Our buildings and energy research has looked at how to shift the UK built stock to net-zero by 2050 in the most cost effective, resilient, acceptable and practical way, maximising the multiple benefits and minimising unintended consequences.
There is a significant resource of untapped energy-saving opportunities in UK homes, with technical potential exceeding 50% and a cost-effective potential exceeding 25% by 2035. We have found that the majority of the long-term energy saving comes from moving to high-efficiency heating systems (like heat pumps), rather than from insulation.
Energy Performance Certificates (EPCs) must be improved
We incorporated smart meter data into energy ratings to cover both flexibility and energy efficiency.
Flexibility: Providing electrical demand response from structural thermal mass has been studied from a modelling perspective and through a small number of commercial trials. Modelling studies do not realistically estimate the transient characteristics of real buildings and their heating systems such as how they cool down and warm up. Commercial trials have not explored perceptions of the occupants and their thermal comfort related to heat-related demand response, nor the real-life behaviour of heat pumps under demand response instructions.
The flexibility work has had two main outcomes. Firstly, the proposal of a flexibility rating system (metric) for domestic buildings. Secondly, the generation of insights into how this flexibility potential may be achieved or limited.
The first outcome was accomplished by trialling and developing different possible metrics, all using smart meter and internal temperature data (the same data as used by the energy efficiency metric below). We collaborated with the Flexibility theme whose work is broader than the building and EPC perspective on which we focus. The metric has been tested on a medium-sized dataset of homes and now requires further testing and validation. This work is starting to have significant impact, with strong interest from the Department for Energy Security and Net Zero (DESNZ), including a jointly organised flexibility metrics workshop.
The second outcome was achieved using three case studies of real heat pumps providing demand response. This small-scale study was the first to report on different control strategies for demand response and their consequences in real homes, and to analyse in detail the thermal comfort of the occupants.
This flexibility metric could allow an estimate of financial savings from time-of-use tariffs to be provided to householders as part of a decision on heat pump installation. Distribution Network Operators (DNOs) could then estimate how many heat pumps will need to run during peak demand times, although there are questions to be resolved in terms of practical implementation.
Efficiency: Existing EPCs are based on estimates of energy use, factoring in square meterage and how quickly the building loses heat (also known as the heat transfer coefficient (HTC).
We have developed methods to calculate the HTC based on in-situ measurements of temperature, and including other data such as solar gain and high-resolution smart meter data that will significantly improve the accuracy of EPCs. This has generated significant insights into their applications, the limitations in their accuracy and gaps in our understanding. This opens up huge potential to characterise buildings on their real performance and predict the energy, cost and comfort implications of building and heating system retrofit.
This work has been shared with DESNZ during their SMETER innovation competition and follow-on conversations resulting in a large impact on policy that has led to the SMETER programme being accelerated and further collaboration with DESNZ.
Performance gaps (the difference in energy performance between design and construction) can be addressed
EPCs are a key policy tool and their usefulness can be considerably enhanced by linking in-use data to obtain in-use heat transfer coefficients (SMETER) and to rate a buildings’ flexibility. Whereas, on average, homes with better Domestic EPCs have lower energy use intensity, this is not the case with non-domestic EPCs and therefore poses a serious challenge to using EPCs as a policy instrument in the non-domestic sector.
Heat pump-ready homes
Modern boilers have up to 70 transducers. This provides a range of data that can be useful in understanding how energy is used in buildings, improving heating system performance and identifying if homes may have heat emitters which are suitably sized for lower temperature heat pumps.
Thermal imaging of buildings
It is now practical and cost-effective for infrared visualisation – using small, new generation cameras – to be undertaken on-site to identify building defects during construction. This helps to reduce the performance gap. Additionally, the experience of ‘seeing’ the construction in thermal view supports the construction professional’s awareness of, and understanding about, critical thermal defects.
Health impacts of energy efficient homes can be considerable
UK homes have issues around being too cold, too hot and too damp. Hence, in planning for net-zero, emphasis needs to be on improving the indoor environmental conditions of our building stock. A substantial number of UK homes experience temperatures that are judged as too low (below 18oC) for the health of vulnerable people (which includes those under age five, over age 60 and those with ill-health). Older dwellings, detached homes, single occupancy and living in the North of England are all associated with the lowest share of hours at the recommended temperature threshold in the bedroom, living room and hallway. Living in cold, damp, and hard-to-heat homes is linked to lower wellbeing, as is struggling with affording heating costs.
However, greater attention is needed to avoid unintended health consequences, such as an increase in radon. Energy efficient homes (which are not leaky) in regions with high levels of radon need to have sufficient ventilation to ensure safe levels are achieved following retrofits.
Policies are needed to create equitable solutions for comfortable, sustainable homes. The UK Government and Local Authorities could support programmes that identify households who are at risk from low indoor temperatures and air pollution such as those with ill-health, the elderly or those who are unable to afford net-zero technologies. Housing associations can use this evidence to support their actions to invest and implement technologies that improve indoor environments and reduce the risks to vulnerable households.
Heat pumps are the key decarbonising technology for buildings
Decarbonising energy use in buildings will rely on the deployment of heat pumps. However, there are policy, technical, public acceptance and cost challenges to be overcome to achieve roll out at the level and speed required to meet net-zero goals. For example, target deployment rates of 600,000 per annum by 2028 are challenging given current deployment rates of around 35,000 per annum (2021) and the small number of installers with the necessary skills in the sector.
Getting heat pumps to work as efficiently as possible is one of the greatest opportunities and challenges to UK decarbonisation. During cold weather, improving the efficiency of heat pumps from ‘average’ to ‘good’ efficiency could save as much energy as insulating all solid walls in UK homes.
Heat pumps could be used flexibly to help manage peak electricity demand, but more standardisation of the heat pump stock would be required. By flexibility we mean providing electrical demand response from structural thermal mass. See EPCs for more information.
Hybrid appliances which combine a gas boiler with a heat pump in a single box that can replace a conventional gas boiler could facilitate a low disruption, low-cost pathway to net-zero. Energy demand could be reduced by 60% (compared to current gas boilers), but also reducing peak electrical demand by 10 GW (compared to air source heat pumps) which is important during a transition. Control and sizing of the hybrid are critical to its impact.
Heat pumps powered by renewable electricity challenge the ‘fabric first’ approach. With offshore wind and photovoltaic (PV) costs reducing, and with heat pumps needing only a quarter of the energy of gas boilers, it is becoming cheaper to generate decarbonised heat than to save it. This may limit the need for ‘deep’ retrofit, with insulation prioritised where it is particularly cheap (e.g. during normal refurbishment/extension) or where it is essential for health and comfort and for the efficient operation of heat pumps. Successful building retrofit and renovation for energy efficiency requires attention to be paid to timings, bespoke/building-specific requirements, and complementary objectives, i.e. more than just carbon reduction.
Buildings modelling as part of the Low Energy Demand scenarios – Positive Low Energy Futures
We examined a number of Low Energy Demand scenarios to explore how the buildings stock might reduce its energy demand to meet net-zero targets. We created ‘simulations’ of potential futures based on a well-developed narrative written by experts across a range of disciplines and fields.
For the residential sector we used the UK National Household Model (NHM) to explore the impact of various measures on future housing stock. The measures included in each of the LED scenarios explore incremental levels of technical ambition applied across the housing stock. They look at faster, deeper, and more widespread roll-out of building fabric retrofits; consider more ambitious heat pump, hybrid heat, and solar hot water programmes; and assume different requirement levels for new build housing apply as energy and infrastructure use in other sectors change.
For the non-domestic sector, we developed a bespoke energy model. The non-domestic sector includes a complex mix of buildings with a wide variety of different uses, from purpose-built retail and commercial spaces, through to storage and refrigeration, hospitality, health, education and public services. The energy demand reductions in the scenarios take a two-pronged approach. On the one hand, they include energy efficiency measures such as energy management systems, building retrofit, building system control, ventilation and cooling and more efficient appliances. On the other, they consider changes to the overall growth in the non-domestic stock itself. The latter results from changes in the wider economy, e.g. reduced retail and office space requirements due to a move to online retail and home-working, and leads to changes in growth expectations for non-domestic floor space.
The outputs of the modelling related to buildings (shelter and non-domestic has been combined with outputs from mobility, nutrition, land use and materials and products to create a narrative that is used to inform a bottom-up analysis of energy service demands in each sector). These are then used in an economy-wide model to construct “net-zero” scenarios for the UK. See the Positive Low Energy Futures report for more information.
Building energy modelling for estimating future energy demand
We have advanced the modelling of the building stock by improving our 3DStock and SimStock models to include representation of every building in the stock and at every level at the same address (geo-located), for example, shops at street level and flats above. We started with the non-domestic stock of industrial, commercial and public buildings, and have now included the domestic stock of houses and flats, as well as mixed-use buildings.
The Greater London Authority (GLA) and London Boroughs are now using the London Building Stock Model (constructed from the 3DStock method) to tackle fuel poverty and improve the energy efficiency of the capital’s building stock. It was launched in September 2020, including a feature in the Evening StandardOpens in a new tab. LBSM covers around 3.5 million properties across the capital and its purpose is to help identify poorly performing buildings so that they can be prioritised for retrofit work to reduce their energy use resulting in money and emissions savings.
3DStock models are being used to support energy planning by other places, including in Sheffield and Wales, as well as in consulting work for DESNZ, and the NHS plan for net-zeroOpens in a new tab. In addition, the team have also developed the London Solar Opportunity Map, for the GLA. It shows the potential output from solar electricity (photovoltaic) and solar hot water installations on all roofs and areas of open land. It suggests that installing PVs on warehouses may be preferential for achieving London’s solar generation targets.
The cost-of-living crisis
The winter of 2022-23 has seen large increases in energy prices and the cost of living in the UK. Both smart meter data and self-reported data show a substantial increase in energy-saving efforts, including a one-degree Celsius drop in thermostat settings. About 40% of households in GB reported turning down their boiler flow temperature – an action that was heavily promoted in the winter of 2022-23 in public energy awareness campaigns – and leading to energy savings in those households that implemented it. However, other actions that householders reported doing most often were not the ones associated with the greatest possible energy or money savings, e.g. closing curtains at night and turning off lights. This emphasises the need for targeted and highly specific advice on energy saving. More than 10% of households were unable to keep comfortably warm in their living room and 15% struggled with affording heating costs.
Banner photo credit: Brandon Griggs on Unsplash