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// CODE SNIPPET

403.3.1 Other Buildings Intended to Be Occupied

Mechanical Code 2018 of Maryland > 4 Ventilation > 403 Mechanical Ventilation > 403.3 Outdoor Air and Local Exhaust Airflow Rates > 403.3.1 Other Buildings Intended to Be Occupied
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ILLUSTRATION
The design of local exhaust systems and ventilation systems for outdoor air for occupancies other than Group R-2, R-3 and R-4 three stories and less above grade plane shall comply with Sections 403.3.1.1 through 403.3.1.5.

403.3.1.1 Outdoor Airflow Rate

Ventilation systems shall be designed to have the capacity to supply the minimum outdoor airflow rate, determined in accordance with this section. In each occupiable space, the ventilation system shall be designed to deliver the required rate of outdoor airflow to the breathing zone. The occupant load utilized for design of the ventilation system shall be not less than the number determined from the estimated maximum occupant load rate indicated in Table 403.3.1.1. Ventilation rates for occupancies not represented in Table 403.3.1.1 shall be those for a listed occupancy classification that is most similar in terms of occupant density, activities and building construction; or shall be determined by an approved engineering analysis. The ventilation system shall be designed to supply the required rate of ventilation air continuously during the period the building is occupied, except as otherwise stated in other provisions of the code.
With the exception of smoking lounges, the ventilation rates in Table 403.3.1.1 are based on the absence of smoking in occupiable spaces. Where smoking is anticipated in a space other than a smoking lounge, the ventilation system serving the space shall be designed to provide ventilation over and above that required by Table 403.3.1.1 in accordance with accepted engineering practice.
Exception: The occupant load is not required to be determined based on the estimated maximum occupant load rate indicated in Table 403.3.1.1 where approved statistical data document the accuracy of an alternate anticipated occupant density.
TABLE 403.3.1.1
MINIMUM VENTILATION RATES
OCCUPANCY CLASSIFICATIONOCCUPANT DENSITY
#/1000 FT2 a
PEOPLE OUTDOOR
AIRFLOW RATE IN
BREATHING ZONE,
Rp CFM/PERSON
AREA OUTDOOR
AIRFLOW RATE IN
BREATHING ZONE,
Ra CFM/FT2 a
EXHAUST
AIRFLOW RATE
CFM/FT2 a
Correctional facilities
Booking/waiting507.50.06—
Cells
without plumbing fixtures2550.12—
with plumbing fixturesg2550.121.0
Day room3050.06—
Dining halls
(see "Food and beverage service")
————
Guard stations1550.06—
Dry cleaners, laundries
Coin-operated dry cleaner2015——
Coin-operated laundries207.50.12—
Commercial dry cleaner3030——
Commercial laundry1025——
Storage, pick up307.50.12—
Education
Art classroomg20100.180.7
Auditoriums15050.06—
Classrooms (ages 5-8)25100.12—
Classrooms (age 9 plus)35100.12—
Computer lab25100.12—
Corridors (see "Public spaces")————
Day care (through age 4)25100.18—
Lecture classroom657.50.06—
Lecture hall (fixed seats)1507.50.06—
Locker/dressing roomsg———0.25
Media center25100.12—
Multiuse assembly1007.50.06—
Music/theater/dance35100.06—
Science laboratoriesg25100.181.0
Smoking loungesb7060——
Sports locker roomsg———0.5
Wood/metal shopsg20100.180.5
Food and beverage service
Bars, cocktail lounges1007.50.18—
Cafeteria, fast food1007.50.18—
Dining rooms707.50.18—
Kitchens (cooking)b207.50.120.7
Hotels, motels, resorts and dormitories
Bathrooms/toilet—privateg———25/50f
Bedroom/living room1050.06—
Conference/meeting5050.06—
Dormitory sleeping areas2050.06—
Gambling casinos1207.50.18—
Lobbies/prefunction307.50.06—
Multipurpose assembly12050.06—
Offices
Conference rooms5050.06—
Main entry lobbies1050.06—
Office spaces550.06—
Reception areas3050.06—
Telephone/data entry6050.06—
Private dwellings, single and multiple
Garages, common for multiple unitsb———0.75
Kitchensb———25/100f
Living areascBased on number
of bedrooms. First
bedroom, 2; each
additional bedroom, 1
0.35 ACH but not less
than 15 cfm/person
——
Toilet rooms and bathroomsg———20/50f
Public spaces
Corridors——0.06—
Courtrooms7050.06—
Elevator car———1.0
Legislative chambers5050.06—
Libraries1050.12—
Museums (children's)407.50.12—
Museums/galleries407.50.06—
Places of religious worship12050.06—
Shower room (per shower head)g———50/20f
Smoking loungesb7060——
Toilet rooms — publicg———50/70e
Retail stores, sales floors and
showroom floors
Dressing rooms———0.25
Mall common areas407.50.06—
Sales157.50.12—
Shipping and receiving2100.12—
Smoking loungesb7060——
Storage rooms——0.12—
Warehouses (see "Storage")—100.06—
Specialty shops
Automotive motor-fuel dispensing stationsb———1.5
Barber257.50.060.5
Beauty salonsb25200.120.6
Nail salons b, h25200.120.6
Embalming roomb———2.0
Pet shops (animal areas)b107.50.180.9
Supermarkets87.50.06—
Sports and amusement
Bowling alleys (seating areas)40100.12—
Disco/dance floors100200.06—
Game arcades207.50.18—
Gym, stadium, arena (play area)7200.18—
Health club/aerobics room40200.06—
Health club/weight room10200.06—
Ice arenas without combustion engines——0.300.5
Spectator areas1507.50.06—
Swimming pools (pool and deck area)——0.48—
Storage
Repair garages, enclosed parking garagesb,d———0.75
Refrigerated warehouses/freezers—10—0.75
Warehouses—100.06—
Theaters
Auditoriums (see "Education")————
Lobbies15050.06—
Stages, studios70100.06—
Ticket booths6050.06—
Transportation
Platforms1007.50.06—
Transportation waiting1007.50.06—
Workrooms
Bank vaults/safe deposit550.06—
Computer (without printing)450.06—
Copy, printing rooms450.060.5
Darkrooms———1.0
Meat processingc1015——
Pharmacy (prep. area)1050.18—
Photo studios1050.12—
For SI: 1 cubic foot per minute = 0.0004719 m3/s, 1 ton = 908 kg, 1 cubic foot per minute per square foot = 0.00508 m3/(s • m2), °C = [(°F) -32]/1.8, 1 square foot = 0.0929 m2.
  1. Based on net occupiable floor area.
  2. Mechanical exhaust required and the recirculation of air from such spaces is prohibited. Recirculation of air that is contained completely within such spaces shall not be prohibited (see Section 403.2.1, Item 3).
  3. Spaces unheated or maintained below 50°F are not covered by these requirements unless the occupancy is continuous.
  4. Ventilation systems in enclosed parking garages shall comply with Section 404.
  5. Rates are per water closet or urinal. The higher rate shall be provided where the exhaust system is designed to operate intermittently. The lower rate shall be permitted only where the exhaust system is designed to operate continuously while occupied.
  6. Rates are per room unless otherwise indicated. The higher rate shall be provided where the exhaust system is designed to operate intermittently. The lower rate shall be permitted only where the exhaust system is designed to operate continuously while occupied.
  7. Mechanical exhaust is required and recirculation from such spaces is prohibited except that recirculation shall be permitted where the resulting supply airstream consists of not more than 10 percent air recirculated from these spaces. Recirculation of air that is contained completely within such spaces shall not be prohibited (see Section 403.2.1, Items 2 and 4).
  8. For nail salons, each manicure and pedicure station shall be provided with a source capture system capable of exhausting not less than 50 cfm per station. Exhaust inlets shall be located in accordance with Section 502.20. Where one or more required source capture systems operate continuously during occupancy, the exhaust rate from such systems shall be permitted to be applied to the exhaust flow rate required by Table 403.3.1.1 for the nail salon.

403.3.1.1.1 Zone Outdoor Airflow

The minimum outdoor airflow required to be supplied to each zone shall be determined as a function of occupancy classification and space air distribution effectiveness in accordance with Sections 403.3.1.1.1.1 through 403.3.1.1.1.3.

403.3.1.1.1.1 Breathing Zone Outdoor Airflow

The outdoor airflow rate required in the breathing zone (Vbz) of the occupiable space or spaces in a zone shall be determined in accordance with Equation 4-1.
(Equation 4-1)
where:
Az = Zone floor area: the net occupiable floor area of the space or spaces in the zone.
Pz = Zone population: the number of people in the space or spaces in the zone.
Rp = People outdoor air rate: the outdoor airflow rate required per person from Table 403.3.1.1.
Ra = Area outdoor air rate: the outdoor airflow rate required per unit area from Table 403.3.1.1.

403.3.1.1.1.2 Zone Air Distribution Effectiveness

The zone air distribution effectiveness (Ez) shall be determined using Table 403.3.1.1.1.2.
TABLE 403.3.1.1.1.2
ZONE AIR DISTRIBUTION EFFECTIVENESSa,b,c,d
AIR DISTRIBUTION CONFIGURATIONEz
Ceiling or floor supply of cool air1.0e
Ceiling or floor supply of warm air and floor return1.0
Ceiling supply of warm air and ceiling return0.8f
Floor supply of warm air and ceiling return0.7
Makeup air drawn in on the opposite side of the room
from the exhaust or return
0.8
Makeup air drawn in near to the exhaust or return
location
0.5
For SI: 1 foot = 304.8 mm, 1 foot per minute = 0.00506 m/s, °C = [(°F) — 32]/1.8.
  1. "Cool air" is air cooler than space temperature.
  2. "Warm air" is air warmer than space temperature.
  3. "Ceiling" includes any point above the breathing zone.
  4. "Floor" includes any point below the breathing zone.
  5. Zone air distribution effectiveness of 1.2 shall be permitted for systems with a floor supply of cool air and ceiling return, provided that low-velocity displacement ventilation achieves unidirectional flow and thermal stratification.
  6. Zone air distribution effectiveness of 1.0 shall be permitted for systems with a ceiling supply of warm air, provided that supply air temperature is less than 15°F above space temperature and provided that the 150-foot-per-minute supply air jet reaches to within 41/2 feet of floor level.

403.3.1.1.1.3 Zone Outdoor Airflow

The zone outdoor airflow rate (Voz), shall be determined in accordance with Equation 4-2.
(Equation 4-2)

403.3.1.1.2 System Outdoor Airflow

The outdoor air required to be supplied by each ventilation system shall be determined in accordance with Sections 403.3.1.1.2.1 through 403.3.1.1.2.3.4 as a function of system type and zone outdoor airflow rates.

403.3.1.1.2.1 Single Zone Systems

Where one air handler supplies a mixture of outdoor air and recirculated return air to only one zone, the system outdoor air intake flow rate (Vot) shall be determined in accordance with Equation 4-3.
(Equation 4-3)

403.3.1.1.2.2 100-Percent Outdoor Air Systems

Where one air handler supplies only outdoor air to one or more zones, the system outdoor air intake flow rate (Vot) shall be determined using Equation 4-4.
(Equation 4-4)

403.3.1.1.2.3 Multiple Zone Recirculating Systems

Where one air handler supplies a mixture of outdoor air and recirculated return air to more than one zone, the system outdoor air intake flow rate (Vot) shall be determined in accordance with Sections 403.3.1.1.2.3.1 through 403.3.1.1.2.3.4.

403.3.1.1.2.3.1 Primary Outdoor Air Fraction

The primary outdoor air fraction (Zp) shall be determined for each zone in accordance with Equation 4-5.
(Equation 4-5)
where:
Vpz = Primary airflow: The airflow rate supplied to the zone from the airhandling unit at which the outdoor air intake is located. It includes outdoor intake air and recirculated air from that air-handling unit but does not include air transferred or air recirculated to the zone by other means. For design purposes, Vpz shall be the zone design primary airflow rate, except for zones with variable air volume supply and Vpz shall be the lowest expected primary airflow rate to the zone when it is fully occupied.

403.3.1.1.2.3.2 System Ventilation Efficiency

The system ventilation efficiency (Ev) shall be determined using Table 403.3.1.1.2.3.2 or Appendix A of ASHRAE 62.1.
TABLE 403.3.1.1.2.3.2
SYSTEM VENTILATION EFFICIENCYa,b
Max (Zp)Ev
≤ 0.151
≤ 0.250.9
≤ 0.350.8
≤ 0.450.7
≤ 0.550.6
≤ 0.650.5
≤ 0.750.4
> 0.750.3
  1. Max (Zp) is the largest value of Zp calculated using Equation 4-5 among all the zones served by the system.
  2. Interpolating between table values shall be permitted.

403.3.1.1.2.3.3 Uncorrected Outdoor Air Intake

The uncorrected outdoor air intake flow rate (Vou) shall be determined in accordance with Equation 4-6.
(Equation 4-6)
where:
D = Occupant diversity: the ratio of the system population to the sum of the zone populations, determined in accordance with Equation 4-7.
(Equation 4-7)
where:
Ps = System population: The total number of occupants in the area served by the system. For design purposes, Ps shall be the maximum number of occupants expected to be concurrently in all zones served by the system.

403.3.1.1.2.3.4 Outdoor Air Intake Flow Rate

The outdoor air intake flow rate (Vot) shall be determined in accordance with Equation 4-8.
(Equation 4-8)

403.3.1.2 Exhaust Ventilation

Exhaust airflow rate shall be provided in accordance with the requirements of Table 403.3.1.1. Outdoor air introduced into a space by an exhaust system shall be considered as contributing to the outdoor airflow required by Table 403.3.1.1.

403.3.1.3 System Operation

The minimum flow rate of outdoor air that the ventilation system must be capable of supplying during its operation shall be permitted to be based on the rate per person indicated in Table 403.3.1.1 and the actual number of occupants present.

403.3.1.4 Variable Air Volume System Control

Variable air volume air distribution systems, other than those designed to supply only 100-percent outdoor air, shall be provided with controls to regulate the flow of outdoor air. Such control system shall be designed to maintain the flow rate of outdoor air at a rate of not less than that required by Section 403.3 over the entire range of supply air operating rates.

403.3.1.5 Balancing

The ventilation air distribution system shall be provided with means to adjust the system to achieve not less than the minimum ventilation airflow rate as required by Sections 403.3 and 403.3.1.2. Ventilation systems shall be balanced by an approved method. Such balancing shall verify that the ventilation system is capable of supplying and exhausting the airflow rates required by Sections 403.3 and 403.3.1.2.

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