Energy and Buildings 43 (2011) 3258–3262 Contents lists available at SciVerse ScienceDirect Energy and Buildings j our na l ho me p age: www.elsevier.com/locate/enbuild The use of occupancy as a surrogate for particle concentrations in recirculating, zoned cleanrooms Luke Strauss, Jeffrey Larkin, K. Max Zhang ∗ Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY 14853, USA a r t i c l e i n f o Article history: Received 14 June 2011 Received in revised form 19 August 2011 Accepted 26 August 2011 Keywords: OBCV SBDCV Cleanroom Human particulate a b s t r a c t 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, support- ing that occupancy can be used as an effective surrogate for particle concentrations. Our data suggest that people release approximately 1.7 × 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. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Cleanrooms represent an energy intensive built environment to most commercial spaces [1–3]. Unlike most commercial spaces, e.g. office buildings, the tolerable interior environmental variation in a cleanroom exists in a narrow range defined by the cleanroom class [4]. Cleanrooms fall generally into two categories: those that clean the entire occupied space, and those that clean the equip- ment space only, using various isolation procedures to separate the dirty room from the equipment (clean cabins) [5]. The primary difference between these two basic classes lies in the presence of people; the former category includes occupants in the cleaned space while the latter category excludes them. The former cate- gory, i.e., whole-room cleanrooms, is much easier to build, and offers greater flexibility in post-construction equipment changes, making them attractive from an infrastructure and management standpoint. The flexibility of a whole-room cleanroom, however, comes at the price of a larger space in need of cleaning and a larger set of contamination sources. This results in greater cleaning requirements and therefore commensurately greater energy use. Several groups have been investigating the feasibility of applying demand-controlled ventilation and system-control techniques in cleanrooms to decrease energy intensity while maintaining a high quality environment within tight tolerances [6,7]. Following up ∗ Corresponding author. Tel.: +1 6072545402; fax: +1 6072551222. E-mail address: kz33@cornell.edu (K.M. Zhang). on the DHC study (a cleanroom in upstate New York) conducted by Kircher and coworkers [8], we investigate the opportunities and difficulties of implementing a sensor-based demand controlled ventilation (SBDCV) system [9], based on an occupancy-based con- trolled ventilation model (OBCV). Research in SBDCV and OBCV in cleanrooms is fairly recent, and depends strongly on the underlying assumption that the pri- mary pollutant source are the occupants, rather than operation of equipment or constant sources like wall and ceiling-tile shed- ding. Unfortunately, a search of literature did not produce any experimental evidence in support of this assumption. We did find, however, many investigations using occupancy as a proxy for the contaminants of concern [6,7,10,11]. While this assumption seems logical due to the inherent properties of living creatures, it also seems plausible to expect a certain amount of shedding from cleanroom processes and equipment. Thus it is imperative to verify the relative magnitudes of the aforementioned source strengths in order to develop effective cleanroom control systems. In a cleanroom setting with particulate loading on the order of ≤10 5 particles m -3 , contamination sources like wall- and ceiling- shedding, floor dust, equipment operation, etc. will introduce con- tamination, but these sources should be fairly constant and should appear whenever the cleanroom machines are in use, regardless of occupancy. Sources of this type set the baseline cleaning rate in a facility. Some may argue that the latter variable is occupancy- related, but machine activity likely is not directly proportional to occupancy. An OBCV cleanroom model, which depends on occupancy-sensors alone cannot be depended upon to maintain a cleanroom environment unless we can show that occupancy is, to 0378-7788/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2011.08.027