C403.2.12 Air System Design and Control
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 C403.2.12.1(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.
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 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 2× 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 (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 in. w.c.|
|Systems without central heating device||- 0.3 in. w.c.|
|Systems with central electric resistance heat||- 0.2 in. w.c.|
For SI: 1 inch w.c. = 249 Pa, 1 inch = 25.4 mm.
w.c. = water column, NC = Noise criterion.
For each fan, the fan brake horsepower shall be indicated on the construction documents and the selected motor shall be not larger than the first available motor size greater than the following:
Fans shall have a fan efficiency grade (FEG) of not less than 67 when determined in accordance with AMCA 205 by an approved, independent testing laboratory. 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.
Exception: The following fans are not required to have a fan efficiency grade:
- 1.1. Single fan with a motor nameplate horse power of 5 hp (3.7 kW) or less, unless Exception 1.2 applies.
- 1.2. Multiple fans in series or parallel 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 covered under Section C403.2.3.
- Fans included in an equipment package certified by an approved agency for air or energy performance.
- Powered wall/roof ventilators.
- Fans outside the scope of AMCA 205.
- Fans that are intended to operate only during emergency conditions.