Special Maintenance Considerations - Effective Building Maintenance: Protection of Capital Assets - page 119

of media.
Gaseous air cleaning can also be accomplished by the process of
“absorption” where the pollutant molecules (along with water vapor
molecules) merge into the filter media, similar to liquid phase mixtures.
The absorption process produces ionization, enabling chemical reaction
to occur. To enhance this process, sorbents can be impregnated with spe-
cific reagents to enhance their ability to chemically react with specific gas-
eous pollutants.
There are no universal test methods of rating and selecting chemical
filters. However, the following general guidelines can be applied:
Carbon is best applied against contaminants that are higher in con-
centration, heavier in molecular weight, and nonpolar and that have
a higher molecular carbon content. This includes most VOCs and
long molecular chain hydrocarbons. It also works best at lower tem-
perature and humidity conditions.
Potassium Permanganate (KMnO 4 ) performs best against lower
molecular weight compounds, polar compounds such as formalde-
hyde, and reactive inorganic compounds such as hydrogen sulfide
and sulfur dioxide.
Zeolite is particularly effective as a cation exchange media. This
makes it perform well against contaminants such as ammonia and
other nitrogen bearing compounds. It also has a higher surface area
than alumina compounds.
CO 2 and Odor Control
Dilutionventilation is a process by which some percentage of “dirty”
indoor air is continuously replaced by “clean” outdoor air. When evaluat-
ing indoor air quality, the litmus test is how close to outdoor ambient air
standards it comes.
Establishing criteria and methods of controlling minimum ventila-
tion airflow in HVAC systems is becoming more and more complex. In
North Carolina, there are numerous codes and/or standards that apply
to establishing and controlling ventilation rates:
ASHRAE Standard 62.1-2007
ASHRAE/IESNA Standard 90.1-2007