Verification of refrigerant evaporating temperature control effect in VRF systems in actual buildings

Abstract

In this study, a refrigerant evaporating temperature control algorithm was developed for the variable refrigerant flow (VRF) system, and its effect was quantitatively examined through a multi-calorimeter experiment and a field test in actual buildings. As previous studies on refrigerant evaporating temperature control have been predominantly conducted through experiments and simulation, aspects such as the impact of refrigerant evaporating temperature control on energy-saving and indoor temperature in an actual building and the change in the energy efficiency of the VRF system due to the Thermo on–off change of indoor units, have not been examined. As such, in this study, an algorithm that predicts the indoor load based on the indoor temperature change and controls the refrigerant evaporating temperature based on the load was developed. Before applying the developed algorithm to actual buildings, the effectiveness of refrigerant evaporating temperature control was evaluated through an experiment. Changes in the performance and efficiency of the VRF system according to the evaporating temperature and the number of operating indoor units were measured in a multi-calorimeter, and the effect of refrigerant evaporating temperature control on the reduction in the actual number of operating indoor units due to the Thermo off was examined under part-load conditions. In addition, the developed algorithm was applied to the office and education buildings in a factory located in Thai Nguyen city, Vietnam, and its energy-saving effect on the indoor temperatures was verified as per the energy effect verification process provided by the International performance measurement and verification protocol (IPMVP). The verification results confirmed that conducting refrigerant evaporating temperature control saves energy by increasing the Thermo on rate and the refrigerant evaporating temperature. It was additionally confirmed through the actual operation data that refrigerant evaporating temperature control has the effect of improving the indoor thermal environment by increasing the accuracy of indoor temperature control.