[Equest-users] Chiller Curves

[Nick Caton]

Hi Rob!

 

Well to start, let's not assume every chiller out there MUST be more
efficient than the default curve at every point.  Better to assume they
can and should differ.

 

With that disclaimer out of the way,  you have noted your coefficients
generated for your custom PLR curve should produce a lower correction
factor at 25% (confirmed in the Var 9 column you attached).  

 

What I think you're missing is that there is indeed more than one
correction factor being calculated every hour, and more than one curve
in play to produce those factors that you need to consider.  The extra
column you chose to include in your spreadsheet hints at this (Var 10).

 

Recommended DOE2 reading that should fill in these specific gaps for
you:  Volume 2: Dictionary > HVAC Components > CHILLER > Chiller Energy
Consumption

 

There much further discussion on this topic in the archives as well, if
you just can't get enough ;).

 

~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 

 

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Rob
Hudson
Sent: Wednesday, July 20, 2011 6:23 AM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Chiller Curves

 

I have a new Chiller Curve question/situation.  I have created a custom
chiller curve for the EIR = f(PLR) as a cubic function using the
following data inputs:

 

1         .3313

.75      .2437

.5        .2201

.25      .1928

 

>From my understanding, the chiller curve seems correct.  However, when i
create a hourly report summary for the Corrected Chiller EIR and compare
it to the default EIR equation for this entry, i get 0.034 for the
default and 0.072 for my curve at 25% ratio.  Why is it that the default
is better than my curve?  I have looked at the equation for the default
entry and got the following equations:

 

EIR = a + b x = c x^2

a = .04812248

b = .69573420

c = .23493889

 

at 25% this equation results in 0.2367, and my equation gets 0.1928

 

Is there any other calculations going on in the background that is
causing some problems?  I have attached an excel snapshot of the
different EIR and the corrected EIR values for two different chillers in
my program.  Neither is currently using the default EIR = f(PLR) curves,
they are using custom curves.

 

Thanks in advance,

-- 
Rob Hudson

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