Systems in Educational Buildings

       Christian Bellina, Christina J. Hopfe, Fatos Pollozhani, Robert McLeod

       Abstract

       Better indoor air quality is becoming more and more important. Especially in educational buildings such as schools and universities, where many people are in a confined space, it is beneficial if ventilation concepts can be compared with each other. In this paper, cost-effective extract ventilation systems are compared with conventional natural window ventilation, with the aim of creating a multi-criteria decision-making tool, which informs decision-makers when retrofitting a room with an additional hybrid system. Both quantitative parameters such as temperature, relative humidity, CO₂ concentration, capital costs, air volume flow and draughts, but also qualitative parameters such as comfort and aesthetics are compared as part of this investigation. With the help of empirical measurements as well as survey data, which are intended to record the subjectivity of the occupants, the data necessary for the preparation of the decision tool were collected. After the development of the multi-criteria decision-making tool, the tool was tested, with the aim of a balanced decision for or against the purchase of the extract system by the test person. In the future, this assistance can be used by schools and universities with the aim of improving the indoor air quality of classrooms or seminar rooms through the constant supply of fresh air, thus improving thermal, acoustic and visual comfort.

   41. An Integrated Hybrid Ventilation Framework for the Optimization of Energy Efficiency and Indoor Air Quality

       Roshan Raghavendra Rao, Riccardo Albertin, Andrea Gasparella, Giovanni Pernigotto

       Abstract

       Ventilation of office buildings affects the indoor air quality IAQ perceived by the occupants, their wellbeing, as well as their task performance. Although many offices are equipped with mechanical systems, new complex and hybrid solutions have been under consideration since the pandemic, combining for instance mechanical and natural ventilation with portable air-purifiers to ensure high IAQ and energy performance.

       In this context, this research proposes a framework aimed at defining an optimized hybrid ventilation strategy by prioritizing, when convenient, the utilization of outdoor airflow, combined with mechanical ventilation and an optimized use of air-purifiers. As a proof of concept, the presented framework is applied through a calibrated multi-zone building energy model representative of public office buildings designed and constructed in the 1990s in Bolzano, Italy. Mass flow rates among the zones of the building, calculated by the simulation model, are used to estimate the pollutant concentrations. The fresh air change rate, required to maintain the pollutant concentrations below the law thresholds, is determined thanks to a mass balance model, prioritizing natural ventilation by opening windows. In the case of unavailability or inefficacy of natural ventilation, to keep adequate IAQ, priority is given to the least energy consuming option between the use of air-purifiers and the mechanical system. Finally, the application of the proposed framework as an advanced control logic, such as a model predictive control strategy, is discussed, considering also its potential implementation to other office buildings.

   42. Using Thermal Comfort Measurement as Feedback to Building Multi-system Indoor Climate Control

       Riccardo Baron, Steffen Petersen, Massimo Fiorentini

       Abstract

       Conventional building heating and cooling systems employ control strategies that predominantly rely on ambient temperature. However, this paradigm may not be expedient in buildings equipped with multiple systems controlling the indoor environment – e.g. mechanical cooling and ceiling fans – as these systems may have conflicting operational modes that could compromise thermal comfort and energy efficiency. This study therefore proposes a systems controller based on the Predicted Mean Vote (PMV) index. The proposal was tested in a simulation-based case study where it was compared to the performance of a conventional air temperature-based controller. The results show that PMV-based controller outperforms the conventional controller in multi-system indoor climate control.

   43. Modelica-Based MPC Control of a CO2 Heat Pump: An Oslo Demo Case

       Ge Song, Konstantin Filonenko, Olger Zambrano, Razgar Ebrahimy, Natasa Nord

       Abstract

       Design and procurement of multi-input multi-output (MIMO) control algorithms in commercial heat, ventilation and air conditioning systems (HVAC) include extensive testing and comfort compromises. Model-based control simulators are being employed to reduce the effort and cost for building control design and deployment. In particular, Modelica-based simulation and optimization workflows utilize dynamic white-box models to test the effectiveness and deployability of different MIMO control algorithms. In this paper, a Modelica price-based control workflow based on Function Mockup Interface and well-established signal processing and hardware control deployment tools is presented. From the white-box Modelica model of the Oslo demonstration site in Norway (as a part of the EU project ARV), the paper proposes a way to digitalize and procure price-based control of a school building HVAC system. The central part of the heating system is a geothermal CO₂ heat pump that serves both the building and a thermal storage tank operated flexibility though price-based and set-point controllers. A standard efficiency-based model with a single condenser from IDEAS library was implemented and implementation of the model in the operational environment by deploying them on a micro-controller is demonstrated. The “toy” deployment model allows us to demonstrate how electrification of commercial HVAC can be fast prototyped with the use of microcontrollers and standard software tools. This approach is applied to simulation that interfaces heat pumps with onsite renewable energy production thereby reducing operation costs.

   44. Monitoring-Based Analysis of Decentralized Domestic Hot Water Preparation in Large Multi-Family Buildings

       Elisa Venturi, Fabian Ochs, Samuel Breuss, Mara Magni, Georgios Dermentzis

       Abstract

       The Smart City Quarter “Campagne-Areal” is a project involving 16 new buildings in Innsbruck. The first four buildings have already been built and occupied. They are served by a central block heating system, which provides hot water for space heating and domestic hot water (DHW). Each apartment is equipped with a fresh water station (FWS) for the DHW preparation. The FWSs in all the 52 apartments of one of the buildings are monitored, collecting data on volume flow, flow and return temperature, power, and energy at time intervals between 1 and 2.5 min. The analysis of the detailed data allows for the study of actual DHW consumption and tapping simultaneity in a large multi-family building, which is crucial for the sizing of the system components. Comparing the DHW consumption among the 52 apartments shows the possible range of DHW usage at apartment-level (e.g., different tapping duration, mass flow, time in the day) and the variability over time within individual apartment. The monitoring data are compared to the recommended profiles from the standards (e.g., EN 16147), highlighting discrepancies and identifying unexpected tappings with different energy characteristics. Undetected minor tappings, identified and incorporated into the analysis, notably influence the simultaneity factor calculations. These findings improve the understanding of DHW usage in large multi-family buildings, offering in-sights into its variability and the impact on system dimensioning.

   45. Advanced Atmospheric Water Generator: A Greenhouse Application for Internal Control and Water Recovery

       Lucia Cattani, Roberto Figoni, Paolo Cattani, Anna Magrini

       Abstract

       Water scarcity is currently affecting an increasing number of countries. In recent years, droughts have begun to affect areas historically untouched by such issues. Growing concern arises for agriculture, and new technological solutions focused on water-saving have been increasingly sought. Hydroponic cultivation in greenhouses is considered one of the most advanced solutions, as it ensures very low water consumption. However, the internal climate must be controlled. In particular, due to global warming, greenhouses more frequently require both heating and cooling. In this paper, a study is proposed on an advanced Atmospheric Water Generator (AWG) linked to a greenhouse to provide water and cooling. The machine is a real-world system capable of extracting water from air through a reverse cycle, simultaneously, providing dry and cooled air and a heat source with the same energy consumption. This paper presents, for the first time, a study of the energy and water cycle in a greenhouse coupled with the aforementioned machine, using dynamic models tuned with real data. Results give that, during summertime, the AWG can recover, averagely, 158 L/day, while maintaining the greenhouse internal conditions inside the desired range.

   46. Comparison of the Energetic Performance of Air-Source Heat Pumps in Renovated Buildings

       Alixe Degelin, Robin Tassenoy, Elias Vieren, Thijs Van den Brande, Ilya T’Jollyn, Steven Lecompte, Michel De Paepe

       Abstract

       While there is a strong focus on the energetic renovations of building to reduce carbon emissions, still a large number of buildings do not meet the set targets. On top of that, the perception exists that the replacement of gas boilers by heat pumps is only possible when an advanced energetic renovation has taken place. This study evaluates the viability of heat pump installations in partially renovated buildings through simulations conducted in Dymola (Modelica). The study compares the energetic performance of a residential terraced building equipped with a gas boiler, an air-to-water heat pump, or an air-to-air heat pump. Two different stages of renovation are considered in the comparison (intermediate and advanced), as well as two levels of thermal comfort (low and high). The results show that even in intermediately renovated buildings, there are opportunities to replace gas boilers by heat pumps. Air-to-water heat pumps are able to meet the thermal comfort criteria while reducing primary energy use and operational cost, if the electricity-to-gas price ratio is favorable. Compared to gas boilers at least 3.2 times less energy is used. After advanced renovations, air-to-air heat pumps emerge as the most efficient alternative, using up to 34.8% less electricity than air-to-water heat pumps. However, in intermediately renovated buildings, thermal comfort is not always met, stressing the importance of assessing the compatibility of indoor units with the room’s heat load.

   47. Performance Analysis of a Coupled Radiative Cooling Panel and an Impinging Jet Ventilation System

       Walid Chakroun, Sorour Alotaibi

       Abstract

       The growing demand for energy and poor indoor air quality (IAQ) in buildings call for sustainable HVAC solutions, as cooling systems account for nearly 70% of total energy use. This study introduces a novel system that combines a radiative cooling panel integrated into a wall with an impinging jet ventilation (IJV) system to enhance thermal comfort and IAQ. The system is tested in a 3 m × 3 m × 2.9 m room simulating an office occupied by two people. A 3 m × 2.335 m × 0.18 m plenum inside one wall contains a network of copper water tubes, where water enters at 14 ℃ with a flow rate of 2 m³/h. The radiative panel absorbs heat from the room, while ventilation air is pre-cooled before being released at 56.5 cm above the floor, creating a thin layer that spreads due to buoyancy forces. Experimental results demonstrate that the radiative cooling panel serves as the primary cooling mechanism, maintaining a head-to-ankle temperature difference of less than 1 ℃, within ASHRAE comfort limits. The IJV system effectively enhances ventilation performance, achieving a comparable IAQ level at lower airflow rates, leading to potential energy savings. Additionally, reducing the airflow rate from 0.039 m³/s to 0.025 m³/s had a minimal impact on thermal conditions, reinforcing the efficiency of the combined system. These findings highlight the potential of integrating radiative cooling with impinging jet ventilation as a sustainable approach for cooling buildings in extreme climates.

   48. Commercial Building HVAC Functional Performance Test Automation Using Brick Metadata Schema

       Aoyu Zou, Carlos Duarte, Paul Raftery, Stefano Schiavon, Gail Brager

       Abstract

       Heating, ventilation, and air-conditioning (HVAC) system functional performance test is a critical commissioning step in ensuring the design, installation, and operation of the building's mechanical system is verified against its intent. HVAC systems in commercial buildings are complex and traditional methods, which are manual and time-consuming, are sometimes incomplete. This is particularly concerning for HVAC controls, where an analyst would first identify all relevant sensor measurements from the building management system, cross-reference them with design drawings, and then compile a sequence of operations to test before implementation and analysis. This process becomes harder to manage as the system scales. In this study, we demonstrate it is possible to enhance HVAC equipment and control sequence commissioning by using a metadata schema called Brick in the performance test. The Brick schema allows for querying required measurement points from the BMS in a standardized, machine-readable format. By further connecting the Brick model to the building's BACnet network, most performance tests can be streamlined to increase the commissioning efficiency. In this study, we developed a generalized workflow based on Brick metadata schema that commissioning agents can directly apply with minimal manual adjustment. We demonstrated the framework by testing the air handling unit functions of a climate chamber at UC Berkeley. The performance tests include adjusting the supply fan speed and damper position and analyzing their impact on the airflow rate at terminal units. By using the Brick schema, the HVAC performance tests can be highly automated and generalized to a variety of buildings, yielding time and cost savings during commissioning while improving robustness.

   49. Assessment of the Impact of Sound Emissions of Central and Decentral Air-to-Water Heat Pumps in a Renovation Project

       William Monteleone, Fabian Ochs, Christoph Reichl

       Abstract

       To reach the European-wide goal of a sustainable, efficient and decarbonized building stock by 2050, the actual renovation rate must be at least triplicated. Heat pumps (HPs) will play in this context a crucial role in replacing the existing fossil-based technologies. On the other hand, multi-family buildings subjected to renovation present non-negligible challenges when HP systems for space heating and/or domestic hot water must be installed, among others source accessibility, destructive installation procedures and noise. To further increase their acceptance, HPs must be therefore efficient, silent and compact. However, incorrect sizing procedures lead frequently to oversizing, which has not only implications in terms of performance but also in terms of sound emissions in the surroundings. Within the research project “PhaseOut”, seven multi-family buildings in Vienna will be renovated. For all of them, the space heating demand will be covered by a centralized monobloc air-to-water speed-controlled HP. For the domestic hot water demand instead, centralized, semi-centralized and fully decentralized options will be adopted. The sound pressure level in the environment surrounding the renovated buildings was evaluated by means of the software CadnaA. Preliminary results highlight that the operation of the centralized air-to-water HPs has the biggest influence on the sound pressure level in the surroundings and that silent mode operation is not sufficient alone in the night to contain the sound emissions below the limit suggested by regulations.

   50. Enhancing HVAC Fault Diagnosis: Leveraging Expert Knowledge to Improve Bayesian Networks for Air Handling Units

       Karzan Mohammed, Wei Luo, Rick Kramer

       Abstract

       Research shows that 5% to 30% of a building's annual energy consumption is wasted due to malfunctioning systems. Automated Fault Detection and Diagnosis (AFDD) systems can help reduce this waste and improve occupant comfort. A widely used tool for AFDD is Diagnostic Bayesian Networks (DBNs), which are probabilistic graphical models linking faults with symptoms. The DBN structure, prior probabilities (the likelihood of faults), and conditional probabilities (the likelihood of faults given symptoms) often require expert empirical estimations. Accurate estimations of these parameters are crucial for effective DBNs, yet current studies often rely on limited expert opinions, typically the researchers themselves.

       This study interviewed seventeen experienced experts from building installation companies with diverse technical backgrounds to address this issue. They were asked to identify the most frequent faults of the Heat Recovery Wheel (HRW) in Air Handling Units (AHUs) and, afterward, estimate the occurrence of these faults over a period of five years. Based on the data, the prior probabilities of the faults were derived. The findings indicate that expert knowledge-based estimation can enhance the performance of DBNs by providing reliable prior probabilities for fault diagnosis.

       Future work should extend this methodology to other AHU components and incorporate structure and conditional probabilities to develop a comprehensive and robust DBN for Heating, Ventilation, and Air Conditioning (HVAC) fault diagnosis.

   51. The Innovative Radiant Heating/Cooling Systems – Theory a Practice

       Eva Švarcová, Dušan Petráš

       Abstract

       This paper explores the efficiency and effectiveness of radiant heating and cooling systems in office buildings, aiming to provide sustainable and energy-efficient solutions. Indoor thermal environment in buildings has been studied for many years, highlighting the importance of thermal comfort and the continuous development of technologies to enhance indoor environments. An innovative material, foamed aluminum, currently under research, was assessed for thermal comfort for employees in an open office. The results show high thermal conductivity of the material and a rapid response of the system. Foamed aluminum radiant ceiling panels provide optimal thermal comfort for year-round operation, although deficiencies were observed in terms of assessing relative air humidity during the winter months. Based on experimental measurement of innovative radiant heating/cooling systems placed in office spaces is clear, that so called foamed aluminum panels can improve the operation of such systems, guarantee the hygienic required indoor environment during the whole year and provide the optimal energy operation for winter and summer period.

   52. Assessing Building Stock Energy Efficiency and Environmental Impact Using the Energy Performance Certificate Database: Latvian Data

       Arturs Palcikovskis, Anatolijs Borodinecs, Tatjana Odineca

       Abstract

       The European Green Deal and others European Regulations designed to encourage building sectors to increase building energy efficiency towards achieving climate neutrality by 2050. Buildings account for about 40% of global energy consumption. In the European Union, 85% of buildings were built before 2000, and 75% of these have low energy efficiency. A significant number of these structures, between 85% and 95%, are expected to remain in use by 2050. Therefore, the building sector is vital to Europe’s decarbonization efforts. This paper discusses the context of assessing the level of energy efficiency of the existing buildings sector. The methodology is based on issued energy performance certificates and real data on the building’s primary energy demand. In the course of the analysis of energy performance certificates, deficiencies were found that the determined primary energy demand data do not always reflect the real situation, as energy auditors use unverified data and Latvian legislation does not verify them. This is a significant shortcoming and can only be eliminated at the national level by introducing amendments to the Law on Energy Efficiency of Buildings. This article aims to help future researchers address existing gaps and contribute to advancing the field.

   53. Techno-Economic Analysis of a Residential Building with Electric Heat Pump and Integrated Solar PV System: A Case Study from Ireland

       Mohammad Saffari, Jean-Baptiste Mestrallet, Adamantios Bampoulas, Eleni Mangina

       Abstract

       This study explores the potential of integrating heat pumps and solar photovoltaic (PV) systems to enhance energy efficiency in Irish residential buildings. The case study involves a 334.7 m² two-story residential building prototype. To assess the energy impact of design modifications, such as those explored in this study, a digital CAD model was utilized. Utilizing energy modelling through DesignBuilder, various retrofit scenarios were assessed, including an air-source heat pump (ASHP), a ground-source heat pump, and their combinations with a PV system. The results indicate that integrating ASHP with PV systems is the most effective approach, achieving a Building Energy Rating (BER) of A2, as opposed to a B2 rating with conventional gas boiler systems. This scenario also offers the highest economic advantages, with a payback period of 3.3 years, alongside a substantial reduction in CO₂ emissions (1,768 kg CO₂) compared to the gas boiler system (3,826 kg CO₂).

   54. Research and Development of Active Load Regulation Strategy and PCM-Based Load Regulator for HVAC Systems

       Yuyang Gong, Hang Wan, Yujiao Du, Gongsheng Huang

       Abstract

       Phase change materials (PCMs) are commonly employed in TES systems due to their ability to store and release substantial latent heat during phase transitions. Typically, PCMs are passively integrated into building envelopes to reduce thermal demand or incorporated into HVAC systems to lower operating costs. However, these applications do not actively improve the operational efficiency of building energy systems. Considering that chillers are the most energy-intensive components in HVAC systems and their coefficient of performance (COP) is highly dependent on the partial load ratio (PLR), this study proposes an active load regulation strategy to enhance chiller energy efficiency. A PCM-based load regulator was designed to integrate with an air handling unit (AHU), charging or discharging in response to AHU load variations to maintain the chiller’s operation within a high-COP range. The energy-saving rates of four chiller brands were analyzed, showing that chillers with COP-PLR curves that rise and then fall achieved the highest energy-saving potential, with a maximum energy-saving rate of 26.19%. This study provides a valuable reference for optimizing flexible load regulation and improving energy efficiency in HVAC systems.

   55. Cost-Optimal Dimensioning of Energy Systems in Kindergarten and Apartment Building with Renewables in a Nordic Climate

       Yuchen Ju, Xinyi Hu, Juha Jokisalo, Risto Kosonen, Altti Meriläinen, Antti Kosonen, Tianchen Xue

       Abstract

       The growing demand for environmentally sustainable energy alternatives promotes the incorporation of different renewable energy technologies. District heating systems, implemented extensively in central and northern European nations, are essential for the conversion and usage of renewable sources. The increasing hydrogen production has created important possibilities to recover the waste heat. However, the determining the cost-optimal dimensioning of energy systems in buildings, considering the utilization of waste heat from hydrogen generation, is still in its early stages. The present work investigated the cost-optimal dimensioning of energy systems which supply energy for a kindergarten and an apartment using the 25-year life cycle cost. A ground source heat pump is base heating and there is district heating backup. In addition, photovoltaics was installed for electricity generation, and some was used for the heat pump. The analysis had two district heat tariffs: the monthly district heat price provided by a company and the renewable district heat price obtained from hydrogen production waste heat. The results indicate that, for the ground source heat pump, the optimal dimensioning covers 20–30% of the total dimensioning heating power. The kindergarten's higher peak heating power results in the power fee imposed by the peak power dominating the overall cost of district heating. Thus, there is a negligible influence on dimensioning when adjusting the district heat energy tariff. However, for the apartment, it has a significant impact of 10% due to a reduced peak power.

   56. Control Strategies for Active Regeneration in a Dual-Source Heat Pump

       Tobias Reum, Christian Natale, David Schmitt, Matteo Dongellini, Claudia Naldi, Thorsten Summ, Gian Luca Morini, Tobias Schrag

       Abstract

       This paper presents a proof-of-concept for active regeneration (AR) in a dual-source heat pump (DSHP). DSHPs include multiple heat sources in a single unit to combine the benefits. Combining an air-source heat exchanger with a ground-based heat exchanger is a common strategy. Reducing the dimensions for ground heat sources is a major challenge to enable installation where space is a limiting factor. Additionally, noise emissions can be reduced by not activating air sources during noise-vulnerable times. In this study, an ice storage (IS) is used. This IS is to be used cyclically for heating during relatively cold periods and using AR with the air source during relatively warm time periods. A proper heat management system (HMS) is developed. A simulation-based analysis of parameter settings for the HMS and IS volumes is conducted. The concept of the HMS is successfully demonstrated and AR can keep small IS volumes charged for usage during cold periods. However, due to an improper HMS setup especially during spring, AR does not have a positive impact on the efficiency of the DSHP. Further technological investigation on AR as well as improvements to the HMS are therefore required to allow a holistic evaluation of AR on both overall efficiency as well as further parameters like space requirement reduction and noise emission control.

   57. About the Impact of the Geothermal System Installed at ELI-NP Research Infrastructure on Groundwater Parameters

       Razvan-Silviu Stefan, Delia Tinca, Mihaela Kelemen

       Abstract

       Due to rising energy demand, awareness of environmental problems caused by fossil fuels, and the aim of reducing greenhouse gas emissions, interest in shallow geothermal use has increased.

       Ground source heat pump technologies are a popular choice due to their high efficiency and relatively low operating costs.

       The ELI-NP research infrastructure was outfitted with the largest shallow ground source heat pump (GSHP) system in Europe to provide the energy needed for air conditioning, heating, ventilation, hot water, and technological cooling.

       Due to its very complexity, the HVAC geothermal system with heat pump units (GSHP) that equips the ELI-NP research infrastructure could be a suitable tool for determining the long-term impact of shallow geothermal systems on the environment.

       The purpose of this paper is to present research that investigates the impact of the GSHP system with heat pump units installed in the ELI-NP infrastructure on ground and groundwater.

       Measurements of the hydrostatic level and temperature have been performed. The real-time data available provide a timeline for the evolution of measured parameters and enable comparison of parameter values upstream and downstream of the geothermal system.

       The results of this study could contribute to improve quality and safety controls of GSHP systems, and it is also important for sustainable use of shallow geo-thermal energy.

   58. Impact Assessment of Space Cooling Demand in EU-27 Under Different Passive Measure Uptake and Technology Development Scenarios

       Aadit Malla, Lukas Kranzl, Andreas Müller

       Abstract

       Driven by factors such as climate change, urbanization, and the growing affordability of cooling technologies, space cooling (SC) demand is rapidly increasing. This study examines how the implementation of appropriate policy measures and technological advancements can effectively manage this rising demand while ensuring sustainability. Using a bottom-up modeling approach with the Invert/EE-Lab model, we projected SC demands across the EU-27. Our focus was on integrating various efficiency levels of passive measures—such as shading, enhanced ventilation, and building design improvements—with technological advancements in cooling systems. The analysis shows that combined strategies could reduce SC demand by up to 55% by 2030 and nearly 80% by 2050, compared to a baseline scenario without these passive measures. Significant energy savings are particularly notable in the non-residential sector, which has a higher baseline energy consumption. Furthermore, the aggressive adoption of energy-efficient cooling solutions is projected to substantially reduce CO2 and NOX emissions, contributing to the EU’s climate mitigation goals. Economic analysis indicates that the levelized cost of cooling could range from 55 to 92 EUR/MWh under various efficiency scenarios. These findings underscore the critical role of policy interventions, including incentives for passive cooling measures and support for the development and diffusion of advanced cooling technologies, alongside the creation of adaptive regulatory frameworks. Implementing these strategies is crucial for aligning the increasing SC demand with broader energy efficiency objectives and ensuring sustainable development amid rising global temperatures.

   59. Exploring Potential of a Student Canteen as a Local Energy Provider Through Building Simulation

       Andra Tanase, Cristiana Croitoru, Charles Berville

       Abstract

       This article explores the integration of renewable energy systems, specifically photovoltaic (PV) panels and heat pumps, into a building energy simulation using IES Virtual Environment (IES VE) software. The study focuses on a student canteen within an academic campus, aiming to evaluate its potential as an energy provider to neighboring buildings. The simulation model incorporates detailed building characteristics, occupancy patterns, and local climate data to assess the canteen's energy demand and production capacity.

       The primary objective is to determine the feasibility of the canteen as a decentralized energy hub that supports nearby residential or institutional buildings. The study assesses the energy balance, potential surplus, and the impact of different operational strategies on both the canteen and neighboring structures. Scenarios include varying the size and efficiency of PV panels, optimizing heat pump operations, and integrating battery storage systems to maximize self-consumption and minimizing grid interaction.

       The results indicate that with optimal system sizing and management, the student canteen can significantly contribute to local energy needs, reducing reliance on external energy sources and enhancing the sustainability of the campus energy network. The findings provide valuable insights for designing and managing similar energy-sharing schemes in urban and campus settings, demonstrating the potential of combining building simulation tools with renewable energy technologies for sustainable community energy solutions.

   60. Comparison of Heat Pump Modelling Approaches for Predictive Controllers to Optimize the Efficiency of Modulating Air-Source Heat Pumps: A Case Study from South Germany

       David Schmitt, Tobias Reum, Thorsten Summ, Tobias Schrag

       Abstract

       This study explores the optimization of the seasonal performance factor of air-source heat pumps using the outdoor temperature. Conducted within the framework of the research project ‘optLWP’, a single-family house in South Germany served as the case study. The heat pump operation was monitored under a rule-based controller. Measurement data was utilized to calculate the seasonal performance factor. A theoretical analysis was conducted subsequently in which the seasonal performance factor was recalculated by assuming an operation shift of the HP towards periods of high ambient air temperatures. The study employed a clustering approach to identify representative periods from the dataset, allowing for the reduction of analytical effort while ensuring accuracy. The theoretical operation shift demonstrated optimization potential of the seasonal performance factor up to 13.5%. However, when considering the influence of increased modulation, the benefits were partially or fully negated. This resulted in reductions of up to 4.8% of the seasonal performance factor in the worst case. The findings underscore the trade-offs between higher ambient temperature operation and the impact of higher modulation on the efficiency of heat pumps. While predictive control strategies offer a promising pathway to enhance the performance of heat pump systems, the impact of a higher modulation is often not considered in optimization algorithms to reduce computational effort. This research highlights the importance of integrating modulation effects into such algorithms. Future work will focus on refining predictive control approaches to balance ambient temperature benefits, modulation rate impacts, and storage losses, ensuring thermal comfort while maximizing efficiency.

   61. Determination of Characteristic Values of Infrared Heaters - Experience Report

       Lars Schinke, Maximilian Beyer, Joachim Seifert

       Abstract

       Infrared heating is increasingly being used in buildings either as the stand-alone heating system or in combination with a water-based heating system, for example to cover peak loads. A standardized test procedure has been defined and implemented in order to be able to compare heating systems and present them in energy calculations. For infrared heating, this is DIN EN IEC 60675-3, which describes the test procedure for determining the radiation efficiency. This measurement method was realised in the Combined Energy Lab at TUD Dresden University of Technology and applied to more than 100 different heaters. The paper will present the test setup and the measurement data. In addition, various influencing variables such as the type of installation (wall/ceiling) and the effect of the temperature of the surfaces surrounding the room on the radiation efficiency will be discussed, the error tolerances will be described and an assessment of the laboratory measurement compared to practice will be given.

   62. Simplified vs Detailed Procedures to Assess the Energy Performance of Heating Storage Systems

       Franz Bianco Mauthe Degerfeld, Ilaria Ballarini, Vincenzo Corrado

       Abstract

       The efficiency of the various technical building subsystems − such as emission, control, distribution, storage, and generation − significantly impacts overall building energy performance. Accurate calculation methods are essential for assessing subsystem heat losses and efficiencies. However, modelling these components while considering the interactions with each other, the building envelope and users is a complex issue, limiting the widespread use of highly accurate procedures. Therefore, numerical approaches that balance simplicity and accuracy in the modelling of the subsystems are needed. Following the publication of Mandate M/480 EN, efforts have been made to improve the assessment of heating and cooling system performance. Nevertheless, several procedures still require improvements to maximize the efficacy of energy assessment. This work specifically focuses on the analysis of thermal storage systems. Current methods often oversimplify heat loss complexities, by simplifying the modelling of the water convective motes in the storage tank. As a result, simplified procedures show discrepancies compared to detailed calculations, highlighting the need for validated approaches. This research analyses simplified calculation methods for assessing thermal storage performance, identifying key parameters that influence energy losses, and aiming for a comprehensive validation. The study includes a comparative analysis of different simplified and detailed methods applied to a residential case study.

   63. Energy Retrofit Respecting Conservation of Architectural Cultural Heritage: Technical and Environmental Feasibility of Selected Technologies

       Fabrizio Ascione, Filippo de’ Rossi, Anna Iaccheo, Teresa Iovane, Margherita Mastellone

       Abstract

       Historic buildings - that strongly characterize European cities and determine unique historical centers and downtown - must actively contribute to achieve the goal of decarbonization of the building sector by 2050, being not negligible because of their number, use and presence, in Italy. The energy retrofitting processes of such buildings often face constraints related to preserving historical, architectonic and artistic value, which limits the possibilities of intervention. This study, starting from a review of the state of the art in the matter of energy efficiency of historic buildings, identifies and classifies the commonly implemented strategies and technologies, proposing a relevant method to select retrofit packages. The identified configurations are then applied, when suitable, to some representative historic case studies, to perform a cost-optimal based retrofit approach, selecting suitable interventions, on the basis of a sensitivity analysis concerning single or multi-family buildings, geometric characteristics (e.g., surface-to-volume ratios, opaque/transparent ratios) and uses. The interventions will be implemented while respecting artistic and/or architectural constraints.

   64. Prediction of Optimum Heat Recovery Using a Calculation Model Based on Non-linear, Partial, Relational and Singular Regressions to Significantly Reduce the Amount of Base Data

       Christoph Kaup

       Abstract

       Since 2020, non-linear multiple regressions have been acknowledged as a viable method for estimating optimal heat recovery.

       With the usage of four additional influence parameters, a multiple regression would require an exponential number of around 8,000 data sets, whereas the partial and relational model requires only seven individual, singular regressions in combination (the original three plus additional four factors).

       The non-linear multiple regressions were already discussed and partially considered as a parallel track in the revision process of the Eco Design Regulation EU 1253/2014. Due to the rapid fluctuation of energy prices as well as the need to accommodate other influencing factors, this study proposes an alternative modeling technique that utilizes a combination of non-linear singular and individual regressions. Change factors were used to represent the optimal temperature transfer efficiency and the required air velocity.

       Furthermore, this study suggests calculating the pressure drop of the heat recovery without employing regressions but instead utilizing a known average pressure drop and calculating the optimal pressure drop based on alterations in the causal relationships.

       A partial error analysis was used to evaluate the quality of the individual regressions based on the quality of the individual regressions, comparing the new partial and relational regression models with the non-linear multiple regression.

   65. Smart Operating Strategies of Heat Interface Units with Heat Pump for Highly Efficient Domestic Water Heating in Multi-Family Buildings – Simulation Study

       Modar Yasin, Peter Pärisch, Christoph Büttner, Oliver Mercker, Carsten Lampe, Raphael Niepelt

       Abstract

       The transition from fossil fuels to renewable energy in multi-family houses is crucial for achieving climate-neutral residential buildings. A key technology in this transition is the heat pump, which operates most efficiently at low supply temperatures of the heating system. However, high temperatures are often required to meet hygienic standards in central water heating systems, as domestic hot water must circulate between the basement and the apartments at temperatures of up to 60 ℃ to disinfect against Legionella bacteria. Heat interface units (decentralized instantaneous water heaters) can hydraulically decouple domestic hot water from heat storage by using decentralized heat exchangers in each apartment, thereby lowering temperature levels in heating centers. Piping losses remain significant for maintaining user comfort but can be reduced through smart operating strategies. This paper examines predictive operating strategies for heating systems with heat interface units and a heat pump. A predictive, demand-based keep-warm function for heat interface units, predictive variable network flow temperatures, and predictive tank charging were tested. These strategies were analyzed using dynamic thermal simulation in TRNSYS for reduction of pipe losses and increasing of the efficiency of the heat pump. The study shows that a smart keep-warm function and predictive variable network temperature can reduce the pipe losses up to 19% and therefore the electricity consumption of the heat pump up to 6%. In contrast, predictive charging of the tank resulted in only marginal savings in the final energy consumption.

   66. The Impact of Building Renovation on Hydraulic Conditions in Primary Heat Network of District Heating System

       Martina Mudrá, Ján Takács

       Abstract

       By renovating residential buildings - by insulating their envelope and replacing transparent constructions, it is possible to significantly reduce the heat demand for heating. However, insufficient attention is paid to the hydraulics of the primary heat networks of district heating systems in connection with this renovation. This results in an uneven heat supply to the dwellings connected to the system. The content of the paper is a comparison of hydraulic conditions in primary heat network of district heating system before and after renovation of residential buildings connected to this system. The aim of the paper is to use hydraulic calculations and pressure diagrams to show the disproportions that exist in the primary heat network.

   67. Dynamic Modelling and Simulation of Faults in a R290-Based Air-to-Water Heat Pump System

       Daniele Scapin, Mirco Rampazzo, Riccardo Pengo, Chiara Corazzol, Willy Muvegi

       Abstract

       Domestic air-to-water heat pumps are becoming increasingly popular due to their high efficiency and environmental benefits. However, their reliability and performance can be affected by a variety of faults, which can result in significant energy losses and maintenance costs. Experimental evaluation of failure effects is often time-consuming and costly, requiring extensive laboratory testing. This paper presents a novel approach to model and simulate the effects of faults in an R290-based domestic air-to-water heat pump using a MATLAB Simscape acausal dynamic simulation model. The developed model accurately captures the dynamic behaviour of the heat pump system and allows the evaluation of various fault scenarios, including heat exchanger fouling, refrigerant leaks, compressor failures, and sensor malfunctions. The simulation results show mainly the impact of evaporator fouling and a little of condenser one on system performance, energy efficiency, and safety. The proposed model enables the identification of critical fault modes and the evaluation of fault detection and diagnosis strategies, reducing the need for costly and time-consuming laboratory experiments. The study also investigates the effects of fault severity and duration on system performance and energy efficiency. The results of this study can be used to improve the design, operation, and maintenance of domestic air-to-water heat pumps, ultimately increasing their reliability and performance. The model developed can also be extended to other types of heat pumps and HVAC systems, making it a valuable tool for researchers and practitioners in the field.

   68. Comparative Evaluation of Outdoor Air Flow Rate Determination Methods for Non-residential Buildings

       Federico Pedranzini, Luca Alberto Piterà

       Abstract

       The revision of the Energy Performance Building Directive (EPBD 2024) introduced new requirements for the energy performance of both new and existing buildings aimed at achieving the 2050 decarbonization targets and at the same time ensuring an adequate level of indoor environmental quality (IEQ) by introducing mandatory monitoring of indoor air quality in non-residential buildings.

       This study deals with air systems and offers a comparative evaluation of the main methods used for defining and managing outdoor air flow rate values, comparing currently available calculation methodologies, including EN 16798–1, and introducing the hypothesis of recently developed optimized methods.

       Through the analysis of a case study concerning an office building supplied by a variable-flow primary air system equipped with terminal VAV boxes, the different design and control methods were applied and compared with the aim of identifying the differences in terms of supply flow rate values and in terms of indoor air quality.

       The results of the comparison show how the combination of different design methodologies and control strategies, influences not only the energy performance of the building but also the comfort and healthiness of the occupied spaces. The comparison also highlights the possible benefits of adopting optimized methods that, combined with the proper use of sensor-based control, allow satisfactory trade-offs between consumption and performance.

   69. A Building Simulation Approach to Achieving Net-Zero Residential Housing in the UK: Learnings and Opportunities

       Shittu Faisal, Mahroo Eftekhari, Amr Suliman, Thomas Steffen, Noman Ashraf, Khalid A. Alshaibani, Faris Almaziad, Badran Alzenifeer

       Abstract

       The residential sector in the UK contributes over 25% of total energy consumption, making it a critical focus for achieving national net-zero carbon targets. This study employs a simulation-based approach to evaluate the feasibility of achieving net-zero energy in typical UK residential dwellings using a staged intervention strategy grounded in the “fabric-first” philosophy. A representative base model—developed from the English Housing Survey and validated against national energy data—was used to simulate three intervention stages: (1) passive design enhancements to Passivhaus standards, (2) electrification through heat pump integration, and (3) renewable energy generation via rooftop photovoltaic (PV) systems. Results indicate that improving fabric performance can reduce heating demand by up to 25%, with additional savings achieved through heat pump adoption, resulting in a total energy consumption reduction of approximately 59.4%. PV systems generated a surplus of electricity, theoretically achieving net-zero performance. However, a significant temporal mismatch between energy generation and consumption patterns—especially in the UK’s temperate climate—necessitates storage or load-shifting strategies, which face cost and space limitations. This research underscores that while net-zero status is technically feasible for UK homes, practical implementation requires a locally tailored, integrated approach that considers building typology, occupant behavior, and seasonal energy demands. Key challenges include the need for scalable storage solutions and behavioral engagement at the household level. The findings support the role of policy, technological innovation, and occupant participation in driving the decarbonization of the UK’s residential sector toward climate targets.

   70. Simulation of the Evaporative Cooling Effect of Super Adsorbent Materials in Building Envelopes

       Michele Libralato, Enrico Dal Col, Giovanni Cortella

       Abstract

       Much work on the potential of including evaporative cooling in building envelopes has been carried out, for example evaporative roofs, green roofs, and pond roofs. This principle is particularly effective in hot climates with water availability, and it has proved to be effective when used in low-cost energy retrofits in low performance buildings. In this work a new approach is proposed: the addition of a layer of a hypothetical super adsorbent material with a wetting system on the external side of the wall and its effect on the cooling loads is evaluated for different climates and building envelope build-ups. The efficiency of the system is evaluated using the software tool WUFI Plus, which is used to perform the building energy simulation of the building considering coupled heat and moisture transfer in the building envelopes.

       These promising preliminary results could be used to evaluate the development of low budget retrofit solutions for low performance buildings subject to relevant heat waves, improving the climate resiliency of existing building stock.

   71. Zonal Control of Radiant Cooling and Heating Ceiling to Enhance Comfort and Energy Efficiency: A Case Study in Palermo

       Marco Beccali, Marina Bonomolo, Tancredi Testasecca, Alessia Alvich

       Abstract

       Building operations still generate a relevant share of global energy-related emissions. Contemporaneously, the digitalization wave is providing new solutions for increasing efficiency in space heating and cooling. One of the most promising approaches for reducing energy use in climate control within buildings involves the development of personal and zonal environmental control systems. Additionally, the integration of artificial intelligence, particularly machine learning algorithms, is becoming increasingly essential in optimizing energy management and environmental comfort parameters. This study introduces an innovative methodology for optimizing HVAC control in partially occupied rooms, integrating thermal comfort estimation, machine learning algorithms, simulated data, and real-time measurements. The results of the dynamic simulation presented are used to assess the effectiveness of implementing a real HVAC system in Palermo, Italy. The model includes a radiant ceiling used for both heating and cooling, which can be controlled by sub-zones. By monitoring indoor conditions, machine learning algorithms will be employed to improve local thermal comfort estimations through limited measurements and investigate their relationship with energy consumption. The direct impact of the radiant ceiling on the mean radiant temperature of the room will be explored through the novel presented framework that combines physics-based approaches with data-driven methods. The scope is to develop a zonal control system based on conventional real-time measurements coupled with learning techniques capable of considering user preferences and local parameters. The results of the simulations demonstrated how it is possible to reduce heating consumption by up to 19% and ensure comfort for users by controlling zones.

   72. Performance Assessment and Optimization of the Operation of R290 Heat Pumps for High-Temperature Heating Systems in Existing Buildings

       Maria Ferrara, Enrico Fabrizio, Michele Babuin, Leonardo Prendin, Marco Zanella, Stefano P. Corgnati

       Abstract

       High-temperature R290 heat pumps offer a promising solution for decarbonizing existing buildings that are equipped with traditional hot water heating systems. Compared to conventional combustion boilers, air-to-water R290 heat pumps can both reduce energy consumption and abate greenhouse gas emissions, especially if the heat pump is driven by green electricity. By leveraging the efficiency of R290 as a natural refrigerant, these heat pumps can provide high-temperature heating (up to 70 ℃), making them suitable for replacing existing boilers without compromising comfort levels. This can be obtained without requiring major renovations on the envelope and secondary systems of the building. However, the discrepancies between expected and actual performance emerging from the monitoring of current heat pump technologies and the limited available dataset of real data highlight the need to investigate what are the performances under real operation of such primary systems considering the annual dynamics of energy demand for space heating and integration with DHW and how the working conditions (e.g. design temperature, radiator sizing, outdoor climate) can affect their final efficiency. In this research, we investigate the energy savings that can be obtained by R290 heat pumps on real buildings of different sizes compared to the most efficient condensing boilers. In particular, how the operation and control of modular heat pumps can be optimized in large systems can also be derived. The primary energy savings and the environmental benefits are evaluated for different climates.

   73. Mean Radiant Temperature Sensing: Comparison of Methods for a Non-uniform Radiant Floor Heating

       Mehmet Furkan Özbey, Dusan Licina, Forrest Meggers, Dolaana Khovalyg

       Abstract

       Non-uniform radiant floor heating is increasingly explored for improving localized and personalized thermal comfort. Accurate mean radiant temperature (T_r) measurement is crucial due to its separation from air temperature (T_a) unlike convective systems. This study evaluates the accuracy of T_r obtained using the globe thermometer versus a novel mini.RES cube sensor and examines the differences between T_a and T_r in non-uniform heating environments. Experiments were conducted in a 62 m³ climatic chamber in Fribourg, Switzerland, with four cases: one without heating, two with non-uniform heating to simulate radiant asymmetry, and one with uniform heating for comparison. Additionally, an uncertainty analysis was performed to evaluate measurement precision for the T_r measurements using the globe thermometer. The results indicate that the globe thermometer method can introduce errors of up to 4% in determining the T_r. Moreover, the uncertainty values for the T_r values were found between 1.60 ℃ and 2.31 ℃. In cases with non-uniform heating available, the T_r was found to vary by more than 2 ℃ than the T_a, highlighting the need to consider T_r separately when assessing thermal comfort. These findings emphasize the error of obtaining the T_r with globe thermometer and the difference between T_r and T_a in non-uniform heating scenarios.

   74. Perspective on Collection of Accessible Indoor Airflow CFD Simulations Datasets

       Giovanni Calzolari, Wei Liu

       Abstract

       The growing capabilities of deep learning and artificial intelligence (AI) have revolutionized numerous fields, including indoor airflow simulations. Computational Fluid Dynamics (CFD) plays a crucial role in simulating airflow, heat transfer, and pollutant dispersion, which are essential for healthier indoor climates. However, the progress in this domain is hampered by the lack of publicly available CFD datasets that are consistent and standardized. With the urgent need to solve the recent COVID-19 crisis there has been a new wave of published studies to inspect airflow patterns in confined spaces. By reviewing many recent CFD applications in indoor environment, this study shows a perspective on the critical importance of establishing a robust, open-access repository of CFD data for indoor airflow simulations. Such a resource would not only accelerate research by providing a rich dataset for training AI models but also ensure that findings are replicable and comparable across different studies. This paper advocates for larger efforts to create accessible and standardized CFD datasets, which will be instrumental in leveraging AI for the development of smarter, healthier, and more sustainable cities.

   75. Cooling Panel with Indirect Evaporative Cooling via Membranes

       Hannes Rosenbaum, Christian Friebe

       Abstract

       To prevent the increase in global warming potential, it is necessary to enhance the energy efficiency of refrigerant-powered systems. Therefore evaporative cooling systems are of particular importance. The option of adiabatic cooling without adding humidity into the supply air flow causes that indirect evaporative cooling (IEC) is considered advantageous although there is a risk of aerosols being discharged into the exhaust air. IEC is almost exclusively used in large HVAC devices. There is currently a lack of suitable solution approach on the market for smaller decentralized or retrofit devices.

       To implement the positive effects of IEC in current buildings and to solve the aerosol problem, the ILK Dresden is developing an innovative cooling panel with a novel membrane heat exchanger (MHE). Therein water evaporates through a vapour permeable membrane into the exhaust air flow. The cooling effect on the supply air side is achieved via a barrier film. Two options, the “evaporative cooling by using supply air recirculation” and “exhaust air humidification in an air-to-air heat recovery system” are being further developed so that they can be used in the new cooling panel.

       The novel MHE is assembled by stacking 4-layer textile laminates. New processing methods and material combinations have been developed for their manufacture. Based on the requirements profile, results from the first development phases (conception, preliminary material investigations, thermodynamic design, constructive implementation and measurement analyses) are presented. Finally, an outlook is given on the optimization and application potential of IEC via membranes in HVAC systems.

   76. AI and IoT-Enabled Home Energy Management Systems (HEMS) for Hybrid Renewable Energy Sources

       Abdul Fatah, Ghous Bakhsh Narejo, Lala Rukh, Mahjabeen Memon, Muhammad Mohsin Memon, Sabir Ali Kalhoro

       Abstract

       This study presents the design and implementation of an AI and IoT-enabled Home Energy Management System (HEMS) tailored for hybrid renewable energy integration in residential settings, focusing on rural areas of Sindh, Pakistan. Buildings contribute to nearly one-third of global final energy use, highlighting the urgent need for smart solutions that optimise energy consumption. The proposed HEMS incorporates real-time monitoring, supply and demand-side management strategies, and automation to enhance energy efficiency and reduce dependence on conventional grid power. The system architecture includes an ESP8266-based IoT module, cloud integration via ThingSpeak, and an Android application developed using MIT App Inventor for user control. Experimental results from a working prototype, consisting of a 3-kWh solar PV system, battery storage, and connected household loads – demonstrate a 23–28% reduction in grid energy consumption. The system also enhances user comfort through temperature-based appliance control. This research contributes a scalable, low-cost model for under-resourced regions, supporting Pakistan’s energy resilience and global sustainable development goals.

   77. The Feasibility Study on the Hollow Fiber Membrane Dehumidification System Coupling with Conventional Air Conditioning System

       Kento Tsuji, Gyuyoung Yoon, Hye-Jin Cho, Seong-Yong Cheon, Jae-Weon Jeong

       Abstract

       This study examines isothermal dehumidification systems using hollow fiber membranes and vacuum pumps, focusing on their integration with conventional air conditioning systems. Since membrane dehumidification technology is still under development, replacing traditional systems entirely is not yet feasible. Therefore, this research explores how membrane dehumidification can supplement conventional air conditioning to enhance dehumidification capacity and improve energy efficiency. The study confirms that membrane dehumidification effectively supports conventional systems, maintaining thermal comfort by preventing excessive room temperature increases. However, it also reveals that the additional energy consumption from increased fan and vacuum pump power leads to higher overall energy use. To address this issue, a control strategy is proposed, in which membrane operation is stopped during intermediate periods to minimize unnecessary energy consumption. It is expected that this approach helps keep energy use at a relatively low level while still achieving significant energy-saving effects. The findings highlight the potential of membrane dehumidification systems as a complementary technology, offering a feasible pathway toward more efficient and comfortable air conditioning solutions.

   78. Seasonal Performance Simulation of Large-Size Air Source Heat Pumps for District Heating Focusing on Evaporator Field Frosting and Defrosting Cycles

       Adelso Flaviano Passarelli, Luca Viscito, Umberto Merlo, Stefano Filippini, Alfonso William Mauro

       Abstract

       Electric heat pumps are a well-established and widely adopted solution for space heating and cooling, offering an efficient solution for decarbonization. In particular, large-size heat pumps are increasingly important in new and retrofitted district heating machines. These systems typically employ large fields of fin-and-tube evaporators, in which frost formation is a critical issue that significantly impacts the seasonal performance, leading to reduced airflow, lower heat transfer efficiency and the need for defrosting cycles that temporarily switch off parts of the heat exchanger field. Consequently, energy consumption increases to meet the heating demands, highlighting the need for accurate design processes focused on evaporator field geometry and defrost strategies. This study presents a seasonal performance model capable to identify the best configuration of evaporators to minimize the seasonal energy consumption. A set of simulations involving variable geometrical parameters such as fin spacing and evaporator field size in terms of number of modules with different airflow velocities for the climatic conditions of Helsinki has been run assuming a fixed defrosting strategy. Through a detailed tube-element modelling approach for the evaporator field, focused on frosting and defrosting cycles, a maximum gap in total costs between the best and the worst solutions up to almost 100% has been obtained starting from a 7.5% without taking into account frosting/defrosting cycles.

   79. Evaluation of the Performance of Machine Learning Algorithms for Time Series Symptom Detection in Air Handling Units: A Case Study

       Srinivasan Gopalan, Rick Kramer

       Abstract

       Buildings constitute 36% of the world’s energy consumption of which up to 30% could be wasted due to improper controls tuning, inadequate maintenance and degradation of equipment. Many of these faults are never detected or at least difficult to detect. Hence, Automated Fault Detection and Diagnosis (AFDD) tools are needed to detect the presence of these faults in the system. The main objective of this research is to perform a comparison of the performance of supervised learning-based Machine Learning (ML) algorithms for time series-based fault detection in the Air Handling Unit (AHU). Additionally, the performance of algorithms with a lower feature set (without any symptomatic feature) was compared to the performance with a higher feature set (possibly including symptomatic features). A real office building (Breda, The Netherlands) served as a living lab where several low-cost monitors and mass flow rate meters were installed and data was logged at a 1-min interval by the Building Management System (BMS) to obtain high-granularity data. Non-faulty, baseline data was used to train models based on seven algorithms: Support Vector Regression (SVR), Random Forest (RF), Decision Tree (DT), XGBoost, CatBoost, LightGBM and Multi-Layer Perceptron (MLP). The best performing algorithms were evaluated for application to symptom detection on data collected through fault experiments. The performances of the algorithms on symptom detection were evaluated using symptom detection metrics. The results showed that the ML models performed better with a greater number of features and XGBoost performed the best in majority of the tested scenarios.

   80. Using UBEM to Study Decarbonisation Strategies of Urban Neighbourhoods: A Case Study in Milan

       Alessia Banfi, Chiara Nardelli, Martina Ferrando, Xing Shi, Francesco Causone

       Abstract

       Buildings are significant contributors to global energy consumption and CO2 emissions, making it imperative to implement strategic intervention scenarios to reduce their energy and carbon footprint. Bottom-up physics-based Urban Building Energy Modelling (UBEM) tools are crucial for this goal. These tools provide quantifiable impacts of intervention scenarios on the building stock, supporting cities in developing roadmaps aligned with national and international environmental targets. This study simulates two intervention scenarios for a mixed-use district in Milan, Italy, using Urban Modelling Interface (umi). The first scenario focuses on renovating low-efficient buildings to meet the 2030 local regulation goals. The second envisions an operationally carbon-neutral district achieved through building envelope improvements and complete electrification of energy uses, aligning with the European Union’s target for climate neutrality by 2050.

       The impact of the proposed measures on heating energy use, primary energy, and operational CO2 emissions is assessed and compared to the current performance of the buildings. An economic analysis, considering Net Present Value and Payback Time, explores the financial viability of the interventions. This study provides actionable insights into effective decarbonisation strategies, offering a practical framework for policymakers. The findings can guide compliance with regulatory directives, enhance urban energy efficiency, and promote sustainable development.

   81. The Role of Passive Building Envelope Elements in Facilitating the Adoption of HVAC Systems Employing Natural Refrigerants: A Case Study

       Martin Ivanov, Borislav Stankov, Ivan Dimchev, Angel Terziev

       Abstract

       According to the EU Directive on the energy performance of buildings, by 2030 all new buildings must be zero-emission buildings, and by 2050 the existing building stock should be entirely decarbonized. The goal is partly to be achieved through electrification, with heat pumps playing a significant role in this shift. Meanwhile, the refrigerants used by most heat pumps today are characterized by high carbon footprints, which is the reason for their gradual replacement with environmentally neutral ones. However, this replacement is often associated with a trade-off—diminished seasonal and annual performance of the respective heating and cooling systems. This study investigates the possibility of utilizing passive building envelope elements—in the presented case, the provision of fixed external shading—as an accompanying measure to reduce the energy demands and to facilitate the replacement of a typical present-day HVAC system, employing a refrigerant with high global warming potential, with a natural refrigerant-based alternative. The analysis involves dynamic simulations with TRNSYS and is based on a case study of an existing lecture hall with substantial solar heat gains.

   82. Eco-Friendly Heat: Solar Air Collector Crafted with Recycled Materials for Low-Income Housing

       Calotă Răzvan, Mandea Bianca-Nicoleta, Barbu Daniel-Constantin, Lungu Cătălin, Charles Berville

       Abstract

       This research explores renewable resources and recycled materials to develop sustainable, low-cost home heating solutions. It focuses on a solar air collector made entirely from recycled materials to reduce fossil fuel use and enhance living conditions, especially for low-income rural households. Aligning with European and global directives, the project utilizes solar energy to decrease heating costs and carbon emissions while promoting circular economy principles by repurposing demolition waste. The collector, based on the Trombe wall concept, captures and stores solar heat using roof tiles and recycled materials. Experimental results showed temperature increases having an average of 9.6 ℃. Future enhancements include integrating air quality monitoring and adapting the system as a solar dryer in warmer months.

   83. Energy and Thermal Comfort Performance Analysis of a Dew Point Cooler for Air Conditioning a School Building

       Frank Bruno, Edward Halawa

       Abstract

       The energy and thermal comfort performance of a dew point cooler installed at a school in South Australia have been evaluated and analysed. The study is based on data recorded at the site and empirical data supplied by the manufacturer. The evaluation, initially based on a limited dataset, was extended using a TRNSYS model to assess system performance on daily, monthly, and annual scales. The performance indicators evaluated include the input power and energy and water consumption of the cooler. The cooler’s energy performance was also compared with a ducted split inverter refrigerative system commonly installed in school buildings. In the absence of recorded data for the refrigerative system, the thermal comfort performance of the unit was compared against the ASHRAE thermal comfort conditions. In terms of indoor air quality, the dew point cooler delivers 100% fresh air to conditioned spaces. This contrasts with split refrigerative systems which do not introduce any fresh air into the cooling coil and therefore necessitate the installation of a ventilation unit to provide fresh air in the conditioned spaces. This paper summarises and discusses the outcomes of the system’s performance evaluation.

   84. Materializing Efficiency: How Building Configurations and Envelope Materials Shape Embodied Energy (E.E.) in Residential Buildings

       Deepali Ranavainshaw, Shankha Pratim Bhattacharya

       Abstract

       The building sector’s energy use is regarded as a significant contributor to greenhouse gas emissions and associated environmental effects. In efforts to significantly reduce energy consumption in this sector, it is crucial to prevent the transfer of burdens from one stage of the building life cycle to another; therefore, a comprehensive understanding of energy consumption throughout the building life cycle is essential for energy efficiency strategies. The body of research on operational energy reduction is substantial and well-documented; however, the influence of embodied energy and its parameters on diminishing the energy demands of buildings during their lifespan is equally significant and merits assessment. The current study tries to evaluate and analyze the impact of parameters like building configuration and material alteration in the envelope on the total embodied energy in mid-rise residential buildings. The process commences with the creation of a detailed inventory of construction materials together with their respective energy intensities (cradle to gate), followed by the calculation of total embodied energy (E.E._T) using the envelope materials for various building configurations (H, O, L, T) with differing wall-to-window ratios (WWR). Analysis indicates that residential buildings with a smaller built-up area or a compact layout demonstrate a reduction in embodied energy of roughly 50% when compared between fireclay bricks and other low-energy materials such as Fly ash, Aerated Autoclaved Concrete (AAC) blocks, and Hollow Cement Concrete (HCC) blocks. The results aid in understanding the embodied energy scenario in the life cycle energy analysis in a building’s service life.

   85. High-Efficient Heat Supply System for a New Multi-family House with a PVT- and Ground-Coupled Heat Pump and Decentral Heat Interface Units in a Four-Pipe System

       Christoph Büttner, Peter Pärisch, Bharat Chhugani, Federico Giovannetti

       Abstract

       A case study for a planned multi-family house with ground-coupled heat pump is presented. The heat supply concept combines a high-level heat source with low temperature heat supply with decentral instantaneous water heaters and underfloor heating in a 4-pipe system. The system is simulated in TRNSYS to dimension the components and to predict the performance. A combination with photovoltaic-thermal collectors with horizontal ground heat exchanger ensures sustainable operation of the ground heat exchanger, and allows to reduce its required area by 50% without reducing the seasonal performance factor. In this study, two types of photovoltaic-thermal collectors are examined in detail: an uncovered collector with fins on the backside and an insulated collector. The uncovered collector’s advantages as the sole heat source for heat pumps are evident only in undersized ground heat exchanger systems, but negligible in properly sized systems. Given that the price of the insulated collector is only one-third that of the uncovered photovoltaic-thermal collector, the insulated collector will be chosen for the building.

   86. Performance of 3D-Printed Hybrid Acoustic Panels: Acoustic Characterization and User Feedback

       Behnam Rosti, Aleksandar Jankovic, Francesco Goia, Vaia Tsiokou, Anna Karatza, Azimil Gani Alam, Guangyu Cao

       Abstract

       This study evaluates the performance of 3D-printed hybrid acoustic panels designed to enhance indoor acoustic environments by combining sound absorption and diffusion. Laboratory experiments conducted in the ZEB living lab measured reverberation time (RT60), revealing improvements in the 500–4000 Hz frequency range, which is critical for speech clarity. The panels were tested using two different assemblies, chosen from ten distinct designs, to assess their acoustic effectiveness. Results showed that the larger assembly achieved an average RT60 reduction of 0.10 s, demonstrating the panels’ capability to enhance sound quality in indoor spaces. Furthermore, field experiments in an office environment indicated positive user perceptions of acoustic comfort and panel aesthetics, although some participants expressed preferences for more vibrant designs and increased panel coverage. These results underscore the panels’ potential as a promising solution for indoor spaces, as they enhance acoustic environments while simultaneously balancing visual integration and functional performance.

   87. Energy Flexibility: A Hotel and Supermarket Case Study

       Michele Libralato, Paola D’Agaro

       Abstract

       In the context of smart grid development, energy flexibility is a critical factor for optimizing the integration of renewable energy sources and improving overall energy efficiency. This study focuses on the energy flexibility analysis of a simulated hotel and a supermarket refrigeration system. The main objective is to evaluate the potential for energy flexibility within the hotel building, that would enable it to dynamically interact with the smart grid by adjusting its energy consumption based on supply conditions and demand response strategies.

       The hotel building was modelled with Type 56, which provides comprehensive capabilities for simulating thermal zones, including heat gains, losses, and thermal storage effects. The building model was then coupled with a PV system, designed to meet part of the hotel’s electricity demand. Additionally, the model included a supermarket equipped with a CO₂ refrigeration system with heat recovery capabilities, here implemented to produce domestic hot water for the hotel.

       The study analyzed several scenarios to assess the hotel’s energy flexibility potential. These scenarios included varying levels of PV generation, different DHW storage sizes, and the implementation of demand response measures.

   88. Validation of Simplified Air-Based Photovoltaic Thermal Performance Model for System Integration Simulation

       Giorgos Aspetakis, Qian Wang

       Abstract

       Solar systems, particularly hybrid Photovoltaic-Thermal (PVT) systems that generate both electric and thermal power can potentially cover significant part of heating and cooling demand of buildings. To evaluate the integration of PVT collectors to building energy system operation, dynamic system simulations are commonly carried out to evaluate the performance. So far, simulation of performance has focused mostly on liquid-based variants. However, for simulation of air-based PVT systems, implementations are limited and usually highly customized. In this investigation, the aim is to simplify such simulations, through already existing components found in the widely used simulation environment, i.e., TRNSYS. To achieve this, long term operation measurements of an Air-Based PVT prototype are used to validate a dynamic simulation system model. Additionally, former Computer Fluid Dynamics analysis aids in identifying key operational and heat transfer parameters. Furthermore, aspects regarding different configurations of Air-Based PVT integration to HVAC are discussed in detail.

   89. An Overview of the Development and Standardization of Fundamental Technologies for Thermal Energy Management Systems

       Ryota Suzuki, Nasiru I. Ibrahim, Niccolo Giannetti, Kiyoshi Saito

       Abstract

       The drive toward sustainable energy and decarbonization has intensified due to growing concerns about climate change. Heat source systems are major energy consumers in buildings, and digital twin technology has emerged as a crucial concept for enhancing efficiency through real-time monitoring and operation optimization. This paper introduces Waseda University's ongoing project, “Development and Standardization of Fundamental Technologies for Thermal Energy Management Systems” (FUTTEMS). The project aims to digitize heat management by integrating various heat utilization devices from different manufacturers. The long-term goal of this project is to develop foundational technology that can optimize the entire energy supply and demand system—including heat, electricity, and hydrogen in the future. The project is organized around three main themes: (1) Carbon-Neutral Campus, which focuses on creating a carbon-neutral environment using Waseda University's campus as a case study. This involves integrating advanced technologies, such as low-GWP turbo chillers, absorption chillers, and innovative liquid desiccant systems for air conditioning and ventilation control through digital twin technology to achieve a 50% reduction in carbon emissions. (2) Sustainable Decarbonized Agriculture and Cold Chains, which aims to reduce greenhouse gas emissions in the agriculture and food supply chain by developing a “Green Value Chain Platform” and implementing energy management systems (EMS). (3) Diversified Utilization of Heat Pumps that seeks to promote the widespread adoption of high-temperature heat pumps through the introduction of EMS and digital twin technology. This initiative is expected to play a key role in achieving carbon neutrality, particularly as renewable energy sources become more prevalent.

   90. Dynamic Simulation and Experimental Validation of a Laboratory-Scale Transcritical CO2 Heat Pump

       Mohammad Shakerin, Natasa Nord

       Abstract

       The global shift towards natural refrigerants has highlighted carbon dioxide (CO₂) as a superior alternative for building heating. Transcritical CO₂ heat pumps adapt well to variable space heating demands and large temperature differentials in hot water production. The transcritical cycle behaviour of CO₂, featuring a unique temperature glide during heat rejection and favourable properties, offers an excellent adaptation to cold climates. However, developing dynamic models for transcritical CO₂ heat pumps that can support efficient control and performance optimisation remains limited, mainly due to the high nonlinearities of CO₂ thermo-fluid behaviour and processes. In this study, a dynamic simulation model of a transcritical CO₂ heat pump was developed and validated using experimental data from a laboratory-scale system composed of a compressor, gas cooler, internal heat exchanger, evaporator, expansion valve, and liquid separator. The model was created in MATLAB Simscape. A sensitivity analysis of key operational factors such as expansion valve setting, discharge pressure, and compressor suction superheat was performed to investigate their effect on the energy performance metrics. The results demonstrate that the dynamic model effectively replicates the system's coefficient of performance (COP) and heating capacity across a wide range of operating conditions, with minor discrepancies at certain lower discharge pressures near the critical point of CO₂. Despite these limitations, the model closely aligned with experimental data trends, particularly for gas cooler inlet and outlet temperatures. The optimal COP was found around 82 bar, close to the actual system.

   91. Experimental Evaluation and Performance Optimization of Large-Scale Magnetic Refrigeration Prototype for Air Conditioning Systems

       Guilherme Fidelis Peixer, Anderson Martins Lorenzoni, Rogério Sawaya Sucaria, Paulo Faria, Alan Tihiro Nakashima, Cristiano Silva Teixeira, Jaime Andrés Lozano Cadena, Jader Barbosa Riso Jr.

       Abstract

       Heating, refrigeration and air-conditioning are responsible for approximately 7.8% of global greenhouse gas emissions and are considered one of the main blind spots in the current energy debate. Magnetocaloric technology stands out as an innovative technology, that could substitute the use of volatile fluids in vapor compression systems with solid-state refrigerants. This study offers a comprehensive experimental evaluation of the thermodynamic performance across three successive iterations of a large-scale magnetic refrigeration prototype, specifically designed for air conditioning systems. Each prototype iteration reflects a series of design modifications, informed by specific constraints, motivations, and underlying rationale, all of which are thoroughly documented in this work. Performance evaluation encompassed key metrics such as cooling capacity and temperature span. Among the three prototypes, the initial version, which adhered closely to the original design principles, demonstrated the most favorable performance. It effectively achieved the required temperature spans for air conditioning, operating between heat reservoir temperatures of 22 ºC and 35 ºC, although it was limited in cooling power, peaking at 480 W. Advanced thermodynamic analysis highlighted that, while magnetic refrigeration shows considerable promise for achieving high efficiency, the system's overall performance is notably degraded by losses in auxiliary components. Despite the advancements realized through these prototype iterations, the study underscores that significant challenges and opportunities persist in refining magnetic refrigeration technology, particularly for its application in energy-efficient air conditioning systems.

   92. Investigation of Transcritical CO2 Heat Pump Integrated with Borehole Thermal Energy Storage for Space Heating

       Jinrong Fang, Chen Xu, Pengyi Wang, Xin-Rong Zhang, Jin Ma, Hui Wang

       Abstract

       The adaptability of heat pump for space heating in extremely cold regions is a significant obstacle hindering the development of heat pump technology. This study proposed and analyzed an integrated heating solution combining a transcritical CO₂ heat pump with borehole thermal energy storage (BTES) system. Firstly, a comprehensive system calculation model was established. Secondly, a novel borehole model was developed to match the characteristics of the transcritical CO₂ heat pump. Finally, energy and exergy analyses were conducted to investigate the effects of variations in intermediate water temperature and borehole heat exchanger inlet temperature on system performance. The results indicated that there is an optimal heat extraction temperature at which the system's COP or exergy efficiency reaches its peak. Besides, as the borehole heat exchanger inlet temperature increases, the optimal heat extraction temperature rises accordingly, leading to enhancements in both COP and exergy efficiency.

   93. Towards Cognitive Buildings: Filling Technological Gap with Enabling Technologies

       Abiodun E. Onile, Ahmet Köse, Eduard Petlenkov, Juri Belikov

       Abstract

       Future buildings aim to enhance residents’ quality of life while improving safety, security, efficiency, and sustainability. Integrating technologies like Industry 4.0, Internet of Things (IoT), Artificial Intelligence (AI), machine learning, and data analytics offers data-driven solutions for optimizing energy efficiency and predictive maintenance. Despite these advancements, a performance gap persists due to the dynamic nature of smart buildings and the influence of human behaviors and preferences, leading to discrepancies between projected and actual outcomes. Energy management sub-systems in buildings, such as lighting and HVAC systems, often operate inefficiently, especially when misaligned with occupant needs, such as heating empty or partially occupied spaces. Device operation flexibility (direct flexibility) presents significant potential for improving energy management, but this remains heavily reliant on effective information exchange between human occupants (indirect flexibility) and cognitive building (CB) interactive energy management systems. By incorporating hybrid digital twin modeling, advanced predictive and prescriptive analytics can be employed to track device behavior and provide customized feedback, creating a bidirectional information channel that enhances occupant engagement. This approach can improve overall building energy efficiency and reduce operational costs without compromising comfort. This study introduces a novel, user-centric cognitive system for energy efficiency, utilizing demand-side recommendations and thermal comfort controls via multi-agent reinforcement learning. Additionally, a conversational chatbot is explored to facilitate user engagement. The results demonstrate promising outcomes, including a 15.5% reduction in energy load, 69% user engagement, and up to 94% improvement in comfort levels.

   94. Use of Digital Twin Tools to Improve Residential House Performance

       Năstase Ilinca, Sandu Mihnea, Calotă Răzvan, Croitoru Cristiana, Georgescu Matei, Tănase Andra

       Abstract

       The building sector holds substantial potential for significantly reducing greenhouse gas emissions and the goal is to diminish the negative impact of buildings on the environment and people through harmonious integration into the urban environment using innovative digital tools. This paper presents the results of implementing a Digital Twin for a residential building with a total footprint of 96 m², a built area of 170 m², a heated area of 118 m², and a total volume of 400 m³. The considered building incorporates a wide range of active and passive strategies to reduce energy consumption, such as shading systems, photovoltaic systems, a heat pump, and facades with integrated phase change materials.

       This study highlights the synergy between Building Information Modeling (BIM), advanced energy simulations, and real-time data analysis in optimizing residential energy performance. Through calibrated simulations in IES VE and continuous data acquisition using iSCAN, discrepancies between theoretical models and real-world performance are quantified, revealing inefficiencies in domestic hot water systems, intelligent lighting, and adaptive shading solutions.

   95. Evaluating the Power Mismatch Dynamics of Deeply Renovated Apartment Buildings with On-Site PV Panels in Estonia

       Tofopefun Nifise Olayiwola, Martin Thalfeldt, Kalle Kuusk, Andrei Blinov

       Abstract

       This paper analyzes the time-dependent energy profile of deeply renovated buildings in various locations across Estonia, employing well-established key performance indicators (KPIs) such as self-consumption, self-sufficiency, and the newly introduced renewable energy use index. One of the key findings of this study is the strong correlation between the specific installed photovoltaic (PV) power and these KPIs. Furthermore, the study investigates the impact of time-dependent electrical measurements and environmental conditions on the accurate assessment of the power mismatch between on-site PV generation and the net building demand. While buildings equipped with exhaust air heat pumps generally outperformed those with heat recovery ventilation, with their KPIs peaking during the summer months, a few notable exceptions were observed. Overall, the insights presented herein aim to serve as a reference for design engineers who are looking for efficient design of on-site PV systems and improvements in the energy autonomy of zero-emission buildings.

   96. Using Global Sensitivity Analysis to Improve Confidence in Building Energy Modelling: From Screening Methods to Qualitative Results in the UniZEB Case Study

       Beatrice Riccardi, Laura Carnieletto, Enrico Sisti, Michele De Carli, Mirco Rampazzo

       Abstract

       The energy consumption of a building is a parameter that holds a key role in the context of building energy performance enhancement. As buildings continue to grow in complexity because of the need for more sustainable technical solutions, dynamic energy modelling tools offer new opportunities for their management and comprehension. Accurate parameter screening is crucial for understanding the relationship between model inputs and outputs, especially as models reflect the building's complexity. In the context of model calibration and verification, a comprehensive overview of the developed model is essential before the availability of monitored data. Global Sensitivity Analysis (GSA) is a powerful tool for such a goal. The work presented advances previous research by employing a more sophisticated version of the TRNSYS-based dynamic model of the UniZEB Living Lab at University of Padova (Italy). This approach studies the most influential parameters affecting energy demand, enabling the identification of potential regulatory, technological or user-centered improvements. The findings aim to enhance the precision and reliability of energy models, contributing to the design and optimization of energy-efficient buildings.

   97. Optimization of a Multi-apartment HVAC System Using Simulation and Monitoring Data

       Samuel Breuss, Elisa Venturi, William Monteleone, Georgios Dermentzis, Fabian Ochs

       Abstract

       The Smart City Quarter “Campagne-Areal” in Innsbruck involves the development of 16 new multi-apartment buildings in Passive House quality split in four project phases. The first phase, with four buildings, was completed and has been occupied since late 2022. These four buildings have 307 apartments along with various commercial and public facilities such as shops and kindergartens. The buildings are heated by a central heating system in a shared technical room, i.e., a groundwater heat pump supplies the space heating, and domestic hot water is provided by the district heating. A comprehensive monitoring system offers detailed insights into the operation of the HVAC system. Heat and electricity meters installed in the technical room, as well as heat meters installed throughout the distribution network, allow the calculation of distribution losses. A dynamic building model has been developed based on the design plans and calibrated by means of monitoring data. The building model includes the shared technical room and all the four buildings, each represented as one thermal zone. Furthermore, an HVAC model has been developed and calibrated, aiming to investigate the potential for optimization. The optimization focuses on improving the system design, as well as enhancing the control strategies. With improved operation the annual electricity demand of the heat pump can be reduced by 7.5% up to 15%. These findings aim to guide the design of the next project phases, supporting planners to pursue optimal design and functional solutions.

   98. Modeling and Simulation of Vapor Compression Systems Using a Graph-Based Toolbox

       Enrico Sisti, Mirco Rampazzo, Alessandro Beghi

       Abstract

       Modeling tools are crucial in the design and development of vapor compression systems (VCSs) and their control systems, enabling engineers to predict system behavior, optimize performance, and develop reliable control strategies. This work presents the application of a specialized modeling toolbox designed to assist engineers in VCS modeling and analysis. The toolbox is based on a graph-based approach, leveraging conservation laws - specifically energy and mass - to compute the system’s dynamic behavior. This methodology ensures a precise representation of the thermodynamic processes within the VCS, capturing the complex interactions between its components.

       In this study, the toolbox is used to model and simulate a simple VCS, demonstrating its effectiveness in reproducing the system's dynamics. The simulation results highlight how the toolbox accurately reflects the performance of main components, such as compressors, condensers, and evaporators. The ability to easily adjust system parameters and analyze their effects on overall performance underscores the tool's utility in the design process. By enabling more efficient and accurate modeling, this toolbox can significantly reduce both the time and costs associated with designing advanced and reliable VCSs.

   99. Data-Driven Insights for University Campus Sustainability Planning: Evaluating Space Heating and Ventilation Systems’ Efficiency

       Sofia Vasman, Karin Krauvärk, Martin Thalfeldt, Eduard Petlenkov

       Abstract

       Retrofitting existing buildings supports sustainability and cost savings. In this study, done as a part of university’s climate neutrality roadmap planning, we evaluated energy-saving potential in campus heating and ventilation systems using sub-meter data. Space heating systems were analyzed via clustering and linear regression to assess how energy use varied with outdoor air temperature during periods with minimal or no heat gains. For ventilation systems, we focused on supply air temperature increase in Air Handling Units (AHUs) heating coils relative to airflow, capturing operational settings and reflecting heat recovery efficiency. The approach identified key retrofit opportunities and drew actionable insights for building operators.