CASE STUDY | Limerick’s positive energy city experiment

Ruth Kerrigan IES

Ruth Kerrigan IES

Limerick in Ireland, together with Trondheim in Norway, have since 2018 been running experiments funded by the EU to find ways that cities can become energy positive. Ruth Kerrigan of IES explains.

The EU Horizon 2020-funded R&D project called +CityxChange is developing feasible and realistic demonstrations of climate-friendly and sustainable environments in seven cities across Europe, led by ‘Lighthouse cities’ Limerick and Trondheim.

Since the project launched in 2018, digital twin technology rooted in building physics has been taking centre stage to assess the viability and logistics of various carbon-saving measures that can support Limerick’s bold vision to become energy positive by 2050. To date, this has encompassed everything from exploring the potential for creating positive energy blocks in the city’s Georgian neighbourhood, to developing a decision support tool to help city decision-makers balance socioeconomic impacts with carbon reductions, as well as a city-wide renewables analysis and the creation of all important citizen engagement tools. Most recently, the project has evolved to deliver an accurate decarbonisation roadmap to see how close Limerick will get to achieving its 2050 ambition if following the guidance of its national government’s climate action plan, with some interesting results.

Creating Limerick’s first positive energy block

A positive energy block is a building or group of buildings of 15,000 square meters or more that produce more energy than they use on an annual basis. The production of energy must be local, which in the case of the Limerick project is defined as energy that is generated in or directly adjacent to the block.

Increasingly communities are making the shift towards local energy systems, with a notable rise in microgeneration, including solar PV and heat pumps, and electric vehicle charging requirements creating an entirely new system that we need to understand how to effectively operate. It is no longer possible to rely on the old substation model of determining supply and demand, and new levels of detail and granularity are needed to truly understand what is happening at the local level.

Icim Limerick

Positive energy blocks aim to understand this below-substation demand, evaluate how much extra energy a block can produce than what it uses and assess how the surplus can most efficiently be fed into neighbouring blocks to reduce the risk of overloading the grid.

Limerick’s positive energy block consists of five buildings which have been modelled to the highest level of detail. The project team began by creating highly accurate digital twin models using IES technology to closely replicate the actual buildings in operation, leveraging a combination of real building data, machine learning, AI and physics-based simulation, providing an incredibly reliable baseline for analysing different decarbonisation options.

Using these highly accurate models, it became possible to identify simple operational measures to improve the overall energy efficiency of the buildings at little or no cost to the building owners, before simulating a series of shallow and deep retrofit measures in sequence to determine which would return the best outcomes in terms of energy efficiency, carbon reductions and costs. By integrating renewable energy sources, including solar PV installations and a tidal turbine placed in the nearby river, it was deemed possible to achieve a surplus clean energy generation to take the block into the realm of positive energy.

Scaling the analysis across an entire city

Scaling this out to model the energy use of an entire city is no small feat. However, progress in digital twin technology is making this more achievable. Now, it is possible to create a virtual replica of a whole city, including its buildings, any sources of local generation or storage, and other assets on the network, to accurately mimic how the city operates. This unleashes new opportunities to truly understand energy interactions across the city, and how local systems can be optimised to operate as efficiently as possible.

Limerick 1

Different scenarios for solar PV installation and EV charging stations around the city were simulated

Scaling up from a single block, the project team were able to provide a broader analysis of the potential for renewable energy generation across the city. In an analysis encompassing over 700 city buildings – a selection of which have had IoT sensors installed to feed some operational data into the model – it was possible to relatively quickly create a city-scale digital twin to calculate the total energy demand of the buildings and identify how to balance supply and demand across the whole city. Different scenarios, for example, the installation of solar PVs on 20%, 40% and 60% of the collective roof space, or placing additional EV charging stations around the city, were simulated and compared to see potential impacts and best ROI.

Beyond energy

While becoming energy positive and improving the sustainability credentials of the city are the key aims for the +CityxChange project, making major changes to a city’s plan inevitably has a knock-on effect on the socio-economic climate within the community. To recognise and support this, IES with Limerick council developed a Decision Support Tool (DST) that assesses the impact on the local people and how this balances against energy and carbon saving measures.

As well as aiming to become a Positive Energy City, Limerick wants to reduce building vacancy rates in its historic city centre. By creating and reinforcing sustainable communities in already existing compact settlements, citizens and businesses are incentivised to occupy these areas, creating thriving neighbourhoods and discouraging property vacancies.

Limerick 2

Using ICL technology, we analysed an area of over 900 buildings with approximately 10% full vacancy and significant partial vacancy within the Limerick Georgian innovation district. This has revealed how reducing carbon emissions in the area would impact the local economy and society – for example, redeveloping all buildings to become A-rated would generate 450 additional tons of CO2 but would increase jobs in the area by 4%. In addition, developing the area to increase inhabitancy would lead to a reduction of the crime rate by about five points.

The DST equips councillors and planners with much richer insight into the impact the built environment has on their communities which can inform decarbonisation and social policy.

Roadmapping Limerick’s route to net-zero

The project has more recently evolved into a full-scale decarbonisation road mapping exercise to help set out a detailed timeline of actions to help Limerick achieve its 2050 vision. Using the digital twin created of the city, the project team began by mapping the policy actions advised under Ireland’s National Climate Action Plan into the model, with measures such as installing smart meters in all buildings by 2024, upgrading all public buildings and a proportion of homes to a BER rating of B2 by 2030, and an upscaling of EV transport amongst those recommended to meet net-zero by 2050.

The analysis revealed that the central government’s plans are not nearly drastic enough. Following the plan would leave Limerick around 39% short of achieving net-zero by 2050. The digital twin model has since been used to ascertain which measures need to be brought forward to actually reach net-zero targets and build a better roadmap.

Project outcomes

The project has revealed that effectively decarbonising on a city-scale requires rigorous testing and balancing of net-zero strategies, using appropriate digital tools to ensure that any proposed actions are in fact adequate. Most importantly, the project has highlighted that cities cannot just blindly follow broad-brush policy recommendations set at a national level and hope for the best.

While the project has provided excellent insight into top-down energy use, it has also highlighted that sustainable energy planning in cities needs to also be carried out from the bottom up. While positive energy blocks are one possible solution, there are questions to be raised around scalability and whether or not this is a financially viable solution for decarbonising on a large scale. Would it, for example, be more effective if the whole of Limerick changed consumption habits and saved 10-20% of energy citywide, rather than having a few very efficient blocks?

Limerick 3

An annual positive balance in city buildings would rely heavily on refurbishment and retrofitting, which raises complications around listed and heritage buildings, high expenditure and wasted embodied carbon. From an embodied carbon perspective, we have to consider whether it is better to retrofit a G-rated building to a C-rated building, which is still not massively efficient, as opposed to demolishing the existing building to make space for a highly efficient A-rated building.

Low-cost IoT smart meters will be installed into 100 buildings across the city in a project that is looking at individual behaviours and the impact of that on decarbonising the built environment. By giving building occupants access to this data, we hope to see behavioural change encouraged which lowers energy use and carbon emissions.

The built environment is naturally carbon-intensive, especially in buildings and infrastructure that have not been designed with performance and sustainability in mind, so decarbonising is inevitably going to be a complicated mission, which is why exploring varying facets and strategies is essential. Technology has a central role to play in these strategies as we are now beyond the point of estimations being adequate, scientific evidence and data are crucial and must be involved in all built environment sustainability efforts or else the results are not likely to be enough.

Ruth Kerrigan is COO of IES

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