Document xk8BJOEaYqbkzj6VDpM18ZKg

112 CHAPTER 6 1955 Guide upon a number of factors, including the dietary and hygienic habits of the occupants (frequently 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. The in tensity of odor sensation has been found to vary as the logarithm of the concentration of the odoriferous substance in the air, or inversely with the logarithmic function of the 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 more.4 The total quantity of outside air to be circulated through an enclosure J 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 occu- , pancy, and the operation of the system distributing the air supply. Fre- - quently, 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 f 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 '5 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 \y/i 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), : where the cubic space per person is less and it is usually impossible to admit untempered outside air without creating drafts, mechanical ventila tion is essential. The present data regarding the effect of cubic space on ventilation . requirements are not universally accepted. The Code of Minimum Re quirements for Comfort Air Conditioning1 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 per- sons still believe there is a stimulating quality in outdoor air (particularly country, mountain and seashore air) under ideal weather conditions, which is lacking in artificially conditioned air. It is apparent, however, that modem 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 has some stimulating effect. Various ; experimenters have attempted to duplicate the invigorating qualities of | Physiological Principles 113 Table 1. Minimum Outdoor Air Requirements to Remove Objectionable Body Odors Under Laboratory Conditions* Air Spacb per Person Cu Ft Outdoor Air Supplt CFM per Person Heating season with or without recirculation. Air not conditioned. jSedentary adults of average socio-economic status.... 100 200 300 500 25 16 12. 7 Laborers.......................... .............................. jGrade school children of average socio-economic status 200 100 200 300 500 23 29 21 17 11 Grade school children of lower socio-economic status--. 200 38 Children attending: private grade schools.. ........... 100 22 Healing season. Air humidified by means of centrifugal humidifier. Water atomization rale 8 to 10 gph. Total air circulation 80 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 SO cfm per person. Sedentary Adults... 200 <4 outdoor air by the use of ozone, ionization, or ultra-violet light, but results to date have been inconclusive or negative.5 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.5 PHYSICAL IMPURITIES IN AIR Dust particles of almost any type can produce irritation of the mucous membranes of the nose and throat, if present in high concentrations. Cer tain dusts may be very harmful, but coal dust is tolerated well. The effects of various industrial dusts, pollens, etc., are discussed in Chapter 8. A certain part of the dissemination of disease in confined spaces may be due to pathogenic organisms floating in the air like dust particles. (See Chapter 7). While in some instances it may be possible to reduce the physical im purities of the air by dilution from a non-contaminated source, such a source is rarely available. Frequently, outside air contains a higher con centration of physical impurities than indoor air. Therefore, it is usually esirable to reduce the concentration of physical impurities by air cleanmg methods. (See Chapter 34.) THERMAL INTERCHANGES WITH ENVIRONMENT dy temperature depends upon the balance between heat production uud heat loss. Heat resulting from oxidation in the body (metabolism)