Design and performance of a constant temperature and humidity air-conditioning system driven by ground source heat pumps in winter

A constant temperature and humidity air-conditioning system driven by ground source heat pumps was designed and constructed in an archives building in Shanghai, China. The system consists of two water-to-water heat pumps and 280 boreholes with 80 m in depth. In order to keep the temperature and humidity constant, the operation mode that one heat pump ran in heating mode and the other one ran in cooling mode was deployed. According to the experimental results under typical winter weather condition of Shanghai, the average COP of the heat pump in heating mode was 5.2. The average temperature and relative humidity of the archives house were 22.8 °C and 52.5%, respectively. It was found that the operation mode we deployed could reduce the heat absorbed from the soil by 20%. Theoretical analysis showed that it was helpful for the earth energy conservation with one heat pump operated in cooling mode in winter. It was also shown that the decrease range of temperature of the soil in the middle of two boreholes would reduce with the increase of the distance between two boreholes. The distance between two boreholes is suggested to be 4–5 m in Shanghai.