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2017-12-06 Comments (0) Help & Advice, UK News

Air Quality and MVHR

Air Pollution and Health

Image Source: Wikimedia

Air pollution is quickly becoming the biggest worldwide issue of our time. As city populations increase so does the amount of traffic and infrastructure. Air pollution levels are rising and governments are finding it harder to tackle these soaring levels.

Although outdoor air quality levels are constantly monitored and reported, air pollution isn’t just an outdoor issue. The average person spends 90% of their time indoors, whether it be at work, at home or pursuing other indoor activities. Indoor air pollutants arise from a number of factors, outsider air coming into a building being one of them. Indoor air pollution can also be caused by building materials and cleaning products. Activities such as smoking or cooking and biological substances such as mould, bacteria, pests and dust mites also contribute (Nice, 2017). When humans are exposed to such pollutants for long periods of time, it can have a severe impact on a persons health. The British Lung Foundation state “It’s no exaggeration to say that air pollution is a public health crisis. It contributes to up to 40,000 early deaths a year across the UK” and around 10,000 of those are in London.

Current Regulations

Action to manage air quality and reduce pollution levels is largely driven by EU Legislation, including The Ambient Air Quality Directive and The Air Quality Standards Regulations. In the UK, responsibility for meeting air quality limit values is devolved to national administrations in Scotland, Wales and Northern Ireland. The Department for Environment, Food and Rural Affairs has the responsibility for meeting the limit values in England and they also coordinate air quality plans for the UK as a whole.

Research and Government regulations focus on outdoor air quality. Directives consider the harmful levels of Nitrogen Oxides, Carbon Monoxide, Radon, VOCs and Ozone.

The Department for Environment, Food and Rural Affairs (DEFRA) publish UK air quality levels online, which are searchable by area and provide daily forecasts to inform people whether the air pollution levels are expected to be low, moderate, high or very high. They also post regular updates regarding air pollution news, highlighting the efforts the government is making to try and decrease pollution levels. Recently the government imposed a T-Charge for older vehicles passing through the Congestion Charge Zone. The T-Charge is £10 per day and is a required payment on top of the Congestion Charge for those vehicles that do not comply with Euro Standards Euro 4/IV and Euro 3 for motorcycles and quadricycles.

Air Quality Management Areas

Since December 1997 each local authority in the UK has been carrying out a review and assessment of air quality in their area. This involves measuring air pollution and trying to predict how it will change in the next few years. The aim of the review is to make sure the national air quality objectives (PDF) will be achieved throughout the UK by the relevant deadlines. These objectives have been established to protect people’s health and the environment (DEFR, 2017).

Local authorities have a unified objective to help the UK, as a nation achieve the target low pollution levels. If a local authority finds any place where objectives are not likely to be met, it must declare an Air Quality Management Area there. An Air Quality Management Area can range from be a couple of streets to an entire neighbourhood.

A report published by DEFRA quotes “The most immediate air quality challenge is tackling the problem of nitrogen dioxide (NO2) concentrations around roads, which is the only statutory air quality obligation that the UK is currently failing to meet.” Nitrogen Dioxide is one of a group of gases called nitrogen oxides (NOx). While all of these gases are harmful to human health and the environment, NO2 is the greatest concern.

 Air Quality Indoors

Indoor air quality has been largely over shadowed by the focus on air pollution outdoors, mostly related to transport and industrial emissions.  The Clean Air for Europe programme (CAFE) was launched in March 2001 with the aim to develop long-term, strategic and integrated policy advice to protect against significant negative effects of air pollution on human health and the environment.

Regulations mainly focus on the energy efficiency of a building rather than the indoor air quality and therefore the health of the occupants. Although cutting energy consumption levels has an effect on air pollution over time, it does not have an immediate effect on the air within a building. Ventilation is key to achieving healthy indoor air and it is vital policies start to consider not just energy consumption levels but the quality of the air we are breathing in our homes, at work or in other public buildings.

Approved Document F, section 4.6 states ventilation is simply the removal of ‘stale’ indoor air from a building and its replacement with ‘fresh’ outside air. It is assumed within the Approved Document F that the outside air is of a reasonable quality.

Building regulations suggest a number of ventilation methods, including mechanical ventilation with heat recovery. As homes are now being built more air tight than their predecessors, MVHR (mechanical ventilation with heat recovery) is an ideal solution for providing fresh air into a building whilst achieving significantly lower energy consumption than previous designs. With heat recovery rates of up to 98%, house builders are finding MVHR is an affordable and effective means to meet building regulations and to provide comfortable living conditions.


Heat Recovery systems not only provide a constant input of fresh air and extraction of stale, moist air but also manage to retain the heat in the process. This is achieved by using the heat from the outgoing air to warm the incoming air to a very similar temperature without the two airstreams ever coming into contact, and in turn cutting down fuel bills.

Image Source: Next Generation

At the very heart of every Heat Recovery system is the Heat Exchanger. These usually consist of an interlaced series of plates that stack warm and cold airways alternately, warming the cold incoming air whilst simultaneously cooling the warm outgoing air and “exchanging” the heat. The air is moved around the ducting system by two fans, one for the extraction and one for the air supply. The unit runs continuously to provide a constant rate of air change, the only time that this air flow changes is when the unit is boosted, either manually or automatically, via a control surface, at times of high occupancy, high humidity or odour.

A great benefit of MVHR is, not only can it provide substantial energy savings; it also allows a great degree of control over the incoming air entering the building. All incoming air passes through a filter in the MVHR system before passing into the habitable areas of a building.

MVHR Filters

MVHR is an immediate solution to managing the pollution levels of indoor air quality as it allows full control of the input air. It is important to consider not only the positioning of the input air (which should be positioned away from busy roads or other highly polluted areas) but to also consider the systems components. The industry filter standard for most MVHR units is G3 and G4 filters, these filters are able to capture larger varieties of pollen and larger particles of atmospheric dust. They have a limited effect against fine dust, fine pollen and carbon black particles and other particulate matter. G4 grade filters are ideal as primary filtration, ideally for optimum air filtration should be followed by further filtration.

Grade F filters are commonly available as an upgrade. It is a Passive House requirement that the filters used at the air suction point are a minimum grade of F7. A development next to a busy road, beside a hay field or close to an industrial estate may have F7 filters as a minimum requirement in the building specification. F7 filters are usually made from fiberglass and are effective for particles >0.1mm. Able to capture pollen, spores, cement dust and smoke (not tobacco), F7 filters should be a major consideration for allergy sufferers and those wanting to decrease indoor pollutants. F7 is also the minimum grade filter for catching carbon black.

Carbon filters are now being used in Heat Recovery systems. Primary filtration such as G3/G4 and F7 filters are used first and then Carbon filters are included because of their ability to efficiently filter NO2 and other harmful pollutants.

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