Modular clean room plenum

Details Modular clean room plenum Modular clean room plenum

2000-10-16

2003-02-04

Joyce, Harold (Department: 3749)

Ventilation

Clean room

C055S385200, C055S484000, C169S054000, C454S228000, C454S232000, C454S234000

Reexamination Certificate

active

06514137

ABSTRACT:

BACKGROUND
1. Field of the Invention
This invention relates to the construction of air delivery systems in clean rooms and, more particularly, to a modular clean room plenum for semiconductor manufacturing, aerospace, pharmaceutical and medical clean rooms and other applications where large volumes of particulate free, temperature and humidity controlled vertical laminar airflow are required.
2. Description of Related Art
Clean room air delivery systems are generally designed to filter out dirt and dust particles of a very small size, correct the humidity and temperature of the air, and supply that air into the clean room in a laminar airflow pattern. The laminar airflow may be either vertically downward from the ceiling to the floor, horizontally from one side of the clean room space to the other, or horizontally across the clean room work surface, and then downward to the floor. The vertically downward airflow direction is the most common in the industry.
The volume of air delivery to the clean room ranges from approximately 30 cubic feet per minute to 120 cubic feet per minute per square foot of clean room floor space. This volume compares to 1.0 to 1.5 cubic feet per minute per square foot of floor space in a typical office building. Such clean room air delivery systems are often used in semiconductor manufacturing clean rooms, but have numerous applications where a particulate-free, temperature and humidity controlled environment is required.
The design and construction process for structures built as clean rooms is typically both lengthy and costly.
FIG. 1
illustrates a conventional clean room and air barrier arrangement. Based on existing design principles, the normal sequence is to construct the building's foundations and shell
11
, including an extensive primary support structure
13
spanning the width and length of the clean room area using a minimum of intermediate support columns
12
. Primary support structure
13
may be constructed of steel trusses, steel space frames, or various types of concrete. A roofing system added to the top of the primary support structure
13
forms a primary air barrier
3
to contain air within the building.
Next, secondary support structure
37
is attached to and supported by the bottom of the primary support structure
13
. Secondary support structure
37
will support a secondary air barrier
35
covering the entire clean room area. The purpose of secondary air barrier
35
is to separate the “conditioned” supply air from the “dirty” return air. The “conditioned” supply air becomes “dirty” as it passes through the clean room space
17
and picks up heat, humidity, and dirt particles from persons, products, and machinery in the clean room space
17
. Depending upon the particular design of the clean room
17
, the “conditioned” supply air may be above the secondary air barrier
35
with the “dirty” return air below the barrier
35
, or the “dirty” return air may be above the secondary air barrier
35
and the “conditioned” supply air below.
Secondary air barrier
35
must be sufficiently strong to support the weight of workers who may have to enter the space above secondary air barrier
35
to conduct maintenance or modifications, and to support the entire underlying ceiling grid
39
and all of its components.
Following installation of the secondary air barrier
35
, a tertiary support system
45
is installed on the underside of the secondary air barrier
35
to support the ceiling grid
39
and its components. The secondary support structure
37
may also be required to support an automated material handling system
63
(a means of distributing product throughout the clean room) or other production equipment. The supports for such a material handling system
63
must penetrate the secondary air barrier
35
and are a source of air leaks, as well as being difficult to construct. The ceiling grid
39
which forms the tertiary air barrier comprises a sealed structural support system that may contain, but is not limited to, air filters, return air grilles, blank panels, and lights. The ceiling grid
39
also provides support for the fire sprinkler system. A piping system is added to the assembled ceiling grid
39
, a sprinkler main (not shown) is connected to the piping system, sprigs are installed, and sprinkler heads are connected to ceiling grid
39
. Electrical wiring and light fixtures are also connected to the ceiling grid
39
.
An exemplary ceiling grid
39
is described in U.S. Pat. No. 5,613,759 to Ludwig, Spradling, and Benson. As described in Ludwig et al., the ceiling grid
39
has a grid of interconnected rails in a rectangular pattern with openings between the rails generally 2′×4′, in dimension. These rails have moat-like channels on each side, which form a continuous moat around all sides of the rectangular openings. All of the rectangular openings will be in-filled with, e.g., high efficiency particulate filters (filters may be of any type well known in the art, such as a HEPA or ULPA filters, similar to those manufactured by, e.g., Flanders or Filtra), blank panels, lights, sprinkler head panels, and return air grills. The items installed in the ceiling grid
39
have downwardly depending flanges around their peripheral edges that fit into the moat-like channels of the grid
39
.
After each rectangular opening is filled, a gel sealant, e.g., BioMed 246 manufactured by Formula Brand Coatings & Products, is poured into the moat-like channels to seal the entire ceiling grid
39
. This sealed ceiling grid
39
forms the tertiary air barrier. Alternatively, other forms of sealants can be used to seal the ceiling grid. In addition, other types of ceiling grids
39
use T-shaped interconnecting rails and filters, blank panels, lights, sprinkler head panels, and return air grills with flat bottoms rather than downwardly depending flanges. These various panels are sealed into the grid system
39
using various forms of gaskets to prevent air leakage. Before the installation of the gel-sealant into the channels of ceiling grid
39
, the interior of building shell
11
must receive a thorough cleaning to remove dirt particles introduced into the space during construction.
After the ceiling grid
39
is installed, transfer air ducts
9
are installed extending from the secondary air barrier
35
to the ceiling grid
39
. In most clean room installations, there is an array of transfer air ducts
9
. However, for clarity,
FIG. 1
illustrates only one transfer air duct
9
. The transfer air ducts
9
may carry either “conditioned” supply air or “dirty” return air depending upon the air flow pattern of the design. If the “conditioned” supply air is above the secondary air barrier
35
, transfer air ducts
9
with balancing dampers
91
and flex connections
31
are installed from the secondary air barrier
35
down to each of the filters in the ceiling grid
39
. These transfer air ducts
9
will deliver “conditioned” supply air through the filters and into the clean room
17
. In this case, “dirty” return air passes through the return air grilles directly into the “dirty” return air plenum
41
below the secondary air barrier
35
. This embodiment is illustrated in FIG.
1
.
If the “conditioned” supply air is located below the secondary air barrier
35
, the “conditioned” supply air passes directly through the filters into the clean room space
17
. The “dirty” return air must then be ducted from the return air grills
5
(
FIG. 3
) in the ceiling
39
up through the secondary air barrier
35
into the “dirty” return air plenum
41
.
The “dirty” return air is taken through a recirculation air handling unit
21
, returned as “conditioned” supply air and delivered through the filters to the clean room space
17
. Recirculation air handling units
21
of this type are typically located outside the clean room space
17
. Alternatively, “conditioned” supply air may be circulated through a fan unit (not shown) located above the ceiling grid
39
and below the secondary air barrier
35
. These units are gene

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