Packaged RTU heat reclaim efficiency appears limited to 30%

asked 2020-04-15 02:23:47 -0600

Jim Dirkes
3554 ●27 ●16

updated 2020-04-15 14:00:15 -0600

__AmirRoth__

4436 ●5 ●17 http://bleedinggreenna...

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?

Thanks!

answered 2020-04-15 10:11:22 -0600

ericringold

10637 ●32 ●8 https://www.nrel.gov/b...

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 ( 2020-04-15 10:22:49 -0600 )edit

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Packaged RTU heat reclaim efficiency appears limited to 30%