Blowing Hot and Cold on Ground Source Heat Pumps
-Geothermal (or ground source) heat pumps can be incredibly efficient, delivering 3-6x as much energy for heating and cooling as you use to power the equipment;-They are in some ways a renewable energy system, since they use the heat contained in the earth to provide heating / cooling;-They do require extensive installation work, including excavation or drilling to install subsurface pipes; and-They are more expensive than traditional heating/cooling equipment, but the payback period is less than five years almost everywhere in the country due to their greater efficiency.
They have done a great job of explaining how they work but I have some issues with their summary.-"Geothermal (or ground source) heat pumps can be incredibly efficient, delivering 3-6x as much energy for heating and cooling as you use to power the equipment;"
True, and it is terrific if you need air conditioning. But in much of the country one does not, if they take design steps like planting trees, shading windows or simply having fans. A GSHP is also not as efficient at heating as it is at cooling, getting only 3.0 to 3.5 times the energy you put in. Since US coal plants deliver electricity at only 30% efficiency, "the source energy winds up being very much the same, as are the emissions." (thanks commenter toad)
If we design our houses properly, then for much of the country, air conditioning shouldn't be necessary. Similarly, if they are properly insulated, then such an expensive heat source isn't required either.
-They are in some ways a renewable energy system, since they use the heat contained in the earth to provide heating / cooling;
I don't think this is true at all; they are simply using the earth as a heat sink. The unit is simply using the ground to dump excess heat, instead of the air as in a normal air conditioner; the ground just happens to be denser and more efficient. You are paying for electricity to dump solar heat picked up in your house into the ground; that is hardly making use of a renewable resource. On the heating cycle, it is drawing what is essentially solar heat from the ground, as a regular air based heat pump is doing, so one could vaguely call that "renewable", but no more so than a conventional above-grade air based unit.
-They are more expensive than traditional heating/cooling equipment, but the payback period is less than five years almost everywhere in the country due to their greater efficiency.
-Only if you need air conditioning. If you are just heating your home I don't know if it would ever pay for itself.
GSHPs have their place, and are a great solution in parts of the country. But in temperate climates, if I had to decide whether to put $15,000 into a ground source heat pump or into more insulation, better windows, and a more carefully resolved design, I wouldn't do the heat pump. ::Green Building ElementsMore in TreeHugger on Heat pumps:Jargon Watch: Geothermal vs Ground Source Heat PumpDrilling for Heat at New York's General Theological Seminary ...On Geothermal heatingExploring Southeast Asia's Geothermal Potential : Is Geothermal Energy the Way of the Future? A Primer to Iceland's Geothermal Power Stations On Designing for no furnace or air conditionerA Passiv Haus in Urbana, Illinois : TreeHuggerDenmark Debuts First Certified Passive House : TreeHugger