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ASHRAE 90.1 2013 Appendix G removes reheat energy from the baseline

asked 2018-08-15 17:22:39 -0500

updated 2018-08-15 17:23:23 -0500

I am having trouble understanding the new requirements for ASHRAE 90.1 2013 that only allows to include 25% of the reheat energy in the baseline model.

Addendum AH added this requirement with the intent to have designers consider using some heat recovery system for reheat when you have a dehumidification system. While I like the intent of this new requirement, I am having trouble implementing it in my baseline model.

Does this only apply to reheat during dehumidification or to all reheat include zone reheat? How can I separate my reheat energy from the rest of my heating energy so I can apply this requirement in my OpenStudio model?

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answered 2018-08-20 03:10:22 -0500

Avi gravatar image

updated 2018-08-20 03:12:16 -0500

To my best understanding reheat energy is wasted energy so I tend to believe that it is the total reheat energy that should be offset from the baseline (but that is just a thought).

I believe you can track the reheat energy in the Energy meters section of the E+ report. You can turn on the following output variables (assuming you use Coil:Heating:Electric):

HVAC,Sum,Heating Coil Heating Energy [J]

HVAC,Average,Heating Coil Heating Rate [W]

HVAC,Sum,Heating Coil Electric Energy [J]

HVAC,Average,Heating Coil Electric Power [W]

You can also create a meter to sum them all to get total Coil:Heating:Electric energy or energy rate. Then you will have to take out times were Coil:Heating:Electric is used for supliment heating if any.

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I guess my concern was there are other ways for Appendix G to reduce the baseline reheat energy through controls or requiring site heat recovery instead of just saying to removing 75% of the heating energy in the end.

Another thing was since this is under the dehumidification section of Appendix G I was thinking this was the reheat energy to take the supply air flow from 50F DP out of the cooling coil to 55F DB at the system level, and not the zone terminal reheat energy from 55F DB to up to 95F DB. Otherwise a 75% heating savings is a lot considering how conservative ASHRAE typically is...

Ken Takahashi gravatar imageKen Takahashi ( 2018-08-20 19:29:22 -0500 )edit

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Asked: 2018-08-15 17:22:39 -0500

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Last updated: Aug 20 '18