Development of a Software Design Tool for Hybrid Solar-Geothermal Heat Pump Systems in Heating- and Cooling-Dominated Buildings Geothermal Project

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Last modified on July 22, 2011.

Project Title Development of a Software Design Tool for Hybrid Solar-Geothermal Heat Pump Systems in Heating- and Cooling-Dominated Buildings
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 In heating-dominated buildings, the proposed design approach takes advantage of glazed solar collectors to effectively balance the annual thermal loads on the ground with renewable solar energy. In cooling-dominated climates, the design approach takes advantage of relatively low-cost, unglazed solar collectors as the heat rejecting component.

The main benefit of hybrid geothermal heat pump systems (GHP) relative to non-hybrid GHPs is reduced initial cost of the ground heat exchanger (GHX). Furthermore, hybrid-solar GHPs have the following advantages: (i) solar thermal collectors can be used to balance the ground loads over the annual cycle, thus making the GHX fully sustainable, (ii) in heating-dominated buildings, the hybrid energy source (i.e., solar) is renewable, in contrast to a typical fossil fuel boiler or electric resistance as the hybrid component, (iii) in cooling-dominated buildings, use of unglazed solar collectors as a heat rejecter allows for passive heat rejection, in contrast to a cooling tower that consumes a significant amount of energy to operate, and (iv) they can potentially expand the residential GHP market by allowing reduced GHX footprint in both heating- and cooling-dominated climates.

The proposed design tool will allow the straight-forward design of innovative geothermal heat pump systems that are currently a design challenge. The motivation for this proposed project is that proper and reliable design of hybrid GHP systems is quite difficult and cumbersome without the use of a system simulation approach, and without an automated optimization scheme coupled to the system simulation program, the design activity itself can become tediously impractical and time consuming. The use of system simulation for analyzing complex building systems is ever increasing, but the necessary computing resources is not at the disposal of every design practitioner, nor is their use always practical or economically justified. As new technologies and design concepts emerge, design tools and methodologies must accompany them and be made usable for practitioners. Lack of reliable design tools results in reluctance of practitioners to implement more complex systems.

State Connecticut
Objectives This project will develop an easy-to-use, menu-driven, software tool for designing hybrid solar-geothermal heat pump systems for both heating- and cooling-dominated buildings. No such design tool currently exists.
Awardees (Company / Institution) University of Hartford

Partner 1 University of Dayton
Partner 2 Oak Ridge National Laboratories

Funding Opportunity Announcement DE-FOA-0000116
DOE Funding Level (total award amount) $146,972.79
Awardee Cost Share $36,766.17
Total Project Cost $183,738.96

Principal Investigator(s) Dr. C. C. Yavuzturk
Other Principal Investigators Dr. A.D. Chiasson

Dr. T.P. Filburn

Targets / Milestones The overall goal of the work proposed here is to develop a menu-driven software tool for the design of hybrid solar GHP systems that is easy-to-use, but based on mathematically robust, validated models. The method is based on current “state-of-the-art”, life-cycle system simulation tools for geothermal heat pump systems using TRNSYS. An automated optimization tool used to balance ground loads will be incorporated into the simulation engine. With knowledge of the building loads (either in an hourly format or simply the peak heating and cooling loads and corresponding annual equivalent full load hours), thermal properties of the ground, the borehole heat exchanger configuration, the heat pump peak hourly and seasonal COP for heating and cooling, the critical heat pump design entering fluid temperature, and the thermal performance of a solar collector (selected from a product database), the total GHX length can be calculated along with the area of a supplemental solar collector array and the corresponding reduced GHX length.

An economic analysis will be provided that shows the lowest capital cost combination of solar collector area and GHX length.

Location of Project West Hartford, CT

Impacts Improves GHP loop design and sizing, potential to improve GHP reliability and performance with lower cost.
Funding Source American Recovery and Reinvestment Act of 2009
References EERE Geothermal Technologies Programs[1]


  1. EERE Geothermal Technologies Programs