692 



GREENHOUSE 



GREENHOUSE 



form a number of vertical coils, each containing from 

 six to ten pipes. The upper ends of the manifolds are 

 joined at the front end of the heater and connect with a 

 'flow pipe, while the lower ends of the rear manifolds 

 are joined to the returns. As a rule, the grate is of the 

 same width as the coil, and from one-half to two-thirds 

 as long. Although a box coil is much cheaper than a 

 cast-iron heater, when we add to its cost the expense for 

 grate, doors and other fittings, and of bricking it in, the 

 amount saved will not be large, especially as the coil 



993. Flow and supply pipe for under-bench flows. 



boilers are, as a rule, not more than one-half as lasting 

 as cast-iron boilers, most of which are complete and re- 

 quire no brick work or trimmings. 



Hot Water Pip ing. Modern hot water heating sys- 

 tems do not differ particularly from those in which 

 steam is used, except that larger sized pipes are required 

 to afford the necessary radiation. Formerly 4-inch cast- 

 iron pipes were used in the piping of Greenhouses, but 

 as the joints are packed with oakum, cement or iron fil- 

 ings, they frequently give trouble by leaking, and it is 

 much more difficult to make changes or repairs than 

 when smaller wrought-iron pipes with screw joints are 

 used. Owing to the large volume of water in the pipes, 

 the circulation is necessarily quite sluggish, and it is not 

 easy to secure the high temperature in the water that 

 can be obtained from smaller pipes. Another objection 

 to these large pipes is, that it is not possible to carry 

 the flows overhead, as is often desirable. 



When the flow pipes supply a number of houses, or 

 if the heater is at some distance from the Greenhouse 

 to be warmed, it is best to start from the boiler with one 

 large pipe, or with two pipes leading out from different 

 sides of the boiler, rather than to carry independent 

 pipes to each house. If there are several houses to be 

 heated, it is advisable to have the heater located at the 

 north end or side of the houses, as near the center as 

 possible, and carry the flow pipe along the ends of the 

 houses just over the doors, although, if necessary, they 

 may be beneath the level of the doorways. From this 

 main pipe one or more supply pipes can lead into each 

 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 radiation that they supply; and, in determin- 

 ing the amount that can be handled by pipes of different 

 sizes, it is advisable to use somewhat larger supply 

 pipes when all of the radiation, both flow and return, 

 is under the benches than when 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 a system in which the radiating pipes are 

 a number of feet above the top of the boiler, since in 

 the latter case a much smaller supply pipe will suffice. In 

 a general way, the following sizes can be used as sup- 

 ply pipes: 1%-inch pipes for 75 to 100 square feet of 

 radiation; 2-inch pipes for 150 to 200 square feet; 2%- 

 inch for 250 to 350; 3-inch for 400 to 600; 3 K -inch for 

 600 to 800; 4-inch for 1,000 to 1,200; and 5-inch for 1,500 

 to 2,000 square feet of radiation. The supply pipes 

 should, if possible, rise vertically from the heater to a 

 point higher than the highest point in the system and 

 then should have a slight fall, say 1 inch in 20 feet, so 

 that there will be no opportunity for the pocketing of 

 air in the pipes. It will, however, make but little dif- 



ference whether the pipes run up-hill or are given a 

 slight downward slope, and the former arrangement may 

 be used where it will best suit the conditions. In case 

 the pipes are carried under the benches, and it is im- 

 possible to sink the boilers much below the level of the 

 coils, it will be well to have the flow pipe run vertically 

 from the boiler to a height of 8 or 10 feet (Fig. 999), and 

 then branch and run horizontally along the ends of the 

 houses, taking off the supply pipes for each and drop- 

 ping them below the level of the benches. 



It is often desirable to have some or all of the flow 

 pipes overhead, as this will greatly improve the circula- 

 tion and will aid in preventing cold drafts of air upon 

 the plants. Some make use of a single large flow pipe 

 in each house. This is located upon the posts, a foot or 

 so beneath the ridge, and carries the water to the farther 

 end of the house, where branch pipes connect with the 

 coils, but a better distribution of the heat can be secured 

 in houses more than 10 feet wide if two or more pipes 

 are used. These can be upon the ridge and purlin posts, 

 and it is often desirable to have one upon each of the 

 wall plates. The number and size of these flow pipes 

 will depend upon the width of the houses and the size 

 of the coils that they supply. The amount of radiating 

 surface in the flow pipe itself should be added to that in 

 the coil, in determining the size of supply pipe that 

 will be required. For long houses it will often be neces- 

 sary to use one or more 3-inch pipes, but ordinarily 2- 

 inch or 2%-inch pipes distributed upon the posts and 

 wall plates will give the best results. 



The size of pipe used for the returns will depend upon 

 the length of the coils and their height above the boiler, 

 as the pipes for elevated short coils may be smaller 

 than those of considerable length that are below the top 

 of the boiler. Ordinarily 2-inch pipe will be desirable 

 for coils more than 75 feet in length, and will be prefer- 

 able to a smaller size when they are only 50 feet in length, 

 if the flows are under the benches and the lowest ] 

 of the coils are below the top of the boiler. For si 

 coils, pipes as small as 1%-inch may be used where thej 

 are somewhat elevated, but for ordinary commercial 

 Greenhouses l>2-inch pipe is better up to 50 to 75 feet, 

 and 2-inch pipe for all others, as, while small pipe fur 

 nishes the most effective radiation, the increased f rictior 

 impedes the circulation. 



If a single large flow pipe is used, it is often desirable 

 to have one or more of the returns elevated upon the 

 purlin posts and wall plates, but ordinarily the radiating 

 surface should be distributed upon the walls (Fig. 1000), 

 and under the benches in houses where, as is now gen- 

 erally the case, there are walks along the^side walls. In 

 houses in which it is undesirable to have Bottom heat, all 

 of the pipes may be upon the walls; and this is also the 

 usual arrangement when solid beds are used, except in 

 wide houses, in which case a portion of the returns may 

 be upon the sides of the beds, beneath the walks, or 

 elevated upon the purlin and ridge posts. 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 the expansion of the 



1000. Pipe work for modern greenhouse 

 heating. A wall coil. 



pipes, which may be done in the case of vertical coils 

 by running them partly across the ends of the houses 

 and in the horizontal coils by the same means, or by 

 placing the header at the lower end of the coil and a 

 foot or so lower, and connecting it with the ends of the 

 pipes by means of nipples and right and left ells. 



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