View Full Version : Ground source heat pump

Paul Fitzgerald
05-20-2010, 03:35 AM
I am considering a new house build in Tasmania, a relatively cool place.

It is 42degrees south, but close to the water so winter temps are above freezing, 1C minimum to 10C maximum in the middle of winter. Summer maximum around 35C.

When I stayed in Steamboat over Christmas, the house had ground source heat pump, which seemed neat. We have air exchange heat pumps here, but not much ground source experience.

I would like to put one into a new build, for heating and cooling, and would appreciate comments on problems, things to look for and costs

Tom M.
05-20-2010, 04:27 AM
I'd say do it if you can afford to. More efficient and way quieter than those noisy air exchange heat pumps. It takes septic-like excavation, and the risk of leaking underground pipes, although I don't know the frequency of failure.

The Bigfella
05-20-2010, 04:36 AM
Isn't Jeff (skuthorp) doing this? He's posted something about it

05-20-2010, 04:45 AM
Not heating, cooling. Quite shallow in the wet clay, heating systems are very deep I think. On Grand Designs there was a house that drilled down 60ft or so. Here's a site mentioning geothermal heat pump works in Tassy, that might help Paul. I use a air sorce heat pump for hot water, and by summer will have a solar sourced AC system with luck.

05-20-2010, 05:13 AM
Groundwater is about a constant 50 degrees F. The basics are something like this: In the summer time, the systems are used to cool the house. They take the excess heat out of the house and put it into the groundwater. In the winter, the pumps take the difference between the outside air temp and the groundwater and put it into the house to heat it. There are closed loop systems that use a product to exchange the heat (that can leak - but may be a small risk these days) or open loop systems that simply move groundwater through the system. Installation costs depend on how deep you have to go to put the loop into the groundwater table. Wells for deep systems are expensive. If groundwater is shallow, you may get by with a shallow gallery. I have a few friends that have systems. The complaints I have heard usually are associated with the lag in the system and the amount their electric bill jumped.

Bob Adams
05-20-2010, 06:03 AM
I'd say do it if you can afford to. More efficient and way quieter than those noisy air exchange heat pumps. It takes septic-like excavation, and the risk of leaking underground pipes, although I don't know the frequency of failure.

Not always, it can be done with a well like hole, no need to spread it all over.

05-20-2010, 06:35 AM
I put a geo-thermal system in the last house I built for a client. The well was 385' deep. It seemed to work pretty well and they are happy with it but it is awfully dry. I would think a humidifier added would make a big difference but the company we used didn't have an in line system perfected yet.

When working on the house though the winter it cost me $300.00 bucks a month in electricity to keep the house at 55F. The home owner found out later there was an electric grid preheater in the system. It is designed to be used not an optional thing but they had it disconnected which made a big difference in the electric bill.

With this system you get both heat and A/C so the cost is competitive with oil/hot water plus stand alone central air.

05-20-2010, 07:38 AM
There is a third type--the closed pond loop. If you have a body of water on the property the heat transfer loop can be run in the pond water.

From what I've read geothermal systems are about double the cost of conventional systems and payback will take 10 to 15 years.

Paul Fitzgerald
05-20-2010, 08:05 AM
I have been thinking of the pond idea. There is a dam on the property but it is a bit far from the house site.

I am required to put in a water supply for firefighter access, and the house supply will rely on rainwater tanks.

It would be attractive to put in a pool to meet the fire requirement, and use it as a heat source as well.

There is no frost line, so a normal pool should be deep enough if it is designed to facilitate heat transfer with the ground, and I use a heat blanket in the winter.

Paul Girouard
05-20-2010, 08:27 AM
There's a article about this in Fine Home buildings current issue. Issue #211.

Looks like they've done a bunch of articles on the subject,


05-20-2010, 08:36 AM
I spent 12 years in the geothermal heat pump ( ground source heat pump buisness). For expert info, Google the International Groudn Source Heat Pump Association for everythign and anythignyou want to know.

The technology is environmentally benign, and the absolute least expensive way to heat, cool, and provide domestic hot water for your home.

Typically you trench down 5-6', lay pipe, and voila you are off and running. That is, if you have the room. 100' of trench needed for every ton of capacity, approx. Well systems are vastly more expensive. Ponds loops are best for perforance and lowest installed cost- need minimum 6-8' of water and a sufficiently sized pond.

Again, contact IGSHPA.

05-20-2010, 09:53 AM
Here is some info for you - but it's a very different climate, which makes a huge difference. I know that in New England it can be challenging to design a system that doesn't use a ton of power.