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)
- 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.
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.
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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