GREENHOUSE 



GREENHOUSE 



1407 



above zero but where the mercury drops 10° to 15° 

 for a short period each winter. By piping the houses 

 so that the desired temperature can be obtained for 

 the houses in ordinary weather by using an open 

 sj'stem, it will then be possible by using a "circulator" 

 to maintain the same temperature in the houses even 

 though the mercury drops 15° or 20° lower. This will 

 make a considerable difference in the cost of piping the 

 houses and the efficiency of the system so far as coal is 

 concerned will be affected only during the few days 

 when the use of the "circulator" is necessary. 



The use of a closed system is also helpful when, owing 

 to local conditions, it is necessary to place the boiler 

 upon or slightly below the level of the walks in the 

 houses. While much can be done to secure a circula- 

 tion by using overhead flows and keeping the returns 

 as high as possible, the circulation can be still 

 further improved if it is run as a closed system. 

 Still another method of increasing the rapidity 

 of the circulation and the efficiencj' of the 

 heating-system is to place either upon 

 the main flow- or return- pipe a 

 pump, worked by steam or elec- 

 tricity, by which it wiU be pos- 

 sible greatly to accelerate the 

 circulation of the water, so that 

 such matters as the relative ele- 

 vation of the boiler and heating- 

 pipes will need but Uttle con- 

 sideration and it wiU be pos- 

 sible to decrease to a consider- 

 able extent the size and number 

 of the heating-pipes. 



Estimating hot-water radiation. 



Owing to the great variations in temperature and the 

 differences in the construction of greenhouses, and also 

 in their exposures, it is impossible to give any exphcit 

 rules regarding the amount of radiation that will be 

 required under all conditions ; but experience has shown 

 that in well-built houses any desired temperature can 

 be secured. Knowing the minimum outside tempera- 

 ture and the temperature to be maintained within the 

 house, it is necessary only to install a heating-plant 

 with a radiating surface having a certain definite 

 ratio to the amount of exposed glass and wall 

 surface. It is, of course, understood that there 

 must be a proper adjustment between the size 

 of the boiler and the radiating surface and that the 

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

 when a temperature of 40° is desired in sections in 

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

 possible to maintain it when 1 square foot of radiating 

 surface is provided for each 5 square feet of glass; if 

 45° is required there should be 1 foot of radiation for 

 4J-^ feet of glass. Under the same conditions, 50°, 55°, 

 60°, 65° and 70° can be obtained, respectively, by using 

 1 square foot of radiating surface for each 4, 3H, 3, 2J^, 

 and 2 square feet of glass. When the outside tempera- 

 tures are sUghtly under or above zero, there should be 

 a proportionate increase or decrease in the amount of 

 pipe used; and, if the houses are poorly constructed or 

 in an exposed location, it wiD be 

 desirable to provide a still further 

 increase in the amount of radiating 

 surface. Under the very best con- 

 ditions, the tem- 

 peratures m e n- 

 tioned can be 

 obtained with, a 

 slightly smaller 

 amount of radia- 

 tion, but the 

 greatest economy 

 so far as coal- 

 consumption and 



labor are concerned will be seciu-ed when the amount 

 of radiation recommended is used. 



In determining the amount of exposed glass surface, 

 the number of square feet in the roofs, ends and sides 

 of the houses should be added, and to this it will be well 

 to add one-fifth of the exposed wooden, concrete or 

 brick waO surfaces. If the amount thus obtained is 



1765. Rose-house, ISO x 20 ft., piped for water. 



divided by the number which expresses the ratio 

 between the area of glass and the amount of radiation 

 which wiU be required, it will give the number of square 

 feet of heating-pipe which must be installed. The 

 unit of measurement of wrought pipe is its interior 

 diameter, while its radiating surface is determined by 

 its outside circumference, and, although it will vary 

 shghtly according to the thickness of the pipe, it is 

 customary to estimate that 1-inch pipe will afford 

 about .344 square feet of radiating surface to the linear 

 foot, while 1H-, l)i-! 2-, 2J^^-, and 3-inch pipe will 

 furnish respectively .434, .497, .621, .759 and .916 

 square feet of radiation for each foot in length of pipe. 

 The following example will perhaps aid in determining 

 the amount of radiating surface and its arrangement 

 in a greenhouse. If a house is 32 feet in width and 200 

 feet in length, with 30 inches of glass in each side wall 

 and with one end only of exposed glass, and a concrete 

 wall 3 feet high on two sides and one end, there will be 

 about 9,000 square feet of glass. To heat this to 50° in 

 zero weather it will be necessary to use one-fourth as 

 much radiating surface, or 2,250 square feet. In a house 

 of this length it will be possible to supply this amount 

 of radiation by means of five 2} i-'mch flow-pipes, and 

 the remaining radiation will be provided by means of 

 ten 2-inch returns which will allow two for each of the 

 flow-pipes. These figures are intended to apply when 

 an open system is used but, if a "generator" is attached, 

 not to exceed four flows and eight returns will be 

 required. 



The use of long, straight runs of pipe 

 will give the best results and, whenever 

 possible, ells and tees should be avoided, 

 but if they must 

 be employed spe- 

 cial hot-water fit- 

 tings should be 

 secured. 



In conservato- 

 ries with high side 

 walls it is desir- 

 able to place the 

 flow-pipes at the 



1766. Violet-house with hot-water heating. 



