1408 



GREENHOUSE 



GREENHOUSE 



plate and the returns on the walls or under the tables. 

 Figs. 1764-1766 illustrate the lay-out of pipes in car- 

 nation-, rose-, and violet-houses. 



Heating by flues. 



When fuel is cheap, and when either a low tempera- 

 ture is desired in the house, or the outside temperature 

 does not drop much below the freezing point, hot-air 

 flues may be used but, while the cost of constructing 

 them is small, the danger of fire is so great that they 

 are often found to be far from economical. A brick 

 furnace is built at one end of the house and from this 

 a 10- or 12-inch flue is constructed to carry the smoke 

 and hot gases through the house to the chimney which 

 may be either at tlie farther end of the house or directly 

 over the furnace, the flue, in the latter case, making a 

 complete circuit of the house. When the houses to be 

 heated are more than 00 feet long, it is advisable to 

 have a furnace in each end, with the flue from each 

 extending only to the center of the house and returning 

 to the end from which it started. For the first 30 feet 

 the lining of the flue, at least, should be of fire-brick, 

 but beyond that the flue may be constructed of sewer- 

 pipe. 



Piping for steam. 



Except that it is possible to use smaller flow- and 

 return-pipes, the arrangement of the piping for steam- 

 heating is not very unlike that described for hot water. 

 Unless the houses are more than 30 feet wide and 150 

 feet in length, only one flow-pipe need be used and that 

 can be carried from 2 to 4 feet below the ridge. In 

 wider and longer houses, it is generally advisable to 

 put in two or more flows. One of these flows can be 

 carried on each wall-plate and in extremely wide houses 

 others may be under the ridge and purhns. 



For determining the size of steam mains, a good rule 

 to use is to take one-tenth the square root of the radia- 

 tion to be suppHed and consider this to be the diameter 

 in inches of the main required. Thus for supplying 

 400 square feet of radiating surface we would take one- 

 tenth the square root of 400 (i/400h-10 = 2), which 

 wiU give 2 inches as the diameter of the main required. 

 As the amount of radiation increases, a shght reduction 

 can be made in the size of the mains and 23^-, 3-, 314; 

 and 4-inch supply-pipes will answer respectively for 

 700, 1,000, 1,400 and 1,900 square feet of radiation. 

 This is intended to apply with low-pressure steam, and 

 as the steam-pressure is increased above five pounds 

 a shght decrease in the size of the mains would be per- 

 missible. 



The size of the pipes to be used for the coils wiU also 

 depend upon the length of the house. For ordinary 

 lengths lJ-:4-inch pipe wiU be desirable, but, when they 

 are more than 250 feet in length, 1 3^2-inch pipe may be 

 used with low pressure steam and, in those much less 

 than 100 feet, 1-ineh pipe wiU answer. The location 

 and arrangements of the coils will necessarily be 

 determined by the openings in the walls and whether 

 beds or raised benches are used. One of the simplest 

 and most satisfactory ways of piping a greenhouse of 

 moderate size, say from 20 to 30 feet in width and up 

 to 1.50 feet in length, is to run the flow-pipe, which 

 would be either 2- or 23^2-inch, overhead and bring back 

 the coils on the walls, or, if raised benches are used 

 and crops for which bottom heat will be helpful are to 

 be grown, from one-third to one-half of the return- 

 pipes may be distributed under the benches and the 

 remainder may be on the walls. The return-coils should 

 of course be given a slight slope toward the boiler, care 

 being taken that no opportunity is afforded for the 

 air to pocket and prevent the free flow of the water 

 from the condensed steam back toward the boiler. A 

 fall of 1 inch in 10 feet will suffice, and even less will 

 answer if care is taken in grading and supporting 

 the pipes. 



In order to prevent the water from backing up in the 

 coils, it is desirable that they should be at least 18 or 

 20 inches above the level of the water in the boiler, 

 while 3 or 4 feet would be even better and will be neces- 

 sary in large ranges. Unless this can be secured it will 

 not be possible to return the water of condensation to 

 the boiler by gravity and either a steam trap or pump 

 should be provided for the purpose. By means of 

 these, the water can be carried to a water feed-tank 

 from which it can be fed into the boilers. 



There should be an automatic air-valve at the end 

 of each coil and, in order to regulate the amount of 

 steam, a shut-off valve should be placed upon both 

 flow- and return-pipes leading to each house. Unless 

 there are several coils in each house, one or more of 

 which could be cut off by means of valves, it will 

 always be well to have valves upon a number of the 

 pipes in the coils so that all but one or two can be cut 

 off if desired. To prevent the water from being forced 

 out from the boiler when the steam is turned into the 

 houses, there should be a check valve in the main 

 return-pipe near the boiler. 



The amount of radiation which wiU be required to 

 secure a given temperature will vary to some extent 

 with the amount of pressure carried in the boiler, or 

 in the coils, when a reducing-valve is used, but as a 

 rule, this is not much more than five pounds and often 

 it is even less. It will be best to provide a sufficient 

 amount of radiation to furnish the temperature desired 

 in ordinary cold weather without carrying any pressure 

 and then, by raising 

 the pressure to five 

 to ten pounds, secure 

 the heat required 



during the cold .,^ j \. 



waves. 



1767. Rose-house, 150 x 20 feet, piped for steam. 



In determining the amount of radiation for a steam- 

 heated house, for zero weather, it will answer if one con- 

 siders that 1 square foot of pipe will heat 9 square feet 

 of glass when 40° are desired, and wiU suffice for 7, 

 5 and 3 where 50°, 60°, and 70°, respectively, are, 

 required. Fig. 1767 illustrates the piping required for 

 heating a rose-house with steam. . L. R. Taft. 



Greenhouse management. 



Persons usually learn to grow plants under glass by 

 rule of thumb. Such practical knowledge is always 

 essential, but better and quicker results are secured 

 if underlying truths or principles are learned at the 

 same time. Even if no better results in plant-growing 

 were to be attained, the learning of prmciples could 

 never do harm, and it adds immensely to the intellectual 

 satisfaction in the work. There is no American writing 

 that essays to expound the principles of greenhouse 

 management, although there are manuals giving direct 

 advice for the growing of different classes of plants. 

 There are two kinds of principles to apprehend in 

 greenhouse management, — those relating to the man- 

 agement of the planus themselves, and those dealing 

 primarily with the management of the house. 



The first principle to be apprehended in the growing 



