Document dY1xrNrxnEKxj0eJa7v7LN339

HEATINC VENTILATING AIR CONDITIONING GUIDE 1943 each pipe of ceiling coils, placed horizontally, is about 126 Btu, 166 Btu, and 175 Btu per linear foot of pipe, respectively, for 1-in., lj^-in., and lJ-^-in. coils. CONVECTORS Standard large or small-tube 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 re sulting in a form of gravity convector. 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 delivered to the room through an opening near the top of enclosure. Since the air can only Table 3. 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 feel of pipe) Sbb or Pipe Single row... Two. ..... Four...... Six, ..... . Eight. ............................................. Ten Twelve 1 In. 132 252 440 567 651 732 . 812 . ` IK In. 162 312 545 702 796 907 1005 1M In. 185 348 616 793 9071020 1135 enter the enclosure at the floor line, the cooler air in the room which always lies at this level, is constantly being withdrawn and replaced by the warmer air. This air movement, accomplishes the desired reduction in temperature differentials and assures maximum comfort in the living zone. < Concealed heaters or convectors are generally available as completely built-in units. The enclosing cabinet should be designed with suitable air inlet and outlet grilles to give the heating element its best performance. Tables of capacities are catalogued for various lengths, depths and heights, and combinations are available in several styles for installations, 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 convector fit as snugly as possible so that the air to be heated must pass through the convector and cannot be by-passed in the enclosure. J 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 262 CHAPTER 13. RADIATORS AND CONVECTORS 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 the 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 19271. 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 square feet. Similar test .methods for convectors are the A.S.H.V.E. Codes for Testing and Rating Concealed Gravity'Type Radiation2, (Steam Code 1931 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. A.S.H.V.E. Code for Testing Radiators (A.S.H.V.E. Transactions, Vbl. 33, 1927, p. 18). 'A.S.H.V.E. Standard Code for Testing and Rating Concealed Gravity Type Radiation (Steam), (a:s.H.V.E. Transactions. Vol. 37. 1931, p. 367); (Hot Water). (A.S.H.V.E. Transactions, Vol. 39. 1933, p. 237). (See also A.S.H.V.E. Transactions, Vol. 41. 1935. p. 38, and Vol. 42, 1936, p. 29). 263