Document kD8G8qRQbOL7g7bvLa6X01yLq

198 CHAPTER 12 1948 Guide reflecting their socio-economic status), the outdoor air supply, air space allowed per person,'odor.'adsorbing capacity of air conditioning processes, and temperature and relative humidity. Perception of odor has been found to vary as the logarithmic function of the odor intensity, or in versely with the logarithmic function of fhe amount of outdoor air supplied and the air space per person. The relation between air,supply and occupancy has been reported by the Harvard School of Public Health2 (Table 1) and the A.S.H.V.E. Research Laboratory 3. Outdoor air requirements for removal of objec tionable tobacco smoke odors are. not accurately known but available information and current practice indicate the need of 15. cfm per person or more4. ' The total quantity of outside air to be circulated through an enclosure is often governed chiefly by physical considerations for controlling tem perature, air distribution, and air velocity. Other factors which must be taken into consideration include the type and usage of the building, locality, climate, height of rooms, floor area, window area, extent of occupancy, and the operation of the system distributing the air supply. Frequently, some of these factors, particularly the need for air movement and good distribution, may be satisfied by recirculation of inside air rather than outside air. It will be noted that, with adequate air space, the rate of air change indicated in Table 1 is from 10 to 30 cfm per person. In rooms occupied by only a few persons such an air change will be automatically attained in cold weather by normal leakage around doors and windows,-and can easily be secured in warm weather by the opening of windows; With a space allotment of 400 cu ft per person, only 1% air changes per hour are necessary to provide a ventilation rate of 10 cfm per person. Therefore, in the ordinary dwelling with adequate cubic space allot ment, no special provision for controlling chemical purity of the air is necessary (aside from removal of fumes from heating appliances). For such conditions, the control of air temperature is the major consideration. In more crowded rooms (large offices, large workrooms, auditoriums), the cubic space per person is less and it is usually impossible to admit untempered outside.air without creating drafts. Here, mechanical venti lation is essential for removal of the heat and moisture produced by the occupants. The present data regarding the effect of cubic space on ventilation requirements are not universally accepted. The Code of Minimum Requirements-for Comfort Air Conditioning 1 prescribes definite minimum requirements which should be familiar to the designing engineer. It should be emphasized, however, that the code fixes minimum, rather than adequate requirements. Notwithstanding the rapid advance made in air conditioning some persons still believe there is a stimulating quality in. outdoor air (par ticularly country, mountain and seashore air) under ideal weather con ditions, which is lacking in artificially conditioned air. It is apparent, however, that modern air conditioning insures control of the phenomena of nature for the service and comfort of man independently of weather conditions. Freedom of movement, action and thought, together with the variability of stimuli experienced by persons under ideal conditions in the country, mountains or seashore, undoubtedly have some stimu lating effect. Various experimenters have attempted to duplicate the invigorating qualities of outdoor air by the use of ozone, ionization, or Physiological Principles__________________________________ 199. Table 1. . Minimum Outdoor Air Requirements to Remove Objectionable Body Odors Under Laboratory Conditions * Type op Occupants Am Space per Person Cu Ft Outdoor Am Supply CFM per Person Heating season with or without recirculation: - Air not conditioned. Sedentary adults of average socio-economic status.-- 100 200 300 500 25 16 12 7 Laborers. Grade school children of average socio-economic status \ :_ Grade school children of lower socio-economic status.... Children attending private grade schools.____________ 200 100 200 300 500 200 100 23 29 21 17 11 38 22 Heating season. Air humidified by means Of centrifugal humidifier. Water atomisation rate 8 to 10 gph. Total air circulation SO cfm per person: Sedentary Adults. 200 12 Summer season. . Air cooled and dehumidified by means of a spray dehumidifier. Spray water changed daily. Total air circulation 80 cfm per person. _______ Sedentary Adults.-- 200 <4 ultra-violet light, but results to date have been inconclusive or negative 6. Ozone in amounts of .0.01 to 0.05 ppm of air is allowable in comfort air conditioning. Above this limit there is a pungent, unpleasant odor and perhaps respiratory distress, depression, and stupor 6. PHYSICAL IMPURITIES IN AIR Dust particlesof almost any type can produce irritation of the mucous membranes of the nose and throat if present in high concentrations. Certain dusts may be very harmful, but coal dust is tolerated well. The effects of various industrial dusts, pollens, etc. are discussed in Chapter 10. A certain part of the dissemination of disease in confined spaces is caused by the emission of pathogenic organisms from infected persons. (See Chapter 13:) While in some instances it may be possible to reduce the physical impurities pf the air by dilution from a non-contaminated source, such a source is rarely available. Frequently outside air contains a higher concentration of physical impurities than indoor air. Therefore, it is usually desirable to reduce, the concentration of physical impurities by air cleaning methods. (See Chapter 33.) THERMAL INTERCHANGES BETWEEN THE BODY AND ITS ENVIRONMENT Body temperature depends upon-, the balance between heat production and heat loss. Heat resulting from oxidation in the body (metabolism)