SUPPLY-CFM smaller than the total specified ZONE EXHAUST-CFM ERROR

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Iam trying to simulate a Lab building with VAV system, Exchaut Fans and
100% OA and getting the ERROR Message:

"has a specified SUPPLY-CFM smaller than the total specified ZONE

I am specifying the same suppley cfm for exhaust cfm for each zone.


shahram at's picture
Joined: 2011-09-30
Reputation: 0

Try setting the supply CFM to auto size.

Shane Newman, PE, LEED AP

Shane Newman's picture
Joined: 2011-09-30
Reputation: 0

Im assuming its because the supply flow is not constant. When the zones airflow cuts back you have a higher exhaust flow.

Charles Land's picture
Joined: 2011-09-30
Reputation: 0

Has anyone done any verification of the eQUEST 3.63 condensing boiler

The performance curve specifies the HIR being dependent on the part load
and the return water temperature with a formula as such:

Z = a + bX + cX^2 + dY + eY^2 +fXY


a = -0.09439243
b = 0.90319633
c = 0.01547839
d = 0.00159793
e = -0.00000645
f = 0.00111453

Since the default curve for a standard boiler seems to be a multiplier
on the EFFICIENCY, which is 1 / HIR, and not the HIR itself, I am
assuming that this curve also modifies the efficiency.

Pulling this formula and coefficient into Excel produces some graphs
that do not resemble at all what a condensing boiler efficiency graph
looks like at all.

For example, the AERCO Benchmark 3.0 looks like the first picture in the
attachment, while the eQUEST default looks like the second picture in
the attachment.

Am I looking at the eQUEST curve wrong in some way? Is it not using the
formula as it says it does in the help file?


Dana Troy's picture
Joined: 2011-09-30
Reputation: 0

Yes, you're looking at this incorrectly. eQUEST performance curves do not
deal with efficiency, but rather energy use. The output of eQUEST
performance curves is a multiplier which is multiplied directly with the
energy use the equipment would consume at full load.

For example, eQUEST calculates boiler energy use as follows:

Boiler Energy Use = Full Load Capacity x HIR x HIRfPLR

Where HIRfPLR = Z in your e-mail below.

Robby Oylear, LEED??AP

RobbyO's picture
Joined: 2010-11-03
Reputation: 0

Hi Dana,
I've also checked the condenser boiler curve in eQuest.
FIrst of all you have to take into account that the ratio of efficiency
at part load to nominal efficiency is not 1/HIR_curve, but
This will bring the curves closer to what you expect.
Besides, you have to input the return water temperature in ?F (Y-value).

However, the part load efficiencies that come out from this curve are
well below the ones of condensing boilers used in europe. In fact, as
RWT increases, the curve produces even worst part load efficiencies than
the ones of low temperture boilers.

*Xavier Garc?a Casals*

Xavier Garcia Casals's picture
Joined: 2011-09-30
Reputation: 0