Page 296 - The Engineering Guide to LEED-New Construction Sustainable Construction for Engineers

LEED Indoor Envir onmental Quality 259

so that they do not become moist or absorb unwanted contaminants. Proper housekeeping
can be facilitated by scheduling these activities into the construction phase.
Scheduling is a constant theme in the SMACNA principles. Scheduling housekeeping
activities into the daily operations of the construction phase is important. Sequencing
installation of permanent or temporary barriers between finished and unfinished areas
can help in pathway interruption. Scheduling the use of high-VOC or toxic materials or
air pollutant-emitting equipment prior to installation of absorbent materials or away
from enclosed areas can keep the sources of air pollutants down, as can scheduling
protection of the HVAC systems and installation of good filtering media.
Moisture Protection In addition to the SMACNA principles, this credit emphasizes that
absorptive material such as sheetrock shall be protected from moisture damage while on-
site at all times, from storage through staging, installation, and after installation. Moisture
damage can result in other air pollutant problems such as mold after occupancy.
Filtration Media Finally, this credit requires that any air handlers used during construction
have filtering media on each return grill, and this medium shall be replaced prior to
occupancy. The filtering media used for construction phase IAQ management should
meet minimum standards for filtering of particulate matter. In earlier versions of LEED,
those with a minimum efficiency rating value (MERV) rating of 13 were recommended, but
this credit is now based on a MERV rating of 8 and the higher rating of 13 is part of
IEQc5. If the project seeks to receive credit for IEQc5, then all the HVAC equipment
should be sized to accept filters with the MERV rating of 13.
These filters are used to remove particulate matter from the air. The MERV ratings
are based on a combination of removal efficiencies for several different size ranges of
particulate matter and a maximum pressure drop. Particulate matter is made up of
many different materials and can be either liquid or solid. Most of the larger particles
are solids such as dust and soot. Particulate matter comes in all shapes and sizes, and
they are classified by listing the size of a particle by the diameter of a sphere of the same
volume. The USEPA regulates ambient (outside) concentrations of PM in two different
size ranges. The two ranges comprise all particulate matter less than or equal to 10
micrometers (10 μm) in equivalent diameter and all particulate matter less than or equal
to 2.5 μm in equivalent diameter. These are commonly referred to as PM10 and PM2.5.
Also PM2.5 is sometimes referred to as fines. Particulate matter in the air larger than 10
μm in diameter is usually entrained particles that will rapidly settle out and can easily
be filtered by our nostrils. Since particulate matter is made up of many substances, both
organic and inorganic, it may have a wide range of densities. Usually an average specific
gravity is estimated as 2, which is in between the value for many liquids and organics
which are closer to 1, and the value for minerals, which is closer to 3. Metals usually
have a specific gravity greater than 3.
For the MERV ratings for HVAC equipment filtering relating to indoor air, particulate
matter is subdivided into three size ranges: 3 to 10 μm, 1 to 3 μm, and 0.3 to 1 μm (large, medium,
and small). For higher MERV values, the removal efficiency will be greater. The MERV
ratings also address the allowed pressure drop across a filter. Some typical MERV ratings
and removal efficiencies are listed in Table 6.3.1. These were taken from ASHRAE 52.2.
Note that there is a minimum size given of 0.3 μm. Usually particles that are smaller than this
have so little mass that they are unstable as a solid. [Typical molecules range in size from
about 74 picometers (pm) for the smaller hydrogen molecule to 50 angstroms (Å) for large
molecules. This converts to about 0.000074 to 0.005 μm. Many of the smaller molecules exist