Energy Efficiency

Published on September 15th, 2010 | by Susan Kraemer


Could A/C Units Vent Heat to a Swimming Pool? You Tell Me

September 15th, 2010 by  

Here’s an idea for harvesting waste energy in a naturally synergistic combination. Many people who have air conditioners have swimming pools. Both take energy: one to cool, one to warm. Could you make use of the waste heat that your air conditioner generates as a byproduct when it cools your home – to warm your pool?

By recovering the heat exhausted, wouldn’t you then get two outputs from one input of energy? Air conditioning and hot water, from one energy input. If you could, that would cut your A/C carbon footprint in half.

Instead of just venting your air conditioner, adding to the heat island effect, heat recovery units could be inserted between your air conditioner and your water heater could tap that waste heat to warm the pool using a closed loop heat exchange (to keep the pool water separate) heating water to warm your swimming pool for free.

Several companies are already using heat recovery to create hot water for inside the home, like  Zero Energy Water Heating Systems. Another, Heat Harvester claims that using their system, a house running a 5 ton air conditioner could generate up to 40 gallons of up to 140 F water an hour.

The savings seem considerable. A white paper on the likely energy savings from heat recovery units attached to A/C or refrigeration units  cautions that if the unit produces too much hot water, the excess capacity might get wasted, reducing energy savings, or conversely, that when you don’t need A/C, this heat recovery will recover no heat, making no free hot water. Well, oh dear. Better put that idea away.

But better to save that energy only during hot weather than never save it at all. And as for the worry about too much heat, here’s an idea. It takes a tremendous amount of hot water to heat the average swimming pool to a comfortable 83 degrees.

Venting the heated water into a much larger “holding tank” than your hot water heater – such as a swimming pool – should take care of that worry. Even on hot days you typically need warm water to take the chill off a swimming pool. I doubt that an average sized home running air conditioning could ever generate enough heat to overheat an entire swimming pool.

I know we have a lot of tech types reading here. I’d be interested to hear from someone who is engaged in swimming pool heating, on this question. So, could an air conditioner heat a swimming pool? You tell me.

Susan Kraemer@Twitter

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About the Author

writes at CleanTechnica, CSP-Today and Renewable Energy World.  She has also been published at Wind Energy Update, Solar Plaza, Earthtechling PV-Insider , and GreenProphet, Ecoseed, NRDC OnEarth, MatterNetwork, Celsius, EnergyNow, and Scientific American. As a former serial entrepreneur in product design, Susan brings an innovator's perspective on inventing a carbon-constrained civilization: If necessity is the mother of invention, solving climate change is the mother of all necessities! As a lover of history and sci-fi, she enjoys chronicling the strange future we are creating in these interesting times.    Follow Susan on Twitter @dotcommodity.

  • tc0nn

    Can you say “MARINE AIR CONDITIONER” ?

  • Louis

    Hello Susan, I am a product designer with a technology development and product manufacturer, company ( in Canada, with links into the US that presently make a system that “will” heat pool water while air conditioning the space/home. It will also switch modes and just heat the pool absorbing heat from surrounding outdoor air, plus it will just air condition when the pool is warm enough. the functionality is fantastic, while the efficiency is unparallelled and it just make sense. The efficiency doubles, when you are in air conditioning the house while heating your pool or any other hot water need, such as a restaurant that may have a high air conditioning need, while they simoultaneuosly need lots of air conditioning. There are many unique products our there that while offer environmentally friendly, while saving money and reducing energy at the grid and I am happy to commnet on just one with this type of format, thank you. Lou

  • Lee

    This company is already doing this. I’m thinking
    about doing both the domestic water heating and the pool heating.

  • milky1018

    I wouldn’t recommend it. It has nothing to do with a basic pool system.

  • seodipu

    Air conditioning saves lives and is a likely adaptation to global warming.
    Unfortunately, it will probably
    also fuel global warming, a new study finds.

    air conditionin
    air conditioner
    ac air conditioning

  • Ainsworth Paul50

    Ok here we go. I am an HVAC/R professional and have done this on several occasions. Most all residential AC condensing units air cooled in other words they use the ambient air to transfer warm air from inside the house to outside. The fan that sits near the top of the unit pulls outside air through the condensing coil,this changes high pressure refrigerant gas to high pressure liquid, which then flows to a control device and becomes a low pressure liquid and finally a low pressure vapor before returning to the compressor to start the refrigeration process all over again. Instead of using an air cooled condenser like what is normally found on residential units I have replaced it with a water cooled condenser sized to the existing unit. Just some modification to piping is required. I then use head pressure switch to regulate the water flow through the exchanger so my condensing pressure is not too low or too high. My existing pool pump has adequate flow and pressure so I do not need an additional pump. I have a 20,000 gallon pool that between the 6 tons of cooling that my systems are and the natural sun heating I have very comfortable 85 degree pool water almost all summer long. The only issue is that in some jurisdictions this is not acceptable practice because of the potential leak concerns between the refrigerant and the pool water. If the heat exchanger should develop a leak then refrigerant and refrigerant oil will mix with the pool water. No problems so far though. I estimate the SEER rating of almost 18 from an ordinary 12 SEER unit.

    • John

      Dear Paul,

      can you supply drawing and spare part lists?
      We would like to modify in the same way.

      Info (at) schulte (dot) co (dot) th

  • Suzy Going

    Hi, I just love your writings. Keep up with writing and we hope to read more from you soon.


  • Steven Wiencek

    I built such a system on Long Island 4 years ago and is still working great to this day. It was in response to LIPA’S Geothermal program. A long story why I was never rebated back the credits, but I think it had to to do with the system being arcane. Anyway to stay on topic, you are not venting (air transfer) heat, but rather rejecting heat to the pool via a water source heat pump.

    The pool is 20,000 gallons and the heat pump is 5 tons. The a/c is zoned and can “remove heat” from the house or the attic, dependent upon the call from the pool or the house. Another 2 zone decide whether the conditioned air is returned to the house or atmosphere. Pool temperature is “controlled” if you will by a small decorative cooling tower. AKA a fountain. The excess heat can be lost to atmosphere so the net back to the pool is zero.This eliminates the need for a water cooled condenser and a air cooled condenser in one unit, as this becomes prohibitively expensive. The initial reaction by engineers to this project said that the heat would become too high in the pool. That is true. Left unchecked , the pool would max out at about 100 degrees f. But a simple bit of automation and water spray take care of this. So to answer your question can a ac unit heat a pool, most certainly.

  • Seamus Dubh

    Honestly the largest hurdle is the integration of the thermal loops.
    The redundant and cross piping alone would drive most plumbers mad, let alone the design process and automation equipment of said system.
    I’m all for it myself.
    Thermal recovery, reuse and regeneration breakthroughs could solve not only issues with heating and cooling, but even ones with power generation.

    • Curtis

      I am a research engineer at UC Davis and have been studying the use of swimming pools as heat sinks for air conditioners for a couple years now. It is hard to control pool temperatures with these systems since cooling is demanded by the thermostat. The most significant pool heating will occur when the cooling demand in the house is largest and pool temperatures are the greatest (during the hottest periods of the year). So when pool temperatures are already high is when you would get the most benefit. More importantly, a system that rejects heat to a swimming pool instead of outside air can reduce air conditioning energy use by 20-40% and will work best in dry climates.

      • Let me know when you get somewhere with the research, it sounds terrific. Hope it leads to a product.

      • itsallgreentome

        what about instead of using the AC unit, you used the kitchen fridge? it’s always on, removes heat in May-Oct period from kitchen, etc. Maybe not a lot of heat, but some?

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  • MD

    You could if you had a industrial size AC unit, however its way cheaper and easier to get a bunch of coiled up U75 pipe, a 12VDC solar panel/pump setup and pump the pool water through the coils. The key is that big nuclear reactor up above us, you know, the sun.

  • Interesting article. Always great to learn better ways to reduce our carbon footprint and save money.

  • Pingback: Could A/C Units Vent Heat to a Swimming Pool? You Tell Me – CleanTechnica | Pool Cleaning & Services()

  • Adan

    One small issue at least compared to investments in other RE projects, projects intended to heat swimming pools are specifically excluded from the federal ITC (business and personal) and thus this project would not be eligible for a cash grant either. Interesting idea, but ceteris paribus there is better low-hanging fruit.

    • Yes that exclusion was dumb. Swimming pools take a tremendous amount of energy to heat. At one time I did estimates for solar water heaters, and found one 9 story apartment building used more than half of its gas from PG&E just to heat the fancy pool in front. A purely decorative apartment complex pool, the kind one ever swims in too! Complete waste of money and literally a carbon sink.

      Likely the pool exclusion was Dems fear that their opponent would whine about taxpayers paying to warm hot tubs in Marin, or Hollywood swimming pools.

      • Jimmy

        There is a company that makes a pool heater like this, it connects to an air conditioner and captures the waste heat, puts it in the pool. It’s called Hotspot Energy.

  • Don’t know where my previous comment went?

    Just another pointer for your research, there is a class of water heater called a ‘Heat Pump Water Heater’ that effectively does what you are talking about.

    These water heaters have a dedicated AC unit (air sourced heat pump) on top with the condenser coil in the tank.

    Because these don’t generate heat, the only move heat from one place (outside air) to another (the water tank) they use much less energy than a resistive element water heater.

    Think of it like a refrigerator in reverse.

    • Sorry, we have just taken the site through a big change. Lost some comments… they might be back

  • We successfully heat the small municipal swimming pool from the waste heat produced by the airconditioners on City Hall in Rossland BC. Not a huge project, but offsets some of the heating costs.

    • Sounds effective though! A municipal swimming pool can’t be that small!

  • Such a system would be a mild variation of a DX (Direct Exchange) ground sourced geothermal system.

    Ground sourced geo-thermal systems often use a large body of water such as a lake as the heat sink so there’s no reason why a swimming pool couldn’t be used in the same manner. It would certainly be cheaper to install than drilling into the ground.

    You can calculate how much energy is needed based on the formula 4.2 Kilojoules to heat 1 kg of water 1 degree C. As you can tell, you need ALOT of energy to heat a large pool.

    Ground source geothermal can reduce energy use for space heating and cooling by up to 70%. Unfortunately, such a system would be warming the pool during summer, and on reverse cycle, cooling the pool during winter, probably not the effect you’re going for.

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