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