An example of CFD
modeling of a Class 1,000
cleanroom that was experiencing
inconsistent airflow and stagnation issues.
After the problem
was identified, CFD modeling
validated the effectiveness of the
and defense research facilities. It’s been estimated that cleanrooms demand between 10
and 100 times more energy than standard office
spaces—mainly driven by air cleanliness standards—and the HVAC system can account for
more than half of the facility’s energy costs. This
impacts operating costs, on top of an already
costly capital facility.
Following are a variety of strategies to help
reduce energy costs related to your HVAC system:
1. To begin, minimize demand. Take a look at
your building. Can you increase the efficiency of
the shell? When building new, carefully orient and
develop the building form. Is there an opportunity
to reduce the volume of your cleanroom? Less volume equates to less air re-circulation with resulting HVAC savings.
2. Make sure you accurately scope the level of
cleanliness and the square footage required.
Going overboard in either category will drive up
your costs. Considering reducing positive pressurization where prudent.
3. Flexibility is key. Design your HVAC system
with an eye towards flexibility, not only for sus-tainability, but for future product line and expansion capabilities as well. Don’t forget to plan your
HVAC equipment to accommodate part load
4. Subdivide your facility’s space classifications. Carefully examine the proposed process
and product requirements when determining
your required cleanroom classification. Don’t
shoot an ant with an Uzi. Do you really need
the entire space to be stringently controlled?
5. Mini- and micro-environments are your
friends; stick or prefab? Consider the use of
micro- or mini-environments (see the May 2013
issue of Controlled Environments) and a mix of
stick built and prefabricated areas—determined by
process specifications and flexibility needs. Utilize
these tools to meet your process requirements
instead of upgrading your entire cleanroom.
6. Invest in high efficiency equipment. Your
upfront costs are an investment with surpris-
ingly short payback periods. And don’t forget to
use high efficiency filters.
7. Consider energy recovery and waste recov-
ery strategies. Energy recovery strategies such
as an exhaust energy recovery system, co-gen-
eration, and equipment or other heat recovery
systems can cut demand and costs.
8. Use alternate energy appropriately. You
can reduce the load on your HVAC system by
carefully analyzing and appropriately using
alternative energy sources throughout your
facility. Consider solar heating and power, day-
light, wind energy, and thermal where techni-
cally sound and fiscally responsible. “Green for
a reason” is the mandate at SMRT, ensuring
that alternate energy sources are operationally
sound, financially responsible, and appropriate
to the application. Don’t let anyone sell you on
being green for green’s sake.
9. Analyze the viability of reducing air change
rates (ACR). The sizes of your motors and fans
are driven in large part by the air change rate in
your cleanrooms. Larger motors and fans drive
increased HVAC investment and operating
costs. You can reduce power usage by approxi-
mately two-thirds if you reduce your ACR by
10. Adjust your airflow to match your produc-
tion load. Scheduling software and timers can
be used to decrease air recirculation and the
HVAC load during periods of reduced produc-
tion. Ditto the wonders of occupancy sensors
that can make automatic adjustments depend-
ing on the occupancy levels of your biggest con-
11. Locate equipment outside the cleanroom
where appropriate. This is a triple bonus strat-
egy. When you locate process tools in an adja-
cent chaseway and provide critical clean access
on the cleanroom side, you will reduce heat
gain as well as the square footage required in
your cleanroom, resulting in less demand on the
HVAC system. You will also make future equip-
ment maintenance easier and less costly.
12. Use variable frequency drives (VFDs).
Variable frequency drives, which adjust HVAC
equipment speed to match conditions, can cut
your energy up to a third compared to con-
stant speed drives.
13. Use particle counters to manage airflow
in real time. Carefully located optical sensors
provide 24/7 particle counts to the building
management system, allowing the HVAC system
to operate with efficiency matched to need.
14. Analyze your air distribution system to reduce
pressure drop. Your HVAC fans have to work
harder in a restrictive air distribution system, rais-
ing energy consumption. Keep the freeway open
with straight ductwork where possible, eliminating
obstructions and carefully sizing duct diameters.
Consider the pressure drop properties of support-
ing equipment like coils, fans, and filters.
15. Don’t be overly conservative or cautious.
Don’t overdesign your HVAC system, or build
in too many safety nets. Those behaviors com-
promise operating efficiencies.
A final word
The world of HVAC design for controlled environments is an always-evolving field with new
equipment and constantly emerging operational
innovations. While this article provides an overview of some key considerations, the unique
properties of your process, product, or research
requirements—coupled with those of your physical plant—will determine best practices.
Richard Bilodeau’s 30-year career includes
plant engineering positions in clean manufacturing. He has designed, operated, and supervised
the construction of advanced technology facilities
and engineered clean manufacturing facilities for
lithium-ion batteries, medical devices, electronics,
and pharmaceuticals. Contact: TheFacilitiesGuy@