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.