Indoor Air Cartoon Journal, June 2020, Volume 3, #107
People started moving back to their air-conditioned buildings in several countries after government ease restriction on stay-home-order because of the need to continue businesses, education, and life in general. Everyone is now scrambling to understand what to do to reduce airborne transmission of the coronavirus (SARS-CoV-2), causing COVID-19, in buildings. One of the prominent recommendations, by ASHRAE (The American Society of Heating, Refrigerating, and Air-Conditioning Engineers), for reducing the transmission is ventilation. Ventilation is the use of outdoor air, regarded as “new” air, to replace and clean aged or “used” air.
The intent of replacing and cleaning aged air with outdoor air is to ensure indoor occupants are exposed to clean or fresh air. The cleaning is done through the dilution effect. The underlying principle of the dilution and replacement effects of the ventilation process is to eliminate and reduce the resident time of pollutants in the indoor air. In essence, ventilation helps turn an unhealthy link between a source of air pollutants and indoor occupants to a healthy link. Air is a link as it serves as a medium that carries air pollutants from the source of air pollutants to wherever occupants are in the buildings. Ventilation ensures exposure to clean air and the absorption of clean air into the human body.
If the coronavirus is emitted into indoor air by infected people (sources) present in a building with little or no ventilation, the concentration of the virus will increase because of little or no cleaning or replacement of the aged air containing the virus with clean outdoor air. No wonder healthy indoor environmental quality conscious professionals are advocating for “adequate” ventilation.
In naturally ventilated buildings, opening windows will help reduce the concentration of coronavirus. In air-conditioned buildings, the focus of this article, the opening of a damper to allow for the amount of outdoor air corresponding to the occupancy density, occupants’ activities, and potential emission rate and duration of emission of air pollutants from sources in the indoor environment will be appropriate.
The underlying assumption is that the ventilation process involves the use of clean outdoor air. What if the outdoor air is not clean? What would be the implications of adopting unclean outdoor air for ventilation? What is the impact of poor air quality on the viability of coronavirus?
The higher the rate at which the outdoor to indoor transport of air pollutants occur and the concentration of air pollutants the outdoor air contains, the higher would be the concentration of air pollutants of outdoor origin in the building. Exposure to a high concentration of air pollutants will increase the pollutants’ probability of finding their way into occupants’ bodies.
It is important to note that the use of ventilation comes with energy implications, especially in parts of the world experiencing a tropical climate. Recirculation of a large proportion of conditioned air is essential for saving energy in such areas. Nevertheless, the need to save energy through recirculation of conditioned air does not mean ventilation should not be used or used inappropriately. The need to achieve thermal comfort contributes significantly to the energy consumption attributed to air-conditioned buildings. How to navigate through energy savings and indoor air quality improvement challenges, especially during a pandemic?
The primary purpose of ventilation is to improve indoor air quality and its effects on indoor occupants. The impact of ventilation on thermal comfort is secondary. You do not necessarily need ventilation to achieve good thermal comfort, as the use of fans to move air and recirculation of thermally conditioned air can perfectly help deliver thermal comfort. Flowing with this line of thought, can decoupling of ventilation and recirculation in the air-conditioned buildings in the tropics or areas experiencing tropical conditions help to achieve the balance between energy-savings and healthy indoor air? What are the potential challenges of the decoupling idea in practice?
Researchers (Sekhar et al.) at the Department of Building at the National University of Singapore have done several research works on the decoupling idea. Their findings suggest potentials for the decoupling idea. It is high time for the industry to explore how this idea can be effectively adopted in practice. How can we ensure the effectiveness of our ventilation strategies to ensure the delivery of clean indoor air at the breathing zone with the least amount of building energy consumption? What does effectiveness mean?
Creative approaches are needed to balance the need to save energy while ensuring healthy thermal and indoor air quality. Unfortunately, it is not uncommon to find building owners and facility managers and operators choosing to go for an easy way out. Some choose non-usage of ventilation or usage in a limited manner to save energy consumption in their air-conditioned buildings.
Such unethical culture could make designers not to pay attention to the design and location of outdoor air intake because of the underlying assumption that ventilation is not a priority at building occupancy stage. The unethical assumption could be the root cause of outdoor air intakes being located near sources of air pollutants, like heavy traffic, exhaust grills, rubbish bin, smoking areas, and delivery bay. Building owners and facility managers now forced to use ventilation more than they typically used because of the coronavirus. The probability of experiencing high outdoor to indoor transport of air pollutants and the offensive smell is high if the outdoor air intake is poorly located.
Consciousness for healthy buildings and awareness on the implications of where the outdoor air intake is located will inform the decision on the specifications, usage, and maintenance and operation of air filters and other air cleaning strategies in the air handling unit. Where is the outdoor air intake of your building located? If the outdoor air intake is situated poorly, what measures are being taken to manage the potential implications while maximising the benefits inherent in ventilation, especially during the COVID-19 pandemic?
Do you want to learn more about this topic? Read Macneill et al. (2016), Quinn et al. (2015), Rock and Moylan (1999), Sekhar et al. (2006), and Seppenen (2008) papers.