Technical and economic feasibility of unitary, horizontal ground-loop geothermal heat pumps for space conditioning in selected california climate zones

Abstract

This work investigates the viability of unitary 3.5kWt, ground-source terminal heat pumps (GTHP) employing horizontally drilled geothermal heat exchangers (GHX) relative to air-source packaged terminal heat pumps (PTHP) in hotels and motels and residential apartment buildings in California’s coastal and inland climates. The GTHP can reduce hourly peak demand for the utility by 7–34% compared to PTHP, depending on the climate and building type. The annual energy savings of up to 5% are highly dependent on the water-pump energy consumption relative to savings associated with the ground-air temperature difference (ΔT). In mild climates with small ΔT, the pump energy use may overcome savings from utilizing a GHX. The levelized cost savings, ranging from $1.7/yr-m2 to $3.6/yr-m2, were mainly due to reduced maintenance and lifetime capital costs. Without these reductions, the GTHP does not appear to offer significant advantages over PTHP in the climates studied. The GTHP levelized cost was most sensitive to variation in installed cost and system efficiency. These results can inform installers and decision makers about the viability of this technology, which is highly dependent on climate and building type.