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Thermal comfort in the office isn’t just more pleasant for employees – but more productive for business

Richard Smith | 04 Aug 2017 | Comments

If you happened to visit – or were working in – the UK in June this year, you’ll appreciate why people and businesses across Northern Europe are becoming increasingly convinced of the benefits of air conditioning. In south-eastern England, mid-June temperatures hit their highest since records began 167 years ago. And according to the climatologists, temperature records will continue to tumble in the coming years.

This all signals a growing challenge for building designers. For decades, we in the industry have been progressively improving our designs to reduce office buildings’ energy consumption and carbon emissions. For modern, low-emission offices in temperate regions such as the UK, energy-intensive air conditioning has been a last resort – and the focus instead has been on finding ways to shade and ventilate buildings during summer to prevent over-heating.

This has resulted in innovative, multi-disciplined design aimed at striking the best balance between day-lighting levels, thermal comfort and carbon emissions – while targeting a goal of not exceeding an internal air temperature of 28°C for 1% of the occupied hours without resorting to air-conditioning. The approaches used to achieve this have included “passive” strategies such as more exposed building mass, improved envelope design, ventilation stacks, atriums and shallower buildings.

But these techniques are now running out of road. For large areas in the warmer parts of England, even the best passive design strategies can no longer prevent office buildings from overheating. The pressure is intensified by changing work patterns, with agile working resulting in fewer empty workstations. Also, with the computer now being the primary workplace interface, there’s a tendency to reduce desktop areas and increase occupational density and screen numbers, all contributing further to heat gain.

Add climate change to the mix, and the full scale of the challenge becomes clear. Following the publication of new future UK weather files in 2016, it’s now apparent that some passive buildings that were designed in 2010 and passed the over-heating test criteria will fail as early as 2020.

What’s more, office over-heating doesn’t just create discomfort. Whether you look at office-workers or school, it also has a demonstrable impact on productivity – an effect that can be measured through Atkins’ Human-Centred Design solution suite. Put simply, keeping employees cool is good business.

So, what to do? Can we further improve passive design techniques to prevent over-heating? Or will we just have to air-condition offices in the warmer parts of the UK?

In my view, building designers have pushed passive design about as far as it can go – meaning we’ve reached a point where, for offices, the only improvements now possible are marginal and insufficient. One option could be greater use of mechanical ventilation, but the amount of air movement required would require large-scale ducts and high-powered fans, both of which would have negative impacts on building design and carbon emissions.

However, there is another way – one that’s been pioneered by Atkins for our new Woodcote office in southern England. Similar in some ways to Swiss office design technology, the approach uses advanced passive design techniques to reduce the solar gain in summer, while ensuring good day-lighting so the office lights can be off for most of the day. The building’s concrete structure is exposed to the occupied areas, and is configured to absorb heat during the day and re-admit it at night, thus levelling out the air temperature profile over the 24-hour cycle.

But this is still only good passive design, and won’t be sufficient on its own to prevent the offices of the future from over-heating. So at Woodcote we’ve embedded arrays of water pipes into the concrete floor and roof slabs. Water at 18°C from a small chiller is fed into the pipes, thus preventing the slabs from over-heating and the office spaces from becoming too warm.

While technically a form of air-conditioning, this solution is rooted in passive design and simply uses cooled water to supplement the passive design strategies. It’s also operated only when needed, which should be less than 10% of the occupied hours. During other periods, there are two other modes of operation – firstly, normal heating and ventilation, and secondly, natural ventilation through the offices and up into the atrium. These three modes make this a ‘multi-mode’ building.

This solution is far more efficient than traditional air-conditioning systems. For most of the year, the building operates like a good-quality passively-designed building – and in ‘comfort mode’ we can run rooms a little warmer without compromising thermal comfort due to the cold radiant effect from the ceilings. Also, since the embedded cooling pipes only need water at 18°C, the building’s chiller can operate up to 60% more efficiently. All this means is that the additional carbon emissions for our new building is only 5% more than a conventionally heated and ventilated building compared to a normally air conditioned building that can be a great deal more.

In a world of rising temperatures, the search is on for ways to bear down simultaneously on heat gain and environmental impacts in office buildings. I believe approaches like the one we’ve taken at Woodcote show the way forward.