Document edo28MqX3m6y4bn1wzeDGogy

American Society of Heating and Ventilating Engineers Guide, 1928 hour for the time elapsing after steam is turned into the radiator. It will be noticed that the maximum condensation in the radiator occurs 10 min. after steam is turned on, and in that case it amounts to about three and one-half times normal condensation. After the end of 25 min., the radiator had 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 short 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, frequently 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. Fig. 2. Chart Shows Demand upon Boiler for Heating-Up 74 Chapter II--Heating by Radiation EFFECT OF PAINTING The effect of painting was originally determined by experiments made with a cast iron ectangular box, and in applying these to radiators of standard type, corrections must he made to allow for the difference between the area of the radiating and converting rfaces. 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, S surface effect and it makes no difference what paints are placed on the radiator as a oriming 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 oaints 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. Table 15 shows the effect of painting an experimental cast iron box of rectangular shape. It should be noted that in this case all the surface emitted heat by direct radiation. Column radiation having a larger ratio of converting surface to radiating surface would show, less effect due to painting. Table 15. Effect of Painting a Rectangular Radiator Percentage, of Effectiveness Based on Values in Tables as 100 per cent Cast Iron, bare--,........ ........ ...... ...................... ............................ 100% Painted with flat black..... --.................. .................... --,......... 100% Painted with aluminum bronze..................... ........:................:. 80% Painted with gold bronze............................................... ............. 81% Painted with white enamel--...................................................... 101 % Painted with maroon japan.......................................... .............. 100% Painted with white zinc paint.................................................... 101% Painted with no-lustre green enamel.... ........................ .......... 96% The effects of painting a six-section 32 in. three-column radiator as found by Wm. H. Severns are given in Table 16. Table 16. Effect of Painting 32 in. Three-Column, 6-Section Cast Iron Radiators1 Radiator No. i 2 3 4 Finish Bare iron, foundry finish........ ........ One coat of aluminum bronze.......... Gray paint dipped.............-................ One coat dull black Pecora paint__ Abba So. Ft. 27 27 27 27 Coefficient of 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 It is generally assumed that an enclosed radiator shows a decreased heat emission. This is borne out by results recently published by Kratz and Fahnestock, Table 1712. This data indicates that the heat emission from the enclosed radiator equals or exceeds that of an exposed radiator only in the case where the enclosure is much higher than the radiator so as to produce a pronounced chimney effect. 1Comparative tests of Radiator Finishes by Wm. H. Severns, Journal, American Society or Heating and Ventilating Engineers, January, 1927. 2Effect of Enclosures on Radiator Performance by A. P. Kratz and M. K. Fahnestock, Journal, American Society qf Heating and Ventilating Engineers, June, 1927. 75