Performance of Horizontal Field Earth-Coupled Heat Pumps

Abstract

An alternative to traditional methods of residential heating and cooling is the heat pump. However, heat pumps which use the outside air as a heat source/sink become inefficient during the periods of highest demand. Another possible heat source/sink is the earth, several feet below the surface. The purpose of this paper is to study the performance of horizontal pipe field, closed-loop, earth-coupled heat pump systems. The effects on system performance of variations in pipe field and soil parameters are discovered through the use of a finite element computer simulation of the system. These parametric studies use heating and cooling loads for Ohio. Total field length and pipe diameter as well as pipe material and soil thermal conductivity are varied in several different sets of simulations. The results of these simulations, summarized as yearly operating costs, are used to determine the system configuration which gives the minimum payback period in a break even economic analysis. For a 2000 square foot house in the Central Ohio area, the optimum earth-coupled heat pump system has a payback of about seven years when compared with the performance of an air-to-air heat pump. The simulation methods used in this paper are easily adapted to systems with other heating/ cooling demands.