In Appendix G comparisons are air side economizers required in IDF/Electrical Rooms

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Hello All,

When performing a 90.1 2007 Appendix G energy model, the baseline system
for the building appears to call for a packaged single zone air handler
and an airside economizer for individual IDF and Electrical rooms. The
proposed systems are designed as FCUs. Although not addressed in
Appendix G, section 6.5.1, would appear to exempt the airside
economizers in rooms requiring a low cooling capacity.

With that said, is it correct to reference other parts of ASHRAE 90.1
(prescriptive path Sec 6.5) when performing a performance based Appendix
G energy cost comparison?

Your help and clarification would be much appreciated. I apologize if
this is not the correct forum for this post and would be greatly obliged
if you were to direct me to the correct forum.

Regards,

Connor Jansen, PE

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Hi Connor,

Since G3.1.2.6 already lists the exceptions that apply to the economizer
requirement, I don't think you should try to claim additional exceptions
based on the Prescriptive Path Section 6.5. While I agree that it might
be unreasonable to expect an owner to install an economizer on a small
PSZ unit, the Appendix G Baseline requirements do not necessarily
represent what an owner would typically do. The flip side of your
situation is that a zone with a low cooling capacity should not penalize
your Proposed design too badly if the Baseline has an economizer but the
Proposed doesn't. You can minimize any penalty by using a higher cooling
T-stat setpoint in both models (assuming your electrical room is not to
be kept at comfort conditions).

Regards,

Bill

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Although this has low chance, but if you are still under V2/90.1-2004,
depending on your area, economizer might not be required based upon the
square footage the system serves.

Lan Li, PE, LEED AP BD+C

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