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37MUA-PRC001-EN
Options
Motorized Return Air Damper
Purpose
To provide a way for recirculating return
air.
Operation
A two position switch controls the return
air damper.
When the two position switch is in the
“RA” position, the RA damper opens.
Fifty percent of supply air is RA,
50 percent of supply air is OA.
RA damper can be set to allow from
0 percent to 50 percent return air by field
adjustment of the linkage rods. The gas
valve opening is restricted when the RA
damper is open.
Code requires that outside ventilation air
be provided to the space in the amount
of 4 cfm per 1 MBh of burner rated
input.
All units are provided with a means that
will allow the customer to interlock OA
fans when the amount of OA provided
by the unit is not sufficient to meet the
4 cfm per 1 MBh requirement.
When the two position switch is in the
“OA” position, the RA damper is closed,
and 100 percent of supply air
is OA.
Note: This option cannot be used with a
two speed fan motor.
Motorized 75/25 Damper
Purpose
To provide a way for recirculating return
air and letting building pressure control
the amount of air which is recirculated.
Operation
If building pressure is less than desired,
the RA damper modulates to a more
closed position and the interlocked
burner profile damper modulates to a
more open position. More OA is brought
into building.
If building pressure is greater than
desired, the RA damper modulates to a
more open position and the interlocked
burner profile damper modulates to a
more closed position. Less OA is brought
into building.
At no time will the unit provide less than
25 percent OA to the building.
In general terms, the minimum OA is
25 percent; however, there are
cases where it can be as high as
40-50 percent, depending upon unit size,
burner size, gas train type and
gas pressure.
Code requires that outside ventilation air
be provided to the space in the amount
of 4 cfm per 1 MBh of burner rated input.
All units are provided with a means that
will allow the customer to interlock OA
fans when the amount of OA provided
by the unit is not sufficient to meet the 4
cfm per 1 MBh requirement.
Note: This option cannot be used with a
two speed fan motor.
Note: This option can be used with
either the Motorized Inlet Damper
option or the Motorized Outlet Damper
option.
Option Includes:
• Return air damper
• Burner profile damper
• Linkage
• Modulating damper motor(s)
• Photohelic differential pressure gauge
Note: This option can be used with
either the Motorized Inlet Damper
option or the Motorized Outlet Damper
option.
Option Includes:
• Return air damper
• Two position damper motor
• Damper switch