Document dYOoy7yDmaZvrnwN7jzqXwqkb

American Society of Heating and Ventilating Engineers Guide, 1935 bution produce drafts with but a few degrees temperature rise, while other systems operate successfully with a temperature rise as high as 35 deg. The total air quantity introduced in any particular case is inversely proportional 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. Small quantities of air reduce the size of equipment, ducts, space, and initial cost, but require lower air temperatures. In any specific case, the cost of refrigeration must be balanced against the extra cost in increased size of equipment and running expense. Outside Air. In order to provide uniform temperature conditions, it is necessary-to maintain a pressure of about O.l in. of water in the room or space to be ventilated or conditioned. This usually requires the intro duction of a certain amount of outside air which depends on the particular conditions involved, and may vary over a considerable range. In rooms in which the only source of contamination is the occupant the minimum quantity of outside or new air to be circulated appears to be that necessary to remove objectionable body odors. The concentration of body odors in turn depends largely upon the temperature of the air; the higher the temperature, the greater the amount of perspiration (sensible or insensible) given off from the skin, and the greater the concentration of odors. NATURAL AND MECHANICAL VENTILATION Under favorable conditions natural ventilation methods properly combined with means for heating may be sufficient to provide for the foregoing standards. As a rule, in instances in which the only source of contamination is the occupant, the requirements may be fulfilled when the following conditions prevail: X. At least 50 sq ft of floor area for each occupant. 2. At least 500 cu ft of air space per occupant. 3. Effective openings in windows and skylights equal to at least 5 per cent of the floor area. Whenever natural means are not sufficient to maintain the standards, resort must be made to whatever modifications or mechanical apparatus are necessary to secure such standards. In large offices, large school rooms, and in public and industrial build ings, natural ventilation is uncertain and makes heating difficult. The chief disadvantage of natural methods is the lade of control: they depend largely on weather and upon the velodty and direction of the wind. Rooms on the windward side of a building may be difficult to heat and ventilate on account of drafts, while rooms on the leeward side may not receive an adequate amount of air from out of doors. The partial vacuum produced on the leeward side under the action of the wind: may even reverse the flow of air so that the leeward half of the building has to take the drift of the air from the rooms of the windward half. Under such conditions no outdoor air would enter through a leeward window opening, but room air would pass out. In warm weather natural methods of ventilation afford little or no 54 Chapter 2--Ventilation and Air Conditioning Standards --V,f indoor temperature and humidity. Outdoor smoke, dust and RECIRCULATION The saving in operating costs due to recirculation of the air, while very considerable, must not be obtained at the expense of air quality. The percentage of recirculated air may be varied to suit the seasonal changes so as to conserve heat in winter and refrigeration in summer, but at no time during occupancy should there be taken from out of doors less than 10 cfm for each occupant. As a general rule, recirculation impairs the ' '' ' u'r humidity (if not conditioned), excessive the influence of this factor on comfort and health is at present a matter of speculation. Toilets, kitchens, and similar rooms, in buildings using recirculation, should be separately mechanically ventilated by exhausting the air from them in order to prevent objectionable odors from diffusing into other parts of the building. ULTRA-VIOLET RADIATION AND IONIZATION In spite of the rapid advances made in the field of air conditioning during the past few years, the secret of reproducing, in indoor spaces, atmospheres of as stimulating qualities as those existing outdoors in the country, under ideal weather conditions, has not as yet been found. In fact, extensive studies have failed to elucidate the cause of the stimulating quality of outdoor country air, qualities which are lost when such air is brought indoors and particularly when it is handled by mechanical