Document 2z4gv8yY4NVZRpJVQ5Y66d57

American Society of Heating and Ventilating Engineers Guide, 1939 and in that case it amounts to about three and one-half times normal condensation. After the end of 25 min., the radiator reached a normal rate of condensation. This curve was made from observations at intervals of 10 min. so that the intermediate points between the 10 min. points are not known, and the form of the curve is not exact. It shows, however, that when a plant is initially started up and the system filled with steam during a^hort period of time the demand made upon the boiler may be very much higher than the normal demand. In practice the rate of steam supply to the radiator while heating-up is however, generally retarded by controlled elimination of air through air valves or traps and if sufficient time is allowed for the heating-up process, overload on the boiler may be practically eliminated. Chapter II--Radiators and Heaters T a b le 8. E ffect of E nclosure on H e a t E m ission .from R ad iato r Time elapsing after Steam is turned into Radiator fin Minutes) Fig. 2. Chart Shows the Steam Demand Rate for Heating-up a Cast Iron Radiator with Free Air Venting and Ample Steam Supply EFFECT OF PAINTING CAST IRON RADIATORS The effect of painting is to change the radiation constant of the radiating surface and has practically no effect upon the heat lost by convection. It is, therefore, a surface effect and it makes no difference what paints are placed on the radiator as a priming coat, the results are always dependent upon the last coat of paint put upon the radiator. In radiators having a large proportion of radiating surface such as pipe coils or wall coils, the effect of painting will be more marked than in four-column radiators having a comparatively small radiating surface in proportion to converting surface. All finely ground materials have about the same radiation constant. Therefore all paints having finely ground pigments will give about the same effect. Metals have a poor radiating effect so that any paint involving flake metal, such as the bronze, will have a low radiating constant. The effects of painting a six-section 32-in. three-column radiator as found by Wm. H. Severns are given in Table 7. Table 7. Effect of Painting 32-in. Three-Column, 6-Section Cast Iron Radiators' Radiator No. i 2 3 4 Finish One coat dull black Pecora paint.... Area So. Ft. 27 27 27 27 CosmcIENT or Heat Trans. B.t.u. Relative Heating Value Per Cent 1.77 1.60 1.78 1.76 100.5 90.8 101.1 100.0 Comparative tests of Radiator Finishes by Wm. H. Severns, Journal, American Society of Heating and Ventilating Engineers, January, 1927. 76 77