SERVICING
49
lation.
Other components such as a Heating/Cooling Thermostat
and Outdoor Thermostats are available to complete the
installation.
The system CFM can be determined by measuring the static
pressure external to the unit. The installation manual
supplied with the blower coil, or the blower performance table
in the service manual, shows the CFM for the static mea-
sured.
Alternately, the system CFM can be determined by operating
the electric heaters and indoor blower WITHOUT having the
compressor in operation. Measure the temperature rise as
close to the blower inlet and outlet as possible.
If other than a 240V power supply is used, refer to the
BTUH
CAPACITY CORRECTION FACTOR
chart below.
BTUH CAPACITY CORRECTION FACTOR
SUPPLY VOLTAGE
250
230
220
208
MULTIPLICATION FACTOR
1.08
.92
.84
.75
EXAMPLE:
Five (5) heaters provide 24.0 KW at the rated
240V. Our actual measured voltage is 220V, and our
measured temperature rise is 42°F. Find the actual CFM:
Answer:
24.0KW, 42°F Rise, 240 V = 1800 CFM from the
TEMPERATURE RISE
CHART, Table 5.
Heating output at 220 V = 24.0KW x 3.413 x .84 = 68.8
MBH.
Actual CFM = 1800 x .84 Corr. Factor = 1400 CFM.
NOTE:
The temperature rise table is for sea level installa-
tions. The temperature rise at a particular KW and CFM will
be greater at high altitudes, while the external static pressure
at a particular CFM will be less.
TEMPERATURE RISE (F°) @ 240V
CFM
4.8
KW
7.2
KW
9.6
KW
14.4
KW
19.2
KW
24.0
KW
28.8
KW
600
25
38
51
-
-
-
-
700
22
33
43
-
-
-
-
800
19
29
38
57
-
-
-
900
17
26
34
51
-
-
-
1000
15
23
30
46
-
-
-
1100
14
21
27
41
55
-
-
1200
13
19
25
38
50
-
-
1300
12
18
23
35
46
-
-
1400
11
16
22
32
43
54
65
1500
10
15
20
30
40
50
60
1600
9
14
19
28
38
47
57
1700
9
14
18
27
36
44
53
1800
8
13
17
25
34
42
50
1900
8
12
16
24
32
40
48
2000
8
12
15
23
30
38
45
2100
7
11
14
22
29
36
43
2200
7
11
14
21
27
34
41
2300
7
10
13
20
26
33
39
Table 5
HTR
KW
3.0
KW
4.7
KW
6.0
KW
7.0
KW
9.5
KW
14.2
KW
19.5
KW
21.0
KW
BTUH 10200 16200 20400 23800 32400 48600 66500 71600
ELECTRIC HEATER CAPACITY BTUH
Table 6
FORMULAS:
Heating Output = KW x 3413 x Corr. Factor
Actual CFM = CFM (from table) x Corr. Factor
BTUH = KW x 3413
BTUH = CFM x 1.08 x Temperature Rise (T)
CFM = KW x 3413
1.08 x T
T = BTUH
CFM x 1.08
S-61A CHECKING HEATER LIMIT CONTROL(S)
Each individual heater element is protected with a limit
control device connected in series with each element to
prevent overheating of components in case of low airflow. This
limit control will open its circuit at approximately 150°F.
