[Equest-users] Condensing Boiler Curves

[Robby Oylear]

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
Mechanical Engineer
direct: 206.788.4571
cell: 206.354.2721
www.rushingco.com


-----Original Message-----
From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Dana Troy
Sent: Monday, October 19, 2009 4:35 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Condensing Boiler Curves

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