Chapter 4 Ventilation Air

The outdoor air ventilation rate and air distribution assumptions made in the design of the ventilation system shall be clearly identified on the construction documents.

Requirements for ventilation air rate for single-family dwellings shall be in accordance with this chapter or ASHRAE 62.2.

Mechanical ventilation for health care facilities shall be designed and installed in accordance with this code and ASHRAE 170.

Spaces, or portions of spaces, to be naturally ventilated shall be located within a distance based on the ceiling height, in accordance with Section 402.2.1.1, Section 402.2.1.2, or Section 402.2.1.3, from operable wall openings in accordance with Section 402.2.2. For spaces with ceilings which are not parallel to the floor, the ceiling height shall be determined in accordance with Section 402.2.1.4. [ASHRAE 62.1:6.4.1]

Spaces, or portions of spaces, to be naturally ventilated shall be permanently open to operable wall openings directly to the outdoors, the openable area of which is a minimum of 4 percent of the net occupiable floor area. Where openings are covered with louvers or otherwise obstructed, openable area shall be based on the net free unobstructed area through the opening. Where interior rooms, or portions of rooms, without direct openings to the outdoors are ventilated through adjoining rooms, the opening between rooms shall be permanently unobstructed and shall have a free area of not less than 8 percent of the area of the interior room nor less than 25 square feet (2.3 m²). [ASHRAE 62.1:6.4.2]

The means to open required operable openings shall be readily accessible to building occupants where the space is occupied. Controls shall be designed to coordinate operation of the natural and mechanical ventilation systems. [ASHRAE 62.1:6.4.3]

Outdoor air intakes that are part of the mechanical ventilation system shall be designed to manage rain entrainment, to prevent rain intrusion, and manage water from snow in accordance with ASHRAE 62.1.

The outdoor airflow required in the breathing zone of the occupiable space or spaces in a ventilation zone, i.e., the breathing zone outdoor airflow (V_bz), shall be not less than the value determined in accordance with Equation 403.2.1.

Az	=	zone floor area: the net occupiable floor area of the ventilation zone, square feet (m2).
Pz	=	zone population: The number of people in the ventilation zone during typical usage.
Rp	=	outdoor airflow rate required per person as determined from Table 402.1.
Ra	=	outdoor airflow rate required per unit area as determined from Table 402.1. [ASHRAE 62.1:6.2.2.1]

The zone air distribution effectiveness (E_z) shall be not greater than the default value determined in accordance with Table 403.2.2. [ASHRAE 62.1:6.2.2.2]

TABLE 403.2.2
ZONE AIR DISTRIBUTION EFFECTIVENESS^{1, 2, 3, 4, 5}
[ASHRAE 62.1:TABLE 6.2.2.2]

AIR DISTRIBUTION CONFIGURATION	Ez
Ceiling supply of cool air.	1.0
Ceiling supply of warm air and floor return.	1.0
Ceiling supply of warm air 15°F or more above space temperature and ceiling return.	0.8
Ceiling supply of warm air less than 15°F above space temperature and ceiling return provided that the 150 feet per minute (fpm) supply air jet reaches to within 4.5 feet of floor level.	1.06
Floor supply of cool air and ceiling return provided that the vertical throw is more than 50 fpm at a height of 4.5 feet or more above the floor.	1.0
Floor supply of cool air and ceiling return, provided low-velocity displacement ventilation achieves unidirectional flow and thermal stratification, or underfloor air distribution systems where the vertical throw is 50 fpm or less at a height of 4.5 feet above the floor.	1.2
Floor supply of warm air and floor return.	1.0
Floor supply of warm air and ceiling return.	0.7
Makeup supply drawn in on the opposite side of the room from the exhaust, return, or both.	0.8
Makeup supply drawn in near to the exhaust, return, or both locations.	0.5

The zone outdoor airflow (V_oz), i.e., the outdoor airflow rate that shall be provided to the ventilation zone by the supply air distribution system, shall be determined in accordance with Equation 403.2.3. [ASHRAE 62.1:6.2.2.3]

The primary outdoor air fraction (Z_pz) shall be determined for ventilation zones in accordance with Equation 403.5.1. [ASHRAE 62.1:6.2.5.1] Where:

The system ventilation efficiency (E_v) shall be determined in accordance with Table 403.5.2 or Section 404.0. [ASHRAE 62.1:6.2.5.2]

MAX (ZPz)	Ev
≤ 0.15	1.0
≤ 0.25	0.9
≤ 0.35	0.8
≤ 0.45	0.7
≤ 0.55	0.6
> 0.55	Use Section 404.0

The uncorrected outdoor air intake (V_ou) flow shall be determined in accordance with Equation 403.5.3(1). [ASHRAE 62.1:6.2.5.3]

The design outdoor air intake flow (V_ot) shall be determined in accordance with Equation 403.5.4. [ASHRAE 62.1:6.2.5.4]

Where it is known that peak occupancy will be of short duration, or the ventilation will be varied or interrupted for a short period of time, the design shall be permitted to be based on the average conditions over a time period (T) determined in accordance with Equation 403.6.1.

T	=	averaging time period, minutes.
v	=	the volume of the ventilation zone for which averaging is being applied, cubic foot (m3).
Vbz	=	the breathing zone outdoor airflow determined in accordance with Equation 403.2.1 and design value of the zone population (Pz), cubic foot per minute (cfm) (m3/min).

1. Zones with fluctuating occupancy: The zone population (P_z) shall be permitted to be averaged over time (T).
2. Zones with intermittent interruption of supply air: The average outdoor airflow supplied to the breathing zone over time (T) shall be not less than the breathing zone outdoor airflow (V_bz) calculated using Equation 403.2.1.
3. Systems with intermittent closure of the outdoor air intake: The average outdoor air intake over time (T) shall be not less than the minimum outdoor air intake (V_ot) calculated using Equation 403.3, Equation 403.4, or Equation 403.5.4. [ASHRAE 62.1:6.2.6.2]

Exhaust rate for parking garages shall be in accordance with Table 403.7. Exhaust rate shall not be required for enclosed parking garages having a floor area of 1000 square feet (92.9 m²) or less and used for the storage of 5 or less vehicles.

Mechanical ventilation systems for enclosed parking garages shall operate continuously.

1. Mechanical ventilation systems shall be permitted to operate intermittently where the system is designed to operate automatically upon detection of vehicle operation or the presence of occupants by approved automatic detection devices.
2. Approved automatic carbon monoxide sensing devices shall be permitted to be employed to modulate the ventilation system to not exceed a maximum average concentration of carbon monoxide of 50 parts per million during an eight-hour period, with a concentration of not more than 200 parts per million for a period not exceeding one hour. Automatic carbon monoxide sensing devices installed to modulated parking garage ventilation systems shall be approved in accordance with Section 301.2.

OCCUPANCY CATEGORY8	EXHAUST RATE (cfm/unit)	EXHAUST RATE (cfm/ft2)	AIR CLASS
Arenas2	—	0.50	1
Art classrooms	—	0.70	2
Auto repair rooms1	—	1.50	2
Barber shops	—	0.50	2
Beauty and nail salons	—	0.60	2
Cells with toilet	—	1.00	2
Copy, printing rooms	—	0.50	2
Darkrooms	—	1.00	2
Educational science laboratories	—	1.00	2
Janitor closets, trash rooms, recycling	—	1.00	3
Kitchens — commercial	—	0.70	2
Kitchenettes	—	0.30	2
Locker rooms for athletic, industrial and health care facilities	—	0.50	2
Other locker rooms	—	0.25	2
Shower rooms7, 10	20/50	—	2
Paint spray booths	—	—	4
Parking garages3	—	0.75	2
Pet shops (animal areas)	—	0.90	2
Refrigerating machinery rooms6	—	—	3
Residential — kitchens7	50/100	—	2
Soiled laundry storage rooms	—	1.00	3
Storage rooms, chemical	—	1.50	4
Toilets — private5, 9	25/50	—	2
Toilets — public4, 9	50/70	—	2
Woodwork shop/classrooms	—	0.50	2

Recirculation or transfer of Class 1 air to other spaces shall be permitted. [ASHRAE 62.1:5.16.3.1]

Recirculation of Class 2 air within the space of origin shall be permitted. Recirculation or transfer of Class 2 air to other Class 2 or Class 3 spaces shall be permitted, provided the other spaces are used for the same or similar purpose or task and involve the same or similar pollutant sources as the Class 2 space. Transfer of Class 2 air to toilet rooms shall be permitted. Recirculation or transfer of Class 2 air to Class 4 spaces shall be permitted. Class 2 air shall not be recirculated or transferred to Class 1 spaces. Where using an energy recover device, recirculation from leakage, carryover, or transfer from the exhaust side of the energy recovery device shall be permitted and the recirculated Class 2 air shall not exceed 10 percent of the outdoor air intake flow. [ASHRAE 62.1:5.16.3.2]

Recirculation of Class 3 air within the space of origin shall be permitted. Class 3 air shall not be recirculated or transferred to other spaces. Where using an energy recover device, recirculation from leakage, carryover, or transfer from the exhaust side of the energy recovery device shall be permitted and the recirculated Class 3 air shall not exceed 5 percent of the outdoor air intake flow. [ASHRAE 62.1:5.16.3.3]

Class 4 air shall not be recirculated or transferred to other spaces or be recirculated within the space of origin. [ASHRAE 62.1:5.16.3.4]

For single supply systems, where the air supplied to a ventilation zone is a mixture of outdoor air and system-level recirculated air, zone ventilation efficiency (E_vz) shall be determined in accordance with Equation 404.3.1. Examples of single supply systems include constant-volume reheat, singleduct VAV, single-fan dual-duct, and multizone systems.

For secondary-recirculation systems where the supply air or a portion thereof to each ventilation zone is recirculated air (air that has not been directly mixed with outdoor air) from other zones, zone ventilation efficiency (E_vz) shall be determined in accordance with Equation 404.3.2(1). Examples of secondary-recirculation systems include dual-fan dual-duct and fan-powered mixing-box systems, and systems that include transfer fans for conference rooms.