Document 158kJbo8a8ojeVDGJ8YgVLZNX

American Society of Heating and Ventilating Engineers Guide, 1937 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 a true index of output. (The engineering unit of output 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 feel. 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 No. of Tithe* . Width of Radiator Length per Section Height with Legs--Inches 4.6-5.1 * co ;o -------------- -- 567 9.1-10.4 11.4-12.8 2.5-3.0 Heat Emission-- Equivalent Square Feet 13-14 16-18 20-21 22-23 25-26 30-32 36-38 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 ^.U-o2.5 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 fpr 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. 534 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. 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., lj^-in., and l)4-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) Size op Pipe Single row.. Two---------Four--------SixEight.-- Ten------Twelve.-- 1 In. In. IH In. 132 162 185 252 312 348 440 545 616 567 702 793 651 796 907 732 907 1020 812 1005 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. Relative Heating Value Btu Per Cent 1.77 100.5 1.60 90.8 1.78 101.1 1.76 100.0 .Comparative Tests of Radiator Finishes, by W. H. Severns (A.S.H.V.E. Transact,ons. Vol. 33.1927). Effect of Superheated Steam Available research data indicates 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 additional tests are necessary with varying degrees of superheat to establish accurate comparisons for all types of radiators and convectors*. Tests of Radiators with Superheated Steam, by R. C. Carpenter (A.S.H.V.E. Transactions, Vol. 7. 1901, p. 206).. 535 N. /