168 GREENHOUSES 



The following table shows the weight of a 

 cubic foot of distilled water at different 

 temperatures. 



32 degrees F.. 62.42 pounds 170 degrees F.. 60.77 pounds 



From the above table it is apparent that a 

 cubic foot of water entering the boiler at 140 

 degrees is 0.82 pounds heavier than an equal 

 quantity leaving the boiler at 180 degrees. 

 It is evident that the higher the columns of 

 water the greater will be the difference in 

 weight, and consequently the more rapid will 

 be the flow. 



The various factors influencing the veloc- 

 ity of water in a gravity hot water system 

 are embodied in the following formula. 



V= * / 2gh (w W) 

 V " (w+W) 



In this formula, V=the velocity in feet per 

 second, g=the force of gravity (32.16), li- 

 the total height of the system, W=the weight 

 of a cubic foot of water when it leaves the 



