geothermal chiller

[Kenfuzed]

I've been trying to find an inexpensive replacement for those Ti coil exchangers. I came across a seller of titanium tubing in 12-18 inch lengths. I'm not a metal worker and was wondering if this stuff can be bent or formed. Otherwise I thought I could buy multiple pieces and join them together in a back-forth configuration like a radiator, using pvc or vinyl tubing as the U bend between each length. I was also thinking someone who was doing an open system could use a few longer lengths burried.

 

[Barto]

<a href=showthread.php?s=&postid=7389835#post7389835 target=_blank>Originally posted</a> by Kenfuzed
Otherwise I thought I could buy multiple pieces and join them together in a back-forth configuration like a radiator, using pvc or vinyl tubing as the U bend between each length.

That sounds like a lot of conections (Connection = potential leak)
Of course all the plumbing we use for everything has connectors, so if the price is right for the straight pieces, and the connectors are thought through adequately, your idea has a lot of good potential vs a high priced TI coil.

 

[Kenfuzed]

Also found this Ti tubing but not sure if its SW safe.
"Valtimet ASTM B338/ASME SB338 Grade 2 Welded Heat # CN-2265B Test 023280-2 Titaniun tube".
The fact that it says "welded" concerns me as to what the tube is welded with. I've seen drop-in elements from chillers with weld marks so maybe this is normal but I want to make sure.

 

[salty joe]

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[douggiestyle]

<a href=showthread.php?s=&postid=7377310#post7377310 target=_blank>Originally posted</a> by cseeton
Definitely on the return piping or closed loop... you will want all the algae and other crap settling in the sump and not clogging the heat exchanger.

If it starts to clog on the return the only thing that suffers is the tank/sump flowrate. If it clogs on the gravity feed to the sump, you will pump water up and over the top of the tank because your overflow capacity diminished. Think Murphy's Laws.

this should be in another thread (my comment that is). but ill bring it up anyways. your sump should never be able overflow your tank. alot of people have designed their sumps in a manner that if the return to the tank gets clogged then the pump will continue to supply water to the tank. if the sump is not properly designed this could lead to overflowing the tank. those nicely desinged bubble traps eliminate this problem if designed with a run dry pump shutdown and manual reset. this possible situation should and is easily subverted.

 

[douggiestyle]

<a href=showthread.php?s=&postid=7389704#post7389704 target=_blank>Originally posted</a> by douggiestyle
havent had time to read all posts so if this was discussed excuse me.

we are not going to redesign nature so what it is, is what it is.

but that 100g situation if it was linear yes. slow it down IF you want a certain temp reached on the 100g. event still you would get better results by increasing the length of the tubing and increasing the flow accordinly. slowing the flow in this situation would only be a bandaid to controll the quality of your output.

but we want to control the temp in the tank. so your best bet would be to put that 100g on a recirc setup and pump the he2xl out of it.

the best way to understand this is wind chill effect. we all deal with this on a regular basis. do not confuse this with evaporative cooling. the stronger the wind blows the faster you freeze. i have mentioned this earlier in this thread. the wind blowing does not create a cooling effect (when you subtract evaporative cooling) because if it was hot out the stronger the wind blew the faster you would cook. ok that would be pretty hot but, you get the idea.

x runner did a better job than i.

 

[Scuba_Dave]

I'm thinking of just burying one of these: 300g or so

 

[cseeton]

<a href=showthread.php?s=&postid=7393416#post7393416 target=_blank>Originally posted</a> by Scuba_Dave
I'm thinking of just burying one of these: 300g or so

Why would you do that? Do you need water storage?

 

[MarkS]

<a href=showthread.php?s=&postid=7393416#post7393416 target=_blank>Originally posted</a> by Scuba_Dave
I'm thinking of just burying one of these: 300g or so

That is exactly what I was about to suggest. It would be easier to bury, would not have to be buried as deep and with the larger volume (over tubing), the temp would stay much more stable. Also, with the manway, it allows for much easier filling, inspection and cleaning.

 

[cseeton]

Much larger water volume; but much, much worse heat transfer.

 

[MarkS]

<a href=showthread.php?s=&postid=7393873#post7393873 target=_blank>Originally posted</a> by cseeton
Much larger water volume; but much, much worse heat transfer.

True, but due to the volume, it will take longer to heat up. If you were to put the liquid in it and wait a week, you'll see the temps that you'll see after it is running, give or take a few. Much more stable.

 

[douggiestyle]

marks idea should work fairly well

 

[cseeton]

If your idea is to provide continual cooling to the tank, I couldn't disagree more. If is is to store cool water, then it has merit.

For cooling, there is not enough earth exposure to provide any cooling effect once the surround ground has reached steady state, it is a conduction heat transfer to infinite medium problem. Remember the earth is a marvelous insulator!

 

[douggiestyle]

on the contrary. our cc pool is unable to get above 80F during mid summer though exposed to full sun. my buddies above ground soars almost to 90F and is partially shaded.
depending on the size of your tank and lighting this may be fine. also location in the states is impotant. arizona might not give the same results, lol.

another note, many with basement sumps need no aditional cooling other than a colling fan for the lights in the hood. they actually need to use a heater to maintain proper temps. and the tanks i am speaking of are large with 4 400watt mh lights etc.. some have been featured in reef keeping. this is something i have
been researching as i am in the process of moving my sump to the basement.

 

[BeanAnimal]

The earth is a "good" insulator, however you need to look at the ambient temperature of the "earth" you are using as a heatsink. You can look at it is an infinite heatsink with regards to the heat we are puting into it.

You want to maintain lets say 78 degrees. Lets say the earth 3 feet down is 68 degrees. Thats a possible 10 degree Delta T.

The "storage" capacity of the 300g tank will only help if the heat cycle is short enough to allow the tank to "recharge" during the night (non heat cycle). That said, any oenght of tubing that has a surface area equal to, or greater than, the surface area of the storage tank will also work.

In other words the mass of the water only helps of the heat cycle is short and fast, otherwise it just becomes a part of the "TUBE" with the surface area being it's only relavant consideation.

 

[Cuby2k]

ARGH! I still like the idea of using the earth's lower temp to cool a tank and I plan on doing just that . . . in the future.

However any newcomer to this thread has got to be thinking that it is so complicated that it may not be worth it. or not. I would be willing to wager that by the time you do all the work and add the cost of materials used in an earth cooling system you would be hard pressed to get a simple payback that beats a packaged chiller. Of course your labor could be considered free in which case the point is moot.

Anyway, I think all of the ideas that have been discussed have some merit, of course some more than others.

The issue of water velocity is important, laminarity is a problem but it is not a deal breaker. Fact is water has a similar (poor) thermal conductivity factor as PEX or concrete. (.348/.219/.54 respectively) . I was always taught that maintaining a water velocity of around 1.5 feet per second or higher was good enough to avoid the problem in typical HVAC applications. For a 1/2"= 1.0 GPM, 3/4" = 2.0 GPM, 1" = 3.6 GPM.

If you run a lower velocity the majority of the flow occurs at the center part of the pipe and the stagnant water around the perimeter of the inside of the pipe becomes an insulator, but it is actually quite small. It also becomes less critical when you are transferring the heat to/from media that has the same or similar heat transfer coefficient. But in no case is it better to run it slow.

In my feeble mind the issue becomes one of maximizing your dollar spent by getting the most out of your system. Using the principle of turbulent water to avoid laminarity is a simple issue that helps to ensure this.

Scuba_Dave, I am not sure where you would get a tank that size for burying but man it's got to set you back a pretty penny. If it's a freebie then give iot a shot but honestly it is less efficient than small tubing running at a greater velocity than 1.5 FPS.

Again, I am sure that you would get SOME cooling out of it but $ for $ it is a whole lot less efficient. I agree with what Bean said in the last sentence of his 5/19 post . . . surface area of the transfer device, be it a tank or tubing is the only relevant consideration.

 

[Cuby2k]

Just one more little thing then I am off to bed . . .

On another thread someone pointed out that using titanium is so much more efficient than say PEX than you could get by with just 12" in lieu of the 1000 feet or so of PEX as a transfer medium in your sump. (Numbers are from my memory so forgive if I am off) Well taint so Jethro, in reality the water becomes the tough cookie to transfer heat to/from. So even though the thermal conductivity of ti is 1000 times greater than PEX (+-), in no way can you get by with 1/1000 the length of ti vs PEX.

That is a very poor sentence as far as clarity I fear but it gets the idea across I hope.

 

[Gudwyn]

I've been working some math, and it seems like maybe pipe length is the key factor not area or pipe diameter. Well at least if we are willing to do total swags.

dQ/dt = k * A * dT/dx (dQ/dt = heat over time, k is coefficient of conductivity, A is area, dT is temp gradiant across distance dx)

PEX k = 0.4W/mC
Soil k varies from 0.2W/mC to 1.1 W/mC

In my case, I'm going to assume 80F water thru 62F ground (10C delta). But the ground next to the pipe is going to warm up, reducing the temp gradient. But how far out does the warming go?

Thinking about it, I can ignore this by simply defining dx as far enough away to get 10C dT. In the case of a pipe, you can assume the pipe is the center of a cylinder of earth. So that cylinder of earth has surface area of length * (dx * 2 *pi).

dQ/dt = k * l * 2 * pi * dT

So for a 10C dT, I'm calculating anywhere from 12W/m to 60W/m of heat transfer. Picking a value that maches PEX conductivity gives me about 25W/m.

My tank maintains temp pretty well with all lights off. I have 3*250W halides and 2*110W VHO. So, I need about 1kW of heat transfer. So, I'm guessing 40m (~150') of PEX.

Really ground temp here is 55F and tank is 80F, so that's 14C dT and the ground is moist year round. So... I figure I'll buy 200' of PEX and that should do it. We'll see...

I'm not a geothermal engineer, not even close. So don't trust anything I say. Haven't even built my loop yet. I'm just sick of running a chiller every day of the year. If it only runs on days that I wish I had AC in the house, that will be a victory.

Yeah, I know more fans, less power, open hood, streams not closed loops, etc. but the looks and noise and closed doors on the cherry canopy are not negotiable with the local "decider"

My streams are out in the garage in a bucket, they didn't make the cut. And neither did the 70cfm orion fans, now it's strictly ultra-quiet 30cfm PC fans. Same with the iwaki pumps, now its dual massive sequence pumps - big, power hungry, heaters in the sealed cabinet, but quiet and invisible.

 

[douggiestyle]

sorry everybody i need to continue.....

the fesibility behind marks idea rides on the fact that he is increasing the amount of water needed to be heated by the lamps. i have no idea what the transfer of heat from the lamps to the tank would be so i will make something up say as in gudwyn case you have 3 250 wat lamps. ill go with 500 watts being tranfered to the tank (as in a 500w heater). 500 watts will heat a 10g tank pretty quickly. by effectivly increasing the the size of the tank to 310g, well 500 watts is not going to do much in comparrison to the 10g tank when only on for 12 hours. then as bean mentioned the 300g will recharge itself by releasing the heat and returning back into a sink. marks idea is wonderfull if digging a 200' long trench is not an option. and similar to pumping pond water through the system for cooling. most importantly though would be the ammount of lighting on the tank and tank size.

would love to come up with a basic rule of thumb for geo cooling systems. we have tables for the area one lives in. the only other variables needed would be tank size, and the temp swing. did i say that correctly?

 

[salty joe]

Say I had a 500 gal. system, the water temp. was 85 F. Without cooling, the system was stable at 85 F. A closed loop geo-cooler provides nonstop 60 F water. Let's say I used 50 ft. of coiled 5/8 in. regular old polyethylene tubing as the heat exchanger in a high flow area of the tank or sump. (about 35 gal./min.) There is 5 gal./min. of 60 F water flowing through the heat exchanger.

Can anyone give an educated guess at what the final temp. of the 500 gal. system would be?

Joe