Hybrid Geothermal Heat Pump System Research Geothermal Project

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Project Title Hybrid Geothermal Heat Pump System Research
Project Type / Topic 1 Recovery Act – Geothermal Technologies Program: Ground Source Heat Pumps
Project Type / Topic 2 Topic Area 2: Data Gathering and Analysis
Project Description Geothermal, or ground-source heat pump systems have been shown to have superior energy performance to conventional heating and cooling systems in many building types and climates. There has been significant growth in the application of these systems; yet, geothermal systems have only been able to capture a few percent of the heating and cooling market. This is due primarily to the prohibitively high cost of installing the necessary ground loop.
Hybrid ground-source heat pump (HyGSHP) systems are an innovation that has the potential to dramatically decrease this high first cost. HyGSHPs connect conventional ground-source heat pump (GSHP) equipment with supplemental devices such as cooling towers (in a hot climate) or boilers (in a cold climate). This innovation allows for the installation of a significantly smaller ground loop while maintaining high system efficiency during most of the operating hours. The installation of smaller ground loops lowers first costs and lowers life cycle costs in many scenarios. While HyGSHPs do not always lead to lower energy use than traditional GSHPs, these economic benefits could allow HyGSHP technology to significantly increase the market share of geothermal systems in general, increasing their overall energy saving potential.

However, hybrid systems are complex to design and control, and there is limited information and research dedicated to the topic. Therefore, HyGSHPs are almost never considered for building projects. Recent research through ASHRAE and other groups has led to some basic design guidelines, conclusions and preliminary software tools to help designers and operators understand these systems. This research includes work by both the principal investigator, the Energy Center of Wisconsin (the Energy Center) and the sub-awardee, University of Wisconsin Solar Energy Lab (UW SEL) of this proposal. A modeling tool was developed—HyGCHP (for ‘hybrid ground-coupled heat pump’)—that can be used both to study the performance of and optimize designs for HyGSHP systems. But there are additional key objectives not reached by this research, and hybrid systems remain a challenging option to most building designers.

State Wisconsin
Objectives Build on previous research experience in hybrid ground-source heat pump (HyGSHP) systems.
Awardees (Company / Institution) Energy Center of Wisconsin
Awardee Website http://www.ecw.org/
Partner 1 University of Wisconsin Solar Energy Lab

Funding Opportunity Announcement DE-FOA-0000116
DOE Funding Level (total award amount) $190,395.00
Awardee Cost Share $55,605.00
Total Project Cost $246,000.00

Other Principal Investigators Scott Hackel, Scott Pigg, Lee DeBaillie, Keith Swartz and Dan Cautley from the Energy Center of Wisconsin, and Dr. Sanford Klein and Dr. Gregory Nellis from the UW SEL
Targets / Milestones - Utilize performance data from actual HyGSHP systems to validate the existing ‘HyGCHP model’; determine accuracy of HyGCHP model and improve if necessary.

- Refine and enhance the HyGCHP model to: a) create more direct interaction between the model and building energy modeling tools, b) improve the general usability of the model, and c) expand the capability of the model to include at least one other hybrid configuration.
- Demonstrate cost savings, overall performance, and calculated life cycle costs of the actual systems; use building models to compare these results to conventional and GSHP systems.
- Report to the building design community: focus on design lessons learned (including the availability of modeling tools) and economic advantages and/or disadvantages of HyGSHPs.

Location of Project Madison, WI

Impacts Will encourage much more widespread adoption of GHPs in the US, including hybrids, which incorporate cooling towers/boilers to minimize loop size/cost and yet offer practical GHP performance.
Funding Source American Recovery and Reinvestment Act of 2009
References EERE Geothermal Technologies Programs[1]


  1. EERE Geothermal Technologies Programs