30 May 2005

PERFORMANCE OF GROUND SOURCE RESIDENTIAL HEAT PUMPS


This paper presents the results of two-year monitoring of two ground-to-floor residential heat pumps,
typical of the Belgian market, used for space heating in single-family houses. Both systems are commontype
vapor compression heat pumps and use ground as cold source, house floor as hot sink and R22 as
refrigerant. Firstly, we present the measurement method to obtain daily COP values from instantaneous
measurements on the refrigerant. Secondly, annual energy consumption, seasonal COP and costs are
presented for a three-year (heat pump #1) and two-year period (heat pump #2). Seasonal COP values from
2.69 to 2.96 are obtained. Finally, daily COP values are correlated to evaporation and condensation
temperatures, and the daily running time of the heat pump is correlated to the day-average outdoor
temperature. Condensation temperatures, which vary from 35 to 38 °C, are well explained by the daily
running time of the heat pump. Evaporation temperatures, which vary from -2 to -9 °C, are related to the
ground temperatures in a complex way, depending on the heat transfer processes in the ground.