ASHRAE Journal - January 2021 - 8

LETTERS

Chiller Plant Optimized
Without Capital
Expenditures
2020

The September 2020 ASHRAE
Journal article, " Chiller Plant
Chiller Plant
Optimized Without Capital
Optimized
Expenditures, " illustrates that
Without Capital
Expenditures
an apparently well-designed
building was inefficiently operated for about 13 years. Figure 1
of the article shows the EUI value
was 134 kBtu/ft2 in 2005 and
was gradually decreased over the next 13 years to an
EUI value of 82 kBtu/ft2 in 2019-and without capital
expenditures. Two obvious question are (1) Is the EUI
value of 82 kBtu/ft2 the best that can be achieved and
(2) Why were these improvements to control and operation not done 12 years earlier?
One tool that might have identified the problems
in 2006 is an energy balance analysis. Figure 2 of the
article gives a peak load of about 320 tons and gives the
building square feet as 640,000; therefore, we have
(6.0 Btu/ft2) chiller load on the day and hour this data
was taken. The two charts I sent with this letter will be
used to demonstrate energy balance analysis.
The top chart on this page is the energy balance of
an ANSI/ASHRAE/IES Standard 90.1-2010 large office
building at design hour conditions of 101°F dry bulb
and 78°F wet bulb. The bottom chart is the same
building at 42°F dry bulb and 42°F wet bulb, defining how much energy this design should be using at
these winter conditions. Both charts are defined by a
system energy equilibrium (SEE) model. The building
square feet of this study is 565,000, so the plant load
for the bottom chart at winter weather conditions is
(4.9 Btu/ft2). If the real building is using more energy
than in the bottom chart, energy waste is probably
occurring.
Perhaps the authors could give all relevant data available for the conditions of Figure 2 in their article, especially the date and/or the outside temperatures. The
chiller load is known, so the other values of an energy
balance must sum to the known. My appreciation to
ASHRAE TECHNOLOGY AWARD CASE STUDIES

All savings in the 640,000 ft2 (55,700 m2) tower were gained from
modiﬁcations to existing equipment and controls that increased
efﬁciency. Since 2005, the EUI has been reduced 39%.

BY KELLEY WHALEN, MEMBER ASHRAE; JASON BROOKS, P.E., MEMBER ASHRAE; ERIC MOBLEY, ASSOCIATE MEMBER ASHRAE

ASHRAE JOURNAL

ashrae.org

JAN UARY 2021

the authors for a well-written article, and I look forward to additional data.

Kirby Nelson P.E., Life Member ASHRAE,
Springfield, Mo.

The Author Responds
Thanks for reading the article and sharing the SEE
modeling example.
To address the first question, Figure 1 in our article
represents the campus EUI and overall program success. The article mentions that since 2005 we have
completed hundreds of energy conservation measures (ECMs) and many retrocommissioning (RCx)
projects. The many projects from 2005 to 2018 did
include capital expenditures. The East Tower Chiller

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ASHRAE Journal - January 2021

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