Checking Supply Air Cfm; Gase Rate - Cubic Feet Per Hour - York DNH 030 Installation Manual

TABLE 12: GASE RATE - CUBIC FEET PER HOUR
SECONDS
FOR ONE
REV.
10
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
42
44
46
48
50
52
54
56
58
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.
18
SIZE OF TEST DIAL
1/2 CU. FT. 1 CU. FT.
180 360
150 300
129 257
113 225
100 200
90 180
82 164
75 150
69 138
64 129
60 120
56 113
53 106
50 100
47 95
45 90
43 86
41 82
39 78
37 75
36 72
35 69
34 67
32 64
31 62
30 60

CHECKING SUPPLY AIR CFM

1
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.
282911-YIM-B-0807
Unitary Products Group