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2023 | Book

Variable Refrigerant Flow Systems

Advances and Applications of VRF

Editors: Napoleon Enteria, Takao Sawachi, Kiyoshi Saito

Publisher: Springer Nature Singapore


About this book

This book compiles the latest research, development, and application of VRF systems with contributions from various experts who pioneered and contributed to the development of the VRF system. This book presents the fundamental issues related to the real application and behaviour of the VRF system based on the long-term monitoring of the installed system. With our experience of pandemic which COVID-19 is an airborne, the spread of the virus is very fast. With this, the heating, ventilating and air-conditioning (HVAC) system is a major player in the maintenance and control of indoor environment to minimize the spread of the virus. As the variable refrigerant flow (VRF) system is a versatile HVAC system in which it can operate at different conditions, the application of the VRF system is very important to control the indoor environmental conditions. Thus, the publication of this book is important with the present situation and the future possible situation which the control of indoor spaces is very important. With this, this book will serve as a reference for building designer, contractors, building regulators and students.

Table of Contents

Chapter 1. Trends in Variable Refrigerant Flow Systems
The requirement to have a quality indoor environment consumes a significant amount of energy. The proper design, selection and installation of a heating, ventilating and air-conditioning (HVAC) system is important to have the efficient maintenance of a quality indoor environment. The selection of the variable refrigerant flow (VRF) system is one of the important options, as the VRF system is one of the most versatile HVAC systems. The operation of the VRF system depends on the indoor environmental requirements and the outdoor conditions. Hence, the VRF system is becoming widely applied to meet different indoor environment requirements and climatic conditions due to its robustness, flexibility, and energy efficiency.
Napoleon Enteria, Takao Sawachi, Kiyoshi Saito
Chapter 2. Evaluating the Ignition Hazard of Alternative Refrigerants for Variable Refrigerant Flow Systems
From the viewpoint of replacing HFC refrigerants to Lower-GWP refrigerants, a series of experimental studies for ignition and combustion behaviors of A2L refrigerants has been carried out to contribute risk management of them. In this paper, experimental results on some cases that A2L refrigerant is leaked from RAC and/or VRF system and it impinges to some ignition source candidates such as electric spark and an open flame are introduced. The following two topics of experimental evaluation of ignition hazards of A2L refrigerant are described; (1) in case that A2L refrigerant impinged to a burning lighter, (2) full-scale ignition experiment that A2L refrigerant which was leaked from VRF system to a model karaoke room impinged to an open flame. In the case (1), R32, R1234yf, R1234ze(E) were tested as the representative A2L refrigerant. There were no cases that the ignition of these refrigerants by a commercial gas lighter. On the other hand, ignition was observed in several cases when a commercial oil lighter was used in the accumulated these refrigerants with air. In the case (2), the accident scenario that all amount of A2L refrigerant installed in the VRF system is accidentally leaked into a narrow karaoke space and it impinges to a burning candle is assumed. The full-scale model of a karaoke space was built up, and actual amount of refrigerant was leaked. R32, and R1234ze(E) were used as the test refrigerant. The working/stopping of mechanical ventilation was set as the experimental condition. If the mechanical ventilation wasn’t worked, both R32 and R1234ze(E) were ignited by an open flame when the amount of refrigerant at which concentration in air became UFL when the entire amount leaked and diffused homogeneously. However, no ignition was occurred when the mechanical ventilation was worked as usually.
Tomohiko Imamura
Chapter 3. Flow Boiling Heat Transfer of Low GWP Refrigerant R1234yf with the Entrancement of Lubricating Oil in Small Diameter Tubes
The effects of lubricating oil on the flow boiling heat transfer of the low global warming potential (GWP) refrigerant 2,3,3,3-tetrafluoropropene (HFO-1234yf) in small-diameter tubes with inner diameters of 2 and 4 mm were experimentally investigated. Measurements of the local heat transfer coefficient and observations of the flow pattern were conducted to clarify the change in heat transfer performance and flow pattern under different vapor quality, mass flux, heat flux, and oil mass fraction conditions. The results showed that with an increasing oil mass fraction, the local heat transfer coefficient increased at lower vapor quality because of intensified foaming phenomena. However, the heat transfer coefficient decreased monotonically with oil mass fraction in the high-quality vapor region. Foaming phenomena were seen at different mass and heat fluxes during the visual observations.
Chaobin Dang, Shizuo Saito, Eiji Hihara
Chapter 4. Analysis of Air Side Cooling and Dehumidification Performance in Evaporator in Direct Expansion (DX) Variable Refrigerant Flow (VRF) Air-Conditioning (A/C) System
Direct Expansion Variable Refrigerant Flow Air-Conditioning (DX-VRF-A/C) units can be seen in buildings of all sizes. The evaporator in a DX-VRF-A/C unit (or DX air cooling coil), normally generates heat and mass transfer in the form of cooling and dehumidifying of hot and humid air flowing through the cooling coil. DX air-conditioning unit with single speed compressors and forced draft fans usually rely on switch control to maintain only the indoor dry bulb temperature which results in an uncontrolled balance of indoor humidity and reduces thermal comfort, and consequently causes poor indoor air quality (IAQ) as well as produces low energy efficiency. Thus, DX air-conditioning unit with variable-speed compressors and forced draft fans are increasingly adopted in pursuit of higher energy efficiency and thermal comfort indoor environment. Hence, study the simultaneous heat and mass transfer performance in DX air cooling coil of DX air-conditioning unit with variable-speed compressor and forced draft fan is essential, however, research work is still lacking in regards to this A/C system. A comprehensive analysis of the airside cooling and dehumidification process in DX cooling coil and its application are illustrated in this chapter. It commences with introducing the calculation of an important dimensionless parameter, namely steady state Equipment Sensible Heat Ratio (SHR) of DX air cooling coil, which is defined as the ratio of the output sensible cooling capacity of DX cooling coil to the total output cooling capacity. An experimental study on estimating on the dehumidification effect on the airside of the superheated region (SPR) in a DX cooling coil is given. The development of the modified Logarithmic Mean Enthalpy Difference (LMED) method for evaluating the total heat transfer rate in a wet air cooling coil operating under both unit and non-unit Lewis Factors (Le2/3) conditions is reported at the end of this chapter.
Liang Xia, Isaac Lun
Chapter 5. Application of Machine Learning and Artificial Intelligence in Design, Optimization, and Control of VRF Systems
Variable refrigerant flow (VRF) technologies, also known as variable volume refrigerant (VRV) systems, are taken into account as one of the most efficient, environmentally friendly, and economically viable alternatives for providing cooling and heating demands in the buildings. The increasing tendency towards using VRF technologies, in addition to the huge progress in the computer science, have led to using machine learning and artificial intelligence for design, optimization, and control of such systems with a fast upward trend. Taking these points into account, this chapter aims at giving an overview of artificial intelligence technologies and machine learning methods utilization for VRF systems. It is done by describing their application in design, optimization, and control of them.
Ali Sohani, Fatemeh Delfani, Mohammadmehdi Hosseini, Yabin Guo, Ala Sadooghi, Siamak Hoseinzadeh, Hoseyn Sayyaadi
Chapter 6. Energy Efficient Variable Refrigerant Flow Systems for Modern Buildings
The growing demand for the primary energy and the associated environmental issues globally, have led to the progress in energy conservative approaches in the recent years. From the standpoint of confronting the energy challenges in buildings, the development of energy efficient systems and energy conservative technologies is becoming increasingly important for satisfying the end-user requirements. In the class of highly energy efficient systems, the variable refrigerant flow (VRF) or the variable refrigerant volume (VRV) system has been developed to meet out the cooling and heating requirements in buildings. VRF/VRV system, basically operate through the modulation of the refrigerant flow according to the energy demand in buildings. In recent years, the amalgamation of control systems in heating, ventilation, air conditioning and refrigeration (HVAC&R) research has provided the impetus for the development of VRF systems with enhanced energy efficiency and energy savings potential for building applications. This chapter primarily aims at reviewing the potential research studies emphasizing the importance of VRF cooling and heating systems dedicated for achieving enhanced energy efficiency and energy conservation in buildings. In the spectrum of VRF systems, the technical revelations pertaining to the refrigerant flow characteristics, single-loop and multi-loop units and combined/hybrid VRF systems with advanced intelligent controllers have been reviewed from a variety of research studies reported in the literature. Furthermore, the roles of key governing aspects which greatly influences the operational performance and feasibility of the VRF/VRV systems integration for modern buildings have been addressed and signified.
R. Parameshwaran, R. Karunakaran
Chapter 7. Behavior of a Variable Refrigerant Flow System in a Controlled Simulated Dynamic Environment
This chapter describes the performance evaluation of a variable refrigerant flow (VRF) system subjected to different operational conditions. An actual VRF system was operated under controlled dynamic environmental conditions simulated in the laboratory. The dynamic operational conditions were mimicked in real operational conditions to be encountered by a VRF system in its actual installation. The results show that the VRS system performance is highly affected by the actual operating conditions as compared to the ideal conditions set by the testing standards. Hence, it is important to consider how and where the VRF system operates in an actual building to optimize the VRF system and minimize energy consumption.
Napoleon Enteria, Hideki Yamaguchi, Masato Miyata, Takao Sawachi, Yasou Kuwasawa
Chapter 8. An Air Enthalpy Method for Measuring the Thermal Capacity of an Installed Variable Refrigerant Flow System
Evaluating the thermal capacity of an installed variable refrigerant flow (VRF) system is important to determine if the system is functioning well according to its design and installation. An air enthalpy method for the measurement of VRF system thermal capacity is an important method, as it can measure thermal capacity even if the refrigerant flow rate is not accurately measurable, such as when in two-phase flow. The VRF system’s thermal capacity was accurately measured using the air enthalpy method based on a comparison with the artificial climate chamber’s thermal load. With this, the air enthalpy method can be used to measure the thermal capacity of the installed VRF system in actual buildings.
Napoleon Enteria, Hideki Yamaguchi, Masato Miyata, Takao Sawachi, Yasou Kuwasawa
Chapter 9. Field Test and Evaluation of VRF System
Heating, ventilation, and air conditioning (HVAC) systems account for almost half of the energy used in buildings due to the rising demand for better thermal comfort in indoor environments. Building energy metering and management have received a lot of attention recently as a means of achieving the Paris Agreement’s objectives of energy conservation and low carbon emissions. As a promising technology for space cooling and heating, the variable refrigerant flow (VRF) system, have been applied in various commercial and residential buildings worldwide in decades. Among the cooling/heating source equipment, cooling/heating performance of water-medium ones can be easily measured by measuring the water flow rate and its temperature difference. However, for air-to-air systems, on-field capacity-related performance of the system is hard to be determined though electricity consumption can be measured. As a consequence, the challenge of performance measurement to air-to-air system impedes the development of energy management, energy-saving operation, system retrofitting. In order to obtain the cooling/heating capacity of VRF system, measurement methods are classified into three methodologies in this chapter, including water temperature difference method, air enthalpy method and refrigerant enthalpy difference method. This chapter introduces the principle and applicability of each method. For water-cooled VRF, the water temperature method measures the water flowrate as well as temperature difference. For air-to-air VRF, capacity can be only measured by air enthalpy difference method and refrigerant enthalpy difference method. The former determines the capacity through air flowrate and air specific enthalpy difference of indoor/outdoor heat exchangers, while the later by refrigerant flowrate and refrigerant specific enthalpy difference. The refrigerant flowrate can be determined by refrigerant flowmeter, compressor performance curve or energy conservation equations. It is of great importance to develop on-field performance measurement technology for VRF system. In this chapter, the accuracy and application of compressor set energy conservation (CSEC) method, which regards the compressor, oil separator, capillary, liquid separator and corresponding pipelines as a compressor set, are introduced in detail. The related standards adopted (or to be adopted) the field test method of VRF for its convenient and reliable. The product standards adopt the built-in field test method to realize operation/maintenance management and performance monitoring. On one hand, it is regarded as the complement for the performance test in the laboratory (SEER, APF). On the other hand, it also provides the original valid data for fault diagnosis and optimal control, which are beneficial to customized energy-saving and comfort control strategies. The standard Specification for measuring field performance of room air conditioners has been published and executed. As the impartial performance test method, it ensures high accuracy on measurement with independence on manufacturers and noninterference to users. Currently, this method has been used in two HVAC (including VRF system) system retrofitting standards.
Wenxing Shi, Baolong Wang, Hansong Xiao, Zixu Yang
Chapter 10. Variable Refrigerant Flow (VRF) System Field Test and Data Analysis Methodologies
Field testing is a reasonable and effective way to measure the performance of the Variable Refrigerant Flow (VRF) systems. While VRF systems demonstrated their high performance in the laboratory, some researchers reported that the Coefficient of Performance (COP) was as low as 1.74 in on-site tests. Thus, studying the VRF system’s field test performance and identifying the cause of the difference is significant. This chapter first provides a literature review of current VRF system field test studies, including the model validation field tests, control comparison tests, and parametric study tests. Then the field test methodology is presented based on the Air-Conditioning, Heating, and Refrigeration Institute standards. In addition, the approaches measuring system capacities, which are at the core of the COP calculation, are discussed from the airside and the refrigerant side. Finally, this chapter uses a case study in a campus office building to illustrate the field test process and compares different data analysis methods. Time-average performance metrics like Daily Performance Factor and Quasi-Steady-State (QSS) performance metrics are mainly focused. In conclusion, choosing an appropriate approach needs to consider both the purpose of the field test and facility constraints. Future VRF systems need a simple-handle and low-cost field test method.
Hanlong Wan, Yunho Hwang, Reinhard Radermacher
Variable Refrigerant Flow Systems
Napoleon Enteria
Takao Sawachi
Kiyoshi Saito
Copyright Year
Springer Nature Singapore
Electronic ISBN
Print ISBN