Document JN8er5x1voQoL6p8dpo9xEQr6

47.4 CHAPTER 25 1948 Guide in factory buildings, but now wall-type radiators are most frequently used for this service. When coils are used, the miter type assembly ;is prefer able as it readily permits expansion in the pipe,. Cast manifolds or headers, known as branch tees, are available for this construction. The heat emission of pipe coils placed vertically on a wall, with the pipes horizontal is given in Table 2 which has been developed from avail able data and does not represent defiriitehesuits 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., l)4-in., and 13^-in. coils. CONVECTORS Cast-iron radiators may be concealed in a cabinet or other enclosure for appearance. In such cases a greater percentage of heat is conveyed to the room .by convection thereby resulting in a form of gravity cbrivedtor. A typical recessed convector, is shown in Fig. 1. The heating element consisting of a large percentage of fin surface is usually shallow in depth and placed low in the enclosure in order to produce maximum chimney effect in the enclosure.. The air enters the enclosure near the, floor line just below the heating element, is moderately heated in passing through the core and is delivered to the room through an opening near the top of the enclosure. This air movement accomplishes a reduction in tempera ture differentials and assures maximum comfort in the living zone. Concealed heaters 'or convectors are generally available as completely built-in units. Combinations are available in several styles for instal lations, such as the wall-hung type, free-standing floor type, recess type set flush with wall or offset, and the completely concealed type. Most of these types may be arranged with a top outlet grille in a plane parallel with the floor, although the front outlet is practically standard. In cases where enclosures are to be used but are not furnished by the heater manufacturer, it is important that the proportions of the cabinet and the grilles be so designed that they will not impair the performance of the assembled convector. It is desirable that the enclosure or housing for the Radiators, Convectors, Coils 475 . Convector fit as snugly as possible so that the air to be heated cannot by-pass the heating element in passing through the enclosure. The output of a convector, for any given length and depth, is a function . of the height. Published ratings are generally given in terms of equiva lent square feet, corrected for heating effect. However, an extended surface heating unit is entirely different structurally and physically from a. direct radiator and, since it has no area measurement corresponding to the heating surface of a radiator, many engineers believe that the per formance of convectors should be stated in Btu. For steam convectors, as for radiators, 240 Btu per hour may be taken as an equivalent square foot of radiation. When more than one heating unit is used, one mounted above the other in the same cabinet, the output of die upper unit or units will be materially less than that of the bottom unit. RADIATOR AND CONVECTOR RATINGS A standard method of testing radiators was adopted by the A.S.H.V.E. in 1927 *. This Code provides for a standard test room, the temperature of which is to be maintained at 70 F, measured in the center of the room at an elevation of 5 ft above the floor. The steam temperature in the radi-' ator is to be 215 F, which corresponds to 15.6 lb per square inch absolute. The weight of condensate per hour, under these standard conditions, multiplied by the difference in the enthalpy of the steam entering the radiator and that of the condensate leaving the radiator, gives the radiator output in Btu per hour. This output divided by 240 gives the steam rating of the radiator in equivalent square feet. Similar test methods for convectors are the A.S.H.V.E. Codes for Testing and Rating Concealed Gravity Type Radiation *, (Steam Code 1932 and Hot Water Code 1933). These Codes recognize a different type of test booth, and the air temperature used is that of the air entering the .convector casing instead of the temperature in the center of the room. The entering air temperature for. standard test conditions is 65. F. For hot water the standard test conditions call for a mean temperature of the water in the convector of 170 F. The Convector Manufacturers Association has adopted the A.S.H.V.E. standard in the formulation of its ratings and has compiled a tentative standard of heating effect allowances for various enclosure heights to be included in the ratings by its members. All published ratings bearing the title C.M.C. Ratings (Convector Manu facturers Certified Ratings) indicate that the convectors have been tested in accordance with the A.S.H.V.E. Code by an impartial and disinterested laboratory and that the ratings have been approved by the Standardiza tion Committee of the Convector Manufacturers Association. Effect of Operating Conditions The heat output of a radiator is proportional to. the 1.3 power of the temperature difference between the air in the room at the 60 in. level and the hedting medium in the radiator. The heat output of a convector is proportional to the 1.5 power of the temperature difference between the air entering the convector and the heating medium, steam or hot water, within the convector*. For hot water the arithmetical average between entering and leaving water temperatures is used. These laws may be expressed as correction factors to change from output under standard