Eliminate
Indoor Air Pollution
There are three
main sources of potential indoor air pollution from heating, ventilating
and air-conditioning systems: standing water, man-made mineral fibers
and combustion products.
Standing
Water
Eliminate the
potential for standing water in ducts and HVAC equipment. Pay particular
attention to coils, drain pans, humidifiers and cooling towers.
Coil drain pans should have:
- a generous
slope to a drain equipped with a trap and a trap primer.
- traps deep
enough to ensure that water will not be drawn back into the pan.
- an air gap
between the pipe end for inspection.
- sufficient
space for continuously sloped drain piping, avoiding high pockets.
Humidifier and
cooling coils should be located so that moisture droplets and condensation
will not accumulate on duct surfaces. Avoid placing duct liners
or other absorbent materials within 10 duct diameters downstream.
Cooling towers
should be located distant from outdoor air intakes, and specified
with drift eliminators with water treatment facilities convenient
to the tower. Post logs at each tower, detailing treatment and inspection
dates and the amount and type of chemicals added. Treatment schedules
should reflect manufacturer requirements and local water quality.
Provide access
hatches and prominent identification signs that make inspection
and cleaning of cooling coils, drain pans and humidifiers simple.
Hatches should allow easy cleaning of equipment and downstream ducts.
Post a log at each, identifying dates and observations of inspections
and cleanings.
Designers, contractors
and commissioning agents should ensure that field installations
do not compromise drain slopes or hide inspection hatches and signage.
HVAC system
operation manuals and operator training should specify a frequent
and regular inspection schedule, with cleaning of potentially wet
areas.
Man-Made
Mineral Fibers
MMMF sources
in HVAC systems include insulation within packaged equipment, duct
liners installed for noise control, and damaged ceiling tiles and
fibrous insulation in contact with return air.
In ducts and
equipment, liners, silencers and equipment insulation should include
a tough waterproof membrane installed on the air side, and exposed
seams should be protected from fraying.
Return air plenums
with fibrous ceiling tiles or exposed fiberglass and rock wool insulation
should be avoided if possible; standard filters do not remove all
damaging fibers from the air stream. Ducted return air systems or
returns directly from conditioned spaces are preferable.
If a return
plenum with exposed mineral fiber is unavoidable, ensure that it
is continually under negative pressure. Obstructions to plenum airflow
can positively pressurize portions of a plenum, resulting in intermittent
puffs of air contaminated with MMMFs and dust. Site review and commissioning
should look for obstructions to plenum airflow, and measure relative
pressures between plenums and occupied areas.
Backdrafting
and Spillage of Combustion Products
Boilers and
furnaces located within a building are vulnerable to backdrafting
and spillage of combustion products, especially with high exhaust
rates and static pressures. To avoid occupant exposure:
- Provide generous
amounts of combustion air, with low-static pressure loss supplies.
- Isolate the
combustion chamber from occupied spaces, using sealed combustion
chambers, forced or induced draft equipment, or by sealing equipment
rooms.
- Consider
the effect of building exhausts on combustion equipment venting.
Provide adequate make-up air for exhausts, especially those with
large flows and static pressures.
Cautions
- Building
owners and contractors should be made aware of the potential health
hazards of exposed mineral fibers in return air plenums if return
ducts are eliminated as a cost-reduction measure.
