AIR CONDITIONING & AIR QUALITY Indoor air quality – nemesis or opportunity?
Indoor air pollution is becoming a bigger proportion of the air quality problem as measures to reduce outdoor air pollution evolve. It’s a significant challenge for the industry, in an increasingly difficult balancing act. Ian Rogers, Gilberts Blackpool sales director explains
I
t matters! Indoor air quality (IAQ) affects people’s health and performance and is still not as good as we would like to hope: think how quickly- even today- illness spreads through a school or office. IAQ affects the building’s performance too. Yet, in the spaces where we spend the majority of our time – at work, play – it is something over which we have little control. Even at home, research shows that, despite the best intentions at design & build stage, our houses do not provide the air quality we think!(1).
In addition, the activities being undertaken in the internal space affect the air quality, making it impossible to develop an all- encompassing ‘rule of thumb’ guideline beyond a minimum requirement (currently 10m3/hr/m2 @ 50Pa). Even then, that may be the designed requirement, but what is achieved in reality? People open and close windows, shut trickle vents, turn off fans… Good IAQ is not just about the amount of
fresh air – air changes – that occur within the space. It is about how and where the air is circulated, in a way which ensures a comfortable, draught-free environment that discourages intervention. It is about controlling airborne pollutants from germs to noise. Climate change mitigation strategies, such as the move to carbon neutral buildings to reach Net Zero targets (via new builds and retrofitting) are actually having significant detrimental effects on indoor air quality: airtightness, temperature and humidity can, unless carefully planned, reduce ventilation, sealing in and increasing the concentration of indoor pollutants. At least aspirational Standards such as BREEAM, LEED do acknowledge the importance of air quality and allocate specific criteria/points to it…. The problem is exacerbated by the fact that no legal controls over indoor air quality exist. The Government’s Environmental Audit Committee was supposed to be reporting on the subject in 2023 but has yet to publish its findings. So, for the moment, best practice is to follow the guidance laid down in Building Regulations Approved Document F and CIBSE’s Technical Memorandi, including TM64 operational performance: indoor air quality(2).
Or maybe it is time for a dedicated non-residential IAQ grading system to be
introduced – an equivalent to the hygiene standard for catering establishments – that puts good IAQ as a legal requirement…?
Building on the opportunity
To my mind, providing good indoor air quality is an opportunity. If we as an industry do our job right, the building occupants and operators should not really be aware of what we’ve done! The tools to achieve this are there, and constantly evolving. Take thermal diffusers as an example, the latest opportunity to deliver great indoor air quality AND sustainability. Using temperature- sensitive technology (that itself requires no electrical input to function), they detect changes in the incoming air temperature and automatically adjust the airflow direction to maintain the ambient preset. This intelligent response ensures faster warm-up or cool- down, eliminates draughts, and directs conditioned air exactly where it’s needed, thus optimising energy, minimising waste and maximising performance. The process still achieves rapid entrainment, minimising stratification and therefore ensuring continued occupant comfort- all happening so
quickly no-one is probably even aware of a temperature change!
Historically, only swirl diffusers offered this technology. Via our Thermastute® range, the technology is now available across linear diffusers, jet diffusers and drum louvres. Together or individually, they help balance the air quality; energy efficiency is simplified. It is also worth noting that these thermal diffusers adjust without the need for fans, so have an added IAQ benefit: no noise.
Factor in advances in computer modelling such as CFD and our opportunity to deliver great IAQ is further enhanced. We can design a scheme, and test it, make minute adjustments and validate performance before we even go to site.
Even something as seemingly insignificant as moving an air distribution unit (grille, diffuser) a few centimetres, or adjusting the size of the Coanda plat on a swirl diffuser can make a massive difference to the overall air quality Such changes ensure that the air streams are thrown correctly without cold ‘dumping’ and do not collide/conflict with each other causing excessive turbulence which in turn can cause draughts, recirculation of airborne pollutants etc. It is a potential issue that can be identified and avoided by CFD and can be critical to the overall performance of the space. Imagine in a surgical theatre having ‘dirty’ air being recirculated around and over the operating table. The air paths also impact the IAQ. The aim after all is to minimise airborne pollutants staying within the internal atmosphere. So we need to position the units that supply and extract the air in such a way that the used air is removed with minimum risk to the occupants. That in part explains a growing trend towards siting the air supply units in the floor (for example Gilberts’ GFS) with extract at high level: the internal, warm air rises, taking with it the pollutants. It reflects the strategy often employed in operating theatres, whereby fresh air enters at high level for low level extraction and is yet another tool in our growing armoury. Further, it demonstrates how technology is advancing: most traditional UfAC systems do not have the air entrainment/intermixing adjustability of swirl diffusers. Obviously, grilles and diffusers are only a small part of the overall ventilation/IAQ strategy but they are vital to its effectiveness, being the frontline controls. The choice is constantly changing. Work with manufacturers to make the best decisions and build on the opportunity!
REFERENCES: (1)
https://researchbriefings.files.parliament.uk/ documents/POST-PB-0054/POST-PB-0054.pdf (2)
https://www.cibse.org/knowledge- research/knowledge-portal/ tm68-indoor-environmental-quality-2022
14 BUILDING SERVICES & ENVIRONMENTAL ENGINEER SEPTEMBER 2025 Read the latest at:
www.bsee.co.uk
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