GREENHOUSE 



GREENHOUSE 



1405 



one boiler, or if the heater is at some distance from the 

 coils, it is better to start from the boiler with one 

 large flow-pipe, or with two pipes leading from different 

 sides of the boiler, rather than carry an independent 

 pipe to each house. When there are several houses to 

 be heated, it is customary to have them side by side 

 and one large flow-pipe can then be run across the 

 nearest end of the houses from the boiler. If the houses 

 run north and south, the boiler may be located at one 

 corner or in the middle of the north end of the range, 

 and either a work- or storeroom, or some other form 

 of a head house, should be constructed in which the 



I 



1762. Supply-pipe for under-bench flows. 



main heating-pipes can be carried, as well as to protect 

 the north end of the houses and facilitate getting from 

 one to another. Sometimes greenhouses run east and 

 west, in which case there should either be a head house 

 at the east end of the range, or if the houses are more 

 than 200 feet in length it may be run through the 

 center of the houses. 



The size of the main feed-pipe as well as of the branch 

 pipes should be in proportion to the 'amount of radia- 

 tion they supply. In determining the amount that 

 can be handled by pipes of different sizes, it is always 

 advisable to use somewhat larger supply-pipes when 

 all of the radiation, both flow and return, are under 

 the benches, than when all of the flow-pipes, at least, 

 are overhead. A similar allowance should be made 

 when the boiler is partly above the level of the returns, 

 as compared with systems in which the coils are a num- 

 ber of feet above the top of the boiler, since in the latter 

 case a much smaller supply-pipe will suffice. In a gen- 

 eral way, the following sizes can be used as supply-pipes: 



Size of Square feet 



pipe. of radiation. 



1 Yi-mch 75 to 100 



2 -inch 150 to 200 



2M-inch 250 to 350 



3 -inch 400 to 600 



3M-inch 600 to 800 



4 -inch 1,000 to 1,200 



5 -inch 1,500 to 2,000 



6 -inch 2,500 to 3,500 



The main supply-pipe or pipes should, if possible, 

 rise vertically from the heater to a point somewhat 

 higher than the highest point in the system, and then 

 as it runs out through the houses should be given a 

 slight fall, say 1 inch in 20 feet, so that there will be 

 no opportunity for the pocketing of air in the pipe. 

 While a slight downward slope will unquestionably 

 give better results than the uphill arrangement which 

 is sometimes used, the difference will be comparatively 

 slight and, if the circumstances make it preferable to 

 run the flow-pipes uphill, satisfactory results will be 

 obtained provided they are considerably elevated above 

 the boiler. Especially, if the flow-pipes run uphill, 

 it will be advisable to have them of good size. 



When taking off the supply for each of the houses, 

 one large pipe of a size sufficient to provide the amount 

 needed may be used, or from two to five smaller pipes 



may lead from the main flow-pipe into each of the 

 houses. For houses up to 250 feet in length, it will 

 generally be found desirable to run 2^-inch flow-pipes 

 through the house, but for longer houses 3-inch flow- 

 pipes should be used. Just how many flow-pipes will 

 be needed will depend not only upon the length of the 

 house, but upon the number of return-pipes to be sup- 

 plied. Thus, while a 2^-inch flow will supply two 

 2-inch returns in a house 250 feet long, the number of 

 returns which it will feed in shorter houses will be nearly 

 in inverse proportion to the length of the return coils. 

 When the amount of radiation to be supplied does not 

 exceed 250 to 350 square feet, one 23^-inch flow-pipe 

 in a greenhouse will be sufficient and this should pref- 

 erably be placed from 1 to 3 feet below the ridge. lor 

 slightly larger houses, two flow-pipes may be located 

 on the wall plates. If as many as five pipes are neces- 

 sary, the fourth and fifth pipe may be suspended from 

 the roof under the middle of the sash-bars. In the case 

 of houses so large that more than five 2^-inch flow- 

 pipes are required, 3-inch flows should be used. 



The length of the coils and their height above the 

 boiler will determine the size of the pipe which should 

 be used for the returns, since a smaller size will answer 

 in short coils and in those that are considerably elevated 

 than for long coils which are but little, if any, above the 

 level of the boiler. For the construction of coils 75 

 feet or more in length, 2-inch pipe should be used, and 

 it will generally be found preferable to a smaller-sized 

 return-pipe when they are only 50 feet in length, 

 especially if the flows are under the benches or when the 

 coils are below the top of the boiler. For short coils, 

 pipes as small as IJ^-inch may be used where they are 

 somewhat elevated but for ordinary commercial green- 

 houses it will be better to use 2-inch pipe for the 

 returns, although 13^-inch pipe might answer in houses 

 up to 75 feet in length, as, while small pipe furnishes 

 the most effective radiation to the square foot, the 

 increased friction impedes the circulation. 



In narrow houses, the return-pipes may be placed 

 upon the side walls, but as the width increases it will 

 be generally advisable to have from one-third to one- 

 half of the returns either under the benches or in the 

 walks when beds are used. From the fact that running 

 the pipes overhead will not only improve the circula- 

 tion but will prevent cold draughts of air upon the 

 plants, it is often desirable when but one overhead 

 flow-pipe is used to bring back one return upon each 

 of the purlins. When the end of the house is much 

 exposed, it is an 

 excellent plan to 

 drop down one 

 feed - pipe from 

 the end of the 

 main, or two 

 when there is a 

 door in the end 

 of the house, 

 and supply coils 

 running in either 

 direction to the 

 corner of the 

 house and thence 



1763. Pipe work for modern greenhouse 

 heating. A wall coil. 



along the walls toward the end where the heater is 

 located. Particularly when the pipes are but little, if 

 any, above the top of the boiler, the circulation will 

 be improved by carrying the return-pipes as high as 

 possible, but of course care should be taken when they 

 are under the benches not to have them so high that 

 they will dry out the soil. 



The returns may be arranged in horizontal coils 

 under the benches, or in vertical coils on the walls, or 

 on the sides and supports of the beds and benches. 

 The pipes in the coils may be connected at their ends 

 either by means of manifolds, or by tees and close 

 nipples, but in either case provision should be made for 



