The best practice approach to Indoor Air Quality
Matteo Dall’Ombra, VRV Specialist, Product Management and Engineering Group at Daikin explains how by taking a whole-building approach to HVAC, it is possible to balance the drive for energy efficiency with the need to improve indoor air quality.
The design of buildings must meet a wide range of requirements. However, a key focus in recent years has been the energy efficiency and environmental impact of buildings. The increased air-tightness that this requires means that indoor air quality (IAQ) can be impacted if the building is not designed correctly.
In December 2021, the Government announced updates to the Building Regulations that apply from June 2022 and require CO2 emissions from new buildings such as offices and shops to be reduced by 27% compared to the current standard, with the emissions from new homes being 30% lower. Approved Document F: Ventilation also received updates to address concerns around IAQ. This includes 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. However, small spaces up to 50m2 floor area and larger spaces over 320m2 floor area are exempted. This means that effective, holistic building design to address IAQ issues while ensuring energy efficiency is now more important than ever.
The importance of good IAQ
Air pollution has long been seen as a major health issue. In fact, the World Health Organisation (WHO) has stated that air pollution from both outdoor and indoor sources represents the single largest environmental risk to health globally and causes around seven million deaths a year. With people spending an estimated 90% of their time indoors, the quality of the air we are breathing is a crucial consideration.
Indoor air quality is affected by a wide range of factors and there are many sources of air pollution, from both inside and outside the building. 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, along with allergens such as pollen, can be brought into a building through natural or mechanical ventilation and via infiltration through the building fabric.
There are also sources of pollution inside a building, including dust, damp and mould, Volatile Organic Compounds (VOCs) given off by wall and floor coverings, furniture and appliances, and emissions from office equipment and industrial machinery. The building occupants themselves also affect IAQ by exhaling carbon dioxide (CO2) and spreading germs and viruses.
In addition to the long- and short-term physical effects of exposure to pollutants, there is also growing evidence that poor air quality may impact mental health and influence conditions such as depression and bipolar disorder. It may also be detrimental to children’s ability to concentrate and learn, affect patient recovery and lower employee productivity. That is why the designs of homes, schools, hospitals, offices and other workplaces are increasingly factoring this in.
Designing HVAC for IAQ and efficiency
When designing and specifying HVAC systems, the main focus is often on operational energy use and efficiency. Not only because it is a key requirement for many clients but also because this attracts the highest weighting of all the factors in BREEAM assessments. 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.
One of the key issues for energy efficiency with regard to ventilation is the heat loss that can occur when exchanging indoor air with fresh outdoor air. Effective heat recovery built into the system can help minimise this and further improve the efficiency of the HVAC. Units with this capability utilise the heat extracted from one area to heat another. For example, servers can generate a large amount of waste heat that can be usefully reused elsewhere. Some systems can also use this heat to generate hot water for use in the building.
Manufacturers typically state Seasonal Energy Efficiency Rating (SEER) figures of 3 and 4 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 6 could be achieved frequently.
Further energy savings can be attained with systems that feature technology such as variable refrigerant temperature control. 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
Another important consideration when designing an HVAC system is the placement of ventilation intakes and exhaust outlets on the exterior of the building. Ventilation intakes should be located as far as possible from the main sources of air pollution, such as road traffic. 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.
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.
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.