I just got blasted for putting this on alt.hvac (apparently they don't help
do-it-yourselfers) so I hope to heck that I don't irritate anybody on this
I am not an HVAC guy, just a home owner with a question, I believe this
is the place to find an answer. I live in Memphis TN, pretty dang hot in
the summer, pretty mild in the winter. I have an in-ground pool, it is
roughly 26,000 gallons. I also have a garden variety AC, it is a 2.5 ton
unit. My question is this, could I use a water cooled heat exchanger as
opposed to the standard over-head fan air-cooled condenser? The water would
be chlorinated pool water. It seems to me that I could kill two birds with
one stone here. I mean the A/C and the pool pump are going to be running
anyway, why not give it a try? I know that the temp gain from a 2.5 ton
unit won't be that much, maybe a few degrees per day, but what the heck, I
am just wasting the heat now (as if summer air needs to be any hotter).
Also, on the hottest of days the pool gets up to 90 degrees all by itself, I
figure on those days I can just run municipal water through the heat
exchanger and discharge it on my lawn, water here is CHEAP, so that is no
concern and it would not be that often. Also on those hottest of days I
would think that even 90 degree water would condense Freon better than 100
degree air, perhaps making life a little bit easier on my compressor. I
think that the real advantage would come early and late in the pools season,
that's when the water is a bit chilly for a swim but the ambient temp is
just high enough that the A/C is running. Any input from the ng here would
be great. And, I know that I cannot use an aluminum exchanger, the chlorine
would eat it up (chlorine levels in a properly maintained pool are about
1.5ppm, however, when you shock the pool once a week it jumps to about 5ppm
for a while), I'm thinking copper or plastic (if such a thing exists).
I don't believe the pool is a large enough heat sink to help much. I
doubt if the chlorine would get along with the equipment well at all and you
better have a very large dry lawn for the lawn watering thing.
If you want to do it, I think you are going to need to do it right and
use one of the established systems using a much larger heat storage tool,
like ground water or the ground itself. These would need to be carefully
sized to meet your needs and you would need to have available good ground
water or the right size and quality of soil conditions. Also I don't know
how well this would work out in your area.
about the only metal that clorine will not eat up is Stainless....i dont
think you gonna help the a/c in the long run...the clorine will eat up
just about everything, maybe not plastic, but then the heat of the a/c
condenser coil will be hard on the plastic... why not just pray for
rain when its hot and this will keep the head pressure down some...
it always helps with a good rain on our house when in july or august and
its 98 Deg. outside and the rain cools the house off....
The real question here is what's the actual benefit. You're basicly
substituting a fan and air with a pump and water for cooling. While
water is a much better coolant, it's still not clear to me that there
will be a significant overall operational savings. A good place to
start would be to measure the power used by the current fan motor and
compare that to the power used by a pump. If they are similar, which
is what I would think, then the only potential gain is if the water
system reduced the temp of the refrigerant leaving the condesnser more
than the air system. There likely would be times when in fact, the
pool water would be warmer than outside air too.
Even worse, the cost of the modifications will likely not be
insignificant. Plus, you're left with problems like, if the pool is
drained or shut down for some reason, so is the air, warranties being
The idea of heating the pool with the waste heat has some pluses.
However you get the most heat when you need it least. At the start of
the season and the end, when you need it most, the air will not be
If you want to look further, I would look at marine air systems. All
of them use sea water for the heat exchanger, so possibly the
condenser from a large unit could be used. However, the price of one
of those is many times the cost of your whole system.
From the university physics course level the idea looks good, but as
a practial matter it may not.
In general - it takes about 10 times more energy to cool your house
10 degrees in summer as it takes to heat it 10 degrees in winter. That
10 degrees is measured from the inside of the heat exchanger, which
could be running as high as maybe 110 degrees. Pool water is not
only cooler than the air, but also a better heat exchanger. So you are
starting from a lower tempurture - if you start from 90 degrees it only
takes half the electric bill to get you down to 70. Can you really swim
in 90 degree water?
You would save even more by running the pool water through the house
in a "forced hot water" heating system during early summer and maybe
during hot spells in the fall. Those FHW systems are popular in the northeast,
I don't know about the south. You should be able to pump the water around
with almost zero electrical bill.
If you pump the return water through an outdoor fountain of some sort the
water will be cooled by "evaporative air conditioning". When I grew up
in the desert all we had were evaporative air conditioners. They work real
well when the humidity is low. In this way the only time you might need to
turn on that refridgerator based device would be on the days that the nightime
tempurature is high, and the humidity is high, namely the hot spells of the
This would work fine, obviously the pool water would need to be kept
contained in a chlorine-friendly environment like the plastic pipes you use
for pools. The challenge is the heat exchange from the pool water to the
A/C unit which could be done with coils of plastic pipe but it would mean
redesigning your A/C unit to flow the air across them.
The other problem in your climate, of course, is now the heat from the house
ends up in the pool and your pool is too warm (hot). Not as big a problem
up here in the north where we actually have to heat our pools sometimes in
Actually here in Arizona those were very common 15-20 years ago. I actually
worked with a guy that had two in his house. Unfortunately he had to replace
the heat exchangers every couple of years. The last exchangers he bought
were from something that you would use on a boat in the ocean. They lasted
less than 3 years. He finally got pissed and changed over to the common air
He was pretty happy about the system, it warmed the pool in the winter. He
said he gained something like 3 months a year more swimming. Summer time
he had to run the aerator all night long because the pool was very warm.
If you can find an exchanger that can resist the chlorine, or convert your
pool to one of those natural bio pools where there are plants and fish in
the water that you swim in, I.E. no chlorine maybe you would have a chance.
If I had a source of water that was un-chlorinated I would consider this,
other wise, I really do not like working on mechanical systems about the
I saw something similar done commercially in the San Fernando Valley.
Very low humidity. They had large decorative ponds with fountains that
served as the heat exchanger. The water started to get too hot so they
raised the nozzles of the fountains about four feet.
Rheam Air Conditioners used to have a condenser with copper coils and
they sprayed water on the coils. That was only really effective in dry
climates. They recirculated the water like an evaporative cooler but
drained off a little to dispense some of the old water.
I am afraid your humidity is too high. In the dry climates it is
necessary to heat the pools because they cool so much due to
evaporation. If you had a dry climate you could improve the efficiency
by putting an evaporative cooler in front of the condenser.
These are made commercially and I know people who have them.
The principle is sound, but practically there are problems: 1. Corrosion of
the heat exchanger. 2. The hottest times of the year, your pool water is
also too warm alreadry (at least here in S Florida).
I've also seen them using pond water. Less corrosion then, but still a
Actually.."they" dont. Alt.hvac isnt for homeowners, thus, why some of us in
there, post here....and while I didnt blast you, notice, I didnt reply to
you either in there..
What you are looking for, is a licenced Water Furnace dealer.
I am about to sign on as one, and we are installing several for homes with
indoor pools. They work fine, and will hold up...chlorine isnt an issue as
long as the levels are kept correct and you service the unit as its designed
They are NOT cheap, and you can not take the unit you have now and convert
it over to work in the pool. It aint that easy...if it was, I would just
take what I sell and do it.
No Richard..I am quite aware of that...however, the coils are designed with
the periodic need in mind.
It does help, of course, when you simply maintain what you have...and of
course...an indoor pool, will not be as bad as an outdoor pool as far as
All the years I had one...I can remember two times the "shock" treatment was
needed...and that was due to my own neglect..
I too own a pool and have been considering an approach to this idea for
some time now.
The best temperatures my pool reaches are 75-78 degrees in the hottest
part of the summer. To me, this is ok, but often too chilly, especially
for night swims, which I love. I would not have a problem with the
water being to warm, even if, it is all to easy make a pool cooler.
I've perused groups like this one for several months, and it is clear
that everyone is ready to tell you how expensive it *has* to be and how
it won't work. I've seen no commercial off-the-shelf units that are
specialized for this purpose.
If you wish to implement something, I think you will have to invent it
an install it on your own.
Here are some of my thoughts on design:
Ideally this is accomplished with minimal or absolutely no material
changes to your existing air conditioning unit.
I would not, as others have suggested, abondon the air-cooling portion
of the condenser radiator. I would never want to rely on the pool water
to be the only way to cool the AC refridgerant in the first place. This
would be begging and pleading for trouble.
In a perfect world, a radiator or big block of metal like copper or
aluminium would be used. Inside this would be two plumbing networks.
One with Freon/Puron and the other with H20. This would be the most
efficient method I could imagine for heat transfer. A few potential
problems though... Coolant temperature can be hot! - over the boiling
point of water. So this system would need to have water flowing through
so quickly that it never boils, lack enough efficiency so it never
boils, or permits this to happen by being open ended, or with pressure
This is complicated by the fact that it needs NOT to be the only way to
cool the refridgerant. Keep in mind, unless you are a blasted engineer
doing a lot of careful professional design here, you're playing with
fire. That kind of heat exchanger, considering the pressures involved,
just isn't feasible anyway. It would be nice to have this
liquid-to-liquid system in line before the liquid-to-air network. This
way you get first dibs at the heat, but if the system is empty of water,
it proceeds on as usual and the system works (although with a hot chunk
of metal sitting there).
That idea sounds good on paper. It is efficient, and barring some
smaller details (I don't want to write a whole book here) it seems like
it could work.
We need something simpler and cheaper.
I've long mourned the loss of the idea of a liquid-to-liquid heat
transfer system because of its efficiency. I have pondered the idea of
running a copper water pipe alongside and within the insulation of the
refridgerant pipe leading into the evaporator. It would take a big run
to make much difference and even at that, I couldn't imagine efficiency
being very good.
A simpler, cheaper and not very efficient design would be to place a
standard radiator above the fan of an existing AC unit. I would think
12-18 inches would be as close as you would want to get. You don't want
to impede the air flow at all because that fan and that air has an
important job to do. Since this is hot air, it heats our water and we
are making some use of the byproduct of the AC unit. It doesn't help
the efficiency of the unit.
We don't have to care too much that it isn't very efficient because it
is cheap, and at least it is something. This radiator could be as
simple as one out of an old car. Yes it is aluminum and yes chlorine
will react with it (gasp!) but you can find these thing for cheap to
nothing in price and exchange them out.
This introduces another problem. I would never want to pipe my pool
water out and over and around some place under my yard, and so forth.
I've lost the pool once or twice due to plumbing defects and the last
thing I want is to introduce a high probability of this happening again.
Therefore, instead of this design
heat <-----------> pool water
I would consider one my like they use at modern nuclear power plants to
protect their coolant water
heat <--------> coolant water <-----------> pool water
In this design, I would have to add another heat exchanging device. The
water would be clean (non acidic) and would circulate through the
radiator and get warm. I would have to install a radiator and either
immerse it into the pool water itelf (safest, no leaking option) or
contrive a liquid-to-liquid thermal transfer system (like referenced
above) and pump both water sources through it. Now my circulating water
system would be only 20-50 gallons at most and if it fails, I don't lose
$100 of pool water (plus chemicals). Again, adding another piece here
means less efficiency, however without doing it, I have no idea how
much. Consider also, that your pipes had better be well insulated. In
my case, it would be about a 100 foot run of pipe. Considering flow
rates would be pretty low, I've got to take insulation seriously in
order to realize any heat at the pool. If I am not mistaken, chlorine
bothers PVC as well as most other plumbing options (it is acid, after
all), but it holds up for a pretty long time. You'd better blow them
out for the winter.
So there are a few things to consider and seeing as how it can get
complicated, I think this is why nobody has any first hand knowledge of
it and nobody is selling anything to do it. Depending on your style
and what you used, I think you could set up a basic system pretty
cheaply. (At minimum a radiator, a few sticks of PVC and use the pool
pump's pressure and then upgrade from there if it works)
I'd love to hear others' thoughts on the topic.
Off the Shelf??? As in DIY?
You wont..since the makers of the units wont sell to non licenced persons,
or persons that are not registered as a legit biz due to the liability
If you cant find them, you have not been looking hard, since they are very
And as far as expense goes...they are more expensive than an air cooled
Arizona Public Service used to sell a thing called "Hot Tap" "Get hot water
from cold air" A huge ad campaign followed the interduction of these heat
exchangers. APS pulled them off the market in less than 6 months. Water was
leaking into the a/c compressors and the would fail. This exchanger was
copper to copper using city water.
Copper and pool water will not last very long. Do some googling before you
destroy your a/c compressor.
Or change your pool over to an natural pool with out chlorine. Fish and
plants in the water usually on one end or in a cove built for them.
Good luck and keep us posted on your project. It would be cool for the
little guy to win for a change.
The Freon in the return line to the compressor must be the hottest
part of the whole system. Perhaps introduce a bypass radiator here
to dump the heat. This radiator can be the automotive oil cooler
radiator that can tolerate high pressure fluids. The Freon return
line heat is transferred into an intercoolant tank of automotive
antifreeze mix; antifreeze because it has anti-rust properties, has a
higher boiling temperature (?) and the tank can be capped to reduce
evaporation. This allows a "cooler" Freon return to the compressor
and therefore decreases the load on the a/c. Even if the intercoolant
tank breaks down the normal heat dump mechanism of the a/c is not
The pool water is circulated through a car engine radiator and picks
up the heat from the intercooler. If in time the pool's chlorine
wreaks the car radiator just replace it with another one from the pick
a part junkyard.
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