TABLE 12: GASE RATE - CUBIC FEET PER HOUR1

SECONDS

SIZE OF TEST DIAL

FOR ONE

 

 

REV.

1/2 CU. FT.

1 CU. FT.

 

 

 

10

180

360

12

150

300

14

129

257

16

113

225

18

100

200

 

 

 

20

90

180

22

82

164

24

75

150

26

69

138

28

64

129

 

 

 

30

60

120

32

56

113

34

53

106

36

50

100

38

47

95

 

 

 

40

45

90

42

43

86

44

41

82

46

39

78

48

37

75

 

 

 

50

36

72

52

35

69

54

34

67

56

32

64

58

31

62

60

30

60

 

 

 

1.EXAMPLE: By actual measurement, it takes 38 seconds for the hand on the 1-cubic foot dial to make a revolution with just a 100,000 BTUH furnace running. Using this information, locate 38 seconds in the first column of Table 12. Read across to the column headed “1 Cubic Foot,” where you will see that 95 cubic feet of gas per hour are consumed by the furnace at that rate. Multiply 95 x 1050 (the BTU rating of the gas obtained from the local gas company). The result is 99,750 BTUH, which is close to the 100,000 BTUH rating of the furnace.

341426-BIM-A-0108

CHECKING SUPPLY AIR CFM

To check the supply air CFM after the initial balancing has been completed:

1.Remove the two ¼ inch dot plugs in the duct panel.

2.Insert at least 8 inches of ¼ inch tubing into each of these holes for sufficient penetration into the airflow on both sides of the indoor coil.

3.Using an inclined manometer, determine the pressure drop across the dry evaporator coil. Since the moisture on an evaporator coil may vary greatly, measuring the pressure drop across a wet coil under field conditions would be inaccurate. To ensure a dry coil, the compres- sors should be deactivated while the test is being run.

4.Knowing the pressure drop across a dry coil, the actual CFM through the unit can be determined from the curve in Coil Delta P vs. Supply Air CFM figure.

Failure to properly adjust the total system air quan- tity can result in extensive system damage.

After readings have been obtained, remove the tubes and reinstall the two ¼ inch plugs removed in Step 1.

De-energize the compressors before taking any test mea- surements to ensure a dry indoor coil.

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Johnson Controls Unitary Products

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Johnson Controls 341426-BIM-A-0108 installation manual Gase Rate Cubic Feet PER HOUR1, Checking Supply AIR CFM