Managing Indoor Air Quality:
Through Mechanical Operation and Effectiveness
Since most people spend the majority of their time indoors, the possibility of exposure to chemical or biological contaminants in problem buildings is widespread. Indoor air pollution problems typically fall into one of the following categories: Sick Building Syndrome (SBS), Building Related Illness (BRI), and Multiple Chemical Sensitivity (MCS). Poor ventilation, moisture intrusion, improper chemical storage and/or use are all conditions allowing for indoor air quality problems. Even though some of these problems have been around since the beginning of man’s construction of indoor spaces, increased awareness of indoor air quality issues has been exacerbated lately because of the confined spaces of many buildings built in the last few decades. Sustainable building technologies must take these risk factors into consideration and improve the quality of indoor air in new and remodeled buildings.
Indoor air quality (IAQ) issues often center on the mechanical operation and effectiveness of the heating, ventilation and air conditioning (HVAC) system. Research has shown that up to 60 percent of IAQ-related problems are caused by HVAC systems. At the same time, 80 percent of common IAQ issues are resolved through HVAC modifications. So, HVAC design, maintenance and operation are all critical elements for maintaining a quality indoor air environment.
1. Address ventilation systems during building design or prior to renovation. HVAC system design and operating parameters should be carefully addressed during all construction and renovation projects. Public buildings are frequently used for purposes other than their initial design and may, in fact, have several different applications during the building lifetime. Thus, many buildings end up being occupied beyond the HVAC systems capability and renovations may occur without readjusting the HVAC system to accommodate the changes.
2. Know your building 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 follow:
Carbon Dioxide (CO2). CO2 is a product of nature and of human respiration. It is also an indicator of ventilation effectiveness within a building. CO2 is present in the open environment in average concentrations of 300 to 400 ppm. ASHRAE recommends that indoor CO2 levels be maintained below 1,000 ppm and other groups recommend below 700 ppm for occupant comfort and productivity. 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.
Temperature. ASHRAE recommends that indoor temperatures during the winter months be maintained between 68 and 75 °F and indoor temperatures during the summer months should be between 73 and 79 °F. In practice, complaints may occur with any temperature not maintained at 72 °F with some air circulation.
Relative Humidity. Relative humidity (RH) is the amount of moisture in the air. ASHRAE recommends RH be maintained between 30 and 60 percent for indoor environments. RH below 30 can cause drying of the mucous membranes and discomfort for many people. RH above 60 for extended time periods promotes indoor microbial growth.
Air Exchange Rate. HVAC systems are designed to supply fresh air into the occupied space supplying fresh air into the building and diluting contaminants preventing buildup. 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). CO is a common result of the presence of or proximity to sources of combustion. It is present to some degree when fuel-operated systems are used. High levels are an immediate threat to life. Lower levels are a cause for health concern. Concentrations should be maintained as close to nondetectable as possible.
3. Remediate water-damaged building materials. Water damaged ceiling materials seem to be the hallmark of modern commercial and public buildings, yet these materials harbor mold growth potential. When coupled with the higher humidity of a water intrusion event, the perfect conditions are met for mold to colonize and reproduce. All porous building materials – drywall, wood and particleboard – exposed to water should be replaced quickly to decrease the potential for mold growth. In addition, products such as wall insulation, carpet and carpet padding should be removed, discarded and replaced, as they get wet.
Care should always be taken to make sure that inclement weather does not affect building materials during new construction or renovation.
Source: Sustainable Lands and Buildings in North Carolina