Delivering indoor air quality

Indoor Air Quality

Martin Passingham explores the subject of indoor air quality and how effective ventilation is the cornerstone of achieving an optimal indoor environment.

At a time when we are all spending more time indoors than ever before, being aware of indoor air quality and, more importantly, understanding how to achieve and maintain it, has perhaps never been so crucial.

Even before 2020 and the months of lockdown, we spend on average 90 percent of our time indoors – with some, such as the elderly, spending even more. This is a shocking statistic and serves to demonstrate the importance of creating a clean and healthy indoor environment. There are numerous factors that contribute to the creation of this optimal internal environment, with perhaps the more obvious being the factors that you can physically see and/or easily control, such as light, temperature and acoustics. But what about air quality?

Indoor Air Quality

Easily forgotten, the air we breathe on a daily basis can have a very real impact on our health and well-being, as well as affecting our experience of a space. Defined as the quality of air in and around a building, indoor air quality can be affected by numerous factors, with pollution from both interior and exterior sources able to disrupt the delicate balance.

Sources of outdoor air pollution can include road traffic, industrial processes and construction and demolition sites, with particles able to enter into a building through natural or mechanical ventilation, as well as infiltrating through the building fabric. Indoor sources can include Volatile Organic Compounds (VOCs), which are given off by wall and floor coverings, furniture and appliances; dust, damp and mould; emissions from office equipment; and, of course, occupants themselves, who breathe out CO2 and can spread colds and viruses.

The effects of poor indoor quality can be significant, worsening as the years of exposure increase. In fact, Public Health England estimates that air pollution is responsible for between 28,000 and 36,000 deaths a year in the UK, costing the NHS and private healthcare sector £20bn annually.

Ranging from the mild to the extremely serious, air pollution can cause irritation to the eyes and respiratory systems, the exacerbation of asthma and can even lead to chronic illnesses, such as cardiovascular and respiratory diseases. In addition to the physical effects, there is also growing evidence of the impact poor indoor air quality can have on a person’s mental health, thought to be a factor in conditions such as depression and bipolar disorder, as well as having a detrimental effect on productivity levels.

Given this, it is clear that indoor air quality should be a key consideration of building design, from homes and offices to hospitals and schools, with effective building ventilation at the core of achieving this.


Fundamentally, ventilation works to remove stale indoor air and replace it with ‘fresh’ outdoor air. While opening a window may, on the surface, appear like a suitable solution, this can in fact do more harm than good, allowing pollution from external sources to easily enter the interior space. Instead, correctly designed, installed, commissioned and serviced ventilation systems – as part of a building’s wider HVAC system – can help to prevent the ingress of outdoor pollution, extract water vapour, airborne pollutants and odours from the air, control humidity and ensure a constant supply of fresh, clean air to occupants.

Striking a balance

In our newer buildings, this can require finding a careful balance between energy efficiency and air quality. Given the pressure to reduce running costs and energy consumption, combined with the targets set by BREEAM and LEED assessments, the emphasis can often fall on achieving high levels of energy efficiency within modern building design. While this focus on making a building well-insulated and air tight can help to lower energy bills, it does also make it more difficult to create a natural flow of air around a building – leading to low oxygen levels and increased potential for allergies and odours, as well as the risk of condensation build-up.

Indoor Air Quality

Through careful design and consideration, however, it is possible to strike a balance, meeting the required energy efficiency levels while simultaneously achieving effective ventilation and a clean, healthy and comfortable indoor environment. For example, there are whole building ventilation systems available with various energy efficiency features, such as variable refrigeration temperature control and the ability to reuse waste heat from cooling and refrigeration.

Building Regulations

In the UK, ventilation design is controlled by the Building Regulations Approved Document Part F, which sets out the criteria for both homes and ‘non-domestic’, primarily offices. Of course, it stands to reason that different building sizes and functions will require differing levels of ventilation. For example, the required ventilation rates for homes are based on the number of bedrooms, from 13 l/s for a one-bedroom home to 29 l/s for a five-bedroom property. In comparison, the total air supply and extraction for office ventilation is 10 l/s per person, with intermittent extract ventilation also required for specific areas, such as WCs, photocopying room and kitchens.


As well as designing and installing the ventilation correctly, regular servicing and maintenance throughout its lifespan is perhaps just as essential to ensure it continues to deliver a high level of performance. Given the system’s role of extracting airborne pollutants and providing a constant supply of clean air, the regular cleaning of a building’s ventilation is understandably crucial. Without the correct attention, dust and dirt can build up and affect the system’s ability to maintain indoor air quality.

While ventilation units are already fitted with filters - primarily to keep the system free of dust, as well as to help remove particulate matter from supply air - there is still more that can be done. Regularly checking the supply intake and exhausts for signs of dirt build-up, pollution or contamination, or damage from weather and animals, is good practice, as is inspecting the ductwork and indoor units. Any dust should be removed from the ductwork, with particular attention to the filters, heating and cooling coils and any change of direction in the ducting.

For further guidance on ventilation maintenance, BS EN 15780: 2011: Ventilation for Buildings. Ductwork. Cleanliness of Ventilation Systems specifies acceptable cleanliness levels for supply, recirculation and extract air, grouped into three classes – Low, Medium and High – depending on the use of internal space.

According to the World Health Organisation (WHO), air pollution from both indoor and outdoor sources represents the single largest environmental risk to health globally. Given this, it is clear that incorporating indoor air quality within modern building design is key, with effective ventilation at the core of achieving this clean, healthy and comfortable indoor environment for occupants to enjoy.

Martin Passingham is Product & Training Manager at Daikin UK

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