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Thread: Geo Thermal Loop Temperatures

  1. #1
    Join Date
    Sep 2013
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    Geo Thermal Loop Temperatures

    Hey guys I have a question on a project we are doing the controls on. Im the control guy and just want to understand the thought process for the pumping.

    The building is in a northern state. The heat pumps were designed for a 32 degree entering temp.

    System consists of 65-70 heat pumps on the building loop. The variable speed pumps for the building building modulate to system pressure.

    The ground loop pumps modulate to maintain supply temperature going to the heat pumps. Above 78 degrees the modulate to maintain 80 degrees supply temp. Between 78 and 40 they are off. Below 40 they modulate to maintain 38 degrees supply temperature.

    This isnt my first heat pump job but its one of my first geothermal. So my question where did they come up its 38 degrees? The 80 makes sense to me. But wouldnt it be better to be higher on the loop temp in winter and just use more pump energy? Or do the heat pumps not work any harder if the supply temp is 38 vs 55?


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  2. #2
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    Thread Starter


    I RTFM and decided yes the HPs are more efficient the warmer the entering water.




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  3. #3
    Join Date
    Jan 2020
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    38 degrees is a nice temperature to operate the pumps at. Could go a little higher, or lower. But I'm betting that they are using this target due to total loop saturation temperature.
    Best to talk to the engineer that designed the system.
    It may just be an arbitrary number and you could get higher heating efficiency with a warmer loop
    You don't squat with your spurs on.
    And you NEVER put the torches away before pressure testing.

  4. #4
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    I thought about this a little more. I think the engineer wants to know that almost all the zones are calling for heating vs some heating and some cooling and is using the 38 loop temp as a proxy for that.

    I think we could add up the number of zones calling for heating vs cooling and reset the setpoint upwards.

    The ground loop pumps are only 7.5 HP so I think there is efficiency gains available.


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