[BLDG-SIM] Major disagreement on Chiller Performance Curves in DOE-2.1E and DOE-2.2

Unfortunately, the ARI data for performance at partial loads is not useful in an hourly simulation program, precisely because it makes an assumption about reduced condenser temperature at reduced load. The assumptions in the ARI curve might be reasonable for a single chiller in a given building and climate, and where you allow the condenser temperature to drop with load and wetbulb. However, many plants have more than one chiller, the cooling tower(s) may be controlled to a fixed condenser temperature, and/or you might be running the chiller in Florida vs. New Mexico, which have very different load/wetbulb relationships.

It would be useful if ARI recognized these issues, and developed a standard method for reporting chiller performance for use in hourly simulation programs (the same problem also applies to packaged rooftop equipment).

Note that "standard" ratings assume the evaporator is operating at 44F leaving temperature and 2.4 gpm/ton, and the condenser is operating at 85F entering and 3.0 gpm/ton. However a centrifugal chiller is custom built to the engineer's specifications. A chiller in a low-wetbulb climate may be configured to run with 75F entering condenser water, and will surge if operated at 44F/85F. In other words, many centrifigal chillers cannot operate at the "standard" conditions!

The default curves in recent versions of 2.2 are based on a manufacturer's proprietary data. They are an improvement over the 2.1e curves, but do not necessarily represent all chillers and all manufacturers.

DOE-2 uses three curves to model chiller performance. The use of these curves is documented in the Topics manual. More recent versions of 2.2 modify performance for off-rated condenser flow. In addition, the PLR curve includes a second term (PLR,dT) to model the condenser relief necessary to achieve savings with a variable-speed drive.

----- Original Message -----

From: Aulbach, John

To: BLDG-SIM@xxxxxxxx

Sent: Wednesday, October 15, 2003 11:23 AM

Subject: [BLDG-SIM] Major disagreement on Chiller Performance Curves in DOE-2.1E and DOE-2.2

I am having a "friendly" disagreement with a colleague on what chiller curves to ask for from a manufacturer to input into DOE-2 (could be either 2.1E or 2.2). We both agree that the infamous ARI point for a 100% load should be input. But the curves are where we disagree.

Is the Default DOE-2 curve for % Power versus % Tons the ARI curve with the allowable reduction in condenser water temperature, or is it based on the FIXED 85°F entering condenser water and FIXED 44°F leaving chilled water ALL the way down the curve?

Therefore, when I am given a chiller with a variable speed drive installed, what parameters should I ask for in such a Power/Tons to be FIXED ???

John R. Aulbach, PE, CEM
Project Engineer
Sempra Energy Solutions
555 West Fifth Street
Mail Location 27F3
Los Angeles, CA 90013
Tel: (213) 244-8551 Cell (213) 219-4875

"Sempra Energy Solutions is not the same company as SDG&E/ SoCalGas, the Utilities. Sempra Energy Solutions is not regulated by the California Public Utilities Commission, and you do not have to buy Sempra Energy Solutions products or services to continue to receive quality regulated service from the Utilities."
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