ASHRAE Journal - July 2022 - 37

HONORABLE MENTION | 2022 ASHRAE TECHNOLOGY AWARD CASE STUDIES | UDIES
Energy Effi ciency
Existing makeup air units were balanced to maintain
proper positive cleanroom pressurization. Cooling and
dehumidifi cation in these units were adjusted to provide
68°F (20°C) and 50% relative humidity return air
(48°F [8.9°C] dew point) from respective cleanrooms.
Once the makeup air unit provided proper humidity
control, the Class 100 and 1,000 recirculating air-handling
unit cooling coils and heating coils could be controlled
in sequence to maintain space temperature. The
submitting engineers discovered that the Class 100 and
1,000 recirculating air-handling units had been cooling
and reheating simultaneously to provide humidity control
before the makeup air units were properly set up.
Cleanrooms are designed to maintain extremely low
levels of particulates, such as dust, airborne organisms,
or vaporized particles. Cleanrooms typically have a
cleanliness level quantifi ed by the number of particles
per cubic meter at a predetermined molecule measure.
Particle counters integrated with the BAS can adjust airfl
ow based on ppm at a given particle size of 0.5 microns.
The submitting engineers' initial concept was to have a
permanent particle counter that regularly passes data to
the new control system.
Airfl ow dampers modulate to maintain the following
setpoints:
* The Class 100 cleanroom setpoint is 10 particles/ft3
at 0.5-micron size (classifi cation limit is 100 particles/ft3
at 0.5 micron size). Using ISO 5 metric system parameters,
the cleanroom setpoint is 352 particles/m3 at
0.5-micron size (classifi cation limit is 3,520 particles/m3
at 0.5 micron size).
* The Class 1,000 cleanroom setpoint is 100
particles/ft3 at 0.5-micron size (classifi cation limit is
1,000 particles/ft3 at 0.5 micron size). Using ISO 6 metric
system parameters, the cleanroom setpoint is 3,520 particles/m3
at 0.5-micron size (classifi cation limit is 35,200
particles/m3 at 0.5 micron size).
* The zone dampers were modulated to allow room
airfl ow quantities to vary between 25 cfm/ft2 and
35 cfm/ft2 of fl oor area (127 L/s·m2 and 178 L/s·m2) when
occupied.
Occupancy sensors were added to all cleanrooms to
determine if the room is in use. Airfl ow dampers modulate
to maintain the following setpoints:
* Occupied setpoint: Control zone dampers were
modulated to allow room airfl ow quantities to be
modulated between 25 cfm/ft2 and 35 cfm/ft2 of fl oor
area (127 L/s·m2 and 178 L/s·m2). Particle count setpoints
remained as noted above.
* Unoccupied setpoint: Control zone dampers were
modulated to allow room airfl ow quantities to be
modulated between 15 cfm/ft2 and 35 cfm/ft2 of fl oor
area (76 L/s·m2 and 178 L/s·m2). Particle count setpoints
remained as noted above.
Indoor Air Quality and Thermal Comfort
Particulate fi ltration is a key aspect of the air handler
design, including a prefi lter, secondary fi lter and ULPA
fi ltration.
Cooling and dehumidifi cation in the makeup air units
were designed to provide constant discharge air control
to provide space conditions of 68°F (20°C) and 50% relative
humidity return air (48°F [8.9°C] dew point) from
respective cleanrooms. The low space temperature was
provided to accommodate the thermal comfort of cleanroom
researchers in full protective clothing.
Innovation
The building has four Harrington scrubbers (toxic,
toxic, acid, and solvent), only three of which run constantly,
which were previously using varying volumes
of city water to clean toxins from the air. Upon investigation
with a fl ow meter, the engineers saw that each
active scrubber was using more than 4.5 gpm (17 L/min).
Water from an aquifer beneath the HTML building that
is collected in a large pit is now used to feed the scrubbers
rather than being sent directly to the sewer, reducing
water and sewer use.
The engineers used a conservative combined average
of 11 gpm (41 L/min) (total) for the calculated water savings.
At 11 gpm (41 L/min), the city water use avoided is
15,840 gallons (59 961 L) per day, or almost 6 million gallons
(22,710,000 L) a year, saving approximately $39,000
each year.
Cost Effectiveness
The total project budget was $5 million (funded
through an energy savings performance contract).
Baseline water and energy expenditure was $2,340,717
annually. The project saved $440,503 (19% reduction) in
2017; $720,315 (31% reduction) in 2018; $848,889 (36%
reduction) in 2019; and $812,583 (35% reduction) in
2020.
J U LY 2 0 2 2 ashrae.o rg ASHRAE JOURNAL
37
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ASHRAE Journal - July 2022

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