ADOPTS WITHOUT AMENDMENTS:

UMC 2018

Heads up: There are no amended sections in this chapter.
This chapter contains requirements for ventilation air supply, exhaust, and makeup air requirements for occupiable spaces within a building.
Occupiable spaces listed in Table 402.1 shall be designed to have ventilation (outdoor) air for occupants in accordance with this chapter.

TABLE 402.1
MINIMUM VENTILATION RATES IN BREATHING ZONE1, 2
[ASHRAE 62.1:TABLE 6.2.2.1]
OCCUPANCY CATEGORY4 PEOPLE OUTDOOR Air Rate Rp (Cfm/Person) AREA OUTDOOR Air Rate RA (Cfm/Ft2) DEFAULT OCCUPANT DENSITY3 (people/1000 ft2) AIR CLASS

CORRECTIONAL FACILITIES

Booking/waiting

7.5 0.06 50 2

Cell

5 0.12 25 2

Day room

5 0.06 30 1

Guard stations

5 0.06 15 1

EDUCATIONAL FACILITIES

Art classroom

10 0.18 20 2

Classrooms (ages 5-8)

10 0.12 25 1

Classrooms (age 9 plus)

10 0.12 35 1

Computer lab

10 0.12 25 1

Daycare (through age 4)

10 0.18 25 2

Daycare sickroom

10 0.18 25 3

Lecture classroom

7.5 0.06 65 1

Lecture hall (fixed seats)

7.5 0.06 150 1

Media centera

10 0.12 25 1

Multi-use assembly

7.5 0.06 100 1

Music/theater/dance

10 0.06 35 1

Science laboratories

10 0.18 25 2

University/college laboratories

10 0.18 25 2

Wood/metal shop

10 0.18 20 2

FOOD AND BEVERAGE SERVICE

Bars, cocktail lounges

7.5 0.18 100 2

Cafeteria/fast food dining

7.5 0.18 100 2

Kitchen (cooking)

7.5 0.12 20 2

Restaurant dining rooms

7.5 0.18 70 2

GENERAL

Break rooms

5 0.06 25 1

Coffee stations

5 0.06 20 1

Conference/meeting

5 0.06 50 1

Corridors

0.06 1

Occupiable storage rooms for liquids or gelsb

5 0.12 2 2

HOTELS, MOTELS, RESORTS, DORMITORIES

Barracks sleeping areas

5 0.06 20 1

Bedroom/living room

5 0.06 10 1

Laundry rooms, central

5 0.12 10 2

Laundry rooms within dwelling units

5 0.12 10 1

Lobbies/pre-function

7.5 0.06 30 1

Multipurpose assembly

5 0.06 120 1

OFFICE BUILDINGS

Break Rooms

5 0.12 50 1

Main entry lobbies

5 0.06 10 1

Occupiable storage rooms for dry materials

5 0.06 2 1

Office space

5 0.06 5 1

Reception areas

5 0.06 30 1

Telephone/data entry

5 0.06 60 1

MISCELLANEOUS SPACES

Bank or bank lobbies

7.5 0.06 15 1

Bank vaults/safe deposit

5 0.06 5 2

Computer (not printing)

5 0.06 4 1

Freezer and refrigerated spaces (<50°F)e

10 2

General manufacturing (excludes heavy industrial and processes using chemicals)

10 0.18 7 3

Pharmacy (prep. area)

5 0.18 10 2

Photo studios

5 0.12 10 1

Shipping/receivingb

10 0.12 2 2

Sorting, packing, light assembly

7.5 0.12 7 2

Telephone closets

1

Transportation waiting

7.5 0.06 100 1

Warehousesb

10 0.06 2

PUBLIC ASSEMBLY SPACES

Auditorium seating area

5 0.06 150 1

Courtrooms

5 0.06 70 1

Legislative chambers

5 0.06 50 1

Libraries

5 0.12 10 1

Lobbies

5 0.06 150 1

Museums (children's)

7.5 0.12 40 1

Museums/galleries

7.5 0.06 40 1

Places of religious worship

5 0.06 120 1

RESIDENTIAL

Common corridors

0.06 1

Dwelling unitf, g

5 0.06 See footnotef 1

RETAIL

Sales (except as below)

7.5 0.12 15 2

Barber shop

7.5 0.06 25 2

Beauty and nail salons

20 0.12 25 2

Coin-operated laundries

7.5 0.12 20 2

Mall common areas

7.5 0.06 40 1

Pet shops (animal areas)

7.5 0.18 10 2

Supermarket

7.5 0.06 8 1

SPORTS AND ENTERTAINMENT

Bowling alley (seating)

10 0.12 40 1

Disco/dance floors

20 0.06 100 2

Gambling casinos

7.5 0.18 120 1

Game arcades

7.5 0.18 20 1

Gym, sports arena (play area)e

20 0.18 7 2

Health club/aerobics room

20 0.06 40 2

Health club/weight rooms

20 0.06 10 2

Spectator areas

7.5 0.06 150 1

Stages, studiosd

10 0.06 70 1

Swimming (pool & deck)c

0.48 2

For SI units: 1 cubic foot per minute = 0.0283 m3/min, 1 square foot = 0.0929 m2

Notes:

1 This table applies to no-smoking areas. Rates for smoking-permitted spaces shall be determined using other methods.

2 Volumetric airflow rates are based on an air density of 0.075 pounds of dry air per cubic foot (lbda/ft3) (1.201 kgda/m3), which corresponds to dry air at a barometric pressure of 1 atm (101 kPa) and an air temperature of 70°F (21°C). Rates shall be permitted to be adjusted for actual density, but such adjustment is not required for compliance with this chapter.

3 The default occupant density shall be used where actual occupant density is not known.

4 Where the occupancy category for a proposed space or zone is not listed, the requirements for the listed occupancy category that is most similar in terms of occupant density, activities, and building construction shall be used.

ITEM-SPECIFIC NOTES FOR TABLE 402.1

a For high school and college libraries, use values shown for Public Assembly Spaces — Libraries.

b Rate is capable of not being sufficient where stored materials include those having potentially harmful emissions.

c Rate does not allow for humidity control. Additional ventilation or dehumidification shall be permitted to remove moisture. "Deck area" refers to the area surrounding the pool that would be expected to be wetted during normal pool use, i.e., where the pool is occupied. Deck area that is not expected to be wetted shall be designated as a space type (for example, "spectator area").

d Rate does not include special exhaust for stage effects, e.g., dry ice vapors, smoke.

e Where combustion equipment is intended to be used on the playing surface or in the space, additional dilution ventilation, source control, or both shall be provided.

f Default occupancy for dwelling units shall be two persons for studio and one-bedroom units, with one additional person for each additional bedroom.

g Air from one residential dwelling shall not be recirculated or transferred to other spaces outside of that dwelling.

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.
Natural ventilation systems shall be designed in accordance with this section and shall include mechanical ventilation systems designed in accordance with Section 403.0, Section 404.0, or both.

Exceptions:

  1. An engineered natural ventilation system where approved by the Authority Having Jurisdiction need not comply with Section 402.2.
  2. A mechanical ventilation system is not required where:
    1. natural ventilation openings comply with the requirements of Section 402.2 and are permanently open or have controls that prevent the openings from being closed during periods of expected occupancy or
    2. the zone is not served by heating or cooling equipment. [ASHRAE 62.1:6.4]
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]
For spaces with operable openings on one side of the space, the distance from the operable openings shall be not more than 2H, where H is the ceiling height. [ASHRAE 62.1:6.4.1.1]
For spaces with operable openings on two opposite sides of the space, the distance from the operable openings shall be not more than 5H, where H is the ceiling height. [ASHRAE 62.1:6.4.1.2]
For spaces with operable openings on two adjacent sides of a space, such as two sides of a corner, the distance from the operable openings shall be not more than 5H along a line drawn between the two openings that are farthest apart. Floor area outside that line shall comply with Section 402.2.1.1. [ASHRAE 62.1:6.4.1.3]
The ceiling height, H, to be used in Section 402.2.1.1 through Section 402.2.1.3 shall be the minimum ceiling height in the space.

Exception: For ceilings that are increasing in height as distance from the openings is increased, the ceiling height shall be determined as the average height of the ceiling within 20 feet (6096 mm) from the operable openings. [ASHRAE 62.1:6.4.1.4]

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]
Where natural ventilation is not permitted by this section or the building code, mechanical ventilation systems shall be designed, constructed, and installed to provide a method of supply air and exhaust air. Mechanical ventilation systems shall include controls, manual or automatic, that enable the fan system to operate wherever the spaces served are occupied. The system shall be designed to maintain minimum outdoor airflow as required by Section 403.0 under any load conditions.
Required outdoor-air intakes shall be covered with a screen having not less than 1/4 of an inch (6.4 mm) openings, and shall have not more than 1/2 of an inch (12.7 mm) openings.
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 design outdoor air intake flow rate for a ventilation system shall be determined in accordance with Section 403.2 through Section 403.9.4.
Ventilation zone parameters shall be determined in accordance with Section 403.2.1 through Section 403.2.3 for each ventilation zone served by the ventilation system. [ASHRAE 62.1:6.2.2]
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 (Vbz), shall be not less than the value determined in accordance with Equation 403.2.1.

Where:

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 (Ez) 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 EFFECTIVENESS1, 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

For SI units: °C = (°F-32)/1.8, 1 foot per minute = 0.005 m/s, 1 foot = 304.8 mm

Notes:

1 "Cool air" is air cooler than space temperature.

2 "Warm air" is air warmer than space temperature.

3 "Ceiling supply" includes any point above the breathing zone.

4 "Floor supply" includes any point below the breathing zone.

5 As an alternative to using the above values, Ez shall be permitted to be regarded as equal to air change effectiveness determined in accordance with ASHRAE 129 for air distribution configurations except unidirectional flow.

6 For lower velocity supply air, Ez = 0.8

The zone outdoor airflow (Voz), 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]

Voz = Vbz/Ez (Equation 403.2.3)
For ventilation systems where one or more air handlers supply a mixture of outdoor air and recirculated air to only one ventilation zone, the outdoor air intake flow (Vot) shall be determined in accordance with Equation 403.3. [ASHRAE 62.1:6.2.3]

(Equation 403.3)

Vot = Voz

For ventilation systems where one or more air handlers supply only outdoor air to one or more ventilation zones, the outdoor air intake flow (Vot) shall be determined in accordance with Equation 403.4. [ASHRAE 62.1:6.2.4]

(Equation 403.4)

Vot = Σall zones Voz

For ventilation systems where one or more air handlers supply a mixture of outdoor air and recirculated air to more than one ventilation zone, the outdoor air intake flow (Vot) shall be determined in accordance with Section 403.5.1 through Section 403.5.4. [ASHRAE 62.1:6.2.5]
The primary outdoor air fraction (Zpz) shall be determined for ventilation zones in accordance with Equation 403.5.1. [ASHRAE 62.1:6.2.5.1]

(Equation 403.5.1)

Zpz = Voz/Vpz

Where:

Vpz is the zone primary airflow, i.e., the primary airflow rate to the ventilation zone from the air handler, including outdoor air and recirculated air. [ASHRAE 62.1:6.2.5.1]

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

TABLE 403.5.2 SYSTEM VENTILATION EFFICIENCY1, 2, 3
[ASHRAE 62.1:TABLE 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

Notes:

1 "Max Zpz" refers to the largest value of Zpz, calculated in accordance with Equation 403.5.1, among the ventilation zones served by the system.

2 For values of Max (Zpz) between 0.15 and 0.55, the corresponding value of Ev shall be permitted to be determined by interpolating the values in the table.

3 The values of Ev in this table are based on a 0.15 average outdoor air fraction for the system (i.e., the ratio of the uncorrected outdoor air intake (Vou) to the total zone primary airflow for the zones served by the air handler). For systems with higher values of the average outdoor air fraction, this table is capable of resulting in unrealistically low values of Ev and the use of Section 404.0 is capable of yielding more practical results.

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

[Equation 403.5.3(1)]

Vou = D Σall zones (Rp•Pz) + Σall zones(Ra•Az)

The occupant diversity ratio (D) shall be determined in accordance with Equation 403.5.3(2) to account for variations in population within the ventilation zones served by the system.

[Equation 403.5.3(2)]

D = Psall zones Pz

Where the system population (Ps) is the total population in the area served by the system.

Exception: Alternative methods to account for occupant diversity shall be permitted, provided that the resulting (Vou) value is not less than that determined in accordance with Equation 403.5.3(1). [ASHRAE 62.1:6.2.5.3.1]

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

(Equation 403.5.4)

Vot = Vou/Ev

Ventilation systems shall be designed to be capable of providing not less than the minimum ventilation rates required in the breathing zone where the zones served by the system are occupied, including all full and part-load conditions. The minimum outdoor air intake flow shall be permitted to be less than the design value at part-load conditions. [ASHRAE 62.1:6.2.6.1]
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.

(Equation 403.6.1)

T = 3v/Vbz

Where:

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).

Acceptable design adjustments based on this optional provision shall be in accordance with the following:

  1. Zones with fluctuating occupancy: The zone population (Pz) 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 (Vbz) 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 (Vot) calculated using Equation 403.3, Equation 403.4, or Equation 403.5.4. [ASHRAE 62.1:6.2.6.2]
Exhaust airflow shall be provided in accordance with the requirements in Table 403.7. Exhaust makeup air shall be permitted to be a combination of outdoor air, recirculated air, and transfer air.
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.

Exceptions:

  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.

TABLE 403.7 MINIMUM EXHAUST RATES
[ASHRAE 62.1:TABLE 6.5]

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

For SI units: 1 cubic foot per minute = 0.0283 m3/min, 1 square foot = 0.0929 m2

Notes:

1 Stands where engines are run shall have exhaust systems that directly connect to the engine exhaust and prevent escape of fumes.

2 Where combustion equipment is intended to be used on the playing surface, additional dilution ventilation, source control, or both shall be provided.

3 Exhaust rate is not required for open parking garages as defined in accordance with the building code.

4 Rate is per water closet, urinal, or both. Provide the higher rate where periods of heavy use are expected to occur, e.g., toilets in theatres, schools, and sports facilities. Otherwise the lower rate shall be permitted to be used.

5 Rate is for a toilet room intended to be occupied by one person at a time. For continuous system operation during normal hours of use, the lower rate shall be permitted to be used. Otherwise the higher rate shall be used.

6 For refrigeration machinery rooms, the exhaust rate shall comply with Chapter 11.

7 For continuous system operation, the lower rates shall be permitted. Otherwise the higher rate shall be used.

8 For unlisted occupancies for a proposed space not listed in the table, the requirements for the listed occupancy that is most similar in terms of occupant density and occupancy type shall be used.

9 Exhaust air that has been cleaned in accordance with the criteria of Class 1 shall be permitted to be recirculated.

10 Rate is per shower head.

The system shall be permitted to be designed to reset the outdoor air intake flow (Vot), the space or ventilation zone airflow (Voz) as operating conditions change. [ASHRAE 62.1:6.2.7]
Air shall be classified, and the recirculation or transfer shall be limited in accordance with Section 403.9.1 through Section 403.9.4. [ASHRAE 62.1:5.16] Recirculated air shall not be taken from prohibited locations in accordance with Section 311.3.
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]
This section presents an alternative procedure for calculating the system ventilation efficiency (Ev) where values in Table 403.5.2 are not used. The system ventilation efficiency shall equal the lowest zone ventilation efficiency among the ventilation zones served by the air handler in accordance with Equation 404.1. [ASHRAE 62.1 :A1.3]

Ev = minimum (Evz) (Equation 404.1)
The average outdoor air fraction (Xs) for the ventilation system shall be determined in accordance with Equation 404.2.

(Equation 404.2)

Xs = Vou/Vps

The uncorrected outdoor air intake (Vou) shall be determined in accordance with Section 403.5.3, and the system primary airflow (Vps) shall be determined at the condition analyzed. [ASHRAE 62.1:A1.1]

The zone ventilation efficiency (Evz) shall be the efficiency with which a system distributes outdoor air from the intake to an individual breathing zone, and shall be determined in accordance with Section 404.3.1 or Section 404.3.2. [ASHRAE 62.1:A1.2]
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 (Evz) 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.

Evz = 1+Xs-Zpz (Equation 404.3.1)

The average outdoor air fraction for the system (Xs) shall be determined in accordance with Equation 404.2 and the primary outdoor air fraction for the zone (Zpz) shall be determined in accordance with Section 403.5.1. [ASHRAE 62.1:A1.2.1]

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 (Evz) 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.

Evz = (Fa+XsFb-ZpzEpFc)/Fa [Equation 404.3.2(1)]

The system air fractions Fa, Fb, and Fc shall be determined in accordance with Equation 404.3.2(2), Equation 404.3.2(3), and Equation 404.3.2(4). The zone primary air fraction (Ep) shall be determined in accordance with Equation 404.3.2(5). For single-zone and single-supply systems Ep shall equal to 1.0. The zone secondary recirculation fraction (Er) shall be determined by the designer based on system configuration. The zone air distribution effectiveness (Ez) shall be determined in accordance with Section 403.2.2. [ASHRAE 62.1:A1.2.2]

Where:

Ep - Primary air fraction: The fraction of primary air in the discharge air to the ventilation zone.

Er - Secondary recirculation fraction: In systems with secondary recirculation of return air, the fraction of secondary recirculated air to the zone that is representative of average system return air rather than air directly recirculated from the zone.

Evz - Zone ventilation efficiency: The efficiency with which the system distributes air from the outdoor air intake to the breathing zone in any particular ventilation zone.

Ez - Zone air distribution effectiveness: A measure of the effectiveness of supply air distribution to the breathing zone. Ez is determined in accordance with Section 403.2.2.

Fa - Supply air fraction: The fraction of supply air to the ventilation zone from sources or air outside the zone.

Fb - Mixed air fraction: The fraction of supply air to the ventilation zone from fully mixed primary air.

Fc - Outdoor air fraction: The fraction of outdoor air to the ventilation zone from sources of air outside the zone.

Vdz - Zone discharge airflow: The expected discharge (supply) airflow to the zone that includes primary airflow and secondary recirculated airflow, cfm (m3/min).

Vpz - Zone primary airflow: Determine in accordance with Section 403.5.1.

Xs - Average outdoor air fraction: At the primary air handler, the fraction of outdoor air intake flow in the system primary airflow.

Zpz - Primary outdoor air fraction: The outdoor air fraction required in the primary air supplied to the ventilation zone prior to the introduction of secondary recirculation air. [ASHRAE 62.1:A3]

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