HVAC systems and Indoor Air Quality

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Heating, ventilating and air conditioning (HVAC) systems are often described as the “lungs” of a building1. They can range in size from small stand-alone units serving a single room to large centrally controlled systems that serve multiple rooms in a building. HVAC systems in modern public and commercial buildings can provide heating, cooling, filtered outdoor air and humidity control to maintain comfort conditions in the building2. However, not all HVAC systems are designed to accomplish all of these functions. Some buildings rely only on natural ventilation while others lack mechanical cooling equipment (air conditioning, AC), and many function with little or no humidity control. Thermal comfort is commonly maintained with heated or cooled air that is mechanically distributed throughout the building.

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The ASHRAE 62.1 standard is intended to protect against “unacceptable perceived indoor air quality”3. According to the ASHRAE standard, acceptable indoor air quality refers to air in which there are no known contaminants at harmful concentrations (verified by authorities such as occupational hygienists) and to which the substantial majority of the occupants (>80%) do not express dissatisfaction. The EPA has stated that health risks associated with breathing indoor air are 2-5 times the risk of breathing outdoor air4. Poor indoor air quality results from failure to control temperature and humidity, moisture, ventilation and sources of pollution5.

Problems with unacceptable indoor air quality and thermal discomfort are likely to occur due to low infiltration of outside air into the building when the occupants keep windows and doors closed due to extreme temperatures5. Poor indoor air quality can lead to building related illnesses such as ‘sick building syndrome’ and multiple chemical sensitivity (MCS). Up to 30% of all buildings suffer from sick building syndrome, which occurs when building occupants experience similar symptoms that occur after entering a building but which subsequently diminish/disappear after leaving the building4. Indoor air quality problems can result in increased absences due to respiratory infections, allergic diseases or adverse reaction to chemicals. These health effects have been associated with the presence of:

  • moisture, water damage
  • microbiological pollutants
  • animal and other biological allergens
  • combustion products such as nitrogen dioxide2,4

According to the ASHRAE 62.1 standard the outside air must also be surveyed and meet ambient air quality standards (i.e. meet the limit values for various air contaminants). The outside air intakes must:

  • be carefully located away from pollutant sources such as vents, chimneys, flues, garages, loading areas, dumpsters and cooling towers
  • prevent rain intrusion
  • manage snow entrainment
  • have bird screens3

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The outside air may have to be treated due to the presence of particulate and vapour contaminants, which can be a significant problem in urban environments. Pollutants include carbon monoxide and particles from vehicle exhausts5. Studies carried out in schools have found that the presence of high levels of outdoor pollutants in the indoor environment can result in increased absenteeism, therefore filtration of the pollutant particles is advisable5-7.

Poorly maintained HVAC systems can exacerbate problems with IAQ such as build-up of dust and moisture2,5,8. Moisture can lead to problems with mold growth, which is difficult to control once it is established4. Therefore proper maintenance of HVAC systems is essential to ensure they provide consistently good thermal and ventilation control while also reducing the risk of biological contamination5. Filters are most often utilized to clean the air in HVAC ducts3. These filters protect the HVAC system components and can reduce the levels of dust, pollens and microorganisms from recirculated and outdoor air streams5. However HVAC/furnace filters must be changed regularly and therefore there are costs associated with this along with the energy costs to maintain the airflow through the filter. New technologies for cleaning HVAC airstreams that are under development include technologies such as ultraviolet germicidal irradiation (UVGI) lamps, photocatalytic oxidation devices, electrostatic devices, activated carbon, treated filters or a combination of these9.

Thanks to Hal Levin of www.buildingecology.com for his comments on this blog post.

Contact Graeme Tarbox if you have any questions on the issues raised in this article: gtarbox@airmidhealthgroup.com or +353 1 633 6820.

This blog is written by Angela Southey PhD
Angela has responsibility for the running of our Virology Laboratory and Environmental Testing Chambers.  Angela qualified with a BSc. in Microbiology from UCC, before going on to complete a PhD in Lung Fibrosis in UCD. She then spent two years working in Japan on Ulcerative Colitis with Tanabe Seiyaku Ltd. Returning to Ireland she took up a senior research position in the Veterinary College, UCD followed by extensive industry experience in the diagnostic area with Wyeth Biopharma and Abbott Diagnostics.

About airmid healthgroup
airmid healthgroup helps clients with products and services related to the built environment to differentiate their customer offerings through health relevant marketing claims. Clients include Dyson, LG, Stanley Steemer, Shaw Floors, 3M, Fellowes, Tarkett, Spring Air and Kenmore. airmid healthgroup creates value for clients through a number of collaborative strategies, including field research projects, environmental test chamber studies and licensing our own intellectual property. airmid healthgroup specializes in studying the relationship between allergens, viruses, bacteria, molds or other ultra-fine particles in the air and on surfaces to the spread of illness and disease in buildings. As a leading authority on biomedical and aerobiology research, they use this deep domain knowledge to improve products and services to make the indoor environment as healthy as possible.


1) Managing Indoor Air Quality by H. E. Burroughs and Shirley J. Hansen, Published by The Fairmont Press, Inc., 2011

2) U.S. Environmental Protection Agency. 2012. Heating, Ventilation and Air-Conditioning (HVAC) Systems

3) ANSI/ASHRAE Standard 62.1-2013 Ventilation for Acceptable Indoor Air Quality

4) U.S. Environmental Protection Agency. What are the trends in Indoor Air Quality and their effects on human health?

5) U.S. Environmental Protection Agency. 2003. ‘Indoor Air Quality and Student Performance’ EPA/402/K-03/006 Washington DC.

6) Chen, L., B.L. Jennison et al. 2000. Elementary school absenteeism and air pollution. Inhalation Toxicology 12(1):997-1016.

7) Makino, K. 2000. Association of school absence with air pollution in areas around arterial roads. Journal of Epidemiology 10(2):292-9.

8) Sieber, W.K. L.T.Stayner., et al, 1996. The National Institute for Occupational Safety and Health (NIOSH) Indoor Environment Evaluation Experience. Part Three: Associations between environmental factors and self-reported health conditions. Journal of Applied Occupational and Environmental Hygiene 11(12) 1387-1392.

9) U.S. Environmental Protection Agency. 2008. Critical Assessment of Building Air Cleaning Technologies. EPA/600/R-08/053.


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