[BLDG-SIM] eQuest Default f(PLR) Skepticism

[Taylor Keep]

eQuest models boiler and chiller plants with default part load curves
that I think may be incorrect. As I understand it, the f(PLR) curves are
used as a direct multiplier on the HIR for boilers and EIR for chillers,
with full load (1.0 PLR) corresponding to a 1.0 multiplier. If this is
true, the f(PLR) curve should increase at part load for atmospheric
boilers (atmospheric boilers become somewhat less efficient at part
load). The default atmospheric boiler curve decreases almost linearly
down to zero! I am having a tough time wrapping my head around this.

On the chiller side, the default f(PLR) is a bi-quadratic function using
both dT and PLR as variables, so it is f(PLR,dT). Since I never have
this dual function information in my general chiller selections, I have
been using a standard f(PLR) function quoted at a fixed dT from the
manufacturer. The curve I get from a McQuay 400-ton chiller selection is
quadratic, with decreasing EIR down to 50% load and increasing EIR below
50% load. I seriously doubt that the eQuest default corresponds with
this entry because changing the function produces a huge change in
performance.

Do any of you have any thoughts or suggestions about the accuracy of
default f(PLR) curves? Should I scrap my "improved," real curves - they
are drastically changing the model performance?!?!

Taylor


________________________________________________________
Taylor Keep
Mechanical, LEED(r) AP
                          
Arup 
901 Market Street Suite 260
San Francisco, CA 94103
tel: 415 946 0279
fax: 415 957 9096
taylor.keep at arup.com
www.arup.com


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