Proceedings of the 12th International Conference on Cold Climate HVAC & Energy (Volume 1)

Table of Contents

1. Sustainable District Heating and Cooling

   1. Frontmatter

   2. Research on Low-Carbon Medium Parameters of Central Heating Under the “Dual Carbon” Goal

      Yuanfang Liu, Jiadong Wang, Jinping Hu, Liu Yi

      Abstract

      Against the background of the “Dual Carbon” goal, this paper focuses on the low-carbon optimization of heating medium parameters in central heating systems. Taking a central heating system in Harbin as an example (with the calculated outdoor temperature of −26 °C during the heating period and a heating load of 21,000 kW), it quantitatively analyzes the impact of changes in supply and return water temperatures and temperature differences on the system. The research aims to clarify the influence law of different parameter combinations on system energy consumption and carbon emissions, providing a theoretical basis and data support for central heating systems to achieve low-carbon and economical operation while meeting heating demands.

   3. Experimental Study of a Refrigerator System Based on a Double-Suction Piston Compressor

      Lu Wang, Yali Bian, Shuxue Xu

      Abstract

      This paper presents an experimental study on a dual-temperature refrigerator system employing a double-suction piston compressor. The system’s working principle involves a secondary suction port on the compressor cylinder, enabling quasi-secondary compression to enhance refrigeration capacity. A test bench was built to evaluate performance under varying ambient temperatures (16 °C, 25 °C, 32 °C) and compressor frequencies (40–100 Hz), with comparisons to a single-suction compressor system. Results show that as ambient temperature rises, the freezer’s refrigeration capacity decreases significantly, while the refrigerator’s remains stable, and compressor power consumption increases with shorter off-periods. Higher compressor frequencies accelerate the freezer’s cooling rate more markedly than the refrigerator’s. When operating alone, the refrigerator maintains a stable exhaust temperature (60–65 °C). Compared to the single-suction system, the double-suction system increases refrigeration capacity by 12–24%, reduces exhaust temperature by 3–8 °C, and exhibits stronger adaptability to rising ambient temperatures, improving operational reliability and service life. This study provides experimental data for advancing double-suction compressor technology in dual-temperature refrigerators.

   4. Ideal Thermodynamic Model and Parameter Analysis of Ejector Large Temperature Drop Cogeneration System

      Jiyou Lin, Fangyuan Li, Jiashuo Zhou

      Abstract

      An ideal thermodynamic model of a complex heat-work conversion system with two finite heat reservoirs is constructed, which indicates the performance limit and optimization potential of a practical two heat reservoirs system with approximately constant heat capacity. The ideal thermodynamic model is qualitatively and quantitatively classified by analyzing the exergy balance relationship between the heat engine region and the heat pump region. The analytical solutions of thermodynamic performance limit and dimensionless process parameters are solved. The influence of different external work input or output conditions on the thermodynamic performance of the system is emphatically analyzed. The results show that the maximum process work of the parallel flow ideal thermodynamic model is more conducive to realizing the thermal process with a large temperature drop. The ideal thermodynamic model is used to evaluate the ejector large temperature drop cogeneration system. The results show that the system heat exchange perfectibility of thermal output mode, power output mode, and cogeneration mode is 62.70%, 43.44%, and 54.13%, respectively. Affected by the efficiency of the expander and generator, the net power output of the ejector large temperature drop cogeneration system with a total heat exchange of 15 kW is only 0.38 kW, and the thermal efficiency of the system is only 4.57%, which indicates that the thermal performance of the system still has great potential for improvement.

   5. Machine Learning-Enhanced Leakage Detection in District Heating Networks: Integrating Improved Hydraulic Modeling and Signal Denoising for High-Accuracy Localization

      Xuejing Zheng, Yuqian Zhou, Yaran Wang, Zhiyun Tang

      Abstract

      Leakage detection of district heating network (DHT) can prevent environmental and financial losses. This work presents a novel method that not only detects the location of leaks, but also takes engineering into account. Considering the effects of orifice shape, pressure, and cavitation, the traditional orifice outflow expression was improved based on the unsteady hydraulic model. For the pressure signals measured at the heat station, the signals are denoised by Shannon entropy-based wavelet transform, after which the PCA-Feature Importance feature extraction method is applied. The features are used to identify leaks using three neural network algorithms (LinearModel, CNN, MultLiM) and three decision tree algorithms (RandomForest, XGBoost, LightGBM). The result shows that decision tree algorithm achieves a leak pipeline localization accuracy of 99%, with a localization length of 10 m for individual pipelines. Even with only 1/6 of the measurement points or a low sampling frequency of 5 Hz, this method can still achieve a leak pipeline localization accuracy of 95%. It also maintains a low false alarm rate (FAR) even for abnormal jumps greater than the leak fluctuation magnitude.

   6. Application of Nonlinear Topology Optimization Method in Staged Construction of District Heating Network Engineering

      Yifan An, Yonggang Lei, Baocun Du

      Abstract

      Against the backdrop of intensifying global warming and the energy crisis, the imperative for green, low-carbon solutions presents new challenges for the energy sector, prompting nations and regions worldwide to enact and implement increasingly stringent building energy codes. These regulations drive the development of more efficient heating systems, where District Heating Networks (DHNs) play a pivotal role. The application of topology optimization to DHNs design is investigated in this study, aiming to minimize capital investment and enhance operational efficiency. We introduce the specific topology optimization framework employed and apply it to a real-world DHNs, demonstrating reductions of 1.3% in capital investment and 2.1% in operational costs compared to a conventional reference design based on expert engineering judgment. Furthermore, considering the project’s phased construction nature, we evaluated two distinct implementation strategies: findings reveal that neglecting long-term heat load projections during phased construction yields lower initial costs but incurs a 16.78% increase in total life-cycle cost, whereas pre-installing interfaces for future load expansion minimizes the total investment cost, representing the optimal overall construction scheme. This conclusion provides valuable guidance for designers in planning the phased development of heating networks, enabling optimal planning and design for such district heating projects.

   7. Modeling and Optimization of a Northern China District Heating System: A Dymola-Based Study

      Ziyang Cheng, Xin Meng, Xinhui Ma, Haofei Cai, Guopeng Yao, Shuai Sha, Xu Jin, Di Yang, Hao Zhang

      Abstract

      With the continuous development of intelligent heating technology, while the district heating system achieves clean and efficient operation, it also faces the practical challenges of uneven hydraulic distribution and energy waste. In order to improve the efficiency of heat energy transmission and distribution, this paper takes a typical northern residential community as a case, constructs a nonlinear hydraulic model of the secondary heating system based on the Modelica language, and integrates an interior - point optimization solver to realize the joint regulation of pump frequency and valve opening. Aiming at the heat load fluctuations at different time scales, two dynamic regulation strategies, namely the hourly - level and daily - level strategies, are designed, and the system operation data are simulated and analyzed. The results show that compared with the daily - level strategy, the hourly - level optimization is more flexible in responding to heat load changes. It not only significantly improves the system hydraulic balance, but also reduces the energy consumption of the circulating water pump by 36.61% and the total water supply flow by 21.36%. This study proves the feasibility and high efficiency of the hydraulic regulation method based on nonlinear optimization in the district heating system, and provides a replicable engineering path for intelligent regulation and energy - saving operation.

   8. Critical Component Identification Study of Uncontrollable Heating Systems

      Ding Mao, Chong Han, Jay Wang, Wei He

      Abstract

      As a complex thermal network ensuring civil and industrial energy supply, the failure of key components in heating systems can easily trigger cascading failures and large-scale heating outages. Aiming at the high computational complexity of traditional failure-simulation-based methods for key component identification, this study proposes a multi-dimensional index system and identification framework integrating graph-theoretic topology analysis and thermodynamic function evaluation. By constructing a modified betweenness index (topological importance), energy index and residual energy ratio (functional importance), and combining with system flow loss rate and user flow loss entropy (failure consequence indices), a complete quantitative evaluation system is formed. Verification using gridded heating system models with 4 to 25 nodes shows that the Spearman correlation coefficients between the modified betweenness and user flow loss entropy range from 0.82 to 0.93, and those between the energy index and system flow loss rate range from 0.65 to 0.96, with all coefficient of variation values less than 0.1, verifying the effectiveness and stability of the indices. The research results provide theoretical support for the efficient and accurate identification of key components in heating systems.

   9. Thermal Load Prediction in District Heating Systems Using GAN-Based Data Augmentation and a Dynamic Weighted LSTM-Prophet Hybrid Model

      Xuejing Zheng, Shisong Yan, Yaran Wang, Zhiyuan Shi, Zhiyun Tang

      Abstract

      Efficient and precise regulation of heating networks constitutes a critical technological pathway for achieving energy optimization and carbon emission reduction objectives. To enhance the prediction accuracy of thermal load in district heating systems while addressing differentiated demands across heat substations, this study proposes a personalized prediction methodology integrating data augmentation and hybrid model optimization. Initially, temperature, humidity, and temporal features were identified as key influencing factors through Pearson correlation coefficient analysis. A deep generative adversarial network (GAN) was subsequently employed for multi-dimensional scenario data augmentation, constructing an extended dataset. Building upon this foundation, an innovative LSTM-Prophet dynamic weighted hybrid model was developed, tailored to the topological characteristics of a regional heating network in Tianjin, China, enabling personalized weight configuration for individual substations to fulfill their heterogeneous operational requirements. Taking heat substation No. 566 as the case study, the impact patterns of weight coefficient w (denoting the weight of Prophet) on prediction accuracy were systematically investigated. Experimental results demonstrate that when w was set to 0.5, 0.7, 0.9, and 0.95, the mean relative errors between predicted and actual thermal load values reached 4.9%, 2.1%, -0.65%, and -1.45%, respectively. Consequently, the model exhibited optimal comprehensive performance at w = 0.9 for this specific substation. Error analysis revealed that negative error values indicate moderately conservative predictions, which strategically enhance operational reliability of the heating system. This weight optimization strategy provides a technical reference for differentiated regulation in district heating systems.

   10. Multi-domain Unified Modeling and Dynamic Characterization of Integrated Energy Systems

       Jin Wang, Yong Qiu, Ruifang Zhang, Yuhui Liu, Jintao Shao

       Abstract

       The integrated energy system provides strong support for energy transition and the realization of the “double carbon” goal through the synergistic optimization and efficient operation of multiple energies, but it covers a variety of energy forms, such as electricity, heat, gas, etc. The nonlinear coupling relationship between different energy systems and cross-domain parameter interactions greatly increase the difficulty of its dynamic modeling. Therefore, this paper adopts a modular modeling approach, establishes a multidomain unified mathematical model of the integrated energy system, and analyzes the dynamic response between different energy flows when the load of the integrated energy system changes, and the results show that: the multidomain unified modeling approach proposed in this paper has a good effect on describing the dynamic characteristics of the network of the integrated energy system, as well as the dynamic response between different energy flows, and the results can provide theoretical and technical support for the control and scheduling of integrated energy systems, optimization of multi-energy synergies, efficient operation, high-proportion renewable energy consumption, and scientific management.

   11. Flexibility Enhancement of Industrial Complex Through Thermal Energy Storage

       Xuran Ma, Peng Wang

       Abstract

       The integration of renewable energy sources and the need for more flexible energy systems make TES a crucial technology for industrial applications. This paper starts with flexibility evaluation of metrics and discusses the impact of energy storage on enhancing the flexibility of industrial parks with different source capacity and load characteristics. Precisely, this paper first conducts capacity configuration for each park with the goal of optimizing economy. After obtaining the configuration results, the system is optimized based on flexibility objectives to compare the flexibility improvement effects of energy storage systems in parks with different capacities and load characteristics. The results show that TES can significantly enhance the flexibility potential of the industrial heating system, ensuring the system has sufficient capability to cope with various uncertainties and the full utilization of flexibility can lead to up to 62% savings in operating costs for the system.

   12. Review of Low-Carbon Planning and Operation of Solar District Heating Systems

       Xiuxin Bi, Yuzhao Zhong, Dongliang Han, Tiantian Zhang, Zhuoyang Li, Yufei Tan

       Abstract

       Solar district heating systems (SDHS) represent a key approach to achieving sustainable and low-carbon heating solutions. To enhance the technical capabilities related to low-carbon planning and operational optimization, this paper first introduces the typical configuration of SDHS, critically reviews the current status and practices of solar district heating system planning (SDHSP), and proposes a conceptual planning framework to support performance-based decision-making. Subsequently, the paper conducts a literature review on two key issues of this framework: carbon accounting and operation strategy/model optimization. The review summarizes commonly used carbon accounting methods and evaluation indicators, as well as representative optimization models applied in SDHS planning. The findings reveal that further research is needed on life cycle carbon emission accounting, dynamic modeling across multiple time scales, and the applicability of alternative optimization models. This study is designed to help expand the use of solar district heating technologies and back the sustainable, low-carbon evolution of heating systems.

   13. Experimental Study on the Performance of Phase Change Energy Storage-Based Airplane Pre-conditioning Air Unit

       jiaqi Chen, meina Lin, gaosheng Xu, lin Cao

       Abstract

       With the rapid expansion of the aviation industry, civil airports have evolved into crucial transportation hubs. However, the power load at these airports exhibits pronounced peak-to-valley fluctuations, particularly during summer when daytime electricity demand surges, imposing significant strain on the power grid. To mitigate this imbalance between daytime and nighttime power consumption, improve power system stability, and optimize the economic efficiency of air conditioning operations, this study introduces a phase change energy storage (PCES)-based airplane pre-conditioning air unit by integrating PCES technology with a cascade air conditioning system. A prototype has been developed, and its operational performance has been experimentally studied. The result demonstrate that during the cold storage phase under ambient conditions of 28 °C and 42% relative humidity (RH), the prototype maintained reliable operation with a total cold storage time of 264 min. Under the environmental conditions (35 °C, 63%RH) during combined cold release operation, the prototype operated stably for 192 min, with the outlet air temperature meeting the operational requirement of not exceeding 2 °C.

   14. Enhancing the Reaction Kinetics of K2CO3 for Low-Temperature Thermochemical Energy Storage

       Hongzhi Liu, Miyuki Arai, Katsunori Nagano

       Abstract

       Industrial sectors release significant amounts of unused waste heat below 150 °C, which matches the temperature range for heating and hot water needs. Thermochemical energy storage (TCES) has the advantage of long-term storage and heat transportation, and K₂CO₃ is a candidate of thermochemical energy storage material, because of its excellent safety and stability. However, K₂CO₃ has the disadvantage of low reaction kinetics. In this research, composite particles were synthesized by mixing 97 wt.% K₂CO₃ and 3 wt.% expanded graphite (EG) with ethanol and water to improve its reaction kinetics.

       The results showed that the composite K₂CO₃ with EG exhibited improvements in both reaction kinetics and thermal conductivity. LiCl-1% exhibited the highest hydration reaction rate of 5.71 × 10⁻³ min⁻¹, greatly surpassing that of pure K₂CO₃ (0.243 × 10⁻³ min⁻¹). Moreover, the thermal conductivity increased by a factor of 1.39 to 1.52. In addition, the dehydration onset temperature decreased by over 7 °C enabling heat storage from lower-temperature heat sources and thereby enhancing the performance of the material as a low-temperature regenerated TCES material.

   15. Control Optimization of Multi-Energy System in Residential Heating and Domestic Hot Water Application

       Chenyu Ma, Yi Yang, Yiqiang Jiang, Kaiyue Liu

       Abstract

       This study addresses the challenge of optimizing control strategies for multi-energy systems in high-density residential buildings, focusing on space heating and domestic hot water applications in cold climates. Due to constrained space, dispersed energy consumption patterns, and limited renewable energy integration in such buildings, a multi-energy system combining solar thermal collectors, air source heat pumps, and sewage source heat pumps with an embedded stratified thermal storage tank is proposed. A novel quality-quantity regulation strategy for the demand side dynamically adjusts both the circulating flow rate and temperature of the heating fluid based on tank energy status and load requirements, enhancing energy utilization and extending heat pump operation compared to traditional constant-flow quality regulation. For the supply side, dead-zone control strategies are optimized for each subsystem: solar collectors (upper/lower dead-band temperature difference), air source heat pumps (control based on supply-required temperature difference), and other. Simulation results demonstrate that the quality-quantity strategy better matches heating loads, improves tank stratification, and increases heat pump runtime. Solar subsystem performance is highly sensitive to the upper dead-band limit, while sewage source heat pumps control has minimal impact on solar operation. The findings provide practical guidance for multi-energy system control design, improving efficiency and reducing auxiliary heating dependence in residential buildings.

   16. Experimental Study on Melting and Solidification in a Trombe Wall Integrated with Multi-row Channel PCM Wallboard

       Yao Yan, Yonggang Lei, Yazi Li, Wuxuan Pan, Chongfang Song, Yonghui Wang

       Abstract

       Phase change material Trombe walls (PCM-TWs) have been demonstrated to be an effective means of reducing indoor heat loads. However, the heat storage efficiency is limited by the low thermal conductivity of PCMs. This study investigates a Trombe Wall Integrated with Multi-Row Channel PCM Wallboard (MCPCM-TW) to address the high thermal resistance problem in heat storage process. This study develops a visualization of solidification and melting of paraffin wax in a rectangular cavity, aimed to analyze the melting and solidification laws of paraffin wax under different heat flux. An experimental investigation was conducted to explore the storage and discharge thermal efficiencies of PCM-TW and MCPCM-TW at the same heat flux. The results show that the MCPCM-TW has obvious benefits over PCM-TW in melting/solidification with similar heating/cooling conditions. The melting process of paraffin wax can be roughly di-vided into three regimes, namely, pure conduction regime, mixed (convection & conduction) regime and convection regime. In the melting process, The MCPCM-TW enhances the heat transfer in the mix regime obviously, the melting time is reduced by 10.9%. In the solidification process, the MCPCM-TW reduces the overall thermal resistance by increasing the heat transfer areas of the internal paraffin, the solidification time is shortened by 13.19%. At the end, the per-formed experiments could be helpful for validation of future simulation with complex features, particularly to provide methods for the design of PCM walls.

   17. Thermal Characterization of Hydrated Salt Phase Change Materials in Thermal Storage Floors

       Yue Han, Jun Wang, Fuyu Qin, Tao Xu

       Abstract

       Building energy consumption is a major global concern, making energy-saving solutions essential. In this study, phase change thermal storage floors (PCMs) offer an effective solution by efficiently storing and releasing heat. Integrating PCMs into radiant heating systems enables heat energy migration through latent heat, enhancing temperature regulation and reducing fluctuations caused by thermal inertia. This study developed a new phase change heat storage floor using a hydrated salt composite stereotyped phase change material (EP-SPCM) with a phase change temperature of 41.2 °C and latent heat of 170.5 J/g. A laboratory model of underfloor heating was constructed, and the coupled phase change thermal floor-room air heat transfer process was simulated and analyzed by FLUENT software. The results show that the thermal inertia effect of the phase change thermal storage floor can significantly suppress the indoor temperature fluctuation, and at the same time effectively prolong the thermal comfort time through the latent heat regulation of the phase change process, so as to improve the stability of the indoor thermal environment.

   18. Optimizing Feature Selection for Load Forecasting Using Multi-Head Attention Mechanism

       Shuqin Chen, Jianan Qian, Jiayi Luo, Wangxi Gu, Binqing Wei, Shuiquan Ye, Yueqin Liu

       Abstract

       Feature selection has a significant impact on the predictive performance of load forecasting models, with historical load features being particularly crucial. Existing studies typically use manual trial-and-error approaches to select historical load data... without dynamically assessing how significantly each time period affects predictions. This often results in the omission of certain key historical information during feature selection, thereby limiting forecasting performance. To address this issue, this study proposes a hybrid short-term load forecasting model for park-level applications based on CNN-GRU-MHA. In this model, a Convolutional Neural Network (CNN) is employed to extract local temporal features, a Gated Recurrent Unit (GRU) is utilized to capture long-term dependencies, and a Multi-Head Attention (MHA) mechanism dynamically assigns weights to historical load features from different time periods, highlighting key time-step information and enhancing feature representation and model interpretability. The proposed model is validated using cooling load data from a typical campus. Test results demonstrate that adding the Multi-Head Attention mechanism (MHA) improves prediction accuracy by 25.51% compared to traditional manual selection of input time periods. Further analysis of the MHA-assigned weights confirms that historical load features from different time periods all contribute to the forecasting results, with varying degrees of importance.

   19. Numerical Study on the Impact of Cylinder Cooling on Energy Efficiency of the Compression Process in a CO₂ Refrigeration System

       Junrui Nie, Guoyuan Ma

       Abstract

       Addressing the issue of low energy efficiency in the compression process of transcritical CO₂ refrigeration systems, this study systematically investigates the influence of cylinder cooling on compression efficiency. A numerical model integrating transient heat transfer equations and a modified R-K real gas equation of state was established. The results indicate that increasing the cooling water flow rate from 0.134 m³/h to 0.957 m³/h significantly reduces the compressor discharge temperature by 1.3% ~ 1.7% and compression power consumption by 0.7% ~ 0.9%, with a more pronounced effect observed at lower flow rates. Thermodynamic analysis reveals that increasing cooling water flow reduces the exergy destruction rate, dimensionless constant of entropy generation, and available energy loss rate criterion, signifying a decrease in the irreversibility of heat transfer between the high-temperature, high-pressure gas within the compression chamber and the cooling water. These findings provide a theoretical basis for optimizing the thermodynamic performance and cooling strategies of transcritical CO₂ refrigeration systems.

   20. Performance Study of Air Source Heat Pump Based Radiant Floor and Fan Coil Synergistic Air Conditioning System

       Huibo Li, Lei Yang, Hongwen Jin, Zhaochao Tu, Zhenyang Zhang, Jingyi Liu, Jiangtao Hao

       Abstract

       The utilization of air-source heat pumps has gradually increased since the “double-carbon” aim was established, and the impact of a heating system that consists of radiant floor terminals and air-source heat pumps as a heat source is becoming more evident. However, few studies has been done on the use of such devices as air conditioners in cold climates. The heat pump and floor radiation heating system’s existing laboratory (159 m2), the fan coil’s new dehumidification function, the floor radiation, the fan coil as the cold source’s end, the combined use of the two indoor comfort systems, the cold load bearing ratio, and other experimental elements are all used in this paper. The findings indicate that: 1) when floor radiation is used alone, the average indoor temperature during the day is 28.5 °C, the room’s humidity is 56%, the comfort is poor, and the energy consumption is low; 2) when the fan coil is used separately, the average indoor temperature during the day is 27.2 °C, the comfort is poor, and the refrigerant parameters are demanded; 3) when the two are used together, the fan coil is supported by 55% of the cold load, the floor radiation is supported by 45%, the average indoor temperature during the day is 26.7 °C, with excellent comfort.

   21. Frosting Loss Assessment and Design Method for Air Source Heat Pumps in High Humidity Regions of China Using CICO-Based Equivalent Temperature Drop

       Zikun Li, Yuying Sun, Wei Wang, Wenzhe Wei

       Abstract

       Reducing the performance degradation of air source heat pumps (ASHPs) due to frosting during the heating season is critical. Previous studies have reported that a higher Characteristic Index for Configuration and Operation (CICO) improves the frosting suppression performance of ASHPs. However, selecting appropriate CICO for different regions is a challenge due to their varying frosting suppression needs. This study proposes two frost suppression grades (FSG 1 and FSG 2) to define acceptable levels of frosting loss, and develops a novel CICO design method based on the CICO-based equivalent temperature drop approach. Taking 161 high-humidity cities in China as examples, the study assesses the impact of different CICO on frosting losses, and determines the recommended CICO value for each region. Results indicate that increasing the CICO from 6 to 10 reduces frosting losses by an average of 37.5% in high-humidity regions, and raises the proportion of cities meeting frost suppression grades from 17% to 80%. To meet FSG 2, CICO values of 8 to 17 are generally sufficient, while achieving FSG 1 requires CICO values above 10 in 90% of cities and above 30 in 17 cities. These findings offer practical guidelines for the efficient application of ASHPs in high-humidity regions.