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Old 10-27-12, 11:03 PM   #1
The master plan
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Default Used Geo heat pump

I am going to go and look at a used Geo thermo heat pump tomorrow. It is a older Terra Thermo or so I am told. Its a add on system...needs connected to a furnace, it makes hot air not water. He is asking $200 for it. May need some R22 added because it leaked some out when he took it out.
He had it running a total loss system...well water. I will be using it in a slinky set-up closed loop.

Anything I should be on the look-out for?

I know it may be old but where else can you get a working geothermo heat pump for $200?? This will be used to heat my garage when I am working out the so I don't need it warm all the time. My loop temp there got to a low of 38F last winter...it is 56F right now with nothing hooked up to it. 1200ft of pipe in the ground as a slinky coil.

I could try it out in the house this winter by drawing water out of a heated tank, 800gal...how high of heat could one of these stand for the input side? Up to 80F or more?

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Old 10-28-12, 12:49 AM   #2
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I am going to go and look at a used Geo thermo heat pump tomorrow... Anything I should be on the look-out for?
It's really a pig-in-a-poke. I'm sure it's 220V, so doing a quick test of the compressor would be pretty tough.

You'll have some control electronics there that need to work, so if you can see that part, look to see that it doesn't look like it got left out in the rain.

It would be real tough to test that out, too.


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I know it may be old but where else can you get a working geothermo heat pump for $200??
Yep, it's a find. And a super find if it works. I don't know about you, but I consider a $200 investment to be tuition in a very interesting school. Even if you can't get the beast to work, you will learn a huge amount by trying to get it going. You will have aquired way more than $200 bucks worth of knowledge.

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My loop temp there got to a low of 38F last winter...it is 56F right now with nothing hooked up to it. 1200ft of pipe in the ground as a slinky coil.
Was that just ground temperature, without extracting any heat energy?

That sounds pretty darn cold...

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I could try it out in the house this winter by drawing water out of a heated tank, 800gal...how high of heat could one of these stand for the input side? Up to 80F or more?

I'd say 80F would be safe. Are you planning to use solar to heat the tank?

[I misread your question when I posted this, I thought you were asking what kind of heat could you get from your heat pump, so I answered it that way.].

Well, your possible maximum temperature out will be going down, the longer you run your test, because the heat energy in your water tank will be going down... but the heat of the lines in your air-handler it should be able to get above 120F.

The air from your air handler will be in the 80ish to 90ish degree F range.

What is the length and depth of your slinky trench?

-AC
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Old 10-28-12, 03:49 AM   #3
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My loop is only about 7 feet down...but it is under the garage slab which has 2 inch foam under it and the rest will be under the driveway which will also have the foam under it. So I hope it will stay warmer this winter. The garage is finally up and closed in. It wasn't last winter. To the south the land goes up 2 feet, we cut into the slope to make room for the garage. So the loop should act like its 8 or 9 feet deep later when everything is done...at least thats the hope.

I can heat the tank of water with a wood stove for the testing...later if everything works it would be solar.

I have much insulating to do on the house to make this work. But the garage will be sealed better than the house. I also built it with 10" think walls for greater insulation. The rafters are "energy heel" type for more insulation also. No part of the slab touches the ground, everything is on top of the foam, I hope to have very little heat loss when it is all done.
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Old 10-28-12, 01:59 PM   #4
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My loop is only about 7 feet down...
I really like what you're doing with the insulation, etc. That will really pay off in the long run.

Since you're going with solar, you should be able to 'charge' the ground with heat during the summer, and harvest it during the winter.

Keep us posted on your new hardware.

-AC
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Old 10-29-12, 11:02 AM   #5
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Well, I bought it but have to run back and get it with a trailer. The guy had it running a total loss system in a 40 ft well pumping 8 gal a min. He got tired of replacing well pumps and pressure tanks. Claimed he could heat his house for $40 a month with oil or wood as back-up or when it got real cold.

It looks real clean and you can clean out the heat exchanger on this one. Paid $175 for it and he is throwing in a flow regulator and few other things.



Said it was a 4 ton unit, the compressor is a big sucker! I have a big 220volt 24-27k BTU window unit that maybe use that compressor and cap off the 4 ton for future expansion. He was pulling 5 degrees out of the water while running at 8 GPM Being I have only 1,200 feet of pipe in the ground it might cycle too much. I have room to put another 1,200 maybe 1,800 ft more...if I can get some good results out of the first loop.

Not much to the inside of it, no electronics just a pressure switch and couple of relays. If I did have it opened up and switch compressor I would put in a reversing valve so I could cool with it also.



Can't believe the draw...28 amps! What would running amps average?

Any input or ideas?

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Old 10-30-12, 01:56 AM   #6
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Well, I bought it but have to run back and get it with a trailer.
Can't believe the draw...28 amps! What would running amps average?

Any input or ideas?
That is maximum amps... my guess for running watts would be around 7000 watts or less. I'm just guessing that the COP is 2 (very pessimistic guess) so...

4 Tons = 48000 BTU/hr / 3.421 = 14068 watts

So COP 2 would require half that much power or 7034 watts or there abouts.

I figure a pessimistic guess like that would only make you happy, when your results turn out better than my numbers.

If I were you, I would ask randen what he calculated for when he put in his loop field. He know more about the relationship between slinky trench length and Tonage. And, if I'm not mistaken, he lives in a northerly lattitude similar yours.

But, my unseasoned intuition would make me guess that your trench will give you about a Ton, or 12,000 BTU per hour.

If you try to run an over-sized compressor on an undersized loop field, you run a serious risk of freezing your loop fluid, and cracking your heat exchanger. I did that very thing, on a very small scale, so I know it to be true. I was sitting right there when it happened, so I shut the compressor down before any damage was done. If you do try it, make sure you closely monitor the temperature of the water coming OUT of your HX, as that is where the trouble will begin.

The heat moves into the loop field fluid pretty slowly, so you need a lot of pipe to get the amount of heat you want.

Maybe that A/C unit you mentioned could make a good starter unit... like you said, cap the 4 Ton unit off, til you're sure your loop field is properly-sized.

Best,

-AC
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Old 10-30-12, 04:17 AM   #7
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That was my guess about a ton...thanks for the info on the freezing of the loop. Didn't think that was possible before the heat exchanger would freeze up. Maybe a smaller unit would have been better. But I just couldn't pass it up for the price.
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Old 10-30-12, 06:39 AM   #8
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I would agree it is a good deal. Without knowing anymore than the length of slinky tube in the ground the 1200 ft is between 1-2 ton. I see two options 1/ use the 4 ton compressor with Propylene Glycol in the loop and a cold limit control like what is used in a refridge. to limit the GSHP from turning the ground to permafrost (block of ice in the ground). This is a double edge sword on one hand there is a lot of heat avalible as the water in the soil changes state from liquid to solid the downside once the ground is frozen you are finished heaating for the season. As well this last bit of heat is expensive to obtain as you COP has dropped dramatically.
A side note: I had been told of a sizable installation in a high rise area inwhich a small loop was installed with a sizable heat pump. Being the loop was always in a shadow and covered with snow and buried deep the ground froze and couldn't recover because of receiving no sun.
2/ Change to the smaller compressor utilizing the larger HX and still install propylene glyco and monitor your loop temp. Remember these things are suppose to run almost continuosly as the heat slowly migrates into your loop. With the smaller compressor you will enjoy lower operating costs. Your super insulation work and being you won't need 75 Deg F in your garage you might sneek by.

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Old 11-01-12, 12:24 AM   #9
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This last year just running the loop with nothing hooked to it the high was 58F the low was 38F. I am going to monitor it again this year. During the summer I will start "charging" the ground with heat from whatever source I can....solar, ambient air,bon fires etc. lol Even if I installed a reversing valve and used it as a A/C during the summer I could add heat to the loop. How much I wonder and how long would it take? I read somewhere they are doing this in Canada.
Why wouldn't the high rise use the heat pump during the summer and thaw out the ground or at least add heat to it?
I think this is going to be a big learning experience and a fun project to tackle.
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Old 11-01-12, 01:35 AM   #10
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...During the summer I will start "charging" the ground with heat from whatever source I can....solar, ambient air,bon fires etc. lol...
This is a really great plan... It will be very useful to know if there is water migration through the area where your slinky loop is. If this is the case, you can be sure that it will 'strip away' any heat or cold that you may want to store there. If there is no water migration, then storage is a good plan.

On the other hand, water migration could be useful to you, as it would bring you more heat or more cool... but it would undermine the storage idea.

Your general rainfall would tell you something... If you are in an arid area, good chance that there is most likely less of a water migration problem. If you live in a wet area, like Portland Oregon (my fair city), where annual rainfall is about 38 inches per year, then water migration is quite likely to adversely affect heat storage... the flip side is that there is a constant source of new heat falling from the sky (in the form of rain), during the winter.

So you need to get a handle on the water migration issue, for your specific location. Maybe your city has somebody that knows about this kind of thing.

But either way, your concept of using the ground as a heat source and heat dump is a good way to go, migration or no migration.

Randen has hands-on expertise in loop field heat estimation, so you should listen to what he has to say.

With that said, in my area, for a slinky trench, an 80 foot trench by 4 feet wide by 6 feet deep (coils buried flat) that has 600 feet of pipe can be relied on for one Ton. That estimate comes from an area that only occasionally goes below freezing in the winter... maybe 7 days at the most.

Your area will be different... so you should ask around and find out what your local GSHP installers are going with. There are many factors to consider, and local installers who have been in the business a while will know these things.

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Even if I installed a reversing valve and used it as a A/C during the summer I could add heat to the loop. How much I wonder and how long would it take? I read somewhere they are doing this in Canada.
Why wouldn't the high rise use the heat pump during the summer and thaw out the ground or at least add heat to it?
I think this is going to be a big learning experience and a fun project to tackle.
Sounds to me like you are already beginning to get your money's worth from your investment.

The fun is just beginning...

Best,

-AC

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