GREENHOUSE 



When all of the pipes are under the benches or upon 

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

 supply all of the others in thf roil, or two or more of 

 the pipes of the same sizi-. as tlic returns may be used as 

 flow pipes. These pipis ran I..- s.. arranged that they 

 will each supply ono nv mure n lurns. or they may con- 

 nect with a header frcmi wliirli all of the return pipes 

 start. Care sli..ul.l Im- laKiii to give all of the return 

 pipes a sliirlit fall, ami ii will be best if this is only 

 enough to iii-mi- tin ii- Im in- kept free from air. It will 

 be safest tu ^i\ n tin- sinallrt- pipes a slope of one inch in 

 15 feet, but2-ini'h 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 sufBcient 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 heater, if it is connected at its own 

 level with the return 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 flow 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 

 sired, the dift'erence in temperature that 

 can be secured at the two ends of 

 the houses will not be marked if 

 the coils are connected w 

 the main flow pipe at the 

 end nearest the boiler. 



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 Badtali.ni.-tfwhvj. to the 

 great variations in temperature ami tlm (iin.inin-cs in 

 the construction of Greenhouses ami m tlm.,- . xposures, 

 it is impossible to give an explicit ruin r.;;ai(ling the 

 amount of radiation to be required under all cuu^litions; 

 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 radiatiuL' surfair- and the 

 amount of exposed glass and wall smin . , n [iiin-jn;;, of 



course, that there is a proper adji, nn the 



size of the boiler and radiating' - .i . ■ ;ii;it the 



system is so arranged as to givn -^ I m-nli , I'luis, 



when a temperature of 40° is dnsired 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 iyi 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 3K, 3, 2H 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-flfth of the exposed wooden or other wall sur- 

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

 between the 

 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 

 f wrought - iron 

 pipe is the in- 

 terior diam- 



and 





main return pipe pass- 

 ing along the farther 

 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 



1001. Carnation 



sed, if tli< 



the 



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 



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 that 1-inch pipe will afford about .344 square 

 feet of radiating surface per linear foot, while 1K-, iVi-, 

 2-, IM- 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 



