Housing

THE INS AND OUTS OF AIR POLLUTION

In this article, Paul Williams, Domus Ventilation Product Manager, looks at indoor air pollutants, which include external NO² and PM2.5 pollutants, but also those generated by activities conducted within the house such as cooking and cleaning. He also covers the ways these can be addressed, from removing the pollutant at source through to dispersing them through effective ventilation.

Air pollution is well and truly headline news, be it clean air zones and debates around their implementation and effectiveness, through to the inquest this year on the death of a nine-yearold girl in 2013, which found she had been exposed to “excessive” levels of pollution near her home in south-east London which contributed to her death. The inquest found surrounding levels of nitrogen dioxide (NO²) exceeded World Health Organisation (WHO) and European Union guidelines. This is the first time air pollution has been recognised as the cause of a person’s death in the UK.

London is far from the only place in the UK to exceed pollution limits and thousands of people are directly affected by continually breathing in toxic air. The Government’s latest data shows that NO² limits are being exceeded in 33 out of 43 air quality assessment zones. Earlier this year, the UK was found guilty by the European Court of Justice of “systematically and persistently” breaching air pollution limits.

Measures to tackle air pollution have been announced by the Government, which cover both NOx (the collective name for oxides of nitrogen) and PM2.5 (particulate matter which is a mixture of solid particles and liquid droplets such as soot). It aims to have new legal air pollution limits in place by October 2022, which will be informed by WHO guidelines. The Government has also said it will invest an extra £6m for local councils to improve air quality.

So, air pollution is being taken seriously and measures are being put in place, but are we in danger of missing the elephant in the room? We spend 80 to 90% of our time indoors and, whilst we are at risk of polluted external air entering our homes, that’s not the full story. By focusing on external air pollution, are we in danger of sidelining indoor air pollution?

What are the indoor pollutants?

When it comes to outdoor air pollutants, the focus is very much on NO² and PM2.5, with the key emissions sources being transport and domestic fossil fuel burning respectively. For those living near busy roads and in builtup areas, these emissions remain a problem indoors, as well as outdoors, as they readily enter homes around closed doors, through windows etc.

But pollution is also generated by activities conducted within the house. Levels of PM increase by burning fossil fuel such as gas cookers and heaters. Cleaning equipment often contains harmful toxins that accumulate indoors. Even seemingly innocuous items, such as furniture and the very materials homes are built from, can release potentially harmful pollutants if properties are poorly heated and ventilated.

Sadly, this is a much under-studied area and our knowledge of the sources and worst effects of indoor air pollution is lacking.

How to address indoor pollutants

The first and easiest way to address potentially harmful pollutants indoors is for tenants to switch to non-toxic cleaning products. However, that is clearly out of your hands.

The second is to move away from fossil fuels in properties. For most, that means moving to electric. Whilst the first two focus on removing the pollutant at source, the third way to address pollutants in residential properties is to disperse them through effective ventilation. Basic mechanical ventilation, such as bathroom and kitchen fans, are essential and will remove a level of pollution, but to truly make a difference you need to turn to mechanical ventilation systems.

Effective ventilation = mechanical ventilation

Mechanical ventilation, in the form of intermittent extract, continuous extract or supply and extract, are recognised as the most proficient means of ventilating a modern property.

Mechanical extract ventilation (MEV) and mechanical ventilation with heat recovery (MVHR) systems actively extract air from wetrooms (kitchens, bathrooms, utility spaces) via ducting to a central ventilation unit which exhausts to the atmosphere. In the case of MVHR, there’s the added benefit of supply and extract ventilation combined as these systems re-use waste heat from the extract air and use it to efficiently pre-warm the fresh air drawn into the building using a heat exchanger. The filtered, pre-warmed air is then distributed around the home, effectively meeting part of the heating load in energyefficient dwellings. Domus Ventilation’s new HRXE-HERA and HRXE-AURA MVHR units feature advanced heat exchange proficiency, enabling up to 95% of waste heat to be recovered.

Both MEV and MVHR systems provide effective ventilation, are energy efficient and extremely effective at dispersing polluted air.

Even with these clever systems, they still rely on bringing outdoor air in so, in more polluted areas such as cities, you will need to combine them with a filter. The Domus Ventilation NOX-FILT, for example, works on the supply leg of the ducting system of a mechanical ventilation system and prevents up to 99.5% of NO² pollution from entering a home. There are two units in the range with the second one having the added benefit of a PM2.5 pre-filter.

Because of the nature of these systems, which require extensive ducting, they are mostly suited to new-build properties. For existing properties, the most costeffective options are bathroom and kitchen intermittent extraction fans (axial and centrifugal) and positive input ventilation units (PIV). PIV units are a cost-effective method of eliminating moisture from the home by gently pressurising a dwelling to expel stale and humid air through natural ventilation points. They can be mounted either in the loft area of a house, or a hallway cupboard of a flat.

Getting to grips with indoor air quality

We certainly don’t want to detract from the work being done to improve external air quality – it’s literally life saving – but we do need to start taking indoor air quality seriously. We should feel safe in our homes.  www.domusventilation.co.uk