Building and Environment 43 (2008) 1545–1552
Characterization of minienvironments in a cleanroom: Assessing energy
performance and its implications
Tengfang Xu
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Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, One Cyclotron Road, Building 90R3111, Berkeley, CA 94720, USA
Received 18 July 2006; accepted 24 September 2007
Abstract
Filtered fans in cleanrooms can demand up to 400 W or more electric power per square meter of floor area to rapidly supply,
recirculate, and exhaust air. ‘‘Minienvironments’’ that control particle concentrations within enclosures may not only maintain a level of
stringent cleanliness, but also offer opportunities in energy savings and reducing operation costs through integration with adjacent
cleanrooms. In order to better understand the total performance of minienvironments in operation, this paper characterizes energy
performance of five different minienvironments (designated as ISO-Cleanliness-Class-3) that were in operation and were housed in a
traditional, larger ISO-Cleanliness-Class-4 cleanroom used in the microelectronic industry. The measured parameters in the field
investigation included electric power demand, airflows, in addition to physical characteristics and cleanliness performance of the
minienvironments. In this paper, measured energy performance and associated metrics are compared to those of cleanrooms of various
cleanliness classes. This paper develops new understanding of energy performance of minienvironments and quantifies the magnitudes of
potential energy savings that could result from integrating minienvironments in traditional cleanrooms while achieving effective
contamination control. Based upon this study, achieving energy savings by a magnitude of up to 60–86% was possible in the cleanroom
facility housing the minienvironments. The paper also suggests means of increasing energy savings in minienvironments applications,
including optimal design and operation, and space management in clean spaces.
Published by Elsevier Ltd.
Keywords: Minienvironment; Cleanroom; Airflow; Fan-filter unit; Energy; Electric power demand; Electric power density; Cleanliness; Contamination
control; Energy performance index
1. Introduction
Cleanroom air-recirculation systems may account for a
significant portion (e.g., 50%) of the HVAC energy use in
cleanrooms. In cleanrooms, high electric power density for
fans to deliver airflows, defined as the fan’s electric power
demand divided by the cleanroom floor area, would
normally be expected because of large volume of airflows
that is supplied, recirculated, and exhausted within a given
time. Therefore, design of cleanroom airflow systems may
have a long-term impact on energy usage [1–3] in that the
amount of designed airflows significantly affects the
operation costs associated with energy, initial equipment
costs, and installation costs. In fact, an efficient and
optimally sized airflow system may not only reduce initial
costs, but also help cleanrooms achieve high performance
that benefits effective contamination control, productivity,
and reliability.
With the demand for better contamination control in
specific applications to achieve higher cleanliness [4,5], e.g.,
within a localized and relatively small space, it is important
to optimize the design of clean spaces, airflows, filtration
system to meet cleanliness requirements and to achieve
effective particle control. As an added benefit, optimizing
airflows, layout, and sizing of clean spaces may potentially
offer energy savings.
Expected to maintain a level of stringent cleanliness in a
tightened volume of clean spaces, a minienvironment is
a localized environment created by an enclosure to isolate a
product or process from the surrounding environment
[6,7]. The purpose is to achieve effective control of particle
ARTICLE IN PRESS
www.elsevier.com/locate/buildenv
0360-1323/$ - see front matter Published by Elsevier Ltd.
doi:10.1016/j.buildenv.2007.09.003
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Tel.: +1 510 486 7810; fax: +1 510 486 4089.
E-mail address: ttxu@lbl.gov