· 5 min read
Abstract
The construction and operation of buildings and the rest of the built environment are responsible for >40% of greenhouse gas emissions. However, although this currently constitutes a major problem for climate change, by changing how we build and operate buildings we can turn this into a significant opportunity to help not only reduce the impact on the climate but potentially also support our efforts to actually reduce the concentration of greenhouse gases (GHGs).
Introduction
There have been many advances in the design of buildings in recent decades and indeed the development of new practices has enabled many societies to benefit from warmer and healthier environments in cold weather as well as cooler indoor conditions in hot weather. These benefits have invariably come with a price, namely that of energy and emissions of greenhouse gases. However, with further advances in technology we might be able to turn this problem into an opportunity.
Building materials
Common building materials vary from country to country, but with certain architectural forms, there is less variation. Skyscrapers, for example, invariably involve the use of large amounts of concrete and steel. These materials are remarkable because of their properties such as strength, durability, and flexibility during the construction process itself; concrete can be poured for example and steel can be formed into different shapes. Unfortunately, the manufacturing process associated with both of these products involves the release of carbon dioxide. Concrete and cement manufacture is associated with around 7% of all anthropogenic emissions of carbon dioxide [1].
However, there are alternatives for many buildings, even in the case of tall ones – for example, timber. In this case rather than worrying about the embodied carbon of the material, which is the term used to account for the hurtful (to the environment) carbon footprint of the product, the building material is in fact storing carbon for us; it can have a negative embodied carbon. Timber can be used in its raw form, but the advent of timber processing products such as cross-laminated timber and Glulam beams now provide opportunities for greater span widths and building heights than were previously considered practical [2]. And recent research is exploring the potential for bamboo to support reasonably tall buildings [3]. We may not see bamboo scaffolding in the UK, but it is commonly used in other parts of the world; it has a very attractive strength-to-weight ratio [4].
But even if some designers and contractors wish to keep using cement, there are options too. The advances in green cement have been significant and are likely to continue. One form of green cement is Geopolymer Cement (GPC). Unlike the conventional method of mixing cement which involves calcium and silicon, GPC uses industrial waste materials such as fly ash. Studies have shown that this method can reduce emissions by up to 80-90% [5]. But we can go further. Rather than just looking at reducing emissions, it is possible to devise a green concrete that actually sequesters carbon from a concentrated stream of carbon dioxide [6]. Similar to the use of timber in buildings the resulting concrete, or perhaps more accurately concrete-equivalent, can have a negative embodied carbon.
Building operations
Reducing emissions
One of the challenges we face with buildings is that they consume significant amounts of energy. In many cases, the heating energy is provided by gas or oil. The first opportunity to reduce the emissions associated with the operation of buildings is to switch the heating source in the building away from fossil fuel to electricity. This doesn’t necessarily eliminate the emissions associated with heating because the ultimate carbon footprint depends on the source of the electricity – but without switching to electricity or another non-fossil fuel the building cannot be converted to a zero-emission one. The second challenge is simply the amount of electrical energy used to provide cooling and ventilation. Many non-domestic buildings are mechanically ventilated, but it is now widely accepted that most buildings can at least in part be ventilated and cooled naturally [7]. A cooling strategy in summer can often be devised based on the exploitation of diurnal temperature variations and the inclusion of thermal mass, which can either be through the use of natural stone, future-green concrete, or phase change materials.
Active GHG removal
Recent advances in thinking are pushing the boundaries of buildings and their role in climate change. Whilst active sequestration of carbon dioxide by the operation of buildings and other forms of the built environment is not yet obvious, there are other greenhouse gases that could in fact be candidates for consideration. Methane is the second most important greenhouse gas; it is responsible for about a third of warming today [8]. But is also possible to include materials in the built environment that can help accelerate the oxidation of methane to carbon dioxide. This reduces the potency of the greenhouse gas. Although it still leaves carbon dioxide, it can nevertheless seriously help the situation.
Research and development is currently underway in various institutions looking at different catalysts and how these could potentially be deployed in the built environment. The first are photocatalysts and could be used to coat surfaces. A key angle is to try and determine what other functions the coatings can provide, such as reduced maintenance of buildings or reduced cleaning bills. The second suite includes electrocatalysts, which could be deployed in the form of coatings on building products such as ventilation duct filters; and if these materials can also improve the air quality in buildings then there may be further benefits too. All of this is the subject of on-going research.
[1] https://www.imperial.ac.uk/news/221654/best-ways-carbon-emissions-from-cement/
[2] https://www.sciencedirect.com/science/article/abs/pii/B9780081027042000172?via%3Dihub
[3] https://www.sciencedirect.com/science/article/pii/S0950061817325710?via%3Dihub
[5] https://www.cbre.co.uk/insights/articles/is-green-cement-making-concrete-progress
[7] https://www.breathingbuildings.com/
[8] https://www.ipcc.ch/report/ar6/syr/downloads/report/IPCC_AR6_SYR_SPM.pdf
