Document 2q7e6Vmdgyb6n2wR92g8eZ8r6

! ||'[ i f ill; Secondary air is drawn into gas appliances by natural draft. As with other fuels, excess secondary air constitutes a loss, and should be reduced to a proper minimum; which usually cannot be less than 25 to 35 percent, if the appliance is to meet ASA approval requirements. Yellow flame burners depend upon secondary air, alone, for combustion. The flame produced by atmospheric injection, burners is non-luminous. Air shutter adjustments for manufactured gas should be made by closing the air shutter until yellow flame tips appear, and then by opening the air shutter to a final position at which the yellow tips just disappear. This type of flame obtains ready ignition from port to. port, and also favors quiet flame extinction. When burning natural gas, the air adjustment is generally made to secure as blue a flame as is obtainable without lifting of flames from burner ports. Manufacturers' instructions for burner ad justment should be followed. Gas designed equipment does not usually incorporate any means for varying the secondary air supply (and hence the CO2). The amount of effective opening and baffling is determined by A.G.A. tests and cannot be varied. Gas conversion burners, however, do incorporate means for con trolling secondary air to permit adjustment over a wide range of inputs according to the type of installation encountered. The manufacturer's specific instructions contained in the installation manual required to be supplied with each burner should be followed. It is possible through the use of suitable indicators to determine whether carbon monoxide is present in flue gases. Carbon monoxide should not exceed 0.04 percent when operating at the maximum gas input to the burners. During recent years, the use of fuel gas (natural, manufactured, and liquified petroleum) has become increasingly popular for heating tourist cabins and motels. Due largely to the intermittent use of such equipment and the fact that so many of the users are entirely unfamiliar with the fundamentals governing its operation, many special and unusual problems arise. The importance of .safe-guarding the public interest has prompted some state and city officials to adopt and enforce legislation governing not only the manner in which these appliances are installed but the extent to which they must be equipped with reliable safety devices, for example, connection to an effective flue is mandatory. Furthermore, all such heating equipment must incorporate an automatic ignition pilot which will shut off gas supply to the main burner or burners in the event of pilot outage. If liquified petroleum gas is used, the automatic pilot must cut off all gas supply to the appliance, including the pilot burner, in case the pilot flame becomes extinguished. Ratings for Gas Appliances Input rating for a gas appliance is established by demonstrating that the appliance can meet the Approval Requirements of the ASA. The tests are conducted at the A.G.A. Laboratories. Output rating is deter mined from the approved input and an average efficiency stated in the Approval Requirements, and is the heat available at the outlet. Sizing Gas-Fired Heating Plants Although gas-burning equipment usually is completely automatic, maintaining the temperature of rooms at a predetermined figure, there are some manually controlled installations. In order to overcome effec tively the starting-load and losses in piping, a manually-controlled gas Automatic Fuel Burning Equipment 389 boiler should have an output as much as 100 per cent greater than the .equivalent standard radiation which it is expected to serve. Boilers under thermostatic control, however, are not subject to such severe pick-up loads and consequently, it is possible to use a lower selec tion factor. For a gas-fired boiler or furnace under thermostatic control, a factor of 20 to 25 percent is usually sufficient for pick-up allowance. In those installations, in mild climates where 100 per cent outside air is used, furnaces should be of larger size in order to provide adequate capacity and quick pick-up under intermittent heating conditions. The factor to be allowed for loss of heat from piping will vary somewhat,, the proportionate amount of piping installed being greater for small installations than for large ones. For selection factors to be added to .installed radiation under thermostatic control, see Chapter 16. Table 1. Capacity op Gas Piping Length of Pipe m Feet Nominal Diameter of Pipe in Inches * i. 2 Capacity--Cu Ft Per Hr with a 0.6 Sp Gr Gas and Pressure Drop of 0.3* Water Column 15 . ' 30 45 6075 90 105 120 150 180 ~"'T72 120 99 86 77 70 65 345 241 199 173 155 141 131 120 , 109 100 750 535 435 380 345 310 285. 270 242 225 850 700 610 545 490 450 920 420 .860 380 780 350 720 Appliances used for heating with gas should bear the approval seal of the A.G.A. Laboratories on the manufacturer's nameplate, together with the official input and output- ratings. It is not permissible to operate a gas heating unit above its stated rating. It niay be necessary to operate below this rating at elevations above 2000 ft, unless the appliance has been tested and approved for operation at altitudes up to 5200 ft, in which case such approval will be shown on the manufacturer's nameplate. Installa tions should be made in accordance with recommendations shown in the publications of the American Gas Association. Controls Temperature controls for gas burners are described in Chapter 39. Some central heating plants are equipped with push-button or other manual control. The main gas valve may be of either the snap action or throttling type. Automatic electric ignition is available. Sizing of Gas Piping Piping for gas appliances should be of adequate size, and so installed as to provide a supply of gas sufficient to meet the maximum demand without undue loss of pressure between the point of supply (the meter) and the burner. The size of gas pipe required depends upon the following: 1- Maximum gas consumption to be provided.