Ian Rogers of Gilberts Blackpool explains the importance of balancing ventilation with carbon reduction strategies in order to achieve the right air quality for users.
Breathing – it’s essential to life not only for humans, but for buildings too. In the drive towards reducing greenhouse gases, achieving the top standards of BREEAM, LEED et al, it is crucial that all involved in the building design – new build and retrofit or refurbishment – remember that crucial fact.
We focus on ‘building tight,’ to prevent the fortuitous air – and therefore energy – leakage, but ventilation is critical, for the health of the building, its occupants and its equipment.
It is a point emphasised in a new report by the National Engineering Policy Centre. Led by CIBSE, the Royal Academy of Engineering and the Institute of Mechanical Engineers, the report stresses that healthier, more sustainable spaces come from balancing insulation and ventilation.
To many, it seems contradictory when designing low or zero carbon schemes, where the very ethos is about minimising heat loss, that we need to focus on letting fresh – therefore, cooler air – in.
The keys are balance and control – choosing solutions that optimise energy efficiency while maintaining healthy, compliant indoor air quality (IAQ), that remove damp, condensation and airborne pollutants without removing too much heat.
It’s easier said than done, as we are constrained by the fact that 80% of our existing buildings will still be in use by the net zero target date of 2050, and, with the rising price of land, we are increasingly building upwards. The taller the building, the greater the variation of air pressure – a fundamental of ventilation – and thus greater air movement within as warm air naturally rises. That means greater potential energy use – and carbon creation – in controlling the internal environment.
It is self-evident that the ‘greenest’ ventilation is natural. It uses no energy, relying solely on natural air movement principles to function. It is, after all, how two of our most iconic buildings – Hintze Hall at the Natural History Museum and the Houses of Parliament – were ventilated when originally designed. But it requires much care at the design stage to balance the air paths and air flow.
Hence the evolution of hybrid ventilation. It centres around stand-alone natural ventilation for each space or zone, complimented by an ‘as and when needed’ mechanical boost, usually via a low energy fan. The system works by mixing the incoming fresh air with the warmer internal exhaust air to maintain compliant IAQ in each stand-alone space. The fresh air is drawn in through the facade at high level, and exhausted through the same route, once natural air movement principles have circulated the air throughout the space.
Most systems can be tailored to individual specification by the inclusion of LPHW heat coils, connected to heat pumps and additional filtration.
It is even possible to adjust the system to run on 100% fresh air, using the optional heat coil to temper the incoming air temperature. Using the heat coil also eliminates the need for radiators, which optimises usable floor space, reduces
overall build costs and embodied carbon, and makes a positive contribution to the carbon footprint.
However, natural or hybrid ventilation does not suit every building. Hence why we see mechanical ventilation – PIV, CAV, VAV, and other variants. With these, HOW that air is controlled – how it is delivered, circulated, exhausted – is crucial to the success and green credentials of the building when operational or occupied.
Thermal diffusers can monitor the indoor air temperature and adjust airflow automatically – with no electrical input – to maintain the preset ambient within seconds and thus avoiding excess loading on the building services whilst the BMS senses and adjusts? And diffusers are being developed that can be easily re-positioned across the ceiling as the space below is re-purposed for agile workspaces.
Strategic positioning of linear slots vertically by a foyer entrance can create an invisible curtain to control cool air and airborne pollutants every time the door is opened. Placing them in the ceiling above and in front of large glazed areas can help control solar heat gain and remove a ‘hot spot’ for condensation – demonstrated at 103 Colmore Row, Birmingham (pictured).
Coanda plates added to swirl diffusers make a dramatic impact on the efficiency of the ‘airthrow’ across exposed ceilings and avoidance of ‘cold dumping’ – improving occupant comfort. Such seemingly insignificant elements make major improvements to the carbon footprint.
Advanced software such as Computational Fluid Dynamics (CFD) enable virtual test and validation of ventilation performance, and adjustments to be made to achieve or surpass the targets.
The technology also means architects can make the diffusers a focal point of the interior; coanda plates can be made bigger, smaller, of different materials; and swirl diffuser face plates can be perforated to reflect a brand identity or logo. Or the air supply inlets can be unobtrusive, concealed behind an interior feature.
To breathe easy going forward, architects need to work with experts – building services consultants and ideally, manufacturers who have the in-depth knowledge to guide architects.
Ian Rogers is sales director at Gilberts Blackpool