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If the air condition in any habitable room becomes objectionable due to causes other than the occupancy by human beings, and the Building Commissioner finds that the health and comfort of the human occupants is endangered, additional ventilation by natural or mechanical means shall be provided in accordance with Article 5, Exhaust Systems, or as approved by the Building Commissioner.
Natural ventilation shall comply with Chapter 12 of the Chicago Building Code.
(Amend Coun. J. 4-10-19, p. 100029, Art. XII, § 3; Amend Coun. J. 9-14-21, p. 35949, Art. IV, § 2)
The air supply for every ventilation system, either natural or mechanical, shall be taken from out of doors, except in the following situations:
Exceptions:
1. Recirculation. When air is supplied by a mechanical ventilating supply system, a portion of the code required air supply may be recirculated, provided the system is equipped with such devices for control of temperature and dust content in the spaces to be ventilated and that the conditions of the air so supplied, (except as to temperature) are substantially the same as though all of the supply air were taken from out-of-doors. Under such conditions, not less than thirty-three and one-third percent of the Code requirements shall be taken from out-of-doors by the mechanical ventilating supply system; and sixty-six and two-thirds percent of the code requirements may be recirculated air, plus any additional air volume of system design capacity in excess of code requirements.
2. When air is supplied by a mechanical ventilating supply system which is not equipped with devices prescribed in paragraph 1, then only such portions of the air volumes of the system design capacity in cfm that exceed the total code requirements in cfm may be recirculated during the time of room occupancy. The air intake and all equipment and ducts shall be so arranged that all of the code required air supplied by the system can be taken from outside, with provisions made for release or exhaust of such air to the atmosphere.
3. Prohibited exhaust. No air exhausted from bath, toilet, urinal, or similar room, lavatory, locker, coat room, kitchen, boiler room, or rooms of similar use in which such air might be contaminated by smoke, gases, or dust which might be noxious, dangerous, or detrimental to health shall be recirculated at any time; except that air exhausted from locker and coat rooms or kitchens may be recirculated when unoccupied.
For Variable Air Volume (VAV) systems, the amount of air delivered to any given space shall be allowed to be reduced to track the load in the space provided that the minimum amount of air delivered to the space is not less than 1/3 of the code required air supply.
The amount of outside air delivered by a mechanical supply system may be reduced during operation below the quantities listed in Table 18-28-403.3 if the system is capable of measuring and maintaining CO2 levels in occupied spaces no greater than 1,000 ppm. The system capacity shall be greater than or equal to the ordinance requirements.
If a system is equipped with a water economizer in accordance with the Chicago Energy Conservation Code, the amount of outside air delivered by the mechanical air handling system shall be no less than 1/3 of the code-required supply air. The area of the outside air intake shall be sized so that at least 1/3 of the code-required supply air can be taken from outdoors at velocities not in excess of 1,000 feet per minute (304.8 mpm) through the free area. The remaining air may be supplied by a recirculating air system if the system is equipped with devices to control temperature and dust content. The total quantity of air delivered to the space shall be 100 percent of the code-required air.
(Amend Coun. J. 9-14-21, p. 35949, Art. IV, § 3)
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