Geothermal Test

[David MC Lee]

I just finished a geothermal test to find out how many BTUs of cooling I could get out of a hole in the ground.
I drilled about a 1.5” hole 13 feet deep. Ran 1 / 2 copper tubing down and up. Set a tank outside with some water in it and let the sun warm it up for a day. Tonight I turned on the pump to measure the flow rate and temperature change of the water in the tank and the water coming back out of the ground. If my calculations are correct, (tschopp can verify) I’m getting around 1000 BTUs/Hour of cooling. I think I need about 10000BTUs/Hour to keep the to keep the tank cool on a hot day. Looks like I need to go deeper or about 10 more holes.
1 Gal per 45 seconds of flow = 3600/45 = 80GPH of water flow. Tank temperature is 76.3 degrees, and water out temperature is 74.8 degrees which is a difference of 1.5 degrees. 80 GPH * 8.8lbs = 704 lbs of water flowing through the copper tube every hour.
704lbs * 1.5 degrees = 1056 BTUs/Hour.

[philagothos]

I'm no expert, but wouldn't the cooling ability also depend on the conductivity of the plumbing? I was just thinking you might want to avoid copper because of the risk to your corals and something reef-safe might have a lower conductivity, and thus less cooling capacity. Feel free to educate me if I'm wrong, you undoubtably know more about this than me.

[ChemE]

<a href=showthread.php?s=&postid=7642357#post7642357 target=_blank>Originally posted</a> by philagothos
I'm no expert, but wouldn't the cooling ability also depend on the conductivity of the plumbing? I was just thinking you might want to avoid copper because of the risk to your corals and something reef-safe might have a lower conductivity, and thus less cooling capacity. Feel free to educate me if I'm wrong, you undoubtably know more about this than me.

The cooling ability does depend on the conductivity of the plumbing but not quite in the way you think. There are actually 3 heat transfer coefficients to worry about here.

1) Heat transfer coefficient between the hot fluid (could be tank water could be something else) and the inner pipe wall. This number increases if the flow in the tube is turbulent (Reynold's number > 2100).

2) Thermal conductivity through the pipe wall. For thin copper this number will be huge thus it is not the bottleneck.

3) Heat transfer coefficient between the outer pipe wall and the soil. This turns out to be quite low and thus the bottleneck.

If we change copper for PEX, the overall heat transfer coefficient doesn't change very much at all because we are still limited by how quickly the outer pipe wall can reject heat to the soil.

[Michelle L]

Oh, you guys are making my head hurt. :(

[epon]

wait till steve chimes in :)

[Sloeber]

:eek1:

[DougSupreme]

why not encase the coils in concrete. I woulod think that would somewhat alleviate the problem of transfer beween pipe and ground

[David MC Lee]

I plan to use a titanium heat exchanger on the tank so there is no worry about using copper. In order to keep the heat transfer low to the soil I’m going to setup some tubes at the top of the holes that will dump my dirty ro/di water down the holes. 200G week will help keep it wet down their.

[Sloeber]

just to clarify, why are you doing this again?

[tcottle]

<a href=showthread.php?s=&postid=7647170#post7647170 target=_blank>Originally posted</a> by David MC Lee
In order to keep the heat transfer low to the soil I’m going to setup some tubes at the top of the holes that will dump my dirty ro/di water down the holes. 200G week will help keep it wet down their.

Best use of RO/DI waste water evar!

[David MC Lee]

After putting my new diy chiller on line my electric bill was over $300.

[epon]

what is the temp range and photoperiod without the chiller ?

[Sloeber]

:eek1:

seriously david, didn't you run the calculations beforehand? ;) :p

[UH_OH_5_OH]

HCS3....you've got a PM.

[David MC Lee]

With out the chiller I'm sure the temperature would to up over 1 degree per 1 hours. MH lights are on about 10 hours a day which would be a 10 degree swing per day at least.
I added more lights than I planned. I really get hit in the summer because the electric company switches to the summer rates and all power is billed at $.075 per KWH. In the fall,winter,spring I pay .075 for the first 930KWH used and then about .032 for the rest. Also my tank really heats my house in the fall and spring.
My chiller may run more efficiently this month due to the fact I now have the correct fan running on it. The entire tank uses about 5KW durning the day with out the chiller. I blow lots of hot air out of the tank room with the large 10" blower fan.
I can keep it cool, it just costs. I figure the chiller running is $100 per month extra durning May, June, July, Aug, Sept. If I can spend that money on geothermal I would be money aheat in two years if my above calculations hold up.

[lglamb]

what you need to do is find out when your farmer friend
goes on vacation and run a few ground loops 1/2 mile
out into the field.

:)

[humbugy]

is there a way for ya to install the evaporator for the chiller outside, so its not dumping all the extra heat inside, and straining your whole house a/c, i think there was a good thread about here on r/c somewhere, about a guy in florida who did that.

[David MC Lee]

The evaporator is outside already outside.

[humbugy]

soooooo, your saying its outside?

[David MC Lee]

Oops yes it is outside.

[honeybee]

Hello,

How about another type of heat sink:

http://reefcentral.com/gallery/data/500/7763Heat_sink_1.jpg

http://reefcentral.com/gallery/data/500/7763Heat_sink_2.jpg

I have been experimenting with heat sinks as a way to cool reef systems for about 16 years. Before you invest too much money you had better find out the capactiy of your heat sink. It is not a question of how much heat can be removed and stored in the short term but how will your sink preform after 5 or 6 hours.

Honeybee

[humbugy]

poiting a fan at the top of your aquarium can do wonders, but it will kick up evaporation, my house ac sits at 78 and the tank with 500 watts of de hqi and two t5, 190 watts of mags + assorted powerheads and etc and the tank hovers around 80.5 or soo most of the time.

[David MC Lee]

Yea I already have a 20" box fan blowing across the tank. Keep coming up with ideas and maybe there is one I haven't tried:)

[honeybee]

Why not a nice fish/lily pond in a shady spot in the back yard, say 14' x 14' x 3'. That would make an excellent heat sink and a great place to relax and watch the sun set?

Honeybee

[rick rottet]

If you put several diffusers running off of air pumps, the bubbles rising to the surface and popping in front of the fan will help evap cooling.
drawbacks = electric for the air pumps and salt splatter.

do you have a window in your tank room (CRS). i was thinking about a wet pad setup....actually, i guess you would need two windows for that.

[honeybee]

If you lived out west you could use a swamp cooler.

Honeybee

[humbugy]

<a href=showthread.php?s=&postid=7665495#post7665495 target=_blank>Originally posted</a> by David MC Lee
Yea I already have a 20" box fan blowing across the tank. Keep coming up with ideas and maybe there is one I haven't tried:)

gimme a minute ;)

[honeybee]

David,

What is this DIY chiller you are using?

Honeybee

[tschopp]

I got slightly different numbers. I got 1056 kJ/hr or 1001 BTU/hr. Don't know how the 1056 matched. I used SI units and you did english, maybe roundoff error. Anyway assuming my number can be trusted we are both getting about 1000 BTU/hr.

The big question I would have is what happens to a hole in the ground after you dump heat into it for a couple of weeks? Does the hole heat up significantly changing your results?

Were you thinking of trying to do the geothermal as the heat sink to your chiller, or did you want to try to directly dump tank heat without using the compressor on your chiller?

There was some talk about Rick's greenhouse dumping heat directly into geothermal and if I remember correctly the opinoin by people who would know like cseeton was that the temp difference would not be large enough to properly dump the heat long term. Basicly after the dirt near your geothermal heats up to 80F you are screwed unless it is the heatsink for your chiller.

A geothermal heatsink for your chiller should help efficency, but I don't know if it will drop your electric bill like you hope.

If you do try more experiments with the direct geothermal I would be interested in the results.

I still think evaporative is one of the cheapest ways to dump heat. I don't see how you could do much better than you do now directly off the tank. One thing I have been considering is a seperatly cooled resovior that you dump tank heat to. You would need a big tank for the water like 1000+ gal and a cooling tower to get good evaporation and possibly some smart electronics to run the cooling tower when outside temps are favorable. The idea is that you run the cooling tower anytime it will help to lower your resivior temp and since you don't have fish in it you can get it cooler than you would like your fish tank to get. If your resivior gets too hot the electronics would have to know to give up trying to dump tank heat to it and just use your chiller.

The evap would help when it is not too hot outside. With weather like we recently had, I think the chiller will be required.

Just started thinking, did cseeton graduate before I got him to make me a chiller?

Steve

[UH_OH_5_OH]

I certainly am the LAST person to come to with mathmatical equin...equhh....equashu.....problems...mainly because the math I do is primarily in the realm of: (Ok Chucklehead....you had 3 grams of meth in your left pocket and two kilos of uncut heroine in the trunk...if you're a three time offender....how many years of federal time are you looking at?) Anyway; if I remember correctly aren't the cooling towers for nuclear reactors super deep, and wide and filled with water ? And again; maybe I am stating the obvious here; but if you line this tank with concrete and the water is constantly moving (flow or O2) wouldn't that handle a great deal of the heat. Sounds to me like your "tower" needs to be considerably deeper to get the effect your looking for.

Again, I apologize if this statement enters the realm of: Go look at the pretty fish while the grown ups talk.

[ChemE]

Actually the cooling towers at nukes are mostly the natural draft design seen here...
http://www.nucleartourist.com/images/ct-natur.jpg

They are actually somewhat shallow and rely on evaporative cooling. Hot damp air rises up the tower and pulls cool dry air in the bottom thus no fan is needed. The open ring at the bottom is typically about 40' tall and having stood next to one the air being sucked in feels like a Category 1 hurricane. The amount of air these things move is truly impressive to say the least.

[badbu68]

DIY mod to your freezer maybe?

[tcottle]

<a href=showthread.php?s=&postid=7719377#post7719377 target=_blank>Originally posted</a> by ChemE
Actually the cooling towers at nukes are mostly the natural draft design seen here...

LOL - Your post made me imagine Dave purchasing a slightly used Russian/Iranian/French cooling tower on eBay and installing it in the corn field behind his house ....

[Sloeber]

:lol:

[tcottle]

<a href=showthread.php?s=&postid=7719978#post7719978 target=_blank>Originally posted</a> by hcs3
:lol:

Cooling Tower on Ebay (http://cgi.ebay.com/Marley-Cooling-Tower-700-GPM-Lot-MS-25_W0QQitemZ280004699954QQihZ018QQcategoryZ42912QQssPageNameZWDVWQQrdZ1QQcmdZViewItem)

Dave - Let me know if you need any more help!!! ;)

[levon15]

Wow, You guys that live outside the big city take the reefing to the next level. The brain power of this forum is outstanding. I would be interested in seeing what everyone thinks of just drilling a well a couple hundred feet deep and running a great deal of piping through it. Not sure about the water table etc. issues that could arise but would this be an option?

If you had a lake in your backyard couldn't you use a deep section of say 6-8 feet of depth to cool the pipes? And the lake unlike dirt is always flowing and replacing the warmer water with colder water. Anyones house butt against a lake?