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# Questions about chiller performance curves and chiller setting.

Hi everyone, here are my specification of chillers that I simulate in EnergyPlus,

I choose Chiller:Electric:EIR as build of CHU-1~2.

But I only can choose Chiller:Electric:Reformulated EIR as build of BHU-1~2, because of my evaporator fliud temperatue is below 0℃.When I use Chiller:Electric and Chiller:Electric:EIR to simulate BHU-1~2 it will show error about my evaprator fluid temperature.

Can anyone tell me why? That's my first question.

My second question is about chiller performance curves.

From documentation [EngineeringReference], the topic of Electric ChillerModel Based on Condenser Entering Temperature says there are three curves to determine chiller operation at off-reference conditions.

1) Cooling Capacity Function of Temperature Curve

2) Energy Input to Cooling Output Ratio Function of Temperature Curve

3) Energy Input to Cooling Output Ratio Function of Part Load Ratio Curve

The equation of curve 1 and 2 are same, how come the coefficients are different?

(From DataSet\Chillers.idf)

It also showed in Commercial Buildings Energy Modeling Guidelines & Procedures (MGP) chapter 6.8.2 CHILLERS link text

I have the same question about different coefficients problem in Electric ChillerModel Based on Condenser Leaving Temperature in [EngineeringReference].

If there is any response, then I would be very grateful.

Sincerely, Yueh-Chin

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For your first question, can you post the error you're seeing? Are you creating a user defined fluid and setting that as the working fluid for the loop? I suspect that you aren't and the error is because you're freezing the water. The change from ...:EIR to ...:ReformulatedEIR is just whether the performance is based off the entering or leaving condenser fluid temperature.

( 2016-06-07 09:17:18 -0500 )edit

I may forgot to change fluid type when I simulate last time, I will go check again, thanks to your answer!

( 2016-06-08 03:24:42 -0500 )edit

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To answer your second question. The equations are the same but they are being used to determine different parameters. The biquadratic functions are simply curve fits with two independent variables. You can fit different dependent variables on the same independent variables using the same equations with different coefficients. In the case of the chillers the capacity may vary differently against leaving CHW temp and enterting CW temp than then energy input does, but they both vary against the same variables. Let me know if I misunderstood the question.

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I was not clearly realize the Multiple Regression early, I didn't notice the dependent variables should be analysis. Thanks to your answer!

( 2016-06-08 07:40:38 -0500 )edit