Thursday, May 26, 2011

Minimum Quantity Of Outside Air For Mechanical Ventilation.

§  27-754  Minimum quantity of outside air for mechanical ventilation.
  The minimum quantity of outside air required for mechanical  ventilation
  in  any  occupiable  room,  where  not  otherwise  prescribed,  shall be
  determined according to table 12-2.
         Table 12-2 Required Minimum Outdoor Air Supply and Exhaust
                              (cfm per sq. ft.)
  Ventilated Rooms    Ventilated Rooms with Natural       without  Natural
  Index for           Ventilation        Ventilation       Air Conditioned
  Ventilation           Openings           Openings             Rooms
  Supply  Exhaust     Supply  Exhaust    Supply Exhaust
     0- 300...       2.5     2.0         2.5     2.0        1.5     1.5
   301- 520...       2.0     1.5         2.0     1.5        1.2     1.2
   521- 850...       1.5     1.25        1.5     1.25       0.9     0.9
   851-1250...        ..     1.0         1.0     1.0        0.6     0.6
  1251-1650...        ..     0.67        0.67    0.67       0.5     0.5
  over 1650...        ..      ..         0.33    0.33       0.4     0.4
    (a)  Window requirements. To be credited as ventilating openings under
  the provisions of this subchapter, windows or other openings shall  meet
  the  requirements  of  section 27-749 of article six of this subchapter,
  and where mechanical supply ventilation is not provided,  shall  have  a
  free  openable  area  of at least one square foot per one hundred square
  feet of floor area.
    (b) Air conditioning.
    (1) In air conditioned rooms, the windows and other openings shall not
  be credited  as  such  in  computing  the  index  for  ventilation.  Air
  conditioned rooms shall be considered as interior rooms.
    (2)  Air  that has been exhausted from an air conditioned space may be
  reconditioned  by  air  conditioning  apparatus  and   recirculated   as
  equivalent  outdoor  air,  provided  that the total of supply air is not
  less than required for air conditioned rooms by table 12-2 and that  the
  amount  of actual outdoor air is at least thirty-three and one-third per
  cent of the required total. The actual outdoor  air  supply  shall  not,
  under  any circumstances, be reduced to less than five cfm per occupant,
  except that these minimum requirements may be reduced by fifty per  cent
  as provided in section 27-755 of this article.
    (c)  Required exhaust. Required exhaust may be accomplished by raising
  the pressure within the space with consequent leakage through doors  and
  windows, or by drawing the vitiated air from air conditioned spaces into
  the  return  air  duct  of air conditioning apparatus or into an exhaust
  duct discharging directly to the outdoor air.
    (d) Make-up air. A sufficient quantity of  air  to  make  the  exhaust
  system  effective  shall be provided to the space being exhausted by one
  or by any combination of the following methods:
    (1) By supplying air to the space by means of a blower system.
    (2) By infiltration through louvres,  registers,  or  other  permanent
  openings  in  walls, doors, or partitions, adjoining spaces where air is
  supplied by one of these methods.
    (3) By infiltration through cracks around window sash and doors.
    (4) By other methods acceptable to the commissioner.
    (e) Prohibited use of recirculated air. Air  drawn  from  any  of  the
  following  spaces  may not be recirculated; mortuary rooms; bathrooms or
  toilet rooms; or any space where an objectionable quantity of  flammable

  vapors,  dust,  odors, or noxious gases is present. Air drawn from rooms
  that must be isolated to prevent the spread of infection  shall  not  be
  recirculated, except that air drawn from hospital operating rooms may be
  recirculated, if in compliance with the following requirements:
    (1)  There  shall  be  a  minimum of twenty-five total air changes per
  hour, of which five air changes per hour shall be outdoor air.
    (2) All fans serving exhaust systems shall be located at the discharge
  end of the system.
    (3) Outdoor air intakes shall be located  at  least  twenty-five  feet
  from   exhaust   outlets   of  ventilation  systems  and  other  exhaust
  discharges,  combustion  equipment  stacks,  medical   surgical   vacuum
  systems,  and  plumbing  vent  stacks,  from  areas  which  may  collect
  vehicular exhaust such as off-street loading bays, and from areas  which
  may  collect  other  noxious  fumes.  The  bottom of outdoor air intakes
  serving central systems if installed above a roof, shall be  located  at
  least three feet above roof level.
    (4) Positive air pressure shall be maintained at all times in relation
  to adjacent areas.
    (5)  All  ventilation  or  air conditioning systems serving such rooms
  shall be equipped with a filter bed of twenty-five per  cent  efficiency
  upstream  of  the  air conditioning equipment and a filter bed of ninety
  per cent efficiency downstream of  the  supply  fan,  any  recirculating
  spray  water  systems  and  water reservoir type humidifiers. All filter
  efficiencies shall be average atmospheric dust spot efficiencies  tested
  in accordance with ASHRAE standard 52-68.
    (6) A manometer shall be installed across each filter bed.
    (7) Duct linings shall not be used in ventilation and air conditioning
  systems  serving  such  rooms unless terminal filters of at least ninety
  per cent efficiency are installed downstream of linings.
    (8) Air supplied shall be delivered at or near the  ceilings  and  all
  exhaust air shall be removed near floor level, with at least two exhaust
  outlets not less than three inches above the floor.
    (f)  Outdoor  air  intakes.  For  high-rise  office  buildings erected
  pursuant to new building applications filed on or  after  the  effective
  date  of  this  section,  outdoor  air  intakes serving spaces above the
  second story and serving spaces greater than ten thousand square feet of
  floor area shall be located at least twenty feet above ground level,  at
  least  twenty feet from exhaust outlets of ventilation systems and other
  exhaust discharges, and at least twenty feet from areas that may collect
  vehicular exhaust such as off-street loading bays.

1 comment:

  1. Its highly informative. I would be visiting your blog hereafter regularly to gather valuable information. Exhaust Sound Control


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