Document Oz69LpgBbKqEzvXQn31X2QBre

600 .CHAPTER 23 1957 Guide ranged as header coils with the pipes spaced from 6 to 18 in. on centers. The coils are generally installed with ii 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 be 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. A 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 OUTSlOC WALL FOOTING WALL' -RECAST SLAB .COMCACTC FLOOR SUPPORTS ANO OIRECTIOMAL VANES ' AIR PLENUM --CONCRETE INSULATION GRAVEL Oft ROCK FILL ART* Fid. 6. Warm Air Floor Panel Construction 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 pliance with any building codes that might apply. (See also section on Warm Air Ceiling Panel Systems in Chapter 19.) 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 41, Electric Heating. HEAT OUTPUT FROM PANEL SURFACES A heated panel transfers heat to a room by convection and radiation. In the following paragraphs, the two transfer mechanisms are first considered separately and then combined to facilitate design calculations. Panel Heating- 601 Radiation Transfer The radiation transfer can be evaluated by means of the Stefan and Boltzmann equation: . m-m 0.173 F. (1) where g, = heat transfer by radiation, Btu per (hour) (square.foot). Tv = temperature of panel heated surface, Fahrenheit, absolute. T, = mean radiant temperature of all unheated surfaces, Fahrenheit, absolute. F, = the configuration factor (dimensionless). F,, = the emissivity factor (dimensionless). A combined configuration and emissivity factor for a simple, box-like room in which there is a uniformly heated ceiling, floor, or wall, all STUB BRACE it-m /""INSULATION riLLCft PANEL INSULATION INSULATION % y*tt*TU*Q CABLES. 5 Stapled to lat>$ finismco plaster Fig. 7. Electric Heating Cables in Plaster SEE OETAIL f INSULATIONIN PANEL HCATING panel attached to joists PREFABRICATE PANEL ATTACMCO TO JOISTS DETAIL CLfeCTftlC RESISTANCE ELEMENT IN PANEL A Fig. 8. Prefabricated Electric Panel other surfaces are at another temperature, and all surfaces, are perfectly diffusing is given by Hottel3 as: F. = FJ\ = (2) where = combined configuration and emissivity factor. Fi- = view factor =1.0. i and e, = emissivities of the .surfaces. di and At = areas of the surfaces. . In practice the emissivity of conventional, non-metallic, non-reflecting rfaces will be found to be about 0.9. When this emissivity is used in b-quation 2, the combined factor will be found to be about 0.87 for most f,0.0?18- Substituting this value in Equation 1, the constant becomes about u-io and the equation can be rewritten: 1' = 0.15 'j~^4 + 460^ _ ^AUST + 46pyj (3) where AT7Wp = ^"Perature of panel surface, Fahrenheit. . = area-weighted average temperature of unheated surfaces in room, Fahr enheit.