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Old 05-02-14, 02:08 PM   #11
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Quote:
Originally Posted by buffalobillpatrick View Post
Geothermal heat pump - Wikipedia, the free encyclopedia

"Recent studies show that utilization of a non-homogeneous soil profile with a layer of low conductive material above the ground pipes can help mitigate the adverse effects of shallow pipe burial depth. The intermediate blanket with lower conductivity than the surrounding soil profile demonstrated the potential to increase the energy extraction rates from the ground to as high as 17% for a cold climate and about 5-6% for a relatively moderate climate.[18]"

This is from:Ground source heat pump pipe performance with Tire Derived Aggregate
So what will you do with this info?

-AC

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Old 05-02-14, 03:51 PM   #12
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Try to decide if insulation over shallow loop field is worth the cost.
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Old 05-08-14, 12:43 PM   #13
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Another large Solar heated slinky loop system 5800ft2 in Alaska,
some videos & nice diagram:


Ground Source Heat Pump and Solar Thermal | Cold Climate Housing Research Center
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Old 05-11-14, 11:23 AM   #14
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Afaik, insulating above a shallow field would be hugely detrimental to the field as the sun is greatly responsible for reheating the ground.

Additionally, if you are considering doing a field in series, be sure to have the panels before it returns to the field. Most heat pumps have a limit on the temperature of the incoming ground loop of around 110. I am not sure why this is, but I've seen it on the specs of every heat pump I've looked at.
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Old 05-11-14, 02:31 PM   #15
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Originally Posted by Blue Bomber Man View Post
Additionally, if you are considering doing a field in series, be sure to have the panels before it returns to the field. Most heat pumps have a limit on the temperature of the incoming ground loop of around 110. I am not sure why this is, but I've seen it on the specs of every heat pump I've looked at.
Huh? What? Who else says don't use a heat pump above a certain temp? EVERYONE? I wonder why the manufacturers would impose such a limit? We were just debating this condition in another thread. Hmmmmm......
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Old 05-11-14, 03:50 PM   #16
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...I wonder why the manufacturers would impose such a limit?..
I think it's one of those inconvenient Physics limitations, concerning the characteristics of the refrigerant.

-AC
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Old 05-11-14, 07:08 PM   #17
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Once the temperature goes that high, it would make more sense to bypass the heat pump in which case it's a moot point. The real limit is how high the suction pressure can go without overloading the compressor.
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Old 05-11-14, 08:58 PM   #18
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I agree. If you have access to 110+ degree water, it would use less energy to just pump it through a traditional hydronic heating setup.
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Old 05-12-14, 10:12 AM   #19
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I agree. If you have access to 110+ degree water, it would use less energy to just pump it through a traditional hydronic heating setup.
Do you actually think that a traditional hydronic heating setup (which is designed for 140F - 160F feed temps) will provide the required heat transfer?

This is exactly the place where traditional thinking fails in low temperature heating installations like solar, geothermal, etc.

Very few hydronic installations (Daox excepted) have built-in efficiency to take advantage of feed temps on the 110 range (and lower).

Vlad's house works with 12" spacing & aluminum heat spreaders because he heats all the floor area, has rigorously reduced infiltration, and put in very good insulation from the start. With three floor levels, his floor area/house volume ratio is fairly high, which favors radiation. Also because his house is large and vaguely tends toward a cubic form, his external area/house volume ratio is relatively low so his house favors lower skin losses.

Did I mention his floor is topped with porcelain tiles, which has a very high U-value?

Lastly, he lives in the Vancouver Canada area and the HDD are not as high as they are in a place like Minneapolis, MN.

Vlad reported feed temps in the 112 range when the weather got really awful.

Of course, awful in Vancouver could be a relief in a Minneapolis winter, or a Colorado winter at high elevation.

-AC
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Old 05-12-14, 01:37 PM   #20
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Quote:
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...Was reading on UK site where a professional GSHP installer runs solar heated water 100% through shallow loop in series with panels before HP. Don't know if that makes sense...
When you compare the HDD of your location at 4000 ft elevation (or whatever) with the HDD of that location in UK, what do you see?

What do you see when you compare the available solar gain of the site in UK with your site located 4000 feet up in Colorado?

Does that comparison make sense?

-AC

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