January 12, 1922 



The Florists^ Review 



31 



^Mi^i^mz{i4yj i M i tLi*it^tAJjiti2.* i ti4^ 



HEATING SYSTEMS 



r<fflfi<i^^ftwsfl»i^;fly^ife^ft^ 



GREENHOUSE HEATING. 



By Hot Water. 



Greenhouse heating is a problem of 

 vital importance to the grower, and the 

 selection and installation of the heating 

 system should be given first considera- 

 tion. 



There has been, and still is, consider- 

 able discussion as to the best system of 

 heating for greenhouses. As far as mod- 

 ern greenhouse heating is concerned, 

 there are two methods adaptable; 

 namely, hot water and steam. The hot 

 water systems may be divided into three 

 distinct forms, i. e., open tank gravity 

 system, pressure system, forced circula- 

 tion system. 



The open tank gravity system is the 

 oldest and has been extensively used, 

 but confined mainly to small installa- 

 tions. If installed correctly in a small 

 house, it serves the purpose quite ad- 

 mirably, due to easy and low cost of 

 operation. 



The pressure system is a later develop- 

 ment of open tank gravity system, and 

 by the use of mercury or safety valve 

 seal, the pressure can be built up to a 

 point where much higher water tempera- 

 tures can be carried. The object of the 

 pressure system is to reduce the amount 

 of radiation and make a wider tempera- 

 ture range to accomplish the same re- 

 sults as the old-time gravity system. 

 The pressure system also materially as- 

 sists the water circulation in the case of 

 poor pipe work and is sometimes used as 

 a "cure-all" for pipe troubles. 



The forced circulation system of heat- 

 ing by hot water is the most satisfac- 

 tory. In this system, the water is circu- 

 lated positively by means of a centrifu- 

 gal (or equally efficient) pump, and the 

 piping is installed as in the usual steam 

 system. This system is adapted to posi- 

 tive temperature regulation at the boiler 

 and can be adjusted on short notice to 

 care for rapid weather changes. This 

 feature admits of some fuel saving. 



By Steam. 



The steam systems may be divided 

 into four distinct forms; namely, low 

 pressure gravity return system, low 

 pressure return trap system, low pressure 

 vacuum return system, high pressure 

 system. 



The low pressure gravity return sys- 

 tem is similar to the hot water gravity 

 system and, although simple in construc- 

 tion and easy to operate, should be con- 

 fined to the smaller installations. 



The low pressure return trap system 

 is similar to the hot water pressure sys- 

 tem and is adapted to larger installa- 

 tions and detached houses. It is in- 

 stalled in similar manner to the low 

 pressure gravity system, except that the 

 condensate is returned to the boiler by 

 special traps. 



The low pressure vacuum return sys- 

 tem is, without doubt, the best system 

 for the larger installations and admits of 

 practically as close regulation as the 

 forced hot water system. With the 

 vacuum system it is necessary to install 

 a vacuum pump to assist the circulation 

 and draw the water out of the return 



piping and also to act as aboiler feeder. 

 In cases of fairly large plants this sys- 

 tem is to be recommended. 



The high pressure system is not in 

 general use, due to the fact that high 

 pressures and temperatures are carried 

 and this is apt to be injurious to plants 

 located near the coils. There is also con- 

 stant trouble from excessive expansion 

 and broken joints, and the operating 

 costs are high. 



Selection of Boiler. 



With any heating system the selection 

 of a boiler is of quite as much impor- 

 tance as the heating system, and the 

 chimney or stack must be ^iven just as 

 much attention, to give positive^ results. 

 For the usual greenhouse in Ohio there 

 are four types of boilers to be consid- 

 ered: Cast-iron sectional boiler, fire 

 box tubular boiler, horizontal return 



Chief among the problems 

 of the grower is that of heat- 

 ing. So the Ohio district of 

 the National Flower Growers' 

 Association, less than a year in 

 existence, has selected this as 

 the first subject on which to 

 obtain for its members expert 

 counsel and advice. A series 

 of six papers on greenhouse 

 heating has been prepared by 

 H. Ralph Hadlow, of the Wat- 

 son Engineering Co., Cleve- 

 land. The first, introductory 

 in character, is summarized 

 here, and the second, on hot 

 water systems, is presented in 

 full for the benefit of Review 

 readers, through the courtesy 

 of the Ohio organization. 



tubular boiler (brick set), water tube 

 boiler (brick set). 



Any one of these types of boilers may 

 be used for either hot water or steam 

 systems. The cast-iron sectional boiler 

 is most generally used in the smaller 

 installations and where it is advisable 

 to dispense with licensed firemen. The 

 next larger installations use the fire box 

 type of tubular boiler almost exclusive- 

 ly. The bigger installations should use 

 the horizontal return tubular boiler with 

 brick setting, and in the case of large 

 installations the water tube boiler is 

 advised. 



The boiler plant must be equipped 

 with stack or chimney of suitable de- 

 sign and size to provide proper draft 

 for the installation. The chimney can 

 be either of brick or steel plate, and the 

 type of chimney is usually' determined 

 by the size of the installation, as the 



cost enters quite materially into the va- 

 rious types. As skid before, the chim- 

 ney is just as vital a feature of the heat- 

 ing system as the boiler, pump or radia- 

 tion, and in laying out the plant this 

 should not be neglected. 



After this summary in introduction, 

 the subject of greenhouse heating will 

 be treated in detail in the following 

 papers: (1) Hot water heating systems, 

 (2) steam heating systems, (3) boilers, 

 (4) chimneys and flues, (5) fuels. 



HOT WATER SYSTEMS. 



Three Forms. 



As stated in the preceding paper, hot 

 water heating systems may be divided 

 into three distinct forms; i.e., open tank 

 gravity system, pressure system, forced 

 circulation system. 



The most used hot water heating sys- 

 tem is the open tank gravity system of 

 the one-pipe upfeed, one-pipe downfeed, 

 two-pipe upfeed or two-pipe downfeed 

 type. 



The pressure system piping is prac- 

 tically the same as that of the open tank 

 gravity system, with the exception that 

 a heat generator or safety valves are 

 used. The forced circulation system may 

 be either upfeed or downfeed two-pipe 

 system. 



Open Tank Gravity System. 



The open tank gravity system is the 

 simplest hot water system in extensive 

 use. It is suitable for small installa- 

 tions only, since the circulation is slow 

 and less positive than in the pressure or 

 forced circulation systems. The circula- 

 tion in the open tank gravity system is 

 produced by the difference in weight of 

 the water in the flow and return risers. 

 The hot water is supplied to the heat- 

 ing coils, where the water cools due to 

 exposure to the greenhouse temperature, 

 thus increasing the density above that 

 in the supply riser, creating a differ- 

 ence in head and a corresponding flow in 

 the system. This system requires an 

 expansion tank placed at a high point 

 in the system to care for expansion of 

 the water in the pipes, due to this varia- 

 tion in temperature. 



The one-pipe upfeed system consists 

 of the flow main taken from the top of 

 the boiler and run uniformly at a slope 

 of not less than three-quarters of an inch 

 in ten feet downward, dropping at the 

 extreme end and looping back to the 

 boiler with an equal or greater slope. 

 The hot water supply risers are taken 

 from the top of the flow main and con- 

 nected to the highest point in the heat- 

 ing coil. Returns lead from the lowest 

 point in the coil and connect to the side 

 of the flow main. It is necessary to keep 

 the flow and return mains as far as 

 possible below the highest pipe coil, but 

 great care must be exercised to avoid 

 dropping the flow main so as to inter- 

 rupt the circulation. This system is not 

 ordinarily adapted to greenhouse heat- 

 ing, due to the necessity of a cellar or 

 tunnel for the flow and return mains, 

 large piping and the sluggish circulation 

 of the water. 



The downfeed system permits the use 



