Fbkkuakv 16. 1922 



The Florists^ Review 



25 



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HEATING BY STEAM 



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LONG-RANGE HEATING. 



By Gravity and Vacuum. 



The most coinmou iiiothod cniployi'd 

 in this country for conveying;' lieat to 

 distant points for lieating purposes is 

 by means of steam. This is frequently 

 accomplished by generatinj^ steam at 

 high pressure — that is, sixty pounds 

 gauge pressure or above — and reducing 

 the pressure at the points of distribu 

 tion to meet the demand of the installa 

 tion to be served. This is most com- 

 monly done in large installations, where 

 it is necessary to use a pump to return 

 the condensate back into the boiler. 

 It is customary and advantageous, when 

 conditions will permit, to generate the 

 steam at low pressure; that is, ten 

 pounds pressure or less for steam heat 

 ing purposes. The low-pressure steam 

 heating systems as applying to green 

 house work may be classified in a gen 

 eral way under the following heads: 

 One-pipe gravity steam system; two- 

 pipe gravity return steam system, and 

 vacuum return system. 



The One-Pipe Plan. 



The true 1-pipe gravity steam heating 

 system has the steam main, risers and 

 branches all below the heating units 

 and uniformly pitched back to a point 

 near the boiler, where the condensation 

 is separated from the steam and flows 

 to a point below the water level and 

 thence through the regular wet return 

 into the boiler by gravity, or flows 

 through a sealing trap into a receiver 

 and thence, by means of a boiler feed 

 pump, is forced into the boiler. The 

 pipes are necessarily large, to allow the 

 condensation to return against the flow 

 of the steam. If the pipes are made too 

 small, or water pockets or water seals 

 exist in the system, water hammering, 

 as well as trouble in getting steam to 

 the heating coils, will be experienced. 

 No little difficulty has been experienced 

 with steam heating systems, such as 

 vyater hammering and difficulty in get- 

 ting steam to the heating units, and in 

 practically every case it may be traced 

 to faulty pipe work or sizing of the 

 pipes, such as water pockets, too small 

 pipe, a restriction in the piping or short 

 circuit between the steam main and 

 the return main. There are also cases 

 where long lines underground may have 

 an excess of heat loss, due to being 

 surrounded by water or improper insu- 

 lation. This may be the case also with 

 long, uninsulated pipes overhead. To 

 make the steam system operate satis- 

 factorily, it is absolutely necessary that 

 the pipes have a clear, open space for 

 the steam to pass through. It is, there- 

 fore, of prime importance that all small 

 pipe he reamed after cutting and eccen- 

 tric fittings be used in steam mains 

 and returns and that all low points be 

 properly drained. 



It is especially important in the l-pijje 

 gravity steam sy.stem that there shall 

 be no water pockets in the steam main 

 and that the slope shall be continuous, 

 back to the wet return leading to the 

 boiler. This system, however, is not 



satisfactory for greenhouse heating, 

 since piiu- coils are generally used in- 

 stead of cast-iron radiators; the pijte 

 coils, being long, are mori' difficult to 

 drain against the flow of steam. 



The Two-Pipe Sy.stem. 



The general character of grecniiouse 

 reciuirements deiiiands a I'-pijie water 

 or steam system. Steam must, there- 

 fore, be transmitted to tlie coils through 

 one system of pijies and the coiidensa- 

 rion removed through a separate sys- 

 tem of returns to the boiler. 



In either the gravity or vacuum sys- 

 tems, the steam mains should be run 

 overhead around the building or through 

 the middle of the greenhouse with a 

 uniform grade of one inch in tvventv 



In choosing his heating 

 equipment the careful grower 

 desires to know whether, in 

 view of the individual condi- 

 tions of his range, steam would 

 be preferable to hot water or 

 vice versa. This determined, 

 there remains the choice of 

 vacuum or gravity systems. 

 The accompanying article, the 

 third of a series prepared by 

 H. Ralph Hadlow for the Ohio 

 growers* organization, ex- 

 plains tested principles and 

 makes suggestions valuable in 

 guiding the judgment of the 

 grower who seeks highest effi- 

 ciency in his heating. The two 

 preceding articles appeared in 

 The Review for January 12. 



feet. The branches leading from the 

 coils should be taken from the top of 

 the main and any water pockets should 

 be provided with a drain or drip line to 

 the return. All steam mains should be 

 dripped at the extreme end. The pipe 

 coils should have a uniform grade down- 

 ward of one inch in fifteen feet in the 

 direction of flow, with drip connection 

 through a check valve at the low end in 

 case of gravity return system, thence 

 to the return main and" back to the 

 boiler. The check valve should be 

 placed horizontally not less than six 

 inches below the lowest point of the coil. 

 The gravity return system has one dis- 

 advantage, as hereinbefore mentioned, 

 that the boiler must be placed so that 

 the water line is below the lowest point 

 in the steam main and pipe coils de- 

 pendent upon the size of the system and 

 pressure carried on the boilers (the min- 

 imum advisable distance is about two 



feet), or a trapped condensate receiver 

 and boiler feed pump must be employed 

 to return the condensate to the boiler. 

 Where low-pressure steam is generated; 

 the boiler feed pump must be driven 

 by electrical power. In the -piiie grav- 

 ity sy.stem, all air pockets in the ])iping 

 must be provided wifli suitabb^ auto- 

 matic air valves. 



There are numerous so-called systems 

 (if steam heating in use. The term ' ' sys- 

 tem" in this case is merely a commer- 

 cial term for different makes of spe- 

 cialties rather than any distinctive fea- 

 ture in the size and arrangement of the 

 piping and boilers as referred to herein- 

 before. The vacuum steam heating sys- 

 tem is the most satisfactory of all steam 

 heating systems for large installations, 

 since it provides positive means for re- 

 moving the air and condensation from 

 the piping and returning the condensate 

 to the boilers and also submits most reg- 

 ularly to thermostatic regulation. The 

 piping system is essentially the same as 

 in the 2-pipe gravity system except 

 that the check valve in the return from 

 the coil is replaced by a thermostatic 

 trap, which permits the passage of con- 

 densation and air only and not of steam. 

 The vacuum pump is connected to the 

 return main in the boiler room, which 

 pumps the condensation and air from 

 the return main and forces the con- 

 densate into the boiler. The return pipes 

 may be made considerably smaller than 

 are used for the gravity system and a 

 limited number of water pockets may 

 be permitted in the return line, pro- 

 vided lift fittings are used. This should, 

 however, be avoided wherever possible. 



Temperature Regulation. 



Temperature regulation may be placed 

 on the steam mains or on the individual 

 coils; that is, one thermostat may be 

 located to control the temperature of 

 the entire building, or thermostats may 

 be located at various points in the build- 

 ing and regulate the steam to the coils 

 in the different sections. This system 

 has the advantage that the regulation 

 is easily changed and the same disad- 

 vantage that sufficient fire must be ke])t 

 in the boiler to generate steam at all 

 times in order that the system shall 

 give off heat; also, that in large in- 

 stallations the boilers will be of such 

 size as to require a licensed fireman, 

 according to the laws of certain states. 

 When high-pressure steam is generated 

 for heating purposes, it is almost in- 

 variably for this type of .system, since 

 the steam can be transmitted to dis- 

 tribution points at high pressure and 

 reduced by means of a pressure reduc- 

 ing valve to any desirable pressure be- 

 low ten pounds. It is necessary in a 

 vacuum .system to use steam at less 

 than ten pounds pressure in the coils, 

 since the thermostatic traps are, ordi- 

 narily, guaranteed for not to exceed 

 ten pounds pressure. 



The advantage in such cases of gen- 

 erating steam at high pressure is that 

 of being able to operate the pumps by 

 steam where electricity is not available 

 and it is not entirely satisfactory to 

 attempt to operate pumps at less than 



