Experimental evaluation and simulation of a variable refrigerant- flow (VRF) air-conditioning system with outdoor air processing unit

Abstract

Variable refrigerant flow (VRF) refers to the ability of an air-conditioning (AC) system to control the amount of refrigerant flowing to the multiple evaporators (indoor units). This study compares the actual energy use of a building, equipped with a VRF system with simulation results obtained using EnergyPlus. Also, the aim of this study is to analyze the performance related to energy and thermal comfort when the VRF system without ventilation is replaced with the VRF system with the energy recovery ventilation (ERV) or VRF system with the dedicated outside air system (DOAS). The measured power use of the VRF system is very similar to the simulated power use of the VRF system. The mean value of the difference between simulation and measured data in monthly power use in summer and winter was 3.3% and 3.6%, respectively. The yearly energy use of the VRF system without ventilation is found to be 213.6kWh/m2a. The VRF system with ERV in case 4 and the VRF system with DOAS in case 8 are found to be 16.8% and 26.0% higher than the VRF system without ventilation, respectively. Through the entire year, it was found that 17.2% of indoor air condition data provided by the VRF system without ventilation in the winter and 16.2% of the data in the summer fall within the ASHRAE winter and summer comfort zones. In order to improve the thermal comfort, the setpoint temperature in winter needs to be increased and the humidity in summer needs to be reduced. On the other hand, it was found that 93.9% of indoor air condition data provided by the VRF system with DOAS in the winter and 83.8% of the data in the summer fall within the ASHRAE winter and summer comfort zones. When the VRF system without ventilation is replaced with the VRF system with DOAS, the thermal comfort percentage is improved during the winter and summer by 76.7% and 67.6%, respectively.