[Equest-users] How to set the COP of a chiller as constant in eQuest?

[Esmireta]

Dear Nick,
Thanks for your patient instruction!
I now know how to set the COP of a chiller. But I also have two quesions:
1 where to find the meaning of these parameters of the curve? Are them in the DOE help?
2 How to verify that the COP is set as constant from the simulation output file of eQuest?
Thanks!
Esmi






At 2013-04-18 08:34:50,"Nick Caton" <ncaton at smithboucher.com> wrote:


Absolutely, and thanks for correcting me guys! 

 

All: Apologies for just throwing the concept out there without thinking it through totally.  Here’s a fresh shot at the procedure with a more complete explanation, to make amends and reinforce the lesson for myself.  I’m wide open for corrections if I’ve missed something =):

 

The typical function for determining a chiller’s hourly energy consumption is:

Elechour = Caphour * EIR * EIRf(t1,t2) * EIRf(PLR,dT) / 3413 Btu/Kw

 

Erik’s direction, setting only the ‘b’ coefficient to 1.0 and the rest to zero, turns EIRf(PLR,dT) into a linear curve that will very simply return the PLR.  This reduces the formula to:

Elechour = Caphour * EIR * EIRf(t1,t2) * PLR / 3413 Btu/kW

 

Following my original direction for coefficients, setting only ‘a’ to 1.0 and the rest to zero, will turn EIRf(t1,t2) into a curve that will always return 1.0.  This reduces the formula to:

Elechour = Caphour * EIR * 1.0 * PLR / 3413 Btu/kW

 

By their respective definitions in this context (see DOE2 entry below), (Caphour * PLR) equals the Hourly Load, in Btuh.  The formula is therefore reduced to:

Elechour = “The Hourly Load (Btuh)” * EIR * / 3413 Btu/kW

 

So now we are finally utilizing the input EIR every hour, as intended!  Interesting to note, one need not even touch the CAPf(t1,t2) curve as its effects are canceled out along the way.

 

~Nick

 

PS: …If all this is looking foreign, here’s the DOE2 help entry I’m starting from:

 

 

 

NICK CATON, P.E.

SENIOR ENGINEER

 

Smith & Boucher Engineers

25501 west valley parkway, suite 200

olathe, ks 66061

direct 913.344.0036

fax 913.345.0617

www.smithboucher.com

 

From:equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Joe Huang
Sent: Wednesday, April 17, 2013 6:56 PM
To:equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] How to set the COP of a chiller as constant in eQuest?

 

Erik,

You're right.  It should be a straight diagonal line from 0,0 to 1,1.

Joe



Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 108D
Moraga CA 94556
yjhuang at whiteboxtechnologies.com
www.whiteboxtechnologies.com
(o) (925)388-0265
(c) (510)928-2683
"building energy simulations at your fingertips"


On 4/17/2013 3:43 PM, Erik Kolderup wrote:

Nick,

 

One point of correction regarding curves to provide constant COP... I'm pretty sure you do not want the EIR-FPLR curve to be constant 1.0. The value of that curve is actually (normalized EIR)*(part load ratio). So if you want constant EIR, then the curve should just equal PLR. That's a straight line between (0,0) and (1,1). So the "a" coefficient should be zero and the "b" coefficient should be 1.0. All other coefficients for that curve should be zero. 

 

-Erik




Erik Kolderup, PE, LEED AP

erik at kolderupconsulting.com | 415.531.5198 | www.kolderupconsulting.com 

 

---------- Forwarded message ----------
From: Nick Caton <ncaton at smithboucher.com>
To: Joe Huang <yjhuang at whiteboxtechnologies.com>, Esmireta <e2fye2 at 163.com>
Cc: "equest-users at lists.onebuilding.org" <equest-users at lists.onebuilding.org>
Date: Wed, 17 Apr 2013 19:40:31 +0000
Subject: Re: [Equest-users] How to set the COP of a chiller as constant in eQuest?

After identifying the curves in play per Joe’s suggestion, you could achieve a constant COP, independent of part load or other variables, by making a set of custom curves (of appropriate/acceptable type) using coefficient inputs. 

 

Example from the library:

 

CentH2O-EIR-fPLR&dT looks like this from the library before modification.  This curve works alongside others to determine how to modify the input EIR for a chiller:

 

What we want is for this and all the other curves to return a value of 1.0, whatever the hourly variables throw at it.  Simply enter all coefficients preceding a variable (b,c,d,e,f) to 0.  Set the coefficient for the curve’s constant (a) at 1.0:

 

 

Doing the same for all associated curves (again, read up in the help/documentation for your particular equipment to be sure), at all hours the chiller in question will operate at the specified EIR without variance.

 

~Nick

 

 

NICK CATON, P.E.

SENIOR ENGINEER

 

Smith & Boucher Engineers

25501 west valley parkway, suite 200

olathe, ks 66061

direct 913.344.0036

fax 913.345.0617

www.smithboucher.com

 

 

 

 
 
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