Pond Boss Forums INTRO Questions & Observations Geo Thermal

I am in the process of building a home, when the subject of heating and cooling came up I was told by my builder that my pond would be a perfect set-up for a geo thermal system. For those not familar with geo thermal, basicly its a trenching system with a polymer type tubing garenteed 50 to 75 years, buried 4 to 6 feet deep in the ground, snaking or coiled about 450 feet and connecting back to the house into a heat pump, an enviormentally friendly ( this next word makes me nervous ) "antifreeze" runs through the pipe and draws the heat from the earth in the winter, in the summer it takes the heat in the home and transfers it to the ground. I am told the advantage of the pond is the option to lay the coils on the bottom ( about 900 feet or so )like a slinky. In Iowa the requirments are to have at least a 8 foot depth and not less than a .5 ac pond. My pond is 2.75 ac and 14 feet. The advantage of sinking the coils in the pond is the savings on the trenching expense which is pretty costly.Has any one had this install done on their pond? Pros.... Cons? Belive it or not the heat is suppose to conduct through the pond better than the earth buried systems, even in the winter. at the very least it would be good fish structure. "RIGHT"? - Thanks

Mr Willy,

Interesting topic. Hopefully you'll get some good input on this from others but I'll throw this out for discussion. My understanding of a geo thermal system is that you use the earth as one big "heat exchanger". You gather heat from it in the winter and use it for cooling purposes in the summer. If I remember correctly, at around 4 feet in depth, the earth remains a relatively constant 51 degrees.

Since your pond could be considered one big thermal mass, I don't see why you couldn't use it as a "heat exchanger" but given your northern location, I would keep the following in mind. For conversation sake, lets say that you will not be using an aeration system in the pond. Holding this to be true, your pond will be subject to temperature differences (at vaious depths) througout the year. In other words, your pond will have a temperature profile. One explanation of this can be found in the publication MANAGING MICHIGAN PONDS FOR SPORT FISHING, Extension bulletin E-1554, page 21.

As shown in the profile, on page 21, during the winter and early spring, pond temperatures below a depth of 10' average between 39-44 degrees. During this time frame, you would want to be drawing as much heat from your geo thermal system as possible. If the temperature of the earth stays at 51 degrees (this you need to verify) and your pond cools to 39-44 degrees, I would think you'd gain more heat benefit from a system buried in earth as opposed to a pond.

Just my thoughts. I welcome all positive and negative responses.

Russ

I agree with Russ, dont understand much about this, but have studied it some. In the winter, you want the earths heat to be cycled into your home. Here in Texas, the below ground temp is between 60 and 65 degrees, year round. So in the winter, colder air could be warmed to about 60 degrees with this system. The real benefit, for TX, comes with summer. At over 100 degrees outside, your run your cooling systems air through the system which cools it greatly, without Freon, or a compressor. If more cooling is needed, a compressor comes on in addition to the ground system. But it takes the air from hot to much cooler without a refrigeration system.

I agree with you guys.The information on the web sites and several heating and cooling contractors that I have spoken to, tell you to look at it differently from how we would believe this to work. My thinking was the same as Russ, If the water temp is sitting at 34 to 40d that this would tend to cool the heated water from the earth,the theory is that the surrounding water actually works as a conduit ( even better than the earth its self) drawing the heat out. every hvac rep I have spoken to claims the pond or underground well source is the best and cheapest route to go.I am not real fimilar with heat pumps, Nick has probably delt with a few living in Texas.My understanding is that the heat pump works well until the temps dip below 10d then your in trouble. But through the ground or your pond the temps never dip below 50 or 55d underground (in southern Ia) Take a look at this photo to get and idea of whats actually going into the pond http://www.morrellcompany.com/services/geothermal.html ( it should be the bottom photo ) one way it was explained to me.. think of a hot frying pan sitting out at 70d in the air to cool, now take the same hot pan and put it in a 70d pan of water. which cools the pan faster? Thanks for the input, fellas.

I Installed a Geo-thermal heating/air conditioning system in my house outside Brenham, Texas around 2 Years ago. There are 2 basic types of Geo-thermal systems Closed loop and open loop. Basicly the main difference between a normal heat pump air conditioning system is the lack of an outside fan to remove the heat from the freon in the summer or use the heat from the freon in the winter. In my case I have a 4 ton unit cooling the house,there are 4 holes drilled 200 feet deep (like a water well)and plastic pipe goes down each hole and back out going to the next hole ect. Instead of an outside fan to cool the freon down after compresion the coils are cooled by a water bath which in turn is circulated down the 4 holes and back to coils. The heat the water pickes up from the coils is trabsfered to thr ground and returns cooler than it went in. Using a water bath to cool the freon coils is 10 times more efficient compaired to blowing air over them. I have found that the energy usage can be as little a 50% of a normal AC/Heating system (because of the increased cooling effect of water bath the compressor required is about 1/3 smaller than a normal system & no electricity needed to run an outside fan). A lot of large buildings have used a simular system for over 20 years, its just now getting close to afordable for smaller home systems. Most closed loop systems (like my system have a small amount of alcohol (non toxic) in the water to keed the water from freezing in winter. The (Loop) can be like mine (in well holes), horizontal (burried 4 feet in ground and long runs of 200 feet per ton of cooling), or use a body of water to cool (or heat) the water in the plastic pipe. Last but not least there is tee open loop system - Simular in theory but you pump cool well water over the coils (heat-exchanger)and dump the water in a lake or stream.

It is an interesting system that costs from 1/2 to 1/3 less to run and costs less to maintain, (that is the up-side). The down side is cost. the cost of drilling 4 well holes 200 feet deep for the loop cost $5,000 ( the cost of the rest of the system is more or less the same as a normal AC system). I expect to break even in about 5 to 7 years. more $'s up front less $'s each month. (my electric bill last month was $58, largest has been $105)

I hope this long winded explanation helps.

Don Stuart

Mr. Willy, Hopefully I can add some infomative infomation. I am a home builder here in Ohio and have reseached geothermal heating. Depending on your well output and other variables such as summer water tables etc. I have found that an open loop system is very effective. Basically you "pump and dump". You pump the water out of your well and it goes through the geo and discharges into your pond. I have a well that produces 25 gal/min. I have 2 hvac contractors that I use and they both have the same system at their own homes. They have told me that anti freeze coolant lines have some problems such as the longevity of the antifreeze producing cooling and heating returns over a long period of time. Both of my contractors recomended a pump and dump (open loop system) vs. a closed loop.

Another advantage that I have with my system is that when my geo is running, I have 4-10 gal./ min. emptying in to my pond to keep it full during drought.

It all depends on what kind of well water you can produce. Here in my area it is not a problem. Hope this may help.

I have a geothermal system in my log home and it is an open loop system. It uses well water from my household well, and dumps the water after use in one of my ponds which is .62 acres. I believe the well pumps about 20 gpms but this is not continuously.

The water is perfectly safe and helped keep the pond topped off before I put in a trout pond and another well in the back that overflows into the .62 acre pond. Now it is not necessary but still dumps into that pond.

The only disadvantage of this Geothermal system was the initial cost, but it has proabably already paid for itself in the 6 or 7 years I've had it. It is also the most effecient way to heat or cool your house. I recently had a technician come out to do maintenance and he said it looked brand new. Mine is a "WaterFurnace and is made locally in Ft. Wayne, Indiana.

I recently built a new home with a open-loop type system. I have since added a pond(half acre) and plan to move the discharge to the pond. Is it better to discharge on the surface so ice can not form over the entire pond or discharge to the deeper area's(15ft at the deepest point) to keep things moving on the bottom?

My Geo discharges at the edge of my pond. I don't think that a geo discharging at the bottem of the pond will keep the ice from forming on top of the pond. It might cause a problem because you would be pushing the water out under the pressure of the water. I could be wrong on this. Where my geo discharges at the side of my pond leaves only a very small hole open free of ice. Lets see what others may think.

It does sound like a great idea Jakeboxer.I think doddblder2 brings up a interesting point. If there is a foot of water frozen on top of a smaller pond in the winter and flow is introduced at a fairly steady rate from the bottom, what is the affect? Could a relief system be incorporated? could a second pipe be added ( a split in the line) that could be switched during the winter months to the top? I believe any time you can get some movment under your pond is a win-win situation.I have city water here and could'nt use a well if I had one.The water is too hard and would gum up the works.What brand do you have Don? doddbldr2 mentioned the antifreeze loosing its punch over time, have you noticed this in the two years since having yours installed?...GO USA!!........

My line is currently running into a drainage ditch, at the time it was installed we didn't have any plans for a pond. It was a bonus for not having enough dirt to back fill after building a new house.
Anyway the company that installed it said to run the line in the deep if you wanted the pond to freeze over or near the surface it you did not. I just don't know wich would be best for the fish.

It really doesn't matter if it discharges near the surface or deep.

The flow is not that significant at least in the north, in that at most, it will only leave a small hole open in the ice if discharge is close to the surface. Mine is about five feet down now but still close to shore(was near the surface). Mine is now deeper due to deepening of my pond banks after installation.

The water discharging does probably not have much D.O. (well water has none) but the amount discharged into a pond that is at least 1/4 acre will not have much effect on D.O. levels. However if I had a choice I would go with a shallow discharge.

Having observed my discharge when it is was near the surface it it like a garden hose that turns on an off. It never runs continuously just turns on more often when the geothermal has to work harder in very cold or very hot weather.

One thing you may want to consider before installing is a bypass on your well so you can occasionally run well water directly into the pond. I filled my pond this way. Since the well pump has to be larger for geothermal use (somewhere around 20 gpms) you can more quickly fill a pond. If anyone has ever tried to use a garden hose they know how piddly that flow is.

Mr Willy

My Geo-Thermal system is made by Trane they have several types of systems. Here is a link to their web site
Trane Geo-thermal

I have not had any problems related to anti-freeze (in texas they have to use a non toxic type). We do not have real hard winters here in central Texas (down to 15 maybe down to 10 for a day or 2) so this is not a major consideration here.

If you have real hard or corrosive water you can fill the closed loop with more friendly water (treated or city water.
I hope this helps some.

Don Stuart