Hi All,

I ran a quick test by creating a simple model with a condensing boiler. I
set the efficiency to 92% at 80?F return temp. Then I used the default
eQUEST condensing boiler curve to manually calculate the boiler?s
efficiency at 140F:

92% (rated eff) / 1.079 (curve output at 140?F and 100% PLR, see line 13 in
Bill?s screenshot of the curve below) = 85%

I then entered this efficiency as a parametric run, also changing the
RATED-HWR-T keyword to 140 F. Theoretically, this should have no effect on
gas usage, since we?re defining the same exact boiler in both cases.

The results: the annual heating usage changed by 10 Therms (out of ~8,000
total). This difference is a fraction of one percent and can be attributed
to rounding error.

My conclusion is that it?s OK to enter the efficiency of condensing boilers
at any return temperature as long as you coordinate this with the curve
you?re using and the RATED-HWR-T keyword.

Mike Karpman

*From:* equest-users-bounces at lists.onebuilding.org [mailto:
equest-users-bounces at lists.onebuilding.org] *On Behalf Of *Bishop, Bill
*Sent:* Wednesday, September 11, 2013 5:17 PM
*To:* equest-users at lists.onebuilding.org
*Subject:* [Equest-users] eQUEST condensing boilers RATED-HWR-T

Has anyone tried verifying that the RATED-HWR-T keyword modifies the hourly
boiler HIR appropriately?

[image: cid:image005.jpg at 01CEAF0F.767C2220]

The default eQUEST condensing boiler curve is normalized at 80?F and 100%
fire (1.0 PLR):

The DOE-2 documentation says that RATED-HWR-T is the temperature at which
the efficiency and capacity is defined. So I guess eQUEST takes this into
account when applying the performance curve.

Has anyone tried to verify this by entering the appropriate combinations of
capacity, HIR and HWR-T for two or more runs and comparing the results?

As Obama said, ?to paraphrase Ronald Reagan, we don?t just *trust* but also
*verify*?.

Thanks,

Bill

*William Bishop, PE, BEMP, BEAP, LEED AP *