Ian Rogers of Gilberts puts the case for how ventilation can be carbon neutral as well as cost saving, for the benefit of schools’ bottom line and students’ air quality
The need for Britain to get back on track in the drive to be ‘net zero’ is putting major pressure on architects to design projects that are as sustainable as possible.
We’re building airtight to address heat and therefore energy wastage, but we still have to allow air in and out of the building, and its occupants to breathe. There is almost as much pressure to deliver good indoor air quality (IAQ) because of its positive impact on health and wellbeing as there is on cutting carbon.
But is that a negative or a positive? We believe it’s a positive; encouraging innovative thinking to achieve sustainable zero carbon commercial building services strategies. But we also live in the real world, and know that architects and manufacturers need to work together to develop practical, cost-effective solutions towards that target. One clear trend is that of natural ventilation, and its latest derivations – being more widely used in taller buildings.
It’s a logical step, when you think about it. After all, how did we air multi-storey structures such as our iconic Houses of Parliament before electricity? Natural ventilation works by using only our planet’s energy (wind), and applying the physics that warm air rises, and air speed increases with height. And the UK’s temperate climate, where we rarely experience extremes of temperature, makes it ideally suited to greater use of natural ventilation. In schools, it is the preferred approach within Building Bulletin B101 guidance.
Natural ventilation is good from the health and wellbeing perspective too. Because you are constantly drawing in fresh air from outside to ventilate the internal space via planned air paths, rather than using reconditioned air, the incidence of sick building syndrome is minimised.
Hence we are seeing a growth in the use of hybrid evolutions such as the inclusion of heat recovery (HV-HR) and a move towards zoning, decentralising the ventilation systems to create a number of stand-alone units without a big, central plant room installation. ‘Hybrid’ because, although predominantly using natural ventilation, designers, manufacturers and consultants appreciate that there are times when we need to supplement extraction (purge) beyond what the prevailing weather outside is capable of delivering; a boost is needed, which is provided by the incorporation of a low energy fan.
On average, most HV-HR systems can only achieve heat recovery of around 40%. It is possible to achieve more: some systems have been proven to achieve up to 75% heat recovery). If the building includes self-generating power capability (via a PV array for example),the NV-HR system can even become carbon negative.
It is also possible to incorporate an LPHW coil within the NV-HR system. This provides additional heating beyond recirculation of the warmth extracted from the heat recovery process, addressing those colder days. It goes beyond that, eliminating the need for – and therefore the design impact, space allocation, installation costs and embodied carbon of – separate central heating emitters (radiators).
And, if the heat source is a ground source heat pump, with addition of a plate heat exchanger it can also provide temperate cooling for just the cost of running a circulation pump. The combination makes it a highly attractive proposition for schools.
Conscious of the wider constraints architects face in designing the school building to modern criteria, as manufacturers we also take into account air leakage and thermal performance in the solutions. However, for a whole raft of factors, natural ventilation or its variations are not always practical or feasible in the diverse environments we find in schools – the open space of sports halls, the high heat level in ICT suites, the possible pollutants in
science labs.
Attention to the design details, such as the choice of air distribution diffusers, can also give a positive contribution towards a low/zero carbon strategy, at very least optimisation of energy efficiency.
Thermal swirl diffusers monitor the incoming air temperature. When it varies beyond a degree or two above or below the preset, the swirls automatically adjust their omni-rotational diffuser vanes, delivering warm air vertically and cooler air horizontally. This process ensures rapid initial warm up and avoidance of uncomfortable draughts. The change happens within seconds, maintaining the equilibrium without any major fluctuation between cool or warm inside. Thus it potentially has a huge impact on energy demand ‘spikes’ compared to alternatives that can take up to an hour to adjust. No external power source is needed. Pupils are not distracted by feeling too hot nor too cold.
Linear grilles or diffusers adjacent to expanses of glazing can help modulate solar gain and avoid risk of condensation, both of which impact the energy consumption of the internal space.
There are, therefore, numerous options to help move towards greener ventilation strategies in our education estate. Today’s architects have the added advantage of computer technology. Software such as BIM and CFD (computational fluid dynamics) mean you have the power to test the theory before a single component is ordered, to make miniscule – or major – adjustments to improve the energy performance and make it as low carbon as possible given the other project constraints.
All we need is a little imagination, to venture beyond the accepted and conventional way of doing things.
Ian Rogers is sales director at Gilberts