Timmie McElwain Gas/Propane Basics President, Gas Appliance Service Riverside, RI Orifices gastc@cox.net Part II After completing an installation, installers must make sure the input to the equipment is correct. Often, this is also necessary when determining if the equipment is operating at its peak efficiency. This procedure is called “clocking the burner.” The meter index on the gas meter is what determines gas usage and reading the index is accomplished either by a meter reader or remotely by an electronic Automatic Meter Reading. Note: With liquefied petroleum (LP) gas there is typically no meter that can do this; we will cover how input can be determined with LP a little further on. The part of the meter index we are going to use for clocking the burner is one of the test dials, as shown in Figure 1. They are ½-foot, two-foot, five-foot and larger on some larger meters. For all practical purposes, the ½-foot dial is the best to use. The procedure involves a stopwatch or the second hand on a traditional watch to clock the burner. With the burner and no other appliances running, let the ½-foot dial go around twice (equivalent to a one-foot dial) and mark the number of seconds it takes to make two full rotations. Divide that number by 3,600 (the number of seconds in one hour) and that will give you cubic feet per hour. That number is then multiplied by the heat value of the gas (BTU/cubic foot). This will give you the input in BTUs (British Thermal Units). This value should match what is stated on the equipment’s rating plate. Formulas Determine the heat value for gas in your area (the gas company can provide this). You can also check the customer’s gas bill and look for BTU/ccf (cubic foot). A lot of companies use 1050. 1050 = Heat value per cubic foot of gas in your area Cubic feet per hour is determined by clocking the meter. BTU = 1050 ∙ cubic feet/hour Measuring Gas Flow Cubic feet /hour = BTU ÷ 1050 In addition to three or more recording dials, all gas meters have one or more test dials. Newer meters use digital readings. Test dials on meters are similar to recording dials with the exception that all test dials will register less than 1,000 cubic feet per revolution. The formula for converting BTUs to cubic feet and vice versa was previously illustrated. It is important to determine the exact heat value of the gas from the local utility. We will use 1,000 BTUs for illustrations here in order to simplify the math. The complete gas flow formula is shown in Figure 2. Gas flow rate from a mater is calculated from the equation: Gas flow, cubic feet per hour = (cubic feet per revolution of meter dial) x 3600 time of one revolution of meter dial (in seconds) Note: 3,600 is the number of seconds in one hour (60 x 60). Figure 2 16 ICM/Sept/Oct 2015
ICM September-October 2015
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