Sunday, January 20, 2008

Understanding what a geothermal system is...

As you can see from our green features list, we are going to use a geothermal heat pump for the heating and cooling of our house, as well as for our swimming pool. It is an extremely effective system that can be up to 2.5 times more efficient than a normal HVAC 12 seer system and uses very little electric. Add that to an air tight, well insulated SIP home, and you'll save yet even more money on cooling your home, probably 75-80% of what a stick frame/batt insulated/regular HVAC home would do.

There is one guy we talked to, J.D. Holt, who owns a 1650 sf SIP home in Austin, TX with a geothermal system to cool his house. In the summertime he pays about $60/month without being conservative with airconditioning. That is rather significant!

In Austin, there are only a handful of geothermal subs that can install geothermal. It is also a very effective system in cold weather climates. In Sweden, it is commonly used for heating, especially large apartment complexes.

At first, I had a hard time truly understanding the science behind a geothermal system and even harder to time to explain it to other people. :-) I copied a Geothermal FAQ from one of the subs we're considering as well as included a link to a video presentation:

Q: What is a geothermal heat pump?
A: A Geothermal Heat Pump is an electrically powered heating air conditioning system that uses the natural heat storage ability of the earth. In Texas the ground temperature 6 foot down stays a constant 68 to 72 degrees.

Q: How does it work?
A: Like any type of heat pump, it simply moves heat energy from one place to another. Your refrigerator works using the same principle. By using the refrigeration process, a Geothermal heat Pump removes the heat from the home and transfers it to the ground.

Q: How is heat transferred between the earth and the home?
A: The earth has the ability to absorb and store heat energy. To use that stored energy, that constant 68 to 72 degrees temperature is extracted from the earth through a liquid medium (water) and is pumped to the heat pump or heat exchanger. In the winter, the heat is used to heat your home. In the summer, the process is reversed and indoor heat is extracted from your home and transferred to the earth throughout the water.

Q: You mentioned heating and cooling. Does it do both?
A: One of the things that make a heat pump so versatile is its ability to be a heating and cooling system in one. You can change from one mode to another, just like you do on a conventional heating and air conditioning system via a thermostat.

Q: What types of loops are available?
A: There are 2 main types of loops: open and closed. The closed loop is the most common in Texas. The same water is circulated throughout the entire system. An open loop is used when a water table, such as a river, lake or a pond is used for the water source.

Q: Which loop system is best, open or closed-loop?

A: The net results in operating cost and efficiency are virtually the same. It all depends on whether you have an adequate groundwater supply and means of disposal.

Q: Where can the loop be located?
A: That depends on land availability and terrain. Most closed-loops are drilled vertically about 250 to 300 feet deep. One hole per ton of air conditioning and about 4 1/2 inches in diameter.

Q: How many pipes are in a hole?
A: Actually, two. Polyethylene pipe in the 3/4 inch (one inch in South Texas) size, one down, a short over, then back up. Then the hole is almost filled with a type of grout called bentonite. This acts like a radiator in the ground for heat extraction and rejection.

Q: how long will the loop pipe last?
A: About 50 to 75 years. Polyethylene is inert to chemicals normally found in soil and has excellent heat conducting properties. PVC pipe should NEVER be used under any circumstances.

Q: How efficient is a geothermal heat pump?
A: Geothermal heat pumps are more than 3 times as efficient as the most efficient gas furnace, and more than 2 1/2 times more efficient than a 12 SEER air conditioner.

Here's a video presentation that will give you a visual on how it works:


Anna said...

I have a geothermal system and love it. Great savings as well. I have a closed loop. I also have my hot water connected to it as well. The summer I receive free hot water because the heat from the geo is dumped into my hot water.

As for the swimming pool. Is the water coming back into your house to be heated? I know my geo guy did not want me to do that because it there was a problem I would have the pool in my basement. Another person who is using his radiant geo boilers has another device (which is escaping me right now) in a pool house so the water is only circulted through the pool and this pump. I don't know how yours is going to be configured. (He has an engineering background.)

We were going to do geo for the pool but the cost for a loop and geo by itself was too expensive. I was not forward thinking enough to know about a system for the pool. My installer did not provide any options about this. Anna

Jan & Myleen said...

Thanks Anna, for your valuable feedback. What area do you live in and do you mind sharing your bills with us as a result of getting your geothermal system? What part of the nation are you in?

For the pool, we are using a water to water heat pump that will cost around $15,000 for a 22,000 gallon pool. It will be nice because we can use the geo to both heat and COOL our pool (believe me it can get hot enough to boil water in the pool sometimes!).

I also enjoyed your blog, and have subscribed to it. Please feel free to come by again, as I can definitely learn a lot from you!

Anonymous said...

I am exploring geothermal for my new home. Can you give me a list of contractors or a lead as to where I can find some?
Ron on Lake Travis

Anonymous said...

I want to explore a geothermal system(s) for my remodeled home on Lake Travis. Where can I find a list of vendors?

Jan & Myleen said...

There are only a few Geothermal contractors in all of Austin, and I found these guys through Austin Energy's green building program or the Renewable Roundup. The two that had good references are:

Victor DeMarco, 219-1465, American Geothermal,

Jack Johnson, 866-272-0051 or 288-7523, AET Inc,

Please let them know, if you use them, that you heard about them through me and my blog. Maybe I can get a discount :-). Let us know how it goes and feel free to post about your experiences on here!


LeGreg said...

The AET inc website doesn't seem to be in service anymore. Did they close shop ?