[Equest-users] Default Performance Curves

[Clifford McDonald]

Thanks for the help on this, but I'm still confused. Are you saying the form
of the equation is:

PLR = (PLR * (EIRcurrent / EIRfull) ) + (PLR * (EIRcurrent / EIRfull) )^2

?  Then, if the equipment has constant efficiency across the full load
range, the EIR/EIR term is one, and you get:

PLR = PLR + PLR^2, which doesn't make sense.

If the form is just:

PLR = PLR [ (EIR / EIR) + (EIR / EIR)^2, then this would mean that the
efficiency has to be constant (divide by PLR on both sides).

What am I missing here?


2010/10/13 Erik Kolderup <erik at kolderupconsulting.com>

>  The DOE2 EIR-FPLR curves include PLR in the value. In other words, you
> might expect the value of the curve to be (EIR at current load)/(EIR at full
> load), but it’s actually PLR*(EIR at current load)/(EIR at full load). So if
> you have a piece of equipment that has constant efficiency across the full
> load range, then the curve will be a straight line between (0,0) and (1,1).
> You have to look pretty closely at the background docs, such as the DOE2.1A
> Engineer’s Manual, to see that.
>
>
>
> -Erik
>
>
>
> *Erik Kolderup, PE, LEED AP*
>
> Kolderup Consulting | 415.531.5198 | erik at kolderupconsulting.com
>
>
>
>
>
>
>
> *From:* James Hansen [mailto:JHANSEN at ghtltd.com]
> *Sent:* Wednesday, October 13, 2010 1:50 PM
> *To:* Clifford McDonald; equest-users at lists.onebuilding.org
> *Subject:* Re: [Equest-users] Default Performance Curves
>
>
>
> Someone will be able to explain this better than me, but eQuest curves are
> not intuitive.  I wish they were, but they aren’t.
>
>
>
> As an example:  when you enter a chiller EIR curve as a function of PLR,
> you would think this would be really easy, right?  0.1, 0.2, 0.3 etc as the
> PLR, and then the corresponding EIR (KW consumed vs current tonnage).  But
> that’s not the case….you end up basically having to square the EIR to get
> proper outputs.  Perhaps the same thing needs to be done here?
>
>
>
> Again, someone will chime in with the real reasoning for this, as I’ve seen
> it discussed before.
>
>
>
> *GHT Limited
> **James Hansen**, PE, LEED AP*
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> *From:* equest-users-bounces at lists.onebuilding.org [mailto:
> equest-users-bounces at lists.onebuilding.org] *On Behalf Of *Clifford
> McDonald
> *Sent:* Wednesday, October 13, 2010 4:29 PM
> *To:* equest-users at lists.onebuilding.org
> *Subject:* [Equest-users] Default Performance Curves
>
>
>
> Hello,
>
>
>
> I'm fairly new to eQuest, but I was looking at the default performance
> curves for VSDs on fans and pumps (EIR as a function of PLR), and with the
> exception of the cooling tower fan (htrej-Fan-Pwr-fSpeed) which is a cubic
> equation, they are all quadratic equations.  Why would this be when, in
> theory, energy use should vary with the cube of motor speed with a VSD?  Why
> would it be quadratic for supply fans and chilled water pumps but cubic for
> cooling tower fans?  Is there anywhere I can go to get more information on
> these default values?
>
>
>
> Thanks for the help...
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