Indoor Air Quality Blurb
Know your Building Indoor
Air Quality (IAQ) Baseline
Most building managers have a through understanding
of how the HVAC system and its limitations work to achieve occupant
comfort. Several comfort parameters should be evaluated periodically
and anytime complaints are derived from occupants. The American
Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE)
recommendations for key parameters include:
-
Carbon Dioxide (CO2)
-
Temperature
-
Relative Humidity
-
Air Exchange Rate
-
Carbon monoxide (CO)
Carbon
Dioxide (CO2)
is a product of nature and of human respiration.
Exhaled breath is approximately 4.5% carbon dioxide. It is also an
indicator of ventilation effectiveness within a building.
CO2 content in fresh air varies and is between 300
parts-per-million (ppm) and 600 ppm, depending on location. ASHRAE
recommends that indoor CO2 levels be maintained below 1,000 ppm and
other groups recommend below 700 ppm for occupant comfort and
productivity.
Concentrations higher than 1000 ppm will cause
discomfort in more than 20% of occupants, and the discomfort will
increase with increasing CO2 concentration. The discomfort will be
caused by various gases coming from human respiration and
perspiration, and not by CO2 itself. At 2000 ppm the majority of
occupants will feel a significant degree of discomfort, and many
will develop nausea and headache. Sleepiness, lethargy and
headaches are early symptoms of higher levels of CO2. A CO2 level
approaching this maximum is an indicator of poor air mixing and
represents a general buildup of air contaminants. The U.S. National
Institute for Occupational Safety and Health limits brief exposures
(up to ten minutes) to 3000 ppm and considers exceeding 4000 ppm as
"immediately dangerous to life and health."
The Environmental Protection Agency (EPA) suggest
that increases in the ventilation rates per person among typical
office buildings will reduce indoor CO2 concentrations to
approximately outdoor levels which would be expected to decrease
prevalence of selected symptoms by 85%.
The bottom line is that adding more people to an area
means adding more ventilation.
As a general rule, office temperatures and humidity
are matters of human comfort. ASHRAE Standard 55 – Thermal
Environmental Conditions for Human Occupancy addresses “thermal
comfort” in an office environment as an employee wearing a
normal amount of clothing, for the season, feels neither too cold
nor too warm.
Temperature
ASHRAE recommends that indoor temperatures during the
summer months be maintained between 73 and 79 degrees Fahrenheit.
ASHRAE recommends that indoor temperatures during the winter months
be maintained between 68 and 75 degrees Fahrenheit. These
guidelines will satisfy 90% of the occupants.
Relative Humidity
ASHRAE recommends that relative humidity be
maintained between 30 and 60 percent for indoor environments.
Low humidity
causes static electricity, dry skin and hair, and itching and
chapping. Mucous membranes in nose and throat dry out, increasing
your discomfort and susceptibility to colds and respiratory illness.
With low humidity levels, body moisture evaporates so quickly that
you feel chilled even at higher thermostat settings.
High
humidity
causes constantly fogged windows, musty odor
and/or a clammy feel to the air. Relative humidity above 60
degrees for an extended time period promotes indoor microbial
growth and structural damage.
Check your temperature and relative humidity readings
and determine your IAQ baseline.
Air Exchange Rate
- The rate at which outdoor air replaces indoor air is described as
the air exchange rate. When there is little infiltration,
natural ventilation, or mechanical ventilation, the air exchange
rate is low and pollutant levels can increase causing bad indoor air
quality, building up pollutants, moisture, irritants, and odors that
cannot be easily expelled.
ASHRAE requires the minimum concentration of outside
air supplied to an occupied building to be 20 cubic feet per minute
(CFM) per person in each occupied zone. If HVAC is shut down
overnight, the system should be started at least one hour before
occupancy to provide adequate ventilation. Other contributors to
stale and poorly mixed air include poor location of supply and
exhaust air diffusers, improper building or system design (often
caused by change of building occupancy from original design
configuration with inadequate attention during remodeling), or
indoor structures that prevent free movement of air.
Carbon monoxide (CO)
is an odorless, colorless and toxic gas. Because it is impossible to
see, taste or smell the toxic fumes, CO can kill you before you are
aware of its presence. At lower levels of exposure, CO causes mild
effects that are often mistaken for the flu. These symptoms include
headaches, dizziness, disorientation, nausea and fatigue. The
effects of CO exposure can vary greatly from person to person
depending on age, overall health and the concentration and length of
exposure.
CO is a common result of the presence of or proximity
to sources of combustion (through make up air). Appliance’s fueled
with natural gas, liquified petroleum (LP gas), oil, kerosene, coal,
or wood may produce CO... Running cars produce CO.
Concentrations should be maintained as close to
nondetectable as possible.
Watch your occupancy and air exchange rates when
remodeling existing facilities and make sure your CO producing
equipment is ventilated properly and know
your IAQ baseline.
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