Page 284 - The Engineering Guide to LEED-New Construction Sustainable Construction for Engineers

LEED Indoor Envir onmental Quality 247

be approximately summarized by the following definitions and sets of equations. In
LEED 2009, additional variables, assumptions, and corrections are included for multiple
zone recirculating systems which have a mix of outdoor and recirculated return air
being supplied to more than one zone.
OAIZ Outdoor air intake to zone i (cfm)
i
BZA Breathing zone horizontal area for zone i (ft )
2
i
2
2
BZAR Breathing zone minimum area rate (cfm/ft ). (It is usually 0.06 cfm/ft as
given in the standard for both versions)
2
BZOD Breathing zone occupant density for zone i (people/ft )
i
BZPR Breathing zone minimum people rate for use j (cfm/person) as given in the
j
standard. (For example, this is 5 cfm/person for general office spaces,
conference rooms, and meeting spaces, and it is 7.5 cfm/person for lecture
rooms and classrooms per LEED 2.2.)
EV Overall system ventilation effectiveness
EZ Zone distribution effectiveness. (This is typically 1.0 for overhead distribution
i
systems and 1.2 for underfloor distribution systems as given in LEED 2.2.)
For all zones i with mechanical ventilation systems, the standard requires that

OAIZ ≥ BZA [(BZOD )(BZPR ) + (BZAR)]/(EZ )(EV) (6.0.1)
i i i j i
Natural Ventilation For naturally ventilated areas, there are two main requirements
for both versions 2.2 and 2009, with additional scenarios available for LEED 2009:

• There must be an operable window or opening (which is permanently open to
this space) within 25 ft of any occupiable area in a room. Note that a roof opening
is also acceptable.
• The total operable vertical areas of the openings in the room must be at least
4 percent of the net occupiable horizontal area in that space or room.
• LEED 2009 also addresses interior spaces without direct openings to the
outdoors which may be adequately ventilated by the following: “. . . can be
ventilated through adjoining rooms if the openings between rooms are
2
unobstructed and at least 8 percent or 25 ft of the area is free.”
• LEED 2009 also allows for engineered natural ventilation systems if compliance
can be shown through acceptable engineering calculations or simulation.

For the requisite submittals when natural ventilation alone is chosen, floor plans must
be submitted showing the minimum 25-ft access to operable windows and both the
operable vertical areas of each of the openings and the horizontal occupiable areas of
the spaces for the standard option. Summaries of these areas showing compliance
should also be included. Figure 6.0.2 shows an example layout of operable windows
that does not comply with the prerequisite.
Mixed Mode Ventilation LEED 2009 requires that mixed mode ventilation meet the
minimum ventilation rates in ASHRAE 62.1-2007 Section 6, regardless of the ventilation
mode based on any acceptable engineering calculation method.