Field Performance of a Ground-Coupled Heat Pump in Abilene, Texas

Abstract

A nominal 10.6 kW (3 ton), vertical-configuration ground-coupled heat pump was installed in Abilene, Texas in December 1989 and was monitored until May 1993 using a remote data acquisition system. The unit was installed in the guest officer quarters at Dyes Air Force Base. Monitored data included: temperature and relative humidity of return and supply air, water temperature entering and leaving the condenser, power consumption of the individual system components, cycling rate, on-time, and soil temperatures at various depths and radial locations. Water and air flow rates were measured twice during the monitored period, and have remained constant. The measured quantities allow calculation of instantaneous capacity, power, coefficient of performance (COP), and ground-coil heat rejection. Data for operation in the cooling and heating mode are discussed here. Based on the experimental data, it was discovered that the water temperature entering the condenser (EWT) exhibited a prolonged minimum after start-up due to cooling of the water during the off-cycle when operating in the cooling mode. The decreased levels of EWT early in the cycle increased capacity and decreased power, both acting to increase the COP. Seasonal COPs for heating and cooling were estimated from the data and are presented.