Document 3eO18oKgVo6NJ10E38Xoa5E2D

Chapter 25 v RADIATORS, CONVECTORS, COILS Heat Emission of Radiators and Convectors, Types of "Radiators,. Convectors, Radiator and Convector Ratings, Effect of Operating Conditions, Heating ' Effect, Heating Up the Radiator and Convector, Enclosed Radiators, Coils, Coil Construction and Arrangement, Steam Coils, Water Coils, Direct-Expansion Coils, Flow Arrangement, Applica. tions. Heat Transfer and Air Flow Resistance, Coil Selection ..... - RADIATORS and convectors' are primarily- used, for heating and, since their performance is affected by many of the same conditions, they will be considered together, while coils will be treated separately in the latter part of the chapter. HEAT EMISSION OF RADIATORS AND CONVECTORS Most heating units emit heat by radiation and convection. An exposed radiator emits roughly half of its heat by radiation, the amount depending upon the size and number of sections. When the radiator is enclosed or shielded, the proportion of radiation is further reduced. The balance of the emission occurs by conduction to the air in contact with, the heating surface, and the resulting circulation of the air warms by convection. A convector emits practically all of its heat by conduction to. the air sur rounding it and this heated air is in turn transmitted by convection to the rooms or spaces to be warmed, the heat emitted by radiation being negligible. The output of a radiator can be measured only by the heat it emits and is generally expressed in units of: Btu per hr; Mbh (1000 Btu per hour); or in equivalent direct radiation (240 Btu per hour for steam or 150 for water radiation). TYPES OF RADIATORS Present day radiators may. be classified as tubular, wall, or window type and are generally made of cast-iron. -Only the small-tube type of tubular radiators.with a spacing of 1% in. per section are now available. Small-tube radiators occupy less space and are particularly suited for installation in recesses. Baseboard radiation consists of long, low units which are made to resemble conventional baseboards and are installed along the outside walls of rooms in place of the usual wooden baseboard. Units are made either of hollow cast-iron panels (with, or without fins on the back) or of ferrous or non-ferrous finned tubing installed behind a metal enclosure. They are suited for use on hot water systems, but may also be used on two-pipe steam systems. Ratings are expressed- in Btu per (hour) (linear foot) and must be obtained from the manufacturer as there is not yet a standardization of outputs for radiation of this type. Among the advantages claimed, for baseboard radiation are that it is inconspicuous;,clean in operation; offers a minimum of interference with furniture placement; distributes the heat near'the floor, thus preventing cold floors sometimes experienced--especially in basementless houses; and blankets exposed walls with a film of warmed air. This reduces floor to ceiling temperature gradient to'about 2 F arid tends to produce uniform temperatures throughout the room. 472 Radiators, Convectors, Coils 473' Table 1. Small-Tube Cast-Ikon Radiators NUMBER TuObFbs per : Section 3d 4d 5d 6d . . . Section Dimension^ Catalog Rating per . Section* AB Width . Height Minimum Maximum c Spacing* Sq Ft ; In. In. ' In. In. 1.6 - 1.6 1.8 2.0 25 19 22 25 3)4 3)4 m4% 4% 4% ... 4% m m m 154 .m2.1 22 - 2.4 25 654 .. . 654 154 154 1.6' 2.3 3.0 3.7 14 19 25 32 6%' 6>% 6% 6% 8" 8 8 8 154 154 154 154 D Leg. , Height In. 2)4 254 2)5 2)4 2)4 2)4, > ; 254 ' 254 2)5 254 mJ| r-- m with steam at 215 F, in air of 70 F; These ratings apply only to installed radiators exposea in a numoirmaaaii manner: not .to radiators installed behind enclosures, grilles, etc.' (See A.S.H.V.E. Code for Testing Radi* a tors adopted January, 1927.) .......... * >Length equals number of sections times in. cOver-all height and leg height, as produced by some manufacturers, are one inch (1 in.) greater than shown in Columns' A and D. Radiators may be furnished without legs. Where greater than standard leg heights are reauired this dimension shall be 4M in. After a study of the demand for various sizes of radiators, the Institute of . Boiler and Radiator Manufacturers, in cooperation with the Division of . Simplified Practice, National Bureau of Standards, established Simplified Practice Recommendation R174-43 for small-tube cast-iron radiators. Table,1 shows the size and dimensions now being manufactured. Wall radiators are now rated in terms of equivalent square feet, the same as small-tube radiators- Tests have shownr.-that the heat emitted from a wall-type radiator may 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 such a large difference in the. temperature between the floor level and the ceiling that it becomes difficult to heat the living zone of the room satisfactorily. ^ ` . ! , Pipe coils are assemblies of standard pipe or tubing (1 in. to. 2 in.) which are used as radiators. In older practice these coils'were commonly used 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 linearfoot of coil per hour (not linear feet ofpipe) S:x.s o? Pips Single row._ Two._______ Four..---------Six. Eight_______ Ten Twelve_____ 1 Is. 132 252 .. 440 567 651.. 732 812 -.. IX Is. 162 312545 702 796 907 , 1005 lHIs. 185 348 616 793 907 1020 1135