GMES96-U Installation Manual

29
GAS INPUT RATE MEASUREMENT (NATURAL GAS ONLY)
The actual gas input rate to the furnace must never be greater
than that specified on the unit rating plate. To measure natural
gas input using the gas meter, use the following procedure.
1. Turn OFF the gas supply to all other gas-burning appliances
except the furnace.
2. While the furnace is operating at high fire rate, time
and record one complete revolution of the gas meter dial,
measuring the smallest quantity, usually the dial that
indicates 1/2 cu. ft. per revolution. You will use this
number to calculate the quantity of gas in cubic ft. if
the furnace would consume if it ran steadily for one
hour (3600 seconds).
3. If the 1/2 cu. ft. dial was used, multiply your number
x 2.
EXAMPLE: If it took 23 seconds to complete one
revolution of the 1/2 ft. dial (23 x 2 = 46).
This tells us that at this rate, it would take 46 seconds to
consume one cu. ft. of gas.
This tells us that in one hour, the furnace would consume 78
cu. ft. of gas. (3600 / 46 = 78)
The typical value range for 1 cu. ft. of natural gas is around
1025 BTU. Check with your gas utility, if possible. In this
example, the furnace is consuming 80,000 BTUH.
NOTE: The final manifold pressure cannot vary by
more than ± 0.2” w.c. for Natural gas from the
specified setting. Consult your local gas supplier if
additional input rate adjustment is required.
4. Turn ON gas to and relight all other appliances turned off
in step 1. Be certain that all appliances are functioning
properly and that all pilot burners (if applicable) are
operating.
TEMPERATURE RISE
Air temperature rise is the temperature differench between
supply and return air. The proper amount of temperature
rise is usually obtained when the unit is operated at the
rated input with the “as shipped” blower speed. If the cor-
rect amount of temperature rise is not obtained, it may be
necessary to change the blower speed.
Temperature rise must be within the range specified on the unit
rating plate. An incorrect temperature rise may result in con-
densing in or overheating of the heat exchanger. An airflow and
temperature rise table is provided in the Specification Sheet on
page 33 applicable to your model. Determine and adjust tem-
perature rise as follows:
1. Operate furnace with burners firing for approximately
ten minutes. Ensure all registers are open and all
duct dampers are in their final (fully or partially open)
position.
2. Place thermometers in the return and supply ducts as
close to the furnace as possible. Thermometers must
not be influenced by radiant heat by being able to
“see” the heat exchanger.
3. Subtract the return air temperature from the supply air
temperature to determine the air temperature rise. Allow
adequate time for thermometer readings to stabilize.
4. Adjust temperature rise by adjusting the circulator blower
speed. Increase blower speed to reduce temperature rise.
Decrease blower speed to increase temperature rise. Refer
to Startup Procedure and Adjustment -Circulator Blower
Speeds for speed changing details.
SUPPLY
AIR
RETURN
AIR
Temperature Rise Measurement
Figure 35
CIRCULATOR BLOWER SPEEDS
This furnace is equipped with a multi-speed circulator blower.
This blower provides ease in adjusting blower speeds. The
Specification Sheet applicable to your model provides an air-
flow table, showing the relationship between airflow (CFM)
and external static pressure (E.S.P.), for the proper selec-
tion of heating and cooling speeds.
T O AVOID PERSONAL INJURY OR DEATH DUE TO ELECTRICAL SHOCK ,
TURN OFF POWER TO THE FURNACE BEFORE CHANGING SPEED TAPS .
WARNING
1. Determine the tonnage of the cooling system installed
with the furnace. If the cooling capacity is in BTU/hr divide
it by 12,000 to convert capacity to tons.
Example: Cooling Capacity of 30,000 BTU/hr.
30,000/12,000 = 2.5 Tons
2. Determine the proper air flow for the cooling system. Most
cooling systems are designed to work with air volume
between 350 and 450 CFM per ton. Most manufacturers
recommend an air flow of about 400 CFM per ton.
Example: 2.5 tons X 400 CFM per ton = 1000 CFM
3. Select the heating speed for your model from the heating
speed chart in the Specification Sheet. The selected speed
must provide a temperature rise within the rise range
listed with the particular model.