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Q. I have a twelve year old heat pump which cools/heats the second floor of my home. It will likely need replacement in the near future. I am interested in a geothermal heat pump and would appreciate your opinion on the pros and cons, as well as where I can find a reliable installer. My property is six and a half acres, mostly woods and is perhaps 100 feet or so above the level of a nearby creek.
A. Traditionally heat pumps have the reputation of lasting eight to twelve years. Some last longer and some quit sooner but that’s the average so you are on the mark to be thinking about it now. Also, that heat pump is most likely much less efficient than what is available today and certainly will be below the now mandated minimum 13 SEER, which is the number that refers to the efficiency rating that is computed by measuring the energy that goes in compared to the heating and cooling quantity that comes out.
Geothermal, or ground source heating and cooling, is a technology that’s been around for a long time and was first employed in this country from early 1970s but the potential was identified long before then. The initial obstacle to installing it comes down the same thing that slows any cutting edge technology and that is initial installation cost.
Quite simply, the way it works is by exploiting the constant temperature of the earth below our feet, which around here below the frost level is about 55ºF. Your traditional air-to-air heat pump struggles against a widely fluctuating outside air temperature and when you want heat the air is cold and when you want to cool the air is hot so the technology strains against that and efficiency suffers.
Couple that with the problem that many heat pump operators don’t understand that a heat pump is just part of an overall system known as the whole house and satisfactory operation depends upon a tight, well insulated house.
In all my years of inspecting houses I can count the number of ground source heat pumps I’ve seen on one hand and not use all the fingers. I spoke with a couple of colleagues at a recent American Ground Water Trust symposium on the subject and asked them and they said the same thing. So that will go to the difficulty in finding an experienced designer and installer. But they are out there. The shortage appears to be well drillers.
The earth’s heat is pulled out through the use of wells, also called bore holes-- lots of them. The wells are drilled and a closed loop of high density polyethylene pipe is installed and the wells are grouted closed to protect the aquifers from contamination. Wells are drilled in clusters of ten wells per cluster and the number of wells needed is part of the calculus of the heating and cooling loads. These wells can be very deep and they sell the closed loop pipe in unbroken rolls up to 450 feet. The water is pulled up via pumps, run through the heat pump where heat is either extracted or rejected (cooling) then run back into the well. Long deep trenches are also an option for the loops so the best method of extraction is part of the design and planning. As you can tell, this is not a do-it-yourself project.
But here’s the good news: with the skyrocketing cost of energy the payback period of this system is getting shorter and shorter. Seven to ten years return on investment appears to be the norm now. The model is one energy dollar into the system yields four to five dollars worth of heating or cooling.
Traditionally, they have been installed in schools, medical facilities, office buildings and churches and are now showing up in certain segments of residential construction. The key seems to be that the buildings in which they get put are long term owner operated to realize the true economic advantage. And that can be your house. Even Habitat for Humanity has installed some. Builders obviously have shied away from them due to the high initial cost and want to keep the front end cost of their products competitive and would prefer to spend dollars on granite counter tops and master bathrooms the size of train stations rather than a super efficient, low carbon footprint heating system.
One presenter at the symposium mused over the futility of drilling oil out of the ground, transporting it halfway around the globe, bringing it into your house to burn for heat when all the heat you’d ever need is a few feet under the house.
Seventy percent of household energy consumption is dedicated to heating, cooling and water heating. Ground source heat pumps also heat your water. Ground source heating and cooling proponents claim they can knock the cost of that down by nearly half. Think about that while you are writing your next electric bill payment. To learn more go to American Ground Water Trust’s website at www.agwt.org or the Geothermal Heat Pump Consortium's Web site at http://geoexchange.us/.