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???: "Nicholas Caton"
????: 2015?05?24? 21:53:33
???: "???"<503271081 at qq.com>;"Julien Marrec";
??: "equest-users at lists.onebuilding";
??: RE: [Equest-users] Reply? The problem of minimum equipment efficiency requirement of Ashrae 90.1-2007

I received some similar review language very recently suggesting 80% efficiency is expected at all/most part load conditions for the baseline boiler?.  Similar context in that case with the boiler rarely operating near full load.

My comment has other issues that would cloud the topic at-hand, but here is  truncated version:

??Furthermore, the average boiler efficiencies in the Baseline PS-C output reports, calculated by dividing the boiler energy consumption by the annual boiler heating energy generated was? [approximately 5% lower than the nominal efficiency input & documented].  Revise the baseline boiler efficiency to 80% and revise the boiler curve for the Baseline case as necessary to have an average efficiency that is near 80%. Provide updated PS-C reports for the Baseline confirming that the average baseline efficiency is near 80%.?

This is the first time I have run into commentary checking up on PS-C?s output at all, and I?m using the same library curves as always for typical baseline boilers.  

I believe the PS-C discrepancy is explained both by the non-flat library curve and by the boiler?s default start-up loads, in combination.

Here is the default library curve ? it is (roughly, but not quite) linear:

[For those unfamiliar, the Y-axis is a unitless multiplier]

If I?m not mistaken, this curve serves double-duty:  it simultaneously applies the hourly PLR to the full capacity (as either input or auto-sized) and also accounts for increased HIR (lower efficiency) as the PLR drops.  My understanding in equation form:

Energy Consumed (for the hour) = (Boiler full capacity as input/autosized) * (Boiler nominal HIR input @ full load) * HIRf(PLR)

If all of that is true, a perfectly ?flat efficiency? curve, returning your nominal input HIR at all efficiencies, would therefore be Z = X.  That?s plotted above for reference with a light/thin line. 

Even with such a ?flat efficiency? curve applied to a test-case, PS-C?s outputs still suggest an annual equivalent HIR higher than the nominal input.  Zeroing out the startup/standby inputs as well is required to get PS-C to report your nominal HIR = annual fuel / annual load:

I think the correct response (which perhaps I?ve mostly composed above) is to demonstrate the causes (library curve shape, startup/standby defaults), and to assert these are all appropriately applied to the baseline boiler, though none of this is regulated by 90.1 to the best of my knowledge so it might be relatively shaky territory.  

I would wager 90% of all eQuest baseline boilers submitted to GBCI to date probably don?t mess with the library curves or standby/startup inputs, but that?s pure speculation on my part.

Has anybody ever tried to explain/justify the default boiler curve and default startup/standby inputs?  Do we know where those defaults come from?

~Nick

NICK CATON, P.E.
Owner

Caton Energy Consulting
  1150 N. 192nd St., #4-202

  Shoreline, WA 98133
  office:  785.410.3317

www.catonenergy.com