Modeling approach for baseline furnaces (regarding auxiliary or pilot light fuel)

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I recently discovered that in my Baseline model (System 3 PSZ-AC), under the PS-E and PS-F reports, that I was using fuel under "pumps & auxiliary" column in addition to fuel for space heating.

I discovered, after searching the boards, that this basically represents a constantly burning pilot light within the furnace.

To research this I went on the forums and it appears the consensus is to go into System "Heating/Unity Power" and change the default "800" Btu/h auxiliary fuel use input to "0" to remove pilot light fuel from all packaged single zone systems since the 2007 version of ASHRAE 90.1 (Table 6.8.1E) states:

"As of August 8, 2008, according to the Energy Policy Act of 2005, units must also include an interrupted or intermittent ignition device (IID), have jacket losses not exceeding 0.75% of the input rating, and have either power venting or a flue damper.  A vent damper is an acceptable alternative to a flue damper for those furnaces where combustion air is drawn from the conditioned space."

This basically implies, as others seem to agree, that constantly burning pilot lights are not allowed in the baseline model (in any baseline systems where warm air furnaces come into play).

However, intermittent or Interrupted ignition devices inevitablydouse electrical energy.  I havent yet searched through the latest version of ASHRAE 90.1 to see if they have changed the specs allowing a modeler to show electrical use by this "IID" at each PSZ system so I'm not sure what the current state of this is in terms of GBC or ASHRAE.

An example of an IID using energy would be this Honeywell unit.  Honeywell manufactures an IID that uses 120V input power with an ignition rating of 550 volt-amps.  It appears a 120V IID would run off of 7.4 Full load amps.

My point is basically that zeroing out the auxiliary inputs would amount to modeling an IID per ASHRAE 90.1 but without using any energy (which would be incorrect based on a real world scenario/thought experiment).  Especially where PSZ systems come into play.

In my view, the modeler should be allowed to specify a "furnace electric auxiliary" of a reasonable KW load (perhaps it should even be in ASHRAE 90.1 based on system capacities?).

The power usage obviously wouldn't be very much.  But considering a real-world baseline scenario where the IID would ignite the fuel anytime heat is called for by any PSZ system, this electrical use by the IID would compound and increase throughout the building over one model year and it would definately not be zero.  It would obviously be more energy efficient than a constantly-burning pilot light.  But that's not the point I'm making.

Does anyone know the current state of ASHRAE and whether or not baseline systems are allowed to show auxiliary electrical use to accurately model a warm air furnace with an electrical IID system (which I would assume would still be the standard for warm-air furnaces)?


Chris Baker2's picture
Joined: 2014-03-25
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