Question-and-Answer Resource for the Building Energy Modeling Community
Get s tarted with the Help page
Ask Your Question

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

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

dhollman gravatar image

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

edit retag flag offensive close merge delete

1 Answer

Sort by ยป oldest newest most voted

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

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.

edit flag offensive delete link more


Thank you Jason

dhollman gravatar image dhollman  ( 2019-03-04 07:34:40 -0600 )edit

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer


Question Tools

1 follower


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

Seen: 359 times

Last updated: Mar 01 '19