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As with any air filtration system, external airflow losses not attributable to the air filtration unit will
reduce the airflow of the system. The following recommendations can minimize airflow losses created
by external static resistance.
1. Always use the minimum length of ducting possible with the fewest possible number of turns
and bends.
2. Rigid metal ducting creates less turbulence and consequently less airflow loss than flexible
ducting. Regardless of the type of ducting used, rigid, “sweep-type’, radiused connections
should be used for all turns and bends.
3. If flexible ducting is used, it must be kept as taut as possible to avoid flattening.
LOCATION OF THE UNITS AND MODES OF OPERATION
1.
Negative Pressure
- used to help ensure that airborne contaminants do not escape from a
contained area, by maintaining negative (lower) air pressure within that area compared to
adjacent areas. This is generally accomplished by placing the unit inside the containment
area and exhausting filtered air from the unit out of the area. The filtered air must be
exhausted outside of the containment area, either directly to the outdoors, or into another
part of the building. To maintain negative pressure, the air exhaust must exceed the air
supply by the greater of: 10% or 100 CFM. To achieve this differential, the air supply volume
to the area may have to be reduced. Negative pressure levels should be continuously
monitored.
2.
Recirculation
-
used to reduce concentrations of airborne contaminants in a room or area
by continuously cleaning the air and exhausting it back into the same room or area.
3.
Positive Pressure
- used to help prevent airborne contaminants from entering a
containment area, by keeping that area under positive pressure compared to adjacent
spaces, so any air leakage will be an outflow of clean air, and not inflow of contaminated air.
This pressure differential can be established by:
a. placing the unit inside the containment area, and using it to pull air into the area by
attaching flex duct between the inlet collar and a location outside of the containment
area.
b. placing the unit outside of containment area, and using it to push HEPA-filtered air
into the area through flex duct attached between the outlet collar and a location inside
the area.
To ensure that the proper pressure differential is maintained, the volume of HEPA-filtered air
supplied to the area must be the greater of: 10% or 100 CFM higher than the volume of air
exhausted from it by the HVAC system. Positive pressure levels should be monitored
continuously.
Important Note: Do not operate the unit unless the pre-filter(s) and HEPA filter are installed,
and the filter access door and panel are in place and closed.
DAISY CHAINING
“Daisy Chaining” refers to the operation of multiple units on one circuit, with only one of the units
plugged into a 120V/15A electrical power supply receptacle. Each subsequent unit is plugged into
one of the GFCI receptacles on the prior unit, up to the maximum number allowed based on the
amperage draw per unit. The National Electrical Code limits the total amperage draw of devices
operating on one circuit to 80% of full load, which means that the total amperage draw on a 120V/
15A circuit, including the unit plugged into the building electrical power supply receptacle, must not
exceed 12 amps.
A total of three PAS1200 units can be “Daisy Chained” on a 15 amp circuit, including the unit
plugged into the building electrical power supply receptacle.
