Next Generation Energy is managed and written entirely by Seed editors and expert guest bloggers. Read more about them When most people talk about geothermal power, they're usually referring to the likes of the large installations that supply much of Iceland's electricity and hot water — centralized complexes that work wonders in those regions where the geophysics are favorable. But there's a simpler and more universal way to use geothermal energy that could make a significant dent in electricity bills and overall energy usage: geothermal heat pumps.
The basic idea is the same as air-source heat pumps, which are essentially refrigerators or air conditioners that can run in reverse. They use electricity to compress a storage medium outside, which stores that energy until it;s releases inside as heat when the medium is allowed to expand. Air-source heat pumps are marvelous inventions that can keep most homes in temperate climates livable for most of the year. But they have their limits. The heat pump in our home, for example, can keep our house at 68°F (62 at night) until the winter temperatures drop to about 35° In other words they can make up for about 33 degrees of heat difference.
When it dips below freezing, radiant heat strips installed in our air-handling system kick in, and increases that share of our electricity bill associated with heating by between 100 and 200 percent.
Geothermal heat pumps, however, don't suffer from similar limits.
The reason is the ground never gets as cold as does the air above it. In most of the U.S., ground temperatures rarely fall below 45°F. That means if you're trying to squeeze heat energy from the ground, by running the pump's heating/cooling medium through a ground heat exchanger, there's a lot less work for the pump to do to keep the house comfortable. No need for radiant strips, ever, as the temperature differential never comes close to the pump's maximum.
You still need electricity to keep your home warm in winter, but a fraction of what radiant heating of any kind would require. (And the same applies to cooling in summer.)
Indeed, the idea makes so much sense, and has been around for years, why doesn't everyone already have a geothermal pump? Because such systems can cost several times as much as conventional heating equipment to install. The fact that it can, according to the U.S. Department of Energy, take only a decade, and perhaps as a little as five years, to recoup the investment suggests that government should be doing what it can to ensure affordable loans. I suggest zero-interest for 10 years would pretty much guarantee that all new homes in the lower 48 (Alaskans have permafrost issues) be built with geothermal heat pumps. Google Earth has a good visual overview of the potential.
Come to think of it, there's no reason why most homeowners couldn't retrofit existing buildings, taking advantage of that kind of incentive. And think of the jobs it would create. As Obama would say, they're jobs that can't be exported. Some folks aren't waiting for government assistance. Federal records show geothermal heat pump demand rose 33 percent between 2005 and 2006.
This won't solve the climate crisis or the foreign oil dependency, but it would go a long way toward such goals, probably cutting most home's carbon footprint by at least 40 percent. With no pollution, and only some unsightly scars on your yard where the trenches in which some pipes were laid.
Graphic: Consumer Energy Center
Environment
Comments
One developer I talked to really likes geothermal, but he said retrofits are too messy -- you need to dig a large trench 100m x 10m x 2m to lay the coils in, or drill wells and deal with thousands of gallons of drilling slop. Both are relatively easy to deal with in new construction since you are landscaping anyway, but in a retrofit, it is a big problem.
Maybe clean well drilling would be a good green job.
Posted by: dave x | September 15, 2008 3:38 PM
For greenfield builds (retro-fit is obviously another issue), ground-source heat pumps are an idea whose time has not only come, it's long overdue. In fact, Ontario Hydro did a pilot project in which they installed a GSHP on a house in Toronto -- in 1961 (I saw the report when I was a summer student there in the late-70's).
Posted by: Eamon Knight | September 15, 2008 4:28 PM
I am glad to see home geothermal heat pumps mentioned here; they are an often overlooked opportunity for reducing a home's environmental footprint and energy expenses.
I am surprised that heat pumps receive as little attention as they do nowadays. One possible explanation is the upfront cost, but solar panels, which could also afford to be used much more widely, have expensive installation too, yet they seem to be more widely implemented and have more people excited about them.
I wonder how much of this has to do with the fact that it is a lot easier to show off how green you are with a shiny solar panel than with a heat pump, which is not visible to the neighbors.
Posted by: Erik D Johnson | September 15, 2008 4:37 PM
One developer I talked to really likes geothermal, but he said retrofits are too messy -- you need to dig a large trench 100m x 10m x 2m to lay the coils in, or drill wells and deal with thousands of gallons of drilling slop. Both are relatively easy to deal with in new construction since you are landscaping anyway, but in a retrofit, it is a big problem.
Maybe clean well drilling would be a good green job.
Posted by: dave x | September 15, 2008 4:51 PM
I think your Google Earth link is referring to the first type of geothermal heat, rather than shallow heat pumps.
Posted by: Steve | September 15, 2008 5:15 PM
New types of air source heat pumps are being developed that work when outside temps go below freezing. I know they've been testing them in central Washington for a couple years (Central WA Univ? I forget ) and if they aren't for sale yet, they will be soon.
Heat pumps have some other problems too: the air ducts have to be enlarged in a retrofit to handle larger volumes of not particularly hot air. But what efficiency! 200%, even 400%. You can't beat that. I'm waiting for my gas furnace to die and hopefully the sub-freezing air source pump will be ready.
Posted by: SeattleDave | September 16, 2008 12:13 AM
You know, if we actually re-socialized (in an operational not just financial sense) Fannie and Freddy, we could easily make this and other sensible efficiency measures standard for new homes by making it a condition on the mortgages they buy. Just saying.
Even without going the mortgage condition route, the government buying loans issued for this sort of thing makes a lot of sense. I should see if CA has any such program.
Posted by: travc | September 16, 2008 4:47 AM
The upfront costs of residential geothermal heat pumps have been discussed extensively in the geo forum on GreenBuildingTalk. The good news is that more options are becoming available to make this technology more affordable. Just take a look at the Colorado Delta-Montrose Electric Association's new geothermal loop tariff. The DMEA pays for the installation of the residential ground-source heat pump loops, then owns and maintains the loop as "utility plant", charging the residential co-op member signing up for the loop tariff an affordable monthly fee. The program allows the homeowner to save 30 to 70 percent on their operating cost. Programs like this can help more people take advantage of this technology and reduce their fossil fuel consumption.
Posted by: Jamie | September 16, 2008 11:50 AM
At this address http://heatpumpathome.blogspot.com you can find 200 FAQs about Geothermal Heat Pumps! - really great resource
Posted by: HeatpumpExpert | September 17, 2008 7:15 AM