ASHRAE Journal - August 2022 - 53

FIRST PLACE | 2022 ASHRAE TECHNOLOGY AWARD CASE STUDIES
(5203 m2) of penthouse area for a total building area of
604,000 ft2 (56 113 m2).
Energy Effi ciency
All chillers are supplied with variable frequency
drives. Since this plant is serving critical processes,
the entire chiller plant is engineered for a fully loaded,
design day condition, which occurs about 1% of the time.
Outside of that we are able to operate more effectively at
part-load conditions (lower building load and less than
85°F [29°C] condenser water). In addition to the VFDs,
the chillers use a variable orifi ce that allows the chiller
control panel to adjust refrigerant fl ow to the evaporator
and maintain the proper refrigerant levels in both
shells. This tighter control of refrigerant fl ow allows for
more effi cient part-load operation.
These specifi c chillers are able to use colder tower
water than most (36°F [2.2°C]), which eliminates the
need to incorporate head pressure control. The magnetic
bearing chillers operate with even colder tower
water than a standard oil-lubricated machine because
they use magnetic bearings and don't have to account
for oil return or oil slugging. They are ASHRAE Standard
90.1-2004, 2007 and 2010 compliant and qualifi ed for
the utility's incentive.
The control optimization solution for the chilled water
system leverages several key algorithms to continuously
operate the Energy Center equipment as effi ciently as
possible. According to an article by Thomas Hartman
published in September 2001 in ASHRAE Journal, any
chilled water system with an annual average plant
effi ciency of 0.70 kW/ton (0.20 kW/kW) or less receives
a rating of excellent. The net result of the algorithms
being implemented and the equipment used at Sterling
Heights Assembly Plant South (SHAP South), allowed for
an average annual total system effi ciency of 0.42 kW/ton
(0.12 kW/kW) over the last three years.
Indoor Air Quality
A major factor infl uencing the design and selection of
the air-handling equipment was the desire to provide a
space with enhanced indoor air quality (IAQ). AHUs are
provided with two stage (MERV 11/MERV 13) fi ltration for
improved air quality. Spaces are provided with cooling
through the AHUs. Spaces were provided with increased
ventilation above the requirements of ASHRAE Standard
62.1-2010.
The Energy Center is served by two constant volume
air-handling units, with direct gas-fi red heat and chilled
water cooling. The Paint Mix Room is served by one
constant volume air-handling unit with direct gas-fi red
heat and chilled water cooling. The South Paint Shop
offi ce area is served by two variable air volume (VAV)
roof-mounted air-handling units with chilled water
cooling and indirect gas-fi red heat. The main Paint Shop
building is served by four process AHUs and several
AHUs and recirculation air handlers serving specifi c
Paint Shop operations. These units use chilled water
cooling and direct-fi red gas heat.
Key HVAC system design notes:
* The AHUs will modulate heating and cooling to
maintain the space temperature and are connected
to the central building management system (BMS) for
scheduling of occupied/unoccupied periods and setpoint
control.
* Energy Center room pressurization is maintained
through general space exhaust, with additional exhaust
connected to the refrigerant monitoring system in accordance
with ASHRAE Standard 15-2013 .
* Spaces with hazardous chemical storage were provided
with 100% exhaust to maintain a negative pressure
with respect to the adjacent spaces.
Innovation
The latest chiller technology was selected-oil-free
magnetic bearing chillers. This technology has allowed
the plant to operate much more effi ciently at part-load
conditions (compared to performance of a standard oillubricated
chiller). The chiller uses the same compressor
but instead uses a permanent magnet motor with
active magnetic bearing technology. The high-speed
permanent magnet synchronous motor is levitated by
magnetic bearings.
These specifi c chillers are also equipped with a feature
designed for critical cooling installations; it minimizes
time to restart and loads the chiller as quickly as possible,
to rapidly achieve the specifi ed leaving chilled water
temperature. It also includes an uninterruptible power
supply that keeps power fl owing to the chiller's control
panel as well as the required portions of the VSD control
circuit. In a process load scenario, downtime is critical,
and this feature allows us to get back to 100% load conditions
within 3.5 minutes after a power failure.
Due to this feature, from a controls perspective, we
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ASHRAE Journal - August 2022

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