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§27-752 Areas Requiring Mechanical Ventilation
Mechanical ventilation shall be provided in all occupiable rooms or spaces where the requirements for natural ventilation are not met; in all rooms or spaces, which because of the nature of their use or occupancy, involve the presence of dust, fumes, gases, vapors, or other noxious or injurious impurities, or substances which create a fire hazard; or where required by the provisions of article eight of this subchapter or subchapters six through eight of this chapter.
§27-753 Index for Ventilation
The index for ventilation for any room or space shall be computed by adding the following:

(a) The contents per occupant, in cubic feet.

(b) The floor area per occupant, times ten, in square feet.

(c) The clear, unobstructed openable area of windows, skylights, and other sources of natural ventilation per occupant times two hundred, in square feet. In all cases, the number of occupants used in computing the index for ventilation shall be the maximum number who will occupy the room or space simultaneously during any two-hour period.
§27-754 Minimum Quantity of Outside Air for Mechanical Ventilation
The minimum quantity of outside air required for mechanical ventilation in any occupiable room, where not otherwise prescribed, shall be determined according to table 12-2.

TABLE 12-2

Index for
Ventilated Rooms with Natural
Ventilation Openings
Ventilated Rooms without
Natural Ventilation Openings
Air Conditioned Rooms
Supply Exhaust Supply Exhaust Supply Exhaust
0-300 2.5 2.0 2.5 2.0 1.5 1.5
301-520 2.0 1.5 2.0 1.5 1.2 1.2
521-850 1.5 1.25 1.5 1.25 0.9 0.9
851-1250 1.0 1.0 1.0 0.6 0.6
1251-1650 0.67 0.67 0.67 0.5 0.5
Over 1650 0.33 0.33 0.4 0.4

(a) Window requirements. To be credited as ventilating openings under the provisions of this subchapter, windows or other openings shall meet the requirements of section 27-749 of article six of this subchapter, and where mechanical supply ventilation is not provided, shall have a free openable area of at least one square foot per one hundred square feet of floor area.

(b) Air conditioning.

(1) In air conditioned rooms, the windows and other openings shall not be credited as such in computing the index for ventilation. Air conditioned rooms shall be considered as interior rooms.

(2) Air that has been exhausted from an air conditioned space may be reconditioned by air conditioning apparatus and recirculated as equivalent outdoor air, provided that the total of supply air is not less than required for air conditioned rooms by table 12-2 and that the amount of actual outdoor air is at least thirty-three and one-third per cent of the required total. The actual outdoor air supply shall not, under any circumstances, be reduced to less than five cfm per occupant, except that these minimum requirements may be reduced by fifty per cent as provided in section 27-755 of this article.

(c) Required exhaust. Required exhaust may be accomplished by raising the pressure within the space with consequent leakage through doors and windows, or by drawing the vitiated air from air conditioned spaces into the return air duct of air conditioning apparatus or into an exhaust duct discharging directly to the outdoor air.

(d) Make-up air. A sufficient quantity of air to make the exhaust system effective shall be provided to the space being exhausted by one or by any combination of the following methods:

(1) By supplying air to the space by means of a blower system.

(2) By infiltration through louvres, registers, or other permanent openings in walls, doors, or partitions, adjoining spaces where air is supplied by one of these methods.

(3) By infiltration through cracks around window sash and doors.

(4) By other methods acceptable to the commissioner.

(e) Prohibited use of recirculated air. Air drawn from any of the following spaces may not be recirculated; mortuary rooms; bathrooms or toilet rooms; or any space where an objectionable quantity of flammable vapors, dust, odors, or noxious gases is present. Air drawn from rooms that must be isolated to prevent the spread of infection shall not be recirculated, except that air drawn from hospital operating rooms may be recirculated, if in compliance with the following requirements:

(1) There shall be a minimum of twenty-five total air changes per hour, of which five air changes per hour shall be outdoor air.

(2) All fans serving exhaust systems shall be located at the discharge end of the system.

(3) Outdoor air intakes shall be located at least twenty-five feet from exhaust outlets of ventilation systems and other exhaust discharges, combustion equipment stacks, medical surgical vacuum systems, and plumbing vent stacks, from areas which may collect vehicular exhaust such as off-street loading bays, and from areas which may collect other noxious fumes. The bottom of outdoor air intakes serving central systems if installed above a roof, shall be located at least three feet above roof level.

(4) Positive air pressure shall be maintained at all times in relation to adjacent areas.

(5) All ventilation or air conditioning systems serving such rooms shall be equipped with a filter bed of twenty-five per cent efficiency upstream of the air conditioning equipment and a filter bed of ninety per cent efficiency downstream of the supply fan, any recirculating spray water systems and water reservoir type humidifiers. All filter efficiencies shall be average atmospheric dust spot efficiencies tested in accordance with ASHRAE standard 52-68.

(6) A manometer shall be installed across each filter bed.

(7) Duct linings shall not be used in ventilation and air conditioning systems serving such rooms unless terminal filters of at least ninety per cent efficiency are installed downstream of linings.

(8) Air supplied shall be delivered at or near the ceilings and all exhaust air shall be removed near floor level, with at least two exhaust outlets not less than three inches above the floor.

(f) Outdoor air intakes. For high-rise office buildings erected pursuant to new building applications filed on or after the effective date of this section, outdoor air intakes serving spaces above the second story and serving spaces greater than ten thousand square feet of floor area shall be located at least twenty feet above ground level, at least twenty feet from exhaust outlets of ventilation systems and other exhaust discharges, and at least twenty feet from areas that may collect vehicular exhaust such as off-street loading bays.
§27-755 Use of Adsorption Devices
In all cases where the use of recirculated air is permitted, the required outdoor air supply may be reduced up to fifty per cent, provided that the recirculated air is passed through adsorption devices. The adsorption devices shall be approved and rated. Means shall be provided for maintaining the effectiveness of the adsorption devices.

(a) Improper maintenance. Should the adsorption devices be improperly maintained so that their effectiveness is impaired, the commissioner may order their removal. If the adsorption devices are removed, the air conditioning or ventilating system shall not be operated without supplying one hundred per cent of the outdoor air required by this article or article eight of this subchapter.

(b) Test records. The building owner shall, at all times, maintain a maintenance record showing the manufacturer's recommendation of the frequency of tests, the method of making tests, and the results of all tests of the adsorption devices. Such tests shall be made and certified by the manufacturer or by a laboratory acceptable to the commissioner at least twice every six months. The records of such tests shall be maintained for a period of at least two years, and shall be available for inspection by the commissioner.

(c) Ventilation of water closet compartments. The use of any device that returns exhaust air from water closet compartments or from toilet rooms after passing through adsorption devices is not permitted as a means of providing ventilation for a water closet compartment for which a mechanical system of ventilation is required.
§27-756 Installation and Operation of Ventilating and Air Conditioning Systems
Where mechanical ventilation is accepted as an alternate for, or a supplement to, natural means of ventilation, or is required under the conditions herein prescribed, or where ventilation is provided by means of air conditioning system, the system, equipment, and distributing ducts shall be installed in accordance with the applicable provisions of subchapters thirteen through fifteen of this chapter. Such required ventilating and/or air conditioning systems shall be kept in operation at all times when the building or space is being used in a normal manner in accordance with the purpose for which it was intended.

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