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IMPROVING VENTILATION IN OFFICES AND SCHOOLS
HVAC SYSTEMS
In houses and some very old buildings you still find radiators
for heat, and windows for ventilation and cooling. Most modern
office buildings have replaced radiators and openable windows
with heating, ventilating, and air conditioning (HVAC) systems.
These systems consist of ductwork to transport air and fans to
push or pull it through the ductwork. The openable windows have
been replaced by dampers or louvers on the fan housings which
open to bring some fresh air into the system. A thermostat calls
for heating or cooling to maintain the temperature. The air is
transported to all the rooms through the ductwork and blown into
each room through the diffusers to both ventilate and maintain
the desired temperature.
The ventilation system is very important to how you feel when
you work in the building as well as to whether you are warm enough
or cool enough. The perfumes and shampoos that people wear, the
materials that we use in very small amounts like whiteout or glue,
residues from cleaning compounds, the new furnishings and carpeting,
even our exhaled breath impacts the air around us. We need the
ventilation system to keep the levels of these contaminants, byproducts
of normal routine, to a minimum. This is done by constantly bringing
in fresh air and removing stale air. For particular sources of
contamination like a heavily used photocopy machines, we cannot
depend on this "general" ventilation system but should
have a local exhaust system which takes the pollutant away before
it can get into the air which surrounds us and recirculates.
FRESH AIR INTAKE
Air enters the building through the outdoor air intake. This
may be on the roof in a roof-mounted unit or it may be in the
wall of the fan room. Amounts of air coming in are usually controlled
by dampers which can be adjusted to take in more or less air depending
on the outside temperature. In order to get adequate ventilation,
the dampers should be adjusted so that they can never completely
close. A minimum setting which allows for 25% of the air to be
outdoor air is recommended. (Since the energy crisis, the start
of indoor air quality problems in many buildings, air intakes
have been set to take in 10% or less to save on heating and cooling
costs.)
Common problems with intakes:
· There are none. No fresh air is coming in. There should
be at least 20 cubic feet per minute (cfm) of fresh outside air
per occupant coming into each space.
· The intake is poorly located and brings in contaminated
air.
· The intake dampers are sealed shut.
· Pigeons are roosting in the fresh air intake.
FILTERS
This fresh air mixes with air returning from the rooms and this
mixture then passes through one or more filters. The first filter
will usually be a fiberglass filter that catches leaves and feathers
and large dust. Small particles or fine dust may pass right through
as will gasses like car exhaust fumes. There may be other filters
to catch finer dust or even to catch volatile organic carbons
(VOCs) but often there is just one filter for large particles.
Common problems with filters:
· The filters are not changed regularly or often enough.
Should be done at least quarterly.
· The filters are not the right type to remove contaminants
that are coming in.
FANS
The fans with their motors move the air. If they do not have
sufficient capacity they will not bring in enough air. If the
fan is not working properly the air doesn't move, or not enough
of it moves.
Common problems with fans:
· Fan belts are broken or slipping, fan blades corroded,
motors burned out
· Additions have been made to the system but the same fan
is still trying to run it and is not strong enough.
DUCTWORK, DIFFUSERS AND RETURNS
The air is forced by the fans along the ducts to the diffusers
which allow the air into the room. Within the room the air should
mix thoroughly so that the temperature is the same throughout
the room and fresh air mixes in. Good mixing is essential for
good temperature control as well as freshness.
The air should then leave the room through the return. They may
look similar, but the air comes in through the diffuser and leaves
through the return. Use a piece or tissue paper to test these.
The tissue should stick to the surface if the air is being drawn
out and wave if the air is blowing into the room.
Common problems with ducts and diffusers and returns:
· The ducts have been damaged and are no longer connected
to the fan.
· The ducts are lined on the inside with fiberglass which
is breaking down -The ducts may have accumulated large amounts
of dust or have become damp and grown mold or bacteria which is
then distributed with the air
· The ducts are delivering more air to the rooms that are
close to the fan and much less to the rooms that are at the end
of the line.
· Some rooms lack diffusers or returns completely because
walls and partitions have been changed but the ventilation system
was never changed.
· Diffusers have been blocked off, often to change temperature.
· Returns have been blocked, often thoughtlessly, by furniture
and stuff.
· Proper air mixing is not occurring because diffuser and
return are close together and the air goes straight from one to
the other.
· The return air does not have a duct to carry it but passes
instead through the open space above the dropped ceiling. Whatever
is up there, asbestos, pigeons or former pigeons, is swept right
into the HVAC system and recirculates.
TEMPERATURE, HEATING AND COOLING
Somewhere in the system, usually near the fan the will be the
means of heating or cooling the air. The cooling system is usually
some metal coils containing chilled water or a refrigerant which
are inside the duct. The air passes over these cold coils and
is cooled. The air also leaves some moisture in the form of condensation
on the coils. There should be a pan underneath to catch the drips
and the pan should have a drain so that it does not accumulate
water. Some form of heat like an electric heater or hot water
coils or other heated surface may also be found inside the duct
to heat the air when necessary. The air may also be humidified
for comfort in the winter.
Relative humidity affects comfort. The official comfort range
is between 30 and 60 percent with temperatures between 68 and
80oF. This doesn't work for everyone.
Potential problems with the heaters and coolers:
· Water accumulates in the condensate drip pan, mold grows,
and gets into the air.
· The heating or cooling coils get dirty, cutting down
air flow and adding dirt to the airstream.
· Refrigerant can leak into the air system
· Flue gas, products of combustion, can leak into the air
system.
THE WHOLE SYSTEM
Some types of systems, called variable air volume (VAV) systems,
have extra thermostats and dampers above the diffusers. If a room
or group of rooms is already at a satisfactory temperature, the
dampers will close and not allow that room to get any more air.
Others will have a constant flow of air but vary the mixture between
return and fresh or the use of heat and cooling.
Common problems with the whole system:
· It is turned on and off by a timer and starts at, say
8, turns off at, say, 5 and people who work other hours have no
ventilation.
· Nobody knows where the components of the HVAC system
are or how it works.
· No one has checked it since 1948. The last time it was
balanced was when the building was built and many changes have
occurred since then.
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