Hi All,

I have a specific question about using Appendix G3.1.2.9 to calculate
baseline system fan power (I have already searched previous posts and
could not find the answer I'm looking for). So, the Appendix G section
reads as follows: System fan electrical power for supply, return,
exhaust, and relief (excluding power to fan powered VAV boxes) shall be
calculated using the following formulas. I understand the formulas,
which essentially use a fan CFM to determine a brake horsepower BHP,
which is then used to calculate the fan power (Watts), but my question
is this: Supposing you have an HVAC system with supply, return, and
small exhaust fans (in restrooms, for example) - how do you calculate
the power to each fan?

Option 1: Use your supply fan cfm to calculate a power, say it comes to
10 kW, and use this as your total "system" fan power. This 10 kW, being
your whole system power, is then distributed among all of your system
fans however you desire (For example, supply fan power = 5 kW, return
fan power = 4 kW, exhaust fan power = 1 kW, for a total of 10 kW for the
fan system)

OR

Option 2: Use each supply, return, and exhaust fan cfm to separately
calculate an individual kW for each fan (For example, supply fan power =
10 kW using the supply cfm, return fan power = 9 kW using the return
cfm, exhaust fan power = 1 kW using the exhaust cfm, for a total of 20
kW for the whole fan system)

Obviously, you will have much more fan energy in a baseline system
calculating fan power with Option 2. Does anyone have a specific
example they can share of a fan system calculation that was accepted by
USGBC for an EAc1 energy model?

Thanks for your help!

Mike Kaufman