PhD Research, Heriot Watt University
School of Engineering and Physical Sciences and School of Energy, Geoscience, Infrastructure and Society
Supervisors: Prof. Tadhg O’Donovan and Dr David Jenkins
I’m currently working on my PhD at Heriot Watt University in Edinburgh, focusing on low-energy building and retrofitting. The research I’m doing explores the impacts associated with retrofitting dwellings in life cycle terms. That is, I’m interested in whether energy invested in a retrofit in the materials and the construction process (called the embodied energy) is higher or lower than the energy savings achieved by the retrofit when the building is in use (the operating energy). This is well explored for new buildings, but much less so for domestic retrofits. And, since older homes are generally the most energy consuming, it is important to reduce their energy use to mitigate climate change, reduce occupants energy bills, and improve the condition of these homes. Simply put:
- There is an urgent need to reduce energy use to meet 2050 Climate Change targets.
- Addressing energy use in UK buildings through retrofit presents a big opportunity to achieve this.
Retrofitting UK Housing
Retrofitting the UK’s housing stock will form a key part of addressing the impacts of climate change. Fabric first retrofits, wherein the building fabric is upgraded as a priority over the installation of renewable energy technology, is necessary to reduce energy demand. However this can come at an energy cost when considering the new materials which will be installed during the retrofit.
Life Cycle Energy Analysis
Life cycle energy analysis (LCEA) allows the quantification of the energy associated with the use of a building (operating energy, OE) as well as that attributed to the building’s materials in their production, construction, use and end-of-life phases, called the embodied energy (EE).
LCEA and the impact of EE (and embodied carbon) aspects of construction are coming to the fore of discussion in relation to new builds and retrofits. Yet there is no clear picture on the proportions contributed by the embodied elements, nor is there data to show how life cycle energy is changing over time. This is largely because detailed LCEA is complex and time consuming. However, evaluation of only OE may overlook significant energy investments in materials and construction processes as EE, which may never be paid back by the OE reductions achieved by the retrofit.
My ongoing PhD research explores the contributions of operating and embodied energy associated with fabric first retrofits. I use a modelling approach to determine operating energy for typical UK dwellings both before and after a theoretical retrofit, using specific interventions and products. The embodied energy associated with the retrofit is then derived based on the specification and using existing EE databases. From this, a balance of OE and EE can be established, which can be used to adjust the design to reduce LCE, or to generate a dataset for comparison between projects.
The literature review phase of my research, recently published in Energy & Buildings (access a free copy online soon!), has highlighted some particular challenges with utilising LCEA in retrofit design. LCEA, by virtue, focuses on such a broad remit that it fails to provide the necessary details for choosing the best fabric first approach. It often conflates building fabric with energy supply, appliances and décor, or other elements of the building which do not contribute to its thermal performance, such as an unheated garage. This makes it difficult to relate thermal performance life cycle impacts to those arising from material choices and retrofit design. Moreover, a lack of consistency in LCEA approaches leads to results which cannot be compared between different buildings, such as life span, building area or spatial unit. The lack of comparability means that we cannot benchmark our progress in reducing LCE, which raises the question of are we learning anything meaningful from LCEA?
My review concludes that in order to ensure that an analysis provides maximum opportunity for the building designer to achieve the best energy savings, LCEA should be deployed with certain constraints and a prescribed approach, as recommended in my paper and summarised here, in order to provide a specific focus on the performance of building fabric, as well as to contribute to a meaningful data set which can serve as a benchmark for future retrofits.
Take a look at my poster, awarded the Best Poster prize at the 2019 EGIS Postgraduate Symposium.