Checking gas heat input
Two Stage Gas Heat
About this task:
This unit has two stages of gas heat. First stage
input is considered the minimum input for the
furnace. The intended input for each furnace
is shown in Table 77. The table applies to units
operating on 60 Hz power only.
To determine the rate of gas flow (Second Stage).
1. Turn off all other gas appliances connected to
the gas meter.
2. Turn on the furnace and make sure the
thermostat is calling for Second stage (100%
input) heat.
3. Measure the time needed for one revolution
of the hand on the lowest increment dial on
the meter. A typical gas meter has a 1/2 or a 1
cubic foot test dial.
4. Using the number of seconds it takes for one
revolution of the dial, calculate the cubic feet
of gas consumed per hour. (See example
below)
5. If necessary, adjust the high pressure
regulator as discussed in the section
"Manifold Gas Pressure Adjustment".
Be
sure not to over-fire the furnace on second
stage.
If in doubt, it is better to leave the
second stage of the furnace slightly under-
fired. Repeat Steps 1-5.
To determine the rate of gas flow (First Stage)
1. Turn off all other gas appliances connected to
the gas meter.
2. Turn on the furnace and make sure the
thermostat is calling for first stage heat.
3. Even when the thermostat is calling for first
stage heat, the unit will light on second stage
and will run on second stage for 1 minute.
Allow this one-minute time period to expire
and be certain the unit is running on first
stage.
4. Measure the time needed for one revolution
of the hand on the lowest increment dial on
the meter. A typical gas meter has a 1/2 or a 1
cubic foot test dial.
5. Using the number of seconds it takes for
one revolution of the dial, calculate the cubic
feet of gas consumed per hour (See example
below).
6. If necessary, adjust the low pressure regulator
as discussed in the section "Manifold Gas
Pressure Adjustment".
Be sure not to under-
fire the furnace on first stage.
If in doubt, it
is better to leave the first stage of the furnace
slightly over-fired. Refer to the table "Gas Rate
Cubic Feet Per Hour" for input value. Repeat
Steps 1-6.
Table 76: Gas Rate Cubic Feet Per Hour
Size of Test Dial
Seconds 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
Note:
To find the Btu input, multiply the
number of cubic feet of gas consumed
per hour by the Btu content of the gas in
your particular locality (contact your gas
company for this information as it varies
widely from area to area).
EXAMPLE
By actual measurement, it takes 19 seconds for the
hand on a 1 cubic foot dial to make a revolution
with a 200,000 Btuh furnace running. To determine
rotations per minute, divide 60 by 19 = 3.16. To
calculate rotations per hour, multiply 3.16 • 60 =
189.6. Multiply 189.6 • 1 (0.5 if using a 1/2 cubic foot
dial) = 189.6. Multiply 189.6 • (the Btu rating of the
gas). For this example, assume the gas has a Btu
INSTALLATION MANUAL ZY SERIES 3 - 10 ton 60 Hertz R-410A
123
Johnson Controls Ducted Systems
Содержание ZY Series
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