Test and Simulation of the Operational Characteristics of a Water Chiller Based on Dual Evaporation Temperatures

In small-to-medium scaled residential buildings, direct-expansion (DX) air conditioning (AC) system cannot meet indoor occupants’ requirements for a healthy, comfortable and energy efficient indoor environment. Based on the annual load of a residential building in Shanghai, a new type of dual evaporation temperatures chiller was proposed based on a dual suctions compressor and two plate heat exchangers as high and low temperature evaporators. The high temperature evaporator produced chilled water at a temperature of about 20°C, and chilled water of 7°C for the low temperature side. High-temperature chilled water was used to remove sensible cooling load, and low-temperature chilled water the indoor latent cooling load by dehumidifying the fresh air, thus realizing independent control of temperature and humidity. The application of high evaporation temperature can effectively improve the energy efficiency of the system. For the novel chiller, the evaporators’ heat transfer model was established to calculate the outlet water temperature of evaporators at different operation conditions, and verified through the test of the prototype. Simulation results showed that the coupling effect of the electronic expansion valves (EEVs) on the high and low temperature side was insignificant. In addition, when the opening of low temperature EEV was about 30%, the temperature of the chilled water for dehumidifying reached lowest, suggesting the maximum dehumidifying capacity of the system.