CHAPTER 4 VENTILATION AIR SUPPLY

Transcription

1 CHAPTER 4 VENTILATION AIR SUPPLY General Applicability. This chapter contains requirements for ventilation air supply, exhaust, and makeup-air requirements for occupiable spaces within a building Ventilation Air General Requirements. Occupiable spaces listed in Table shall be designed to have ventilation (outdoor) air for occupants in accordance with this chapter Construction Documents. 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 Dwelling. Requirements for ventilation air rate for single family dwellings shall be in accordance with this chapter or ASHRAE Natural Ventilation. Use of nnatural ventilation systems shall be designed in accordance with this section and shall be permitted in lieu of or in conjunction with include mechanical ventilation systems designed in accordance with Section and Section [ASHRAE 62.1:5.16.4] Exceptions: (1) An engineered natural ventilation system when where approved by the Authority Having Jurisdiction need not meet the requirements of comply with Section and Section (2) A mechanical ventilation system is not required where natural ventilation openings comply with the requirements of Section and are permanently open or have controls that prevent the openings from being closed during occupancy. (3) A mechanical ventilation system is not required where the zone is not served by heating or cooling equipment Location and Size of Openings. Naturally ventilated spaces shall be permanently open to and within 25 feet (7620 mm) of by way of operable wall or roof openings directly to the outdoors, the openable area of which is a minimum of 4 percent of the net occupiable floor area. Where the openings are covered with louvers or otherwise obstructed, openable area shall be based on the free unobstructed area through the opening. Where interior spaces without direct openings to the outdoors are ventilated through adjoining rooms, the opening between rooms shall be permanently unobstructed and have a free area of not less than 8 percent of the area of the interior room nor less than 25 square feet (ft 2 ) (2.3 m 2 ). [ASHRAE 62.1: ] Control and Accessibility. The means to open required operable openings shall be readily accessible to building occupants whenever where the space is occupied. Controls shall be designed to coordinate operation of the natural and mechanical ventilation system. [ASHRAE 62.1: ] Mechanical Ventilation. 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 under any load conditions Outsidedoor Air Inlet Intake Protection. Required outsidedoor-air inlets 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 inch (12.7 mm) openings. Exception: An outside-air inlet serving a nonresidential portion of a building shall be permitted to be covered with a screen having openings larger than 1 4 of an inch (6.4 mm), but in no case exceeding 1 inch (25.4 mm) Weather Protections. 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 Ventilation Rates General. The design outdoor air intake flow rate for a ventilation system shall be determined in accordance with Section through Section Zone Calculations. Zone parameters shall be determined in accordance with Section through Section [ASHRAE 62.1:6.2.2] Breathing Zone Outdoor Airflow. The design outdoor airflow required in the breathing zone of the occupiable space or spaces in a zone, i.e., the breathing zone outdoor airflow (V bz ), shall be determined in accordance with Equation [ASHRAE 62.1: ] V bz = R p P z + R a A z (Equation ) Where: A z = zone floor area: the net occupiable floor area of the zone in square feet (m 2 ). P z = zone population: The largest number of people expected to occupy the zone during typical usage. If the number of people expected to occupy the zone fluctuates, P z shall be permitted to be estimated based on averaging approaches described in Section If P z cannot be accurately predicted during design, it shall be estimated based on the zone floor area and the default occupant density listed in Table UNIFORM MECHANICAL CODE 35

2 R p = outdoor airflow rate required per person as determined from Table R a = outdoor airflow rate required per unit area as determined from Table [ASHRAE 62.1: ] Zone Air Distribution Effectiveness. The zone air distribution effectiveness (E z ) shall be determined using Table [ASHRAE 62.1: ] Zone Outdoor Airflow. The design zone outdoor airflow (V oz ), i.e., the outdoor airflow that must shall be provided to the zone by the supply air distribution system, shall be determined in accordance with Equation [ASHRAE 62.1: ] V oz = V bz /E z (Equation ) Single-Zone Systems. Where one air handler supplies a mixture of outdoor air and recirculated air to only one zone, the outdoor air intake flow (V ot ) shall be determined in accordance with Equation [ASHRAE 62.1:6.2.3] V ot = V oz (Equation ) One Hundred Percent Outdoor Air Systems. Where one air handler supplies only outdoor air to one or more zones, the outdoor air intake flow (V ot ) shall be determined in accordance with Equation [ASHRAE 62.1:6.2.4] V ot = all zones V oz (Equation ) Multiple-Zone Recirculating Systems. Where one air handler supplies a mixture of outdoor air and recirculated return air to more than one zone, the outdoor air intake flow (V ot ) shall be determined in accordance with Section through Section [ASHRAE 62.1:6.2.5] Primary Outdoor Air Fraction. Where Table is used to determine system ventilation efficiency, tthe zone primary outdoor air fraction (Z pz ) shall be determined for ventilation zones in accordance with Equation [ASHRAE 62.1: ] Uncorrected Outdoor Air Intake. The design uncorrected outdoor air intake (V ou ) shall be determined in accordance with Equation (a1). V ou = D all zones R p P z + all zones R a A z (Equation (a1)) The occupant diversity, D, shall be permitted to be used to account for variations in occupancy within the zones served by the system. The occupancy diversity is defined as determined in accordance with Equation (2): D = P s / all zones P z (Equation (b2)) Where the system population (P s ) is the total population in the area served by the system. Alternative methods shall be permitted to be used to account for population diversity when calculating V ou, provided that the resulting value is no less than that determined by Equation (a1). [ASHRAE 62.1: ] Outdoor Air Intake. The design outdoor air intake flow (V ot ) shall be determined in accordance with Equation [ASHRAE 62.1: ] V ot = V ou /E v (Equation ) Design for Varying Operating Conditions Variable Load Conditions. Ventilation systems shall be designed to be capable of providing the required ventilation rates in the breathing zone whenever the zones served by the system are occupied, including all full and partload conditions. [ASHRAE 62.1: ] Short-Term Conditions. Where it is known that peak occupancy will be of short duration or the ventilation rate 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 by in accordance with Equation [ASHRAE 62.1: ]: T = 3v/V bz (4-9 50v/V bz ) IP (Equation ) Z pz = V oz /V pz (Equation ) V pz is the primary airflow to the ventilation zone from the air handler, including outdoor air and recirculated return air. [ASHRAE 62.1: ] System Ventilation Efficiency. The system ventilation efficiency (E v ) shall be determined using in Table or Section [ASHRAE 62.1: ] Acceptable design adjustments based on this optional provision shall be in accordance with the following [ASHRAE 62.1: ]: (1) Zones with fluctuating occupancy: The zone population (P z ) shall 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 UNIFORM MECHANICAL CODE

3 (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, 403.4, or Where: T = averaging time period, (minutes) v = the volume of the zone for which averaging is being applied, ft 3 (m 3 ) V bz = the breathing zone outdoor airflow calculated using shall be determined in accordance with Equation and design value of the zone population P z, cfm (L/s m 3 /min) Exhaust Ventilation. Exhaust airflow shall be provided in accordance with the requirements in Table Exhaust makeup air shall be permitted to be any a combination of outdoor air, recirculated air, and transfer air Dynamic Reset. The system shall be permitted to be designed to vary the design outdoor air intake flow (V ot ), or the space or zone airflow, and the exhaust air flow as operating conditions change. [ASHRAE 62.1:6.2.7] Multiple-Zone Systems General. This section presents an alternative procedure for calculating the system ventilation efficiency (E v ) where values in Table are not used. E v is equal to the lowest calculated value of the zone ventilation efficiency E vz, as shown below: Ev = minimum (Evz) (Equation 404.1) [ASHRAE 62.1: Equation A-38] Zone Ventilation Efficiency. The zone ventilation efficiency E vz, is an efficiency which a system distributes outdoor air from the intake to an individual breathing zone. The zone ventilation efficiency shall be calculated using Equation or Equation [ASHRAE 62.1: Appendix A] Single Supply Systems. Equation or Equation shall be used for single supply systems, where all the ventilation air is a mixture of outdoor air and recirculated air from a single location (e.g., reheat, single-duct VAV, single-fan dual-duct, and multizone). [ASHRAE 62.1: Appendix A] it with outdoor air (e.g., dual-fan dual-duct, fan-powered mixing box, and transfer fans for conference rooms). [ASHRAE 62.1: Appendix A] Evz = (Fa + Xs Fb Zd Fc)/Fa (Equation ) [ASHRAE 62.1: Equation A-23] Where: Ep - Primary air fraction to the zone: Ep = Vpz/Vdz (Ep = 1.0 for single-duct and single-zone systems). Er - In systems with secondary recirculation of return air, fraction of secondary recirculated air to the zone that is representative of average system return air rather than air directly recirculated from the zone. Fa - Fraction of supply air to the zone from sources outside the zone: Fa = Ep + (1 Ep) Er. Fb - Fraction of supply air to the zone from fully mixed primary air: Fb = Ep. Fc - Fraction of outdoor air to the zone from sources outside the zone: Fc = 1 (1 Ez) (1 Er) (1 Ep). Xs - Average Outdoor Air Fraction: At the primary air handler, the fraction of outdoor air intake flow in the system primary airflow, Xs = Vou/Vps. Vps - System Primary Airflow: The total primary airflow supplied to all zones served by the system from the airhandling unit at which the outdoor air intake is located, Vps = ΣVpz Zd - Discharge Outdoor Air Fraction: The outdoor air fraction required in air discharged to the zone, Zd = Voz/Vdz. Z pz - Primary Outdoor Air Fraction required in the primary air supplied to the ventilation zone prior to the introduction of a secondary recirculation air, Z pz = V oz / V pz Vdz - Zone Discharge Airflow: The expected discharge (supply) airflow to the zone that includes primary airflow and locally recirculated airflow. E vz = 1+X s Z dpz (Equation ) [ASHRAE 62.1: Equation A-12] General Case. Equation shall be used for systems that provide all or part of their ventilation by recirculating air from other zones without directly mixing UNIFORM MECHANICAL CODE 37

4 OCCUPANCY CATEGORY 4 TABLE MINIMUM VENTILATION RATES IN BREATHING ZONE 1, 2 [ASHRAE 62.1: TABLE 6-1] PEOPLE OUTDOOR Air Rate R P (cfm/person) AREA OUTDOOR Air Rate R A (cfm/ft 2 ) DEFAULT OCCUPANT Density 3 (people/1000 ft 2 ) CORRECTIONAL FACILITIES Booking/waiting Cell Day room Guard stations EDUCATIONAL FACILITIES Art classroom Classrooms (ages 5-8) Classrooms (age 9 plus) Computer lab Day care (through age 4) Day care sickroom Lecture classroom Lecture hall (fixed seats) Media center A Music/theater/dance Multi-use assembly Science laboratories E University/college laboratories Wood/metal shop FOOD AND BEVERAGE SERVICE Bars, cocktail lounges Cafeteria/fast food dining Kitchen (cooking) Restaurant dining rooms GENERAL Break rooms Coffee stations Conference/meeting Corridors 0.06 Occupiable Sstorage rooms for liquids or gels B HOTELS, MOTELS, RESORTS, DORMITORIES Bedroom/living room Barracks sleeping areas Laundry rooms, central Laundry rooms within dwelling units Lobbies/pre-function Multipurpose assembly OFFICE BUILDINGS Breakrooms Occupiable storage rooms for dry materials Office space Main entry lobbies Reception areas Telephone/data entry MISCELLANEOUS SPACES Bank or bank lobbies Bank vaults/safe deposit Computer (not printing) Electrical equipment rooms Elevator machine rooms General manufacturing (excludes heavy industrial and processes using chemicals) UNIFORM MECHANICAL CODE

5 OCCUPANCY CATEGORY 4 TABLE (continued) MINIMUM VENTILATION RATES IN BREATHING ZONE 1, 2 [ASHRAE 62.1: TABLE 6-1] PEOPLE OUTDOOR Air Rate R P (cfm/person) AREA OUTDOOR Air Rate R A (cfm/ft 2 ) DEFAULT OCCUPANT Density 3 (people/1000 ft 2 ) Pharmacy (prep. area) Photo studios Shipping/receiving B Sorting, packing, light assembly Telephone closets 0.00 Transportation waiting Warehouses B PUBLIC ASSEMBLY SPACES Auditorium seating area Courtrooms Legislative chambers Libraries Lobbies Museums (children s) Museums/galleries Places of religious worship RESIDENTIAL Common corridors 0.06 Dwelling unit F, G F RETAIL Barber shop Beauty and nail salons Coin-operated laundries Mall common areas Pet shops (animal areas) Sales (except as below) Supermarket SPORTS AND ENTERTAINMENT Bowling alley (seating) Disco/dance floors Gambling casinos Game arcades Gym, stadium (play area) Health club/aerobics room Health club/weight rooms Sports arena (play area) 0.30 Spectator areas Stages, studios D Swimming (pool & deck) C 0.48 For SI units: 1 cubic foot per minute = 0.47 L/s m 3 /min, 1 square foot = m 2 Notes: 1 Smoking: This table applies to no-smoking areas. Rates for smoking-permitted spaces must be determined using other methods. 2 Air Density: Volumetric airflow rates are based on an air density of lbda/ft 3 (1.2 kgda/m 3 ), which corresponds to dry air at a barometric pressure of 1 atm (101.3 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 Default Occupant Density: The default occupant density shall be used where actual occupant density is not known. 4 Unlisted Occupancies: 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 a For high school and college libraries, use values shown for Public Spaces Library. b Rate may is capable of not being sufficient when 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 be required to remove moisture. d Rate does not include special exhaust for stage effects, (e.g., dry ice vapors, smoke). e No class of air has been established for this occupancy category. 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 space outside of that dwelling. UNIFORM MECHANICAL CODE 39

6 TABLE , 2, 3, 4, 5 ZONE AIR DISTRIBUTION EFFECTIVENESS [ASHRAE 62.1: TABLE 6-2] 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 at least 15 F 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 1.0 per minute (fpm) supply air jet reaches to within 4.5 feet of floor level. Floor supply of cool air and ceiling return provided that the 150 fpm (0.8 m/s) supply jet reaches at least 4.5 feet 1.0 above the floor. Floor supply of cool air and ceiling return, provided low velocity displacement ventilation achieves unidirectional 1.2 flow and thermal stratification. 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 or return. 0.8 Makeup supply drawn in near to the exhaust or return location 0.5 For SI units: t/ C=(t/ F-32)/1.8, 1 foot per minute = m/s, 1 foot = mm Notes: 1 Cool air is 1.8, 1 foot per minute 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 As an alternative to using the above values, determine E z in accordance with ASHRAE Standard 129 for all air distribution configurations except unidirectional flow. TABLE SYSTEM VENTILATION EFFICIENCY [ASHRAE 62.1: TABLE 6-3] MAx (Z P ) E v > 0.55 Use Section Notes: 1 Max Zp refers to the largest value of Zp, calculated using Equation , among all the zones served by the system. 2 Interpolating between table values is permitted. 3 The values of E v in this table are based on a 0.15 average outdoor air fraction for the system (e.g., the ratio of the uncorrected outdoor air intake Vou to the total zone primary airflow for all 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 will yield more practical results. 1, 2, 3 40 UNIFORM MECHANICAL CODE

7 OCCUPANCY CATEGORY 6 TABLE MINIMUM ExHAUST RATES [ASHRAE 62.1: TABLE 6-4] ExHAUST RATE (cfm/unit) ExHAUST RATE (cfm/ft 2 ) Arena Art classrooms Auto repair rooms Barber shop Beauty and nail salons Cell with toilet Copy, printing rooms Darkrooms Science lab classrooms Educational science laboratories Janitor closets, trash rooms, recycleing Kitchen commercial Kitchenettes Locker rooms Locker/dressing rooms Parking garages 3, Pet shops (animal areas) Residential kitchens 50/100 - Soiled laundry storage rooms Storage rooms, chemical Toilets public 4 50/70 - Toilet private 5 25/50 - Woodwork shop/classroom For SI units: 1 cubic foot per minute = 0.47 L/s m 3 /min, 1 square foot = m 2 Notes: 1 Stands where engines are run shall have exhaust systems that directly connect to the engine exhaust and prevent escape of fumes. 2 The rates do not include exhaust from vehicles or equipment with internal combustion engines. 3 Exhaust rate is not required for open parking garages as defined in accordance with the building code. 4 Rate is per water closet or urinal. Provide the higher rate where periods of heavy use are expected to occur, e.g., toilets in theatres, schools, and sports facilities. 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 may shall be used. Otherwise use the higher rate. 6 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. 7 Exhaust rate is not required for enclosed parking garages having a floor area of 1000 square feet (92.9 m 2 ) or less and used for the storage of five or less motorized vehicles. 8 For continous system operation, the lower rates shall be permitted. Otherwise the higher rate shall be used. UNIFORM MECHANICAL CODE 41

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