Section 120.1 Requirements for Ventilation
Nonresidential, high-rise residential and hotel/motel buildings shall comply with the requirements of Sections 120.1(a) through 120.1(e).
(a) General requirements.
- The outdoor air-ventilation rate and air-distribution assumptions made in the design of the ventilating system shall be clearly identified on the plans required by Section 10-103 of Title 24, Part 1.
(b) Design requirements for minimum quantities of outdoor air. Every space in a building shall be designed to have outdoor air ventilation according to Item 1 or 2 below:
- The means to open required operable openings shall be readily accessible to building occupants whenever the space is occupied.
- The conditioned floor area of the space times the applicable ventilation rate from Table 120.1-A; or
- None of the spaces from which air is transferred have any unusual sources of indoor air contaminants; and
- The outdoor air that is supplied to all spaces combined is sufficient to meet the requirements of Section 120.1(b)2 for each space individually.
(c) Operation and control requirements for minimum quantities of outdoor air.
- Pre-occupancy. The lesser of the minimum rate of outdoor air required by Section 120.1(b)2 or three complete air changes shall be supplied to the entire building during the one-hour period immediately before the building is normally occupied.
- They have an air economizer; and
- They serve a space with a design occupant density, or a maximum occupant load factor for egress purposes in the California Building Code, greater than or equal to 25 people per 1,000 square feet (40 square feet or less per person); and
- Single zone systems with any controls; or
- For each system with demand control ventilation, CO2 sensors shall be installed in each room that meets the criteria of Section 120.1(c)3 with no less than one sensor per 10,000 square feet of floor space. When a zone or a space is served by more than one sensor, a signal from any sensor indicating that CO2 is near or at the setpoint within a space shall trigger an increase in ventilation to the space;
- CO2 sensors shall be located in the room between 3 feet and 6 feet above the floor or at the anticipated height of the occupants heads;
- CO2 concentration shall be assumed to be 400 ppm without any direct measurement; or
- CO2 concentration shall be dynamically measured using a CO2 sensor located within 4 feet of the outdoor air intake.
- When the system is operating during hours of expected occupancy, the controls shall maintain system outdoor air ventilation rates no less than the rate listed in Table 120.1-A times the conditioned floor area for spaces with CO2 sensors, plus the rate required by Section 120.1(b)2 for other spaces served by the system, or the exhaust air rate, whichever is greater.
- CO2 sensors shall be certified by the manufacturer to be accurate within plus or minus 75 ppm at a 600 and 1000 ppm concentration when measured at sea level and 25°C, factory calibrated and certified by the manufacturer to require calibration no more frequently than once every 5 years. Upon detection of sensor failure, the system shall provide a signal which resets to supply the minimum quantity of outside air to levels required by Section 120.1(b)(2) to the zone serviced by the sensor at all times that the zone is occupied.
- The CO2 sensor(s) reading for each zone shall be displayed continuously, and shall be recorded on systems with DDC to the zone level.
- Occupant sensors shall meet the requirements in Section 110.9(b)4 and shall have suitable coverage and placement to detect occupants in the entire space ventilated. Occupant sensors controlling lighting may be used for ventilation as long as the ventilation signal is independent of daylighting, manual lighting overrides or manual control of lighting. When a single zone damper or a single zone system serves multiple rooms, there shall be an occupancy sensor in each room and the zone is not considered vacant until all rooms in the zone are vacant.
- One hour prior to normal scheduled occupancy, the occupancy sensor ventilation control shall allow pre-occupancy purge as described in Section 120.1(c)2.
- Within 30 minutes after being vacant for all rooms served by a zone damper on a multiple zone system, and the space temperature is between the heating and cooling setpoints, then no outside air is required and supply air shall be zero.
- Within 30 minutes after being vacant for all rooms served by a single zone system, the single zone system shall cycle off the supply fan when the space temperature is between the heating and cooling setpoints.
(d) Ducting for zonal heating and cooling units. Where a return plenum is used to distribute outdoor air to a zonal heating or cooling unit, which then supplies the air to a space in order to meet the requirements of Section 120.1(b)2, the outdoor air shall be ducted to discharge either:
- Within 5 feet of the unit; or
- Within 15 feet of the unit, substantially toward the unit, and at a velocity not less than 500 feet per minute.
(e) Design and control requirements for quantities of outdoor air.
- All mechanical ventilation and space-conditioning systems shall be designed with and have installed ductwork, dampers and controls to allow outside air rates to be operated at the larger of (1) the minimum levels specified in Section 120.1(b)1; or (2) the rate required for make-up of exhaust systems that are required for an exempt or covered process, for control of odors, or for the removal of contaminants within the space.
- All variable air volume mechanical ventilation and space-conditioning systems shall include dynamic controls that maintain measured outside air ventilation rates within 10 percent of the required outside air ventilation rate at both full and reduced supply airflow conditions. Fixed minimum damper position is not considered to be dynamic and is not an allowed control strategy.
- Measured outdoor air rates of constant volume mechanical ventilation and space-conditioning systems shall be within 10 percent of the required outside air rate.
MINIMUM VENTILATION RATES
|TYPE OF USE||CFM PER SQUARE FOOT OF CONDITIONED FLOOR AREA|
|Auto repair workshops||1.50|
|Bars, cocktail lounges and casinos||0.2|
|Coin-operated dry cleaning||0.30|
|Commercial dry cleaning||0.45|
|High-rise residential||Ventilation rates specified by the California Building Code|
|Hotel guest rooms (less than 500 ft2)||30 cfm/guest room|
|Hotel guest rooms (500 ft2 or greater)||0.15|