Laboratory for Integrated Science & Engineering Cleanroom at Harvard Univ. Image: Wilson Architects.
Photographer: Anton Grassl|Esto
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their daily search for the truth.
In addition to the complexities and hazardous nature of the facility, the project is being
designed to meet one of the most stringent
energy codes in the U.S., the California Energy
Code 2013. The facility will also be designed to
achieve LEED Gold certification.
The chilled water and heating hot water is
Right-sizing energy-efficient cleanrooms: Lessons learned
produced using a heat pump chiller. The office
area is served via a variable refrigerant flow
(VRF) system, which can exchange heating
and cooling energy between spaces before
using any compressor energy. The air from
the offices is transferred into the lab area for
make-up air when needed by the fume hoods.
The general exhaust from the lab goes through
an energy-recovery device before exiting via
the manifolded exhaust system.
Gurdaver Singh brings over 25 years of expe-
rience as principal engineer in mechanical and
electrical design for building services in health-
care, higher education, defense and civic/public
projects. He’s a proponent of sustainable design
with a strong track record of delivering high-per-
formance, low- to net-zero-energy buildings.
Russell McElroy, AIA, NCARB, has over 20 years
of diversified experience as an architect focused
on designing labs and medical examiner facilities.
He is responsible for leading MWL Architect’s lab
from Harvard LISE and other peer institutions
By: Jacob Werner, Associate, Wilson Architects and
Jacob Knowles, Director of Sustainable Design,
Bard, Rao + Athanas Consulting Engineers LLC
Cleanrooms are energy hogs. But clean- room energy use serves direct experi- mental needs. How do we balance these
demanding requirements against institutional
goals for greater sustainability?
The Harvard Univ. Laboratory for Integrated
Science and Engineering (LISE) cleanroom
began operation in 2006. Following Harvard’s
desire for maximum research capability and
future flexibility, the design team, including
Wilson Architects (WA) and BR+A mechanical
engineers, created an enormously robust facility.
But almost immediately upon opening, Harvard
realized actual ongoing experiments didn’t
demand the full capacity of the design. Harvard’s
on-site building management began a program
of energy-efficiency improvements designed to
“set back” the building’s environmental controls.
Through a process of post-occupancy evaluation and targeted research, WA, BR+A and
Harvard have collaborated on a research case
study of the LISE energy-efficiency projects,
using metered data and input from the process
of fine-tuning. WA and BR+A have extended
that research to an extensive survey of cleanroom facilities across the U.S.
Since cleanrooms are widely varied and often
part of larger buildings, it’s misleading to compare cleanrooms with broad metrics, such as
total energy use per square foot (EUI). Our study
evaluates several finer-grain metrics, including
tool load, supply air temperature, recirculation
air change rate, recirculation airflow efficiency,
make-up air change rate and dewpoint.
Designs for electrical power and cooling
capacity tend to be conservatively high. Some
cleanrooms are designed for 70 to 110 W/sf,
whereas actual tool loads are in the range of 4
to 36 W/sf. At the fully fit-out Harvard LISE
cleanroom, tools only result in roughly 3 W/
sf of air-side cooling load, once process chilled
water is accounted for.
SUPPLY AIR TEMPERATURE
In summer, cleanroom make-up air-handling
units (MAHUs) typically sub-cool the air to extract
moisture, then reheat it to neutral temperature
(60 to 68 F). The recirculating AHUs then re-cool
the air to offset the internal heat in the cleanroom.
This inefficient cool-reheat-recool sequence can be
improved by allowing the make-up air to reset to a
cooler temperature, such as 50 to 55 F.
RECIRCULATION AIR CHANGE RATE
Although Class 100 cleanrooms are often
designed for well over 200 ACH, the Class 100
cleanrooms surveyed typically operate between 130
and 175 ACH. To allow lower ACH, the Harvard
LISE facilities team connected the particle counters to the building automation system, creating a
demand-based control loop. Some facilities rely on
occupancy sensors for the same purpose.
RECIRCULATION AIRFLOW EFFICIENCY
The efficiency of recirculating AHUs
(RAHUs) is measured in terms of airflow per
unit of energy (cfm/k W). RAHUs, the pressurized plenum and the ceiling grid of filters
can be designed to minimize pressure drop.
Additionally, turning down the recirculation
ACH results in significantly improved cfm/k W.
Based on the survey results, RAHUs are often
designed for 2,000 to 4,000 cfm/k W (at peak
airflow). But, when turned-down, the operating
performance improves to 4,000 to 7,000 cfm/
k W. For facilities designed with very low pressure
drop, including 100% filter coverage in the ceiling