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6.5.3.1.1
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 6.5.3.1.1A. This includes supply fans, return/relief fans, exhaust 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.
Exceptions:
  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 may use variable-volume fan power limitation.
  2. Individual exhaust fans with motor nameplate horsepower of 1 hp or less.
TABLE 6.5.3.1.1A
Fan Power Limitationa
  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
  1. where
    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)
    where
    PD = each applicable pressure drop adjustment from Table 6.5.3.1.1B in in. w.c.
    L/S = the design airflow through each applicable device from Table 6.5.3.1.1B in cubic feet per minute
TABLE 6.5.3.1.1B
Fan Power Limitation Pressure Drop Adjustment
Device Adjustment
   
Credits  
Fully ducted return and/or exhaust air systems 0.5 in. w.c. (2.15 in. w.c. for laboratory and vivarium systems)
Return and/or exhaust 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 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 in w.c. for each airstream
Coil Runaround Loop 0.6 in. w.c. for each airstream
Evaporative humidifier/cooler in series with another cooling coil Pressure drop of device at fan system design condition
Sound Attenuation Section 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./100 ft of vertical duct exceeding 75 ft
6.5.3.1.2 Motor Nameplate Horsepower
For each fan, the selected fan motor shall be no larger than the first available motor size greater than the bhp. The fan bhp must be indicated on the design documents to allow for compliance verification by the code official.
Exceptions:
  1. For fans less than 6 bhp, where the first available motor larger than the bhp has a nameplate rating within 50% of the bhp, the next larger nameplate motor size may be selected.
  2. For fans 6 bhp and larger, where the first available motor larger than the bhp has a nameplate rating within 30% of the bhp, the next larger nameplate motor size may be selected.

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