Document ppV622kZ5pmyKjwrKg4zQvgdX

Heating Ventilating Air Conditioning Guide 1938 Cannon showed that excessive loss of heat is associated with increased activity of the adrenal medulla1*. The extra output of adrenin hastens heat production which protects the organism against cooling. Bast13 found a degeneration of thyroid and adrenal glands upon exposure to cold. A moderate amount of variability in temperature is known to be beneficial to health, comfort, and the performance of physical and mental work. On the other hand, extreme changes in temperature, such as those experienced in passing from a warm room to the cold air out-of-doors, appear to be harmful to the tissues of the nose and throat Which are the portals for the entry of respiratory diseases. C. Experiments show that chilling causes a constriction of the blood vessels of the palate, tonsils, throat, and nasal mucosa, which is accom panied by a fall in the temperature of the tissues. On re-warming, the palate and throat do not always regain their normal temperature and blood supply. This ansemic condition favors bacterial activity and it probably plays a part in the disposition of common cold and other respiratory diseases. It is believed that the lowered resistance is due to a diminution in the number and phagocytic activity of the leucocytes (white blood cells) brought about by exposure to cold and by changes in temperature. Sickness records in industries seem to strengthen this belief. The Industrial Fatigue Research Board of England13 found that in workers exposed to high temperatures and to changes in temperature, namely, steel melters, puddlers, and general laborers, there is an excess of all sickness, the excess among the puddlers being due chiefly to respiratory diseases and rheumatism. The causative factor was not the heat itself but the sudden changes in temperature to which the workers were exposed. The tin-plate millmen who were not exposed to chills, since they work almost continuously throughout the shift, had no excess of rheumatism and respiratory diseases. On the other hand, the blast-furnacemen, who work mostly in the open, showed more respiratory sickness than the steel workers. This experience in British factories is well in accord with the findings in American industries15, 16. According to these data the highest pneumonia death rate is associated with dust, extreme heat, exposure to cold, and to sudden changes in temperature. ACCLIMATIZATION Acclimatization, and the factor of psychology are two important in fluences 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*- ``Studies on the Condition of Activity of Endocrine Glands, by W. B. Cannon, A. Guerido, S. W. Britton and E. M. Bright {American Journal of Physiology, Vol. 79, 1926, p. 466). ``Studies in Exhaustion Due to Lack of Sleep, by T. H. Bast, J. S.-Supemaw, B. Lieberman and J. Munro (American Journal of Physiology, Vol.-85, 1928. p. 135). "Fatigue and Efficiency in the Iron and Steel Industry, by H. M. Vernon (Industrial Fatigue Research Board, Report No- 5, 1920, London). "Iron Foundry Workers Show Highest Percentage of Deaths from Pneumonia (Statistical Bulletin, Metropolitan life Insurance Company. 1928). `The Pneumonia Problem in the Steel Industry, by D. K. Brundage and J. J.' Bloomfield, (Journal of Industrial Hygiene, 14, December, 1932). 56 i & Physiological Principles or Air Conditioning 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 the present knowledge of air conditioning these views are not justified. Acclimatization to extreme conditions involves a strain upon the heat regulating system and it 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. The same holds true of northern races with respect to cold, although the effects are mitigated by artificial control. All this seems to indicate that adaptation to an environment averaging between 60 and 80 F is a very primitive trait17; Within these limits, however, there does occur a definite adaptation to external temperature level. People and animals raised under conditions of tropical moist heat have a lower rate of heat production than do those who grow up in cooler environments. This causes them to stand chilling poorly as they are unable to quickly 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 respiratory infections. Likewise, people living in cool climates suffer greatly in the moist heat of the tropics until their adrenal activity has slowed down. Within a couple of years, however, they find themselves standing the heat much better and disliking cold. They become acclimated by a definite change in the combustion level within the body18. In certain individuals the psychologic factor is more powerful than acclimatization. A fresh air fiend may suffer in a room with windows closed regardless of the quality of the air. As a matter of fact, instances are known in which paid subjects refused to stay in a windowless but properly conditioned experimental chamber because the atmosphere felt suffocating to them upon entering the room. EFFECTIVE TEMPERATURE INDEX OF WARMTH 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. 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. On the other hand, in cold environments an increase in humidity produces a cooler sensation. The dividing line at which humidity has no effect upon warmth varies with the air velocity and is about 46 F (drybulb) for still air and about 51, 56 and 59 F for air velocities of 100, 300 and 500 fpm, respectively. 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 con- "Civilization and Climate, by Ellsworth Huntington, Yale University Press, 1924. "Air Conditioning in its Relation to Human Welfare, by C. A. Mills (A.S.H.V.E. Transactions,..Vol. 40, 1934; p. 289). 57