ASHRAE Journal - September 2021 - 51

COLUMN IEQ APPLICATIONS
feedback signal to control supply fl ow rate not only to
meet a cleanroom's heating and cooling loads, but also to
maintain the room's air cleanliness class automatically.
The strategy is to modulate the supply rate to maintain
the same cleanliness based on real-time particle sensing
value; signifi cant fan energy can be saved especially
during partial load and unoccupied times.
Conclusions
Cleanrooms' unique HVAC techniques can achieve
ultralow airborne contamination to meet industrial
specifi cations and to protect human, room and products
in providing much higher air purity and lower contaminant
concentrations than commercial spaces.
These techniques include but are not limited to: adding
air recirculation loop with ceiling FFU units to deliver
a higher air change rate to achieve superb air cleanliness
without much extra fan energy; using contaminant
source-strength reduction, isolation and removal, plus
transmission controls before applying a large quantity of
fi ltered dilution air; arranging cascading airfl ow direction
in up-mid-down streams; applying pressurization and
installing anteroom/airlock to reduce external contaminant
migration; and applying particle sensor-based
VAV demand fl ow control to prevent airfl ow oversupply.
Engineers could be inspired to imitate some less-intense
approaches for commercial applications in achieving
enhanced contamination control only if feasible, applicable
and cost-effective. Some fi ndings of this article are
from the ongoing ASHRAE RP-1604 Research Project.
References
1. ISO. 2015. " ISO 14644-1:2015, Cleanrooms and Associated
Controlled Environments-Part 1: Classifi cation of Air Cleanliness
by Particle Concentration. " International Organization for
Standardization.
2. Sun, W., et al. 2010. " Development of cleanroom required
airfl ow rate model based on establishment of theoretical basis and
lab validation. " ASHRAE Transactions 116(1).
3. IEST. 2015. " IEST-RP-CC012.3. Considerations in Cleanroom
Design. " Institute of Environmental Sciences and Technology.
4. Sun, W. 2020. " Controlled environments: room pressure, fl ow
offset, airtightness and pressurization strategies. " ASHRAE Journal 62(12).
5. Sun, W. 2018. " Cleanroom airlock performance and beyond. "
ASHRAE Journal 60(2).
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ASHRAE Journal - September 2021

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