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Striking a balance

Martin Passingham, Product Manager at Daikin discusses how both improved indoor air quality and a drive for increased building energy efficiency can be achieved by taking a whole-building approach to HVAC

In order to improve energy efficiency, building air-tightness has increased in recent years, potentially having a negative impact on indoor air quality (IAQ) if the building HVAC system is designed incorrectly.

The current requirements concerning building efficiency are set to increase, with the Government announcing updates to the Building Regulations that apply from June 2022. In the update, CO2emissions from new buildings, including shops and offices, are to be reduced by 27 per cent compared to the current standard. To address concerns regarding IAQ, Approved Document F: Ventilation also received an update. This included indoor air quality monitoring in all occupiable rooms in offices, rooms where members of the public gather and rooms where ‘aerosol generating activities’ take place, such as singing and aerobic exercise. The changes do not apply to small floor spaces, up to 50m2, and larger floor spaces, over 320m2.

The importance of IAQ

The health risks associated with air pollution are well understood and the fact that people spend an estimated 90 per cent of their time indoors should makes IAQ a key consideration.

Road traffic, industrial processes, waste incineration and construction and demolition activities all generate air pollutants, including particulate matter, nitrogen dioxide (NO2) and carbon monoxide (CO). These substances, as well as allergens such as pollen, can be brought into a building through natural or mechanical ventilation and via inadequate filtration through the building fabric.

There are also sources within a building, including dust, damp, mould and Volatile Organic Compounds (VOCs), which can be given off by wall and floor coverings, furniture and appliances, and emissions from office equipment and industrial machinery. Building occupants also affect IAQ, by exhaling CO2 and spreading germs and viruses.

Designing HVAC for IAQ and efficiency

When designing and specifying HVAC systems, the main focus is often on operational energy use and efficiency. However, BREEAM also rewards the use of HVAC that maintains high air indoor quality by controlling temperature, humidity and pollutants and ensuing a sufficient supply of fresh air for occupants. By choosing the right system there is an opportunity to satisfy both requirements.

Heat recovery

The heat loss that occurs during the exchange between indoor air and fresh outdoor air is the primary issue for energy efficiency with regard to ventilation. To help minimise this, effective heat recovery implemented into the system can further improve the energy efficiency of the HVAC. For example, in an office space, servers can generate large amounts of heat. With considered planning, this heat can be reused elsewhere in the building.

Manufacturers typically state Seasonal Energy Efficiency Rating (SEER) figures of three and four for heat recovery systems. However, it is possible, for a system’s efficiency ratio to nearly double under certain conditions, when taking into consideration recovered energy. In reality, a SEER in excess of six could be achieved frequently.

Utilising other technology within a system, such as Variable Refrigerant Temperature control, can lead to further energy savings being made. This varies the amount of refrigerant flowing through the system and alters the evaporating and condensing temperatures to match demand. This means significantly less energy is needed and efficiency is increased.

Protecting supply air quality

An important consideration is the placement of ventilation intakes and exhaust outlets on the exterior of the building. To ensure that air is sourced from the freshest supply, ventilation intakes should be located as far away from sources of outside pollution, such as road traffic, as possible. Typically, the roof is preferred location unless there is a pollution source at this level. It is also important to avoid cross-contamination from both boiler flues and HVAC exhaust outlets. These should be sited as far as possible from the ventilation intakes.


To ensure good operation and maintain energy efficiency, all HVAC units must be fitted with filters that are designed to keep them free of dust. 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

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.

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.

When designed correctly, taking a whole building approach to a HVAC system can enable facilities managers to minimise wasted heat and energy use, whilst also delivering high quality levels of indoor air quality.

About Sarah OBeirne

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