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AWHP and booster for DHW with Setpoint Control

I am working on a system in OS with and AWHP for space heating (underfloor heating) and DHW that required different temperatures: 35 and 60 degree respectively. The AWHP produces water at 40 degree which goes in parallel to both an HX (then connected in a secondary loop to the Low Temp Rad Var Flow) and a DHW tank. In this case, the WaterHeater:Mixed of the HP, being a "direct system'', has Tank Volume and Heater Maximum Capacity equal to zero. The DHW tank, on the other hand, has a certain volume (230 L) and Heater Maximum Capacity equal to 4000 W. I was wondering how to set the setpoints of the DHW tank so that the internal heater is activated to bring the water from 40 to 60 degrees. Having AWHP and DHW tank 2 different setpoints, I was thinking of setting the Source Side Flow Control Mode as IndirectHeatAlternateSetpoint equal to 60 degrees, while the Setpoint Temperature Schedule Name should be 40 or 60 (?). The internal heater of the DHW Tank does not seem to activate and the temperature in the tank remains that which comes from the AWHP (around 40 degree). How should I proceed? Thank you.

lollokai's avatar
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lollokai
asked 2024-05-07 05:40:16 -0500
Aaron Boranian's avatar
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Aaron Boranian
updated 2024-05-07 07:22:13 -0500
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I have carefully reread the definition of IndirectHeatAlternateSetpoint in the Source Side Flow Control Mode field of the WaterHeater:Mixed and that of Indirect Alternate Setpoint Temperature Schedule Name.

After a few attempts, I set the main setpoint of my DHW tank (Setpoint Temperature Schedule Name) to what I actually want (60 degrees) and the Indirect Alternate Setpoint Temperature Schedule Name to the temperature up to which the primary source side (the HPWH in my case) can heat the water, so 40 degrees. This seems to give the desired result.

lollokai's avatar
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lollokai
answered 2024-05-09 04:45:04 -0500
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