Document nkqk0a7w3O32K6nxBqQ8dkw86

556 CHAPTER 24 ROOTING WALL POURED SLA0 PRECAST ilW / CONCRETE H.OOB SUPPORTS - poeCTIONH VANES AIR' PLENUM CONCRETE INSULATION CRAVCL OR ROCK TILL EARTH 4954 Guide Fig. 6. Warm Air Floor Panel Construction 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.1 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 Panels 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: .STUD SPACE wJ-r. ^INSULATION 1SLavAIGtO LATH H^MCATINO CABLES jij (staplCO to lath) FINISHED PLASTER Fig. 7. Electric Heating Cables in Plaster \w / INSULATION-1 SEE DETAIL V / IN PANEL f. SEATING PANEL ATTACHED TO JOISTS WNct^TTACH 0 TO JOISTS DETAIL I RESISTANCE CINLEPMAENNETL A Fig. 8. Prefabricated Electric Panel Panel Heating 557 ' 0.173 F.F. [`-O'] (1) wnere q, = heat .transfer by radiation, Btu per (square foot) (hour). T, = absolute,temperature of panel heated surface, Fahrenheit. Tw = absolute; mean radiant temperature of all unheated surfaces, Fahrenheit.- - F = the configuration factor (dimensionless). F. == the emissivity factor (dimensionless). . For. large parallel planes or large enclosed surfaces as` ordinarily en countered in panel heating practice: p-7(;n-') 'Where ei and e, = emissivities of the respective surfaces. In heating practice ei and e2 are usually equal to 0.9 and 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: [(/-]gr = 0.142 (3) . Irregularities in room surfaces and materials may introduce some error Jb the application of this radiation relationship. However, most author ities are in agreement that the heat emission by radiation, as calculated bi this manner, can be considered accurate within 10 percent. Radiation