Article from REHVA Journal 1, 2022 – Prof. dr. Philomena M. Bluyssen, Delft University of Technology; Dr. AnneMarie Eijkelenboom, EGM Architecten

Health and comfort of people in the built environment, at home, at work, at school, commuting or during leisure time is a complex matter involving physics, behaviour, physiology, energy use, climate change, architecture, engineering, and technology. The way people feel, experience, and behave is related to the quality of their environment, described by the thermal, air, light and sound qualities. In addition, the resilience of buildings and systems to changing demands and preferences and the ability of people to respond to new buildings and systems affect their perception and behaviour. 

Studies worldwide show that relationships between the indoor environmental conditions (thermal aspects, indoor air quality, light and sound) and well-being (health and comfort) of occupants of office buildings, schools, homes, and hospitals are complex, and not easy to unravel. There are many indoor environmental stressors that can affect health and comfort either additively or through complex interactions. These include thermal aspects (e.g., draught, temperature), visual aspects (e.g., reflection, view, luminance ratios), air quality (e.g., odours, moisture, mould, radioactive radiation, chemical compounds, particulates), and acoustical aspects (e.g., noise and vibration). There are many diseases and disorders related to staying indoors, such as mental illnesses, obesity, cardiovascular and chronic respiratory diseases (think of asthma in children and COPD in adults), cancer, and COVID-19. The COVID pandemic has shown that buildings and systems must be able to provide a resilient environment not only in the long term (with regards to climate change) but also in the short term (during a pandemic, for example).

Ventilation to reduce infectious diseases
If we assume that airborne transmission of SARS-CoV-2 is a serious route of transmission, it is clear that it is not just a question of how much ventilation is required, but also how to ventilate in different situations. ‘Good’ or proper ventilation means, first of all, to provide sufficient and effective ventilation. Ventilation that ensures the supply of ‘clean’ air and exhaust of polluted (infected) air from the breathing zone of each individual person. Preferably, without passing through the breathing zones of other persons, and without recirculation (reusing) of air. If general ventilation is not enough or recirculation cannot be avoided, air cleaning is an option.

How much ventilation is needed? This is not an easy question to answer. Current guidelines for spaces occupied by multiple persons are based on the CO₂ concentration in the air. CO₂ is used as an indicator for the presence of people. With each breath, CO₂ is exhaled. However, it is not clear whether CO₂ is a good indicator for exhaled ‘infectious’ aerosols, because CO₂ is a gas, and exhaled droplets and aerosols are not. This raises many questions about the correct methods for determining threshold limit values for the amount of ventilation. Do aerosols and exhaled droplets behave like gases or do they behave differently? Are there other models we can use if CO₂ is not a good indicator for exhaled infectious aerosols?

Indoor environmental quality in energy-efficient & refurbished buildings
In addition, we must not forget that ‘infectious’ aerosols are not the only possible pollutants present in a space. The debate about other sources of pollution than the presence of people in a space has been going on for a long time, such as emissions of building and furnishing materials, outdoor air pollutants, or pollutants from poorly maintained ventilation systems, as well as all those volatile organic compounds and particles that are released during the activities that we carry out in our homes, offices or other buildings. We must also consider the effects that measures taken to improve ventilation may have on other aspects of the indoor environment. Think about how opening a window introduces outside noise and allows cold air to flow inside. Last winter, many children at school sat in chilly classrooms with all the windows and doors open to get as much fresh air as possible. There were also more problems with noise, caused by the airflow in the supply ducts, because systems were running at their maximum. Moreover, draughts can occur if the supply grilles are not properly adjusted.

In addition, research shows that buildings renovated to address climate change can pose a serious risk to the health and comfort of their occupants. Respiratory, eye and skin problems can occur as a result of certain renovation measures. Insulating and making our buildings airtight can lead to moisture problems, build-up of air pollutants, lack of control, noise and/or overheating. HVAC-systems, although efficient, can cause air pollution, draught, and noise.

Research also shows that such measures do not always yield the desired energy savings. This is partly due to the residents and their behaviour, and partly due to the technologies used and their feedback systems. When renovating energy-efficiently, it is therefore important to take into account the preferences and needs of the occupants.

Flexible systems and climate-resistant buildings
It is important to re-think the way we ventilate, specifically for indoor areas with a hogh density of people during a long period of shared time, such as in classrooms, landscape offices, restaurants, nursing homes, theatres, sports clubs, etc. The new generation of ventilation systems should not just focus on ventilating a space but should offer a range of options so that the changing demands of occupants over time can be met, be it for health or comfort. Flexibility is therefore the key. The COVID pandemic has shown us that more knowledge is needed about the way potential pathogens spread within buildings, about the best conditions and ways to fight infections, as well as ways to create affordable, flexible, energy-efficient, and effective ventilation. The need for related research is obvious. Collaboration between different disciplines, such as epidemiologists, virologists, aerosol experts, structural engineers, architects, psychologists, sociologists, and mechanical engineers is indispensable. The fight against future diseases will have to be taken up together with the challenges that climate change poses to the built environment.