ASHRAE Journal - July 2021 - 43

TECHNICAL FEATURE
charged at $30/ton ($8.53/
kW), savings will be $123,000.
Based on current energy
savings, reduction is only
2,100 tons (1908 metric tons)
per year.
Due to the reduced air
compressor cooling load,
6.6 million gallons (24,980
m3 ) per year (average
12.6 gpm [2.9 m3/h]) valued
at $11,000 will be saved at the
cooling towers, with an additional
$31,000 saved in cooling
tower chemical treatment.
Challenges
The project required a very complex modeling study
and implementing re-piping and equipment retrofi t
space planning in an already crowded facility. Several
booster pumps were required. Construction implementation
required a detailed plan and procedures to mitigate
adverse impacts to an operating factory.
New control sequences and software were provided to
implement the strategies. During start-up and control
tuning, system owners had to be trained to operate the
systems in accordance with the revised sequences and
strategies. Invariably, there were surprises, such as a
single undersized control valve that limited raising the
chilled water system temperature setpoint above the
original design value, causing an implementation delay
until the valve was replaced.
To avoid disruption of oil free air operation during the
occasional reverse osmosis shutdown, motorized control
valves were added, enabling oil free air cooling to revert
to the original confi guration with CHWS, bypassing the
industrial city water plate-and-frame heat exchangers.
Conclusions and Recommendations
The authors believe no " silver bullet " shortcuts exist
to achieve energy effi ciency. This project was one of 14
studies conducted over four years. Each project began
with the kernel of an energy savings strategy researched
by the company's energy engineer, followed by a loosely
co-defi ned analysis/modeling scope executed by the
consultant that evolved throughout the analysis as
insights were gained from modeling. All models were
FIGURE 4 Chilled water plant-specific power improvement after partial implementation of Options 2 through 5.
kW/ton Chilled Water Plan-Before and After System Changes
Consecutive Hours
1.00
0.95
0.90
0.85
0.80
0.75
0.70
0.65
0.60
kW/ton After
Linear (kW/ton After)
kW/ton Before
Linear (kW/ton Before)
FIGURE 5 Condenser water temperature, before and after setpoint reset implemented
for non-heat recovery chillers (reset after 12/13/18).
80
75
70
65
60
55
Oct 27
Before
After
2018
Dec 6 Jan 15 Feb 24
|
Apr 5 May 15 Jun 24
2019
FIGURE 6 Chiller-specific power impact adding variable speed drive to chiller
compressor motor and condenser water/chilled water temperature reset.
Chiller kW/ton Before (0.64 Avg.) and after (0.39 Avg.) Chiller VSD with Condenser Water
Temperature Lowered and Chilled Water Temperature Optimized
0.75
0.65
0.55
0.45
0.35
0.25
Oct 7
2016
Jun 14
2017
Before Chiller VSD
After Chiller VSD
Feb 19
2018
Oct 27
2018
Jul 4
2019
developed by the consultant with data provided by the
coauthor and customized to the specifi c scenario.
Maximizing energy saved can only be accomplished
by operating the systems precisely to the new strategies.
To this end, buy-in from and adequate training
for the operating technicians cannot be ignored nor
J U LY 2 0 2 1 ashrae.org ASHRAE JOURNAL
43
kW/ton
1
319
637
955
kW/ton
Temperature (°F)
1,273
1,591
1,909
2,227
2,545
2,863
3,181
3,499
3,817
4,135
4,453
4,771
5,089
5,407
5,725
6,043
6,361
6,679
6,997
7,315
7,633
7,951
8,269
8,587
8,905
9,223

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ASHRAE Journal - July 2021

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