[BLDG-SIM] Design Air Flow Sizing per 90.1-2004 App G

Paul Riemer PaulR at TWGI.com
Fri Jul 7 10:05:39 PDT 2006

I would appreciate any clarifications that can be shared on the underlined sentences in these two excerpts from Appendix G of ASHRAE 90.1-2004.  They seem contradictory so I must be missing the author's intent.
G3.1.2.8 Design Air Flow Rates. System design supply air flow rates for the baseline building design shall be based on a supply-air-to-room-air temperature difference of 20°F. If return or relief fans are specified in the proposed design, the baseline building design shall also be modeled with fans serving the same functions and sized for the baseline system supply fan air quantity less the minimum outdoor air, or 90% of the supply fan air quantity, whichever is larger.

G3.1.3.12 Supply Air Temperature Reset (Systems 5 through 8). Supply air temperature shall be reset based on zone demand from the design temperature difference to a 10°F temperature difference under minimum load conditions. Design air flow rates shall be sized for the reset supply air temperature, i.e., a 10°F temperature difference.

Thank you,

Paul Riemer
PaulR at twgi.com

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