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Community and Q&A

Using well water for air conditioning

Reid Baldwin | Posted in Mechanicals on

A random thought occurred to me while I was thinking about the Chiltrix system. For air conditioning, water at about 55 degrees would be circulated through the fan coils. That is about the temperature of the water coming out of my well all year. If the system was only used for air conditioning, could the well be the source of the cold water as opposed to running a compressor? I don’t see a problem with this idea, but I expect that if it was simple at least some people would be doing it. Am I missing a major flaw?

Since the system would be open loop, we would need to do something with the water after it ran through the fan coils. Lawn watering occurs at the correct time of year to use this flow, but not usually the correct time of day. Would I need a return well like an open loop GSHP?

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  1. charlie_sullivan | | #1

    Two flaws. One is that at 55, you will get only minimal dehumidification, and the other is that depleting the aquifer is not a good thing to do, so returning the water as with a gshp is the thing to do, making the setup more complex and expensive.

    I think a good approach is to use something along those lines on the incoming ventilation air, to remove the worst of the high humidity there. That is what the Zehnder ground loop add-on for their heat exchangers does. But that is an expensive system for what it does. Ultimate Air offers parts for that too, at lower cost, but not as a complete system so you need to do your own design and setup.

  2. GBA Editor
    Martin Holladay | | #2

    If your water is dependably cool as you report, the idea might work. But as Charlie said, the cost of the equipment (and the significant pumping energy) would probably result in a system that isn't cost-effective.

    Before compressors were available, Vermont dairy farmers cooled their milk cans in running water. You divert a spring located uphill from your barn to a concrete trough near your milking parlor. After each milking, you submerge the milk cans in the flowing spring water. The system worked.

  3. Well_well_well | | #3

    This thread is pretty old, but I just commissioned my well water-cooled air conditioner late in the summer of 2021 - and it works. From a modest flow rate of 2.5 gal/min, I can cool a 120 sq ft room from a stifling 96°F to a livable <80°F using a car radiator plummed into the well. I then send the discharge to to my fruit orchard, so it does double duty. When I put an electric motor-powered Baker Monitor Pump Jack on the well, my electricity bill didn't change an iota, but my water bill dropped by half or more.

    It's definitely a special arrangement that allows it to work so well, but it does work. It's kinda ugly as my wife reminds me, but so am I. We make a nice pair (my wife & I, that is).

    1. Expert Member
      MALCOLM TAYLOR | | #4

      I may have messed-up the math, but it seams like you are using 3600 gallons of water a day to cool one small room?

  4. Expert Member
    BILL WICHERS | | #5

    It's a little confusing when you talk about having a water bill and a well. Typically you'd have a well when you didn't have city water available, so you end up essentially with an electric bill only. Running your pump all the time WILL increase your electric bill.

    You can certainly get some 'free' cooling with a radiator and a supply of cold water, but it's only really cost effective if the water would be getting used anyway. If, for example, you're running this water to water your orcharge, and you have to do that regardless, then adding a radiator for some free cooling at the same time works -- the orchard might even be a little happier with slightly warmer water.

    If you would not otherwise be using this water, then what you have is similar to an open loop ground source heat pump, just without the heat pump part. These systems are not permitted in many areas since they can cause problems with water, and aren't efficient in their use of resources. You could potentially build a linear heat exchanger coil that you could lower down inside your water well to use the well as a ground source for a heat pump using a closed (recirculating) loop, which would be much more efficient, and could use a much smaller pump if you use it for passive cooling with your radiator.


  5. Expert Member
    NICK KEENAN | | #6

    If you are running AC, a heat pump water heater is kind of free because it cools and dehumidifies the home while heating the water, and saves the HVAC from having to do it. The question then becomes, is there any reason not to run a simple heat exchanger ahead of the heat pump? The water is coming in at 55F, the air might be 75F in cooling season, why not mix them together and get water at 75F and air at 55F in the output?

    I can't think of any theoretical reason why it wouldn't work. OK, so then why not run all of the water, not just the hot water supply, through a heat exchanger? Unless you're drinking it having your tap water at room temperature isn't an issue, and in humid climates it helps prevent sweating.

    OK, then why isn't this a thing? Because there's no way no one has ever thought of it. I'm just spitballing, but I can think of two practical issues: the first is, as others have noted, that 55F or so isn't cool enough to dehumidify your air in a humid climate, you couldn't use this as your sole source of AC. You'd have to supplement it with either regular AC or dehumidification. The second has to do with the way that water tends to be used residentially: a lot all at once, then none at all for a while. In order to capture all that "coolth" you'd have to have either a really big heat exchanger, or some sort of buffer tank. It would work better if you had some long-running consistent use of water, like watering the lawn.

    Let's run some numbers. Say you're using 2 gallons per minute, the water comes in at 55F and your room temperature is 75F. That's 16 pounds per minute or about a thousand pounds per hour, and about 20,000 BTU/hr, or a ton and a half. That's not insignificant.

  6. leon_g | | #7

    Reid, if you're still reading this, just wanted to say "hi" to you - think back to your time at Aerospace Corp about 36 years ago :).

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