C403.8.1 Allowable Fan Horsepower (Mandatory)
Each HVAC system having a total fan system motor nameplate horsepower exceeding 5 hp (3.7 kW) at fan system design conditions shall not exceed the allowable fan system motor nameplate hp (Option 1) or fan system bhp (Option 2) shown in Table C403.8.1(1). This includes supply fans, exhaust 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.
- Hospital, vivarium and laboratory systems that utilize flow control devices on exhaust 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.
- Individual exhaust fans with motor nameplate horsepower of 1 hp (0.746 kW) or less are exempt from the allowable fan horsepower requirement.
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|
For SI: 1 bhp = 735.5 W, 1 hp = 745.5 W, 1 cfm = 0.4719 L/s.
|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 C403.8.1(2) in. w.c.|
|CFMD||=||The design airflow through each applicable device from Table C403.8.1(2) in cubic feet per minute.|
FAN POWER LIMITATION PRESSURE DROP ADJUSTMENT
|Return air or exhaust systems required by code or accreditation |
standards to be fully ducted, or systems required to maintainair pressure differentials between adjacent rooms
|0.5 inch w.c. (2.15 inches w.c. for laboratory and vivarium systems)|
|Return and exhaust airflow 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||For each airstream, (2.2 × energy recovery effectiveness — 0.5) inch w.c.|
|Coil runaround loop||0.6 inch w.c. for each airstream.|
|Evaporative humidifier/cooler in series with another |
|Pressure drop of device at fan system design conditions.|
|Sound attenuation section (fans serving spaces with design |
background noise goals below NC35)
|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.|
|Systems without central cooling device||- 0.6 inch w.c.|
|Systems without central heating device||- 0.3 inch w.c.|
|Systems with central electric resistance heat||- 0.2 inch w.c.|
For SI: 1 inch w.c. = 249 Pa, 1 inch = 25.4 mm.
w.c. = water column, NC = Noise criterion.