Dual Source Heat Pumps

Subject: UFTO Note – Dual Source Heat Pumps
Date: Thu, 20 Feb 1997 16:59:16 -0800
From: Ed Beardsworth

| ** UFTO ** Edward Beardsworth ** Consultant
| 951 Lincoln Ave. tel 415-328-5670
| Palo Alto CA 94301-3041 fax 415-328-5675
| http://www.ufto.com edbeards@ufto.com

Dual Source Heat Pumps

New types of heat pumps are coming on the market. Dual Source heat pumps combine both ground-source (geothermal) and air-source, and promise significant cost and performance improvements over existing systems. (E-Source will issue a major report in the very near future entitled “Dual Source Heat Pumps, The Sleeping Giant”.) Note that is not the same thing as “dual-fuel”, which usually refers to gas/electric systems.

Compared with ground source, the dual source uses a smaller ground loop, which is easier and cheaper to install, especially in retrofit situations. It’s cold weather performance and overall efficiency is better than air source systems.

There are two basic types. One is “direct expansion”, where the refrigerant itself is circulated in the ground loop. The other uses a glycol solution in the ground loop.

Geothermal Technologies, Inc. (GeoTech) offers the direct expansion type of system that circulates refrigerant through both ground loop and air coil. In the milder portion of the heating and cooling seasons when conventional heat pumps are still very efficient, the heat pump provides heating or cooling via the air coil. During extreme temperatures, the system relies entirely on the ground coil for heat exchange. According to the manufacturer, this configuration allows their dual-source system to operate most efficiently in middle latitude states.

Currently, GeoTech dual-source heat pumps operate in 12 test homes. According to preliminary findings, GeoTech expects its energy-efficiency to be within 5% of geothermal heat pumps but with a total installed cost of $1,000 to $2,500 less. Although payback periods for most geothermal systems are said to range from 3 to 7 years depending on climate, GeoTech expects its system to have a payback of 1-1/2 to 4 years.

GeoTech also offers an improved lower cost ground source heat pump system, based on design inprovements over poorly performing units sold by U.S. Power which went out of business.

Contact: Mike Housh, (513)423-1923.
Geothermal Technologies, Inc. , Middletown OH 45042

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