# Apendix G3.1.2.9

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Hello All,

I am trying to understand the stated appendix for the baseline model.

When I am calculating the Pfan for a system, do I need add up supply,
return, system and room exhaust cfm's?

I got this comment from GBCI: "Revise the sum of the supply, return,
exhaust, and relief fans for each HVAC system to be equal to the volume
calculated in G3.1.2.8 and power calculated in G3.1.2.9 (where CFM
refers to supply air volume)."

Thanks,

Fareed Syed EIT, LEED(r) AP

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No, you use only the fan supply cfm to calculate the total fan power, then cut that fan power up into supply, return, etc.

Best Regards,

Gregg Liddick, EIT, LEED(r) AP

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Gregg,
Is there guidance on what portion of the Pfan goes to each? What percentage goes to supply, what percentage to return, etc?
Kimberly Killian

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Hi Kim,

I'm fairly certain that there's no specific guidance in Appendix G. What most people do is break it up so that it's proportional to the proposed case. For example if the baseline fan power is 34.5 kW and the actual parameters call for 20 kW supply and 10 kW return you would break the baseline case up into 23 kW supply and 11.5 kW return. I hope that helps.

Gregg Liddick, EIT, LEED(r) AP

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Hi Greg,

My basic question is which cfm do I take to calculate Pfan? Just the
supply to come up with kW/cfm or sum of supply, return, relief, and
exhaust fans?

Thanks,

Fareed Syed EIT, LEED(r) AP

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Fareed,

Set your supply air to room temp delta t equivalent to 20F. Run the sim, if I am not mistaken this should generate usable airflow quantities to be used in point 9. Make sure you have oversizing in place before any of this. I have not been told this but I think G is set up to be done step by step from the beginning. In some instances you need to update your model in order to proceed with the next step. Good luck.

Kevin

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To calculate total bhp, you would use the cfm across each fan and calculate
using the pressure increases across each fan and the efficiency's of each fan
(along with a constant).....then add them all up. I don't know if this has
anything to do with G3.1.2.9. Depending on whether your in IP or SI units,
you will come up with hp or kW. If it was up to me, I would use (bhp or
kW)/(supply cfm) to do an energy analysis. But, I'm not gbci.

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Re: [Bldg-sim] Apendix G3.1.2.9I am working on a model doing the exact same thing for LEEDS baseline. I have calculated my Pfan but cant seem to input it or get the correct outputs.

The model wont allow me to enter anything in the kW/cfm screen. My equipment is a PSZ

Should I adjust the Static Pressures and efficiencies to get the same value?

Regards,
W. Peter Anderson, P.E

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Peter---

Are you using eQUEST for modeling? If so, you can right click in the
"Static in WG" box and hit "Restore Default". This will enable the
"Design kW/CFM" input field.

Andrew Craig EIT, LEED AP

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Re: [Bldg-sim] Apendix G3.1.2.9Excellent, thanks. Never would have thought of that.

Regards,
Peter

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