Chiller Part Load Curves

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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

Todd Lagus's picture
Joined: 2011-09-30
Reputation: 0

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

RobbyO's picture
Joined: 2010-11-03
Reputation: 0