4
SDRA heaters can be easily field if modified to vary the fan
speed. There may be some circumstances where the use of
short lengths of duct may not create sufficient pressure drop
to achieve the desired temperature rise. This may also be the
case of using the unit without a duct. This insufficient static
pressure drop may result in high air flow, with the maximum
temperature rise below the desired level, (even after the fan
speed has been reduced to the minimum rpm). An accessory
AD-16, adjustable damper, is available and can be attached
to the heater to produce a static load, ranging from .1” to .19”
H2O which will act to reduce the amount of air flow.
The “Friction Loss” Graph below provides the actual test
data on the friction loss for the AD-16 damper attachment.
The losses are stated as the equivalent length in feet of 20”
duct.
Friction Loss AD-16 Damper
10
60
40
20
0
2000
1600
1400
1800
2200
2400
Fan RPM
Equivalent Duct Length FT
30
50
70
80
90
Damper Full Closed
Damper Full Open
The SDRA Dragon includes 2 thermostats. The thermostat on
the air inlet end of the unit is for the minimum air temperature
desired. The thermostat on the discharge end of the heater
is for the maximum air temperature desired. The two thermo-
stats are wired in series with the heating element contactor
coil. The temperature range of both thermostats is 60 - 180°F.
Temperature Rise vs Duct Length
30 kW
100
75
50
25
0
0
100
75
50
25
125 150
175
Duct Length in Feet
Temperature Rise ˚F
1500
RPM
1800
RPM
2200
RPM
Temperature Rise vs Duct Length
48 kW
100
60
40
20
0
0
100
75
50
25
125
150
175
Duct Length in Feet
Temperature Rise ˚F
120
140
160
1800
RPM
2200
RPM
1500
RPM
80
Temperature Rise vs Duct Length
60 kW
100
60
40
20
0
0
100
75
50
25
125
150
175
Duct Length in Feet
Temperature Rise ˚F
120
140
160
1800
RPM
2200
RPM
1500
RPM
80
180
200
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General