Applications of the gravity factor converts the figures given in table 1 to capacities with another gas of different specific gravity. Such application is accomplished by multiplying the capacities given in table 1 by the multipliers shown in table 5.
To determine the size of each section of gas piping in a system within the range of table 4 proceed as follows:
•Determine the gas demand of each appliance to be attached to the piping system. When table 4 is to be used to select the piping size, calculate the gas demand in terms of cubic feet per hour for each piping system outlet. The gas demand for an appliance can be found by dividing its heat input rate by the gas’s heating value.
•Obtain or determine the length of piping from the gas meter or service regulator to the appliance(s).
•In table 1, select the row showing the distance to the most remote outlet or the next longer distance if the table does not give the exact length. This is the only distance used in determining the size of any section of gas piping. If the gravity factor is to be applied, the values in the selected row of table 4 are multiplied by the appropriate multiplier from table 5.
•Total the gas demands of all appliances on the piping system. Enter table 4, on the left hand side, at the row equal to or just exceeding the distance to the most remote outlet. Select the pipe size in the row with a capacity equal to or just exceeding the total gas demand. This is the required main gas supply line size leading away from the gas meter or regulator. To determine the pipe size required for each branch outlet leading away from the main supply line, determine the gas demand for that outlet. Enter table 4 on the same row, and select the branch pipe size for a capacity equal to or just exceeding the demand at that outlet. The main line can be resized for a lesser capacity after each branch outlet, since the gas demand is reduced. Total the gas demands of all remaining appliances branching off downstream on the main gas line. Re-enter table 4 in the same row and select the appropriate pipe size with adequate capacity. Repeat the branch sizing and main line re-sizing for any remaining appliances in the system.
EXAMPLE
Job Condition:
Determining the required gas pipe size for a system composed of two A. O. Smith 720 boilers and two 960 boilers to be installed as a multiple group, 50 lineal feet from meter. Gas to be used has a
.60 specific gravity and heating value of 1,000 Btu per cubic foot.
Solution: | | | | | |
Two 720 Boilers | = | 1,440,000 | Btuh | | (422 kw) |
Two 960 Boilers | | = | 1,920,000 | Btuh | | (562 kw) |
Total Btuh Input | = | 3,360,000 | Btuh | = | (984 kw) |
Total Btuh Input | = | 3,360,000 | Btuh | = | 3,360 cf/h |
| | | | | | |
Btu per Cubic Foot of Gas | | 1,000 | | | |
With a cubic foot per hour demand of 3,360 and with 50 lineal feet of gas supply line, table 4 shows a pipe size of 3" is required.
NOTE: For other than .60 specific gravity, apply multiplier factor as shown in table 5.
HIGH ALTITUDE INSTALLATIONS
IN CANADA
Acceptance of these models for use at altitudes above 2000 feet (610 m) is based on field test of the individual installation by the provincial/state authority having jurisdiction.
IN THE U.S.A.
WARNING
INSTALLATIONS ABOVE 2000 FEET REQUIRE REPLACEMENT OF THE BURNER ORIFICES IN ACCORDANCE WITH SECTION
8.1.2OF THE NATIONAL FUEL GAS CODE (ANSI Z223.1).
FAILURE TO REPLACE THE ORIFICES WILL RESULT IN IMPROPER AND INEFFICIENT OPERATION OF THE APPLIANCE RESULTING IN THE PRODUCTION OF INCREASED LEVELS OF CARBON MONOXIDE GAS IN EXCESS OF SAFE LIMITS WHICH COULD RESULT IN SERIOUS PERSONAL INJURY OR DEATH.
You should contact your gas supplier for any specific changes which may be required in your area.
Ratings specified by manufacturers for most boilers apply for elevations up to 2000 feet (610 m). For elevations above 2000 feet (610 m) ratings must be reduced by a rate of 4% for each 1000 feet (305 m) above sea level.
Example: A Dura-Max is rated at 720,000 Btu/hr. (211 kw) input at sea level. To operate the boiler at 5000 feet (1524 m) it must be derated by 20% (4% x 5) to a new rating of 576,000 Btu/hr. (169 kw) input.
The input reduction is primarily achieved by reducing the size of the main burner orifices. To do this, the main burner orifices require replacement with orifices sized for the particular installation elevation. When ordering, be sure to state the model number and the altitude of the location where the boiler is being installed.
Upon field deration of the boiler, adjustment to the gas pressure regulator is required. See CHECKING AND ADJUSTING THE INPUT in this manual for inlet and manifold pressure requirements.
Also, due to the input rating reduction required at high altitudes, the output rating of the appliance is also reduced and should be compensated for in the sizing of the equipment for applications.
WIRING CONNECTIONS
1.CONVENTIONAL INSTALLATIONS
All electrical work must be electrically bonded to ground in accordance with the requirements of the authority having jurisdiction or, in the absence of such requirements, with the National Electrical Code, ANSI/NFPA 70 and/or the Canadian Electrical Code Part 1, CSA C22.1, Electrical Code.
The electrical connections must be made so that the circulator will operate before the gas valve opens. At no time may the controlling system allow the burner to fire when there is no water flow through the boilers.
AN ELECTRICAL GROUND IS REQUIRED TO REDUCE RISK OF ELECTRIC SHOCK OR POSSIBLE ELECTROCUTION. Make the ground connection to the screw provided in the electrical supply junction box on the boiler.
