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# Hot gas reheat for an air loop in EnergyPlus

There's not much on this forum regarding hot gas reheat coils, so I'm trying to get an update... So far as I know, hot gas reheat coils can be modeled ONLY using the "Coil:Heating:Desuperheater" object AND the amount of reheat is limited to 30% of the available energy.

This is a big restriction for models that use DX coils and also control relative humidity. We run into them a lot and the workarounds are cumbersome.

1) Is my understanding correct?

2) Have any of you created a workaround that you like? (our best at the moment is to add a heating coil with "Other" fuel so electricity and natural gas use are not affected. This coil is available only during summer cooling months. Another heating coil is used for winter months.)

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There is a new coil model, Coil:Cooling:DX, that was recently added. And more recently added to that was alternate modes of operation in the Coil:Cooling:DX:CurveFit:Performance object.

Coil:Cooling:DX:CurveFit:Performance,
A5, \field Base Operating Mode
A6, \field Alternative Operating Mode 1
A7; \field Alternative Operating Mode 2


And each of these fields point to a new set of performance curves in the Coil:Cooling:DX:CurveFit:OperatingMode object. So if you had performance curves that defined how the combination of cooling coil and reheat coil operated as a pair, one with only the cooling coil operating, and another with both coils active, you could model that equipment. I haven't tried this yet but you might look at the example files that use these new objects to get a feel for the complexity. They are UnitarySystem_DXCoilSystemAuto.idf and UnitarySystem_FurnaceWithDXSystemRHcontrol.idf, I have not reviewed these files lately. Also, this is the new cooling coil model that will eventually replace all others.

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Richard, I did not know about that new capability. Thanks for letting me know; I'll check it out.

( 2020-12-01 23:42:41 -0600 )edit