Greenhouses, their construction and equipment . Fig. 26.—Diagram showing how heat and light are lostby reflection angle, the amount reflected increases as theangle of incidence increases. The amount ofthe suns energy lost by reflection when therays strike the roof at various angles isshown in the following table. Table showing per cent, of suns energy lost when therays strike the glass at different angles Angle of ray Loss by reflection 60 degrees per cent. 504030201510 It is apparent that the maximum amountof the suns energy may be secured by a roofpresenting to its
Greenhouses, their construction and equipment . Fig. 26.—Diagram showing how heat and light are lostby reflection angle, the amount reflected increases as theangle of incidence increases. The amount ofthe suns energy lost by reflection when therays strike the roof at various angles isshown in the following table. Table showing per cent, of suns energy lost when therays strike the glass at different angles Angle of ray Loss by reflection 60 degrees per cent. 504030201510 It is apparent that the maximum amountof the suns energy may be secured by a roofpresenting to its rays an angle of 90 is especially important that the energy GENERAL CONSIDERATIONS 45 of the sun be conserved during the short daysof winter. At its lowest period the sun rises,in the latitude of New York, scarcely morethan 25 degrees above the horizon at order for the roof to present an angle of90 degrees to the suns rays at this season,it would need to have a pitch of 65 Fig. 26a.—Diagram showing pitch of roof necessary topresent an angle of 90 degrees to the suns rays in winter Such a roof would be (i) very expensive tobuild and maintain, (2) would present toolarge an amount of radiating surface for thespace covered and (3) would be too high tobe practical in houses more than 10 or 15feet wide. If, however, we reduce the pitch to 35 de-grees, the suns rays will strike the roof atan angle of about 55 degrees which, by refer-ence to the table, will be seen to incur a loss 46 GREENHOUSES by reflection of between 2 and 3 per cent, on-ly. Roofs of this pitch are not difficult tobuild, and do not present so large a radi-ating surface for the area covered as do roofshaving a pitch of 65 degrees. Roofs havinga pitch of less than 26 degrees are seldomsatisfactory because the snow does not clearfrom them well and they are likely to water of condensation which forms onthe inside of the roof is also likely to drip up-on the plants when the pitc
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Keywords: ., bookcentury1900, bookdecade1910, bookpublishernewyorkorangejuddc
