# Thread: Geothermal loop temps help

1. Originally Posted by Carnak
It may only get chilled a degree or so going to the lake, maybe 2 degrees coming back. Just guessing

If he was living there year round, he would be making ice at the bottom of the lake, loop temp will drop, even with the headers buried if he was running it longer to keep the place at 68 to 70F instead of 60.

Closed loop in Canada, you were supposed to pick out the equipment based on its capacity at an EWT of about 32F.

Horizontals with 600 ft per ton (non-slinky) will still get down around freezing for february to march, getting your heat by making frost 5 to 6 feet below surface of the ground.

Verticals ran a bit warmer.
we design loops at default temps of 30 degrees, and fat loop the heat pump. it doesn't cost a lot extra in the scope of the project, as long as you don't exceed the pump curves. We do 800 feet per ton on non slinkies.

2. you are mild climate in Oregon, curious as to the loop temp with 800 ft per ton say mid february

3. Professional Member
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Here in NE PA most are about 500'-550'/ton. This time of year, the loops are getting down to about 35 deg. If you do the simple math, it works out about that temp.

First at about 7'-8' deep the ground temp will change max about +/- 10-12 deg seasonally. That is a starting point of around 30-35 deg at its coldest. Now calculate the heat flow in the ground. Most common soils (not sand or rock) in this area is 1 BTU/deg/foot. So lets say 3 tons (36,000 BTU) and 2000' of pipe will cause an additional 18 deg drop. This is a worst case pulling a continuous 36,000 BTUs, while in reality it is usually 1/2 of that number of BTUs on average over time. So in the end you might see a coldest loop temp of 26 or so degrees.

It is a bit ironic that when the ground around the loop is coldest, usually around the end of March, we don't need AC until June or so, when the ground has mostly recovered. It would be super efficient if the ground were still at 30 deg.

The jobs I have done with vertical boreholes have done much better. Most are wet holes and the max temp deviation we see seasonally is about +/- 10 deg from 50.

paul

4. Most of my jobs are really big homes 4000-12000 square feet. So I try to fat loop everything. Depending where we are in the valley here, my loop temps in feb/march are low 40's . In some areas like my own loop, I am up in the mountains a bit, When spring melt off occurs my loop temps get under 40, in april and early may. The ground water temps flowing under ground, lower!!! end of april one year I was 34 degrees! And i was running the heatpump half as much or less. I have a three ton with 3000 feet of one inch and 1.25 headers with a single pump flow center. the ground is sand and rock as far down as you can dig. We bedded the pipes with 3 feet of top soil and covered the remaining 2 feet with the sand and rock. works great. we have two loops installed this summer, we are tracking temps starting 20' away from the loop at (five feet down) all the way to the middle of the loop. The program will track daily outdoor temps, stat settings, indoor temps and water in and out and soil temps. Should be fun.

5. In a cold area like Northern Ontario, you can put a mile of pipe in but you will hit freezing. Snow cover stops the frost going down, but you are really getting your heat from the latent capacity of the wet soil.

The vertical ones stayed above freezing, the horizontal ones you hit freezing and it stays there from late January through the end of March and into April.

There was a big boom on them for a while with rebates in the 80s. Mfg's were pushing to undersize them (Water Furnace) and use low pipe/ton (Climate Master) to lower installed costs.

Some (Climate Master) went too low on the pipe, and got screwed when when it got very cold but there was no insulating snow cover and mother nature made the frost not the geo.

Sweden did a lot of testing, and what seemed to be ideal was just over a meter deep for a single pipe in a trench. They went deeper, like 8 to 12 feet but found they were making permafrost, it was too deep to thaw out in the spring, not a big cooling load either.

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