The substantial energy demands of today's cleanroom environmental-maintenance systems provide large opportunities for energy conservation. However, cleanroom environments are subject to much more stringent standards and operate with much smaller tolerances, and therefore simple application of industrial/commercial controls is not sufficient. We conducted a set of measurements in a Class 1000 cleanroom to confirm that humans are the predominant source of particles in a cleanroom. supporting that occupancy can be used as an effective surrogate for particle concentrations. Our data suggest that people release approximately 1.7 x 10(4) particles per minute into the cleanroom and raise the local concentration of particles by 1742 +/-481 particles m(-3) person(-1). Furthermore, our timescale analysis on control system and ventilation unit responses indicates that a predictive-occupancy system is required for implementing demand-controlled ventilation. (C) 2011 Elsevier B.V. All rights reserved.