The coronavirus disease 2019 (COVID-19) pandemic continues to sweep across the globe since the first outbreak in December 2019, has resulted more than 170 million confirmed cases and nearly 3.7 million of deaths across nearly 200 countries, as reported by World Health Organisation (WHO)1.
The COVID-19 is an air-borne virus, which transmits among people through contact of droplets and small airborne particles, when a carrier breathes, sneezes or coughs or through other small respiratory particles. Transmission can also occur if splashed or sprayed with contaminated fluids, in the eyes, nose or mouth, and, rarely, via contaminated surfaces.
Transmission of COVID-19 is found to be more severe in indoors, where people are in close proximity and may come into contact with droplets and aerosolised particles easily. The risk increased significantly in inadequately ventilated spaces where the aerosol particles can be suspended in the air for longer and spread more efficiently.
Precautions is better than cure. Understanding and controlling building ventilation can improve the quality of the air in the indoor spaces and reduce the risk of transmission of COVID-19.
Ventilation is the Key Strategies for Healthy Indoor Spaces
Ventilation is intentionally to introduce fresh air into a space while removing the stale air. The general purpose of ventilation in buildings is to ensure that healthy air is introduce to occupants by removing pollutants. Ventilation is also used for odour control, containment control and often combined with climatic control (temperature and relative humidity).
Enhancing indoor air ventilation strategies has been incorporated in the sustainable building design for decades since the development of green building guideline. ASHRAE 62.1 outlined the methodologies of ventilation design for acceptable Indoor air quality2 and it has been adopted in various of building benchmarking certification guideline such Leadership in Energy and Environmental Design (LEED) and WELL Building Standard. Nevertheless, the green building guideline that emphasis on energy efficiency shall be re-evaluted during this the pandemic, by focusing in the upgrades or improvements to increase the delivery of clean air and dilute potential contaminants.
Overall, there are three main elements contributed to a good ventilation in an indoor space: Fresh air, Filtered air, and Flowing air (the 3F)
Fresh air
Fresh air brings the outdoors into buildings as a new source of clean air that is less contaminated. To introduce fresh air, the simplest way is to just open up the windows or doors to allow improve indoor air exchange. While for fully air-conditioning spaces without openable windows, the introduction of outdoor air can be realised through opening outdoor air dampers beyond minimum settings to reduce or eliminate air conditioning and mechanical ventilation (ACMV) system air recirculation. Apart from that, the demand control ventilation (DCV) controls that reduce air supply based on temperature or occupancy shall be turn off to allow maximum outdoor air supply during occupancy hours.
Filtered air
Filtered air refers to the removal of contaminants from the indoor air space. Most of the ACMV system incorporate with filtration strategy, shall be constantly inspected to ensure a proper filter seal, installation, and model that balances functionality with efficiency. If the indoor spaces required higher level of hygiene (such as hospital and clinic), a high-efficiency particulate air (HEPA) filter such as MERV-13 is recommended. The ACMV filtration system can also be supplemented by adding portable air purifiers to the space. Air portable cleaners not only play a key ancillary role, but they can also act as critical standalone filtration in buildings without a central ACMV system.
Flowing air
Flowing air refers to the circulation of air throughout the indoor environment. The predominant principle of airflow is to prevent the concentration of infectious particles in the air, ideally with the routing of contaminated particles out of the enclosure. Open multiple windows or doors to allow cross ventilation or stack ventilation will improve the air circulation. Apart from that, additional fans such as potable fan or wall mounted exhaust fan will also assist in improving the airflow exchange rate. The fans shall be strategically placed in same direction the air is naturally moving. Avoid placing fans in an orientation where they might directly blow air particles from one individual onto another, which could inadvertently facilitate the spread of COVID-19.
Ventilation Guideline for Different Indoor Spaces
AHSRAE published one of the first building operational guideline during COVID-19 Pandemic where it highlighted some HVAC operational strategies in air-conditioning spaces3. WHO also established a roadmap aims to address the key questions on the assessment of indoor ventilation and provide recommendation to indoor air quality under different setting in order to reduce the risk of spread of COVID-19 4. Centers for Disease Control and Prevention (CDC) provided a ventilation intervention that can help reduce the concentration of virus particles in the air5. Most recently, the Singapore Building and Construction Authority (BCA) provided a Guidance Note to building owners and facilities managers on the key strategies of building ventilation for different indoor spaces6.
We summarised the key ventilation strategies for different indoor spaces for your easy references.
A) Air-conditioning Spaces with mechanical ventilation system
The air-conditioning buildings such as for commercial offices, shopping complex, and hotels usually have the provision of mechanical ventilation system which using fans and ducts to bring in fresh air from outside. To enhance the ventilation system:
- Ensure the mechanical ventilation system are well maintained in line with manufacturers’ instructions.
- Maximise the fresh air intake and increase ventilation rate according to system capabilities
- Disable DCV controls that reduce air supply based on temperature or occupancy (CO2 concentration)
- Purging indoor air daily before occupancy
- Reduce air recirculation
- Keep toilet exhaust fan running
B) Air-conditioning Spaces without mechanical ventilation system
Some air-conditioning spaces do not have a provision of mechanical ventilation with unitary air-conditioning system. The air normally is cooled and recirculated in the indoor spaces which could potentially increase the risk of air contamination. The following strategies shall be considered to improve the air ventilation:
- Provide an opening through door or windows to allow natural ventilation
- Installing window mounted fan system to extract indoor air and bring in fresh air
- Keep toilet exhaust fan running
- Ensure the intact water is sealed in sanitary system
C) Non-air-conditioning or natural ventilation spaces
Natural ventilation spaces rely on passive air flow through windows, doors and vents that can be fully or partially opened. Even with an open window or door, natural ventilation spaces could be exposed to risk of covid-19 contamination if ventilation rate is low with similar inside and outside temperatures. The following strategies shall be considered to improve the air ventilation:
- Enlarge the opening through door or windows to maximize the ventilation exchange rate
- Installing outward-facing fans at window to increase ventilation
- Installing window-mounted fan system to extract indoor air and bring in fresh air
- Keep toilet exhaust fan running
- Ensure the intact water is sealed in sanitary system
While the list of ventilation strategies and guidelines advised by the different authorities can be universally applied across indoor environments, applying those strategies to different building types, occupancies, and activities under environmental and seasonal changes can be challenging. It falls on the building manager, with expert consultation as needed, to identify which guidelines are appropriate for each building throughout the year. Reach out to us if you would like to enhance your building ventilation with a professional advisory!
Reference
- World Health Organization. 7 June 2021. https://covid19.who.int/
- ASHRAE Standing Standard Project Committee 62.1. ANSI/ASHRAE STANDARD 62.1-2013: Ventilation for Acceptable Indoor Air Quality. Atlanta: ASHRAE; 2013.
- American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE). Guidance for Building Operations During the COVID-19 Pandemic. May 2020.
- Roadmap to improve and ensure good indoor ventilation in the context of COVID-19. Geneva: World Health Organization; 2021. Licence: CC BY-NC-SA 3.0 IGO
- Centers for Disease Control and Prevention. Ventilation in Buildings. 2 June 2021
- https://www.nea.gov.sg/our-services/public-cleanliness/environmental-cleaning-guidelines/advisories/guidance-on-improving-ventilation-and-indoor-air-quality-in-buildings-amid-the-covid-19-situation
