Geothermal heat pump systems in cold regions: efficiency improvement by use of ambient air

Abstract

We examine the problem of efficiency in both air-source and geothermal heat pumps in regions with low ambient air temperature, and the advantage of using a combination of both systems in one equipment. Both geothermal and air heat pumps have their advantages and disadvantages. Geothermal heat pumps are more expensive to install and, in colder climates, experience a progressive decrease in efficiency with constant use during the winter season because of chilling of the ground adjacent to geothermal heat exchangers during heat extraction. Air-source heat pumps are less expensive to install and experience a decrease in efficiency as ambient temperature is getting lower. A numerical model simulation was conducted using the program “INSOLAR.GSHP.12” for a 200 sq.m. house in Moscow. The model tested the efficiency of combined use of a ground heat pump at ambient temperatures below -10°C, and air heat pump for ambient temperatures above -10°C. The results were compared to simulation of using only a geothermal heat pump. The results show a 13.3% reduction in energy consumption using the combined ground and air heat pumps over the energy requirement of using only the geothermal heat pump.