Airflow Design for Cleanrooms and Its Economic Implications

A cleanroom is designed to control the concentration of airborne particles. As a result, large amount of cleaned air is often required to remove or dilute contaminants for satisfactory operations in critical cleanroom environment. Cleanroom environmental systems (HVAC systems) in semiconductor, pharmaceutical, and healthcare industries are much more energy intensive compared to their counterparts (HVAC systems) serving commercial buildings such as typical office buildings. There is a tendency in cleanroom design and operation, however, to provide excessive airflow rates by HVAC systems, largely due to design conservatism, lack of understanding in airflow requirements, and more often, concerns such as cleanliness reliability, design and operational liabilities. A combination of these likely factors can easily result in HVAC systems over-design.

Energy use of cleanroom environmental systems varies with the system design, cleanroom functions, and critical parameter control including temperatures and humidities. In particular, cleanroom cleanliness requirements specified by cleanliness class, often cast large impact on energy use. A review of studies on cleanroom operation costs indicated that energy costs could amount to 65-75% of the total annual cost associated with cleanroom operation and maintenance in some European countries. Depending on cleanroom cleanliness classes, annual cleanroom electricity use for cooling and fan energy ranged approximately between 1,710 kWh/m² and 10,200 kWh/m² (or 160 kWh/ft² and 950 kWh/ft²) in California, USA. Cleanroom fan energy use typically consumed half of total HVAC energy use in three states in the USA. For cleanrooms in a wafer-process semiconductor factory in Japan, HVAC systems used 43% of power consumption of an entire cleanroom factory, while air delivery systems account for 30% of the total power consumption. Fan energy use for cleanrooms of ISO Classes 3,4,5 collectively account for approximately 80% of the fan energy use for cleanrooms of all classes. It is evident that biggest factors dictating cleanroom operating energy costs often include the magnitude of cleanroom airflow and how efficiently the HVAC systems deliver the cleaned and conditioned air to cleanrooms.