Residential Geothermal Heat Pump - Where does it work?


Let's get one thing straight:  Geothermal power production is very different than residential geothermal.  Geothermal power production is when wells are drilled over an area of high thermal activity in the earths crust, then water is put down the wells to create steam, which turn a turbine, which create electricity.  Residential geothermal usually refers to a geothermal heat pump.  The ground is still used as a source of heat (or cool) for your home, but the temperatures are much, much lower.

I was stumbling around the internet tonight when I realized  Popular Mechanics just put up a great article on residential geothermal.  The article has some nice diagrams and pictures, and is a good introduction, but it's not very in depth.  From the article:

Geothermal works more efficiently because the system’s mild starting point (the article is referring to the nearly constant temperature of the earth below the frost line) creates an efficient shortcut to the target temperature. Imagine a 100-degree Florida day or a 0-degree Michigan night: Spot the system 50 degrees, and it doesn’t work so hard to get the house comfortable.

So to sum it up, if the ground where the geothermal wells are drilled is 50° F year round , then the geothermal heat pump is going to pump water into the ground (which brings the water temperature close to the ground temperature), then use the water in a heat exchanger to pass the heat it has gained in the ground to your home.

In most parts of the U.S. this works in the winter (when the outside air temperature is usually colder than the ground temperature) to heat your home.  But this also works in the summer, when the ground temperature is cooler than the outside air temperature and the water that is pumped into the ground is used to cool your home.  It heats/cools your home year round!  And it is more efficient than using electricity/gas/oil to heat/cool your home because it is only moving heat from one source to another (the ground <--> your home) not having to create the heat.

With all that being said, the burning question I have is how well geothermal heat pumps work in different parts of the country and for different home types.  While there are multiple websites extolling the virtues of geothermal heat pumps, there are few sites that really highlight where they work and more importantly, where they dont.  I wouldnt want to spend $30 - $40 k on geothermal heat pump system then realize it really doesn't satisfy my heating/cooling needs.

Take my situation for example:  I live in Atlanta where it gets real hot in the summer, and can get pretty cold (but rarely freezing) in the winter.  I'm not that worried about the summer cooling (but maybe I should be.  Would a geothermal heat pump have enough cooling power to cool the house on a 95 degree day?), but more worried about the winter heating.  My town-home is 3 stories, but we only really heat/cool the upper two.  If it gets down to 40º F at night, but the heat pump can only get the inside temp to 50° F , am I still going to have to rely on a natural gas furnace to get to a comfortable 68° F?  None of the articles I've found have really addressed this. Also, how well does it handle multiple story dwellings?  I guess these systems must work pretty well though, because my utility's sister utility recommends geothermal heat pumps right next door in Alabama.  The California Energy Commission also has a pretty good review on geothermal heat pumps, so they must work there, but California has desert regions and very cold regions.  I'd love to see some information on how geothermal heat pumps work in both!

Basically, a geothermal system can never heat up your home to a higher temperature than the ground temperature all by itself.  So something is going to still have to make up the difference.  (see comment below.  I made a big error when writing the post originally) I still think this can be a useful technology, but it would nice to be able to know when to invest in a geothermal heat pump, or if a solar PV array or new windows would make the better investment.  Does anyone have a geothermal heat pump that could shed some light on this discussion?

Additional Links:

Check out Scientific American's "Solar at Home" blogger George Musser's experience with a Geothermal heat pump.

Energy Savers : Geothermal Heat Pumps

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Recommend going to the International Ground Source Heat Pump Association website for better information and directory of ground source heat pump installers. If a system was designed right for the home then it should work properly for heating and cooling. If it was under designed then additional ground loops can be installed or additional insulation or low e windows may be added to improve the home envelope. Ground loops may not function well if improperly flushed and purged to remove air in the ground loop.
We have had a Geothermal system in our house for 10 years. We live about 25 miles west of Charlottesville, VA at the base of the Blue Ridge Mountains. We keep our thermostat set at 72 degrees year round. It never waivers. The heating and cooling is far superior to forced air furnaces. We are surrounded by an envelope of conditioned air. Our house is approximately 4200 SF. Electric bill (we are a total electric house) about 200-265 per month. We have the added benefit of almost free hot water in the summer. Our system is by Water Furnace, it was installed by Boyers H&AC a certified Water Furnace installer.
I live in central Maryland and have had a Geo-thermal system in my home for the past 2 years which we bought 3 years ago back in 2007. We had it installed because our electric bills were extremeley high and the normal air heat pump system was unable to cool our home in the summer. The house was a sweltering 80 degress with the previous heat pump but now with a Geo-thermal system it cools our home quite easily down to the low 70's. Geothermal is the best air conditioning out there, truly amazing! As for the Geo-thermal system providing heat, it is much easier for a Geo-thermal system to get heat from the ground temp than an normal heat pump system drawing heat from outside air when temperatures drop below freezing. However, with either, normal air heat pumps or Geo-thermal heat pumps, both types of systems will lose its heating efficiency once temperatures drop below 30 degrees. Gas powered furnaces are more recommended for regions with long winters with low temperatures. In colder regions should should probably stay away from Geothermal unless you have some sort of heat supplement like wood or pellet stove. Sure our system struggles a bit to keep up when it gets very cold in the 1 or 2 weeks during the year that the temperatures are bone chilling cold but then I manually turn on the auxillary heat. I plan on helping out our Geothermal heat pump in the winter time by installing a pellet stove. Those that have Geothermal and notice the heat doesn't feel as warm as gas/oil furnace heat might want to look into installing a humidifier. Long story short, after installing a Geothermal heat pump in the moderate region of central Maryland we have seen our electric bill reduced by 33%!!! I have calculated that the system we installed will have paid for itself (in reduced electrical costs) within 8 years. After living in our home for 3 years, and asking our electric company to check to make sure our meter was working properly in our first year when our electric use was through the roof (and they said it was fine), they recently just totally replaced the meter as our electrical use (after installing the Geothermal) has been reduced by an average of 33% for the past 2 years. The electric company of course gave no explanation, just showed up and replaced it. If we lived even further south the savings would be even greater. I am a firm believer in Geo-thermal! Just make sure you have a well recommended installer.
Rick, Thanks for the great comment! Out of curiosity, how big of a house do you have and how much was your geothermal system? Did you get all the tax incentives available for it?
Bud, Thanks for the great feedback. How much did your system cost to install?
i have geo in a new house in northwestern pa. i am not at all happy with it. the house does stay warm, but it cost more than gas to run, partly because it uses electric auxillery heat. we keep the temp turned up pretty high - 73 degrees, but that is partly because geo heat does not feel as warm as gas heat (we kept that at 70, when we had gas). i am thinking about going back to gas. if you go with geo, make sure you get something in writing
I live in Northern NY and purchased a home with a 3 year old Geo-thermal system. We cannot maintain a comfortable (68 degrees) in the winter. I called the original installer and was informed that the system is only designed to function effectively, with temperatures down to approx. 15 degrees F. As I live in an area where the temperature drops below 15 most of the winter months, the system is not very effective. It seems the prior owners chose not to add the optional supplemental gas system. So, I have to use the old baseboard electric. With the cost of this, I am not seeing any savings by having the Geo-thermal (actually it is costing more). We will be replacing or supplementing the system in the Spring. If you are considering this type of system, I would be sure to get all the data up front.
Hello fellow persons, I'm requesting on how is geothermal made and how does it get to your house buisness or whatever? I have geothermal energy and I am very curious.So please accept my asking. Thankyou verny much Al Bino.
Al, There are different types of Geothermal: Geothermal electricity generation and geothermal water heating. Which one are you referring to when you say geothermal energy?
My home in coastal AL has ground source geothermal heating/cooling (closed loop). In the 7 years since the house was built, keeping it cool or hot enough has never been an issue. The coldest outside temp we've experienced so far was 18 degrees. Last winter alone, we had at least 3 nights when the temperature dipped to 20 degrees or below. We've had over a week of 100 degree weather in the summer also. No problem. The only problem we've had so far had to do with "formicary corrosion" in the coils, which is not unique to geothermal at all. Electric bills are very reasonable (under $200/mo average for a 4000+ sf house which has 4-6 residents over a year, 3 of whom are retired or work from home full time. Bills were even lower before energy rates went up in the last 5 yrs.


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