GREENHOUSE 



Vhen all of the pipes are under the benches or upon 

 fie walls, a single large pipe may be used as a flow to 



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

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

 . >\v pipes. These pipes can be so arranged that they 

 /ill each supply one or more returns, or they may con- 

 iect with a header from which all of the return pipes 

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

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



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

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

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

 upported at intervals of 10 feet, will give good results 

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

 ften of considerable importance in long houses where 

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

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

 aended. It should be understood that better circulation 

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

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

 >f the return pipe at the lower end, than when the coil 

 la.s a much greater fall in running from one end of the 

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

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

 irculation in a coil fed by an urider-bench flow will be 

 luite iinsatisfactory when the lower end of the coil is 

 >elow the top of the heater, if it is connected at its own 

 evel with the return pipes from other coils, that are 

 ;onsiderably higher, and especially if they are fed by 

 levated flow pipes. When overhead flow pipes are used, 

 he slope of the returns will necessarily be toward the 

 leater, but when the pipes are all under the benches 

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

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

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

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

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

 an be run across the farther end of the houses, to which 

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

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

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

 hese pipes down hill; although, if there are only onebr 

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

 siderably above the heater, a good circulation can be 

 secured if the flow pipes run up hill to the farther end 

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

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

 )f the house, has two advantages, as it does away with 

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

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

 lighesfin the system, and it provides for a somewhat 

 nore even distribution of the heat, the farther end of 

 t :he houses being fully as warm as the end near- 

 ^st the boiler. Where there is a large range -? 



)f houses and overhead pipes are not de- 

 sired, the difference in temperature that 

 ^an be secured at the two ends of 

 ;he houses will not be marked if 

 :he coils are connected with 

 :he main flow pipe at the 

 ?nd nearest the boiler, 

 md are joined with a 

 naiii return pipe pass- 

 ing along the farther 

 3nd 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 



GREENHOUSE 



693 



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 Radiation. Ovf ing 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, in 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 4% square feet of ; glass. Under the same 

 conditions, 50 can be secured when there is 1 foot of 

 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, 2% and 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 

 of wrought - iron 

 pipe is the in- 

 terior diam- 



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



Y 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- 

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

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



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 that 1-inch pipe will afford about .344 square 

 feet of radiating surface per linear foot, while 1%-, 1%-, 

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

 .497, .621, .759 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 



