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Sustainable futures

COP26: using technology to decarbonise our buildings and cities

Buildings currently account for over 30% of final energy use in the UK, and around 38% of its greenhouse gas emissions. A drastic reduction of energy use and CO2 emissions is required to significantly reduce the built environment’s dependence on primary energy resources and curtail household energy bills, thereby meeting the UK government’s ambitious carbon neutrality target by 2050. Our work at the Buildings, Energy and Environment (BEE) Research Group is taking on this challenge.

Changing how our buildings are powered

One strategy is to adapt existing buildings to be more energy-efficient – known as Deep Energy Retrofit (DER). However, challenges remain in maximising the cost-efficiency of DER, slowing its uptake in the building sector. Furthermore, a critical aspect that is often ignored during DER studies is the evaluations of long-term performance (i.e., summer overheating risks) in a rapidly changing global climate, raising questions about its suitability.

However, an emerging strategy, Holistic Electrification Retrofit (HER) seeks to alter the very source of energy in buildings. Through HER, buildings can be adapted to reduce dependence on fossil fuels and to switch to electrical power, which is increasingly generated by renewables. Our research compares the HER and DER building retrofit strategies to analyse the energy performance, cost, and sustainability at the community scale.

We have found that community-scale HER could bring multiple advantages. Firstly, and perhaps of most interest to consumers, is that it is more affordable, saving more than 67% of the costs of DER. Secondly, installation is 30% quicker. In addition, HER suffers less from the issues of indoor overheating commonly seen with DER. Finally, communal grid security and stability can be assured by integrated battery storage, management and distribution.

From this, we are able to highlight some clear policy recommendations:

  • Regulation and legislation for communities, the Carbon Performance Certification (CPC), should be designed and enacted to monitor and incentivise reductions in carbon emissions by methods like HER.
  • Higher-rated communities (such as those showing more than 60% carbon emission reduction from retrofitting) could be offered two further incentives to accelerate the process.
    • Firstly, they could be offered a 5-20% council tax reduction
    • Secondly, a scheme could be developed (such as ‘Help-to-retrofit’) with up to 50% loan interest rate reduction or 25-50% tax reduction for purchasing high-efficiency heat pumps, electric/thermal batteries and stand-alone renewable technologies.

In this way, our modelling results indicate that 20-41% more carbon emission reductions could be achieved than the traditional DER strategy.

Keeping the energy where it’s needed

While using greener energy sources is important, it is only worth doing if the energy can be efficiently used. The main culprits for energy loss in buildings are windows. If you were born in England before the 70’s, you can easily tell the difference that having double glazing makes, especially when it comes to keeping your home cosy during winter.

We are proposing a thinner solution to the bulkier double-glazing windows by producing a new ‘photovoltaic’ (turns solar energy into electricity) vacuum glass. This window, with thickness comparable to tempered glass, could reduce the energy demands and therefore bills in the average UK household.

The principle is very simple. The window insulates glass by using a thin layer of vacuum – this provides greater insulation than any existing window on the market. Consumers will also have the option to include a translucent photovoltaic panel (similar to tinted glass), that can produce electricity directly to their homes. This will save customers from having the heating turned on during winter, while providing electricity during the summertime.

This novel insulated window is a very promising solution towards carbon reduction and their price is comparable to double glazing solutions, at £400 per square metre. These newer windows are able to return their installation cost in less than 9 years, and this time can be even shorter in sunnier places.

"A drastic reduction of energy use and CO2 emissions is required to significantly reduce the built environment’s dependence on primary energy resources and curtail household energy bills"
Ke Qu

Mitigating the environmental impact of warming cities

The Urban Heat Island (UHI) phenomenon describes the higher temperatures in urban areas compared with the rural areas that directly surround them. Nowadays, it is a global phenomenon, compounded by a warmer climate, that can subsequently increase energy consumption, air pollution, and carbon dioxide emission. Furthermore, the intensity of UHI has recently increased due to the change of regional urban microclimates. Also, absorption of heat from the sun has been increased by the extensive reduction of vegetation and the use of manufactured building fabric.

UHI can negatively affect human health, with thousands of deaths occurring annually due to heat-related illnesses. It is therefore one of the most critical problems for high-density cities.

Our research has investigated microclimates caused by UHI by using computer software to simulate a range of scenarios. By studying the UHI changes between 2000 and 2020 in a subtropical city centre, the modelling predicted a UHI increase of 0.5℃ to 0.9℃ in the future – if effective mitigation strategies are not taken by local government.

Mitigation could be achieved, for example, by increasing the reflectance of the sun’s energy through strategies such as expanding the green spaces in cities and using highly reflective pavements to dissipate excess heat.

This research can provide valuable guidance to local governments on which UHI mitigation strategies are most effective and suitable for the local city centre, attracting local policymakers, urban designers and planners, construction material developers and researchers. The policy implications based on this research can optimise building and guide subtropical climate cities to be more sustainable in the future.

Ke Qu

Ke Qu is a research fellow in the Buildings, Energy & Environment Research Group (BEE). Yuhao Wang, Jorge Luis Aguilar-Santana and Tianhong Zhen are PhD researchers in BEE.

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