Document wEE5a5jB6v5EdyG3GQgnMOGV

Heating Ventilating Air Conditioning Guide 1939 in factory buildings, but now wall type radiators are most frequently uSC(j for this service. When coils are used, the miter type assembly is to be preferred as it best cares for expansion in the pipe. Cast manifolds or headers, known as branch tees, are available for this construction. OUTPUT OF RADIATORS The output of a radiator can be measured only by the heat it emits. The old standard of comparison used to be square feet of actual surface, but since the advance in radiator design and proportions, the surface area alone is not true index of output. (The engineering unit of outputs is the Mb or 1000 Btu.) However, during the period of transition from the old to the new, radiators may be referred to in terms of equivalent square feet. For steam service this is based on an emission of. 240 Btu per hour per square foot and for hot water service 150 Btu per hour per square foot. Table 1. Variation in Dimensions and Catalog Ratings of 10-Section Tubular Radiators (Steam) No. of Tubes____ _ Width of Radiator __ Length per Section-- __ ------ -inches -Inches 3 4.6-S.l 2.5 4 6.0-7.0 , 2.5 5 8.0-8.9 2.5 6 9.1-10.4 2.5 7 11-.4-I2A 2.5-3.0 Height with Legs--Inches Heat Emission---Equivalent Square Feet 13-14 16-18 20-21 22-23 25-26 30-32 36-38 20 28.5 15.0-17.5 20.0-22.5 25.0-31.2 30 20.0-21.3 25 30.0-33.9 35 20.0-26.7 25.0-27.5 32.5-39.8 37.5-40.0 25.0-30.9 33.3-35.0 40.0-48.6 50 30.0-36.7 40.0-42.5 50.0-56.5 60 25.0-32.5 30.0-38.3 36.7^-45.0 40.0-45.2 50 0-53.5 63.3-62.5 70.0-75.4 Output of Tubular Radiators Table 1 illustrates the difficulty in tabulating tubular radiator outputs since there is so much variation in design between the products of the different manufacturers. Only on the four-tube and six-tube sizes is there any practical agreement in output value. The heat emission values appear as square feet but are entirely empirical, being based on the heat emission of the radiator and not on the measured surface. Output of Wall Radiators -An average value of 300 Btu per actual square foot of surface area per hour has been found for wall radiators one section high placed with their bars vertical. Several recent tests1 show that this value will be reduced from 5 to 10 per cent if the radiator is placed near the ceiling with the bars horizontal and in an air temperature exceeding 70 F. When radiators are placed near the ceiling, there is usually so noticeable a difference in temperature between the floor level and the ceiling that it becomes dif ficult to heat the living zone of a room satisfactorily. 1 University of Illinois, Engineering Experiment Station Bulletin No. 223, p. 30. 270 ir--j. 7. p--- -- ;Chapter 14. Radiators and Gravity Convectors Output f PiPe The heat emission of pipe coils placed vertically on a wall with the . horizontal is given in. Table 2. This has been developed from availbledata and does not represent definite results of tests. For such coils' die heat emission varies as the height of the coil. The heat emission of Sch pipe of ceiling coils, placed horizontally, is about 126 Btu, 156 Btu, and 175 Btu per linear foot'of pipe, respectively, for 1-in., lj^-in.t and ijfin. coils. Table 2. Heat Emission of Pipe Coils Placed Vertically on A Wall (Pipes 1 Horizontal) Containing Steam at 215 F and Surrounded with Air at 70 F Btu per linear foot of coil per hour {not linear feet of pipe) 0 Four...... Six.------EightTen....... Twelve- Size of Pipe 1 In. 132 252 440 567 651 732 812 IK In. 162 312 545 702 796 907 1005 1M In. 185 348 616 793 907 1020 1135 Effect of Paint The prime coat of paint on a radiator has no material effect on the heat output, but the finishing coat may influence the radiation emission and thus affect the heat output. Within the range of temperatures at which radiatore/operate, color has no appreciable influence on the radiation emitted^ Thus, finishing coats of oil paints of various colors will give the same results. However, a bronze paint, applied as the finish coat will change the character of the surface and reduce the amount of heat emitted by radiation. No paint has a noticeable effect on the portion of heat which is given off by convection. The larger the proportion of direct radiating surface, the greater will be the effect of any finish coat of paint which changes the character of the surface. Available tests are on oldstyle column type radiators which give results as shown in Table 3. Table 3. Effect of Painting 32-in. Three Column, Six-Section _______________ Cast-Iron Radiator3 Radiatob No. i 2 3 4 Finish Bare iron, foundry finish One coat of aluminum bronze........... Gray paint dipped............ .;..J.... One coat duH.black Pecora' paint.... Area Sq Ft 27 27 27 27 Coefficient of Heat Trans. Btu Relative Heating Value Per Cent 1.77 1160 1.78 1.76 100.5 90.8 101.1 100.0 1927Cpm41)rative TeStS of Radiator Finishes, by W. H,: Severn* (A.S.H.V.E. Transactions, Vol. 33. Effect of Superheated Steam Available research data indicate that there is probably .a decrease in heat transfer rate for a radiator or gravity convector with superheated steam in comparison with saturated steam at the same temperature; the decrease is probably small for low temperatures of superheats and 271