[Equest-users] Pilotless DW Heaters

Nick Caton ncaton at smithboucher.com
Thu Jun 26 10:04:39 PDT 2014

Acknowledging pilot lights can be a significant deal... your reviewer might be right to question you on the matter.  We can all learn a thing or two however by exploring what these curves really mean:

[cid:image001.png at 01CF9132.11B3EBB0]

[cid:image005.png at 01CF9136.CE009580]

Above is an excel plot of the library curve you're referencing for a pilotless water heater (I don't know why, but the trendline equation on this chart is just trying to be hip/different... I assuredly used zero for the constant coefficient).

The X-axis is a multiplier against your entered heating input ration (HIR) for full load operation, plotted against the part load ratio (PLR) on the Y-axis.  Notice it's basically a straight line starting at zero and ending with 1.0 for both axes.  Pretty simply, as you approach zero part load, this curve effectively drops the energy consumption to zero (the "a" coefficient) in a linear fashion.

The gap I'm seeing in your phrasing is that this is apparently differentiated from "the standard curve."

I presume you are referencing the library curve DW-Gas-HIR-fPLR (you should be explicit in your explanation/response to the reviewer):

[cid:image008.png at 01CF9132.766AB250]
Without plotting the second curve, can you see the critical difference in the coefficients?

"a" is no longer zero.  When there is no hot water demand, this curve essentially calls for 2.1826% of the full load gas consumption (as determined via your HIR input and full load capacity, as input or auto-sized).  The curve is still essentially and equally linear to the pilotless curve (c is very close to 0.0).

If you wanted to modify this curve to match "actual" or "representative" equipment with a different percentage ("p"), all else being equal, the corresponding coefficients would be
a = p/100
c = 0.00054300 (maintaining the same curve shape of being nearly but note quite linear)
b = 1-a-c (resulting in a factor of 1 applied against your HIR at full output:  where x=1, Z = 1)

Where you may fall short is, I don't think there's a terribly solid case for asserting that the baseline model water heating equipment should reflect the inclusion of a pilot light.  A careful scanning of Chapter 7 in 90.1 reveals only a few instances where pilot lights are even mentioned, but none are in a prescriptive context.  There is the statement that the prescribed values in the equipment table do not apply if a few conditions are met (including no pilot light), which taken inversely suggests pilot lights may be (but are not necessarily) included in determining the prescribed performance ratings.  You might however find a solid case if you investigate the referenced testing standard appropriate to your baseline equipment type/capacity, if said standard establishes the inclusion of a pilot light.

If you can make such a solid case, please share it with the lists - this is a potentially valuable and useful strategy you've stumbled into =)!

In any case, I expect sticking to differing curves after your reviewer has called this into question will require documenting and explaining their differences in a clear fashion.  Perhaps my response will serve as a useful template for that cause ;).

Best of luck!

[cid:489575314 at 22072009-0ABB]


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

From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Singhal, Harshul
Sent: Thursday, June 26, 2014 9:33 AM
To: Matthew Goodwin; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Pilotless DW Heaters


As per this article, heaters without pilot should give more savings (ofcourse duh! to me). I am not sure if changing the curve also removes the "extra" energy that pilot needs.

Harshul Singhal
Project Consultant
Thornton Tomasetti
386 Fore Street, Suite 401
Portland, ME  04101
T 207.245.6060  F 207.245.6061
D 207.245.6074
HSinghal at ThorntonTomasetti.com<mailto:HSinghal at ThorntonTomasetti.com>
From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Matthew Goodwin
Sent: Thursday, June 26, 2014 10:22 AM
To: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: [Equest-users] Pilotless DW Heaters

I have a project which includes pilotless DW Heaters.  I used the "DW-Gas-Pilotless-HIR-fPLR" performance curve in order to mimic this but the savings compared to the standard curve are higher than I would have expected.  Does anyone have experience using this curve or know the basis of where/how eQUEST developed it?

Note-I'm using the energy model to calculate savings for LEED EAc1 and have received some pushback relating to that curve.


Matt Goodwin, CEM, CMVP, LEED(r) AP
Project Manager
[cid:5572060c-7b96-4281-936e-0636e44b1e21 at LILKER.COM]
        Lilker EMO
Energy Solutions
3130 Fairview Park Dr.
Suite 125
Falls Church, VA 22042
t.  703-205-0445 x151
c. 610-322-1823
f . 703-205-0449

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