Document 2jpZdXOY6ML4D1m6VMOY8OMEb

HEATING VENTILATING AIR CONDITIONING CUIDE 1941 are sufficiently accurate for most practical applications. Where greater precision in the applications of the results is required, or for extreme variations in temperature and humidity, the reports22 covering the A.S.H.V.E. Laboratory work may be consulted. The curves in Figs. 3, 4 and 5, and proper interpolation between these curves make it possible to apply the data to persons engaged in any type of work or physical activity, providing the resulting metabolic rate is known. As an example, if it is found that a certain type of work results in a metabolic rate of approximately 760 Btu per hour for an average person working in an atmosphere of 70 ET, then his total rate of heat dissipation to atmospheres of various temperature will be approximately as given by the broken-line curve in Fig. 3. The broken line curves in Figs. 4 and 5 give the rate of sensible and latent heat dissipation of the person for different dry-bulb temperatures. ACCLIMATIZATION Acclimatization and the factor of psychology are two important influences in air conditioning which cannot be ignored. The first is man's ability to adapt himself to changes in air conditions; the second is an intangible matter of habit and suggestion. Some persons regard the unnecessary endurance of cold as a virtue. They believe that the human organism can adapt itself to a wide range of air conditions with no apparent discomfort or injury to health. In the light of present knowledge of air conditioning these views are not justified. Acclimatization to extreme conditions involves a strain upon the heat regulating system and interferes with the normal physiologic functions of the human body. Thousands of years in the heat of Africa do not seem to have acclimatized the Negro to a temperature averaging 80 F. Thesame holds true of northern races with respect to cold, although the effects are mitigated by artificial control. An environment averaging 64 F for the 24-hour period is associated with minimal mortality23. Within limits, however, there does occur a definite adaptation to ex ternal temperature level. People and animals raised under.conditions of tropical moist heat stand chilling poorly as they are unable quickly to increase internal combustion to keep up the body temperature. For this reason they have trouble standing the cold, stormy weather of the temperate zones, and when exposed to it are very susceptible to respira tory infections. Likewise, people living in cool climates suffer greatly in the moist heat of the tropics until their adaptive mechanism has been trained. Within a couple of years, however, they find themselves standing the heat much better and disliking the cold. MA.S.H.V.E. Research Report No. 830--Heat and Moisture Losses from the Human Body and Their Relation to Air Conditioning Problems, by F. C. Houghten, W. W. Teague^ W. E. Miller and W. P. Yant {A.S.H.V.E. Transactions. Vol. 35. 1929, p. 245). Thermal Exchanges Between the'Human Body and Its Atmospheric Environment, by F. C. Houghten, W. W. Teague. W. E. Miller and- W. P. Yant (American Journal of Physiology, Vol. 88. 1929. p. 386). A.S.H.V.E. Research Report No. 908--Heat and Moisture Losses from Men at Work and Application to Air'Conditioning-. Problems, by* F. C. Houghten. W. W. Teague. W. E. Miller and W. P. Yant (A.S.H.V.E. Transactions. Vol. 37, 1931. p. 541). Thermal Ex changes Between the Bodies of Men Working and the Atmospheric Environment, by F. C. Houghten. W. W. Teague. W. E. Miller and W. P. Yant {American Journal of Hygiene, Vol; XIII, 1931, No. 2. p. 413). A.S.H.V.E. Research Report No. 1106--Air Conditioning in Industry, by W. L. Fleisher, A. E. Stacey. Jr., F. C. Houghten. and M. B. Ferderber (A.S.H.V.E. Transactions, Vol. 45, 1939. p. 59). ^Civilization and Climate, by Ellsworth Huntington. Yale University Press. 1928. 52 CHAPTER 2. PHYSIOLOGICAL PRINCIPLES The adaptive level changes somewhat with the season24. There are also marked differences between the sexes. In the cold zone the thickness of the thermal insulating tissues of women is almost double that of men, although the sensory responses to cold are similar. In the hot zone, the threshold of sweating and skin temperature levels are both higher for women. Finally, the thickness and insulating value of the clothing worn is an important factor in the determination of the comfort level. EFFECTIVE TEMPERATURE INDEX Sensations of warmth or cold depend, not only on the temperature of the surrounding air as registered by a dry-bulb thermometer, but also upon the temperature indicated by a wet-bulb thermometer, upon air movement and upon radiation effects. Dry air at a relatively high temperature may feel cooler than air of considerably lower temperature with a high moisture content. Air motion makes any moderate condition feel cooler. Radiation from cold or warm surfaces is another important factor under certain conditions. Combinations of temperature, humidity, and air movement which induce the same feeling of warmth are called thermo-equivalent condi tions. A series of tests25-26-27,28 at the A.S.H.V.E. Research Laboratory, Pittsburgh, established the equivalent conditions met with in general air conditioning work. This scale of thermo-equivalent conditions not only indicates the sensation of warmth, but also determines the physiological effects on the body induced by heat or cold. For this reason, it is called the effective temperature scale or index. Effective temperature is an empirically determined index of the degree of warmth perceived on exposure to different combinations of tempera ture, humidity, and air movement. It was determined by trained subjects who compared the relative warmth of various air Conditions in two ad joining conditioned rooms by passing back and forth from one room to the other. The numerical value of the effective temperature index for any given air conditions is fixed by the temperature of calm (15 to 25 fpm air movement) saturated air which induces a like sensation of warmth or cold. Thus, any air condition has an effective temperature of 60 deg, for instance, when it induces a sensation of warmth like that experienced in calm air at 60 deg saturated with moisture. The effective temperature index cannot be measured directly but is computed from the dry- and wet-bulb temperature for a given air velocity or using charts (see Figs. 6, 7 and 8) or tables. The relation of winter and summer sensations of "The Reactions of the Clothed Human Body to Variations in Atmospheric Humidity, by C.-E. A. Winslow, L. P. Herrington and A. P. Gagge (American Journal of Physiology. Vol. 124. December. 1938, p. 692). "A.S.H.V.E. Research Report No. 673--Determination of the Comfort Zone, by F. C. Houghten and C. P. Yagloglou (A.S.H.V.E. Transactions, Vol. 29. 1923, p. 361). "A.S.H.V.E. Research Report No. 691--Cooling Effect on Human Beings by Various Air Velocities, by F. C. Houghten and C. P. Yaglou (A.S.H.V.E. Transactions. Vol. 30. 1924, p. 193). "A.S.H.V.E. Research Report No. 717--Effective Temperature with Clothing, by C. P. Yaglou and W. E. Miller (A.S.H.V.E. Transactions. Vol. 31, 1925. p. 89). "A.S.H.V.E. Research Report No. 755--Effective Temperature for Persons Lightly Clothed and Working in Still Air, by F. C. Houghten. W. W. Teague, and W. E. Miller (A.S.H.V.E. Transactions. Vol. 32. 1926, p. 315). 53