New method for measuring field performance of variable refrigerant flow systems based on compressor set energy conservation

In recent years, variable refrigerant flow (VRF) systems have gained popularity in commercial and residential buildings. It is extremely significant to obtain the real performance of VRF systems in order to improve design. However, the measurement of the field cooling or heating capacity of air-cooled VRF systems has not yet been thoroughly addressed. In this paper, a novel field measurement method for the capacity of VRF systems is proposed based on the energy conservation of a compressor set. The compressor set consists of the actual compressor, oil separator, and capillary with the corresponding pipelines. The validation results indicate that the compressor set energy conservation method yields 15% accuracy for cooling capacity and 13% accuracy for heating capacity. Furthermore, the novel measurement method was applied to a VRF system in an office building over four weeks during the heating season. The field test results demonstrate that the average part-load ratio of the VRF system was 0.33, which revealed that the sizing of the VRF system was relatively excessive.