Modulating furnace

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What is the appropriate way to model a gas furnace that modulates with a
16:1 turndown?

Thank you,

*Mike Campbell, E.I.T., LEED AP O+M*
*Sustainability Specialist*
*Sustainable Solutions Corporation*
Office: 610-569-1047

Mobile: 609-923-1743
www.SustainableSolutionsCorporation.com
*Sustainable Solutions Corporation is WBENC and BCorp Certified.*

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Under the boiler, set the min ratio = .06.

Brendan Hall, PE, LEED AP BD+C
Engineer, Mechanical
karpinski
ENGINEERING
3135 Euclid Avenue
Cleveland, OH 44115
P 216.391.3700 Ext 3111
E bhall at karpinskieng.com
W www.karpinskieng.com

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Thanks for the reply. However, to clarify, this is an AHU with gas furnace
heat, so there is no boiler.

*Mike Campbell, E.I.T., LEED AP O+M*
*Sustainability Specialist*
*Sustainable Solutions Corporation*
Office: 610-569-1047

Mobile: 609-923-1743
www.SustainableSolutionsCorporation.com
*Sustainable Solutions Corporation is WBENC and BCorp Certified.*

*This email message and any attachments are for the sole use of the
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*From:* Hall, Brendan [mailto:BHall at karpinskieng.com]
*Sent:* Wednesday, March 12, 2014 3:45 PM
*To:* Michael Campbell; equest-users at lists.onebuilding.org
*Subject:* RE: [Equest-users] Modulating furnace

Under the boiler, set the min ratio = .06.

Brendan Hall, PE, LEED AP BD+C

Engineer, Mechanical

karpinski
ENGINEERING
3135 Euclid Avenue
Cleveland, OH 44115
P 216.391.3700 Ext 3111
E *bhall at karpinskieng.com *
W *www.karpinskieng.com *

*From:* equest-users-bounces at lists.onebuilding.org [
mailto:equest-users-bounces at lists.onebuilding.org]
*On Behalf Of *Michael Campbell
*Sent:* Wednesday, March 12, 2014 3:41 PM
*To:* equest-users at lists.onebuilding.org
*Subject:* [Equest-users] Modulating furnace

What is the appropriate way to model a gas furnace that modulates with a
16:1 turndown?

Thank you,

*Mike Campbell, E.I.T., LEED AP O+M*
*Sustainability Specialist*
*Sustainable Solutions Corporation*
Office: 610-569-1047

Mobile: 609-923-1743
www.SustainableSolutionsCorporation.com
*Sustainable Solutions Corporation is WBENC and BCorp Certified.*

*This email message and any attachments are for the sole use of the
intended recipient(s) and may contain confidential and privileged
information. Any unauthorized review, use, disclosure or distribution is
prohibited. If you are not the intended recipient, please contact the
sender by reply email and destroy all copies of the original message and
any attachments.*

MikeSSC's picture
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Right, that is a bit trickier. I would say that it is going to be very infrequent that it would call for a load between 0 and 6%. The AHU fan can only go down so much so by the time it comes out of economizer you should have more than enough load to justify it running. I guess the question would be if you had something with a much lower turndown. The curve that modifies the HIR(PLR) is pretty much linear even though it is in cubic form so there is no variation in efficiency as you go down in capacity, but check that against your equipment info. Not a whole lot of options, but I'm sure that's why you asked in the first place.

Brendan Hall, PE, LEED AP BD+C
Engineer, Mechanical
karpinski
ENGINEERING
3135 Euclid Avenue
Cleveland, OH 44115
P 216.391.3700 Ext 3111
E bhall at karpinskieng.com
W www.karpinskieng.com

Hall, Brendan's picture
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I would also suggest to investigate/review/modify the system's library FURNACE-HIR-FPLR curve to fit actual performance. I'd have to plot it to visualize, but from there you could establish a curve fit that effectively forces your minimum turndown by raising HIR as you approach zero load - crunch the math in a spreadsheet, and remember this curve is normalized to the input HIR efficiency (at full load).
~Nick

[cid:489575314 at 22072009-0ABB]

NICK CATON, P.E.
SENIOR ENGINEER

Smith & Boucher Engineers
25501 west valley parkway, suite 200
olathe, ks 66061
direct 913.344.0036
fax 913.345.0617
www.smithboucher.com

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Michael,

You could create a custom efficiency curve for the burner using manufacturer
data - Engineered Air has an efficiency curve for its 15:1 turndown burner,
refer to the attached.

Alternatively in Canada, our EE4 software uses the following curve fit data
which could be used to create a custom curve for modulating burners; I'm not
sure where they got this from though.

MODCURVE = CURVE-FIT TYPE = QUADRATIC

DATA = (1,1) (0.9,0.901) (0.8,0.802)

(0.7,0.704) (0.6,0.605) (0.5,0.506)

(0.4,0.407) (0.3,0.308) (0.2,0.209)

(0.1,0.11) ..

Regards,

Aaron

Aaron Smith, P.Eng

M&R Engineering

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