Document jZVOmDZaa86kB4NnbDrwG7nZ

218 KENNETH E. ROBINSON that give the same sensation of warmth as, say, 75 saturated still air, hav^g effective temperature of 75 F. Such combinations are easily read from the cba- The effective temperature scales were derived by a "cut and try" procelr wherein test subjects moved from a control room into an adjacent test chara' and immediately recorded their thermal sensations. By repeated trials combi tions of temperature, humidity, and air motion that, subjectively, felt like-cp ditions in the control chamber were identified. Despite its limited basis, laboratory and field experience with the ET scale has indicated thatStei useful in defining the thermal comfort zone, and also that it -correlates objective measurements of physiological response to heat. In practice, the* scale overemphasizes somewhat the influence of humidity in the comfort and tends to underestimate its effect in hot environments. It is, nonetheless valuable .scale, which combines most successfully the several thermal facto^ the environment into a single index value. The comfort zone outlined in Figul may be used as the basis for specifying air-conditioning requirements for offi light industry shops, and so forth. (For a discussion of the heat problem in| hot industries see Chapter XXI.) It is of interest to note the close agree' between the comfortable environmental temperature and the external condi under which thermal neutrality is maintained, as suggested in Figure 1. II. Environmental Control Thermal comfort in the environment is' the primary purpose of air condif ingrlt-has'been-shown-that'-low-temperatures-Teduce-manual'dexterity'andh: accident frequency;4 however, comfort, not accident prevention, has beens motivating force behind most heating installations (cf. also page 110). Most industrial cooling installations have been decided upon because-^,, expected monetary return on the investment. Many articles have appeal the literature pertaining to the savings that have been made by the install of summer air conditioning and it is rapidly gaining acceptance.5 Inasmuch as man generates heat and is comfortable at room tempera below body temperature, it should be remembered that the problem, is aljjjone of controlling the heat loss from the body, not of heating the man. To m; tain an environment that will regulate the loss of heat from the body, it mai necessary-to-supply~heat-or-humidity7'-to--cool-:or-dehUmidify,7-drt;o~TOf velocitySof .thhi'-air movement in the area. Many installations will reqqfl consideration of more than one of these to arrive at'a satisfactory condition A. ADDING HEAT TO A SPACE The heat loss from a building is usually calculated in order to -determin' amount of heat that must be added to maintain suitable inside temperp `E. E. Osborne and H. M. Vernon, Ind. Fatigue Research Bd. (London), Kept. N( H. M. Stationery Office, 1922. Is air conditioning worth the investment? Heating, Piping Air Conditioning, 26 (August, 1964). 4 f-r\ . V AIR CONDITIONING 219 % AJ )| Stheir complexity these calculations will not be discussed here; they ihj^jn.',-the chapter on heating loads in the Heating, Ventilating, Air, *`Ti$($tiide published annually by the American Society of Heating and ^iffqnmg Engineers. nayfb.e supplied to a space in two ways: by radiation or by convection. 1. Radiation radiation is the transmission of energy by means of electro- |||||! of very long wave length. Radiant energy of any wave length bed, become thermal energy and result in an increase in the lAbsorbing body (see Chapter XXI). The most common method |a^B^radiation is with the ordinary'radiator or some form of iBlse units may be'heated by steam, hot water, or electricity and v^-ipy of shapes and sizes. The wall radiator is rapidly becoming s a tendency to overheat anyone close to it while not supplying farther away. effy/written. regarding radiant panel heating. The heat source Smstially buried in the floor or Concealed -behind- the plaster of |1|: It was thought that the. use of low temperature radiation Jplgpmfort even though low air temperatures were maintained. ^|cases, this has been just another way of heating the air. In ^pfi|ngan-s, and similar buildings where men workypii, the floor and r*comfcfr1rhasT,estfltd-with''hat^"floor panels. Illpahel. -heating has not-always been satisfactory in factories Jlijfthe controls: has been too great to accommodate the rapid jffigppure caused,by a.large sun load or. the heat; gain resulting ^mmgfprpcesses;'> - ... ^^rof'possible or practical to heat the surrounding air at a reason* ||!|pir|able conditions -have been provided, (by means of . portable receiving dock at a large :*oUA,,3e js a g00cj example. Figure 5 illustrates an installation of S ant heaters used as the only heat source in a partially opened, juuwaing. |||gigheat transfer is the transmission of heat by .either natural or |t||||o||a_ fluid (liquid or gas). In general, any heat* source that air M^^^^necomes'X'cbnvectorrTfiis maybe "a wall'XiTdiat'brj "a unit r co*'s; eit^er mounted so that air moves over it because of ^^^.i|pcreated by the increase in the temperature of--the air, or fitted