HEATING 



39O3 



HEATING 



Healing. Plan showing system of steam beating 



up the walls of an apartment, and 

 heated from a fireplace outside or 

 underneath the building. 



The open coal-fire is an ineffi- 

 cient means of heating, since much 

 of the heat escapes up the chim- 

 ney ; while the closed coal stove, 

 standing in the room and connected 

 with the chimney by a pipe, is pro- 

 bably the cheapest and most 

 economical. Oil, gas, and electric 

 stoves are very efficient, but com- 

 paratively costly to run. On the 

 score of efficiency, convenience, and 

 cleanliness combined, the many 

 systems of central heating are 

 superior to any form of isolated 

 heating , and one or other of them 

 is almost invariably adopted for 

 factories and other large buildings, 

 even in countries where open fires 

 and stoves are commonly used in 

 dwelling-houses In central heat- 

 ing the source of heat is a furnace 

 or boiler in the basement. 



DIRECT HEATING BY WATER. 

 Under the low-pressure system 

 water heated in a boiler circulates 

 through pipes and radiators in 

 various parts of the building. The 

 circuit usually consists of a flow 

 main from the top of the boiler, and 

 a return main entering the boiler 

 near the bottom. Each radiator is 

 connected with the two mams by 

 branch pipes provided with regu- 

 lating valves. Circulation is 



natural the hotter water rising 

 and the cooler sinking unless the 

 distances are great, when forced 

 circulation by pump may be neces 

 sary. The pressure on the pipes at 

 any elevation is merely that of the 

 head of water. The radiators are 

 fitted with air-escape cocks at their 

 highest points ; and the system of 

 pipes is kept full by an open tank 

 which also permits tree expansion 

 of the water while being heated. 



In the high-pressure system steel 

 pipes of small diameter are used 

 for the boiler and the circulating 

 mains, and the radiators are of very 

 strong construction. The arrange- 

 ment is the same as that described 

 above, except that a closed expan- 

 sion chamber takes the place of the 

 open tank at the highest point. 

 Pressures up to 300-500 Ib. per 

 sq. inch are used ; the pipe and 

 radiator surfaces have a heat corre- 

 sponding to the pressure. 



DIRECT STEAM HEATING. Here 

 again there is a low-pressure and 

 a high-pressure system. The first 

 takes steam from a boiler or the 

 exhaust of an engine at or below 

 atmospheric pressure, and main- 

 tains a partial vacuum in the 

 pipes and radiators by means of an 

 air pump. The condensed water is 

 returned to the boiler. This 

 system is very economical, especi- 

 ally for buildings wherein steam 



power is used for other purposes 

 The high-pressure method em 

 ploys steam at pressures up to 15 

 Ib. above atmosphere, and the con- 

 densed water drains back through 

 the supply main, or through a 

 separate return to the boiler. 



Direct heating by hot air is com- 

 bined with ventilation. Fresh air, 

 passing through a heater surround- 

 ing the furnace, is warmed and 

 rises by convection through pipes 

 to registers in different parts of the 

 building, where its heat can be 

 tempered at will by mixing in cold 

 air admitted direct to the flue from 

 outside. For buildings requiring 

 great volumes of air, a large steam- 

 heated radiator is sometimes sub- 

 stituted for a furnace, and the air 

 is driven through it and the flue,* 

 by a centrifugal or disk fan. 



Indirect heating by air is a varia 

 tion of the foregoing. Several 

 radiators, all steam- or water- 

 heated by a central boiler, are dis- 

 tributed over the basement in 

 chambers at the c oot of flues run- 

 ning to the rooms above. Each 

 radiator heats the air for one flue. 

 ELECTRIC HEATING. Electric 

 heating may be considered from 

 two points of view, domestic and 

 industrial ; from either electricity 

 has many advantages over any 

 other form of artificial heating -. it 

 is easy to transmit and can be deve- 

 loped precisely where it is re- 

 quired : it is under perfect control , 

 the amount of heat given off into 

 the atmosphere admits of simple 

 regulation ; while any temperature 

 may be attained, from a gentle 

 warmth to a temperature sufficient 

 to melt the hardest steel. 



Principles of Electric Heating 

 Its cost still makes it prohibitive 

 for such major operations of indus- 

 try, but it is used for special 

 smelting processes, and new appli- 

 cations in these directions are 

 being constantly made For the 

 heating of household rooms, offices, 

 and some other buildings, and for a 

 number of the minor processes ot 

 industry, electricity is steadily dis 

 placing coal and gas, its great con 

 venience and cleanliness largely 

 compensating for its greater cost. 



The principle on which all forms- 

 of electric heaters depend is that o. 

 electric resistance. In all cases the 

 heat is developed by trying to force 

 a current of electricity through 

 some medium which resists the 

 passage of the current, and has its 

 temperature raised in consequence 

 The heat is almost universally 

 applied by radiation from the hot 

 element supplemented by convec 

 tion set up by contact of the aii 

 with the electrically heated surface. 

 The resisting medium may be a fila- 

 ment, pencil or slab of carbon, a 



