Development of a graph method for preliminary design of borehole ground-coupled heat exchanger in North Louisiana

Heating and cooling of a building is a major energy demand and a source of CO2 emission in the atmosphere. Using geothermal energy in the form of borehole ground coupled heat exchanger (GHX) can be an effective and economical alternative. To make the GHX design quick and easy to do in its preliminary stage, a simple and easily implemented method is needed. This paper synthesizes relations between the GHX spacing, diameter, soil thermal conductivity and peak heating/cooling energy output for a typical building foundation in Louisiana by proposing a graph method. One set of design graphs were developed for northern Louisiana, where subsurface soils are mainly stiff clays and dense sands. The GHX boreholes were designed without any tedious calculation by using these graphs. The GHX solutions from the developed graph-method were reliable and accurate, and agreed fairly well with the results from the industry-popular software packages GLD 2012 and GLHEPRO for a house cooling example that was selected in Ruston, Louisiana.