Document NGOXORd77dzMn47v8y2dxY3Bp

340 CHAPTER 17 1948 Guide i" _ 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 some what, 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 18. Appliances used for heating with gas should bear the approval seal of the A.G.A. Testing 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 may be necessary to operate below this rating at elevations above 3,000 ft.. Installations 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 34. 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. FUEL BURNING RATES The burning rate for automatic fuel burning devices is determined by the gross heat output required of the boiler, or furnace, to carry the net heating load plus allowances for system losses, and pick-up. General values for these allowances previously have been noted. Detailed infor mation for piping and pick-up allowances for steam, and hot water systems is given in Chapter 18 and for warm air systems in Chapters 21 and 22. When the gross output, operating efficiency, and heat value of the fuel are known, the required rate of burning can be determined by means of Figs. 21, 22 and 23 for the several fuels. Fig. 21. Coal Fuel Burning Rate Chart CROSS OUTPUT-THOUSAND B.T.U PER HOUR 4 6 8 10 12 14 GROSS OUTPUT - HUNDRED FEET STEAK RADIATION 5 10 - IS 20. 25 GROSS OUTPUT- HUNDRED FEET WATER RADIATION Fig. 22. Oil Fuel Burning Rate Chart3 This chart Is based upon No. 3 oil having a heat content of 143,400 Btu per gallop. If other grades of ire used multiply the value obtained from this chart by the following factors: No. 1 oQ (139,000 Btu gallon) 1.032; No. 2 oil (141,000 Btu per gallon) 1.017; No. 4 oil (144,500 Btu per gallon) .0.992; No. 5 [146,000 Btu per gallon) 0.982; and No. 6 oil (150,000 Btu per gallon) 0.956. GROSS CALORIFIC VALUE 8 O 8 B.T.U. PER CUBIC FOOT Ao o 700- ~r, T57 * s GOO- 500- sV .6004 400 O' 300 g 400-J 200 100- A r* s. * 7 r 100 200 300 GROSS OUTPUT* THOUSAND aT.U PER HOUR 4 6 8 10 12 14 -CROSS OUTPUT* HUNDRED FEET STEAM RADIATION . 5 K> 13 20 25 GROSS OUTPUT* HUNDRED FEET WATER RADIATION Fig. 23. Gas Fuel Burning Rate Chart As the rate of fuel burning is directly proportional to the load for a given efficiency, these charts can be extended by moving the decimal points the same number of digits in both vertical and horizontal scales.