[Equest-users] Condensing Boiler HIR

[Bishop, Bill]

Steve,

To model a condensing boiler that is 96% efficient at 100% fire and 80°F return water temperature, enter "1.042" (=1/0.96) for the HIR if you use the default curve.

For condensing boilers, the HIR-fPLR curve modifies fuel consumption based on boiler part-load ratio and return water temperature (HWR). For boilers, I believe the hourly part-load ratio is simply the hourly load divided by the design boiler capacity.
The default performance curve for high efficiency condensing boilers is "CondBlr-HiEff-HIR-fPLR&HWR". The data points for this curve are shown below:

[cid:image002.jpg at 01CE91D0.4CAAF360]

The Indep-1 (X) values are part-load ratio, and the Indep-2 (Y) values are HWR (°F). Depend (Z) is the multiplier of HIR. Data point 1 is for PLR=1.0 (100% fire) and 80°F HWR, and the output for this point is "1.000", meaning no adjustment is made to the entered value for HIR. Therefore, the value you enter for HIR should be for 100% fire and 80°F. Your manufacturer data show 96% efficiency at this point, so you would enter 1.042 for your HIR.

The other manufacturer data point you mention is 86.5% efficiency at 100% fire and 160°F. That corresponds with Data Point 17 in the default curve, with an output (HIR multiplier) of 1.121. If you enter HIR=1.042, the hourly HIR will be 1.121x1.042=1.168. And 1/1.168=85.6%. This is close, though slightly less, than the manufacturer data. So the default HIR-fPLR curve does not perfectly match your boiler, but you may decide it is close enough. Alternatively, you could create your own curve, and share it with me. ;)

BTW, sorry for the delayed reply. Better late than never.

Regards,
Bill

William Bishop, PE, BEMP, BEAP, LEED AP | Pathfinder Engineers & Architects LLP
Senior Energy Engineer

134 South Fitzhugh Street                 Rochester, NY 14608
T: (585) 325-6004 Ext. 114            F: (585) 325-6005
bbishop at pathfinder-ea.com<mailto:wbishop at pathfinder-ea.com>           www.pathfinder-ea.com<http://www.pathfinder-ea.com/>
P   Sustainability - the forest AND the trees. P

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Steve Tobin
Sent: Friday, December 23, 2011 2:45 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Condensing Boiler HIR


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All,
I am trying to settle a dispute within our office.

Our design utilizes Fulton Condensing Boilers with a design Return water temperature of 160 deg. F and an outdoor air reset schedule.
Our dispute is what to enter as the HIR for the boiler.  The boiler is 86.5% efficient at 100% fire and 160 deg. F return water temperature, and 96% efficient at 100% fire and 80 deg F.

It is my understanding from everything I have read that the HIR needs to be 1.156 which would be 86.5% efficient.  Is this correct?  Also how does the default e-quest HIR-fPLR curve function?
Thanks for any help.

[Description: cid:image001.jpg at 01CCA5C8.288E04E0]
Steven C. Tobin Jr., P.E.
PROJECT ENGINEER
25501 west valley parkway
olathe ks 66061
direct 913 344.0061
fax 913 345.0617

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