fan power calculation

Your number 2 is closest to the correct approach.

Calculate P_fan individually based on supply cfm of each BL system with all Pressure Drop Adjustments, except no pressure drop adjustment should be taken for heat recovery where it is not required in the BL. See footnote to Table G3.1.2.9.

Interesting thread..
One question though:
You might have scenarios whereby you have 8 systems for the proposed (depending on the design) and 5 systems for the baseline (depending on the number of floors).
"Zone A" (served by HVAC System P1) in the proposed has a ducted return air, whereas "Zone B" (served by HVAC System P1) has a free return.
Both zones ended up in the Baseline being served under the same system B1 (same floor). Do we then have to adjust the baseline fan powers corrections of system B1 to accommodate for the ducted return, knowing that Zone 1 has a ducted return in the proposed but Zone 2 does not?

Thanks!

The pressure drop adjustment of 0.5 is only applied to the return CFM for zone A. It would not be applied to return CFM for zone B. Refer to Table 6.5.3.1.1A which defines CFMd.

Thanks Marcus,

However, my understanding was that I should enter the adjustment on the System level (AHU) and not on the zone (I think that's the way it is done using eQUEST).

The information is entered at the system level.

The pressure drop is not entered directly in eQUEST. It is included in the calculation you do to determine the kW/cfm you enter in eQUEST. To calculate this value determine the total kW of all fans, then divide by the supply cfm and enter the kW per cfm in eQUEST at the system level.

There is a calculator in the Documentaion Toolkit related to Appendix G calculations for fan power. So for example, assume your system serving zones A and B has a total supply cfm of 1000 and the return cfm is 500 each. Enter 1000 in the column CFMs, the appropriate pressure drop in the PD column (0.5 for zone A and 0 for zone B) and the CFMd (500 each) for each zone in that column. The wattage should then be calculated as 1,208.3 watts. In eQUEST you enter 1.21 kW/1,000 cfm = 0.00121 kW/cfm at the system level.

Hello Marcus,

I am trying to find this documentation toolkit related to the Appendix G calculations for fan power, but cannot find it. Could you please tell where is it?

Many thanks!

Hi Marcus,
I have two questions regarding the calculator.
1- Why you assumed 0 pressure drop for zone B.
2- Is always total return cfm (CFMd) is equal to total supply cfm.

Thanks

Santiago,

Go to the top of the page and click on Documentation Toolkit.

Morteza,

1 - see citation above regarding 0 pressure drop in zone B.
2 - not always