Document LpDdbgjREXpyjjkrqO6Odwam5

American Society of Heating and Ventilating Engineers Guide, 1925-26 The percentage of air recirculated may be varied to suit the seasonal changes so as to conserve heat in winter and refrigeration in summer. The schools where the requirements are not so severe and it is not neces sary to provide for summer conditions as much as 90 per cent of the air can be successfully recirculated. The use of ozonation for eliminating odors and for otherwise refreshing the air is advisable wherever recircula tion is regularly and intensively employed. Present methods of measuring and comparing qualities of ventilation not taking into account any of the functions of the relative humidity of the air except that.bearing upon effective temperature. This means that air of any temperature and relative humidity, within proper physical range, i.e., below 64 deg. wet bulb, may be made to meet the comfort line by either heating or cooling without addition or deduction of moisture. Absolutely dry air may be heated or cooled to 78 deg. and be 100 per cent perfect as far as effective temperature is concerned and still be far from desirable in its effects on .the membranes of nose, throat and lungs. Such dry air is also very cqnducive to the increase of dustiness in the atmosphere of a room from the standpoints of dryness and electrostatic agitation. The air washer and humidifier correct these difficulties and there should be some definition of limits for the relative humidity in the measure of ventilation. It is not unusual to find from 1 to 2 million particles of dust per cu. ft. in the outside air surrounding city buildings and unless this is eliminated it will give dust counts in rooms equivalent to a deduction of from 5 to 20 per cent in the perfection of ventilation. A good air washer should eliminate 80 to 90 per cent of the dust entering the intake and perhaps reduce the dust penalty in the rooms to less than one-half of the figure given. It will be seen, therefore, that air washing and humidification may improve the quality of ventilation about 10 per cent in the effective temperature department, plus another 10 per cent in the dust department, plus other improvements in the quality of ventilation by maintaining proper humidity and removing other injurious substances and. odors. Where effective temperature is controlled, according to the usual method, from the dry bulb temperature in the room there may be a wide variation in this effective temperature due to the varying amounts of moisture in the air, unless humidifying apparatus with accurate humidity control is employed. Between the condition of absolute dry air at 70 per cent and absolutely saturated air at 70 deg. there is a difference of 10 deg. in effective temperature which means an average difference of 25 per, cent in fhe quality of ventilation. This may be taken to mean about 10 per cent on each side of the neutral point for ordinary Ventilating conditions so that the air washer and humidity should improve the ordinary ventilating plant another 10 per cent on this count. Good dry air filters will of course serve the same purpose for cleaning the air of suspended matter, and may improve the ventilation about 10 per cent. 198 / ie American Society of Heating and Ventilating Engineers Guide, 1925-26 SPECIAL CONDITIONS In connection with the ventilation of schools the condition in the class rooms for average winter weather is that the body heat given up to the room from the occupants is less than the heat loss from the building to the outside air so that the incoming air may be maintained at a higher temperature than that of the air surrounding the occupants. This means that the effective temperature may be controlled within 1 deg. above or below the comfort line. Assuming that 95 per cent'ventilation is required for class-rooms, that the distribution is 85 per cent and there is no deduction for dust, bacteria or odors, could have a deduction of 85 per cent of 2.5 per cent which is equivalent to about 2 per cent for CO*. This would mean 15 cu. ft. of air per pupil per minute. The usual requirements of state laws is 30 cu. ft. per pupil which would mean a deduction of 1 per cent for CO* leaving a 4 per cent deduction for effective temperature, dust, bacteria and odors. Allowing a deduction of 2J^ per cent for effective temperature there would be a possible deduction of 1J4 per cent for these other items. It will depend therefore upon the quality that can be maintained for these other item's as to the actual quantity of air required between 15 and 30 cu. ft. per minute per pupil. Where intensive recirculation is employed the extent of the recircula tion will depend on the quantity of CO*, odors and other objectionable factors which can be removed from the.recirculated air and also upon the ability to keep the relative humidity from rising to an undesirable point on account of the vapor given up to the air by occupants of the building. The ventilation of school auditoriums where the occupancy of the rooms is of a relatively short duration of from 1 to 2 hours the initial air in the rooms may be relied upon to reduce the intensity of ventilation re quired so that from 15 to 20 cu. ft. of air per person per minute is usually sufficient. In the ventilation of hospitals the wards may be treated much the same as the class-rooms of a school with the exception that it is inadvisable to use recirculation on account of the danger of contagion. School toilets should be separately ventilated with an air change of from 2 to 5 min. employing mechanical supply and exhaust with the exhaust in excess of the supply in order to prevent objectionable odors from diffusing into other parts of the building. Kitchen and lunch rooms should be ventilated with about a 5 min. air change for lunch rooms and a 1 to 3 min. air change for kitchens with at least a part of the exhaust taken from the lunch rooms through the kitchen so as to keep all of the air travel towards the kitchen, thus preventing the kitchen odors from diffusing into the lunch rooms. Exhaust from kitchen range hoods should be discharged by a separate exhaust fan through a fireproof metal duct extending above the roof of the building.and provided with automatic fire damper and steam jet fire extinguisher for use in case of emergency as the accumulation of the grease . vapors in this flue frequently cause a fire. 199