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60 Chapter 2 1945 Guide --Satisfactory comfort.conditionsfor persons at work39 are found to vary depending upon the rate of work and the ambunfof clothing worn. -In-- general, the greater the degree of activity, the lower the effective tem perature necessary for optimum comfort. However, recent work by the A.S.H.V.E. Research Laboratory40 indicates that under certain condi tions moderate activity on the part of a person standing up and moving about may result in a slightly higher optimum effective temperature than for a person seated at rest, because of the larger body surface area exposed to heat elimination and the increase in effective air movement over his body. Where few workers occupy a large space in hot industries, reCfent work by the A.S.H.V.E. Research Laboratory41 shows that they may be made reasonably comfortable by blowing relatively small volumes of slightly cooled air over them or through their clothing. For prematurely born infants, the optimum temperature varies from 100 to 75 F, depending upon the stage of development. The optimum relative humidity for these infants is placed at 65 per cent42. No data are yet available on the optimum air conditions for full term infants and young children up to school age. Satisfactory air conditions for these age groups are assumed to vary from 75 to 68 F with natural indoor humidities. For school children, the studies of the New York State Commission on Ventilation-place the optimum air conditions at 66 to 68 F temperature with a moderate humidity and a moderate but not excessive amount of : air movement43. A great number of persons seem to be fairly content with a higher plane of indoor temperature, particularly when the matter of first cost and operating cost of a cooling plant is given due considera tion. Recent studies by the University of Illinois44 in cooperation with the A.S.H.V.E. Committee on Research indicate that effective tempera tures as high as 74.5 deg are acceptable in the living quarters of a residence, and while this condition is not representative of optimum comfort it provides sufficient relief in hot weather to be acceptable to the majority of users. It should be emphasized, however, that these are borderline cases that may be acceptable largely in the interest of economy. Com prehensive studies by the A.S.H.V.E. Research Laboratory45 in cor operation with office staffs in widely distributed regions, including San Antonio, Minneapolis, Washington, D. C., and New York City (see Fig. 7), show conclusively that lower effective temperatures are required for optimum comfort. PHYSIOLOGICAL OBJECTIVES OF HEATING AND VENTILATION Aside from the removal of toxic fumes and dusts from heating appli ances and industrial processes, the chief task of the heating and venti lating engineer is to keep his clients warm in winter and cool in summer. For the normally vigorous person, normally clothed, and at rest, an air temperature of 65 F should be provided at knee-height, 18 in. in order to "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). "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). 4lLoc. Cit. Note 25. "Application of Air Conditioning to Premature Nurseries in Hospitals, by C. P. Vaglou. Philip Drinker and K. D. Blackfan (A.S.H.V.E. Transactions, Vol. 36. 1930, p. 383). "Ventilation Report of the New York State Commission on Ventilation (E. P. Dutton Co., N. Y., 1923). "A.S.H.V.E. Research Report No. 1012--Study of Summer Cooling in the Research Residence for the Summer of 1934, by A. P. Kratz, S. Konzo, M. K. Fahnestock and E. L. Broderick (A.S.H.V.E. Trans actions, Vol. 41. 1935. p. 207). "Loc. Cit. Note 32. Physiological Principles 61 prevent chilling of the legs and feet. With some heating systems, this will correspqnd to 70 F at a 5 ft height. Air temperature may be increased or decreased in order to" compensate for deviations- oi- mean radianttemperature above or below air temperature. In rooms occupied by persons of sub-normal vitality, knee-height temperatures must be higher than 65 F. Since dwellings are designed for occupancy by old people and children, the heating system should be able to provide a temperature of 70 F at knee-height under ordinary winter conditions. The maintenance of such conditions as these in winter depends on three major factors, the heat produced in the occupied space, the heat absorbed from the sun and the heat loss through the walls, floor and ceiling of the structure to cold air and earth. Taking these up in the order in which they occur, in planning a new structure it is essential to remember the important effect of orientation and fenestration of the building with respect to the absorption of radiant heat from the sun. It has recently been shown that, in the vicinity of New York, effective sun-heat on a wall facing south is almost five times as great in winter as in summer, but on a wall facing west-north-west it is six times as great in summer as in winter46. The orientation of the same one-story house (in a laboratory model) was changed from a position in which its principal rooms faced northwest .to. a position in which these rooms (with re arranged and slightly increased fenestration) faced west of south: This change decreased average summer sun-heat to one-ninth and increased average winter sun-heat to fourfold of its value with the original ori entation. The choice between the various methods of heating depends, of course, on many engineering and other factors. From the standpoint of human health and comfort, however, it is important to minimize floor-ceiling differentials as far as possible to avoid hot heads and cold feet. Further more, when the problem is a heating one, low. air movement is desirable, .since air temperature must be raised to balance the cooling effect of air motion. Where occupants are closely congregated, a new problem comes in, the removal of the excess heat and water vapor produced by the human body. If the temperature of such a space be correctly adjusted when the occu' pants enter, it will rise steadily during the period of occupancy as a result of the heat given off by the occupants. Of the 400 Btu per hour given off 100 would perhaps be lost in evaporation, leaving 300 Btu per person per hour to warm the air. In a room containing many persons, the effects of this body heat can be neutralized by admission of outside air without producing unpleasant and dangerous drafts on those near the windows or other inlets. The supply of air before it reaches the occupant should be so tempered as to avoid drafts but in an amount and at a temperature which will remove the sensible-heat produced by metabolism. With no heat loss through walls (as in an-iriteriormyditoriutn^-thiS ydll .Tfquire 28 cfm of air per person when admitted.a,t 60 F, and an average tempera ture of 70 F for air leaving the room. lender practical conditions, with one or more cold walls, and a room containing-a-moderate number of occupants and ample cubic space, window ventilation with deflectors and a gravity exhaust duct may suffice. With crowded rooms, and with any rooms containing 50 or more occupants, forced ventilation will be essential. "Solar Radiation as Related to Winter t'tcrct Foundation, January 20, 1936). Heating in Residences, by H. N. Wrigbt (Report of John B.