Appendix G Fan Simulation

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I've seen multiple posts regarding 2004 Appendix G Fan Power and one
post from Ming Zeng suggested the following:
"Baseline model fan usually gives 0.00078KW/cfm. For proposed fans,
typically it is 0.00016-0.00018 KW/cfm/in static*"*

I have two problems related to this because my Baseline KW/cfm is closer
to 0.001 KW/cfm for a bunch of unitary Type-3 systems, which is
indefinitely way too high.

FIRST
Many people have referred to the calculated fan power as an allowance,
which to me, would appear to be a threshold not to exceed based on the
20deg-F delta for Appendix G Fan Sizing. I figure this is not the case
because others refer to the fan power as something that is simulated in
the model as a KW/cfm.
I've also seen posts where numbers are expressed as KW/kcfm, which would
indicate fan power KW per thousand cfm; which again is not an applicable
figure for simulation using eQuest.

SECOND
I'm struggling with these items because a recent GBCI reviewer has asked
me to re-calculate my fan power because my BHPs are a bit higher than
they should be. When I "re-calculate" these values I do not come up with
the numbers they do (BHP ASHRAE - attached).

I'm trying to reconcile my response and eQuest inputs before we
re-submit, but I'm not sure what to do.

Much thanks.

--
Matthew Higgins, LEED AP + ASHRAE-HBDP

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Nevermind, Vikram's email to Lars today has answered my question and
brought my KW/cfm, ACTUALLY BHP/cfm, within acceptable ranges and eased
my concerns.

Indirectly, Thanks

Matthew Higgins, LEED AP + ASHRAE-HBDP

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Hi to all:

I believe that the?kW/CFM is based on the Baseline BHP and Baseline Fan Power formula in ASHRAE 90.1-2004 G3.2.1.9.? The CFM is the total building CFM; see the air-side summary report for the total bulding CFM.?

To get the correct total building CFM, set the Baseline supply-air-to-room-air at a 20-degree F differential.? For instance, if your summer (cooling) set-point temp?= 75 degreesF, then the cooling supply air temp from the unit is 55-degree F.? If your winter (heating) set-point temp is 70-degree F, then your heating?supply air temp from the unit is 90-degree F.? Run a simulation and eQUEST will determine the CFM for each system based on this differential; then balance the systems to be?under the 300 unmet hours limit.? Then?open the air-side summary report to see?the total CFM of all your systems.? Use that total CFM in the BHP and Baseline Fan Power calculations under G3.2.1.9.? To use the formulas, you need to use a calculator with a "natural log" button and an "e" button for the energy constant (e=1.28....just like?"pie" = 3.14).

For a Baseline Type 3 PSZ System, the fan power should be in the neighborhood of 0.0007; this may be why GBCI questioned?your result.? Then assign this fan power to each baseline PSZ system in your building and re-run the simulation.? Include the formula in the LEED submittal template or narrative to demonstrate how its calculated; as well as including the Air-side Summary Report.? GBCI will see both the total baseline CFM and the baseline fan power calculations.

The Proposed conditions are the proposed set-points, proposed supply air temps, and proposed kW/CFM for each system as designed.? If the RTU fans run continuously during occupancy periods, separate the supply air fan power, which is the kW to use,?from the RTU power.? This allows design teams to take credit for using high efficient HVAC systems (low kW/CFM).

Hope this helps.

Ron Lamarre, AIA, NCARB
Architect - LEED AP

?

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Although this may be obvious I would like to add that the temperature set points should be the same in both design cases per Table G3.1.1b.

Best Regards,

Gregg Liddick, EIT, LEED(r) AP

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Ron, to comment on your statement, "I believe that the kW/CFM is based on the Baseline BHP and Baseline Fan Power formula in ASHRAE 90.1-2004 G3.2.1.9. The CFM is the total building CFM", 90.1-2007 makes it the most clear that the CFM is actually ONLY the Baseline's peak SUPPLY CFM. The same is true for 90.1-2004, it's just not very clear. However the reviewers do know that this is true and have most recently been asking for a demonstration of calculation methodology.

Regards,

Paul Erickson LEED AP

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