Energy Savings in Cleanrooms from Demand-Controlled Filtration

In cleanrooms, very low particle concentrations are maintained by recirculation of air at a high rate (e.g., 600 room air volumes per hour) through highly efficient air filters. We report results in a Class M3.5 (Class 100) cleanroom with 28 m² (300 ft²) floor area, where significant energy savings were realized by controlling the rate of air recirculation through the filters in response to real-time measurements of particle concentrations. An inexpensive, $2500, optical particle counter was used to measure particle concentrations. The effect of varying the recirculation air flow rate on particle concentrations was investigated. Changes in recirculation fan speeds of 10% or greater did not cause a noticeable particle release from filters or resuspension from indoor surfaces. With new automatic control system s in operation, there were occasional, usually fewer than 10 per day, non-consecutive one-minute episodes in which the particle concentration exceeded Class M3.5 (Class 100) status. Depending upon the choice for baseline energy use, the energy consumption of the recirculating fans was reduced by 60% - 80% and the estimated payback period for a 90 m2 (1,000 ft²) Class M3.5 (Class 100) cleanroom is from 1 to 4 years.