Energy-efficient air conditioning system using a three-fluid heat exchanger for simultaneous temperature and humidity control

Abstract

Room air conditioners are unable to simultaneously control the temperature and humidity of the air supply. Although temperature-regulating dehumidifiers can simultaneously control the temperature and humidity, they have complex refrigerant pipelines, and the heat exchanger exhibits air resistance when the reheat demand is low. This study proposes an air conditioning system for simultaneous temperature and humidity control, using a three-fluid heat exchanger. The supply air temperature is adjusted by changing the air volume ratio and cooling water flow rate through the three-fluid heat exchanger, which is used as the condenser. Free cooling can be realized by supplying low-temperature cooling water to treat the return air. Numerical models were built to simulate the performance of the devices in the system, and were validated by experimental results. The temperature-regulating performance and energy consumption under different conditions were numerically calculated using a case-studied air-conditioned room in Beijing. The results are summarized as follows: 1. The proposed strategy can regulate the supply air temperature over a wide range of temperatures. 2. Compared with those of the temperature-regulating dehumidifier system, the compressor and fan energy consumption of the proposed system are reduced by 19.1% and 15.5%, respectively, with a total energy-saving rate of 15.8% in the cooling season. 3. Compared with those of the room air conditioner system, the compressor energy consumption of the proposed system is reduced by 11.5%, and the energy-saving rate of the entire system is 6.3%. The initial investment of the proposed system does not increase significantly compared with conventional systems, and the refrigerant pipeline and valves can be simplified, resulting in acceptable economic performance for the proposed system.