Steve,

ASHRAE 90.1 Appendix G talks about that a little bit.

See sheet 4 of 47 - "Trade-Off limits"

http://web.cecs.pdx.edu/~sailor/CoursePages/ME422_Spr09/ASHRAE90_1Appendix_G.pdf

Basically, it is possible but very specific guidelines must be met - as the document talks about.

Also, if you have, for example, heating and air-side systems serving both the newly-renovated area and the other parts of the building the energy results of the model could potentially be much better (more energy efficient) than it actually is.

This means that the results of the energy model have a possibility of being misconstrued and skewed somewhat which ASHRAE specifically frowns upon because it can be dishonest and not reflective of the ACTUAL energy use of the building. It also means the energy cost comparison is undermined by the fact that the ACTUAL cost savings could be much lower than the client is expecting and that could cause some issues.

Sheet 3 of 47- "Include All Energy Components" talks about this.

But if the minimum requirements are met, you have an argument and a direct reference in ASHRAE at your defense.

I've never heard of someone modeling only a portion of a larger building but apparently ASHRAE sais it is possible. But to do it accurately the portion of the building being modeled would need its own air-side system, it's own heating system, etc... It would be the only way to accurately model the building.

I would think you would also need to calculate energy cost for the overall building before doing any kind of realistic or accurate cost comparison for the client.

Especially since the model would only reflect cost savings for the renovated portion, not the entire building.

I'd be interested to see what others think about this.

Chris Baker
CCI CAD Drafter