| Application Considerations Figure A-5 - Possible Air Handler
Location for Particulate Filters
National, state or local codes established by government bodies or occupational
groups may dictate more specific or stringent
filtration requirements for a building, depending
on its type and/or location. Trane offers several types of particulate filters
— including pleated, bag, cartridge and HEPA
— that allow you to match filtration efficiency
with the application needs. See "AHU Components: Filter Module" for selection and application considerations.
Controlling Gases and Vapors. The presence of
certain undesirable gases and vapors (particularly
formaldehyde, radon, oxidants and volatile organic
compounds or "VOC’s") indoors can be detrimental to a building’s occupants, materials and contents. Controlling
VOC concentrations is particularly challenging:
hundreds of them are present, few are unique to any one source, and there are many potential sources, some of which emit several
VOC’s.
Therefore, a common way to control gaseous contaminants
is to dilute them with outdoor air. This approach is
appealing since many VOC’s defy individual treatment. However, it is only practical
if the quality of the outdoor air is suitable and if
the resulting supply airflow is consistent, appropriate
and mixes effectively with the air in the occupied space.
Another method of gaseous contaminant abatement is the
installation of carbon or potassium permanganate filter beds in the air stream.
These gas-phase filters reliably control some VOC’s,
but the costs of acquiring, installing, operating and
maintaining them are high. No approved method for testing gas-phase filters
exists either, making it difficult to effectively
evaluate and apply them. See "AHU Components:
Filter Module" for other application
considerations.
Proper Filter Placement. To promote effective
particulate and gas-phase filtration, apply the
following guidelines when designing the air handler
(Figure A-5):
- Do not place filters downstream of a
blow-thru cooling coil; otherwise, moist air (fog) from the cooling coil may develop and saturate the filter.
- Always place HEPA-type (i.e., > 99- percent efficient) filters in the last section of the air handler to prevent infiltration
through the unit casing from degrading the
filters’ otherwise high performance.
- Provide easy access to encourage regular filter maintenance.
- Establish even air distribution over the entire filter surface to reduce the potentially damaging effect of high air velocities.
Discourage Microbial Growth
While filtration effectively removes a number of common particulate and gaseous
contaminants from the building environment,
microbiological or "microbial" contaminants
like molds, fungi and bacteria are sometimes too small to be filtered entirely from the air stream. Designing the
air handler to include screens on intake and exhaust
openings, a steel liner and easy access to heat exchanging components helps control microbial growth. So does regular cleaning and
disinfecting with nonpolluting cleansers and antimicrobial coatings. But none of these measures totally eliminates the growth
of ever-present microorganisms. Consequently, moisture control becomes another important
means of combatting microbial contaminants. |
