Document v6aJMaQ7gyrkpJr7o2mk5J1RR

American Society of Heating and Ventilating Engineers Guide, 1935 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 cam 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 a true index of output. (The engineering unit of output is now 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. Table 1. Variation in Dimensions and Catalog Ratings of 10-Section Tubular Radiators Width of Radiator ________Laches Length per SectionInches 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 11.4-12.8 2.5-3.0 Hbiqbt with Lbqs--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 0-37 5 30 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 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. - `University of Illinois. Engineering Experiment Station Bulletin No. 223, p. 30:- . 492 Chapter 30--Radiators and Gravity Convectors Output of- Pipe Coils ' The heat emission of pipe coils placed vertically on a wall with the pipes horizontal is given in Table 2. This has been developed from avail able data and does not represent definite results of tests. For such coils the heat emission varies as the height of the coil. It is customary to use an average emission of 100 Btu per linear foot of pipe, 10 ft high. The heat emission of each pipe of ceiling coils, placed horizontally, is about 126 Btu, 156 Btu, and 175 Btu per linear foot of pipe, respectively, for 1-in., l}4-in., and lJ/^-in. coils. Table 2. Heat Emission of Pipe Coils Placed Vertically on a Wall (Pipes 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) Sns of Pipe Single row................................................ Two.... ............i................................ -....... Four...... -........... .............................:....... , Eight.............. --........-.............--........... Ten.:.-..------- ----:---------:-- ; Twelve::-:........ ...............................; 1 In. 132 252 440 567 . 651 732 812 m In 162 312 545 702 796 907 1005 m In 185 348 616 793 907 1020 1135 ' Effect of Paint The prime coat of paint on a radiator has little effect on the heat output, but the finishing coat' of; paint does influence the radiation emission. Since this is a surface effect; there is no noticeable change in the convection loss. Thus, the larger the proportion of direct radiating surface, the greater will be the effect of painting on the radiation. Available tests are on oldstyle column type radiators which gave results shown in Table 3. Table 3, Effect of Painting 32-in. Three Column, Six-Section Cast-Iron Radiator3 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.... Area Sq Ft 27 27 27 27 Coefficient of Heat Trans. Btu ; Relative Heating Value Per Cent 1.77 1.60 1.78 1.76 100.5 90.8 101.1 100.0 Comparative Testa of Radiator Finishes, by W. H. Severos (A.S.H.V.E. Transactions, Vol, 33,1927).. HEATING EFFECT - For several years the healing effect of radiators has been considered by engineers in order to use it for the rating of radiators and in the design of heating systems. Heating effect is the useful output of a radiator, in the comfort zone of a room, as related to the total input of the radiator2. *Tbe Heating Effect of Radiators, by Dr. Charles Brabble (A.S.H.V.E. Transactions, Vol. 33, 1927. P. 33). 493