[Equest-users] Chiller Part Load Curves

[Robby Oylear]

The outputs of the chiller-PLR curve is not actually an efficiency, but a
multiplier on the absolute energy use of the chiller.  As the PLR
decreases, the chiller will obviously use less energy, albeit less
efficiently.  Once you realize that the PLR curve is spitting out kW
numbers and not kW/ton, it should make more sense.  

 

Robby Oylear, LEEDR AP

Mechanical Engineer

direct: 206.788.4571

cell: 206.354.2721

www. <http://www.rushingco.com/> rushingco.com

 

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Todd
Lagus
Sent: Thursday, April 02, 2009 9:06 AM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Chiller Part Load Curves

 

Hello All,

 

I searched the archives and found some mention of chiller curves, but not
much dealing with this particular issue.  I understand the concept of the
three different ratios for the condenser water temperature, PLR and dT,
and capacity curve.  What concerns me is the part load curve.  I was doing
some investigation and put the DOE2 default coefficients into an excel
file (attached) for a water cooled, centrifugal hermetic chiller.  Only
changing the part load ratio, the kW/ton of the chiller decreases
dramatically,  which isn't correct. Logic tells me that decreasing the
condenser water temperature should increase efficiency, and decreasing the
part load ratio should decrease efficiency.  Am I missing something here?
Has anyone run into this issue or corrected it?

 

Todd Lagus, EIT

Mechanical Engineer

Sebesta Blomberg 
sebesta.com | P  651.634.7236 | F  651.634.7400

 

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