Document 44wvrN8prvmypVjJn6Yopn6q1

HEATINC VENTILATINC AIR CONDITIONING GUIDE 1943 BRITISH EQUIVALENT TEMPERATURE The British Equivalent Temperature (BET) is the mean temperature of the entire environment which is effective in controlling the rate of sensible heat loss from a black body in still air when this body has a surface temperature equal to that of the human body, and a size comparable to Fig. i. Coils in Wall Surfaces Fig. 2. Air Ducts for Floor Heating Flow drop pipe / from above Fig. 3. Continuous Coil in Floor ELEVATION Fig. 4. Coils Embedded in Floors the human body. The BET is, therefore, a function of both the air tem perature and the mean radiant temperature of the surrounding objects. Its numerical value in a uniform environment with the walls and air at the same, temperature is equal to the. temperature of the walls and air. In a non-uniform environment, with the walls and air at different tem perature, the BET for America is at present considered to be equivalent to that of a uniform environment in which a body with an 80 F surface 806 CHAPTER 45. RADIANT HEATING temperature will lose sensible heat at the same rate as in the given nonuniform environment. As originally defined in England, the BET was based on an average body surface temperature of 75 F, while 80 F seems to be more nearly conforming with American conditions. The most suitable temperature to assume will, depend in part on the clothes worn by the individual. This explains why ladies in evening dress require a higher BET for comfort, than a man having only hands and head uncovered. The higher the BET, the less the heat loss from the body, as the rate of heat loss in still air is approximately proportional to the difference between the BET and the mean body surface temperature. If- the BET were 80 F, there could be no sensible heat loss from a surface at that temperature; so the temperature of a normal body surface would have to rise to a point where the heat generated in the tissues could be dissipated. Broadly speaking, it may be stated that with a BET of about 65 to 70 F, the sensible heat losses from the assumed average individual will approximate those previously stated. APPLICATION METHODS The several methods of applying radiant heating to a structure are: 1. By warming the interior wall and ceiling surface of the building. Pipe coils are embedded 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 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 embedded. 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 lb per square inch. 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 large 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. 3. By placing hot water or steam pipes 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 quanti ties 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 surface. In some cases where pipe coils are installed in the air space 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 tem perature than when pipes are actually embedded in the floor. Pipes may be 1or 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 exceptionally 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 attaching 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 807