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Packaged RTU heat reclaim efficiency appears limited to 30%

asked 2020-04-15 02:23:47 -0500

Jim Dirkes's avatar

updated 2020-04-15 14:00:15 -0500

I'm attempting to model a packaged RTU with hot gas reheat in EnergyPlus and using:

  • Coil:Cooling:TwoStagewithHumidityController

  • Coil:Heating:Desuperheater

Manufacturer equipment (so far as I can tell) routinely makes 100% of the condenser heat available to a hot gas reheat coil, but E+ limits the heat recovery to 30% - not enough for humidity control in my case.

Am I missing something? How can I make ALL of the condenser heat available to the hot gas reheat coil?


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answered 2020-04-15 10:11:22 -0500

You aren't missing anything as far as modeling hot gas reheat with the Coil:Heating:Desuperheater object - the 30% heat reclaim recovery efficiency is a hard-coded limit.

However, it appears that EnergyPlus v9.3.0 now includes a different method of modeling condenser hot gas reheat in the Coil:Cooling:DX object (relevant PR here). I haven't tried this out yet, but based on this description it appears promising:

The goal of this new feature is to provide a DX cooling coil capability to meet all possible demand with different sensible and latent loads by using different mode operation in a single cooling coil. In other words, the coil itself can meet sensible and latent loads simultaneously without any additional help.

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Sweet! I have not yet started using v9.3, but will take a look

ps, Since posting this originally, it occurred to me that I could use a Coil:Heating:Fuel object with "Other" fuel. The heating coil picks up the needed reheat without adding to natural gas or electricity usage.

Now moving on to v9.3.....

Jim Dirkes's avatar Jim Dirkes  ( 2020-04-15 10:22:49 -0500 )edit

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Asked: 2020-04-15 02:23:47 -0500

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Last updated: Apr 15 '20