ASHRAE Journal - November 2019 - 47

ASHRAE - CELEBRATING 125 YEARS

into three general categories:13,14
* Conventional cleanrooms did
not have a self-cleaning capability to
offset contamination brought into
the room by personnel and equipment or not captured by the air
filtration system.
* Airflow patterns in conventional cleanrooms are generally not
uniform, nor are they directed in a
manner that carries particulate matter away from critical work areas. In
addition, they will not remove airborne contamination from the room
as quickly as it is brought in.
* Since all personnel in a conventional cleanroom contribute heavily
to room contamination, rigid personnel controls were required.
Whitfield's team focused on the
need for self-cleaning, examining
the airflow volume and air patterns
within the space. It appeared that
greater airflow would be a partial
solution. However, it was known
that when airflow was increased in a
previous cleanroom design, the contamination level rose. This is partly
due to agitation of settled particles,
and partly to the fact that particles
blown off personnel and equipment
was dispersed into the air. The use
of air blasts was also evaluated, but
the same problem of just moving the
particles around the room persisted.
Therefore, they wanted to avoid an
air blast from supply diffusers.15
Trying to avoid the air blast problem, the team initially considered a
design using single-pass unidirectional airflow using the ceiling as a
large diffuser. This solution would
slow the air down and mitigate the
perceived air blast and particle
dispersion, avoid the perception of
draft by the workers and provide a
quieter environment. This solved

Figure 2 Willis Whitfield's "laminar flow" cleanroom
design.13

the supply side-but how to remove
the air from the space?
At first Whitfield's team was going
to use a large number of return
grilles located near the floor at the
walls. The problem with this was
larger particles would still settle
to the floor. The concept of using a
perforated floor was proposed and
a pilot test conducted. Having the
air leave at the floor would allow for
air movement to assist in the natural settling of particles by gravity.
A prefilter was installed just below
the floor to capture the particles and
avoid their being reintroduced into
the space (Figure 2). Early concerns
that the constantly moving air would
irritate workers in the space were
allayed by the actual rate of movement. The air moved at about 1 mph
(1.6 km/h), resulting in about 10
changes of air per minute.
By the end of 1961 the team had
constructed a "laminar flow" cleanroom. The room was relatively small,
only 6 ft × 10 ft (1.8 m × 3.0 m) with
a 7 ft (2.1 m) high ceiling (Figure 3).
After testing the first version, a "portable" version was also built (Figure 4),
and later a knock-down version was
built, allowing for disassembly of the
room where all components could fit
through a 3 ft (0.9 m) wide door.
This cleanroom was 1,000 times
cleaner than the contemporary
cleanrooms of the time and 100

Figure 3 Willis Whitfield in prototype "laminar flow"
cleanroom. 13

Figure 4 Willis Whitfield's "knock-down" portable
cleanroom.13

times cleaner than clean work
hoods. Circulating large amounts of
air provided a "sweeping" function
over the working area. Whitfield
said "the room almost 'cleans'
itself." 16 Whitfield gave his initial
paper on what was then called the
"ultra-clean room" at the Institute of
Environmental Sciences meeting in
Chicago in 1962.13,17 (Figure 5).
The success of the laminar flow
cleanroom and clean bench quickly
spread to other agencies and contractors supporting military products and space products. Even the
popular press jumped into anointing Whitfield "Mr. Clean." 18 Sandia
was inundated with requests to
see the ultra-clean room.19 The
ability of laminar flow to reduce

N O V E M B E R 2 0 19

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ASHRAE Journal - November 2019

Table of Contents for the Digital Edition of ASHRAE Journal - November 2019

Contents
ASHRAE Journal - November 2019 - Intro
ASHRAE Journal - November 2019 - Cover1
ASHRAE Journal - November 2019 - Cover2
ASHRAE Journal - November 2019 - 1
ASHRAE Journal - November 2019 - Contents
ASHRAE Journal - November 2019 - 3
ASHRAE Journal - November 2019 - 4
ASHRAE Journal - November 2019 - 5
ASHRAE Journal - November 2019 - 6
ASHRAE Journal - November 2019 - 7
ASHRAE Journal - November 2019 - 8
ASHRAE Journal - November 2019 - 9
ASHRAE Journal - November 2019 - 10
ASHRAE Journal - November 2019 - 11
ASHRAE Journal - November 2019 - 12
ASHRAE Journal - November 2019 - 13
ASHRAE Journal - November 2019 - 14
ASHRAE Journal - November 2019 - 15
ASHRAE Journal - November 2019 - 16
ASHRAE Journal - November 2019 - 17
ASHRAE Journal - November 2019 - 18
ASHRAE Journal - November 2019 - 19
ASHRAE Journal - November 2019 - 20
ASHRAE Journal - November 2019 - 21
ASHRAE Journal - November 2019 - 22
ASHRAE Journal - November 2019 - 23
ASHRAE Journal - November 2019 - 24
ASHRAE Journal - November 2019 - 25
ASHRAE Journal - November 2019 - 26
ASHRAE Journal - November 2019 - 27
ASHRAE Journal - November 2019 - 28
ASHRAE Journal - November 2019 - 29
ASHRAE Journal - November 2019 - 30
ASHRAE Journal - November 2019 - 31
ASHRAE Journal - November 2019 - 32
ASHRAE Journal - November 2019 - 33
ASHRAE Journal - November 2019 - 34
ASHRAE Journal - November 2019 - 35
ASHRAE Journal - November 2019 - 36
ASHRAE Journal - November 2019 - 37
ASHRAE Journal - November 2019 - 38
ASHRAE Journal - November 2019 - 39
ASHRAE Journal - November 2019 - 40
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ASHRAE Journal - November 2019 - 45
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ASHRAE Journal - November 2019 - 47
ASHRAE Journal - November 2019 - 48
ASHRAE Journal - November 2019 - 49
ASHRAE Journal - November 2019 - 50
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ASHRAE Journal - November 2019 - 52
ASHRAE Journal - November 2019 - 53
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ASHRAE Journal - November 2019 - Cover3
ASHRAE Journal - November 2019 - Cover4
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