Staying safe indoors

Air purification kit
A 5-step air purification system is used in LG cassettes

Improving air quality in our indoor spaces has never been more important. Andrew Robinson of Exi-tite explains why. 

Most of us recognise that air pollution is a major threat to health in the modern world. We have all seen warnings of the impact emissions from diesel and petrol engines, plus the effect burning fossil fuels, can have on our daily lives.

Public Health England figures show that pollution causes between 24,000 and 36,000 deaths in the UK every year, making it the fourth biggest killer after cancer, obesity and heart disease.

But perhaps one of the biggest hidden dangers is an assumption that we can protect ourselves from the airborne perils of the outside world by heading inside and closing the door. In fact, indoor environments are between 5-10 times more polluted than outside, due to a combination of affected outdoor air and further impurities generated inside.

 Cocktail of risk

Particulate matter is viewed by the World Health Organisation as one of the pollutants most damaging to health because it can penetrate deep into the bloodstream and organs, via the lungs. The smaller the particles, the more harmful they are because they are more easily moved through the airways to other parts of the body. The size of fine particulate matter is PM2.5 or below, with increasing attention now being focused on PM1.

Further indoor impurities are caused by the air we breathe out, dust from people and processes, and from fixtures and fittings including carpets and furniture. Added to that is carbon monoxide (CO) from gas appliances, carbon dioxide (CO₂) build-up in poorly ventilated areas, volatile organic compounds, radon, mould and excessive humidity.

Finally, the Covid-19 pandemic underlined the serious threat viruses pose, particularly when they can spread through the air in the form of droplet particles. Airborne viruses can infect the respiratory system and spread easily in crowded spaces without proper ventilation.

That’s a pretty potent cocktail of risk and, with most people estimated to spend up to 90% of their time inside, it is clear to see why the way we address the issue of indoor air quality (IAQ) is so important for the health of this and future generations.

The good news is that, while outdoor pollution is dependent on many factors which individuals and organisations may feel they are unable to influence, at least in the short term, the ability to manage our IAQ is well within reach.

 Creating a healthy space

Correct operation and maintenance of HVAC systems to improve the indoor environment while reducing risks hold the key, with four main factors involved in managing airflow and creating a healthy space with minimal risk of infection:

  1. Ventilation – With 100% fresh air, provides highly filtered outdoor air to occupants
  2. Air purification and filtration - Single-space particle filtration units can help reduce or lower concentrations of infectious aerosols
  3. Hygienic technology - Ultraviolet germicidal irradiation can inactivate microorganisms
  4. Temperature and humidity - Microorganism are less likely to survive in relative humidity (RH) between 40-60%, with RH below 40% likely to increase infections

Ventilation is required in all occupied buildings. It is particularly important in areas where moisture is produced, such as kitchens or bathrooms, as excess moisture can lead to mould growth. Whether natural or mechanical ventilation is used, contaminants are reduced by bringing fresh air into the building.  All systems need to be tested for correct flow rate and must be maintained regularly, including changing filters, to keep them working efficiently.

 Choosing the right filter

Mechanical ventilation with heat recovery (MVHR) systems can reduce energy consumption while maintaining the required ventilation. They are an important tool in maintaining good IAQ and should always be equipped with the highest appropriate quality of filtration.

The introduction of fresh air is clearly important but external conditions can have a major impact. For this reason, filters have a crucial role to play in removing major pollutants from the outside air as it enters a building via ventilation and air conditioning systems. As well as recognised standards for the application of filters, there are also ratings for low energy filters. The use of ePM1 class filters is recommended in buildings that are close to roads and in city centres, but the higher grade of filtration typically results in lower airflows and deviation of system design when used on retrofits, or increased airflow requirements and upscaling in fan size on new equipment.  This consequence is because of the increased airflow resistance of higher-level filtration.

Life cycle costings

Whilst thought of as a minor factor in ventilation equipment, the investment in the type of filters that are used can have a large impact on equipment life cycle costs.  We can calculate the expected energy requirement using the formula in Figure 1 that takes into account airflow, pressure drop, service time and fan efficiency.

Q = Energy demand (kWh)

Figure 1
Figure 1

Dp = Average pressure drop over the filter during the service time (Pa)

h = service time (hours)

qv = the flow rate by volume (m3/s)

h= Total fan efficiency (%)

Example of an eight-pocket bag filter with a filter grade of ePM1

Air flow rate = 1 m3/s

Average PD = 170 Pa

Service time = 8,760 h

Fan efficiency = 50 %

A normal configuration of filters within an air handling unit would consist of coarse panel filters acting as a pre filter and then bag filters offering further air filtration. Using a panel filter as a pre filter would lead to increased overall pressure drop and, when relating back to the equation above, would result in a higher energy demand.

Recent developments by filter manufacturers like Mann + Hummel have led to eco filters being manufactured with the sole aim of reducing the life cycle cost of equipment without compromising on IAQ. These filters include integrated pre filters and utilise nanofibres into the construction to provide low pressure drop characteristics usually found in glass bag filters with the added benefit of the depth loading that comes from synthetic material.

When comparing complete life cycle costings that include purchase and disposal costs, we can realise an overall cost saving of up to 50% using eco filters instead of traditional filter media in addition to similar percentage gains in reduction of CO₂ emissions.

Purification and filtration

In addition to ventilation, IAQ can also be improved locally by the use of air purification and filtration. Solutions such as the indoor cassette range from LG (including Dual VANE 4-Way, Round and 1-Way units) feature a powerful 5-step air purification system which removes odours, germs, and PM 1.0 fine dust. With indoor air cleaning, 99% of ultra-fine dust (size 50nm~ 100nm), bacteria and viruses can be removed. The process comprises pre-filter, dust electrification, PM 1.0 filter, deodorisation filter and ioniser. The PM 1.0 sensor monitors air quality and with the central controller or monitor units, IAQ can be managed in real time with a remote control or smartphone.

Wall-mounted units from the same manufacturer include an AirCare system with the following benefits:

  • Pre-filter - Traps large dust particles from the outset
  • UVnano - Removes 99.99% of bacteria on the fan (Including 0.1~0.3 ㎛ in size)
  • Plasmaster Ionizer+ - Removes more than 99.9% of bacteria (Including 0.1~0.3 ㎛ in size)
  • Auto Cleaning - Prevents bacteria and mould and dries the moisture inside the indoor unit to keep it clean.

Efforts to combat the threat of indoor air pollution have been magnified by the need for improved air management during and after the Covid-19 pandemic. Effective ventilation and air treatment solutions have never been higher on the agenda and making the right choices on equipment to manage IAQ has never been more important.

Andrew Robinson is MD of Exi-tite

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