Northwind MAC1211 Engineering, Installation And Service Manual page 13

EVAPORATOR DUCT ADAPTER
The evaporator duct adapter is used to transition the evaporator discharge opening to round duct. The standard grille
can be lifted out of the opening and the adapter can be dropped in its place. By attaching duct to the adapter, cold air
can be delivered to a location some distance from the unit.
Evaporator duct adapters can substantially reduce air noise and increase the number of options used for solving diffi-
cult and unusual cooling applications. All NorthWind units use a dedicated, automatic, 2-speed evaporator blower
controlled by the fan speed switch mounted on the unit control panel. Another important topic to consider is the
amount of duct that can be attached to a unit. Adding duct adds resistance to airflow. Too much duct will prevent the
unit from operating properly. For proper application, "equivalent feet" must be calculated. To calculate equivalent
feet, add the number of feet of duct on the inlet side of the blower (inlet air plenum) plus the number of feet on the dis-
charge air side (duct connected to evaporator duct adapter).
Then, for every 90° elbow in the ducting, add 6 feet to the calculation. Here is an example of an equivalent feet calcu-
lation:
This quick reference chart illus-
trates maximum equivalent feet and
maximum E.S.P. (External Static
Pressure) allowed for the evaporator
section of NorthWind units.
EVAPORATOR AIR PLENUM
Evaporator Air Plenums are used to connect round duct to the evaporator inlet air of the unit. The plenum attaches to the unit
by removing the grille and dropping in the plenum in its place on all models.
Evaporator air plenums can substantially reduce air noise and increase the number of options used for solving difficult and
unusual cooling applications. All NorthWind units use a dedicated, automatic, 2 speed evaporator blower controlled by the
fan speed switch mounted on the unit control panel. Another important topic to consider is the amount of duct that can be
attached to a unit. Adding duct adds resistance to airflow. Too much duct will prevent the unit from operating efficiently.
For proper application, "equivalent feet" must be calculated. To calculate equivalent feet, add the number of feet of duct on
the inlet side of the blower (inlet air plenum) plus the number of feet on the discharge air side (duct connected to evaporator
duct adapter).
Then, for every 90° elbow in the ducting, add 6 feet to the calculation. Here is an example of an equivalent feet calculation:
Number of feet of duct attached to discharge flange
Number of feet of duct attached to inlet plenum
Number of 90° elbows in discharge run, 1 (= 6 feet)
Number of 90° elbows in inlet run, 2 (= 12 feet)
The quick reference chart illustrates
maximum equivalent feet and maxi-
mum E.S.P. (External Static Pres-
sure) allowed for the evaporator sec-
tion of NorthWind units.
Number of feet of duct attached to discharge flange
Number of feet of duct attached to inlet plenum
Number of 90° elbows in discharge run, 1 (= 6 feet)
Number of 90° elbows in inlet run, 2 (= 12 feet)
Evaporator Duct
Adapter Model
EDA12, 18
EDA36
EDA60
EDA90
Total equivalent feet
Evaporator
Plenum Model
EAP12
EAP18
EAP36
EAP60
EAP90
15
20
12
Total equivalent feet 53
Round Duct
Size, Inches
8
16
16
18
15
20
6
12
53
Round Duct
Size, Inches
12
12
16
16
18
13
6
Maximum Maximum
Equivalent Feet
40
80
110
120
Maximum
Equivalent Feet
30
40
80
110
120
E.S.P.
.50
.50
.70
.90
Maximum
E.S.P.
.40
.50
.50
.70
.90