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Desuperheater water heater

user_953789 | Posted in Mechanicals on

I always understood that if you had a GSHP with a desuperheater, that your water heater should be an electric tank type. A client we are designing a home for would prefer a gas tank over electric, and our MEP engineer has not suggested that this would create any issues. Please advise.

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Replies

  1. charlie_sullivan | | #1

    There's no reason it wouldn't work, but a gas tank typically has much higher standby losses than an electric tank, so it would be a little sad to be using a tank with high standby losses during the part of the year that the desuperheater is providing most or all of the water heating.

    I think you can find a gas tank with low standby losses, but that might take a little research, as that's not always listed. If you find one with efficiency and EF listed, low standby loss would mean those two numbers would be close to each other.

    A two-tank desuperheater setup is preferred especially when the system is running in cooling mode, as the superheat temperature might not be very high, and it might only work for preheating, not for final DHW temperature. If you use a single tank, controls for the desuperheater should make sure it isn't operating when it isn't actually boosting the temperature of the tank, and/or it should be shut off during cooling operation.

  2. user_953789 | | #2

    Thank you. What if the geothermal tank was electric then the second tank was gas? Seems like that could be a good solution.

  3. charlie_sullivan | | #3

    The first tank doesn't need heating capability at all, but usually a mass-market electric tank is cheaper than a storage tank without a heater, so that's the way to go. But the second tank standby losses still matter so I'd still look carefully at that spec.

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