ASHRAE Journal - September 2020 - 54

2020

ASHRAE TECHNOLOGY AWARD CASE STUDIES

from modiﬁcations to the existing equipment and controls that increased efﬁciency.

Existing Operation Before This Retrocommissioning Project
In 2005, ADTRAN created an energy program, and
since then hundreds of ECMs and many retrocommissioning (RCx) projects had already taken care of the lowhanging fruit.
Below are highlights of activities that took place under
this retrocommissioning project:
* Trended over 300 points pertaining to the plant in
one-minute time intervals, capturing over 131 million
readings using the BAS, which aided in analysis of the
plant's current operation and aided in monitoring as
changes were made.
* Installed four power loggers/analyzers capturing
over two million power consumption readings over 10
months. This data is used for measurement and veriﬁcation of savings calculations. Virtually all the equipment in the building was monitored including chillers,
pumps, cooling towers and air-handlers. Space temperatures and water temperatures are also trended.
* Developed equations to calculate plant energy use for
individual equipment and total plant energy consumption, which allowed for the modeling of the plant's energy
use to aid in decision-making and savings calculations.
These equations were developed using regression analysis
of power data from the loggers versus an independent
variable (such as speed for pumps) from the BAS.
* Performed functional testing, evaluated all existing
plant programming, monitored the chilled water system
and reviewed several years of historical building data.
* Modiﬁed chilled water ﬂow and condenser water ﬂow to maximize the amount of cooling capacity
delivered to air-handling units with the highest cooling
demand, which allowed those units to meet their cooling
demand, a feat the units previously could not achieve.
* Simulated the building and chiller plant in multiple
iterations of models with various conﬁgurations to help
visualize the effects that various changes would have on
the system.
* Developed new energy saving sequences of operation by reprogramming 30 inefﬁcient existing programs
while measuring the actual plant energy consumption
reductions.
* Modiﬁed control setpoints so they are automatically
calculated based on real-time building inputs received
54

ASHRAE JOURNAL

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SEPTEM BER 2020

FIGURE 1 EUI history.

140
135 134
130
EUI
130
Trend (kBtu/ft2)
125
121
118
120
118
115
109
108 110 107 110
110
104 103
105
100
94
95
89
90
85
82
80
2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019
Since 2005 baseline, EUI has been reduced 39%. (Revised 1/8/20)

from the building automation system, allowing the system to have better response times to changing building
conditions.
* Tested all new programming through various
scenarios, temperatures, ﬂows, modes of operation and
building loads to ensure that the sequences would work
across all situations.
As this project was speciﬁc to the East Tower, the following descriptions detail the previous operation of
some of the key pieces of equipment and the associated
changes made to them.
* Chiller Operation. If the chilled water supply temperature (CHWST) got 2.5°F (1.38°C) above the CHWST
setpoint of 38°F (3.3°C) for 30 minutes, an additional
chiller is enabled and starts until the difference between
the CHWST and chilled water return temperatures
(CHWRT) gets below the setpoint. The chiller add sequence was modiﬁed so that the ∆T required for another
chiller to come on varies with time of day (see Innovation section). A CHWST reset was also added based off
building load. A reset was programmed previously, but
it was not able to operate correctly due to the decreased
ﬂow from the chillers. This was rectiﬁed in this project.
* Cooling Tower Operation. The cooling towers
were staged so that once one of them reached its max
speed, the next tower would turn on and ramp up. The
condenser water setpoint was set to 78°F (25.5°C). The
cooling towers staging was modiﬁed so they ramp together to take advantage of the power savings associated
with the fan laws. The condenser water setpoint was
programmed to track the wet-bulb temperature with an
offset so that the cooling towers would output the coldest
water possible to increase the efﬁciency of the chillers.
* Heat Exchanger (HX) 2 operation. The auxiliary

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ASHRAE Journal - September 2020

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