INDOOR AIR QUALITY BASICS
Indoor air quality (IAQ) is paramount to occupant productivity and health. The benefit can be several times the energy cost to operate a facility. Unfortunately, IAQ is often ignored and misunderstood. Today's society is focused on energy reduction and savings, and as a result, outside air intake flow rates are often reduced to levels below those required for proper dilution of contaminants. Owners and facility managers lose sight of the fact that the primary purpose of the ventilation system is to ensure human well-being and comfort. Acceptable indoor air quality is not a simple metric. Unlike temperature and humidity, poor IAQ is not always easy to identify.
Poor indoor air quality can occur when contaminant levels in a space build up as a result of inadequate dilution with outside air. Contaminants can come from building materials, furniture and fixtures as well as from the occupants themselves in the form of bioeffluents (body odor).
Not all contaminants can be easily measured, and not all contaminants have documented safe levels. Therefore, ASHRAE (the American Society of Heating, Refrigerating and Air conditioning Engineers) has established the Ventilation Rate Procedure (VRP) in their Indoor Air Quality Standard (Standard 62.1-2010). The VRP specifies the minimum ventilation rates of outside air that must be provided to the breathing zone of occupied spaces to adequately dilute contaminants to an acceptable level. It is a MINIMUM standard, and higher ventilation rates have been shown to improve occupant productivity and health.
Outdoor air is brought into a building by the mechanical HVAC system air handling units. Outdoor air intake flow rates are controlled by dampers (air control valves) or fans. Outdoor air ventilation rates are dynamic, and can change as a result of system design, load and population. In addition, external factors such as wind and stack pressure variations will affect the outdoor air intake flow rate into a building.
The best way to ensure that the outdoor air ventilation rate is maintained is to directly monitor the outside air intake flow rate. Depending on the complexity of the control system and the building dynamics, dampers and/or fans can be modulated to precisely maintain the desired outside air intake flow rate under all conditions as measured by an accurate, repeatable and reliable airflow measuring device.
Ebtron thermal dispersion airflow measuring devices provide the accuracy, measurement repeatability and reliability required for the direct measurement of outside air intake flow rates.
For additional information:
Overview of ANSI/ASHRAE Standard 62.1 – 2010 Ventilation for Acceptable Indoor Air Quality
Overview of International Mechanical Code – IMC 2009 Requirements
IAQ: Productivity vs. Energy
Application Engineering and Control Strategies
Dilution Ventilation
Pressurization Strategies
Control Strategies
Multiple Sensor Densities Allow for Placement Flexibility
