Each HVAC system having a total fan system motor nameplate horsepower (kW) exceeding 5 hp (3.7 kW) at fan system design conditions shall not exceed the allowable fan system motor nameplate horsepower (kW) (Option 1) or fan system brake horsepower (kW) (Option 2) as shown in Table E503.5.6.1(1). This shall include supply fans, return or relief fans, exhaust fans, and fan-powered terminal units associated with systems providing heating or cooling capability that operate at fan system design conditions. Single-zone VAV systems shall comply with the constant-volume fan power limitation.
For SI units: 1 horsepower = 0.746 kW, 1 cubic foot per minute = 0.00047 m3/s
For SI units: 1 inch water column = 0.249 kPa, 1 foot = 304.8 mm
- Hospital, vivarium, and laboratory systems that utilize flow control devices on exhaust, return, or both to maintain space pressure relationships necessary for occupant health and safety, or environmental control shall be permitted to use variable-volume fan power limitation.
- Individual exhaust fans with motor nameplate horsepower of 1 hp (0.7 kW) or less. [ASHRAE 90.1:188.8.131.52.1]
|LIMIT||CONSTANT VOLUME||VARIABLE VOLUME|
|Option 1: Fan system motor nameplate (hp)||Allowable nameplate motor (hp)||hp ≤CFMs • 0.0011||hp ≤CFMs • 0.0015|
|Option 2: Fan system (bhp)||Allowable fan system (bhp)||bhp ≤CFMs • 0.00094 + A||bhp ≤CFMs • 0.0013 + A|
|CFMs||=||the maximum design supply airflow rate to conditioned spaces served by the system in cubic feet per minute (m3/s)|
|hp||=||the maximum combined motor nameplate horsepower (kW)|
|bhp||=||the maximum combined fan brake horsepower (kW)|
|A||=||stun of(PD x CFMD/4131)|
|PD||=||each applicable pressure drop adjustment from Table E503.5.6.1(2) in inch water column(kPa)|
|CFMD||=||the design airflow through each applicable device from Table E503.5.6.1(2) in cubic feet per minute (m3/s)|
|Return or exhaust systems required by code or accreditation standards to be fully ducted, or systems required to maintain air pressure differentials between adjacent rooms||0.5 in. w.c. (2.15 in w.c. for laboratory and vivarium systems)|
|Return, exhaust, or both airflow control devices||0.5 in. w.c.|
|Exhaust filters, scrubbers, or other exhaust treatment||The pressure drop of device calculated at fan system design condition|
|Particulate Filtration Credit: MERV 9 through 12||0.5 in. w.c.|
|Particulate Filtration Credit: MERV 13 through 15||0.9 in. w.c.|
|Particulate Filtration Credit: MERV 16 and greater, and electronically enhanced filters||Pressure drop calculated at 2x clean filter pressure drop at fan system design condition|
|Carbon and other gas-phase air cleaners||Clean filter pressure drop at fan system design condition|
|Biosafety cabinet||Pressure drop of device at fan system design condition|
|Energy recovery device, other than coil runaround loop||For each airstream [(2.2 x enthalpy recovery ratio) - 0.5] in w.c.|
|Coil runaround loop||0.6 in. w.c. for each airstream|
|Evaporative humidifier or cooler in series with another cooling coil||Pressure drop of device at fan system design condition|
|Sound attenuation section (fans serving spaces with design back-ground noise goals below NC35)||0.15 in. w.c.|
|Exhaust system serving fume hoods||0.35 in. w.c.|
|Laboratory and vivarium exhaust systems in high-rise buildings||0.25 in. w.c. per 100 feet of vertical duct exceeding 75 ft|
|Systems without central cooling device||-0.6 in. WC|
|Systems without central heating device||-0.3 in. WC|
|Systems with central electric resistance heat||-0.2 in. WC|
For each fan, the selected fan motor shall be not larger than the first available motor size more than the brake horsepower (bhp) (kW). The fan brake horsepower shall be indicated on the design documents to allow for compliance verification by the Authority Having Jurisdiction.
- For fans less than 6 bhp (4.5 kW), where the first available motor larger than the bhp (kW) has a nameplate rating within 50 percent of the bhp (kW), the next larger nameplate motor size shall be selected.
- For fans 6 bhp (4.5 kW) and larger, where the first available motor larger than the bhp (kW) has a nameplate rating within 30 percent of the bhp (kW), the next larger nameplate motor size shall be selected.
- Systems that are in accordance with Section E503.5.6.1, Option 1.
- Fans with motor nameplate horsepower of less than 1 hp (0.7 kW). [ASHRAE 90.1:184.108.40.206.2]
Fans shall have a fan efficiency grade (FEG) of 67 or more, based on manufacturers' certified data in accordance with AMCA 205. The total efficiency of the fan at the design point of operation shall be within 15 percentage points of the maximum total efficiency of the fan.
- Individual fans with a motor nameplate horsepower of 5 hp (3.7 kW) or less that are not part of a group operated as the functional equivalent of a single fan.
- Multiple fans in series or parallel (e.g., fan arrays) that have a combined motor nameplate horsepower of 5 hp (3.7 kW) or less and are operated as the functional equivalent of a single fan.
- Fans that are part of equipment listed under Section E503.4.
- Fans included in equipment bearing a third party-certified seal for air or energy performance of the equipment package.
- Powered wall/roof ventilators (PRV).
- Fans outside the scope of AMCA 205.
- Fans that are intended to only operate during emergency conditions. [ASHRAE 90.1:220.127.116.11.3]