This model shows the interrelationship among key factors that are discussed in the series of modules that are part of this guide. A very simple mass balance model based on this figure could be written as:

Consider the following:

Co: introducing contaminated air is a “root cause” of poor air quality. Most filters collect only a fraction of particles present in the air stream and none of the gas contaminants. The quality of the outdoor air and location of the outdoor air intakes relative to potential sources of contamination are critical.

V: ventilation is a basic component of IAQ management and indoor contaminant dilution. During occu- pancy, ventilation should be continuous, reliable and adequate for the types of activities that are being carried out in the building. It is important to maintain good hygienic conditions in the HVAC system to prevent it from becoming a source of contaminants.

K: supply air must be well mixed and distributed in the occupied areas. “Short circuits” not only reduce the efficiency of ventilation, but rob the building of the benefit: money is spent to heat or cool air that did not provide the anticipated level of comfort and air quality for the occupants.

Think about S: reducing or eliminating indoor sources of contamination is an effective and efficient method of maintaining acceptable air quality. It is better, simpler and less expensive to not introduce contaminants than trying to remove the contaminants after they are brought into the building. When selecting any material, furniture or product that will be inside the building, enquire about emissions and custodial requirements (cleaning products, etc.)

Think about R: the removal of indoor sources of contaminants may be active (controlling entry, filtra- tion, custodial practices, etc.) or passive (settling on surfaces, absorption into materials or “sinks”, i.e. places into the space where contaminants are soaked-up). While useful and sometimes necessary, remo- val is not a substitute for inadequate source management.

For more of the basics of Understanding IAQ, download our module by clicking here.