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].
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 x 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.
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:
- For fans less than 6 bhp (4413 W), 1.5 times the fan brake horsepower.
- For fans 6 bhp (4413 W) and larger, 1.3 times the fan brake horsepower.
- Systems complying with Section C403.8.1 fan system motor nameplate hp (Option 1).
Exception: Fans with motor nameplate horsepower less than 1 hp (746 W) are exempt from this section.
Fans shall have a fan efficiency grade (FEG) of not less than 67, as determined in accordance with AMCA 205 by an approved, independent testing laboratory and labeled by the manufacturer. 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. Individual fans with a motor nameplate horsepower 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 in Section C403.3.2.
- 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.
Motors for fans that are not less than 1/12 hp (0.062 kW) and less than 1 hp (0.746 kW) shall be electronically commutated motors or shall have a minimum motor efficiency of 70 percent, rated in accordance with DOE 10 CFR 431. These motors shall have the means to adjust motor speed for either balancing or remote control. The use of belt-driven fans to sheave adjustments for airflow balancing instead of a varying motor speed shall be permitted.
Exceptions: The following motors are not required to comply with this section
Each cooling system listed in Table C403.8.5.1 shall be designed to vary the indoor fan airflow as a function of load and shall comply with the following requirements:
- Direct expansion (DX) and chilled water cooling units that control the capacity of the mechanical cooling directly based on space temperature shall have not fewer than two stages of fan control. Low or minimum speed shall not be greater than 66 percent of full speed. At low or minimum speed, the fan system shall draw not more than 40 percent of the fan power at full fan speed. Low or minimum speed shall be used during periods of low cooling load and ventilation-only operation.
- Other units including DX cooling units and chilled water units that control the space temperature by modulating the airflow to the space shall have modulating fan control. Minimum speed shall be not greater than 50 percent of full speed. At minimum speed the fan system shall draw not more than 30 percent of the power at full fan speed. Low or minimum speed shall be used during periods of low cooling load and ventilation-only operation.
- Units that include an air-side economizer in accordance with Section C403.5 shall have not fewer than two speeds of fan control during economizer operation.
- Modulating fan control is not required for chilled water and evaporative cooling units with fan motors of less than 1 hp (0.746 kW) where the units are not used to provide ventilation air and the indoor fan cycles with the load.
- Where the volume of outdoor air required to comply with the ventilation requirements of the International Mechanical Code at low speed exceeds the air that would be delivered at the speed defined in Section C403.8.5, the minimum speed shall be selected to provide the required ventilation air.
|DX cooling||Any||≥ 65,000 Btu/h|
|Chilled water and |
|≥ 1/4 hp||Any|
For SI: 1 British thermal unit per hour = 0.2931 W; 1 hp = 0.746 kW.