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Hello, I'm thinking of ways to cool my home (active cooling, already lots of passive implemented). Been toying with the idea of radiant cooling. I live in the Chicagoland area so it is hot and humid in the summer and realize that condensation could be a problem.

I've been thinking about running an underground pex field as a heat sink, using a 12v pump powered by solar panel to pump the cooled water/antifreeze mix through copper or aluminum tubing that has been wrapped around the intake plenum of our forced air furnace. In the summer just run the furnace fan to circulate cooled air.

If anybody has any input/feedback on this idea it would be greatly appreciated. Thank you!


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`86 Volkswagen Jetta NA: 9 Gallon Marine Tank>Transmission Cooler Tank Heater>TIH>FPHE>Coolant Wrapped Veg Filter>2, 3 Port Hydraforce Valves>Temp. Probe>Line Heater Specialist Injector Line Heaters>Vegtherm on Return>"Crud Catcher">Loop

Everyone Should Read "Ishmael" by Daniel Quinn
 
Location: Woodstock, IL | Registered: May 28, 2006Reply With QuoteReport This Post
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Not exactly - but close. I used 1000 gallons of water in an outdoor cistern and an actual radiator as the indoor heat exchanger, worked fine after I added a second outdoor radiator to help cool the cistern water at night. This was done about 90 miles south of Chicago, 20 miles north of Champaign.

This links to the archived discussion. (Note: irrigation valves referanced in discussion didn't work, they are pilot operated valves and need high pressure water to operate)

From the experience I was surprised to find that dirt does not absorb heat very fast, I heated the 1000 gallons of water up in only 3 days and it did not release heat into the surrounding earth even over several days once I stopped adding heat. Your buried tubing will need to be below your local water table to get good heat transfer, even then you might get a localized heat buildup such that heat won't get absorbed into the ground, can't say for sure but it would be an expensive experiment. I also suspect you would not get good heat transfer simply by wrapping cool tubing around the air duct but it would be simple enough to add a radiator inside the air duct just like is done with central air conditioning. Condensation might be a problem if ducting the air but I did not have any problem with it using a radiator on a stand in the corner of the room.

I did not continue the testing of this setup after I added the outside radiator to cool the cistern water, I realized that if I simply opened a door and a window to allow the cool nighttime east/west air (normal breeze flow) through the house the bedroom stayed just as cool without any added equipment or cost, at least at night. Eventually I added a cheap timer to a big exhaust fan set in the east facing bedroom window to pull the cool nightime air through the house, the fan timer was set to turn on once the air temp dropped to something comfortable, time changed as the summer progressed. If some sort of thermostat was used to detect the outside air temp something could be rigged up to turn the fan on automatically based on air temp, did not find resetting the timer every couple weeks to be a big deal.

There are usually only a few days in August where the nighttime temps don't drop into the 60's by 10-11 PM, plenty cool for sleeping. My house is small and it still takes a couple hours to cool the bedroom even with cool evening air so if you go to bed early the early evening air temps may not be cool enough for this "air flow" approach, also not good if you have allergies.
 
Location: fisher,illinois,usa | Registered: June 03, 2003Reply With QuoteReport This Post
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Hi Tim, thanks for your response. Could the slow heat transfer into the soil have to do with all 1000 gallons in a single container (cistern) and the small amount of surface area actually in contact with the soil? I was thinking about running a single ~400' loop of ~1/2" PEX in the ground. Would you think that the greater surface area of this method would increase the cooling ability of the soil?

I'm all for passive cooling methods. East/West windows opened on the top floor creating a venturi effect pulling cool air from the lower floors. I also have a basement with a cellar door that can be opened (with a screen door) for a nice thermo-siphon (air gets pretty cool coming up from the basement). I do this at night, to cool the house from the heat retained during the day, but I am trying to keep the house from warming up too much during the day (as the warmer months approach I'd like to be ready).

What would you think of this method (PEX line in ground)?


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`86 Volkswagen Jetta NA: 9 Gallon Marine Tank>Transmission Cooler Tank Heater>TIH>FPHE>Coolant Wrapped Veg Filter>2, 3 Port Hydraforce Valves>Temp. Probe>Line Heater Specialist Injector Line Heaters>Vegtherm on Return>"Crud Catcher">Loop

Everyone Should Read "Ishmael" by Daniel Quinn
 
Location: Woodstock, IL | Registered: May 28, 2006Reply With QuoteReport This Post
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I don't think you need to go the expense of using "PEX", most geothermal heat pump websites seem to use the much cheaper "POLY" (polypropylene. I think) black plastic pipe. I have played with this stuff for solar heating in the Arizona summertime sun, a 1/4 inch stream of water going in one end of a 100 foot length of this plastic pipe laying out on the sand had STEAM coming out of the other end, had to increase the amount of water to just get very hot water. The Poly pipe is tough stuff, A relative here in Arizona was a maintanance guy on a local ranch, they used buried poly pipe to deliver water to drinker tanks across the ranch, one line was 6 miles long, several were about 4 miles long. They placed the 1 inch diameter plastic pipe a few inches deep in the rocky desert and it worked well but sharp stones directly contacting the pipe would cause tiny leaks over a few years, one of his duties was to follow the lines a couple times a year and fix the tiny leaks, bedding the pipe in clean sand would eliminate this problem.

I wish I knew the answer concerning surface areas and heat transfer, from reading "GEOTHERMAL HEAT PUMP" websites (one such site with basic info about "ground loop" heat exchangers) They seem to indicate that using ground water is the best heat source/sink but I have seen a lot of the "SLINKY" type plastic pipe ground heat exchangers discussed. The trenches for these are wide enough to place coiled tubing along there length and there depth is only a few feet rather than down a deep well type bore hole. There are rough heat transfer calculators on some geothermal heat pump web pages but these are for setups using air conditioning type heat pumps, these operate with a much larger heat differential than the few degrees available if simply circulating water through the tubing.


The testing I did indicated that it was considerably more usable to cool a tank of water using cool nightime air temps and then use the cooled water during the day to cool the house, I did not think to place temp sensors in the ground at different distances from the underground cistern, would have been an interesting test? You are about as close to farm country as I am in Illinois, my local salvage yard gets several old tractor towed spray rigs each summer, these have plastic tanks from a couple hundered gallons up to 500 gallons on them, They give me the tanks for free because they have to pay someone to use a skill saw to cut them up in smaller pieces to get rid of them. New plastic tanks are also available at most farm stores. OR - for a test - a cheap "Doughboy" type above-ground plastic swimming pool would work for testing, sure cheaper (sometimes even free from a neighbor with kids) and easier than trenching tubing into the ground, you could even add a lawn sprinkler to the filter pump and spray the water through the air and back in to the pool for some additional evaporative cooling, or do this at night to cool the water without using radiators and fans, don't know how effective it would be but it would be something to try.

I am spending this winter in southern Arizona and am about to do some temperature testing of solar water heating. I have found a reasonably priced ($15.00 including shipping) temperature sensor with data collection software on Ebay (one such sale on Ebay), these plug into the USB port of a computer and will automatically collect temperatures at presettable intervals and log them as a list or graph them over time. I suspect several of these can be plugged into an external USB hub using USB extention cables to monitor several points in the system but I have yet to try more than one. These sure make automatic temp monitering pretty easy, no comparison to using my original round faced "instant read" thermometers, and they cost about the same.
 
Location: fisher,illinois,usa | Registered: June 03, 2003Reply With QuoteReport This Post
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Whew,

I've been in St. Louis in the summer without AC. Not my favorite place in the world. Roll Eyes Of course there are many hotter places as the St. Louis temps rarely got over 95.

The one thing I did find in St. Louis is that it depended a lot on your schedule. By 7 or 8 PM the temperatures normally would drop significantly. So if you are gone during the day and get home in the evenings, a good window fan (or attic fan) would do wonders.

I'm wondering if you want air, or water in your underground piping. You might be able to suck air through the pipes and into the house. There has been a lot of discussion about using some kind of a "chimney" (not a fireplace chimney, but something that opens near the ceiling peaks) to move hot air up and out of the house.

One of my favorite websites for power issues for a house is:

http://www.fieldlines.com/

Here is a search for "cooling".

http://www.fieldlines.com/?op=...50&orderby=relevance

I found this like with some notes on cooling:
http://www.builditsolar.com/Pr.../passive_cooling.htm

And this has several links to "earth tubes" from the site above.
http://www.builditsolar.com/Pr...ve_cooling.htm#Other

Good Luck & Keep Warm (now)... and Keep Cool (later),
Cliff
 
Location: Oregon | Registered: October 17, 2007Reply With QuoteReport This Post
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The thing below works 4 of these on a bowling alley lowered the roof cavity temp by 15C.
The air con couldn't cope on hot days before fitting but worked fine after. The boss reckoned it cut his power bill.
 
Location: Nimbin Australia | Registered: December 04, 2007Reply With QuoteReport This Post



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Did a bit of web searching and found this 9 page PDF document describing a "spray water at night for cooling" system that is being tested here in Arizona and in California. The system may not be something you would want to adapt but the article does have some tech info that might be of interest. The concept is very close to what I had envisioned for my use here in Arizona on a smaller scale, use it as described during the summer for cooling and also use it during the winter to solar heat the water during the daytime for use in heating the building.

The paper describes this concept for use in warm dry climates but my Illinois testing showed that Illinois summer nighttime air temps are usually plenty cool enough for the idea to work there even without the extra 10-15 degree cooling attributed to "night sky radiational cooling" or the added cooling due to evaporation. (My testing used a closed loop system with radiator heat exchangers to the cool night air, the cooling water was not directly exposed to the atmosphere)
 
Location: fisher,illinois,usa | Registered: June 03, 2003Reply With QuoteReport This Post
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I did a quick web search using the search term of horizontal ground coupled water flow heat exchanger, one of the documents found is Horizontal Ground Heat Exchanger Design for Ground-Coupled Heat, this 8 page paper has general info about the length of tubing, trench design, heat transfer calculations, and the like. The info in this and other papers should at least allow you to guestimate the heat transfer capacity for your yard.
 
Location: fisher,illinois,usa | Registered: June 03, 2003Reply With QuoteReport This Post
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