Modelling enclosure losses from a packaged or built-up RTU

asked 2020-12-28 18:15:29 -0600

willyJohan gravatar image

updated 2021-01-22 12:15:02 -0600

I need to model the impact of increased enclosure insulation on the energy used by a roof top unit. I was planning making a small zone with the an exterior boundary condition wall having UA equal to that of the purposed RTU and using that space as a supply plenum. Depending on the size of unit and the location of the coils, I would also perhaps do the same with a return plenum to capture any gain/losses driven by the return air delta T.

Assuming I can come up with a reasonable UA approximation, would this work? Is there a better way.

Concerns I have about this approach

  • Appropriately modelling the inside convective heat transfer
  • Accounting for the variation of air temperature as it move though the RTU / estimating the area of enclosure that is subject to the return or supply air temperatures (or even something in between like the air between the fan and heating coil on a blow through unit).

Using EnergyPlus.

Any advice on how best to model this would be appreciated.

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