I have been doing some research on cooling systems using geothermal transfer. I plan to eliminate my outdoor unit entirely and use geothermal lines to pump cool water through my existing Aframe on my furnace. Currently we use a pellet stove as primary heat for the winter and I have some ideas I cant seem to find much info on. I am considering building a solar water heater and using it in conjuction with an electric water heater, providing some heat in the winter, possibly providing primary heat even. I am concerned about efficiency, but I believe I can build this system cheap enough that if I can just save a fraction then it will be worthwhile. I will be able to complete this project entirely on my own, including the excavation. I am a carreer electrician so all the components will be electrical grade equipment as I have ready access to all these. My design is as such. Install 2000 ft or so of 3/4 pvc lines 5-6 foot deep in 1' wide trench. Lines spaced 5-6 foot apart. Bring that into the house and run that through the aframe with a pump circulating it. Using the existing squirrel cage as circulation. Of course this will be Tstat controlled. Install an additional squirrel cage and damper with an additional tstat outdoors to pull in cool or warm air which ever is appropriate for the season from outside automatically. Build a solar water heater and install it on my south facing roof above my attached utility shed. This will be plumbed into a large water heater(or possibly multiple) to provide some "free" hours of heat through the day. Possibly utilizing the electric water heater(s) to provide heat through the night. This will also be piped in through the Aframe and circulated as before. I am not sure exactly wheather or not to place a heat exchanger in the H2O heater or just pipe it in. I would like to also use this system to provide hot water for the house also. It seems logical as I would be able to get most if not all of my hot water all summer this way. I am concerned about freezing in the solar heater at night. I was considering a seperate closed system for the solar heater using antifreeze and the DIY exchanger, but I am concerned about leaking antifreeze into my potable water. So I am still kicking that design around a bit. I have also considered installing a couple or 3 4" lines from outside connected to my second squirrel cage to give some "emergency" cooling if needed, as well as fresh air. Pretty much I am just wanting to initialize a conversation regarding this design and see if any of you have any experience with such a system. I know it can be done. I havent done the math yet and any help you can provide is appreciated. As well if there are other threads here regarding this type of system I would appreciate being pointed to it. Any help you can provide is much appreciated.

I would think that solar heating and geo-cooling would be climate dependent. I did not see your location mentioned in your comments.

Install 2000 ft or so of 3/4 pvc lines 5-6 foot deep in 1' wide trench.

Are you aware that HDPE pipe with fusion fittings is used for geothermal loops? There is a reason for that.

You also might check the engineering on your heat exchanger to calculate how much cooling or heating you can expect from it with the water temps and volumes you can generate.

PEX is also OK and easier for DIY.

Location is SW Missouri. I'm thinking of building the heat exchanger from 3/8 coiled copper tubing two coils of 25 ft each. These will be in the H2O tank. I'll use the same tubing but 100ft in the solar heater. Again in parallel. Thinking of building a panel with sheet metal backing and the copper tubing soldered to it in spots. Will use a line voltage t stat to control a circulating pump for the solar heater exclusivley. I believe the smaller diameter tubing will transfer the heat better than larger diameter tubing.

I have no problem at all using P.E. pipe. I want to get that part right the first time for sure. The cost is about the same from what I'm seeing. Where can you rent the tool for welding the joints?

I have no idea how to do the calcs and would appreciate some help with that.

Posted By jonr on 15 Aug 2011 07:10 PM
PEX is also OK and easier for DIY.

I am pretty sure I have seen it done with PEX elsewhere. I appreciate your input. I havent ruled it out if it will work well. I can get long lengths of the pex so as to have no splices underground. However if the P.E. is the way to go then so be it.

Years ago at the Minnesota state fair I saw a system that took air into a 4" plastic drain tile ran through the ground below the frost line and into the building. They said you could cool chicken or turkey barns with this for the cost of running a fan. What the formula is I do not know. I think it would include the qubic ft. of the building, length of tile and speed of fan. They also said in the winter instead of bringing below zero air into the building the air would be 55 dergees. Which cost less to bring up to 65. Hope this helps. Does any one know the formula? Tanks!

Pipes for air cooling (or no heat pump hydronic) sounds like a great way to grow mold.

Greetings,

I'm all for passive and DIY sys. I recommend them to my customers.
BUT, unless you have radiant insulation in your ceil'g and walls I'm afraid your going to be disappointed as far as cooling goes. If you have enough collector area heating will probably be a go.

Using outdoor air (earth tempered or otherwise) is a lousy cooling strategy in a place with summer dew points as high as those found in SW MO- most of the time you'd be increasing the latent load, adding to the mold hazard indoors.

Unless your house is VERY air tight (under 3ACH/50) and relatively high-R (R25+ whole- wall R values, R50+ whole roof values, R12+ on the foundation) don't expect to get much of a space heating fraction out of solar. Even then you'd need more than a coupla HW heaters worth of buffer to handle a larger active solar array. No matter how cheap the solar approach is, most homes would be better of spending the money on air-sealing and spot-insulation. Most homes do not have insulated foundations, and are >10ACH/50.

The cheapest most cost-effective solar heating tends to be DIY thermal air panels (active or passive), not hydronic. By using air as the heat transfer fluid you don't have freezing or leakage issues to be concerned with. Unless you're expereienced with hydronic heating design I'm doubtful that you'd be able do just hack an active solar system together that works, and works efficiently. That said, if you pay close attention to the approach (including caveats about stagnation temps, steam explosions,and the effects of oxygenated water on pumps, etc.) it's possible to build drainbacks that run at atmospheric pressure, and build unpressurized insulated buffer tanks that might get you some benefit:

http://www.builditsolar.com/Projects/SpaceHeating/SolarShed/collectors.htm

http://www.builditsolar.com/Experimental/PEXColDHW/Overview.htm

http://www.builditsolar.com/Projects/SpaceHeating/DHWplusSpace/Main.htm

OTOH, add it all up, then figure how much mini-split and photovoltaics you might buy for the same money (after air-sealing the hell out of the place and fixing any insulation gaps, adding more where it's cheap.)

So far over your head the sun cannot be seen from that depth. DIY geo-thermal (more correctly ground source heat pump...seriously? I thing I missed the part about the compressor (heat pump). It is hard to calculate the amount of materials and wasted man hours on so many of these DIY projects. You are in the trades and must know an HVAC tech or two. Even the ditch diggers could help you find the right pipe and maybe even the right size depth and length. With so much information available this is hardly the place to start a DIY geothermal "design".

Ungracious, perhaps. But at least I am honest.

I do not design nor sell Geo systems, real or imaginary, nor do I go for the contemptable practice known as astroturfing (however it may be couched). I would give our hapless DIYer one more pearl...beware the man baring "free" gifts.

This does not mean that I am unfamiliar with geothermal, groundsource or the simplest pump and dump chillers. Of course proximity has nothing to do with good HVAC design practice or respect for another man' s time. PS It is not the horse's mouth that worries me.

is hard to calculate the amount of materials and wasted man hours on so many of these DIY projects.

I agree. But on the other hand, if people like to work on such projects as a hobby, that's great. Hobbyists learn, educate and even come up with some good ideas now and then.

http://www.igshpa.okstate.edu/

information you can use close to where you live

I celebrate the DIY spirit and encourage people to roll-their-own provided no one gets hurt and resources are not wasted.
A little more research and a little less DIY up front would serve most better than what amount to little more than gossip. If you have a hobby, it
should be fun. This is more about saving resources, yours and ours. Waste is waste. Though ground source heat pumps may save
the environment they use considerable resources with a small return on investment (most residential applications).

It is all time about time and money. I would like people to know or at least think about both before diving in. Of course many professionals
waste both but at least have a more ready supply of support than the average homeowner. I hire other trades because I respect their investment
and want my work done right.

IMO, if you don't have nat gas and can get a reasonable price on installation, ground source heat pumps usually have a good return on investment.