Two forms of indirect radiators are shown in Fig. 7, Part I, a1d Fig. 3, Part II (Heating and Ventila tion), the shallow sections being used largely for house heating, the deep ones for schoolhouse systems. The latter am provided with extra long nipples for spac ing the sections about 4 inches on centers, to give a proper passage for a large volume of air.
Indirect Radiators. The direct radiators are enclosed in galvanized-iron casings about 30 inches deep, giving a space of 6 or 8 inches above and below the radiators. The beams over the radiators are commonly covered with rough boards, to which tin or tin and asbestos is nailed, the casing being flanged at the top and screwed or nailed to these boards.
The casings should be made with corners of a type that will per• mit the ready removal of the sides in case of repairs being needed; and the bottom of the casing should be provided with a slide for inspection and cleaning. The sections, when used for schoolhouse heating, are arranged as shown in Fig. 19, with a mixing damper designed to cause a mingling of the warm and cold air in the flue, the volume discharged being but slightly reduced, with a decrease in tem perature due to opening the damper to cold air. The space for the passage of air between the shallow sections contain ing about 10 square feet each, is about } of a foot; the space between the sections of the deep pattern is not far from a foot when the sections are properly spaced.
Heat Given Off by Steam Radiators. Of the heat emitted by direct radiators, approximately one-half is by radiation, the balance by convection or the contact of air. Since practically no heat is radiated from con cealed radiators, it is very important that proper provision should be made for the passage of an adequate volume of air over the heating surface.
Heat Units Emitted from Radiators and Coils Radiation per square foot of radiating surface per honr.—In rooms at F. ture.—With steam at 8 to 5 pounds' pressure.
Concealed cast-iron direct radiators 175-200 Ordinary cast-iron vertical-section radiators 250 Wall radiators 300 Pipe coils on walls 325 Pipe coils overhead (pipes side by side) 350 Ordinary cast-iron extended-surface indirect radiators (air admitted from outdoors) 400 Wall radiators and coils give off more heat under the same con ditions than is emitted by ordinary vertical cast-iron radiators.
Much might be said regarding the efficiency of radiators due to their height, form, and arrangement. For the purposes of this course, however, only fair average values will be given, as set forth in Table I, a discussion of radiator tests, etc., being omitted to avoid unnecessary detail.