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Heating Ventilating Air Conditioning Guide 1938 Table 2. Desirable Inside Conditions in Summer Corresponding to Outside Temperatures3 Occupancy Over Ifi Min Chrrsids Dbt-Bulb FDeo Effective Temperature AmInside Conditions Dry-Bulb Deg F Wet-Bulb Deg F Dew-Point Deg F 100 75 83 66 56 75 82 67 59 75 81 68 61 75 80 70 65 95 74 82 64 53 -74 81 66 57 74 80 67 60 74 79 68 62 74 78 70 66 90 73 81 63 52 73 80 64 54 73 79 66 59 73 78 67 61 85 72 80 61 48 72 79 63 53 72 78 64 56 72 77 66 60 80 71 78 61 49 71 77 63 54 71 76 64 57 . J 71 75 66 61 "Applicable to individuals engaged in sedentary or light muscular activity. Relative Humid ity Per Cent 40 45 51 60 36 44 51 57 68 36 41 50 56 32 41 46 56 36 45 52 .61 but a few minutes in the cooled space, observations36 indicate a schedule about 1 deg dry-bulb or effective temperature higher than that shown in Table 2. Laboratory experiments with exposures of 2 to 10 min indicate temperatures 2 to 10 F higher than those in Table 2 but with much lower ^ relative humidities. It should be kept in mind that southern people, with their more sluggish heat production and lack of adaptability, will demand a comfort zone several degrees higher than that for the more active people of northern climates. Instead of the summer comfort line standing at 71 deg as here given, it was found to be much higher for foreigners in Shanghai where climatic conditions are similar to those of our gulf states. This difference in adaptability of people forms a very real problem for air conditioning engineers. Cooling of theaters, restaurants, and other public buildings in southern climates cannot be based on northern standards without con siderable modification. Optimum Humidity Just what the optimum range of humidity is, is a- matter of conjecture. There seems to exist a general opinion, supported by some experimental and statistical data, that warm, dry air is less pleasant than air of a andVMi&S'l Ctetolier,TI932LratUre ShU`d DePend UPn Type f ""paIICy- b* J-* Walker {Heating 68 - --mi 3 physical & Physiological Principles or Air Conditioning Chapter moderate humidity, and that it dries up the mucous membranes in such a way as to increase susceptibility to colds and other respiratory dis orders ** 38' Owing to the cooling effect of evaporation, higher tem peratures are necessary, and this condition may lead to discomfort and lassitude. Moist air, on the other hand, interferes with the normal evaporation of moisture from the skin, and again may cause a feeling of oppression and lassitude, especially when the temperature is also high. For the premature infant, a high relative humidity of about 65 per cent is demonstrably beneficial to health and growth40 until the infants reach a weight of about 5 lb. No such clear-cut evidence exists in the case of adult persons. In the comfort zone experiments of the A.S.H.V.E. Research Laboratory, the relative humidity was varied between the limits of 30 and 70 per cent approximately, but the most comfortable range has not been determined. In similar experiments at the Harvard - School of Public Health, the majority of the subjects were unable to detect sensations of humidity {i.e., too high, too low, or medium) when the relative humidity was between 30 per cent and 60 per cent with ______ _ ordinary room temperatures. This is in accord with studies by Howell41, --J Miura42 and others. . The limitation of the comfort zones in Fig. 6 with respect to humidity must not be taken too seriously. Relative humidities below 30 per cent may prove satisfactory from the standpoint of comfort, so long as ex tremely low humidities are avoided. From the standpoint of health, however, the consensus seems to favor a relative humidity between 40 and 60 per cent. In mild weather such comparatively high relative humidi ties are entirely feasible, but in cold or sub-freezing weather they are objectionable on account of condensation and frosting on the windows. They may even cause serious damage to certain building materials of the exposed walls by condensation and freezing of the moisture accumulating inside these materials. Unless special precautions are taken to properly insulate the affected surfaces, it will be necessary to reduce the degree of artificial humidification in sub-freezing weather to less than 40 per cent, according to the outdoor temperature. Information on the prevention of condensation on building surfaces is given in Chapter 7. The principles ' underlying humidity requirements and limitations are discussed more fully elsewhere4?. The purpose of artificial humidification may be easily defeated by failure to change the spray water of the humidifier at least daily. Where this condition occurs, the air is characterized by a lack of freshness, and under extreme conditions by a musty, sour odor in the conditioned space. "Reactions of the Nasal Cavity and Post-Nasal Space to Chilling of the Body Surface, by Mudd, Stuart, et al {Journal Experimental Medicine, 1921, Vol. 34, p. 11). "Reactions of the Nasal Cavity and Post-Nasal Space to Chilling of the Body Surfaces, by A. Goldman, et al and Concurrent Study of Bacteriology of Nose and Throat {Journal Infectious Diseases, 1921, Vol. 29, p. 151). "The Etiology of Acute Inflammations of the Nose, Pharynx and Tonsils, by Mudd, Stuart, et al {Am. Otol., Rhinol., and Laryngol., 1921). "Loc. Cit. Note 24. "Humidity and Comfort, by W. H. Howell {The Science Press, April, 1931). "Effect of Variation in Relative Humidity upon Skin'Temperature and Sense of Comfort, by U. Miura (American Journal of Hygiene, Vol. 13, 1931, p. 432). "Humidification for Residences, by A*. P. Kratz, University of Illinois {Engineering Experiment Station Bulletin No. 230, July 28, 1931). 69 . /