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HEATINC VENTILATINC AIR CONDITIONING CUIDE 1944 ditions in Fig. 6 and determined prior to 1932, has more recently been checked; first, by occasional observations, and second, by consistent laboratory study*3, indicating that a higher optimum of 67 deg ET was preferred by a majority of the eight male college students whose opinions were ascertained. This can be checked with larger groups when con ditions permit. On the basis of present knowledge, for different geographical regions and age groups, the total spread in optimum comfort conditions ranges from a low of 66 deg ET for winter heating and air conditioning, to a high of 73 deg ET for summer cooling and air conditioning. The spread for summer cooling and air conditioning for optimum com fort is confined entirely to an effective temperature range of from 69 to 73 deg,' and it may be presumed that for winter conditioning a like spread would be had; while for inter-seasonal conditions there will be a fluctua tion between these two ranges. Recent studies34 indicate that for the average individual a temperature change of about 3 deg ET is required to change a person's sensation from ideally comfortable to cool or warm. From this it may be observed that necessary variations in the effective temperature of air conditioned space for optimum comfort for most persons, need little differentiation for either the winter season or the summer season, and not more than about 4 deg on the average between seasons. Acclimatization and habits of clothing and diet account for these varia tions. As a result of a recent analysis36 of all of the evidence available by the A.S.H.V.E. Technical Advisory Committee on Sensations of Comfort, a variation of 3 deg spread in optimum effective temperature'for summer cooling and air conditioning with geographical location has been proposed. However, it should be recognized that variations in sensation of comfort among individuals may be greater for any given location, as shown in. Fig.. 7, than for variations due to a difference in geographical location. The available information indicates rather clearjy that changes in weather conditions over a period of a few days do not acclimate people to a desire for different indoor conditions, but in general, people experiencing low temperatures over an extended period of time become acclimated to desiring lower indoor temperatures, while those experiencing higher temperatures become acclimated to a desire for higher indoor tempera tures. It is obvious that-a person spending a considerable portion of his time in space conditioned to his comfort will become acclimated to his indoor environment. While few people spend more than a small per centage of the total time within an air conditioned enclosure, there is some evidence that persons experiencing comfort air conditioning a large part of the time tend to become acclimated to about 70 or 71 deg ET. The entering shock to occupants of summer cooled and air conditioned space may at times be important, and is due to the rapid evaporation of "A.S.H.V.E. Research Report No. 1172--Radiation as a Factor in the Sensation of Warmth, by F.C. Houghten, S. B. Gunst and J. Sudu, Jr. (A.S.H.V.E. Transactions, Vol. 47.1941. p. 93). **Loc. Cit. Note 33. "A.S.H.V.E. Research Paper--Comfort with Summer Air Conditioning, by Thomas Chester. N. D. Adams, C. R. Bellamy, G. D. Fife. E. P. Heckel. Dr. W. J. McConnell, F. C. McIntosh. A. B. Newton. B. F. Raberand C. Tasker. Transactions, Vol. 48. 1942, p. 107). 62 CHAPTER 2. PHYSIOLOGICAL PRINCIPLES perspiration on the skin, accumulated during the incoming occupant's previous subjection to hot and humid outside conditions. While recent studies36 show that for healthy individuals this shock is usually a pleasant experience, for others it may result in unpleasant or even harmful chills. This fact should be taken into consideration in applying summer cooling and air conditioning, particularly to spaces where a large number of the occupants may enter for only a short time, 15 min or less. Such occupants may be satisfied with less cooling. For long occupancy very little devia tion from the optimum effective temperature }s desirable. Radiation between the occupant of an enclosure and the surfaces of the room itself and objects within the room, including windows, heating and Wall and Air Temperature cooling equipment, and other occupants, has an important bearing on the feeling of warmth and may alter to some measurable degree the optimum conditions for comfort indicated previously. Fig. 1037 shows the necessary elevation in the dry-bulb temperature of the air to compensate for the lower temperature of three of four side-wall surfaces, which indicates that for this condition each degree reduction in the average of the three wall surface temperatures there must be an elevation of 0.3 deg in the dry-bulb temperature of the air to compensate. Recent studies by the A.S.H.V.E. Research Laboratory38 on the effect of radiation within an enclosure, including the effect of panel heating, indicate that for each degree eleva- "A.S.H.V.E. Research Report No. 1102--Shock Experiences of 275 Workers After Entering and Leaving Cooled and Air Conditioned Offices, by A. B. Newton, F. C. Houghten. Carl Gutberlet, R. W. Qualley and M. C. W. Tomlinson (A.S.H.V.E. Transactions, Vol. 44, 1938, p. 571). "A S H.V.E. Research Report No. 946--Cold Walls and Their Relation to Feeling of Warmth, by F. C. Houghten and Paul McDermott (A.S.H.V.E. Transactions, VoL 39, 1933, p. 83). Loc. Cit. Note 33. 63