22 May 2002
The term geothermal heat pumps (also known as GHPs, ground-coupled heat pumps, and GeoExchange systems) refers to a family of systems that meet heating, cooling, and water heat-ing needs while using 20 – 40% less energy than conventional space-conditioning systems. The GHP industry evolved from a few refinements in commercially available water-source heat pump and natural gas distribution pipe technology. Closed-loop ground heat exchangers made of high-density polyethylene, in combination with water-source heat pumps modified to operate over an extended range of entering water temperatures, enabled GHP systems to operate cost-effectively for both residential and commercial/institutional buildings in virtually any climate. Electric utilities in the United States, led initially by the rural electric cooperatives, embraced GHPs as a means to reduce utility peak loads, improve load factors, and gain market share. Policy makers took notice and estimated that widespread use of GHPs would enable the United States to save as much as 2.7 quads of energy, or over 3% of the nation’s total. As part of the U.S. Department of Energy’s overall GHP effort, several programs were launched to support mainstreaming the use of GHPs — including the National Earth Comfort Program and the Federal Energy Management Program’s GHP technology-specific program. This paper describes these two major GHP programs, reviews their technical and market results, and discusses the lessons learned.