John McComb from Reynaers Aluminium examines the challenges of naturally ventilating properties in high density urban areas, and how a collaboration on a new window design could offer a viable solution
The population of cities globally is continuing to grow, with the UN predicting that almost 70% of us will be living in urban areas by 2050. This means that more and more people are living and working in high density areas, making our homes in large residential blocks, or commuting to high rise offices.
Clearly, city living offers many big advantages. But there are also challenges, not least in how we keep our expanding city populations comfortable in their homes and workplaces while minimising the environmental impact.
One issue that encapsulates this is overheating, where the temperature of a building regularly exceeds what would be classed as comfortable. There are multiple interrelated reasons for this increasing trend. On a simple level, larger buildings mean more heat is being generated through work equipment or keeping homes and leisure spaces warm. Some of this heat passes into other parts of the building, with the temperature rising the higher up you go.
In tandem is an unintended consequence of our drive to reduce greenhouse gas emissions (GHG). In the UK, for example, around 40% of total GHG emissions are understood to come from the built environment. This has led to the design of buildings being more airtight, preventing heat loss and therefore reducing energy, such as gas, needed for heating.
However, this also means that as buildings overheat, they now lack the natural ventilation that historically would have helped to keep them cool. Occupants are left with two options – either use an air conditioning system, or open a window. While air conditioning systems are effective, they of course require energy to run – meaning that an increasing reliance on them will negate many of the positive effects achieved through better thermal efficiency.
Where windows are able to open, this clearly does not require energy usage, but does open a different dimension in building comfort – noise. In busy cities that ‘never sleep’, noise from traffic and other sources can be present around the clock, with window systems designed to mitigate this – provided they are closed.
In short, occupants struggling with overheating are caught between a rock and a hard place – either increase their carbon footprint and energy bills or face a noisy night’s sleep or day’s work.
What’s more, with the appearance of Covid there has been greater focus on the importance of natural ventilation in helping to keep shared spaces healthy with a regular flow of fresh air. This has meant more occupants are now experiencing the distractions and disruptions of a noisy workplace in order to maintain a good level of ventilation.
Collaboration
We felt there must be a better way around the problem of achieving the thermal efficiencies we need in order to reduce GHG emissions, while allowing occupants to manage natural ventilation for both comfort and health. This led to a collaboration between Reynaers and Arup that involved experts from a range of related fields such as building envelopes, materials, sustainability, building physics, acoustics, and building services coming together to discuss the challenges.
A result of our collaboration was a window range which has been designed to provide superior air flow and cooling in comparison with conventional window systems, while attenuating sound to minimise noise. In addition, the range has been developed to eliminate the need for mechanical ventilation systems.
John McComb is technical services director at Reynaers Aluminium