My geothermal cooling loop seems to work

[Yaktop]

I was just thinking, my cellar floor is already almost 4 ft below grade. I could just dig there and be almost there

How far below the concrete do you think I should go and how far apart do you think these aluminum tubes should be seperated. if they ever did rot it wouldnt be that big of a deal.

thoughts ?

 

[~Flighty~]

I think if you are going to dig a big hole in a cement floor, I would just sink a big sump of some sort. The advantages of having a large extra volume of water have so far been great. I just need to figure out how to have it insulated in the winter and use it for cooling in the summer. All of my ideas so far involve draining the tank to do it, so I'm still thinking.

 

[~Flighty~]

Even just sinking a water tub not connected to the system and running a cooling line through that would work.

 

[Yaktop]

interested in a geothermal system not more water to change, humidity and the like. thanks for the thought though.

 

[~Flighty~]

Ahhhh, but a closed container adds no more humidity and reduces the impact of current topoff amounts. Fewer water changes required (dilution pollution solution) and the extra volume of water minimises the warming impact of lights, pumps etc.

 

[Moe_K]

I think heat exchange would be much easier using a bunch of thin tubes rather than one big tub. Perhaps Greg, Matt, or any other brainiac in the group can confirm.

 

[Greg Hiller]

The problem is the surface area. You need a large surface area for the heat to disapate. For a small tank adding a large volume of water, or burying a big tub is probably enough.

I think the point (one of them) that Ed is trying to make is that if you increase your total tank volume, then to make a significant water change you need a huge volume of water.

If something bad happens in your tank people always say...oh, do at 20% water change. On a 100 gallon system...20 gallons. On a 1,000 gallon system to remove the same fractional amount of the pollutant it would take a200 gallon change.

 

[Yaktop]

I was just thinking, my cellar floor is already almost 4 ft below grade. I could just dig there and be almost there

How far below the concrete do you think I should go and how far apart do you think these aluminum tubes should be seperated. if they ever did rot it wouldnt be that big of a deal.

thoughts ?

now back to geothermal. Greg/Marc, any thoughts on above?

NO MORE HIGHJACKING, please

 

[marco67]

at 4 ft below grade you will be at a constant temp. depending on your soil and where you are it should be at about 54degF.
The only thing you would be fighting is the slab it's self heating up the soil under it, acting as a radiator.
How were you thinking of installing ? cutting a section, installing, and then repouring?
If so why not just go a couple of feet below just to be safe?

 

[Scuba_Dave]

Are you in a low lying area at all?
My cement floor is 50+ years old & with all the rain we had I had some water seeping up thru the concrete floor. That makes it impossible for me to do this.
How warm does your basement stay in the summer?
My basement stays between 68-73. Do to the existing tank/sump.
To really achieve better cooling then water in the basement, I think I'd want to go down another 2' at least

 

[Yaktop]

was thinking 2 or 3 ft to overcome the slab. I have a little section cut our now for spillage and never had any water issues. thinking of cutting and then putting in circular forms like they use for concrete but fill the outside rather than inside the forms and sit the heat exchanger in each; filled with sand, and use a trap or plate as a means to re-enter as necessary (leaks or a few years from now).

why parallel why not series to ensure the liquid is actually chilled to 54 degrees ?

still curious to the exchanger inside the sump though. how much as you each figuring is enough?

 

[marco67]

In that RC thread I linked to above, one of the guys suggested this http://www.repairclinic.com/0081.asp?RccPartID=12857 as the tanks side exchanger, I think it's worth some consideration.
Length ?
Just make it long enough
LOL it should be easy to find ...just start with your best "guess" then add a length until temp exiting the exchanger equals tank temp.
FWIW
I'm picturing a separate exchanger/sump that has raceway baffles in it. Each raceway will have one (2,3 or 4) of these SS exchangers in it, you could measure temp from one baffle to the next as well as in the cooling loop to monitor progress and efficiency. Then add exchangers as needed.

 

[Yaktop]

In that RC thread I linked to above, one of the guys suggested this http://www.repairclinic.com/0081.asp?RccPartID=12857 as the tanks side exchanger, I think it's worth some consideration.
Length ?
Just make it long enough
LOL it should be easy to find ...just start with your best "guess" then add a length until temp exiting the exchanger equals tank temp.
FWIW
I'm picturing a separate exchanger/sump that has raceway baffles in it. Each raceway will have one (2,3 or 4) of these SS exchangers in it, you could measure temp from one baffle to the next as well as in the cooling loop to monitor progress and efficiency. Then add exchangers as needed.

all good ideas. greg whats your angle on all of this for inside the sump?

this should had been a winter project

 

[jaiden]

OK I've been watching this thread a while now and I want to throw in my 2c

The stability of temperature at a given depth is subject to change by the addition of heat. now, I'm not saying these things won't work, but pumping hot water through underground pipes will heat up the ground around it somewhat. Dirt doesn't have much ability for convection, and it's a decent insulator against radiation.

This is why I think the "below the water table" idea was a good one. Water DOES convect, and also has a much higher thermal conductivity than dirt. So, it will remove heat more readily, and "move along" due to the natural movement of the water table, and due somewhat to convection.

I think a sump in the ground would very quickly heat up to near tank temperatures, but that's just a guess. I'd want to know for sure before *I* did any digging in my place!

I am not an expert on any of this, and not trying to rain on anyone's parade. Just some food for thought.

 

[Scuba_Dave]

I go down 2' & I hit water - so no problem on colling effect of wet soil
My garage floor is actually being raised up 1' to eliminate digging down too far to obtain the 4' frostline mark

 

[Matt L.]

I have to agree with jaiden.

The more I think about this problem, the more I begin to worry that my original assertions may bear out.

I feel that unless you're heat exchangers are below the water table, you're simply going to spend your energy heating the soil, which will give you limitted returns.

Matt

Matt

 

[Yaktop]

OK I've been watching this thread a while now and I want to throw in my 2c

The stability of temperature at a given depth is subject to change by the addition of heat. now, I'm not saying these things won't work, but pumping hot water through underground pipes will heat up the ground around it somewhat. Dirt doesn't have much ability for convection, and it's a decent insulator against radiation.

This is why I think the "below the water table" idea was a good one. Water DOES convect, and also has a much higher thermal conductivity than dirt. So, it will remove heat more readily, and "move along" due to the natural movement of the water table, and due somewhat to convection.

I think a sump in the ground would very quickly heat up to near tank temperatures, but that's just a guess. I'd want to know for sure before *I* did any digging in my place!

I am not an expert on any of this, and not trying to rain on anyone's parade. Just some food for thought.

absolutely the better case scenario which is may aim. but if you used numerous smaller exchangers spread over a larger area it should have some benefit since the surrounding ground around each would then cool down that warmer dirt.

 

[Greg Hiller]

>why parallel why not series to ensure the liquid is actually chilled to 54 degrees ? <

Good question. The reason I run most things parallel is due to the pressure drop. It will be a lot more if run in series. If the tubing you are using is large enough, then it may not matter. Remember, you are looking for the maximum transfer of heat, not necessarily will that happen with the temp of the cooling water dropping to the lowest temperature (if flowrate slows). Remember, the heat transfer rate is proportional to the temperature difference. In this case if water is entering the loop at 78 and the ground is at 54 the driving force is 24F, at least at the start of the loop. If the water in the loop has cooled to 56, then at that point in the loop the driving force is only 2F.

Of course when the water enters the loop in your sump if it is very cool that will enhance the rate of transfer in your sump. The thing is that the heat removal from your sump always has to equal that put into the ground. It's easy after the fact to increase the heat transfer rate in your sump (add more length of 1/4" tubing, increase water flow around the tubing, etc.), but once you buried your tubing in the ground, you cannot mess with it anymore.

>still curious to the exchanger inside the sump though. how much as you each figuring is enough?<

I currently have 4 lengths of 25 ft 1/4" tubing, all running in parallel. Thus far I've made no effort to increase the turbulence of the water in the sump running around the outside of the loop.

>In that RC thread I linked to above, one of the guys suggested this http://www.repairclinic.com/0081.asp?RccPartID=12857 as the tanks side exchanger, I think it's worth some consideration.<

Looks okay, but will it last? If we got a hold of a few lengths of this we could probably do some tests on how efficient it is for heat transfer compared to the 1/4" plastic tubing. These tests are not hard to do.

FWIW, I have another idea that might help us out with these problems. I'll 'disclose' it later today!

 

[marco67]

FWIW, I have another idea that might help us out with these problems. I'll 'disclose' it later today!

Now that's just not right....now we have cliff hanger threads

 

[Greg Hiller]

I won it:

http://cgi.ebay.com/ebaymotors/ws/e...=4643958484&rd=1&sspagename=STRK:MEWN:IT&rd=1

This is an aluminum marine gas tank. The total surface area is quite large. Volume is 82 gallons. I'll likely bury this in the ground behind my house. It will likely be deep enough to be nearly submerged in water. Anybody want to help dig.....frags for diggers?