Document G5KLnoomkjBdv1arQa5q8ajDN

Heating Ventilating Air Conditioning Guide 1939 AIR QUALITY AND QUANTITY Air Quality In occupied spaces in which the vitiation is entirely of human origin, the chemical composition of the air, the dust, and often the bacteria con tent may be dismissed from consideration so that the problem consists in maintaining a suitable temperature with a moderate humidity, and in keeping the atmosphere free from objectionable odors. Such unpleasant odors, human or otherwise, can be easily detected by persons entering the room from clean, odorless air. In industrial rooms where the primary consideration is the control of air pollution (dusts, fumes, gases, etc.), or contamination not removable at the source of production, the clean air supply must be sufficient to dilute the polluting elements to a concentration below the physiological threshold (see Chapters 4 and 26). Air Quantity The air supply to occupied spaces must always be adequate to satisfy the physiological requirements of the occupants. It must be sufficient to maintain the desired temperature, humidity, and purity with reasonable uniformity and without drafts. In many practical instances there are two air quantities to be considered, (a) outdoor air supply, and (b) total air supply. The difference between the two gives the amount of air to be recirculated. When the only source of contamination is the occupant, the minimum quantity of outdoor air needed appears to be that necessary to remove objectionable body odors, or tobacco smoke. The concentration of body odor in a room, in turn, depends upon a number of factors, including socio-economic status of occupants, outdoor air supply, air space allowed per person, odor adsorbing capacity of air conditioning processes, tem perature, and other factors of secondary importance. With any given group of occupants and type of air conditioner the intensity of body odor perceived upon entering a room from relatively clean air was found to vary inversely with the logarithm of outdoor air supply and the logarithm of the air space allowed per person. The minimum outdoor air supply necessary to remove objectionable body odors under various conditions, as determined experimentally at the Harvard School of Public Health44, is given in Table 3. Outdoor air requirements for the removal of objectionable tobacco smoke odors have yet to be determined. Practical values in the field vary from 5 to 15 cfm per person; this air quantity may and should be a part of that necessary for other requirements, i.e., removal of body odors, heat, moisture, etc. The total, quantity of air to be circulated through an enclosure is governed largely by the needs for controlling temperature and air dis tribution when either heating or cooling is required. The factors which determine total air quantity include the type and nature of the building, locality, climate, height of rooms, floor area, window area, extent of occupancy, and last but not least, the method of distribution. Serious difficulties are often encountered in attempting to cool a room MLoc. Cit. Note 3. Chapter 3. Physical & Physiological Principles op Air Conditioning with a poor distribution system or with an air supply which is too small to result in uniform distribution without drafts. Some systems of distribu tion produce drafts with but a few degrees temperature rise, while other systems operate successfully with a temperature rise as high as 35 F. The total air quantity introduced in any particular case is inversely pro portional to the temperature rise, and depends largely upon the judgment and ingenuity of the engineer in designing the most suitable system for the particular conditions. Table 3. Minimum Outdoor Air Requirements to Remove Objectionable Body Odors (Provisional values subject to revision upon completion of work) Type op Occupants Air Space per Person Cu Ft Outdoor Air Supply CFM per Person Heating season with or without recirculation. Air not conditioned. Sedentary adults of average socio-economic status-- Sedentary adults of average, socio-economic status-- Sedentary adults of average socio-economic status.__ Sedentary adults of average socio-economic status.__ Grade school children of average class.......................... Grade school children of average class............................ Grade school children of average class............................ Grade school children of average class............................ Grade school children of poor class.................................. Grade school children of better class.- .......................... Grade school children of best class_______ ___________ 100 200 300 500 200 100 200 300 500 200 200 100 25 16 12 7 23 29 21 17 11 38 18 22 Heating season. Air humidified by means of centrifugal humidifier. Water atomization rate 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 80 cfm per person. Sedentary Adults.. 200 <4 Impressions upon entering room from relatively clean air at threshold odor intensity. The changes in moisture content resulting from occupation in the atmosphere of a room supplied with various volumes of outside air is hown in Fig. 7. Data are given for an adult, 5 ft 8 in. in height, weighing 150 lb and having a body surface of 19.5 sq ft and for a child, 12 years of age, 4 ft 7 in. in height weighing 76.6 lb and having a body surface area of 12.6 sq ft. Also given in Fig. 7 is the temperature of incoming air necessary to maintain a room temperature of either 70 or 80 F as indicated assuming that there is no heat gain or loss to the room by transmission through the walls, solar radiation or other sources. 69 X