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Old 04/26/2006, 09:25 AM   #1
looser
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Any cooling experts/engineers out there? Geo Thermal Cooling Questions

Hi.

Rather than install an expensive to buy and operate chiller, I basically want to run well water through a coil in my sump to cool my tank. I would use my temp controller to open and close a valve as needed.

Here’s the specifics.

The total water volume of my system is about 300 gal.

The ground water temp is about 55 degrees Fahrenheit all year round.

Assume a worse case scenario of an ambient room temperature of 100 degrees. (that would be on a hot summer day with no fans on my lights and no AC running in the house)

My questions are:

Is my idea at all feasible to begin with?

How large of a coil would I need to put in my sump?

Can I use the same type of tubing that I use on my RO/DI unit and just coil it up or do I need a “real” cooling coil?

Would some type of in line coil be better. (maybe on the sump return)

What quantity of flow would be required both of the well water through the coil and of tank water around the coil?

What flow valve would you recommended (I assume normally closed).

Anything else I should be considering?

Thanks!


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Old 04/26/2006, 09:33 AM   #2
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Oh ya. One more piece of the puzzel. I want to keep my tank at 80 degrees.


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Old 04/26/2006, 07:01 PM   #3
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Anyone?


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Old 04/26/2006, 08:47 PM   #4
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from what I've been told you will need a titanium coil to real make the heat transfer. I think a better way is to bury a potable water tank underground and cycle a closed loop through it


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Old 04/26/2006, 09:04 PM   #5
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Plastic tubing just won't transfer heat very well.

I run approximately 50 feet of coiled ro/di tubing through my sump in the summer to:
1. cool off the water
2. heat up the water running into the ro/di

It actually does transfer a few degrees of heat each way...I'm considering extending it to see what effects it may have.


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Old 04/26/2006, 09:45 PM   #6
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I'm considering similiar but pumping system water directly out from a basement sump through a 1/2"poly loop buried in a trench 25' long about 3' deep then dumping back into sump.


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Old 04/26/2006, 10:02 PM   #7
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The thermal conductivity of titanium is about 200 times that of polypropylene. Meaning that a titanium loop will transfer heat 200 times faster than a polypropylene loop of the same size. Or, you'll need a polypropylene loop of 200 times the surface area of a given titanium loop to transfer the same amount of heat in the same amount of time.


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Old 04/26/2006, 11:17 PM   #8
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Not being a premium member can't search but references on WWM to previous geothermal threads on this forum (2003). Appreciate if someone can share the links.


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Old 04/27/2006, 01:58 AM   #9
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How deep is the well? What are the tank dimensions and material thickness? Would the well water go back to the well?

G1


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Old 04/27/2006, 07:40 AM   #10
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Johnsteph 10 - very creative idea with the ro/di water supply! I think I will do that in addtion to whatever else I end up doing. thanks!

nyvp - why do think a buried water supply with closed loop would be better?

das75 - I miss read your post the first time but you ended up giving me another idea. I have a sump pump (like as in on that removes water from my basement). Its below ground level, and always has at least some water in it. I'm just not sure that the water turnover rate in the sump barrel would keep it cool enough to be an effective heat sink. Worth further investigation though. I like it! Also, I have been doing some searches on geo thermal cooling but they all deall with closed loop underground coils. My situation is a little differant. I'm just looking to use water from my well.

Atkinsig - great information. Looks like a titanium coil is the way to go. Any suggestions on where to get one and what size I would need?

goby1 - My well is about 400' deep but thats only because I had them drill it deeper than it needed to be. (bad experiances running out of water in my past) However the water table is much higher than that. In fact I think its only about 10' below the surface. Not sure how far down the top of the water is in the well. The tank is 72X31X24 3/4" acrylic on the front and back, 1/2" acrylic on the sides. The water would not go back in the well. (I'll probably use it to water my garden). thanks for any help!


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Last edited by looser; 04/27/2006 at 07:59 AM.
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Old 04/27/2006, 08:21 AM   #11
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I just typed it all out, then realized that das75 already mentioned my idea. I cant picture how you would store all the water that is being circulated through the coil for 'garden water'. I assume it would be running a good bit, and that would end up being a good bit of water to store. If you are set on using well water, then maybe you could return it to the well. I think you will have better luck running it in an underground loop like das75 said. Another option would be running the tubing through the well water instead of the ground, but I doubt it would be that much more effective. The velocity of water is going to play a big part in the equation as well.

What kind of hose did you use das75?


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Old 04/27/2006, 08:33 AM   #12
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sttroyiii - I wasn't planning on storing it. Just running some tubing from the output of the coil to a drip line in the garden, so basically the entire garden would be watered everytime the tank was cooled. Of course it would all depend on how much water is required to cool my tank. It might be a lot, or very little? Thats one of the things I need some help with. If I'm only using 10 gallons a day than it might not be worth doing anything with it other than letting drain on my lawn. If its 500 gals a day than that would be a diffeant story all together.


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Old 04/27/2006, 08:54 AM   #13
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ok here is my very amature attempt at figuring out how much water I would need move through a coil to keep my tank at 80 degrees. Keeping it very simple. With an ambiant temperature of 100 degrees, lets just guess that it would take 10 hours for the water in my tank to go from 80 to 100 degrees with no cooling at all. That’s 300 gallons, increasing in temp by 20 degrees in 10 hours. Now lets just say that the water going into the coil is 55 degrees and coming out of the coil its 75 degrees. (coincidently a 20 degree temperature change). So ..... I would need to push 300 gallons through the coil over 10 hours to offset the heating. Is this even close?


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Old 04/27/2006, 09:51 AM   #14
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ok now I'm really pushing my luck. Lets say you plot the ambiant temperature on a bell curve over the 10 hrs like this 80,85,90,95,100,100,95,90,85,80. That would require only half the cooling capacity of 100 degrees for the entire period. So per my post above, in a worse case senario, I would need to push 150 gallons through the coil in a 10 hour period. (as sick as it sounds I actually enjoy trying to figure this stuff out, I just don't have the skills/training to know wheather or not I'm completly out to lunch) Any help?


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Old 04/27/2006, 10:28 AM   #15
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If you stuck with me this far than I guess your hooked (or ROTFLOL). So what the heck. If I need a 150 gallons over 10 hours the average GPH would be 15. If you put that on a bell curve over 10 hours the max GPH would be about 26 during peek load. So I would need a coil that would exchange 20 degrees of water temp at 26 GPH. So now...what diameter tube would pass lets say 30 GPH (being safe) with a PSI of 40, and how much surface area would the coil need in order to exchange the 20 degrees in temp? My WAG. 1/4" tube, 80sqft of titanium surface area.

I'd love for someone who knows what the heck they are talking about to tell me if I am even close :-).


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Old 04/27/2006, 06:00 PM   #16
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OK, lets do this thing.

Post a list of all your equipment that is adding heat to the tank as well as how long it runs per day. From this we can determine how much heat you need to reject to the Ti coil which is also how much heat your geothermal loop needs to reject to the ground. Both of which are very easily calculated (I'll post the calcs). I think you'll be surprised how little flow rate you need to make this happen.


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Old 04/27/2006, 07:14 PM   #17
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ChemE - THANK YOU, THANK YOU, THANK YOU!!!

Heres the equipment list.

- Dolphin pump for the sump return 115 volt 1.3 amps. But the pump is isolated from the motor so probably not much heat transfer. Just a little friction in the pump. Its placed in my garage so no additional ambient temp. Runs 24/7

- Mag 24 for the skimmer 254 Watts, 3 Amps, Fully submerged runs 24/7

- 1 Tunze Wave Box 12/7 - not sure about amps. but I belive the pumps are low voltage (24V)

- 2 Tunze streams 24/7 output cycles from max to min. - not sure about heat load created by these either

- 1 Magnum 350 for carbon runs 24/7 couldn't find anything about power usage but its basically just a small power head thats not fully submerged.

Thats it. I included the lighting load in the 100 degree worse case ambient temp.


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Old 04/28/2006, 01:17 AM   #18
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Almost there...

Which Tunze's are you using the 6000's, 6100's, or 6200's?

How many watts of lighting are you running and for how many hours?


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Old 04/28/2006, 05:28 AM   #19
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Tunze 6100s

800 watts of MH 8 hrs per day

420 watts of VHO 10 hrs per day


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Old 04/28/2006, 05:56 AM   #20
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ooops. forgot the fuge lighting.

3 - 100 watt incandescent 24/7


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Old 04/28/2006, 07:29 AM   #21
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So how do you get the water out of the well? Would you have to to set the pump outside of the well? Maybe there is some way you can suspend the pump in the water so its not 400' down. The water will keep the pump cooler than one sitting in the summer air. You might want to list how much it will cost you to build this setup, versus a ground loops setup, versus a chiller. Then figure out how long it would take to get your money back by not using as much electricity through geothermal means. The chiller will eat some electricity I imagine, and that will be the determining factor. Unless you just want to be different of course.


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Old 04/28/2006, 07:42 AM   #22
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you will have to run 4 gal min through the coil to get it to work right.


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Old 04/28/2006, 08:01 AM   #23
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sttroyii - I would just use the existing pump that feeds my house. In fact I would just tap into the cold water pipe that feeds my work sink right behind my tank :-) But the bottom line is that I want to 1 - at least maintain my current electric bill (as ridicules as it is) 2 - avoid having to shell out the money for a chiller, and 3 - at least try to be a little conscientious of the carbon load that I'm putting in the atmosphere/environment. But you are right, when I/we figure out what the cost would be of geothermal I would have to weigh that against 1-3 above.

BTW - I'm also looking at a Geo Thermal heat pump to heat/cool my house. Seems very promising given the cost of oil these days.

I'm already different, just ask my kids. :-)

RGibson – Would that be a maximum amount in a worse case scenario? Otherwise I’d be looking at 240 gallons per hour. . . seems like a heck of a lot. Also what size coil would I need? Any ideas on where I can get one? (see that. . . . you provide and answer and all you get is more questions – its starting to sound like work :-)


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Old 04/28/2006, 08:56 AM   #24
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That flow rate is for 12,000 btu of cooling.If you will chech with Oklahoma State University them have done more work on ground source heat pumps then any one i know and will tell you how to put it in.There is a installation guide that you can buy that would help you with heat and air and allso some good ways to cool your reef tank.


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Old 04/28/2006, 09:00 AM   #25
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Your library may have the guide ISBN:0-929974-01-8 is the number the library will need.


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