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Re: DIY Cooling Systems



>I live in western PA, and so have relatively low ground temperature year
>round.   A pipe (say, 1.5 inch diameter, for example, with an end-cap, could
>be pushed into the bored hole.  Length of the bore might be something like
>10 to 15 ft. A smaller diameter tube would then be inserted into the larger
>pipe, stopping just short of the end (maybe an end piece on the tube would
>provide for a defined gap at the end of the tube to the pipe plug).  A
>temperature controller (or thermostatically controlled) pump could pump
>water into a the tube to the end of the pipe, with the return path being the

I'm in a rather unique position to comment on this since I've actually
tried it (although to cool a room, not a tank). I used my well to pump
water up from about 180' down and was running the water through a radiator
which had a fan blowing through it. The water from the well was in the
45-54F range, and there was some pretty good cooling power. For any
long-term setup with a well, I'd use a linear coil made of copper pipe with
maybe 100-200 feet of piping. This would then be lowered into the water
column in the well, and a supply and return line (polyethelene pipe) would
run from the surface to the coil. Running as a closed system like this is
*much* more efficient since it lets you use a little circulation pump
rather than a big 1.5+ HP well pump.

>The plumbing could use PVC components, which would be inert relative to the
>aquarium water chemistry.

Use polyethelene pipe for the runs outside since it will be MUCH cheaper,
easier to work with (poly pipe is flexible and uses clamp-on fittings), and
it is UV resistant. For the most efficient heat exchange, use copper piping
for the heat exchanger in the well/ground, and another heat exchanged in
your tank (stainless steel maybe?). That way you have a closed system and
you can use additives in the circulating water to prevent freezing,
corrosion, and other forms of nastiness.

>The ground boring may be tricky, but is also a matter of using some
>ingenuity.  For a 1.5 inch pipe system, the hole should not be that
>difficult.  Could be done by hand with a home-made tool of some sort (maybe
>a cutting blade fixed to a long strip of wood), and a good shop-vac.  And
>then boring patiently.  getting through the basement wall is also a job, but
>is possible.

Actually, the commercial geothermal heat pump systems use a trench and a
big loop of polyethelene pipe as the heat exchanger in the ground. As I
recall, the pipe is only put down maybe 2' or so here -- which is
significantly higher than the frost line which is in the 4-5' range. You
can rent trenchers that dig up to a 3' or so trench at lots of tool rental
places. If you want to bore a vertical hole, I suggest you talk to a
commercial well driller and have them sink a well for you. You'll want to
get down to an aquafer since you will want the well to be full of water so
that you have a transfer medium for the heat between the walls of the well
and your heat exchanger coil. You might also want to have them sink a steel
casing rather than a PVC casing since it will transfer the heat better.
Typical well casings are 4" diameter.

To drill through your basement wall, use a hammer drill with a coring bit
for a hole that size (for masonry), or a hole saw (for wood). The hammer
drill will make the job MUCH easier in anything resembling rock...

>The pumping should not be that difficult, as the sizes of the tube and pipe
>would be fairly healthy.  Slow flow through the system will actually help
>the performance anyway.

Any of the mag-drive or centrifugal aquarium pumps will work fine as a
circulation pump in this application.

>I have not actually made this, and have not really calculated cooling
>efficiency (can be done) or pumping needs.  I believe that a year-round
>ground temperature of 45 to 60 F at 6 to 8 ft. can be assumed where I live
>(also need to check that).

Once you reach your frost depth, you have relativly constant temperature.
Your local water and sewer department will know this as will your building
department, since both water lines and foundations have to go down to the
frost line.

The cooling calculations can be taken from any book that deals with liquid
heat exchange. I would look into a mechanical engineering textbook dealing
with fluid systems, specifically commercial liquid chiller systems. Almost
all large commercial buildings use some form of hot water heat and chilled
water cooling so this is a well-defined science.

>Any thoughts?  Anybody ever seen such a scheme?  (There are home
>heating/cooling systems based on the same idea, though with much larger
>dimensions and heat capacities, and using more traditional heat exchange
>fluids and heat pumps).

Around here the local electic company (http://www.detroitedison.com)
installs geothermal heat pump systems to heat and cool houses using the
basic idea you're talking about here. There is some info on their site
about how they install their systems that you might want to look at to get
an idea of how you might want to build your own ground heat exchanger.

I think the easiest way for you to expieriment with a system like this is
to do the following:

Dig a trench maybe 20-30' long and 2-3' deep. Bury a loop of 1" or so
polyethlene pipe in there, and make sure the two "sides" of the loop are
seperated by a fair amount of earth so that the "hot" side doesn't heat up
the returning "cold" side from being too close. Inside, use a heat
exchanger, preferably of metal pipe (thin-walled plastic would be OK too)
in your tank. Circulate the water through the outdoor system and the pipe
in your tank heat exchanger. Do NOT circulate your tank water in the
outdoor system! Stuff might gradually find it's way into your outdoor
system that you don't want in your tank, and you are probably going to need
to use additives in the circulating water as I described earlier.

Even a small system like that can probably drop the temperature of your 180
gallon tank 10-20 degrees on a reasonable day. The ground is able to sink
an amazing amount of heat.

     -Bill

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Waveform Technology
UNIX Systems Administrator