[Bldg-sim] chiller performance curves?

[xiao dongyi]

Hi Joe,
 
Could you please shed more light on this topic? --
 
Assuming the performance equations are the same in DOE2 and EnergyPlus. If I just wanted to convert the curve coefficients from IP units to SI units (for example, the chiller capacity performance curve (function of chilled water supply temperature and entering condenser water temperature, of type Bi-quadratic-T in DOE2), do I have to derive the unit conversion formula for the curve coefficients manually, based on the curve type and the unit conversion rule for temperature? As the curve coefficients in this case can not be converted independently.
 
I tried to derive the units conversion formula for one particular curve type before, and got the same results as those in the EnergyPlus library. But I am wondering if there is any more systemmatic way of converting the coefficients between SI and IP, so that the conversion work could be done in an automatic way. As you are one of the developers of EnergyPlus, I believe you are the right person to ask this question.Thanks,Dongyi
 



From: joe at drawbdl.comTo: chien.harriman at iesve.com; bldg-sim at lists.onebuilding.orgDate: Mon, 8 Dec 2008 17:05:14 -0800Subject: Re: [Bldg-sim] chiller performance curves?


Chien Si, others,
 
The problem is more complicated than what you're asking, because EnergyPlus and DOE-2 do not necessarily express their curves using the same equation formulation. When I worked a few years back in translating DOE-2 inputs to EnergyPlus, I  (or others in the then LBNL team!) had to  reformulate many of the equations and coefficients, and in some cases, redo the curve fit from scratch.  As several people have already pointed out, even if the equation is the same, the coefficients are unit-specific and hence differ between IP and SI. 
 
Joe Huang
White Box Technologies

----- Original Message ----- 
From: Chien Si Harriman 
To: bldg-sim at lists.onebuilding.org 
Sent: Monday, December 08, 2008 12:08 PM
Subject: [Bldg-sim] chiller performance curves?

Hi all-
 
Sort of technical question here that requires some knowledge of the inner workings of either EnergyPlus or DOE2/eQuest...hoping there is someone out there who knows the answers to this.  What does either an EnergyPlus or DOE2 user have to do when dealing with different units, particularly when it comes to the curve fits?  Obviously, the same coefficients do not apply for both units.  Do the default curve coefficients for the chiller, for example, have both IP and metric equivalents?  
 
Does anyone know how this works?  Has anyone bumped into a regression model that can take raw data in metric units, and create a set of coefficients in one set of units (let's say IP for starters), and then use those newly-created coefficients, generate an new set of raw data, and then create a new regression to produce a new set of coefficients in converted units (Metric, in this case?)  
 
Has either DOE2 or EnergyPlus already solved this problem, and I don't need to even think about itanymore?
 
Thanks,
 
 
 
 
 



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