[Bldg-sim] chiller performance curves?

[Steven Gates]

Dan,

 

I think I misspoke in my reply below.

 

I believe the standard version of eQUEST/DOE-2 allows you to input curve fit
DATA using either English or metric; if metric independent temperatures are
used, the Building Design Language processor should convert the metric
temperatures to English before doing the curve fit.  The coefficients
generated would then expect hourly temperature in English.  However, if you
do a curve fit independently of BDL using metric temperatures, and simply
give the program the COEFFICIENTS rather than the DATA, then the curve would
expect metric temperatures, and the hourly curve algorithm would feed it
English; resulting in a severe error.

 

So, as long as you generate the curve using BDL, I believe you can use
either English or metric units.  It should be easy enough to test to
confirm. Just input the same curve with both English and metric temperatures
(specifying METRIC input), and see if you get the same coefficients. If this
is not the case, please let me know.

 

The refrigeration version of the program has a curve-fit routine that allows
either English or metric curve coefficients to be used; there is a keyword
that allows you to specify which values you are using.  So the library could
have curves of both types in it.  On an hourly basis, if the curve is
metric, the program converts the input temperatures from English to metric,
feeds them into the curve, and converts the output from metric back to
English (if the output has dimensional units).  Hopefully, we will port that
algorithm over to the standard version in the future.

 

Steve

 

 

  _____  

From: Steven Gates [mailto:stvgates at pacbell.net] 
Sent: Monday, December 08, 2008 1:51 PM
To: 'Dan Russell'; 'Chien Si Harriman'; 'bldg-sim at lists.onebuilding.org'
Subject: RE: [Bldg-sim] chiller performance curves?

 

In eQUEST a curve that references temperatures or other dimensioned
variables must be fit using English units. We plan to address this at some
point in the future.

 

  _____  

From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Dan Russell
Sent: Monday, December 08, 2008 1:42 PM
To: Chien Si Harriman; bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] chiller performance curves?

 

It is my understanding that the chiller curve data are dimensionless ratios,
so the curve-fits should work regardless of units-system.  The raw data
would be different, but the curve coefficients should be identical.

 

Can someone confirm this?

 

Thanks,

 

 Dan Russell, EIT 

 

cid:image001.jpg at 01C840A4.E711B250

 

From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Chien Si
Harriman
Sent: Monday, December 08, 2008 1:08 PM
To: bldg-sim at lists.onebuilding.org
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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