350 APPLIED SCIENCE 



towards the windows. Pipe coils in mills may be run along the 

 walls on brackets under the windows. The cold air dropping 

 downwards from the windows meets the current of warm air 

 rising from the coil and is tempered and warmed at once. 

 When it is desirable to have the hot-steam coils near the 

 working space they are generally hung from the ceiling near 

 the outer walls. This plan works well in a shop or mill where 

 there are shafts with whirling pulleys and belts in constant 

 motion. The air is churned by such motion and the heated 

 air is brought downward and mixed with the cool. In office 

 buildings and stores, coils placed near the ceiling are not 

 effective, for there is nothing to cause circulation and the 

 warm air naturally tends to remain at the top of the room. 



393. Measurement of Heat Radiation. The quantity of 

 heat given off by radiators or steam pipes, in the ordinary 

 methods of heating buildings by direct radiation, will vary 

 from 1% to 3 heat units per hour per square foot of radiating 

 surface for each degree of difference in temperature. An 

 average of from 2 to 2J4 heat units is a fair estimate. 



One pound of steam at about atmospheric pressure con- 

 tains 1146 heat units. If the temperature in the room is to be 

 kept at 70, while the temperature of the pipes is 212, the 

 difference in temperature will be 142. Multiplying this by 

 2J4, the emission of heat will be 319J^ heat units per hour per 

 square foot of radiating surface. A boiler must always be 

 capable of generating as much steam as the radiators arc 

 condensing. There should be 1 sq. ft. of heating surface in the 

 boiler for every 8 to 10 sq. tt. of radiating surface. 



394. Main Piping. All piping must be carefully put up, 

 and horizontal piping must have a pitch or slope of l / to l /^ 



