SCHEDULED MAINTENANCE
31
Example:
It takes forty (40) seconds on the gas meter for the hand on
the cubic foot dial to make one complete revolution, with all
appliances off, except the unit. Using the gas rate chart,
observe the forty (40) seconds, locate and read across to the
one (1) cubic foot dial column. There you will find the number
90, which shows that ninety (90) cubic feet of gas will be
consumed in one (1) hour.
Let's assume the local gas utility has stated that the calorific
value of the gas is 1025 BTU per cubic foot.
Multiplying the ninety (90) cubic feet by 1025 BTU/ft
3
gives us
an input of 92,250 BTU/hr.
Checking the BTU input on the rating plate of the unit being
tested.
EXAMPLE:
GPG153609041**
INPUT:
92,000 BTU/HR
OUTPUT CAP:
72,900 BTU/HR
Should the figure you calculated not fall within five (5) percent
of the nameplate rating of the unit, adjust the gas valve
pressure regulator or resize orifices.
In no case should the
input exceed that shown on the rating plate.
CAUTION
ALWAYS CONNECT A MANOMETER TO THE 1/8" PIPE
TAP AT THE GAS VALVE BEFORE ADJUSTING THE
PRESSURE REGULATOR. IN NO CASE SHOULD THE
FINAL MANIFOLD PRESSURE VARY MORE THAN
PLUS OR MINUS .3 INCHES WATER COLUMN FROM
3.5 INCHES WATER COLUMN FOR NATURAL GAS OR
10 INCHES WATER COLUMN FOR PROPANE GAS.
To adjust the pressure regulator on the gas valve, turn down
(clockwise) to increase pressure and input, and out (counter-
clockwise) to decrease pressure and input.
Since propane gas is not normally installed with a gas meter,
clocking will be virtually impossible. The gas orifices used
with propane are calculated for 2500 BTU gas per cubic foot
and with proper inlet pressures and correct piping size, full
capacity will be obtained.
With propane gas, no unit gas valve regulator is used;
however, the second stage supply line pressure regulator
should be adjusted to give 11" water column with all other gas
consuming appliances running.
The dissipation of the heat transferred to the heat exchanger
is now controlled by the amount of air circulated over its
surface.
The flow rate (CFM) of air circulated is governed by the
external static pressure in inches of water column of duct
work, cooling coil, registers and etc., applied externally to
the unit versus the motor speed tap.
A properly operating unit must have the BTU input and flow
rate (CFM) of air, within the limits shown to prevent short
cycling of the equipment. As the external static pressure
goes up, the temperature rise will also increase. Consult the
proper tables for temperature rise limitation.
