Comparative analysis of the energy efficiency of air-conditioner and variable refrigerant flow systems in residential buildings in the Yangtze River region

Abstract

Two types of air-conditioning systems, named as room air conditioners (RAC) and multi-connected air-conditioners (variable refrigerant flow (VRF) systems) have become popular heating and cooling facilities for residential buildings featured with ‘part-time-part-space’ operation characteristics in the Yangtze River region. However, the research on the energy efficiency of these two systems in residential buildings is currently lacking. Based on the actual measured air-conditioning operation hours and demand characteristics, this study analyzed the annual operation performance of the two systems by modelling and simulation. In addition, a field test of twelve RACs and five VRFs in residential buildings was conducted in the Yangtze River region, showing the annual performance factors of VRFs and RACs ranged from 3.7 to 5.3 kWh·kWh−1 and 3.0 to 4.6 kWh·kWh−1, respectively. It is found that for the same operation hours and the total cooling capacity of VRF systems RACs, the VRF has low energy efficiency at low load ratios (generally less than 25%); which is the key barrier to its application in residential buildings in the Yangtze River region. It is suggested the RAC is the appropriate solution for heating and cooling a residential building with a ‘part-time-part-space’ operation mode as it is more energy-efficient. New advanced technologies for VRF systems are expected to be developed in order to adapt the part-load operation mode to achieve high energy efficiency. This study contributes to providing evidence for the decision-making of RAC and VRF systems for policymakers, and building and engineering designers in the context of energy efficiency for the region.