from Jon in Madison, WI:
#239
Geothermal heat pumps don't burn fossil fuels, but are they really the "green" alternative?
Geothermal may be the green choice.
The short answer is “it depends.” This is a simple question, but the answer can get quite complicated since there are many variables. To say a technology is "green,” you need to define what technology you're comparing it to. Let's talk about heating and cooling separately.
Heating: A ground-source (geothermal) heat pump system uses an electrically driven system to extract and boost the temperature of low-quality heat energy in the ground or ground water. So the system consumes electricity to move the heat from one place to another. What are we comparing this system to? In Wisconsin, most heating systems burn natural gas or LP (propane) gas. Some systems use electric resistance heaters. Compared to electric resistance, ground-source heat pumps are an easy winner, since the system uses electricity 3 to 5 times more efficiently than resistance heat. But it's more complicated when comparing to natural gas and propane because these are very clean burning fuels. In this case, it all depends on where you get your electricity from. If your electricity is made by burning coal (which is most common in Wisconsin), the gas heating system actually emits less pollution (SOx, NOx, carbon dioxide) than the coal-fired electricity consumed by your geothermal system. In this case, it would not the “green” alternative. But if you get your electricity from renewable energy, a geothermal system probably is the “green” alternative.
Cooling: In cooling mode, a ground-source (geothermal) heat pump system runs in reverse. Instead of pumping heat out of the ground, the unit pumps heat out of your building and stores it in the ground. In cooling mode, a geothermal system is clearly the "green" choice, assuming we're comparing it to standard electric air conditioners. Standard air conditioners use electricity to extract heat from the cool building and force it into the hot air outside. Geothermal systems in cooling mode use electricity to extract heat from the cool building and transfer it into the even cooler ground. It's much easier (and requires much less electricity) to make heat go into the cool ground than to make that heat go into the hot outdoor air.
Conclusion: So, putting this all together, if you heat with electric resistance (rare) and cool with a standard air conditioner (common), ground-source heat pumps are definitely the "green" alternative. But if you heat with natural gas or propane (common) and cool with a standard air conditioner (common), it may or may not be a "green" alternative.
Published Thursday, June 04, 2009