Can I make a chiller using cold outdoor weather instead of electricity?

Discussion in 'Tank Talk' started by rryyddeerr, Aug 5, 2010.

  1. rryyddeerr

    rryyddeerr Vampyroteuthis Registered

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    ive been thinking of ways to regulate the temperature of a large amount of water. when i finally build something in the next five years or so, when i move into a purchased house, i plan to dig a trench leading away from the basement on the outside of the wall about 6-8' deep. through the wall will be an inlet and an outlet for 4"pvc. outside the wall, in the trench i plan to run a circuit of pvc, the ends of which will attach to the inlet/outlets in the wall. the idea will be to pump water out of the house, through the pvc, which will be buried and cool, and back into the house/aquarium system. depending on the locale, it could serve as a very effective cooling measure for whatever size system you have.
    id love to have a really big cold water octo tank someday. but i cant imagine its cheap to keep a tank chilled in the summer.
     
  2. DWhatley

    DWhatley Cthulhu Staff Member Moderator

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    I wish there was more commercial work with this idea for homes. We met one couple trying to do it for heating and AC here in Gainesville and they were having all kinds of permit problems. We are doing without AC this summer and are blowing the cooler air up from the basement. The unfinished part (only partially underground) stays at least 10 degrees cooler than the rest of the house. Unfortunately, this is also true in the winter so piping would need to be deeper to serve both functions.
     
  3. Joe-Ceph

    Joe-Ceph Haliphron Atlanticus Supporter

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    First the good news:
    If you do it carefully, it's not very expensive. By "do it carefully" I mean study how heat works (convection, conduction, radiation, insulation, etc) and do everything you can to keep heat out of your cold system:
    1) Add the least amount of heat possible
    . Use external (air cooled (Iwaki)) pumps instead of submersible pumps.
    . Use a single pump instead of several
    . use low powered lights that don't radiate a lot of heat and/or cover the tank with
    . glass, which reflects radiant heat
    . Don't let the warm lighting unit rest on the tank top, and conduct heat into the top.
    2) keep the heat of the room out of your system:
    . Insulate the bottom, back, and maybe one or two sides with styrofoam insulation (1"-2" thick)
    . Add a 2nd pane of glass to the uninsulated sides of the tank, w/ 1/4" airspace in between.
    . Keep plumbing short, and covered with pipe insulation.

    Not to dash your dreams against the rocks or anything, but ...
    That won't work. After a day or two the warm water will simply warm up the dirt around the pipes. Even if there were snow on the ground, the dirt would just take a few more days to warm up. The dirt will act as an insulator. It would knock your temp down a couple of degrees, but that's about it. Once the heat goes into the dirt, most of it has no other place to go, except to slowly seep into the air. I know, the water coming out of your faucet gets cool if you let the faucet run for a while, because the pipes are buried in the cool ground. True, but that's because the water is holding still in the pipe 99% of the time. Your tank will supply a never ending moving stream of warm water, and the ground can't absorb a continuous flow of heat. The dirt will "fill up" with heat after a few days.
     
  4. DWhatley

    DWhatley Cthulhu Staff Member Moderator

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    Joe-Ceph,
    Could you put passive "exhaust" piping to the surface to facilitate removing the heat (something on the order of the gas release pipes on the roof)? I have never played with any of this but, given our temperture differences in the house, have been interested in how cooling using underground piping might work.
     
  5. rryyddeerr

    rryyddeerr Vampyroteuthis Registered

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    aahhhrrgg. JOE, your killing me.
     
  6. DWhatley

    DWhatley Cthulhu Staff Member Moderator

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    Not ME, Joe-Ceph is the kill joy here, I am only a curious observer. (just D, not Di, not Dee - it comes from my initials - all D's - before taking on the Whatley surname :grin:)
     
  7. rryyddeerr

    rryyddeerr Vampyroteuthis Registered

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    geez i must have been tired. i saw your avatar on the post below it as i read and just attached your name. my bad.
     
  8. Joe-Ceph

    Joe-Ceph Haliphron Atlanticus Supporter

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    I'm just the messenger. Blame those pesky laws of physics; they mess up all the best ideas (solar powered cars, warp speed, time travel, Flubber, alchemy...)
    Better to find out now than to find out after you pay a contractor.

    Don't despair! Something similar might be practical. When the air outside is colder than you want your tank to be (at night? During the winter?) you could circulate tank water through a titanium radiator, or even just a network of pvc pipes that are exposed to the air. If they are out of the sun, and you use a thermostat to control a pump and/or a valve, you could have free chilling at least part of the time. In fact, if there is more "cold" outside than you can use, you could keep a large insulated reservoir of water that you allow to get extra cold at night, and then use it as needed during the day to keep the tank temp down. You would need to build a smart controller and use thermostats to turn valves and/or pumps on and off as needed, but it's totally doable for people who live where it gets cold sometimes (just don't let the water freeze in the pipes).
     
  9. rryyddeerr

    rryyddeerr Vampyroteuthis Registered

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    yeah, the water would freeze in the pipes. back to my drawing board. lucky for me, im several years off from trying to get this going.
    and holy lol: a titanium radiator! thats hysterical. id have to have this thing running for 350 years to pay back what that would cost.
     
  10. rryyddeerr

    rryyddeerr Vampyroteuthis Registered

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    how about a normal radiator coated with epoxy resin?! i mean on the inside!
     
  11. Joe-Ceph

    Joe-Ceph Haliphron Atlanticus Supporter

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    Can I make a chiller using cold outdoor weather instead of electricity?

    If you live where it gets cold enough to freeze, you can't just run tank water through pipes outside, but this idea should work. You can get a length of titanium tubing on ebay for a reasonable price ($50 ?) and bend it into a spiral. If you ran tank water through this spiral, and the spiral were immersed in a cold liquid, then the tank water would cool (this is called a "heat exchanger"). You can use antifreeze for the cold liquid (motor home antifreeze is non-toxic) and run it through a conventional steel or aluminum car radiator (or just metal pipes), outside, to cool it off. During winter you could easily maintain a reservoir of very cold, but still liquid, antifreeze, and pump it, as needed, into the heat exchanger. You would need a couple of temp sensors, pumps, electro-mechanical valve actuators, and a controller smart enough to run them, but it would totally work, and use little electricity. If the nights during the summer are colder than you want your tank, it would work then too. It may not be worth the hassle, but if you really want a large tank, and running conventional chillers would be out of the question expensive, then it might be worth the hassle.
     
  12. Joe-Ceph

    Joe-Ceph Haliphron Atlanticus Supporter

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    I've thought about that, and it might work. Chiller manufacturers tried it 15 years or so ago, but I don't think it worked out well because they don't do it any more. If the "paint" gets a crack, you'll end up with rust in the water, not good.
     
  13. Joe-Ceph

    Joe-Ceph Haliphron Atlanticus Supporter

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    That would only help a little. The air at the surface of the water would be warmed, and the exhaust pipe would be warmed. The air inside the pipe is mostly stagnant, and would tend to just sit there (like the warm dirt), but the air around the outside of the exhaust pipe would also warm, and it would blow away, and be replaced by cooler air, repeatedly, so heat would flow out of the water that way, but that's like a pin hole leak, and the pumps and lights are adding much more heat per minute than can leak out that way, so we've only made a tiny dent. If there were dozens of "exhaust pipes" and they were made out a really good conductor, like titanium, then it would totally work, but a couple of PVC ones - not so much.

    We need to move the heat form the water to another cooler object, through physical contact (heat moving by "conduction"). So the warm water needs to heat pipes or a radiator. Then the newly warmed object needs to heat the air around it (also conduction). Then that newly warmed air needs to blow away, and be replaced by more cool air (that's heat moving by "convection"). A good conductor (like metal) moves heat quickly, while a bad conductor (like trapped air (like in the fibers of a blanket or the bubbles in styrofoam)) moves heat very slowly, and is called an insulator.

    With clever placement of good conductors and good insulators, we can "conduct" heat from our tank water into cool outside air, and let that warm air blow away (convection). The air trapped between the particles in dirt make dirt a reasonably good insulator. Even after heat eventually does conduct into the dirt, there's no way to move the warm dirt away and replace it with new cool dirt (no convection).
     
  14. DWhatley

    DWhatley Cthulhu Staff Member Moderator

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    So, if most of the underground pipe was suspended in a tunnel (like a sewer pipe) with a fan to move the heat out (the tunnel being completely outside the house so that a small part of it was underground or exposed), would that move enough air to keep the surrounding dirt cool or would the tunnel be useless (except for keeping the sun off) and produce no more cooling than the water pipe suspended above ground since the air blowing through the tunnel would be at ambient (or slightly more from the fan itself) and still heat the dirt? If the area was damp, you would get evaporative heat removal but I don't think you would be allowed to utilze the sewer piping :grin: (although I keep thinking we should be piggy backing such pipe work for electricity and other cableing).
     
  15. snowmaker

    snowmaker Vampyroteuthis Registered

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    I believe that if a trench was dug - you said 6' - 8' deep, a coil or whatever is buried in there, the heat you are removing will "sink" off into the ground which will be around 50 - 55 degrees.
    True, you may warm up the earth very near your coil, but that heat will dissipate - or "sink" out into the earth. There are geothermal projects up here that work w/ out 300' drilled wells.

    I think your idea will work Noah, but would get a thermal engineer to determine how much of a coil you'd need to shed however many BTU's produced.

    Your "little" coil, may warm the immediate earth surrounding it, but the rest of the planet will draw that heat out no problem.
    I would consider fanning out 200' of pex or similar tubing in a deep trench, have valving just inside basement.
    Additionally, you may only need cooling during the days. A solenoid valve on a thermostat / thermocouple will close cooling valve as your tank cools off and this would give additional time for the geothermal heatsink to recover.
    I think it's a great idea!
     
  16. Thales

    Thales Colossal Squid Staff Member Moderator

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    I know some people have done/tried similar. I haven't been able to dig up a link though. Sorry!
     
  17. rryyddeerr

    rryyddeerr Vampyroteuthis Registered

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    my assumption was that it would, to a great degree, depend on the composition of the soil, or whatever material contained the coil. my thought was to suspend the coil in the hole, like you might rebar in a footing, keeping as much space between the coils as you could within the allowed space and then pour concrete over it to protect it.
     
  18. snowmaker

    snowmaker Vampyroteuthis Registered

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    My guess - but the concrete (thermal mass) may not dissipate heat as well as plain old earth. I thing it will hold heat - like when you heat a concrete slab or 2nd story floor.
    I was thinking:
    4' x 20'? trench maybe 6' deep. Spread out a coil of plastic well pipe. cover with hard board insulation (insulate from above, not below) and bury it.
     
  19. CaptFish

    CaptFish Colossal Squid Staff Member Moderator

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    I don't think you want the hard board insulation, it may hold the heat in. I would cover it with good old grass.
     
  20. Joe-Ceph

    Joe-Ceph Haliphron Atlanticus Supporter

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    I found a table that shows the thermal conductivity of various materials. Concrete actually conducts heat a little bit better than "earth, dry", but it's hard to say whether either one is a really bad conductor of heat, or a really bad insulator. The truth is, without knowing the equations and running the numbers (like a real engineer could) I can't say how well such a system would work (despite the fact that I already said "it won't work"). Heat will leak through the PVC, and into the earth at some rate, call it RL (loss). Your tank will produce heat at another rate, call it RG (gain). After the dirt warms up to a stable temperature, if RL is > RG, then it will work great. RL increases as the length of the buried pipe increases, so if you buried enough pipe, it certainly would work (assuming the sun doesn't keep the dirt warmer than your tank water). I'm guessing that you would need to bury so much pipe that it wouldn't be practical, but again, I'm guessing. Maybe I'll look up the equations and do this right some time, just to make sure I'm not giving bad advice.

    Or you could forget the math and just try it. An easy way would be to tap into an existing sprinkler system (long network of buried pipes) and pump water from a tank with a heater in it (constantly running) through the pipes. Eventually the temp will stabilize, and you'll know how much heat that system can continuously dissipate.
     

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