32 



The Florists^ Review 



January 12. 1922 



of smaller risers and is more positive 

 in action than the upfeed system, and 

 also facilitates the automatic removal 

 of air from tlie pipes. In the one-pipe 

 downfeed system the flow main or riser 

 is run from the boiler to the top of the 

 building. Then the main is run around 

 the building horizontally to serve all the 

 coils. The supply lines are taken from 

 the bottom or sides of the main and 

 dropped to the coils. This system may 

 have single or double risers. In the sin- 

 gle riser system the returns are con- 

 nected back into the flow riser, while 

 the double riser system has a flow riser 

 for supplying the hot water to coils, and 

 a separate return riser leading from the 

 coils to the return main; thence back 

 to the boiler. The flow main should 

 grade up uniformly to the main riser 

 and down from the top of the main 

 riser not less than three-quarters of an 

 inch in ten feet. The risers for the dou- 

 ble-riser system may be made somewhat 

 smaller than in the single-pipe system. 

 Either the single-pipe or the two-pipe 

 system may be operated with an open 

 expansion tank only, or with a pressure 

 generator and expansion tank. 



Pressure System. 



Theoretically, it is possible to heat 

 water to a temperature in excess of 212 

 degrees Fahrenheit by increasing the 

 pressure, since the boiling point of water 

 varies with the pressure to which the 

 water is subjected. This, however, is 

 not practicable in the open tank system, 

 since the hot water will immediately rise 

 to the expansion tank and boil. Various 

 devices have been employed to increase 

 the temperature, thus accelerating the 

 circulation in the system as well as in- 

 creasing the temperature difference be- 

 tween the water in the heating coils and 

 the air in the greenhouse. 



The most common type of generator is 

 known as the Honeywell generator, 

 which maintains the increased pressure 

 on the system by moans of a mercury 

 seal, the open end of which is connected 

 to the expansion tank. This permits 

 the increase in pressure of the water to 

 ten pounds, which is equivalent to 240 

 degrees Fahrenheit. The expansion tank 

 in this system is just as essential as 

 in the old type of gravity system. The 

 radiator tappings may be made much 

 smaller than necessary in the old steam 

 controlled systems. Minimizing the size 

 of pipes and valves eliminates as much 

 water as possible from the system and 

 thus increases the capacity and effi- 

 ciency of the boiler, since heat from the 

 fuel is more rapidly taken out, due to the 

 higher temperature which is maintained, 

 in turn establishing a more rapid circu- 

 lation of water over the heating sur- 

 face of the boiler. The smaller quantity 

 of water and the increased rate of cir- 

 culation facilitate the more rapid heat 

 transmission. The rate of heat trans- 

 mission between the hot gases and water 

 increases in proportion to the tempera- 

 ture difference. Sluggish circulation 

 will, under certain firing conditions, 

 materially reduce the rate of heat trans- 

 mission and, therefore, the efficiency of 

 the furnace. 



Forced Circulation System. 



The forced circulation system is the 

 most positive of all hot water systems 

 and is best adapted for use in large in- 

 stallations or where conditions do not 

 favor the gravity system. The circula- 

 tion is maintained by means of a pump, 

 preferably of the centrifugal type. The 



piping scheme is essentially the same as 

 for two-pipe upfeed or two-pipe down- 

 feed gravity systems, with the exception 

 that the pipes may be made smaller and 

 the heating surface may be reduced, due 

 to more rapid and positive circulation of 

 the hot water through the circulation 

 coils. The pipe must be carefully sized 

 for any heating system. However, spe- 

 cial care should be exercised in sizing 

 the pipes for this particular system. 



We recommend the installation of the 

 forced circulation systems where the 

 gravity system of hot water is not espe- 

 cially favored. This applies particu- 

 larly to the larger ranges. 



Hot Water vs. Steam. 



This system has an advantage over 

 the steam heating system from the 

 standpoint of the generation of heat. 

 In the hot water system the circulation 

 commences sooner after starting new 

 fire than with steam. The water may be 

 circulated in the system above green- 

 house temperature and give off heat to 

 the surrounding atmosphere, while steam 

 has a definite lower temperature below 

 which it ceases to exist and, therefore, 

 no heat is transmitted through the pipes. 

 This advantage is one of firing. In mild 

 weather, the water may be maintained 

 at a low temperature which is suitable 

 for the weather conditions. 



With the hot water systems, less fre- 

 quent attention to the fires is required 

 than with the steam boiler, which will 

 in many cases eliminate the necessity of 

 a night fireman. In the case of the small 

 greenhouse, where a regular night man 

 cannot be afforded for night firing, the 

 temperature may be maintained through- 

 out the night sufficiently to prevent in- 

 jury to the plants, by long firing periods, 

 while with the steam system the fire may 

 become low and fail to generate steam, 

 jn which event the system would not 

 give off any heat at all and the tempera- 

 ture might fall to a point which would 

 be injurious to the plants. 



The hot water system contains a con- 

 siderable amount of water which will 

 continue to give off heat until the green- 

 house temperature is attained, while the 

 steam at atmospheric pressure will be 

 condensed and will cense to give off heat 

 below 212 degrees Fahrenheit. 



For small greenhouse heating, under 

 ordinary conditions, the two-pipe down- 

 feed gravity or pressure system-is most 

 practical. If electric current is avail- 

 able, the forced circulation system could 

 be installed and operated economically. 



For the large installations we would 

 recommend the forced circulation system 

 of hot water heating, due to the positive 

 and rapid circulation of the water, which 

 makes it possible to meet sudden changes 

 in the weather. A thermostatic control 

 may be used with any of the hot water 

 heating systems, so as to maintain a 

 specific temperature of the water. 



Combination of Steam and Hot Water. 



There is one system which we have 

 not heretofore mentioned, which under 

 certain conditions is quite satisfactory. 

 This system consists of the use of a 

 steam lioiler operated at high pressure, 

 supplying steam to a closed water 

 heater. The heat from the steam is ab- 

 sorbed by the water in the system, which 

 is circulated through the heater tubes. 

 The idea of generating high pressure 

 steam is chiefly to supply steam for 

 operating the boiler feed pumps, as well 

 as the pumps for the circulation of water 

 in the system. This system is quite eco- 



nomical, it being possible to use the 

 exhaust steam from the pumps in con- 

 junction with the live steam at reduced 

 pressure. 



The piping of the radiation system it- 

 self is essentially the same as the 

 forced circulation system herein de- 

 scribed. Where electric current for 

 driving the pumps is not obtainable, this 

 system is quite desirable. In the forced 

 circulation systems, the heating coils 

 may be made of pipe and branch tees 

 or of pipe and return bend fittings. 

 More uniform heating can be obtained 

 where the return bend fittings are used, 

 since it is possible to supply hot water 

 to the coil at the same end where the 

 return is taken, thus keeping a uniform 

 mean temperature throughout its length. 

 The consideration of the length of pipe 

 to be traversed is much more important 

 with water than with steam; however, 

 it is less important with the forced cir- 

 culation than with the gravity or pres- 

 sure systems. 



Noteworthy Points. 



There is little difference in coal con- 

 sumption of the two systems, the hot 

 water having the edge on the steam, if 

 any. 



Crooks or angles in the piping are a 

 decided disadvantage in hot water and 

 steam without pressure, while steam un- 

 der low pressure shows practically no 

 effect. In all hot water systems the flow 

 main decreases in size when the branches 

 are taken off, and the return main in- 

 creases correspondingly. The return 

 main usually has its flow in the opposite 

 direction, so as to give equal water 

 travel for all coils. 



All changes in size of pipes should be 

 made with eccentric fittings with the 

 straight side of the pipe at the top, to 

 avoid water pockets. All piping should 

 be carefully graded not less than three- 

 quarters of an inch in ten feet and provi- 

 sion made for expansion. The coils must 

 be properly valved, and all risers and 

 mains must be provided with suitable 

 drains, so that the system may be com- 

 pletely drained in case of shut-down of 

 the system. Air pockets must be avoided 

 wherever possible and where unavoid- 

 able must be provided with suitable auto- 

 matic air vents. 



Coils should not be made too long, since 

 this makes the circulation less positive 

 and more sluggish. All piping should 

 be reamed after cutting and run as 

 straight as possible, so as to use as few 

 ells and tees as possible. 



Expansion Tank. 



The expansion tank should be provided 

 with an automatic make-up water line, 

 gauge glass, vont to ntmosphere and over- 

 flow, and must be of adequate capacity 

 to take care of expansion and contrac- 

 tion of the water, since the volume of 

 water increases about four per cent 

 from 40 degrees to 212 degrees Fahren- 

 heit. It should be located where there is 

 no possibility of freezing of the tank or 

 piping. 



It is customary to make the tank 

 capacity two gallons for each twenty-five 

 gallons of water in the heating system. 

 The volume of one lineal foot of l-inch 

 piping is approximately .0447 gallons; 

 1%-inch piping, .0779 gallons; 1%-inch 

 piping, .1060 gallons; 2-inch piping, .1747 

 gallons. 



The bottom of the tank should be not 

 less than three feet above the highest 

 point of radiation. 



