Hello:

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

EXHAUST-CFM"

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

Thanks,

Try setting the supply CFM to auto size.

Shane Newman, PE, LEED AP

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

Has anyone done any verification of the eQUEST 3.63 condensing boiler

curves?

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

where:

X = PLR

Y = RWT

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?

Thanks,

Dana

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

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

1/(HIR_curve*PLR).

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*