Indoor Air Cartoon Journal, January 2019, Volume 2, #43

The primary role of the HVAC system is to condition air for the comfort and well-being of the people occupying the space it is conditioning. However, if proper care is not taken, the air conditioning effort could turn to discomfort for the occupants. The discomfort is mainly related to thermal, air quality or acoustic problem. Air quality is the most challenging of the three as there are many contributing factors to indoor air pollution in an HVAC system. The decision made to improve the acoustic condition, be it duct size, air volume, and speed control, or acoustic material used in the HVAC system, could have implication on indoor air quality. Decision made to improve the thermal condition, be it temperature or humidity control, air volume and speed control, or movement of air in indoor space could have implication on the air quality.

Furthermore, since occupants cannot do without breathing and air supply comes from the HVAC system, any problem with the HVAC system and its components will have implication on occupants’ comfort, wellbeing, and activities. Therefore, it is essential to understand how things could go wrong with the HVAC system. This statement begs the question, what could go wrong and how to prevent the situation?

Evidence in the literature suggest that emission sources and problems in HVAC systems are mainly (i) chemical, biological or particle emissions caused by the nature of HVAC system components and joints, (ii) contamination of HVAC system components with chemical, biological or particle contaminants, and (iii) impact of poor HVAC system design and operations on indoor air pollution reduction, building pressurization needed to manage infiltration and exfiltration, ventilation, airflow and air exchange rate, and environmental conditions, e.g. temperature  and humidity. Infiltration is the unintentional introduction of outdoor air, which may be polluted or have unfavourable air temperature and humidity, into building through cracks or gaps in the building envelopes. Exfiltration is the leakage of indoor air, which may be conditioned, to outdoor through building cracks or gaps. Both infiltration and exfiltration have energy and acoustic implications.

The first two points – (i) and (ii) – are related to emission sources. Reduction or avoidance of emission from sources will improve indoor air quality. Paying attention to and improving the impact of HVAC system design and operations will reduce building occupants’ exposure to indoor air pollution. What does this understanding mean to facility managers, especially those managing and operating large commercial buildings adopting a centralized air-conditioning system?

Do you want to know more about this topic? Read Batterman and Burge (1995) paper.