GREENHOUSE 



GREENHOUSK 



693 



When all of the pipes are under the benches or upon 

 the walls, a single large pipf niay be used as a flow to 

 supply all of the others in the coil, or two or more of 

 the pipes of the same size, as the returns may be used as 

 flow pipes. These pipes can be so arranged that they 

 will each supply one or more retiirns, or they may con- 

 nect with a header from which all of the return pipes 

 start. Care should be taken to give all of the return 

 pipes a slight fall, and it will be best if this is only 

 enough to insure their being kept free from air. It will 

 be safest to give the smaller pipes a slope of one inch in 

 15 feet, but 2-inch pipes, if carefully graded and securely 

 supported at intervals of 10 feet, will give good results 

 if the fall is not more than 1 inch in 30 feet. This is 

 often of considerable importance in long houses where 

 it is not possible to sink the heater so as to give the 

 returns a fall of 1 inch in 10 or 15 feet, as is often recom- 

 mended. It should be understood that better circulation 

 can be secured when a return pipe has but a slight slope 

 if sufficient to keep it free from air, with a vertical drop 

 of the return pipe at the lower end, than when the coil 

 has a much greater fall in running from one end of the 

 house to the other, if this brings the lower end of the 

 coil down to about the level of the main return. The 

 circulation in a coil fed by an under-bench flow will be 

 quite unsatisfactory when the lower end of the coil is 

 below the top of the lu-ater, if it is connected at its own 

 level with the nturn pipes from other coils, that are 

 considerably higher, and especially if they are fed by 

 elevated flow pipes. When overhead flow pipes are used, 

 the slope of the returns will necessarily be toward the 

 heater, but when the pipes are all under the benches 

 the slope may be in either direction, and if connected at 

 the end nearest the heater it will be necessary to run a 

 return pipe of the same size as the supply pipe, back 

 from the farther end of the house, unless there are a 

 number of houses in the range, when a main return pipe 

 ■can be run across the farther end of the houses, to which 

 coils can be connected. If a coil is made up of two or 

 more pipes of the same size, a part of which are flows 

 and the others returns, it will be advisable to run all of 

 these pipes down hill; although, if there are only one or 

 two flow pipes, and the lower end of the coil is con- 

 siderably above the heater, a good circulation can be 

 secured if the (low pipes run up hill to the farther end 

 and are brought back with a downward flow. The down- 

 hill system, with a flow pipe running to the farther end 

 of the house, has two advantages, as it does away with 

 the necessity of air valves, or other openings for the es- 

 cape of air, except at one point, which should be the 

 highest in the system, and it provides for a somewhat 

 more even distribution of the heat, the farther end of 

 the houses being fully as warm as the end near- 

 est the boiler. Where there is a large range 

 of houses and overhead pipes are not de 

 sired, the difference in temperature that 

 can be secured at the two ends of 

 the houses will not be marked if 

 the coils are connected with 

 the main flow pipe at the 

 end nearest the boiler, 

 and are joined with a 

 main return pipe pass- 'J 

 ing along the farther 1 

 end of the houses, and : 

 if the coils upon the 

 walls are carried along 

 the ends of the houses 

 to the doors. 



For all hot water 

 heating plants an ex- 

 pansion tank is neces- 

 sary (Fig. 999). This 

 may be made from heavy galvanized sheet-iron, or a 

 riveted boiler iron tank may be used. It should be con- 

 nected with the heating pipes, but the point of connec- 

 tion will make little difference, although when the 

 downhill system is used, if the pipe leading to the ex- 

 pansion tank starts from the highest point of the sys- 

 tem it will make the use of air valves unnecessary. 

 The tank may be located only slightly above the high- 

 est point of the system, but it will be best placed at 

 least 10 to 15 feet higher, as the elevation of the tank 



will lessen the danger of the boiling over of the water 

 in the system, and make it possible to secure a higher 

 temperature in the water of the coils than when the 

 tank is not thus elevated. Trouble from the boiling of 

 the water in the heater is most likely to occur when 

 the flow or return pipes are too small, and when the 

 fire surface in the boiler is composed of small, wrought- 

 iron pipes or drop tubes. When there is a proper ad- 

 justment between the size of the boiler and the radi- 

 ating surface, and the return connections are of suffi- 

 cient size, there will be little danger from it. 



Estimating Hot Water Had iat ion. — Owing to the 

 great variations in temperature and the differences in 

 the construction of Greenhouses and in their exposures, 

 it is impossible to give an explicit rule regarding the 

 amount of radiation to be required under all conditions ; 

 but experience has shown that, ia well-built houses, 

 any desired temperature can be secured, for various 

 minimum outside temperatures, when there is a certain 

 ratio between the amount of radiating surface and the 

 amount of exposed glass and wall surface, supposing, of 

 course, that there is a proper adjustment between the 

 size of the boiler and radiating surface, and that the 

 system is so arranged as to give good results. Thus, 

 when a temperature of 40° is desired in sections 

 where the mercury does not drop below zero, it will be 

 possible to maintain a temperature of 45° inside the 

 Greenhouse when there is 1 square foot of radiating 

 surface to 4K square feet of glass. Under the same 

 conditions, 50° can be secured when there is 1 foot 4if 

 pipe to 4 of glass, and 55°, 60°, 65° and 70° can be ob- 

 tained when there is, respectively, 1 square foot of pipe 

 to each 3%, 3, 2H imd 2 square feet of glass. For out- 

 side temperatures slightly under or above zero, there 

 should be a proportionate increase or decrease in the 

 amount of pipe used, and if the houses are poorly con- 

 structed, or in an exposed location, it will be desirable 

 to provide increased radiating surface. Under the best 

 conditions the temperatures mentioned could be ob- 

 tained with a slightly smaller amount of radiation, but 

 the greatest economy, so far as both coal consumption 

 and labor are concerned, will be secured when the 

 amount of radiation recommended is used. In deter- 

 mining the amount of exposed glass surface, the num- 

 ber of square feet in the roof, ends and sides of the 

 houses should be added, and to this it is always well to 

 add one-fifth of the exposed wooden or other wall sur- 

 face, and if this sum is divided by the number which 

 expresses the ratio between the area 

 of glass and the amount of radi- 

 ation, it will give the number 

 of square feet of heating 

 pipe to be required. The 

 unit of measurement 

 o f wrought - iron 

 pipe is the in- 

 terior diam- 



1001. Carnation house, 100 x 23 ft. 6 in., piped for hot water, 



eter, while its radiating surface is determined by its out- 

 side circumference; and, although it will vary slightly ac- 

 cording to the thickness of the pipe, it is customary to 

 estimate tliat 1-inch pipe will afford about .344 square 

 feet of radiating surface per linear foot, while 1H-, l/^-» 

 2-, 2K- and 3-inch pipe will supply, respectively, .434, 

 .497, .621, .7.59 and .916 square feet of radiation for each 

 foot in length of pipe. The best results can be secured 

 only when the pipes are in straight runs. The use of 

 ells and tees should be avoided whenever possible, but 



