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  1. #105
    Join Date
    Feb 2010
    Newnan Ga,
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    Quote Originally Posted by dave sulz View Post
    How do you think a compressor hat runs above freezing work below freezing. I hate nonsense. I'm not smart but recoconize dumbass. Sorry stupid should be told
    Wow you should be don't belong on this forum...

  2. Likes Gernby, HVAC_Marc liked this post
  3. #106
    Join Date
    Aug 2016
    Post Likes
    Thread Starter
    Do any of you guys have any suggestions about how I can derive some sort of "performance index" based on weather parameters, indoor parameters, power usage, and / or electric cost, in order to dial in my system a little quicker? It doesn't have to be elegant, and could even be unit-less. I just need some way to know whether some change to the system causes a positive or negative result.

  4. #107
    Join Date
    Sep 2002
    Post Likes
    1. No heat change process is 100% efficient - something is always lost in each step of the exchange process.

    2. The nature of an A/C evaporator's design is such that it cannot tolerate any frosting.

    3. So the refrigerant evaporating temperature cannot fall below about 30-32 F.

    4. The approach of the evap is unlikely to be less that 10, and may be greater, so your minimum air 'off-the-evap' temperature is unlikely to ever be less than 42.

    5. Getting the heat out of water without large surface areas is difficult and slow.


    Quote Originally Posted by Gernby View Post
    Hi, I'm working on an HVAC project, and am trying to figure out the best way to chill some barrels of water. My current plan is to buy an air-to-water heat exchanger (like a car radiator), and install it in an air box next to the air handler in my attic. I would connect that box to the air handler with 2 flex ducts (1 to the return side and the other to the supply side). I would also put a motorized damper in one of those ducts to prevent air flow through the air box during normal operation.

    The damper would be closed almost all the time, but whenever the AC is running AND the thermostat is about to turn the system OFF, I would have a "piggy-back" controller take control of the system. If the temperature of my water tanks is higher than I want, then the controller will keep the AC running while the motorized damper is opened up and water starts pumping through the heat exchanger. While running like this, I believe there will be very little air flowing through the rest of the ducting, since most of the air should be "short circuited" through the heat exchanger.

    I haven't done the math about how large the ducts and heat exchanger need to be, but it seems that as long as I can pump enough heat through the heat exchanger to maintain 15-20F across the evaporator coil, then I should be able to chill the water down near freezing. That might take a large sized exhanger and water pump, but it seems possible.

    Do you guys agree? Am I correct that the air looping over and over between the evaporator coil and exhanger can be super-cooled (at or below freezing), as long as a 15-20F temp drop is maintained across the evaporator?
    The conventional view serves to protect us from the painful job of thinking.

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