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  1. #1

    Desuperheater hookup to water heater

    I have a FHP GS062 geothermal hvac. Apparently it has the desuperheater already in it.

    I want to start using it to heat up the water in the home. I've seen a few diagrams and a few discussions as to how it should be hooked up. Some people have two tanks, others seem to have just one tank. Currently I have 1 80 gallon electric water heater.

    Anyways, I have a few questions.

    What are the downsides of using just one tank? What temperature does the water come out of the desuperheater at? I'm thinking the main issue would be if my water heater is always keeping the water higher than the desuperheater gets the water up to then the desuperheater will be kind of useless.

    With two tanks, tank 1 has the desuperheater, tank 2 has power. Tank 2 gets the already warm water from tank 1. But tank 2 still has to keep the water warm. Is it basically just a savings from not having to heat up the water as much as it would if it had just come straight from the water main? is the cost of keeping the water warm pretty small then?

    Now for hooking it up. Can I use pex?
    I've seen some diagrams where the water that goes into the desuperheater comes straight out of the cold and goes back in through the drain at the bottom. Wouldn't it make more sense for the water that goes into the desuperheater to come out of the bottom of the tank?

    I'm attaching a couple of pictures of my hvac if that helps.

    Thanks.
    Attached Images Attached Images   

  2. #2
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,292
    Standby losses are one source for requiring reheating of water in a hot water tank, injection of cold water from the tap or well is the other. The latter will require much more use from the electric elements, depending on how cold the incoming water is. If you have two tanks, with one kept hot by the desuperheater feeding supply to the other tank where the electric heating elements are, the amount of time the elements must be on to recover heat loss will be less, since the incoming water isn't nearly as cold. Both tanks should be well insulated, with thermal breaks in the piping connections between tanks and between tank and desuperheater.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  3. #3
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,914
    I would like a 2nd tank. You'd get more use out of the hot gas heating 50° water coming in than heating 100+ water out of the single tank.

  4. #4
    Quote Originally Posted by BaldLoonie View Post
    I would like a 2nd tank. You'd get more use out of the hot gas heating 50° water coming in than heating 100+ water out of the single tank.
    Does the tank that is hooked into the desuperheater need to be of a similar size as the 80 gallon tank I already have?

    The reasoning behind this is that we never use 80 gallons of hot water (except on the bathtub which we rarely use or when we have tons of family visiting), so the desuperheated tank will only be feeding a few gallons at a time to the 80 gallon tank.

    Or if the temperature of the desuperheated water is high enough then I could do the opposite. Use a smaller electric/gas tank and make my 80 gallon tank work with the desuperheater. That way if the smaller tank runs out of hot water it gets the already desuperheated water out of the 80 gallon tank. But that only works if that water in the desuperheater tank is hot enough to use on its own.

  5. #5
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,292
    The desuperheater can only heat water when the geothermal is running. If you never need 80 gallons of hot water, why not consider downsizing total tank capacity and splitting it between two tanks as described above? Say 30 + 30 = 60? By downsizing the tank with electric elements, you also downsize the wattage of those elements = reduced electrical demand to recover against usage and standby loss.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

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