Demand-controlled Filtration Case Study

LBNL has completed a case study of the potential for demand-controlled filtration, conducted in a 300-square-foot Class-100 cleanroom located at LBNL. The photo shows the instruments used for the measurements: Lasair Model 1003 by Particle Measuring Systems with particle sizing from 0.1 to 2.0 microns separated into 8 size bins and a sample flow rate of 0.001 cfm. Integrating Nephelometer, Model M903 by Radiance Research Climet Ultimate 1000, 0.10 to 1.0 micron with 6 size bins (0.1-0.15, 0.15-0.2, 0.2-0.3, 0.3-0.5, 0.5-1.0, & 1.0) at a sample flow rate of 1 cfm. Study Objectives Identify a type of particle counter that is well suited for DCF and enables fast control response. In our previous study of DCF in the LBNL cleanroom, the particle counter used could detect particles no smaller than 0.3 microns, and the number of counts in that bin was not adequate for good control of recirculation fan speed. Examine how changes in recirculation fan speed control affected particle concentrations.

Major Findings

1. Particle counts of particles <0.3 microns were about 10 times as great as for those of larger-sized particles.
2. The counts for 0.1- to 0.15-micron particles and the 0.15- to 0.2-micron particles were nearly the same. Thus the lowest size particle detected needs be no smaller than about 0.15 to 0.2 microns.
3. The particle counter should have a sample flow rate of 1 cfm or higher.
4. Higher speeds of the recirculation fans did not always produce the lowest particle counts. Thus, there may be an optimum recirculation fan speed for minimizing particle counts.

Benefits of Demand Controlled Filtration

• Estimated payback times for implementing DCF are from 1 to 4 years. If a facility already has variable speed drives on the recirculation fans for the cleanroom, then the payback will be closer to 1 year. Because the energy used by a fan is approximately proportional to the cube of the fan speed, small changes in fan speed can translate into large energy savings. The concept of varying ventilation speed has been applied at a major industrial site, which setback cleanroom fan speeds at night and on the weekend.