Location: The Building Centre, London
Date: Tuesday 28 November 2017
Sue Roaf, Professor of Architectural Engineering at Heriot-Watt University
Chris Twinn, Twinn Sustainability
Jack Harvie-Clark, Director, Apex Acoustics
Steve Williamson of the Happold Foundation, who chaired the Conversation, reports on this exploration of the changing balance between energy conservation, natural ventilation and acoustics in the built environment of the city.
Active cooling systems are the default response to overheating in city office buildings. Sealing the envelope to protect the interior from noise, dust and fumes is the justification. But many believe we are entering a new era where reduced impact from new technologies and cleaner cities – will change this development dynamic. A greater understanding of the impact of ‘control’ and ‘productivity’ on the wellbeing of occupants is also a driving factor. This Conversation looked at whether we are entering a new era of passive design and environmental engineering and, if so, how we should prepare for it.
A previous Conversation on the advent of electric vehicles anticipated the possibility of greater opportunities for natural ventilation as a result of a quieter external environment resulting from this form of transport. Our acoustics expert reminded us to be cautious in this respect as only 50% of the noise comes from the motor – the rest comes from the tyres and the body of the vehicle itself. Good news for cyclists who need to hear danger as well as see it – not so good for those who were hoping for a more liberating future city soundscape. Nevertheless, there are wider opportunities for reducing vehicle noise in cities just as there are other pressing reasons to consider natural ventilation of buildings.
Perhaps the most ironic reason will be driven by our growing appetite to consume electricity, of which the electric car is one major facet. Can we match demand into the future or will we be faced with electricity shortages at times of crisis such as natural disasters? Our panelists presented real examples from around the world of where the atmosphere of mechanically ventilated buildings quickly becomes ‘toxic’ if there is any break in the electricity supply for prolonged periods of time.
There seems to be fundamental agreement that more naturally ventilated buildings are a good thing. Better energy consumption, a healthier internal environment, greater control for the occupants leading to a greater sense of wellbeing. The question is how this can be achieved in cities now, with high levels of noise and pollution, with a highly risk-averse development community and an engineering profession that is incentivized to deliver the opposite.
Jack Harvie-Clark is the founder of Apex Acoustics, the current Chair of the Association of Noise Consultants (ANC) and a Board member of ATTMA, overseeing the air tightness testing industry. His company provides consultancy and testing in acoustics and air tightness across the construction industry. Jack has a strong interest in the interdependence of acoustics, ventilation and thermal comfort, and has instigated the production of the forthcoming Guide by the ANC.
He considers that ignorance and a lack of coordination are contributing to the poor conditions for designing well-ventilated buildings. Professionals are used to calculating the trade-off between energy efficiency and air movement, but not many have heard of the professional practice guidance for planning and noise. This is new guidance for those who have an interest in design and planning of new residential developments and the environmental conditions they might need to respond to, out with the Building Regulations. Acoustics is dealt with in the planning system rather than the Building Regulations. Currently major developments have overheating assessments that assume windows can be opened to mitigate overheating. At the same time acoustic assessment assumes that windows are closed to achieve acceptable noise levels. The result is that we are building things where occupants can enjoy comfortable temperatures or reasonable noise levels, but not both at the same time!
ANC are about to publish guidance on how to deal with acoustic considerations in the ventilation strategy. An integrated approach is required, but this is an ambitious objective because there is very little research into the building occupants’ tolerance to the three variables. There is also a further dimension – control. If the occupant is able to control their environment there is likely to be a greater degree of tolerance.
The other thing to note is that we often mean several different things by ‘ventilation’. There are different functions: background ventilation that is needed all year round for good air quality, ventilation to control overheating, purge ventilation for when you ‘burn the toast’. They are entirely separate things and acoustic engineers should associate different noise conditions with the separate parts of the ventilation strategy.
However he is clear on one thing from an acoustic point of view: there is never a need to ‘seal people in’. There is value in having some means of controlling overheating, even if it is not used very often. Dealing with overheating is complicated because it depends on many factors: how often, how noisy it is, whether it is during the day or night. It is also about the balance between wellbeing and climate change. The easy solution is to do it mechanically but there is a growing understanding of passive systems. Albeit there are only a couple of examples in the UK.
Swirles Court, Cambridge: sliding solar shading in the pattern of an oak tree leaf, with attenuated passive vent on right hand side of window
Courtesy of Nick Conlan, Apex Acoustics
There are other lines of research. In Denmark they are looking at acoustic shutters and plenum windows tested in the refurbishment of social housing. It works well from an acoustic point of view but restricts the airflow. In Hong Kong and Singapore with many residences in high-rise buildings exposed to high noise levels. They are not trying to eliminate mechanical cooling – they are trying to find ways to shorten the cooling season with natural ventilation using acoustic windows and staggered openings on the balcony.
Chris Twinn is Principal of TwinnSustainabilityInnovation and is an independent consultant focusing on where sustainability goes next. His background is in building design, planning and implementation, including 28 years with Arup, as a director and Arup Fellow, and three years based in Shanghai. His projects including the world renowned BedZED, the Kingspan Lighthouse first home to achieve Code for Sustainable Homes level 6, through to Eco-city masterplanning and zero carbon projects in China and elsewhere. Chris has been involved in many decentralised energy projects including Kings Cross Central and London 2012.
When designers say we need air-conditioning because of the heavy cooling loads, it is worth checking that the goalposts haven’t moved: tablet computers, cloud servers and wireless technology, task lighting, low energy equipment, passive temperature control from things like thermal mass, smaller plant, greater control for the occupants and energy targets – all these are building a case against the ‘cooling load’ mentality.
Glazing is another area where the goalposts might have moved. In guidance 20 years ago, glazing may have been designed to compensate for the ‘gas-guzzling’ lighting. These days with low energy and task lighting, plus a little bit of background lighting, the glazing we were arguing for in the 1980s and 90s is no longer needed. Something in the region of 20% – 35% of perimeter area may be more appropriate. And as a result, the cooling load may come down by about 25%, which is another reason why we may be more inclined to consider natural ventilation.
The outside environment obviously makes a big difference. The other aspect of electric vehicles that is not often considered is the difference they may make to the urban heat island effect. They are 80% more efficient than internal combustion engines and there is an equivalent reduction in heat output that will make a considerable difference to the external environment. Similarly a naturally ventilated building uses half the energy of an air-conditioned one, so it also is putting half the heat energy into the surrounding environment. Add to this extensive urban vegetation and it will have the combined effect of lowering and in some cases eliminating the urban heat island effect.
Dudley College is a recent example where the benefit of natural ventilation had to be proven. Not an easy task even though the mechanical ventilation might cost twice as much as a naturally ventilated one. One of the key elements is giving building users adaptive comfort control – giving people the perception of control so that they will accept a range of conditions. It is calculated that you don’t need heating in such a strategy until the external temperature gets down to about 5 degrees.
From experience working abroad we must ask why we are not looking at natural ventilation in high-rise, both in London and other UK cities. Simple cross ventilation strategies have been proven to be very effective in some taller buildings in the Far East, for example.
When looking at ventilation and energy efficiency Chris points out another area of contradiction: choosing a mechanical method of cooling is as easy as ticking a box. The modelling software for Part L differentiates between mechanical and natural systems and makes no penalties for the extra energy consumed if mechanical is chosen. Indeed you are allowed twice the quantity of carbon emissions if you choose the air-conditioned route. Are we not to blame for the situation if we allow this to continue?
Sue Roaf is one of the most eminent researchers, teachers and practitioners in the architectural profession. She took up teaching at Oxford Brookes University (1990 – 2007) and then a position as Professor of Architectural Engineering at Heriot Watt University (2007 – 2016). She is an award winning author, architect, solar energy pioneer and was an Oxford City Councillor for seven years (2001 – 2008). Her research has covered work on the
windcatchers and nomadic architecture of Iran, Mesopotamian archaeology and technologies, photovoltaics, low carbon, and resilient and sustainable design. She is best known for her pioneering work on the Oxford Ecohouse, built in 1995 with the first PV roof in Britain and Ecohouse: A Design Guide. She has written 20 books, most recently focusing on Thermal Comfort.
Sue takes a different perspective by looking at adapting cities to prepare for climate change events in the future: “we have to redesign how we design buildings”. It is ludicrous what developers can get away with in the UK. There are, however, a number of identified problems which we need to deal with.
Over-glazing – leading to a chronic overheating problem. In San Francisco a large architecture practice has just paid out millions in an out-of-court settlement to a housing association for designing 590 units that were virtually uninhabitable in hot weather. It was proven that the designers were responsible. Lightweight and flimsy construction and detailing which is liable to damage during extreme weather conditions. Rising fuel poverty and its impact on health and the growing inequality in society that results. Energy insecurity brought on by ‘peaky’ building loads, leading to power outages. Poor use of natural ventilation due to poor information for the public and the industry alike. We can design better buildings that overcome these – so why don’t we?
Why does it matter where we set the thermostat? Because this has a significant effect on energy consumption. The future of building must be in natural ventilation. But will people be comfortable? Researchers have developed a concept of ‘Comfort Clouds’ – human beings have a diverse and enormously robust tolerance to different levels of acceptable temperatures.
The rules and design strategies that we are being asked to follow develop over time. Lightweight modernist tendencies were derived at a time when energy ’wasn’t worth metering’. Then in the 1970s and 80s following the oil crisis we had a programme called Energy efficiency. In the 1990s and early 21st century we had ‘Sustainability’ where everything was thrown into the mix: this has been somewhat devalued by the tick box validation systems that went with them. ‘Passivhaus’ followed by the ‘Active House’ movements still don’t really deal with overheating. We are now at a stage where we are looking at ‘resilience’ – we don’t want to get sued – buildings that will last in a very different world: we have to think about buildings in the long term.
Here are some of the aspects of ‘resilient’ architecture that Sue feels we should be designing – buildings as climate refuges, climate-ready and future proof. Buildings run on solar energy and employing energy storage. Adaptive opportunities for comfort and control for the occupants. A better understanding of occupant behaviours as part of the solution
This was a fascinating conversation – extremely rich in knowledge and ideas. It demonstrates how we need to be aware of how rudimentary our knowledge of building practice can be when faced with the complexity of temperature and noise control, energy efficiency and occupant wellbeing. Cities change and will bring about new challenges for building designers – conversely designers can also have an impact on the urban heat island effect. Climate change also brings a new challenge to any complacency of building practice. Will regulations have to change also to keep up with this challenge and bring natural ventilation onto an equal footing with the mechanical lobby?