Document Ozrv76Ge6r6VpggDKz5M4M2DK

574 CHAPTER 24 1956 Guide Embedded Piping for Floors The construction for piping embedded in floors will depend upon whether (a) the floor is laid on grade, or (b) the floor is above grade. a. Both ferrous and non-ferrous pipe and tube are used in floor slabs which rest on grade. The coils are constructed as either sinuous^continuous pipe coils, or ar ranged as header coils with the pipes spaced from 6 to l8 in. on centers. The coils are generally installed with 1J to 4 in. of cover above the coils. It is recommended that insulation be used to reduce the perimeter and reverse losses. Fig. 4 shows the application of pipe coils in slabs resting on grade. Coils should be embedded com pletely and should not rest on an interface. Any supports used for positioning the heating coils should be non-absorbent and inorganic. It is suggested that reinforc ing steel, angle iron, pieces of pipe, or stone concrete mounds he used. No wood, brick, concrete block or similar materials should be used for support of coils. Gen erally, a waterproofing layer is desirable to protect insulation and piping. b. Where the coils are embedded in structural load supporting slabs above grade, construction codes may affect their position. Otherwise, the coil piping is installed in the same manner as described for slabs resting on grade. c. \ warm-up and start-up period for concrete panels should be similar to that outlined for plaster panels. , , Air Heated Ceilings, Walls, and Floors Several methods have been devised to warm the interior room surfaces by circulating heated air through passages behind these surfaces. In some cases, the heated air is recirculated in a closed system. In others, all or a part of the air is passed through the room on its way back to the furnace to provide supplementary heating and ventilation.2 Figs. 5 and 6 indicate two common types of construction. Care must be exercised to assure com- STUP IP*C <--INSUiATtOM j3|L~aiOIO LATM rmiSHCO PLASTER Fig. 7. Electric Heating Carles in Plaster Fig. 8. Prefabricated Electric Panel Panel Healing 575 pliance with any building codes that might apply. (See also section on Warm Air Ceiling Panel Systems in Chapter 20.) Electrically Heated Ceilings, Walls, or Floors Several different forms of electric resistance units are available for heating the interior room surfaces. These include: (1) resistance cables that may be embedded in a manner similar to hot water piping in concrete or plaster; (2) prefabricated electric heating panels to be attached to room surfaces; and (3) electrically heated fabrics or other materials for applica tion to, or incorporation into, finished room surfaces. Figs. 7 and 8 indi cate two methods of installation. The constructions of electric panels for ceilings, walls, and floors are described in greater detail in Chapter 42, Electric Heating. OUTPUT FROM PANEL SURFACES The heat transfer from a panel is accomplished by radiation and con vection, which are considered in following paragraphs. Radiation Transfer. The radiation transfer can be evaluated by means of the relationship set up by Stefan and Boltzmann: where q, = heat transfer by radiation, Btu per (square foot) (hour). T, = absolute temperature of panel heated surface, Fahrenheit. T,, = absolute mean radiant temperature of all unheated surfaces, Fahrenheit. F = the configuration factor (dimensionless). = the emissivity factor (dimensionless). For large parallel planes or large enclosed surfaces as ordinarily en countered in panel heating practice: K (2) where i and e% = emissivities of the respective surfaces. In heating practice ei and e2 are usually equal to 0.9 and F,, to 0.82. Also, the configuration factor Fa is equal to 1 for large parallel planes, long concentric cylinders, or smaller bodies in large enclosures. There fore, for ordinary rooms with parallel walls, regular floors and ceilings, with an emissivity factor of 0.82, Equation 1 can be simplified to: -""[(isMs)'] Irregularities in room surfaces and materials may introduce some error