Written by Victor Charpentier
The world’s population will increasingly become urbanized. In the 2014 revision of the World Urbanization Prospects, the United Nations (UN) estimate that the urban population will rise from 54% today to 66% of the global population by 2050. Therefore it is no surprise that cities and buildings are at the heart of the 11th Sustainable Development Goal of the UN: “Make cities and human settlements inclusive, safe, resilient and sustainable”. With an ambitious time objective of 2030, the goal is set to improve the sustainability of cities and the efficient use of their resources.
The impact of buildings on the energy consumption
Energy consumption is often described in terms of primary energy – that is, untransformed raw forms of energy such as coal, wind energy, or biomass. Buildings represent an incredible 40% of the total primary energy consumption in most western countries, according to the International Energy Agency (IAE). A growing awareness of energy issues in the United States led the Department of Energy (DOE) to create building energy codes and standards for new construction and renovation projects setting requirements for reduction of energy consumption (e.g. revised ASHRAE Standard 90.1 2010 & 2013). The LEED certification created in 1994 by the non-profit US Green Building Council for the American building industry has proven that there is a private sector interest to recognize the quality of new buildings. The DOE’s building energy codes mainly focus on space heating and cooling, lighting and ventilation, since these are the main energy consumers in buildings. Great energy savings can thus be reaped from improving the performance of new buildings and renovating existing ones in these categories. Refrigeration, cooking, electronic devices (featured in category ”others” in Figure 1) and water heating, related to the occupants’ activity, are comparatively minor.
Energy end-uses play a significant role in driving energy transitions
Despite the regulatory efforts that have been implemented in the past decade, significant improvements remain necessary to reach the ambitious goals set by the UN. To help achieve them in the US, the DOE has listed strategic energy objectives in its 2015 Quadrennial technology review. One of them reads: “Increasing Efficiency of Building Systems and Technologies”. This report notes that in the case of lighting technologies, for instance, 95% of the potential savings due to advanced solid-state lighting remains unrealized due to lack of technology diffusion. This underlines the need for implementation incentives in addition to research and development in the field of building technologies.
In contrast with this dire need for investments in end-use innovation, scientists showed in a 2012 study that the current investment levels in energy related innovation are largely dominated by energy-supply technologies. Energy-supply technologies are those that extract, process or transport energy resources, while end-use technologies are those that improve energy efficiencies and replace pollutant energy sources when feasible with clean sources (e.g. electric buses in cities). The discrepancy is high between supply and end-use investments. End-use technologies only represent about 2% of the total investments in energy innovations, as shown in Figure 2 below.
The consequences are that buildings technologies receive less investment to finance R&D than they should. In addition, the study suggests that end-use investments provide greater return-on-investments than energy-supply investments. The reason for this misalignment is mainly political as public and financial institutions, and policy makers tend to privilege the latter. The authors of the study suggest that this may be linked to a lack of coherent influence or lobbying for the end-use sector in great contrast with large energy supply companies such as oil or nuclear companies. Thus, to make longer strides in reducing our carbon footprint from the energy sector this needs to change.
Building energy efficiencies: application to the design of better building skins
One way of improving energy efficiency in buildings is by focusing on the design of their skins or envelopes, which shelter their inside from the conditions outside. As interfaces between the controlled interior environment of buildings and the weather variations on the outside, building skins regulate the energy flow between these two environments. High insolation through windows, for instance, can result in large energy consumption needed for cooling the building. The extreme case imaginable would be in a skyscraper with an all-glass façade in a moderate or warm climate. In fact, balancing the heat coming from the sun (mainly through the windows) represents in average almost 50% of the cooling load in non-residential buildings and more than 50% in residential buildings. The warming that climate change will bring to many regions around the world will also make this worse.
Conventional shading devices such as fixed external louvers and Venetian blinds (see examples in Figure 3) can have a strong impact on the reduction of cooling loads. If they are controlled correctly and regularly adjusted, the building’s annual cooling load can be decreased by as much as 20%.
One can add an additional level of performance by making these skins adaptable such that they provide benefits under varying conditions (weather, urban context, occupancy) through the physical change of their geometry. Implementations of such adaptive building skins have demonstrated reduction of energy demand by as much as 51% and high efficiency in moderate to hot climates. For instance, the Al Bahr twin towers (in Abu Dhabi), seen on Figure 4, are a good example of modern building skin implementation.
As those two systems demonstrate, there is great potential for these advanced shading systems and for building innovation in general, but their development is still slowed down by the lack of innovative policy and desire to invest in energy efficient building technologies.
Let’s get buildings on board with the energy revolution
Buildings do not get as much attention as automobiles or new technologies but they may be equally important in our long-term future. This is because the energy consumed for heating and cooling spaces, lighting, ventilation and others represents a very large part of our total energy consumption. However, there are solutions and fixes to this situation. Buildings have been greatly improved over the 20th century but we need to take them a step further to prepare better, more efficient homes and offices that will meet our new standards of living in a warming world. The facts call for stronger investment and political commitment. Let’s get buildings on board with the energy revolution!
Victor is a second-year PhD student in the Department of Civil and Environmental Engineering advised by Professor S. Adriaenssens. His research interests lie in reducing energy consumption of buildings and elastic deformation of shell structures.