Greenhouse Heating 



writer's opinion there are many features about a hot-water apparatus of 

 this type which especially commend it for the heating of large greenhouse 

 establishments. Inasmuch as the factor of friction in the boiler and pipe 

 circulation is overcome by mechanical force, there will be no longer the 

 necessity to hold fast to the large water mains and runs which are abso- 

 lutely essential to every hot-water heating apparatus in which the circu- 

 lation is impelled by heat and the resulting expansion of water. If we 

 assume that the difference in temperature between the outflow and the 

 inflow of the boiler is less than 19 degrees Fahr., say, outflow 180 degrees 

 and inflow 170 degrees, a cubic foot of water would increase in weight 

 22-100, or an increase of .0036 per cent, per pound. Assuming the appa- 

 ratus to contain one ton of water at the point of entrance to the boiler, this 

 ton would be increased by 7.2 pounds. Allow a fall of six feet in the appa- 

 ratus, and we have a power of 43.2 pounds to keep one ton of water in 

 motion, to overcome the friction in the heater and a long run of pipe con- 

 taining many short bends. 



It is this small and insignificant force which the engineer has to hus- 

 band so carefully in order to make the hot-water job efficient and suc- 

 cessful. The pump, as a compelling force, does away with all this refine- 

 ment of calculation, and he is free to use such small radiating pipes as one 

 and one-quarter-inch, one and onc-half-inch, or two-inch, if he so elects. 

 The mains may be materially reduced in size. In short, we have now an 

 apparatus as compact and neat in appearance as any steam system can be; 

 a system absolutely noiseless, and under almost perfect control. The heater 

 might be managed to maintain automatically a boiler temperature propor- 

 tioned to the requirements caused by variations in the outdoor tempera- 

 ture. The operator controls the heat in a block of houses by regulating 

 the speed of the pump. The heat in each individual house, or side of a 

 house, is regulated by opening or closing the valves on the runs, which 

 should be gate valves. 



In a layout on this system, pipes could be run practically regardless 

 of height in pitch in relation to boiler, which in the other three systems 

 must be carefully considered. It must, however, be admitted that such a 

 system leads slightly away from the highest economy, for having started 

 out to overcome friction by mechanical force, one must consider that this 

 increase of friction means an absorption of heat units from the furnace ; 

 that is to say. whatever excess of friction there is must be measured by its 

 equivalent in coal. In the opinion of the writer this loss is so slight, and 



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