Document 5k7LL2k1Bdv1yN8yL0QG57ozV

HEATING VENTILATINC AIR CONDITIONING CUIDE 1942 in summer, but on a wall facing west-north-west it is six times as great in summer as in winter44. 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 aggregated, a new problem comes in, the removal of the excess heat produced by the human body itself. If the temperature of such a space be correctly adjusted when the occupants enter, it will steadily rise during the period of occupancy as a result of the heat produced by the occupants in the process of metabolism. Of the 400 Btu given off in metabolism 100 would perhaps be lost in evaporation, leaving 300 Btu per person per hour to warm the air. In a room contain ing many persons, the effects of this body heat can be neutralized by 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 interior audi torium) this will require 28 cfm of air per person when admitted at 60 F, and an average temperature of 70 F for air leaving the room. Under practical conditions, with one or more cold walls, and a room containing a moderate number of occupants and ample cubic-space, window venti lation 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. SUMMER COMFORT The problem of keeping cool in summer is physiologically as important as keeping warm in winter. In summer the relative humidity of the atmosphere is of great importance, along with air temperature, air move ment, and wall temperature. There is no very practical method of cooling walls, but summer comfort can be promoted by modifying either one of the other three factors involved. Increase of comfort by air movement may be had by the promotion of natural circulation by crpss on through ventilation; and here the architect is responsible for: providing fenestration which will make such natural 4Solar> Radiaiioh as Related to Winter Heating in Residences, by H. N. Wright (Report of John B Pierce Foundation, January 20. 1936). 62 I CHAPTER 2. PHYSIOLOGICAL PRINCIPLES ventilation possible. In the lowest cost housing this should be con sidered as essential. The direct control of air temperature and humidity is, of course, the ideal solution where the cost of a complete air conditioning equipment can be met. Where this objective is attained, there are two schools of thought concerning the relation between temperature and humidity to be maintained. For a given effective temperature some engineers favor comparatively low temperature with a high humidity as this results in a reduction of refrigeration requirements. Preliminary experiments at the A.S.H.V.E. Laboratory45 would seem to indicate no appreciable impair ment of comfort with relative humidities as high as 80 per cent, provided the effective temperature is between 70 and 72 or 73 deg. The second school favors a higher dry-bulb temperature, according to the prevailing outdoor dry-bulb, with a comparatively low humidity (well below 50 per cent), the main purpose being an assumed reduction in temperature contrasts upon entering and leaving the cooled space and to keep the clothing and skin dry. This second scheme requires more refrigeration with the present conventional type of apparatus. INFLUENCE OF HUMIDITY The limitation of the comfort zones in Fig. 6 with respect to humidity are not final but must be adhered to closely. Relative humidities below 30 per cent may prove satisfactory from the standpoint of comfort. In mild weather comparatively high relative humidities seem to be entirely feasible, but in cold weather they are objectionable on account of con densation and frosting on the windows. Information on this subject is given in Chapter 4. As to the effects of dryness of the air, per se, and irrespective of thermal effects, there is a common belief that dry air in itself exerts a harmful effect upon the skin and mucous membranes; but there is no convincing evidence that the increase of atmospheric moisture which can practically be introduced by humidification into the air of cool occupied rooms has any effect upon health and comfort. All controlled experiments on this point have yielded negative results; and the respiratory membranes of industrial workers exposed to hot moist air are distinctly abnormal compared with those of workers exposed to hot dry air46. For the premature infant, a high relative humidity of about 65 per cent is demonstrably beneficial tb health and growth47 until the infants reach a weight of about 5 lb. No such clear-cut evidence exists in the case of adults. 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 sensa- A.S.H.V.E. Research Report No. 1035--Comfort Standards for Summer Air Conditioning, by F. C. Houghten and Carl Gutberlet (A.S.H.V.E. Transactions, Vol. 42, 1936, p. 215). A.S.H.V.E. Research Report No. 105&--Cooling Requirements for Summer Air Conditioning, by F. C. Houghten, F. E. Giesecke C. Tasker and Carl Gutberlet (A.S.H.V.E. Transactions. Vol. 43, 1937, p. 145). Loc. Cit. Note 37, nLoc. Cit. Note 40. 63