Document BRZxOLNZr3NEKDYBE6XMq66N8

554 CHAPTER 31 '1946 Guide FUNDAMENTAL COMPUTATIONS The mean surface temperature of an inert body, which will cause given rates of heat loss by radiation and by convection in a uniform environ ment, having a given air temperature and a given mean wall temperature, may be calculated from fundamental equations1 for radiation and natural convection, with substitution of comparable cylinders for the irregular human body. * " 0 1730 where (I1T\)0.2 x(/t1J\0.181 x. (/rs - .ra\) 1.286 qr = heat loss by radiation, Btu per (square foot) (hour.) qc = heat loss by convectioir, Btu per (square foot) (hour.) T6 = absblute temperature of the body surface, Fahrenheit degrees. Tw .= absolute temperature of the walls, Fahrenheit degrees. ra = .absolute temperature of the air, Fahrenheit degrees. . ~ _ Ts + ra (1) (2) D = diameter of cylinder, inched. e = the ratio of actual emission to black body emission. If it is assumed that an average adult has a height of 5 ft 8 in., a body surface of 19.5 sq ft for convection, and 15.5 sq ft for radiation, an-equivaleiit effect can be worked out for two cylinders, 5 ft 8 in. high by 13.15 in. diameter and 10.45 in: diameter, respectively. However, while the effects on a cylinder, of a particular size and shape may be used to estimate average similar effects on the human body, it should be remembered that the heat loss from the body varies greatly. Every movement alters not only its shape, but also the heat generated by the body, the velocity of the air passing over it and the surface exposed to radiation. This fact renders the results of any such computation only approximate. APPLICATION METHODS The several methods of applying panel and radiant heating to a structure are: 1. By warming the interior wall and ceiling surface of the building. Pipe coils are -' imbedded in the concrete or plaster of the walls or ceilings,^the heating medium being hot water circulating through the pipe coils. These coils are generally constructed of small pipe M or % in. I.D. and spaced about 6 to 9 in. apart.. See Fig. 1. This has the effect of warming the entire concrete or plaster surface in which the pipes are imbedded. Since the temperature of the heating medium should never exceed about 130 F, due to the possibility of cracking the plaster the area of the warmed surface must be sufficient to supply the requisite quantity of heat at this low temperature. When carefully designed, this method produces very comfortable results and great operating economy, but offers some slight obstacles when alterations or additions to the building are desirable.. Normally the hot water circulation is maintained by means of a circulating pump and facilities have to be provided to eliminate all air at the top of the system. All coils and circulating pipes are welded together and tested after erection to a hydraulic pressure of 300 psi. . 2. By circulating warm air through shallow ducts under the floor.. In this design the entire floor surface of a room is heated as in Fig. 2. This method was used 2000 years ago in many parts of the Roman Empire. While this method is more expensive in con struction, it is effective and quite suitable for cathedrals and iarge public buildings. To provide a uniform floor temperature, one should give special consideration to the design of the air ducts so that equal heat distribution is obtained. ^r-f-: Panel Heating and Radiant Heating . . ______ ' 555 3. By placing hot water pipes in or under the floor. With this arrangement the whole floor surface of a room is raised to a temperature sufficient'to give comfortable conditions. * Floor heating is recommended for schools and hospitals where large quantities of outside air are desirable. The floor surface may be.of concrete, wood blocks, marble or any other . material unaffected by heat, and while it is true that heat will be conducted through all. materials used in floor construction, it is important that due consideration'be given to the emissivity of the floor. In some cases where pipe coils are installed in the air space - Fig. 1. Coils in Wall Surfaces Fig. 2. Air Ducts for Floor Heating under the floor, special floors are constructed in sections so that the whole floor can be lifted to examine the coils. See Fig. 3. Pipes supported thus may be larger and the heating medium maintained at a higher temperature than when pipes are actually imbedded in the floor. Pipes may be or 2 in. in the former, but for the latter ^ or 1 in. pipes are recommended. See Fig. 4. Where the heat losses from a. room are ex ceptionally high it may be necessary to supplement the warm floor by either adding some coils in the ceiling or forming heated panels in the side walls. 4. By attacking separate heated metal plates or panels to the interior surfaces.- These plates or panels are placed either in an insulated recess so that the surface of the panel is flush with the surface of the walls or ceilings, or they may be secured to the face of the wall. They may be covered with wood veneers and decorated to harmonize with other