For the means to cheaply heat and cool just look outside in the dirt. Ground-source heat pumps provide a home with comfort without emissions and at substantial cost reductions from oil, gas or electric systems. The initial investment will pay off at a good return. The only requirement is digging and the space to do so.
The technology is variously called ground-source, earth-coupled or geothermal. Heat pumps move heat from outside to inside in the winter and in reverse in the summer. Typically, a GSHP circulates a mixture of water and antifreeze through tubing that is buried in the ground into radiators in the home. Since the ground is at temperature different from the air, it can provide heating in the winter and cooling in the summer. The only energy used is for an electric pump to circulate the transfer fluid. When compared to electric heating, a heat pump is 300-400% more efficient.
There are water-based open looped systems which obtain heat from well water, but the most popular systems are closed loop, which use a circuit of sealed pipe to exchange heat with the earth. The pipe in these is high-density polyethylene plastic which has an expected life of 50-75 years. Sections are joined with heat fusion for a reliable seal. A small pump circulates a mixture of water and non-toxic antifreeze (usually propylene glycol) through the pipe and the mixture exchanges heat with the surrounding soil.
The length of loop depends on the size of the heat pump equipment, the moisture content of the soil and the climate. Where we live in Western Oregon, the average soil temperature is 53F, the typical earth loop requires 110 feet of pipe per ton of conditioning. (One ton is roughly equivalent to 12,000 Btu per hour heat output when the air is 47F outdoors, or 12,000 Btu cooling at 95F.)
Horizontal loops, like that pictured above, are more common because they only require a 4-6 foot deep trench which can be dug with a rented trenching machine. On a small lot though, a vertical drill would be used to install pipe -- a more expensive job.
As you get into more detail, it helps to think about how your fridge removes heat from its inside. As with the fridge, the main components are:
See how it all works in winter, and in summer, courtesy of www.geoexchange.org.
The initial cost of a GSHP system varies greatly according to local labor rates, geological profile, type of system installed, and equipment selected. The initial cost of GSHP systems does come at a premium when compared to conventional HVAC systems. For either though, the cost of distribution should be identical. Equipment costs can be 50-100% more expensive for a GSHP when the circulating pump, indoor tubing, and heat pump are considered. This 50-100% premium translates to $1000 - $2000 for a 3-ton system.
The ground loop is generally the most expensive component of a GHP system and is highly dependent on local labor rates and drilling conditions. An installed ground loop stubbed out in a home can run between $1000 and $3000 per installed ton. Allow one ton per 350-500 square feet of conditioned area in a home. A terrific article on containing initial costs is found here .
Overall, one could expect to pay between $4000 and $11000 more for a source heat pump system. Many consumers justify this initial investment with the savings they expect to realize on their heating and cooling bills over time. Payback occurs via 50-70% savings in fuel or electricity. Here in western Oregon, we pay about $800 per year for oil. If we have a high COP, we can expect annual benefit starting at $400 per year, increasing at the same rate as the price for oil. Our air conditioning needs are fairly limited so we'll just count the cooling as $100 per year.
In Oregon, heat pumps qualify for the Residential Energy Tax Credit of up to $1500. For other incentives by state, see http://www.geoexchange.org/incentives/incentives.htm.
Installers in the Portland area that are accredited by the International Ground Source Heat Pump Association:
| The Heat Exchange | Tigard | 503-312-0835 | theheatexchange@juno.com |
| Thermal Supply, Inc. | Portland | 503-238-8833 | |
| Peerless Pacific Co. | Portland | 503-289-1888 | peerlesspacific@att.net |
