ASHRAE Journal - April 2024 - 49

2024 ASHRAE TECHNOLOGY AWARDS CASE STUDY
The upgrades were conducted to meet extended
business needs and replace air-cooled chillers with
water-cooled ones for energy conservation. The
centralized, water-cooled chiller plant has a total cooling
capacity of 8,000 tons (28 135 kW) (i.e., one 1,000 ton
[3517 kW] chiller on G2 roof and seven 1,000 ton
[3517 kW] chillers in the New Energy Centre [NEC])
to replace individual aged, air-cooled chiller plants.
These chillers are connected to a freshwater cooling
tower condensing water circuit for heat rejection. The
chilled water distribution is a decoupled bypass system
with variable flow on the secondary side. The chilled
water supply to the STRC Grandstand is served by four
secondary chilled water loops, specifically for G1 Main
Ring, G2 High Zone, G2 Low Zone and JC Box. They are
operated via variable speed chilled water pumps to
provide chilled water to the entire Grandstand area.
After these ACI upgrades, retro-commissioning (RCx)
was introduced to review the performance of the entire
chiller plant in terms of energy efficiency and system
optimization with reference to ASHRAE Guidelines
0.2-2015 and 1.2-2019. The RCx project was divided
into three phases: 1) Using a continuous monitoringbased
commissioning (MBCx) program to deploy data
analytics for identifying any abnormalities of chiller
plant operational data collected from the building
management system (BMS) to define corresponding
rectification works; 2) Implementation of energy saving
opportunities (ESOs) based on MBCx findings; and
3) Further refinement of MBCx monitoring data to
optimize the chiller plant and system performance.
ENERGY EFFICIENCY
For the first stage of this RCx project, a continuous
monitoring-based commissioning (MBCx) software
platform was installed in 2016 for acquiring operational
data as well as analyzing chiller plant performance.
Following the investigation and identification of those
abnormalities via the MBCx platform, a number of
rectifications were performed, such as adjusting
cooling tower fan speed, cleaning chiller condenser
tubes, replacing and recalibrating faulty field sensors,
modifying the BMS program, etc., with a result of
263,401 kWh (948,243.6 MJ) of annual energy savings
(4.3% of total consumption).
Moreover, two major energy wastage aspects were
also found: low delta temperature phenomenon in
both secondary chilled and condensing water systems
and over pumping phenomenon in the primary chilled
water system. Consequently, the following ESOs were
identified for the second stage of RCx.
Secondary Chilled Water Pump Speed Optimization
The chiller plant operation pattern of STRC
Grandstand is based on two operational modes:
Raceday Mode and Non-Raceday Mode. Different
differential pressure (DP) settings are adopted to
govern secondary chilled water pump (SCHWP)
running speed to supply sufficient chilled water for
cooling. MBCx identified the occurrence of low delta
temperature phenomenon (<5.0°C [9°F]). To optimize
the pump speed control under different cooling
demands, additional DP sensors, water temperature
sensors and pressure independent control valves were
installed. Moreover, an automatic DP setpoint reset
algorithm was developed based on outdoor enthalpy so
that maximum efficiency can be achieved. The energy
saving is about 160,284 kWh (577,022.4 MJ), which is
equivalent to 2.6% total annual energy consumption of
the chiller plant.
Primary Chilled Water Pump Speed Optimization
MBCx detected excess flow on the decoupler that
caused over pumping in the primary chilled water loop.
To eliminate this phenomenon, variable speed drives
(VSDs) were installed for primary chilled water pumps
(PCHWPs) to reduce pumping flow, resulting in energy
savings during operation. The speed of PCHWPs can be
adjusted to maintain a constant differential pressure
throughout the system. There has been a reduction
of approximately 14% in the total surplus flow rate of
chilled water passing through the decoupler, resulting
in an energy saving of 182,450 kWh (656,820 MJ) (3% of
total consumption).
Condensing Water Pump Speed Optimization
MBCx also revealed a low delta temperature (<5.0°C
[9°F]) across the condensing water loop. Based on
the condensing water flow demand, the minimum
VSD speed settings of the condensing water pump
(CDWP) were adjusted from 30 Hz to 25 Hz. Energy
savings achieved was approximately 156,514 kWh
(563,450.4 MJ), which is equivalent to 2.5% of the chiller
plant's total annual energy consumption.
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49
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ASHRAE Journal - April 2024

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