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Unfortunately our new outdoor AC unit – a usual with a fan and aluminium heat exchanger – does not contain plugs to a water heat exchanger.

That's a pity as the waste heat in summer could be used to heat a pool or perhaps water for showering too.

I found online some commercial setups that plug between the compressor? and heat exchanger, but 1) the AC unit probably does not have easy access to this pipe and 2) the total cost is way too steep (around 10x the pvc pool cost).

I calculated that for a 20 tonne pool a modest AC usage could heat it up around 3° Celsius every day.

The solution must not involve modifying the coolant line as the cost would be too high.

So pretty much that results in spraying or pouring water in the unit on the aluminium blades. Probably not the chlorinated pool water but a normal water that would form some kind of primary circuit which would interface in a heat exchanger with the pool water.

But I have two questions.

How much water the AC unit can safely tolerate. (It should perfectly withstand heavy rains, right?)

Will the water heat up, or rather just evaporate? (Thus not actually heating up the water.) That probably depends on the amount of water sprayed/poured on the system.

  • AFIK the cold condensate water from inside of the house is conducted to the back of the unit and used to remove heat from the condenser coils. Either the first coil is immersed in this condensate or the tips of the fan blades sling it over the coils. Any other use of water to cool the coil would have to go through a deionizer before being sprayed on the coil (to prevent buildup and corrosion). – Jim Stewart Aug 11 at 12:24
  • @JimStewart So I could use distilled water or filtered rainwater, if there's such a danger. But I'm afraid that the condensate from inside does not go to the outside unit but rather to drainage in our AC setup. At the end, it shouldn't be hard to horizontally mount a small tube with small holes that would pour water at the top of the aluminium heatsink. The water would then flow along the blades to the bottom casing that already has holes for the condensate when the unit is in heating mode. – Adam Aug 11 at 14:27
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    Would it not be simpler to just direct pumped pool water to and through a finned-tube exchanger mounted above the condenser unit? – Jimmy Fix-it Aug 11 at 16:28
  • My mistake! I was thinking of a window unit. I now understand that you have a central "split" unit. There are advertised products employing deionized water spray to help cool the air going over the condenser coils. Since the a/c manufacturers don't offer these as an option I have concluded that they are more trouble than they are worth. – Jim Stewart Aug 11 at 16:59
  • @JimmyFix-it so that's another option. So I need to decide w.r.t. its availability/price in my country and the actual heat transfer efficiency. There are some water/ pool water heat exchangers (smallest around $80). I don't know how the evaporation heat loss in the 1st option would compare to seemingly (to me) imperfect air-to-water exchanger. First, I should probably just try to spray distilled water (try different flow rates) on the AC unit's fins and measure the exchange power. As it requires the least investment to try it. – Adam Aug 11 at 18:02
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You do not want to run water over your coils, this will cause any hard water deposits to build up quickly and even if the aluminum fins are coated to protect from salt air this layer will be destroyed in a short time by flowing water over the coils. I agree with @jimmy fix-it , a separate system would be better. I have several rolls of black drip irrigation tube on the roof of my arena , any roof would work, we had to shut it off for a few days already because when the water temps get into the 80’s it’s not refreshing at. Don’t cut the service life of your expensive condenser & compressor unit short.

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A simple solution to your idea is not possible since you can't just pour water over the condensing unit coils or hot piping then collect the heated water. As @Ed Beal and @ Jimmy Fix-it have said each idea has it's draw backs and losses with probably no heat gains for the pool water. It is a good idea but there is nothing to be gained. The only solution would be a heat exchanger mounted in the compressors hot gas discharge line and those devices are expensive.

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