[Equest-users] VSD Centrifugal Chiller Performance EIR-f(PLR, dT) and EIR-f(t1, t2)

John Forester jforester at dmiinc.com
Tue Jul 1 11:08:04 PDT 2008

Hello Equest users,


I have a question regarding variable speed centrifugal chillers and
generating the EIR performance curves.


The DOE-2 help information regarding the EIR-f(PLR) curve explains that it
is equally important to include the "dT" term when considering variable
speed chillers due to the relationship between the impeller speed and the
suction/discharge pressure (or temperature) differential.  This affect can
be seen when comparing a VFD chiller with condenser water temperature reset
to a constant speed chiller with condenser water reset.  Without the
condenser water reset, there is little efficiency gain from the variable
speed compressor.


The second EIR performance curve is the EIR-f(T evap leaving, T cond
entering) or EIR-FT.  This curve adjusts the EIR based on the leaving
chilled water temperature and the entering condenser water temperature.


It seems that if the "dT" term is included in the EIR-f(PLR) curve, the
efficiency increase due to a reduced condenser water temperature is being
double counted since Equest calculates the chiller demand by multiplying the
design EIR by these two results together (plus the capacity curves).  Can
anyone provide some insight on this topic?  What is the difference between
the affects of the "dT" in the EIR-f(PLR) and the EIR-f(T evap leaving, T
cond entering) on the design EIR?


Thanks for your thoughts,




John T. Forester, LEED AP
Demand Management Institute
35 Walnut Street
Wellesley, MA 02481
Phone: 781 431 1100 x14
Fax: 781 431 1109
email:  <mailto:jforester at dmiinc.com> jforester at dmiinc.com
<mailto:jforester at dmiinc.comweb> 
web: www.dmiinc.com


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