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Addressing 40% of global greenhouse gas emissions in the built environment

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Shaun Fitzgerald

Director of Centre for Climate Repair at Cambridge University. Speaks and writes regularly about climate change & the need for repairing the climate.

With the climate continuing to change and severe weather events becoming more frequent and more severe, there needs to be increased focus on addressing the root cause of these changesemissions of greenhouse gases.

The built environment is associated with at least 40% of annual carbon emissions, and there are significant opportunities to reduce them.

The first area involves making our existing buildings and those which we are about to build more energy efficient. Much of the work required involves increasing the levels of insulation and making the buildings more airtight, so that ventilation is provided only when required. However, there are also significant opportunities to reduce energy use through improved design of lighting and use of LEDs, and through improved strategies and equipment for heating, ventilation and air-conditioning. Research undertaken at the University of Cambridge in the early 2000’s showed that heating energy use could be halved in some buildings just by changing the strategy for ventilation in colder weather, whilst still maintaining the appropriate levels of ventilation during occupied hours.

This research resulted in the formation of Breathing Buildings, a spin-out company from the University of Cambridge. The company developed a range of controlled ventilation equipment based on a cold weather strategy of exploiting the internal heat gains in a space to ameliorate cold draughts rather than energy profligate pre-heaters; this type of equipment is now widely used across the UK.

The second area involves looking more carefully at the overall building design and in particular the building fabric and the relationship of the building with the natural environment. As summers become increasingly hotter there is likely to be an increased demand for air-conditioning, which in turn requires more energy.

However, there are low energy ways of keeping internal environments cool in summer, especially in climates where the summer weather is dry rather than humid. In drier climates the night-time temperatures typically fall much lower than in humid conditions. If a building is ventilated at night and there is sufficient thermal mass then the night-cooled thermal mass can be used to help cool the air during the hot summer day. Furthermore, if the thermal mass is within the building and exposed to occupants then the cooler surfaces can also provide some radiative cooling to the occupants and reduce not just the air temperature but the perceived temperature. 

Shading of buildings through the use of foliage adjacent to the building can reduce the solar radiation incident on the building; even with a well-insulated building with low-e glass, the heating by solar radiation can be a challenge. One of the features of a building as part of a well-designed landscape is that the exterior environment can be a place which occupants can use even in summer – with natural shading and experience of other elements of nature. Depending on the extent of the landscaping there can even be opportunities to include water features which not only have some impact on the temperature through evaporative cooling but also on the acoustic environment.

Finally, the overall design of a new building or the work involved in refurbishment needs to consider the embodied carbon. The amount of material used and its type can have a significant impact on the overall carbon footprint, especially within the first few years. One of the fundamental design principles which should be pushed even harder is not just how little material is required to meet a requirement but whether additional space is needed at all; however, this does need to be balanced with the impact that an improved environment might have on people especially for example in a work or living environment. But more broadly, there are choices of materials for building components and even if the costs of those with lower embodied carbon are higher, then serious thought should be given to them; and if these different designs involve more natural aspects such as roof gardens for provision of thermal mass and insulation, then we should be promoting these for the sake of our planet.

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