Geothermal (Ground Source Heat Pump)

[Razl]

I've decided to go with geothermal heating and cooling for my new house. It's going to cost me an extra $50 on my monthly mortage, but I'm going to recover more than that in energy savings each month. So, to say the least, I'm stoked

As I understand it, the system heats and cools by transfering heat. That is, in the summer, it absorbs the heat from the house and transfers it to ground (in my case, a vertical closed loop system). OK, so the earth acts like a gigantic heat sink...I got it. Then, in the winter, it works in reverse and tranfers the heat from the ground to the house through a heat exchanger.

That's the part that leaves me,

If the earth's temperature is about 50F year round, how does that heat my house to 70F. Is it the compressor that raises the temp of the refrigerant in the loop? I've read many resources, but the physics behind the heating is always vague.

 

[kanling]

You know how a can of air duster or other spray gets cold when you spray it? It's because you are letting out the pressure. If you were pumping it up, it would get hot.

That's how any air conditioner/heat pump works, just in a continuous cycle. To heat your house, the pressure in the refrigerant coil is boosted to release heat into your house. Then it is pumped outside and the pressure is relieved, the fluid becomes much colder than 50F, so heat from the ground is drawn into it.

So through a continuous process of pressure changes, heat from the ground is moved into your house and cold from the house is moved in the ground. In summer, the high and low pressure sides are reversed and heat is moved the opposite way.

 

[Razl]

The basic principles of an AC, right? So in the summer, the coils in heat exchanger act like the cold evaporator, and in the winter, like the hot condenser.

I think I got it. However, the refrigerant in my case (closed loop) is water with a polypropylene antifreeze additive. I'm no chemist, but isn't H2O hard to compress? I though a good refrigerant should be able to change phases easily, such as Freon and 134a.

 

[kanling]

Truthfully, I'm not much familiar with the geothermal systems like yours other than to know that they are very efficient but very, very expensive to install.

I didn't know that water/antifreeze was circultated.

Maybe there is an indoor heat exchanger where the water exchanges to a refrigerant? That would kind of make sense because you would need a boat load of traditional refrigerant to fill the in-ground tubing.

 

[brianl703]

Commercial air conditioning systems often use rooftop units which use a standard condensor/compressor/evaporator setup with Freon to produce chilled water which is then distributed to the air handlers on the various floors.

You probably have something that uses a similar method, except that the water is used to carry heat away from the "outdoor" coil in summer, and to provide heat to the "outdoor" coil in winter. (The "outdoor" coil being that part which functions as an evaporator in A/C mode and a condenser in heat-pump mode).

 

[Bill]

Razl,

You will be very happy with your Geothermal system,
my brother bought a home that has a Geothermal home system, he is amazed how well the system works for cooling and heating, his heating and cooling costs are very low for his size home.

kanling explained how the system will heat the home, I to am surprised the Geothermal system can heat a home with temperatures of about 45° from below the surface of the ground but it works

 

[kanling]

Yes, according to this link, there is a heat exchanger between the water/antifreeze and the refrigerant. This keeps refrigerant piping out of the ground. Another type of system, called "direct exchange" does put the refrigerant directly in the ground. More efficient, but not surprisingly big trouble if there is a leak.

dx vs non-dx

If I were building a new house, I would definitely consider this type of system. It has the efficiency advantages of a traditional heat pump, but without (hopefully) the drawbacks. It shouldn't need "aux electric" heating when it gets really cold. You'll have to tell us if it blows cold air around in the winter.

 

[DKT]

I found this link that has some good illustrations. http://www.geoexchange.org/illustrations/graphics.htm

 

[Razl]

Geez, I was on that site but missed those diagrams. Thanks DKT.

kangling, I did look into the HP that uses you domestic water heater as the aux heat, but that unit was $800 more. The HVAC contractor said that he sized the unit accurately so that it should not need the aux electric element, and I would be spending money that would not be recouped. I hope he's right

I did work with him and an engineer closely on the heat loss analysis. I'll keep you guys posted.

 

[Shannow]

Razl,
my in laws have a reverse cycle air con system, in an area that ranges from -7C to 45C.

When heating, it has to pump heat from (potentially) -7c into a 25C room. When cooling, it has to pump heat from a 17C room into a 40 degree environment.

Each of those is about a 20C shift.

A Geothermal, when cooling extracts heat at 15C, and heats the room at 21 (6 degrees dif), when cooling, it's the same.

So you use considerably less energy than trying to fight the environment.

 

[Schmoe]

Don't know how effective or efficient or the SEER rating or whatever is for those systems up north, but here in Oklahoma, my experience has been the opposite. First, in the summer time, it takes FOREVER to get these things to cool off the house. It constantly runs and runs. This is nothing like the traditional systems that we are used to now. Second, payback will be between 10 to 15 years, about the time for you to replace your old system with a newer one and start all over. For heating, same complaints. This system will not warm up your house any time soon. It takes a while. These geothermal systems have to be deep enough to reach ground water. Principle is that groundwater temperature stays constant and that temperature is what your dependant upon. I would surely want an auxillary unit attached with the geothermal system. We have been installing these things all over Fort Sill and every office that has one, complains constantly about them in the summer time.

 

[k1xv]

I would have loved to have a ground coupled heat pump here in Vermont, but it is not technically feasible. This is because, at this location, we only have about 1 foot of surface soil, and below that it is pretty much solid, dry rock. Too much excavation cost, and too little heat conductivity between the piping and the ground.

 

[Razl]

k1xv,
Sounds like an asteroid landed in your town a few thousand years ago. The pine trees in your area must be short

Where I am, bedrock is about 40 feet down, but I'm not sure how deep it goes. My installation will require 2 bore holes at 350ft each. For me, the sooner I hit bedrock, the better, since he needs to install casing until he reaches that bedrock, which adds to the cost.

Schmoe, is your bad experience with an air heat pump (like Shannow's inlaws) or a ground source heat pump? They are not the same, as you probably know. I've talked to several local geothermal owners and most of them love it. I hear the most problems occur when you go with an open loop system (one that uses well water) because of water sediment clogging the flow. The second problem is that people have a poorly insulated house (minimum code-approved insulation R-values and high air infiltration).

 

[JHZR2]

OK, a few OTs to pipe in.

Im looking to buy a home (existing). Is there a map of areas where these systems are usable or widespread or easily installable?

Can they be retrofitted into existing homes? Would said home HAVE to have a forcedair type system? Id assume no steam or hot water systems could use such temp differentials.

The area Im looking at living in central NJ has a well-known, very high water table. I assume this is optimal, right?

How much $$$ and space does such a system take up?

Thanks!

JMH

 

[Razl]

JHZR2,

I'm in CT on the RI line, so we have similar winters. The nice thing about ground source is that it's about 50F all year round regardless of temp swings, so location is not a factore where we are. Alaska, might be a different story

Water is not a problem, in fact, it will work more efficiently. If you're right off of a a lake or large pond, that can be great way to run piping.

Here's an idea of cost. The cost to install a gas furnace and electric central air, including duct work for my new house is about $25,000. Going Geo is costing me an additional $10,000, that's were I get the roughly $50 per month mortgage payment. I figure, I'll save at least 3X that in energy cost at any given month, usually more. An efficient gas furnace is about 90%-95% efficient, a good Geo heat pump is 300%-400% energy efficient. Gas is cheaper than electricity in most parts, but at this efficiency, Geo wins big!

The duct work is the same, but 1 geo unit replaces the furnace and exterior A/C compressor(s). Its footprint is no bigger than a new furnace and much quieter, producing zero emissions (hydrocarbons, CO2, CO, etc) in the house. The only fossil fuel used is what it takes to make the electricity to run the pump, fan, and compressor. If you have the unit installed in a basement, life expectancy has been calculated as double that of a traditional system (anyone with central air and external compressors know what I mean).

Forced air is ideal for heating and cooling as far as cost because the duct work handles everything. If all you need is heat, radiant heat is a better match for geo and more efficient to run. The drawback is that radiant heat tends to cost more to install.

Retrofitting can get expensive. You'll need a well driller to come out and drill the bore holes and lay the pipe. If you have a large lot, a horizontal loop is less expensive since you only need to go down a few feet past the frost line. If you already have a working well, than that will be the cheapest way to go. I want to say the drilling is costing me about $5,000, but I'll check. As for the cost to install the geo heat pump, I'll have to check with my builder and get back to you.

 

[JHZR2]

Thanks very much!!!

 

[pa04prius]

My son-in-law has geothermal and it has worked flawlessly for 4 years. In Ohio, there was grant money available from the utility to help with the installation - done when the house was built.
Natural gas has gotten so bad here that I'm going to buy an insert for my fireplace and start using wood. I have 4 acres of good hardwood and should be able to harvest sustainably for the rest of my days.
Anyway, the electric bill for his goethermal is not too bad at all - about $80 per month year-round. Everything else (stove, dryer) is electric so it sounds great. A very wise choice.