Geothermo theory

[wroughtn_harv]

I was informed the other day (yup, vacation will be over tomorrow) /forums/images/graemlins/frown.gif that we'll be going with a geothermo HVAC system with the pond we're preserving as the heat sink.

So-o-o-o I need to learn as much as possible in the next couple of days about geo thermo theory as I can. I'm facing possible weather complications (rain) and the limited access to a directional drilling rig this coming week.

Any and all help will be appreciated.

 

[Bird]

</font><font color="blue" class="small">( facing possible weather complications (rain) )</font>

Now I wouldn't want you to have problems with that project, but it seems overly optimistic to me for you to expect rain. /forums/images/graemlins/wink.gif

 

[avorancher]

I looked into it a couple years ago and bookmarked this site. The publications section has some information and I'm sure if you follow some of the links you will find more.

Geo Exchange

 

[KennethBrown]

I don't have anything to add about the geo but I can say I'm glad to see you back.

 

[KennethBrown]

I guess I was wrong. I was looking back through old posts and seen this- Old message

 

[Piedmont3]

Wroughtn_Harv,
We built a new home last year. approx 2700 sq ft. 3 bedroom, 2.5 bath. We have a geothermal heat and air unit.
The basics if the way the system works is osmosis... the heat moves from the location of greatest content to the location of least content. Fluid moves through tubes that are laid in a location that has an almost constant temperature. (Our are in 6 each 4" diameter wells that are 115 feet deep) The temperature is at 65 degrees F. so when you need hot air in the winter it is 25 degrees outside it is still 65 degrees in the well. The heat in the well will warm the fluid in the tube and then the heat condensor will condense the heat into the air and blow the air into your house. In the summer it works the same, only in reverse. 110 degrees outside and still 65 degrees in the well.
Our heating and air conditioning bill has been wonderful in our new house. We also spent good money on very good windows, and additional insulation. Our house is total electric. including water well pump. Our largest electric bill so far has been $128 and change. Mostly due to the efficiency of the geothermal unit. Here is another site that will give you some good info. Geothermal Link
Here is another Second link
Here is the kind of unit we bought.
Water Furnace
Hope this helps /forums/images/graemlins/grin.gif
Jeff

 

[dooleysm]

We put a geothermal system in our house that we built last year. 2300 sq feet, 2 stories. Ours is not fed off the pond, but is buried. Not straight down, but in a 300 foot trench. 300 feet out and 300 back in the loop. It's about 6 feet down. It is great. I absolutely love it. Our house is all electric except for an LP oven/range and ventless fireplace, which is mostly just used for looks. Highest bill was $100 last winter. Never got that high in the summer.

In addition to all those benefits, there's a side benefit with pre-heated hot water in the summer. Since you are raising the temperature of the water in your geothermal loop, you can make use of that pre-heated water (usually around 100 degrees, I believe) to pre-heat the cold water input of your water heater. Our geotherm furnace came equiped with this water/water heat exchanger internal. All we had to do was buy a cheap water heater to serve as a storage tank for this preheated water. That water then gets fed into our main high efficiency water heater. That second water heater ended up being free. It cost $150 from the supply yard, but the electric co-op gives a $150 credit for electric water heaters!

Another thing along those lines is that our co-op gives a $250 credit for electric furnaces. Pretty small compared to the cost of the unit, but still...not bad. I've heard of other counties in IN giving up to a $1000 credit. Also, the state of Indiana gives a tax break for home owners who install geothermal units. You take your information to the clerk's office and they deduct the cost of your geothermal unit from the assessed value of your home. This in turn reduces your property taxes. This benefit is given for the life of the geothermal system, although I'm unsure of how you would go about informing them if you switched for some reason.

I love our system and recommend it every chance I get. The cost savings will only go up, as heating fuel pirces continue to rise. Also, I kept my house at 72 all winter and 68 all summer, very comfortable in both seasons.

 

[Toiyabe]

The theory is pretty simple. The terminology is a bit confusing, though - When someone says "geothermal" I think of systems that pump very hot water out of the ground. Usualy people mean a ground-coupled heat pump, as opposed to an air-coupled heat pump like the standard AC units.

I like to use the water pumping analogy. Say you want to keep the house at 65 degrees year round. In the winter the air temp is 0 degrees, and in the summer its 100 degrees. Think of that as feet in elevation. You want to keep the water at 65 feet in the house, and you can only pump that into a reservoir that is at 100 feet in the summer and 0 feet in the winter.

So if your reservoir is the air, in the summer any extra "water" (i.e. heat) that gets into the house has to be pumped up from 65 feet to 100 feet. In the winter in order to get more water into the house you have to pump it up from 0 feet to 65 feet. That's a lot of pumping.

However the ground is often a more moderate temperature year round - say 70 in the summer and 60 in the winter, then you only have to pump at most 5 feet. That's a lot less pumping, and requires a lot less energy.

If you're really lucky, you can have a reservoir that's higher than your house in the winter or one that's lower than your house in the summer. Then you don't have to do any pumping. Those are the situations that I think of as geothermal.

 

[Ray2210]

I have always felt the same as Toiyabe about the use of the geothermal term and really like his explanations. I tend to think of true geothermal as a process that doesn't require a large energy input to recover the temperature difference (delta T) for the operation of the system.

 

[RonR]

Years ago (70's energy crisis), I toured a local house built by a guy who wanted a nearly energy independent house. Sorry that I don't have exact detail or a source, but here's some of the stuff he did. The house was beautiful and according to him, very efficient. A lot of this stuff ties together, but I'll just list them:

1. The house was earth bermed 100% on the north, about 50% in ground on the east and west, and open on the south. Think of a giant lean-to with the south being the open end, and that's kinda how it was constructed.

2. The south side was about two stories tall, with floor to ceiling, highly insulated glass. These south windows had photo sensing heavy quilted blinds that closed as dusk and opened at sunrise in the winter.

3. The south 10-12 feet, the length of the house, was an integral greenhouse, about two stories tall. The floor was a heat absorbing rock. The theory was sun heated the greenhouse, stored the heat in the rock, and then was able to draw that heat through the house in cool nights.

4. Air Movement from the greenhouse ran from the top of the greenhouse to the north rear of the house, through a couple of enclosed rafters. Small electric fans at the peak forced the warm air through the house from the north to the south, dumping back into the greenhouse to complete the loop. Oh, he had calculated the sun angle, so in summer, the eves kept the sun off the glass!

5. For cooling, he had buried 3 two foot diameter culverts that were probably 100 ft long. At the far end of each culvert, he had a two ft diameter vertical tube to allow outside air into the system. This system fed into the south side of the house. The details escape me, but at the peak of the roof, he had electrically operated louvered doors that opened to the outside. During a normal summer south wind, the opened roof doors created a venturi effect to suck the hot air (the ceilings were vaulted) out and draw the cooled air in. If the wind was not blowing, he had installed 1/4HP squirrel cage fans in each culvert to move the air.

6. All these doors, shades, and such were on a control panel that was temperature sensitive, so a lot of it was automatic. He also had a wood stove inside, but said he had not used it much yet (the house was about a year old).

I was impressed!

Ron

 

[yak651]

Going to be building in the next couple of years, just wondering some ball park figures for the geothermal system? If we went this way the trenches would be horizontal instead of vertical, have plenty of room. Approx. sq footage around 2000.
Thanks!

 

[Luremaker]

Speaking of lowering heating costs... the book, SAUNDERS SHREWSBURY HOUSE, by Shurcliff, W. A. was published in 1982 about this 100% solar house built near Boston and designed with no back up heat source. I think the house was about a 2800 sq ft. The house was designed using water and tons rock to store heat.

The house would be close to 24 years old by now and it would be interesting if it is still 100% solar heated. I can find references to it in google only as an out of print book.

 

[Piedmont3]

The difference in the up front cost is quite substantial.
they qouted us $12,800.00 for the highest efficiency electric heat pump and central air conditioning system they sold. The Geothermal unit cost us $20,500.00. The man that installed the system is someone I have known and done business with for about 15 years. /forums/images/graemlins/grin.gif It didn't seem to help with the cost. /forums/images/graemlins/frown.gif

 

[dooleysm]

I wish I knew more about the costs of the one I installed. However, it was installed by the same company that did our plumbing, floor coverings, and sold us some furniture, so I never saw a breakout of the individual prices of everything.

When I hear my parents complaining of two and three hundred dollar gas bills in the winter for a similarly sized house though, and all I have is a $100 electric bill, I know I made the right choice. Cost savings like that will add up very quickly. I've heard that the average household can expect to come out even in 10 years compared to gas heat. That is, the cost of the geothermal unit plus electricity to run it for 10 years is equal to the cost of a gas furnace and traditional A/C plus gas and electricity to run them for 10 years. After 10 years, the geothermal unit is clearly the winner. This doesn't account for the other financial incentives that may be available for each system.

 

[CTyler]

We have 2500 on the main floor and a full basement. We had bids ~28k-32k two years ago. We went with a high efficiancy furnace and heat pump. I figured the Geo would be about a 20 year payback and will probably need a new system by then and what kind of maint during that time???

 

[Charlie_in_TX]

I don't know. It sounds like something of a wash. If it cost $10k more for geo, finaced at 6% for 10 years (the life expectance of the unit), the monthly additional cost is $111.

In my opinion, $10k more is far more than the additional cost the installer incures. The heat exchangers should be within $1k installed. The water lines run under ground should cost no more than installing a syptic system. I had a quote of $3200 to do that a couple years ago.

As to how is works. It is a heat pump first. It 'pumps' heat from the outside to the inside in winter and inside to outside in summer. A component of a heat pump is the heat exchanger (the outside unit that makes all the noise in a air source unit). It is different in a geo and air source heat pump. As the name implies, in a geothermal it is ground source, in an air it is air source.

 

[dooleysm]

The installation was more involved for the geothermal than a septic system. I helped my father-in-law do both. The trench for the geothermal is a very deep trench, 6-8 feet deep, 300 feet long. Then, someone has to crawl down in that trench and install the lines. Ours were affixed to the edges of the trench at different heights, to keep more dirt between them and better disappate the heat.

The geothermal unit itself is a very heavy beast as well. I talked to the guys who broght it in and they told me it was well over 300 pounds.

I am still very happy with my decision to go with geothermal, and I'm of the opinion that it will only look like a smarter decision as the relative cost of heating fuels continue to rise, compared to electricity.

 

[BobRip]

When I built my house I did a little investigation into geothermal. Most of what I learned has been mentioned by others. One item that I have not seen is system life. The geothermal system does not have to work as hard as a standard heat pump since when it is 20 degrees outside the heat source temperature is still at about the same temperature as when it is 60. Consequently the system should last much longer. This was just an article that I read. Can anyone confirm this?

Bob Rip

 

[buckeyefarmer]

I'm trying to do a quick cost benefit analysis, and I can't see geo paying for itself if you have to pay $20K to have it installed.
In 8 yrs my electric has cost $7105, averaged $74 month, with 10 seer ac (used 3-4 months/yr), and oil fired hot water heat. my last yr electric cost is 18% above the average.
My heat cost for last 8 yrs is $6073 averaged $760 yr/ or $63 month. (last yr oil is 25% above the average).
my totol energy cost averages $137 month.
geo claims to use 1/5 the energy, so I'll subtract 4/5 of the oil cost, figuring the 1/5 will be the increased electric usage, so monthly bill is $87. I save $50 per month, so it will take 400 months, or 33 yrs to recoup the $20K cost, 15 yrs to recoup a $10K cost. Energy cost increases (oil and electric) will track about the same., as my history has shown.

 

[dooleysm]

Well, I would think that you'd be more interested in the difference in price between your A/C and oil heat setup and the geotherm system than the total cost of the geotherm system. That's the number you want to reach to recoup your investment.

Also, from what I've heard, the geotherm systems work better on larger houses, 2000 sq. feet and up. By work better, I mean you recoup your investment quicker. It may take 50 years of heating/cooling a small house to realize any benefits of a geothermal system; in which case, a more conventional setup would probably be advised.

Buckeyefarmer, you heating/cooling costs look to be a good bit less than the numbers I was seeing, which leads me to believe you have good, high-efficiency systems or a smaller sq. ft. house, or both. But really, the only numbers I know for certain are the ones on my own current house.