Document rBbKJEw03JeXdK8DMnKZy06bG

148 CHAPTER 10 1962 Guide And Data Book SCRATCH COAT EMBEDDING PIPES PLASTER CEILING BELOW JOISTS Fig. 2 .... Coils in Plaster Above Loth are installed below the lath. Generally, the surface tempera, ture of plaster panels should pot exceed 120 F, and this is usually met by limiting the water temperature in the pipes or tubes in contact with the plaster to a matimnTn 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 th* heated room. Iu order to protect the plaster installation and to assure proper air drying of the plaster, it is recommended that no 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 of 90 F). Water should be circulated at this temperature for about two days. Then the water temperature should be increased at a rate of approximately 5 deg increase per day to 140 F. 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. After paint and paper have been applied, a further shorter wprm-up period, similar to that for the first tim< starting, is also recommended. Embedded Piping for Walls Although not so universally used as wiling panels, wall panels may be constructed by any of the methods outlined for ceilings. 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. 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 1H to 4 in. of cover above Fig. 4 .... Coils in Root Slab on Grade 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 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. b. Where the eoils are embedded in structural load support ing slabs above grade, construction codes may affect their position. Otherwise, the coil piping is installed in the TM manner as described for slabs rating on grade. c. A warm-up and start-up period for concrete panels should be similar to that outlined ior plaster panels. Rg. 6.... Warm Air Floor Panel Construction panel Heating Air-Heated Ceilings, Walls, and Floors Several methods have been devised to warm the interior loom surfaces by circulating heated air through passages behind surfaces. In some cases, the heated air is re- .jreulated in a closed system. In others, all or a part of the r.oeeed through the room on its way back to the furnace to provide supplementary heating and ventilation.* Figs. 5 ^ 6 indicate two common types of construction. Care Qiust be to assure compliance with any building cod that might apply. (See also section on Warm Air ^riling Panel Systems in Chapter 5.) Electrically Heated Ceilings, Walls, or Roots 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 yy.nnor 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 mf^Tia.la for application to, or Incorporation into, finished mom surfaces. Figs. 7 and 8 indicate two methods of in stallation. The constructions of electric panels for ceilings, walls, and floors are described in greater detail in Chapter 11, Electric Heating. 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. Radiation Transfer The radiation transfer can be evaluated by means of the Stefan and Boltzmann equation: -[(ay-()] o> where ?r " beat transfer by radiation, Btu per (hour) (square foot). T, -- temperature of panel heated surface, Fahrenheit, absolute. Rg. 7.... Electric Heating Cables in Plaster 149 Rg. 9.... Heat Output by Radiation Tr = mean radiant temperature of all unbeated surfaces, - Fahrenheit, absolute. Ft = the configuration factor (dimensiooless). Ft *= 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 other surfaces are at another tem perature, and all surfaces are perfectly diffusing is given by Hottel* as: i-G-'KG-OFt " P*F, (2) uAere Ft = combined configuration and emissivity factor. Fj_* view factor = 1.0. and e -- emissirities of the surfaces. At and At = areas of the surfaces. ^ In practice the emissivity of conventional, non-metallie, 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, (he constant becomes about 0.15 and the equation can be rewritten: OfTAIL A Rg. 8 .... Prefabricated Electric Panel where I, = temperature of panel surface, Fahrenheit.__ AUST area-weighted average temperature of iinhe&ted 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