Bryant Model 378 - Manual (Page 6)

Determine gas input as follows:
a. Determine the number of seconds required for
the gas meter test dial to complete one revo­
lution.
b. Divide 3600 by the nuniber of seconds in
Item (a) above.
c. Multiply result of Item (b) by the number of
cubic feet shown for one revolution of the
test dial. This gives you cubic feet per hour
of gas flow.
d. Multiply result of Item (c) by the heating
value of the gas in BTU (consult local util­
ity for value). This gives you the total meas­
ured input in BTUH. Compare this value with
that on your rating plate.
Example: Suppose that the size of the test dial is
1/2 (.5) cu. ft.; it takes 20 seconds for the dial to
complete one revolution; heating value of gas is
1050 BTU/cu. ft. Proceed as follows:
a. 20 seconds to complete one revolution.
b. 3600 divided by 20 equals 180.
c. 180 X 0.5 equals 90 cu. ft. per hour of gas
flow.
d. 90 X 1050 equals 94,500 BTUH input.
Only minor changes should have to be made at the
pressure regulator. If the manifold pressure must be
changed more than ±.3 w.c. to obtain rated input,
the orifices should be changed accordingly.
4. Air Flow and Temperature Rise
The furnace is approved for operation under the
temperature rise conditions shown in Table I.
TABLE
Model No.
Input Btu
per hr.
Temperature Rise Air
through Furnace
36W, 54W, 48R,
60R,&l50-378 150,000 45 ° F to 75 ° F
100,000 20 ° F to 75 ° F
90W, 108W, 90R
120R, 8s300-378 300,000 45 ° F to 75 ° F
200,000 20 ° F to 75 ° F
The pulley setting has been made at the factory to
give an air flow compatible with the intended use of
the equipment; i. e., the setting varies with the
type of cooling coil to be used. Table II gives the
pulley setting as the furnace leaves the factory,
and shows also how the pulley can be adjusted to
give the desired air flow if the duct resistance is
higher than normal.
The static pressure against which the furnace is
operating is the difference in pressures in the
return air duct and the discharge duct hear the
furnace. If this differential pressure, determined
when the filters are clean and the pulley is opened
the number of turns shown for normal static, is more
than shown for normal static in Table II, the blower
speed should be increased by changing the pulley
setting to that shown in the column for higher than
normal static pressures.
The temperature rise is the difference between the
temperature of the air in the return duct and in the
discharge duct near the furnace. This temperature
rise, measured after equilibrium has been attained,
should be within the range shown in Table I. The
pulley setting shown in Table II should give an air
rise within the approved range.
TABLE II
Model Normal Static (ARI) High er Static *
No.
Static Factory Setting of Static Pulley Setting
in. w.c. Pulley Turns Open in. w.c. Turns Open
36W - 378 0.15 31/2 0.50 1V2
54W - 378 0.20 4 0.50 2
48R - 378 0.20
IV 2
0.40 0
60R - 378 0.20 3 V 2 0.50
IV 2
150 - 378 0.20 21/2 0.50
V2
90W - 378 0.25 11/2 0.45 0
108W - 378 0.30 21/2 0.50 1
90R - 378 0.25 ya 0.35 0
120R - 378 0.30 1 0.40 0
300 - 378 0.25
V 2
0.35 0
* The furnaces are approved for operation up to 0.50 in. w.c.
EH 378 . 6 -