# LEED-ASHRAE 90.1-App G - Fan Power calc

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All,
Can anyone please confirm/clarify how the fan power calc should be performed for the baseline model for ASHRAE 90.1- App G (with addendum ac).

I have an air handling system that contains a supply fan, a return fan, and a room exhaust fan. Article G3.1.2.8 states:...."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 it goes on to specify how those return and relief fans should be sized.

My question is:
When determining the baseline fan power, do I only get to perform the calculation once based on the supply air cfm (plus adjustments per addendum ac for each applicable SA, RA and EA component)? And then that equals my total fan KW allowed for all the fans in the system? If this is the case, would that total fan KW then be spread across the 3 fans in a prorated fashion?

Or, do I get to perform the calc 3 times: once for the supply fan, once for the return fan, and once for the exhaust fan....(each calc including their respective adjustments allowed for for that fan).

Obviously, I'm hoping the answer is the latter since the other (single calc) method yields a puny total horsepower number.

Your feedback and experience regarding successful applications for LEED submittals in this regard is appreciated.
Julia

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Joined: 2011-10-01
Reputation: 3

Julia,

The total allowed fan kW is for all three fans that are part of your system. Appendix G does not really give direction on how to divide up this fan power. If they are all running with the same schedule, then it does not matter. If they are not, I would use a ratio based on the fan power of your three fans in your proposed design.

Michael Rosenberg

Can anyone please confirm/clarify how the fan power calc should be performed for the baseline model for ASHRAE 90.1- App G (with addendum ac).

I have an air handling system that contains a supply fan, a return fan, and a room exhaust fan. Article G3.1.2.8 states:...."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 it goes on to specify how those return and relief fans should be sized.

My question is:
When determining the baseline fan power, do I only get to perform the calculation once based on the supply air cfm (plus adjustments per addendum ac for each applicable SA, RA and EA component)? And then that equals my total fan KW allowed for all the fans in the system? If this is the case, would that total fan KW then be spread across the 3 fans in a prorated fashion?

Or, do I get to perform the calc 3 times: once for the supply fan, once for the return fan, and once for the exhaust fan....(each calc including their respective adjustments allowed for for that fan).

Obviously, I'm hoping the answer is the latter since the other (single calc) method yields a puny total horsepower number.

Your feedback and experience regarding successful applications for LEED submittals in this regard is appreciated.
Julia

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Joined: 2011-10-01
Reputation: 0