Considering the shortcomings of temperature and humidity-independent control in small and medium-scale residential and office buildings

a novel water chiller/heater based on dual evaporation temperatures was developed. The operating conditions of the unit were investigated through experiments in which the compressor speed and valve opening were varied. The compressor speed was varied from 30–80 Hz and the high and low-temperature sides of the electronic expansion valves (EEV1 and EEV2) were opened from 80%–100% and from 10%–50%

respectively. The experimental results were analyzed to reveal the operational and regulatory characteristics of the unit. The results showed that the cooling and heating capacities of the unit were proportional to the compressor speed in the cooling and heating modes. In the cooling mode

when the EEV2 opening was < 30%

the cooling capacity at the high and low temperature sides and the total cooling capacity of the unit decreased as EEV1 opening increased. When the EEV1 opening was fixed and the EEV2 opening increased

the cooling capacity on the high-temperature side was largely constant. The cooling capacity on the low-temperature side and the total cooling capacity first increased and then decreased

reaching a maximum with EEV2 opening at 30%. The highest low-temperature cooling capacity suggests a better dehumidification capacity.