A Techno-economic Analysis of Heat-Pump Entering Fluid Temperatures, and CO2 Emissions for Hybrid Ground Source Heat Pump Systems

Abstract

Hybrid ground-source heat pumps (GSHPs) that include a ground loop for the base heating and cooling needs, and an auxiliary system (natural gas boiler and electric air conditioner) for peak loads, are an economical and environmentally cleaner alternative to conventional systems. For a ground-source heat pump (GSHP) system, the choice of entering fluid temperature (EFT) to the heat pump plays a crucial role in determining system efficiency of and operating costs. To continue expanding the knowledge base of efficiently sizing GSHPs as a component of a hybrid system, this study explores the economic effects of choosing an EFT for a heat pump. In addition, system CO2 emissions are calculated and analyzed for a variety of building types. Using a computational approach to size hybrid GSHP systems recently published in [Alavy et al., Renewable Energy, 57 (2013) 404-412], the effects of optimizing EFT for a heat pump, and CO2 emissions were studied for a variety of commercial installations. In the present study, using ten buildings situated in Southern Ontario, Canada, by varying cooling and heating EFTs for a heat pump, savings ranging from 0.47% to 3.6% can be achieved compared to using a fixed EFT pairfor a heat pump. In addition, comparisons were made between the CO2 emissions of optimally sized (based on economic factors) hybrid GHSPs and those of non-hybridized GSHPs. Both the optimally-sized hybrid GHSPs, and the non-hybridized GSHPs significantly reduce CO2 emissions compared to the use of conventional natural gas/electrical systems. The additional environmental benefit of the non-hybridized GSHPs over that of the optimally-sized hybrid GSHPs was found to be negligible in most cases analyzed.