Greenhouse Heating 



there should be no relief of pressure in the receiver, but full pressure of the 

 radiation pipes should be maintained, less such slight loss as may occur 

 from friction in the radiation pipes. Assuming that in zero weather a 

 pressure of ten pounds of steam is being carried in the radiation pipes, 

 the return water, if conveyed to the receiver of the pump at that pressure, 

 will have a temperature of about 240 degrees Fahr. 



If, in an emergency,, a pressure of twenty pounds is used, there will be 

 in the receiver a temperature of about 259 degrees. Take off this press- 

 ure in the receiver and the temperature drops to 212 degrees. This entails 

 a loss of heat which is too great to be permitted. Therefore, no florist 

 can afford to return the water of condensation into the receiver at any 

 reduction of the normal radiation pressure. Inasmuch as heating plants 

 of this design cannot be safely installed without the advice and superin- 

 tendence of a competent engineer, there is no reason why this problem 

 should not be properly taken care of. The temperature of either of the 

 pressures considered, ten pounds or twenty pounds, is too high for any- 

 thing but a metal-packed pump. The water end of such pump should be 

 bronze or brass-fitted throughout. Rubber valves will not do. The water 

 end must be all metal. The pumping of water at such high temperature 

 involves upon the engineer more than ordinary care, and, perhaps, more 

 than ordinary experience and skill. It is, however, the writer's experi- 

 ence that when the necessary conditions are properly met and provided 

 for, returning the water at the temperature here named is just as reliable, 

 and the pump will work just as well, as when pumping water at 200 

 degrees, or less. We have never noticed but what the ordinary greenhouse 

 fireman handled either pump the high or low temperature equally well. 



Pump Exhaust 



The exhaust of the steam pump should be directed into the steam 

 main which supplies the radiation pipes. This is a material saving, and 

 should not be neglected. The pump exhaust should have an outlet to 

 the atmosphere. A valve on each pipe will give the operator control, enabling 

 him to turn the exhaust either way. In practice, the exhaust will very 

 rarely be turned into the atmosphere. 



The Vacuum Method 



The third system is that which has been aptly named the vacuum 

 system. It possesses many features which commend it in a special way 

 to the florist. In this sstem all air valves are eliminated from the entire 



