Each HVAC system at fan system design conditions shall not exceed the allowable fan system motor nameplate hp (Option 1) or fan system bhp (Option 2) as shown in Table C403.2.10.1(1). This includes supply fans, return/relief fans, and fan-powered terminal units associated with systems providing heating or cooling capability. Single zone variable-air-volume systems shall comply with the constant volume fan power limitation.
1. Hospital, vivarium and laboratory systems that utilize flow control devices on exhaust and/or return to maintain space pressure relationships necessary for occupant health and safety or environmental control shall be permitted to use variable volume fan power limitation.
2. Individual exhaust fans with motor nameplate horsepower of 1 hp or less.
FAN POWER LIMITATION
|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.|
|hp||=||The maximum combined motor nameplate horsepower.|
|Bhp||=||The maximum combined fan brake horsepower.|
|A||=||Sum of [PD × CFMD / 4131].|
|PD||=||Each applicable pressure drop adjustment from Table C403.2.10.1(2) in. w.c.|
|CFMD||=||The design airflow through each applicable device from Table C403.2.10.1(2) in cubic feet per minute.|
FAN POWER LIMITATION PRESSURE DROP ADJUSTMENT
|Fully ducted return and/or exhaust air systems||0.5 inch w.c. (2.15 in w.c. for laboratory and vivarium systems)|
|Return and/or exhaust air flow control devices||0.5 inch 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 thru 12||0.5 inch w.c.|
|Particulate filtration credit: MERV 13 thru 15||0.9 inch. 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||(2.2 × energy recovery effectiveness) – 0.5 inch w.c. for each airstream|
|Coil runaround loop||0.6 inch w.c. for each airstream|
|Evaporative humidifier/cooler in series with another cooling coil||Pressure drop of device at fan system design conditions|
|Sound attenuation section||0.15 inch w.c.|
|Exhaust system serving fume hoods||0.35 inch w.c.|
|Laboratory and vivarium exhaust systems in high-rise buildings||0.25 inch w.c./100 feet of vertical duct exceeding 75 feet|
For each fan, the selected fan motor shall be no larger than the first available motor size greater than the brake horsepower (bhp). The fan brake horsepower (bhp) shall be indicated on the design documents to allow for compliance verification by the code official.
1. For fans less than 6 bhp (4413 W), where the first available motor larger than the brake horsepower has a nameplate rating within 50 percent of the bhp, selection of the next larger nameplate motor size is allowed.
2. For fans 6 bhp (4413 W) and larger, where the first available motor larger than the bhp has a nameplate rating within 30 percent of the bhp, selection of the next larger nameplate motor size is allowed.