What is the 90.1-2013 Appendix C "envelope performance factor"?

ashrae-90.1

asked 2019-02-28 09:10:37 -0600

dhollman
397 ●11

updated 2019-02-28 09:11:04 -0600

ASHRAE Std. 90.1-2013 Appendix C states that you have to compute an "envelope performance factor" for both your proposed and 'base' buildings. This seems to be intended to be done using energy simulation software.

But it seems to leave out a precise definition of how this factor is to be computed.

I get the impression that the factor for each model may just be the total annual energy cost for the building. It does say in one spot (C3.3 Purchased Energy Rates) that:

"... rates for purchased energy shall be used to determine the proposed envelope performance factor and the base envelope performance factor"

Is my interpretation correct? (That the total energy use is what is required?)

Are there any materials which clearly define these terms? Thanks

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I am still confused by this. How is it not defined anywhere? In 90.1-2022, the envelope performance factor plays a big (potential) role in compliance via Chapter 11 "Additional Efficiency Requirements" (11.5.2.1). Anyone have any insight into this?
Specifically, I'm confused about the difference between Envelope trade-offs, Energy Cost Budget method, and regular old App. G energy modeling. Any help would be much appreciated - I'm a BE consultant, not an energy modeler.

Axelarris ( 2024-07-03 16:39:45 -0600 )edit

I have no update about why some formula isn't defined, but I hope someone will fix it. As far as the differences between tradeoff methods. If it is just envelope components, then just use the envelope tradeoff method which is part of COMcheck, but if you are trading off between two or more major sections of 90.1 (lighting, envelope, mechanical, swh, ...) then you need to use either ECB method or PRM, your choice.

JasonGlazer ( 2024-07-08 13:19:13 -0600 )edit

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answered 2019-03-01 08:14:05 -0600

JasonGlazer

6905 ●26 ●12 http://www.gard.com/

updated 2019-03-01 08:18:03 -0600

I believe, the envelope performance factor is the annual cost for the whole building based on the model described in Appendix C and using the purchased energy rates described in C3.3. The proposed envelope performance factor is based on the proposed building and it is compared to the base envelope performance factor (sometimes called budget envelope performance factor) that is the proposed model modified to meet the prescriptive requirements. I was a little surprised by your question but in looking through 90.1-2013 and 90.1-2016, it is not explicitly described.

Please note that this is my personal opinion and is not an official interpretation from ASHRAE. To request an official interpretation see this page.