[Equest-users] Big Baseline Boilers - COMBUSTION efficiencies!?

[Jim Fowler]

I smile at this quandary (sorry
), having asked it myself, but not in the
context of eQuest
 I’ve rationalized that the combustion and thermal
efficiencies are identical when the boiler is in a conditioned space,
because the jacket losses heat the space.  I typically use a 1-2% downrate
of the combustion efficiency to get to thermal, if the boiler is in an
unconditioned space.

 

 

 

Jim Fowler, PE, CBCP, CEA

++206-954-3614

GEA logo cropped 

Audits and Commissioning of Industrial 

Municipal and Commercial Buildings

 <http://www.globalenergyaudits.com/> www.globalenergyaudits.com

 

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Nick Caton
Sent: Monday, April 29, 2013 7:55 AM
To: Busman, Michael R; equest-users at lists.onebuilding.org
Cc: The Watt Doctors - Dave Weigel (Dave.Weigel at thewattdoctors.com)
Subject: Re: [Equest-users] Big Baseline Boilers - COMBUSTION efficiencies!?

 

Mike – thanks a bunch for your response!  

 

I can appreciate and relate to your experience with the boiler industry
marketing folks
 it’s very easy to get the run-around, and is often
difficult/impossible to get information needed for modeling from product
literature.  I’ve come to the same conclusion as you advised, and here’s my
accounting/reasoning for those interested:

 

The footnote in 90.1 Table 6.8.1-F defines combustion efficiency as “100%
less flue losses,” so I that was the basis of this query.  There’s
additionally reference to this procedure: 10 CFR part 431
<http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&tpl=/ecfrbrowse/Title10/10cfr43
1_main_02.tpl> 

 

That procedure defines combustion and thermal efficiency as follows
<http://www.ecfr.gov/cgi-bin/text-idx?c=ecfr&SID=bceba9fa026032bc4b393f9c462
988bf&rgn=div8&view=text&node=10:3.0.1.4.19.5.54.2&idno=10> :

Combustion efficiency for a commercial packaged boiler is determined using
test procedures prescribed under § 431.86 and is equal to 100 percent minus
percent flue loss (percent flue loss is based on input fuel energy)

 

Thermal efficiency for a commercial packaged boiler is determined using test
procedures prescribed under § 431.86 and is the ratio of the heat absorbed
by the water or the water and steam to the higher heating value in the fuel
burned.

 

Clearly they’re not quite the same thing, where combustion efficiency does
not account for jacket/standby/other losses affecting net output.

 

I haven’t seen numbers to verify this, but perhaps ultimately jacket losses
are such a small fraction (at these largest capacities) that it’s accepted
to be irrelevant.  Put another way, the actual values for Et and Ec for
boilers larger than 2.5MBtuh/h just aren’t very different.  

 

Running with that assumption, and unless anyone can answer further to this,
I’ll treat baseline thermal and combustion efficiencies identically moving
forward for large boilers:  HIR = 1/Ec = 1/Et.  If nothing else, it’s a
“safe/conservative” approach for LEED, in the sense that if there is an
error of procedure here it is only artificially helping the baseline and
would in turn prove a beneficial correction for the performance rating down
the road.

 

Thanks again!

 

~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 

 

From: Busman, Michael R [mailto:MBusman at chevron.com] 
Sent: Friday, April 26, 2013 1:47 PM
To: Nick Caton; equest-users at lists.onebuilding.org
Subject: RE: Big Baseline Boilers - COMBUSTION efficiencies!?

 

Nick,

 

It has always been my understanding that combustion efficiency includes flue
losses as it is calculated based on CO2% or O2% in the stack gas and net
stack temperature (stack temp.-boiler room ambient temp entering the
burner).  The only other thing I can think of that would affect the thermal
efficiency or useful Btu’s output as steam or hot water/fuel Btu’s input
would be radiant and convective jacket losses from the boiler shell at 100%
firing rate.  Although manufacturers are reluctant to publish data on jacket
losses, they could typically range from about 1%-4% based on the design and
mfg.  This will be a fixed quantity of Btu’s no matter what the firing rate
is, so this loss as a % of boiler load increases as % load decreases.

 

As an example, look at an Ajax or Rite Boiler.  They look pretty similar and
are both manufactured within a fairly close proximity of each other.  The
front and back ends have uninsulated steel head plates about 1” thick to
gain access to the tube bundle.  Below the head plates are uninsulated thin
sheet metal panels to gain access to the burners.  With the boilers firing,
I’ve measured temperatures of the upper plates in the 200-300 deg. range and
the lower sheet metal panels in the area of 450 deg.  This is kind of an
extreme scenario, but the jacket losses are probably a significant number
even though the rated or measured combustion efficiency might be 82%.

 

The other piece of the puzzle when it comes to seasonal boiler efficiency I
don’t know how DOE-2 handles would be cycling losses.  If you take that Rite
or Ajax boiler equipped with an atmospheric burner, the seasonal efficiency
could easily approach 50%.  During every off cycle, boiler room air will
flow up through the boiler cooling the firebrick and mass of the boiler.
The next firing cycling, those draft cooling losses need to be replaced by
additional Btu’s.  A cycling boiler with a power burner could also have a
low seasonal efficiency as the result of cooling losses from pre-purge and
post-purge operation to get rid of unburned fuel.

 

I don’t know if that helps or confuses the matter.  After that long
dissertation, I would suggest using the rated combustion efficiency.

 

My best,

 

Mike Busman

 

 

Michael R. Busman, CEM

Lead Project Engineer II

 

Chevron Energy Solutions

A Division of Chevron U.S.A., Inc.

145 S. State College Blvd.

Brea, CA  92821 

Direct  714-671-3561

Fax     714-671-3438

eFax   866-420-0335 (Include my Full Name followed by "CAI:MHTZ" on Cover
Sheet)

Mobile 310-387-2083

mbusman at chevron.com

 

 

 

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Nick Caton
Sent: Friday, April 26, 2013 10:55 AM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Big Baseline Boilers - COMBUSTION efficiencies!?

 

Hi everyone!

 

90.1-2007 Table 6.8.1F for boilers prescribes a minimum combustion
efficiency (EC) of 82% for gas boilers larger than 2.5MBtu/h.  This is the
burner’s efficiency before flue losses.  

 

The same boiler’s thermal efficiency, inclusive of flue losses, would be a
lesser figure.

 

When modeling such boilers for an Appendix G baseline, what is actually
appropriate to enter for the boiler’s HIR input?    As I understand it, this
HIR input in eQuest is the inverse of thermal efficiency (net input vs. net
output), and would be inclusive of flue losses.

 

This is for a LEED project, so I’d like to cite something solid to
demonstrate what thermal efficiency is appropriate to assume for a baseline
boiler of this size.  Has anyone gone down this path before?

 

Thanks!

 

~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 

 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20130429/ef1fff91/attachment-0001.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: image/jpeg
Size: 3191 bytes
Desc: not available
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20130429/ef1fff91/attachment-0004.jpeg>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: image/jpeg
Size: 1459 bytes
Desc: not available
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20130429/ef1fff91/attachment-0005.jpeg>