ALL ABOUT THE
CPA
The environmental system controlling critical process
room air of course includes diffuses and ducting.
However, the most important element is the CPA
critical process air-handling unit itself. It has the
system’s air moving devices and provides the rooms
heating, cooling, dehumidification or humidification,
pressurization, and the air filtration requirements. The
CPA unit is designed with ultimate flexibility so it can
be designed to match each room’s particular needs.
Many design decisions are necessary to select the proper size CPA unit (see “CPA –
Formal Selection” section), however once the size unit is selected, the particular
features of the unit must then be determined. The following discussion will aid in
selecting the proper CPA features.
Casing:
The CPA unit has an option of two panel types and three insulation options.
The basic CPA exterior casing is constructed
of 18 gauge, G235 galvanized steel,
unpainted, with 2” of rigid non-combustible
fiberglass insulation. The inner liner of the unit
consists of a watertight, sanitary liner
constructed of 16 gauge, G235 galvanized
steel. The panel construction is a self-framing
construction with the panels forming the
structure for the unit casing. Casing fasteners are internal to the panel, or outside
the unit, with no panel fasteners on the inside of the unit. All interior seams are
sealed air and water tight with an FDA approved sealant so the interior is
watertight. Unless customer specified, the fiberglass insulation would be used
down to a 55°F discharge air temperature.
An alternate of 2” polyurethane is also available. Again, unless a customer
specifies differently, this insulation would be used down to 32°F discharge air
temperature.
With either of the 2” panel designs there is the option of an 18 gauge 304 stainless
steel inner liner. With this option, the inner walls, all drain pans, closures, filter
frames and dampers are stainless steel. Unless specified differently, the blower,
motor, and coil will be of a standard construction.
The third option is a 4” polyurethane foamed in
place cam lock panel construction with 26 gauge
white galvanized exterior and a 26 gauge
galvanized interior. An option of a 26-gauge
stainless steel liner is also available. This panel
construction is available for all temperatures
however would typically be used for applications
where the leaving air is below 32°F. The roof on the
unit shall be an EPDM rubber roofing material.
Roof:
The roof of the 2” panel casing is a minimum of 18 gauge, G235 galvanized steel,
standing seam type construction, pitched away from the service doors for good
water runoff. (On CPA units size 12 and larger only). All exterior seams are sealed
air and water tight with an FDA approved sealant.
The interior liner of the roof shall be a minimum of 16 gauge, G235 galvanized steel
or the optional 18 gauge, 304 stainless steel. As with the walls, the interior of the
unit shall be completely sealed watertight using a food grade sealant.
Drain Pans:
Each section of the unit, no matter what the wall
construction, shall be complete with drain pans, which
shall be a minimum of 16 gauge, G235 galvanized
steel. Each drain pan shall be fully welded and
individually tested to ensure they are leak free.
On all units with a cooling coil section, the drain pan
under the cooling coil shall be constructed of 304
stainless steel.
When the stainless liner option is selected, all the drain pans are stainless steel.
The drain connection for the drain pans are designed so the pans drain out the
bottom of the drain pan for full drain pan drainage with the drain connection then
extend out the side of the unit. This construction prevents standing water in the
drain pans.
Frame:
The frame on all CPA units size 12 and larger is constructed of a double Cchannel, G235 galvanized steel all welded frame.
On CPA units size 8 and smaller, the base shall have a 10 gauge single channel,
G235 galvanized steel all welded frame.
Removable lifting lugs are provided at the base of the corners of each section of
the unit.
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On the 2” panel construction, the space between the bottom of the unit and the
bottom of the drain pan is fully insulated. On the 4” cam lock option, the bottom
of the unit is also a cam lock 4” panel.
Access Doors:
Access doors are provided with an extruded aluminum full perimeter frame. The
frame extrusions shall be miter cut at the corners and assembled by mechanically
staking the frame into concealed gussets made of extruded aluminum.
Each door is pressure injected with 2.5# of polyurethane foam per cubic foot of
door.
The interior and exterior panels are constructed of 24 gauge, G90 hot dipped
galvanized steel with the option of 304 stainless steel.
The doors are mounted to the frame by a minimum of two (2) polycarbonate
adjustable hinges.
The doors can have an optional 8” x 8” plastic window.
On units operating below 55°F, the doors and door frames will have a thermal
brake. This is standard on both the 2” and 4” cam lock construction.
Each door is complete with a minimum of two (2) 90-degree polycarbonate
handles, operable from the interior and the exterior of the unit.
Outside and Return Air Dampers:
The dampers are parallel blade (optional
opposed blade), with nylon bearings and
stainless steel spring loaded side closures.
The construction will be a minimum of 16 gauge
galvanized steel single blade design, with 304
stainless as an option, and a 12-gauge casing.
Airfoil blades have a hollow core, with are
typically not sealed (and therefore becomes a
cleaning issue), and therefore are not
recommenced.
The dampers have a low leak rating of less than 6.5 CFM per square foot at 4” of
differential static pressure. The standard operator is a direct drive motor requiring
no linkage. Lower leakage rating dampers are also available.
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Blowers:
The blowers are a centrifugal backward curved or
airfoil plenum type blower.
The blower have inlet screen as a standard
component.
The wheel is be supported by two (2) self-aligning
outboard bearings, which shall be self-aligning, ball
bearing, pillow block and shall be designed for at least
200,000 hours of average life.
The blower shaft are ground and polished.
The blower wheel, inlet funnel and support are of a steel construction, completely
coated with an air-dry enamel coating. Other coatings available for special
applications.
The overload service factor used for the V-belt drive selection is at least 1.50.
Fixed sheaves are standard and are a cast iron type (optional – adjustable motor
sheaves for plus or minus 5% adjustability). The V-belt drives are of a standard
capacity and furnished with reinforced rubber belts.
The blower will be in the draw through position (optional – blow through position
depending on the application).
Optional - the blower, motor and drive shall be spring isolated and be complete
with a flexible connection.
Optional - the drive shall be complete with a belt guard.
Optional - the blower shall be complete with a discharge screen.
Optional – The bearings shall have plastic extended greaselines run to the outside
of the unit casing.
Optional – The shaft shall be stainless steel.
Motors:
The motors shall be Epact efficient TEFC duty, 1800 nominal RPM with an option for
premium efficiency or wash down duty. Motors are mounted on an adjustable
motor base.
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HEATING OPTIONS:
Steam Coils:
The steam coil number of rows and fins are selected for the specified project.
Typically no more than 8 FPI are used.
The steam coil is typically in the reheat position (optional - pre-heat position).
Since it is fully modulating, it works well for both heating outside air and for low
temperature rises, such as during a reheat mode.
Steam coils are typically constructed with 035” wall copper tubes and 0.0095”
thick aluminum fins (optional – heavier tubes and fins or stainless steel tubes and
aluminum fins or carbon steel tubes and aluminum fins).
The coils are designed for a maximum operating pressure of 25 psi (optional - 100
psi steam) and for a maximum face velocity of 800 feet per minute.
Optional: Face and bypass dampers on the steam coil. The dampers shall be
the same construction as the other dampers in the unit. Face and bypass
dampers are typically used with systems requiring large percentages of outside
air.
Hot Water or Glycol Heating Coils:
The hot water coil or glycol coil will have the rows and fins selected for the
project. Typically no more than 8 FPI is used.
The coil shall be supplied in the reheat position (optional - pre-heat position).
The coil shall be constructed with 0.025” wall copper tubes and 0.014” thick
aluminum fins (optional – 0.022” fins or stainless steel tubes and aluminum fins).
Headers shall be stainless steel.
The coil shall be designed for a maximum face velocity of 800 feet per minute.
Hot Gas Ammonia Heating Coil:
The hot gas ammonia heating coil will have the rows and fins required for the
project.
The hot gas coil is typically supplied in the reheat position (optional - pre-heat
position). Since the heat output is minimal with hot gas, it is not a good option for
heating large volumes of outside air.
The hot gas ammonia coils can be constructed with hot dipped galvanized steel
construction, Thermal-Pac® design, all aluminum construction, Thermal-Pac®
design, or stainless tube/aluminum fin. The hot dip galvanized construction will
have no more than 6 FPI with the aluminum fin coil at 8 FPI.
The coil shall be designed for a maximum face velocity of 800 feet per minute.
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Direct Fired Heating Section:
The unit is can be designed with a direct-fired burner
located in the outside air section of the unit. Directfired burners must be in the outside air stream, by
code, since the flame is in the air stream and the
particles of combustion go into the air. The direct-fired
burner has a cast iron header with stainless steel baffle
plates. The burner will have the capacity to meet the
project needs. Direct-fired burner by definition is 100%
efficient.
The standard burner is designed for 1-5 PSI natural gas
pressure (optional - 8-14” or high pressure systems above 5 PSI – both having a
cost add) and is fully modulating with a 25 to 1 turndown ratio. The burner shall
have adjustable profile plates.
The controls will be fully modulating and be designed in accordance with
Factory Mutual (FM) insurance guidelines (optional - IRI insurance guidelines).
The gas train shall be complete with all safety devices and controls.
Typically direct-fired burners can be used for both production heating and for
the cleanup cycle. However for proper burner operation a minimum of
approximately 20% outside air is usually required.
Indirect Fired Heating Section:
The unit can be designed with an indirect fired
heating section. Indirect fired heating is typically used
when direct fired cannot be used because of a local
code or when the food product in the room cannot
accept direct fired.
The indirect fired burner is fully modulating. The heat
exchanger, primary and secondary, shall be 300 series
stainless steel and be complete with drain connection.
Proper disposal of any condensate formed shall be by the installation contractor
or the end user.
The burner shall have the capacity specified for the project.
The burner shall be designed for 1-5 PSI natural gas pressure (optional - 8-14” or
high pressure systems above 5 PSI – which have a cost add).
The controls shall be full modulating and be designed in accordance with
Factory Mutual (FM) insurance guidelines (optional - IRI insurance guidelines).
The gas train shall be complete with all safety devices and controls. Turndown
shall be a minimum of 8 to 1 (optional 10 to 1 and 20 to 1). Due the low
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turndown, an indirect fired system is probably not a good choice for reheat
applications.
The heat exchanger is complete with flue stack and rain cap (shipped loose for
field mounting).
Typically indirect fired heat exchangers are 75-80% efficient.
COOLING OPTIONS:
Recirculating/ Direct Expansion/ Flooded Cooling Coils:
Cooling coils will have the rows and fins necessary to
meet the project capacity requirements.
The coils can be designed for recirculating ammonia
(minimum 3 to 1 feed rate typically). The coil must be
supplied with a minimum of 28°F liquid temperature.
Lower liquid temperatures can cause the coil to form
ice.
As an option, the coils can be supplied for direct
expansion or flooded ammonia.
The coil(s) for ammonia use can be constructed using EVAPCO’s exclusive
Thermal-Pac® design, with 0.060” wall tubes and 0.014” thick fins hot dipped
galvanized steel (maximum of 6 FPI), aluminum coil with 0.058” thick aluminum
tubes and 0.014” thick aluminum fins (typically no more than 8 FPI) or 0.025” wall
stainless tubes and 0.014” thick aluminum fins (typically no more than 8 FPI), or all
stainless steel). Coils will meet strength requirements of ASME/ANSI B31.5. All
coils shall be charged with nitrogen prior to shipment.
Option - The coil(s) for R-22, R-404a, R-134a or any of the similar refrigerants and
will be constructed using 0.025” wall tubes copper tubes and 0.014” thick
aluminum fins (typically no more than 8 FPI). Headers shall be stainless steel. All
coils shall be charged with nitrogen prior to shipment. Coil shall meet strength
requirements of ASME/ANSI B31.5.
The coils shall be designed for a maximum face velocity of 625 feet per minute.
Flooded coils can be supplied with an ASME certified
surge drum with a special support so the drum can be
mounted on the top of the CPA unit. All
interconnecting piping must be field supplied. The
surge drum and roof support are shipped loose for field
mounting on top of the unit.
Option – Roof access ladder and catwalk with railing for
access to the drum and controls.
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Chilled Water or Glycol Cooling Coils:
Cooling coils shall have the rows and fins per inch to meet the project cooling
requirements.
The coils can be constructed with 0.025” thick copper tubes and 0.014” thick
aluminum fins (optional – 0.022 thick fins) or stainless steel tube and aluminum
0.014” thick fins (optional – 0.0.22” thick fins), or all stainless steel. Coil shall meet
strength requirements of ASME/ANSI B31.5.
FILTRATION:
Although food plants are not classified as “clean rooms” by the classical sense, they
certainly are operated as rooms that have similar filtration levels. What makes them
different is possibly the level of access to them, the amount of traffic, the type of
processes, and the clothing worn by the personnel.
Clean room air cleanliness levels are defined by the number of particles of a certain
size and larger per cubic foot of air when the room is tested with a particle counter.
An ISO 5 (old class 100) clean room can have a maximum of 100 particles .5 micron
and larger in a cubic foot of air. The number and location of sampling points within a
room should be based on the specified cleanliness level and the number of critical
locations within the room.
The table below will define Class of room and the type filters for a traditional
clean room.
ISO CLASS OF
ROOM
RANGE OF %
OF FILTER
COVERAGE
TYPE OF
FILTERS
ISO 3 (Class 1)
100%
ISO 4 (Class 10)
100%
ISO 5 (Class 100)
100%
ISO 6 (Class 1000)
ISO 7 (Class 10,000)
ISO 8 (Class 100, 000)
30% TO 55%
10% TO 20%
5% TO 10%
ULPA OR
BETTER
ULPA OR
BETTER
HEPA OR
ULPA
HEPA
HEPA
HEPA
Recently the methods for testing and rating filters have been changed to what is called
the MERV (Minimum Efficiency Reporting Value). The following table gives the current
filter ratings:
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Standard 52.5
MERV
Dust Spot
Efficiency
Arrestance
Typical Controlled
Contaminant
20
n/a
n/a
<0.30 micron
19
n/a
n/a
Virus (unattached)
18
n/a
n/a
Carbon dust
17
n/a
n/a
Combustion Smoke
16
n/a
n/a
0.3 to 1.0 micron
15
>95%
n/a
All Bacteria
14
90-95%
>98%
13
89-90%
>98%
12
79-75%
>95%
1.0-3.0 micron
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60-65%
>95%
Legionella
10
50-55%
>95%
Milled Flour
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40-45%
>90%
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30-35%
85%
Most Tobacco Smoke
Pre-filter
The CPA will always use a filter at the inlet to the unit. This is typically used as a pre-filter
however can be the only filter too, as in the CPA-XX-30 unit. A pre-filter is used to help
keep the interior of the unit clean and to extend the life of the final filter.
Pre-filters:
Pre-filters are pleated 4” thick and have an average efficiency of 25- 30% (MERV
8), with synthetic media (optional - aluminum or stainless steel washable filters).
The standard units, at maximum capacity, will have a filter velocity of 625 FPM.
The unit shall be supplied with one initial set of filters (option – the unit shall be
supplied with two sets of filters).
The prefilters shall be held in individual holding frames for upstream service. The
filter frames shall be constructed of hot dipped galvanized steel (stainless steel if
the interior is also of stainless steel).
Optional – pre-filter differential pressure gauge to indicate when the filters should
be changed.
The typical initial pressure drop is approximately 0.4” w.g. with the final pressure
drop of 1.0” w.g. Depending on the application, the filters will last 30-90 days.
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Final Filters:
The final filters shall be a 95% (MERV 14) efficient;
mircofine glass wet laid paper with aluminum
separators (the same material used in HEPA,
absolute filters). The filters shall be of a cartridge
type. The 95% filter shall have a rating of 95%
efficient on a 1 micron particle size. The standard
unit, at maximum capacity, will have a filter velocity
of 625 FPM.
The CPA unit is also available with an optional 99.97% DOP absolute HEPA filter.
The media on the HEPA filter shall be a microfine glass. The HEPA filter shall have
a rating of 99.97% on a 0.3 micron particle size. Depending on the application,
a 65% intermediate filter can also be supplied which will greatly extend the life of
the HEPA filter.
Each of the final filters shall have their own individual holding frames for upstream
service. The holding frame shall be constructed of galvanized steel with stainless
steel used in units with stainless liners.
The typical initial pressure drop on the 95% filter is approximately 0.6” w.g. with
the final pressure drop of 1.2” w.g. and for the HEPA filter approximately 1.2” w.g.
initial drop and a 2.0” final pressure drop. Depending on the application, the
filters will last 8-12 months.
The unit is supplied with one set of final filters (optional - unit supplied with two
sets of final filters).
The final filters are complete with a differential
pressure gauge. The gauge is used to determine
when the filters should be changed. The gauge
can be a visual gauge on the side of the unit or
can be a differential pressure switch or
transducer that can be used to provide a remote
indication of the condition of the filters. The
gauge is also available for the pre-filter section.
See the appendix for additional information on contaminants and airborne
contamination control.
ACCESSORIES
Outside Air Inlet Hood:
The unit includes an outside air inlet hood
constructed of G235 galvanized steel.
The hood shall be complete with a bird screen
(optional - insect screen).
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The hood shall be shipped separate from the unit.
Integral Exhaust Section:
The integral exhaust section comes complete
with direct drive exhaust fans located within the
casing of the CPA unit.
Each of the fans shall be constructed of with a
cast aluminum hub and adjustable
polypropylene blades. Fans are direct drive.
(Optional cast aluminum blades).
Service for the integral exhaust fans shall be
accomplished through full sized walk-in access doors (no internal hatches).
Each fan shall be driven by a TEFC or TEAO fan direct drive motor. Motors shall
be VFD duty if used for room pressure or economizer control. The standard
motor is Epact efficiency with an option for premium efficiency.
Each fan shall have a low leakage gravity back draft damper (optional double
damper for lower temperature applications). The material of the dampers will
match inner liner and exterior casing material.
Desiccant Dehumidification Section:
The dehumidification section consists of a rotor
(wheel) of media impregnated with a silica gel
desiccant. The wheel has of a process section
(where the moisture is removed from the air
stream) and a regeneration section (where the
moisture is removed from the air stream).
The section will include a heated regeneration
section with a heat source to drive the moisture
from the wheel. The heat source shall be
direct-fired natural gas (optional steam, electric, or indirect fired natural gas).
ESS Ultra Violet Light System:
The optional ESS system is mounted on the
leaving air side of the cooling coil so the coil
and the drain pan are bathed in the UVC light.
On the average the unit will require one bulb
per 4 sq. ft. of coil face area. Each bulb will
draw approximately 0.7 amps (120 volt, 1
phase, 60 Hz) and will last one year. See the
appendix for a complete discussion on ESS –
“White Paper – ESS Ultra Violet Light Systems”.
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ELECTRIC CONTROLS:
Each unit can be supplied with an electro-mechanical control system (optional –
PLC system).
The following are some of the many options, which are available for the control
System:
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Main control panel, control transformer
and terminal blocks.
Outside air and recirculated air controls
which use outside air on an economizer.
Outside air and recirculated air controls
providing a fixed amount of outside air.
Outside air damper controls for systems
with100% makeup air.
Room thermostats or RTD’s (typically
mounted in the remote panel).
Return air thermostat or RTD’s
Outside air thermostat or RTD’s
Motorized steam valve (field mounted). Trap by others.
Magnetic motor starters mounted in the control panel.
Disconnect switches mounted in the control panel.
Remote stainless steel control panels which can include (just a few of the
possible options):
- blower on/off switch
- blower indicating light
- cleanup switch
- cleanup indicating light
- dirty filter light
- burner Indicator light
Steam coil freezestats.
Hot water or glycol 3-way control valves.
Chilled water or glycol 3-way control valves.
Room de-humidistat located in the remote
control panel (or return air).
Natural gas heating controls – either direct
or indirect fired.
Discharge air ammonia detector.
Smoke detectors.
CO2 detectors
Interior service lights.
Service receptacles.
Room pressurization control.
Heating coil face and bypass dampers and
damper controls.
Two-speed motors and starters.
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VFD motor control
Exhaust motor starters.
Cleanup cycle system and controls.
UVC coil/drain pan light systems.
Blower door interlock switches
Dirty filter lights/contacts.
RVS, ASME surge drums mounted on top of the
unit complete with dual relief valves.
PLC or DDC controls with customer specified
alarms, interface, and data collection.
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