Furnace AFUE, Et, HIR and furnace fuel auxiliary

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When selecting "furnace" for the heat source, eQUEST adds 800 Btu/h for
furnace fuel auxiliary (pilot light) as default. The default 800 Btu/h
adds 12% to my baseline heating energy, so it is not trivial.

ASHRAE Standard 90.1, Table 6.8.1E lists minimum furnace efficiency
requirements.

What should I enter for Furnace HIR and Furnace Fuel Auxiliary for
Baseline System 3 (PSZ-AC) and the new 90.1-2010 Baseline System 9
(Heating & Ventilation; Warm-air furnace, gas-fired)?

First, which equipment type applies? Table 6.8.1E has three gas-fired
equipment types - Warm Air Furnace, Warm Air Duct Furnace, and Warm Air
Unit Heaters. I think both Systems 3 and 9 would be Warm Air Furnace,
since packaged (System 3) and ventilation (System 9) systems would seem
to preclude duct furnaces and unit heaters.

Second, does the note, "Units must also include an interrupted or
intermittent ignition device (IID)" mean that no pilot light should be
modeled? This note to Table 6.8.1E does not apply to Warm Air Furnaces
<225,000 Btu/h in 90.1-2004 or 90.1-2007, but applies to all Warm Air
Furnaces in 90.1-2010. This is a LEED 2.2 project but the building is
currently under construction.

Third, Warm Air Furnace minimum efficiency is 78% AFUE or 80% Et .
Should I use HIR=1.282 (78%) or HIR=1.25?

Thanks for your thoughts,

Bill

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Bruce Easterbrook's picture
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Thanks Bruce.

I appreciate your insight on the reasonable range of furnace
efficiencies. I was more concerned with how to model the baseline per
minimum ASHRAE efficiencies. Using my question numbering, I'm going with
these answers:

1.) Warm Air Furnace

2.) No pilot light

3.) HIR=1.25

Bill

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Hi Bill,

I agree with your conclusions but got curious about boilers and pilot lights
and their usage. I have to admit to being fairly ignorant when it comes to
gas using equipment. So I did what I usually do and Googled *energy use of a
pilot light* and came across this nice little website:
http://energyexperts.org/EnergySolutionsDatabase/ResourceDetail.aspx?id=4407
that had a link to a nice little calculator that can be used to calculate
pilot light energy use:
http://www.wisconsinpublicservice.com/home/gas_calculator.aspx
When you are in the calculator there is "more info" next to the furnace line
and it includes the following information "natural gas furnaces and boilers
have been required to have pilotless ignitions since 1980". That would mean
that the eQUEST default should be modified to be 0, right?

Carol

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Carol,

I'll defer to Bruce's expertise on furnaces. Between his comments below,
and the note in 90.1, Table 6.8.1E that I quoted below (in my second
question), it would appear that we should use 0 as the default eQUEST
value for Furnace Fuel Auxiliary. You can still enter a non-zero value
if modeling an old furnace, using your pilot light calculator to show
savings as an ECM. Now Google "energy use of air conditioner crankcase
heater" and help me figure out the eQUEST default for CRANKCASE-HEAT. ;)

Bill

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Bruce Easterbrook's picture
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Yes and the quote from the calculator "furnaces & boilers after 1980 are to
not have pilot lights" backs it up. So we all agree. I'll get right on those
crankcase heaters for you.....

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Hi all,

The advice to invert the efficiency and zero out the pilot light is solid and something I've put into practice before as well... if anyone was still on the fence =).

If anyone's interested, on a related note I've got a top-secret baseline system calculator project... one of those pet projects I'm sure many of us have undertaken...? It's not complete yet (and likely will be ready to go as soon as 90.1-2010 makes it obsolete), but I along the way I have dug up and kept reference of a good resource for turning AFUE ratings into HIR inputs:

HIR = f(AFUE):? [Reference: California Energy Commission's 2005 "Nonresidential Alternative Calculation Method (ACM) Approval Manual"]

For single packaged central furnace (baseline system #3):? HIR = (.005163*AFUE+0.4033)^-1

For Boilers where 75 ? AFUE < 80 (Baseline systems #1, #5 ): HIR = (0.1*AFUE+72.5)^-1*100

For Boilers where 80 ? AFUE < 100 (Baseline systems #1, #5 ): HIR = (0.875*AFUE+10.5)^-1*100

~Nick

NICK CATON, P.E.

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