Here are the general calculations. These are not all of them so refer to the Eng. Ref. for other information.
You have an available full-load chiller capacity:
! Available chiller capacity as a function of temperature
AvailChillerCap = ChillerRefCap*CapFTemp
Then you can calculate a part-load ratio:
PartLoadRat = MAX(0.0d0, MIN(ActualLoad/AvailChillerCap,MaxPartLoadRat))
Then you know what the evaporator heat transfer is:
QEvaporator = AvailChillerCap * PartLoadRat
Then you can calculate power:
Power = (AvailChillerCap/ReferenceCOP) * EIRFPLR * EIRFTemp
Then you can calculate operating COP:
COP = QEvaporator/Power
As for your shortcut derivation of operating COP, I'll let you work that out from Hydeman's paper or the Eng. Ref. But just so you know what each performance curve derivation is, here they are:
DesignCOP = Qref / Pref
CapFT = Q / Qref
EIRFTemp = P / Q / Pref / Qref = P / (Pref * CAPFT), and
EIRFPLR = P / (Pref * CAPFT * EIRFT)
The EIRFPLR term in the EIR chiller is a little tricky and the actual performance curve used in the simulation needs to be derived correctly. I would check the curves used even if you found them in the example files. I believe they are correct, but as you can see, this curve is particularly tricky.
On 6/1/2011 1:37 PM, wenzelm75513 wrote:
I am using an energy plus model with a chiller using the reformulated EIR model. Results are outputted on a minutely basis. I am trying to reproduce some of the calculations because it is not behaving as expected. The model has three functions:
EIRFPLR = EIR as a function of part load ratio
EIRFTemp = EIR as a function of the cond, chilled water temperatures leaving the chiller.
CapFTemp = Capacity as a function of part load ratio.
I am tracking these three function outputs as well as the COP minutely with outputs. I have varified the three above function outputs and get them to match. (Although energy plus does not used the adjusted capacity when calculating the PLR that is input to the EIRFPLR function. I have seen it the other way in literature as well, but the difference is fairly small).
My questions is "Given that we have EIRFPLR EIRFTemp and CapFTemp how should one calculate the chiller COP?"
Based on my understanding of the Reformulated EIR calculation the correct calculation should be...
(Design COP)/(EIRFTemp * EIRFPLR)
I do not get this result in energy plus. I am off by more that just a multiplicative factor as I have tested a couple points and the diffence (or ratio) of the expected based on the above equation and the energy plus results changes. They differ by more than 100% A COP of 2.3 offered by energy plus and a COP of 5.8 per the calculations.
Any information about this calculation in energy plus would be appreciated.
Michael
-- Richard A. Raustad Senior Research Engineer Florida Solar Energy Center University of Central Florida 1679 Clearlake Road Cocoa, FL 32922-5703 Phone: (321) 638-1454 Fax: (321) 638-1439 or 1010 Visit our web site at: http://www.fsec.ucf.edu UCF - From Promise to Prominence: Celebrating 40 Years
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