GREENHOUSE 



When all o£ the pipes are under the benches or upon 

 the ivalls, a single large pipe may 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 returns, or they may con- 

 nect with a header from which all of the nturii pipes 

 start. Care should betaken to give all of the r.timi 

 pipes a slight fall, and it will be liest if tlii-^ i^ only 

 enough to insure their being kept free Irom :iir. 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 i< 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- 

 nirndeil. It should be understood that better circulation 

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

 if sutHoient 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 un.li i-1"ih1i flow will be 

 quite unsatisfactory when the |o«,.r ,ii,l of the coil is 



below the top of the heater, if it i uim . te.l at its own 



level with the return pipes from otlier 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 wnll necessarily be toward the 

 heater, but wlien tlie ]ii|.es 



GREENHOUSE 



693 



the 



under the benches 

 iid if connected at 

 necessary to run a 



from the 



supply pipe, back 



-I', unless there are a 



;.. w Ion a main return pipe 

 end of the houses, to which 

 L coil is made up of two or 

 , 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 riinnins,' to the farther end 

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

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

 caj.e of air,'exre].t at one iiomt, which should be the 

 hiu'li'-^t in tho s\ sf, ni. and it j.tovides for a somewhat 

 iiioi, .\Mi .listnl.n'ion ..t tij. In, it, the farther end of 

 tin- lion-, s li, 111-; tull\ a- M.iiiii as the end near- 

 est the lioiler. Wliere t)it-re is ;, 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 

 th. . II- ,iti 'iiiiected with 

 tin I o at the 



.1 i.oiler, 



an.l I iMth a 



will lessen the danger of the boiling over of the water 

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

 temperature in tin- water of the coils than when the 

 tank is not tlius elovated. Trouble from the boiling of 

 the watii- in tie- letter 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- 

 irou 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. 



E.ili,„„i>,vi JI;I \V„ler Badiatioit.-Owinf; to the 

 great xamitions in t.niperature and the differences in 

 the con-iruiiioii oi i ineuhouses and in their exposures, 

 it is inijiossilile to ;^ive 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 . v|,o-rd -lass and wall surface, supposing, of 

 coursr, :li:iT ili, rr i- ;i proper adjustment between the 

 size of iIlo l.oil' r and radiating surface, and that the 

 system is so arian^ed 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 ii4 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 thire is, respectively, 1 square foot of pipe 

 to each :;' , ::, -J' nnd 2 square feet of glass. For out- 

 side t< ' • :■. 'iL-!:ily uniler or above zero, there 

 shouM nil. iiiiiease or decrease in the 

 amouiii . j .; ' :. :. ..ml it Uie houses are poorly con- 

 structeci. el HI ail L..i"'sed location, it wiU 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 glas.s 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 

 and the amount of radi- 

 , it will give the number 

 f square feet of heating 

 pipe to be required. The 

 unit of measurement 

 f wrought ■ 



tenor i 



pansion tank is neces- 1001. Carnation 



sary (Fig. 999). This 



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

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

 nectiMl ivith til.- heating pipes, but the point of connec- 

 tion will mall.- little difference, although when the 

 downliill sv-toiii 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 highe ,. . . 



the elevation of the tank 



house, 100 X 23 ft. 



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

 side circuiiiterence ; and. although it will vary slightly ac- 

 cording' to I'll. tlii.1:n. -- of i!,.. |,i|,r, it is customary to 

 estinia- • ■ 1 ' • •■■ ■" " I aliout .344 square 

 feet oi ., ' •. while 1M-, 1M-, 



2-, 'J' o i . , . ns|iectively, .434, 



.497, .ij-l. .T.'.J anil .Dill .-.iiuaii lie! ol radiation for each 

 foot iu 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 



