Modern Building Services

MODERN BUILDING SERVICES FEBRUARY 2022 21 FEATURE INDOOR AIR QUALITY More information can be found at www.daikin.co.uk/ indoorairquality Filters Filtration is another important element of ensuring effective ventilation. All HVAC units will be fitted with filters that are designed to keep them free of dust, primarily to ensure good operation and maintain energy efficiency. Choosing indoor units with auto-cleaning filter capabilities ensures that dust can be removed quickly and easily. This not only prevents contaminants and odours circulating in the room but also ensures the unit operates efficiently. Filters are also fitted to remove particulate matter (PM) from supply air. The type of filter required will depend on what is needed to achieve the PM threshold level. This is based on the Air Quality Guidelines published by the WHO. The recommended limits are: an annual mean for PM2.5 of less than 10 micrograms per cubic metre (µg/m3) and an annual mean for PM10 of less than 20 µg/m3. Additional measures In addition to following best practice design, there are further steps that can be taken to improve indoor air quality. Plasma ionisation technology can help remove harmful particles, VOCs, bacteria and viruses from the air. These low- maintenance and cost effective ‘fit and forget’ units can be installed in new or existing systems. While some plasma ionisation devices have to be housed in a separate unit due to their size, there are options that are compact enough to be fitted within the existing system housing. Plasma ionisation, which does not affect the performance of the ventilation, works by producing a stream of positive and negative oxygen ions. The positive ions are missing an electron while the negative ions contain an extra electron. In an effort to restabilise, these ions seek out atoms and molecules in the air to trade electrons with. This effectively neutralises pollutants that come into contact with the ions. Airborne particles such as smoke, dust, pollen and mould spores are charged by the ions and stick together, increasing their size and allowing them to be captured easily, even by lower grade filters. Meanwhile, bacteria and virus cells bond with the oxygen ions as they divide to reproduce and are destroyed. Odorous gases and aerosols are oxidised and neutralised on contact with the ions. When the ions come into contact with VOCs it causes a chemical reaction that breaks down their molecular structure. Good ventilation is an integral part of maintaining a high level of indoor air quality. When designed correctly, taking a whole building approach, the HVAC system can achieve this while also minimising wasted heat and energy use.