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Walk-in Cooler in Basement – Using a Coolbot

klepperbuildingco | Posted in General Questions on

Hello All,

I have recently been tasked with constructing a walk-in cooler in the basement of an older building to hold beer kegs. The owner would like to utilize a CoolBot controller combined with either a window unit AC or a mini-split. The most affordable option would be the window unit type ac, but I have some questions about placement. The plan is for the cooler to be built inside of a larger room within the basement. With this cooler being in an old windowless basement, the supply air would be coming from the larger room within the basement, cooling the inside of the cooler. Do you foresee any issues with this? The other alternative that I see would be to install a mini-split with the condenser sitting outside of the building. Thoughts?

Thank you,

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  1. Expert Member
    Akos | | #1

    Depending on the size of the two places and how well they are insulated, it should be doable. Common to have basement wine caller cooled with a through the wall unit into the rest of the basement. Something along a 4:1 ratio is in the ballpark without the space overheating.

    You can't use typically window units for this as most (none?) go low enough. You need special units that can go down to 40F. Same for mini split, some can do low temperature cooling, but you'll have to dig through the spec to confirm.

  2. James Howison | | #2

    Coolbot hacks the units to allow them to go lower: I'm not 100% clear on quick glance how it does it, though, whether it's just sensing freeze up (and backing off to let it clear) or whether it adds heat to the fins to fight freeze up.

  3. Walter Ahlgrim | | #3

    How cold do you want the cooler?

    If the goal is over 45° it could work but the factory controls may not go that low.

    If your goal is 33° you are going to have ice buildup in your cooling unit. Units made to work that close to freezing have provisions to defrost themselves.

    Often you can find used walk in coolers for short money.

    If this is a restaurant/ bar it is unlikely the health inspector will approve any homemade cooler or used cooler without a NSF approval label.


  4. Sam S | | #4

    This isn't a project I loved, but we once installed a wall mounted Mitsubishi split where the condenser was in the basement. The owner has to be ok with the waste heat getting dumped into an interior area, but it does work. The project was designed to reduce a particular heat load in one room, so the basement only saw a small increase in ambient temperature.

  5. Expert Member
    DCContrarian | | #5

    Just so everyone understands what he's talking about, this is a one-sentence description of the CoolBot from their website: "The CoolBot uses multiple sensors, a heating element and a programmed micro-controller to direct your air conditioner to operate in a such a way to cool the room to 36° F without ever freezing up. "

    To the original poster: you're asking an engineering question. Can the heat that is removed from the fridge be expelled into the basement successfully? The answer to that is, "it depends." It depends on a lot of things, like how much heat needs to be removed, and how the basement is constructed.

    Basements are notoriously hard to model, how the ground absorbs heat defies easy prediction. The cooler itself should be fairly easy to model based on the insulation level, the interior temperature and the basement temperature. From that you could do a test where you find a heat source of similar capacity (I'm thinking propane heat lamp, although they're scarce right now I hear) and just run it in the basement and see what happens to the temperature.

    The failure scenario is the basement is unable to shed heat as fast as the cooler produces it. The basement heats up, and the more it heats up the more cooling demand the cooler feels. It enters a runaway mode where the cooler is running 100% of the time and unable to achieve the set point of the thermostat.

    1. Expert Member
      DCContrarian | | #7

      To put some numbers in to give context:

      Imagine your cooler is a cube, 8 feet on a side, and the walls are 4 inches thick with a R4 insulation. Further imagine your basement is at 68 degrees in the summer and your cooler will be at 38 degrees. The formula for heat transfer through a wall is:
      A = area of the wall
      Td= Temperature difference between the two sides
      R = R value of the wall.
      The cooler has six sides of 64 square feet, or 384 square feet of area. The temperature difference is 30 degrees, and the wall is R16.
      So H=384*30/16=720 BTU/hr.

      That's how much heat is moved. The air conditioner itself is going to produce some heat, let's say it has a COP of 2.0 so it produces 360 BTU/hr. So a total of 1080 BTU/hr. The question is whether the basement can absorb that without thermal runaway.

      For a quick practical check, you can run a heat-producing device and see what the basement does. A load of 1080 BTU/hr is equal to slightly under 320 watts. You could run a heating device down there during the hottest part of the summer and see if the temperature rises much.

      Most basements could dissipate that without noticeable effect.

  6. Jean-Noel Ragot | | #6

    The CoolBot works, very well as a matter of fact. A friend used one for a cheese cave. At the time he and his wife were raising goats and doing dairy products. He got a used window ac unit for free, tagged on the CoolBot and instant walk in cooler.
    I’ve no idea on how the operating costs compare but the acquisition cost is hard to beat.

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