Document Dv5N8zZ2LOO79xZrRNKKb7GQ5

420 CHAPTER 30 1959 Guide Panel Hearing 421 SCRATCH COAT Air-Heated Ceilings, Walls, and Roars Several methods have been devised to warm the interiot room surfaces by circulating heated air through passages ivhmrl tbp*a surfaces. In some cases, the heated air is re circulated in a closed system. In others, all or a part of the air is through the room on its way back to the furnace to provide supplementary heating and ventilation.' Figs. 5 and 6 indicate two common types of construction. Care must be exercised to assure compliance with any building codes that might apply. (See also section on Warm Air Ceiling Panel Systems in Chapter 18.) 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 gimilftr to hot water piping in concrete or plaster; PLASTER CEILING BELOW JOISTS (2) prefabricated electric heating panels to be attached to room surfaces; and (3) electrically heated fabrics or other Fig. 2 .... Coils in Plaster Above Lath Fig. 4 .... Coils in Floor Slab on Grade materials for application to, or incorporation into, finished room surfaces. Figs. 7 and 8 indicate two methods of in stallation. The constructions of electric panels for ceilings, are installed below the lath. Generally, the surface tempera walls, and floors are described in greater detail in Chapter Fig. 9 .... Heat Output by Radiation ture of plaster panels should not exceed 120 F, and this is the coils. It is recommended that insulation be used to reduce 17, Electric Heating. usually met by limiting the water temperature in the pipes the perimeter and reverse losses. Fig. 4 shows the application or tubes in contact with the plaster to a maximum tempera ture of 140 F. Insulation should be placed above the coils to reduce the reverse loss which is the difference between the heat supplied to the coil and the net useful output to the heated room. In order to protect the plaster installation and to assure of pipe coils in slabs resting on grade. Coils should be em bedded completely 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 reinforcing 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. Generally, a waterproofing layer is desirable to protect insulation and piping. HEAT OUTPUT FROM PANa 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 com bined to facilitate design calculations. T, -- mean radiant temperature of all unheated surfaces, Fahrenheit, absolute. F *= the configuration factor (dimensionless). F4 " the emissivity factor (dimensionless). A combined configuration and emissivity factor - for a proper air drying of the plaster, it is recommended that no . b. Where the coils are embedded in structural load support Radiation Transfer simple, box-like room- in which there is a uniformly heated heat be applied to the panels for two weeks after all plaster ing work has been completed. When the system is started for the first time, the water supplied to the panels should be at a temperature not more than 20 deg above the pre vailing room temperature at that time (but not in excess of ing 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 tor plaster panels. The radiation transfer can be evaluated by means of the Stefan and Boltzmann equation: -()'] 0) calling, floor, or wall, all other, surfaces are at another tem perature, and all surfaces are perfectly diffusing is given by Hottel* as: (2) 90 F). Water should be circulated at this temperature for about two dayB. Then the water temperature should be where *(i increased at a rate of approximately 5 deg increase per day to H 140 F. gr " heat transfer by radiation, Btu per (hour) (square where . During the air-drying and preliminary warming-up periods, adequate ventilation should be provided to carry off moisture from the panels. No paint or paper should be applied to the panels until these periods have been completed. No paint or paper should be applied while the panels are being operated. foot). T, -- temperature of panel heated surface, Fahrenheit, absolute. Ft = combined configuration and emissivity factor. Fi-t * = view factor ** 1.0. t\ and e* a emissivities of the surfaces. Ai and At = areas of the surfaces. After paint and paper have been applied, a further shorter warm-up period, similar to that for the first time starting, is also recommended,. Fig. 5 .... Warm Air Plaster Ceiling Construction i Embedded Piping for Walls 1 Although not so universally used as ceiling panels, wall panels mav be constructed by any of (he methods outlined | for ceilings.' s Embedded Piping for Floors The construction for piping embedded in floors will depend ! upon whether (a) the floor is laid on grade, or (6) the floor is above grade. Fig. 7 .... Ejectric Heating Cables in Plaster In practice the emissivity of conventional, non-metallic, non-reflecting surfaces will be found to be about 0.9. When this emissivity is used in Equation 2, the combined factor will be found to be about 0.87 for most rooms. Substituting this value in Equation 1, the constant becomes about 0.15 and the equation can be rewritten: t, + 460V YAUST + 460 \100 ) 100 where tp temperature of panel surface, Fahrenheit. AUST - area-weighted average temperature of unheated 7 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 arranged as header coils with the pipes spaced from 6 to 18 in. on centers. The coils are generally installed with IK to 4 in. of cover above Fig. 6 .... Warm Air Floor Panel Construction Fig. 6 .... Prefabricated Electric Panel surfaces in room, Fahrenheit. The actual radiation transfer in a room may be somewhat different from that given by Equation 3 because of nonuniform temperatures, irregular room surfaces, variations in