Decision support tool for improving energy and environmental performance of public sector multi-energy systems

Decision support tool for improving energy and environmental performance of public sector multi-energy systems

Dr Muditha Abeysekera, Cardiff University
Dr Sathsara Abeysinghe, Cardiff University
Prof Nick Jenkins, Cardiff University
Prof Jianzhong Wu, Cardiff University
John Nangle, Cardiff University

The public sector consumes 6% of the UK’s energy, spends around £2 billion per annum on its energy bill and is expected by the UK Government to lead the de-carbonisation agenda. The higher education sector has a voluntary target of a 30% reduction in greenhouse gas emissions by 2020/21 across its estate with a view to increase this to 50% by 2030. As the largest public sector emitter of carbon emissions, the health system is expected to meet the UK’s de-carbonisation targets by contributing 34% reduction in carbon emissions by 2020 and 50% by 2025.

Many of the larger public sector establishments such as hospitals and universities own and operate their own multi-energy supply systems and there is a clear need to reduce their energy use, carbon footprint and at least control their costs of operation. These multi-energy systems typically use combined heat and power generators and increasingly include a range of on-site renewable energy technologies (e.g. wind turbines and solar panels) and energy conversion technologies such as gas boilers, electrical and absorption chillers, and heat and electricity storage. Many have complex commercial agreements for buying electricity and gas, and for selling electricity back to the network.

In order to optimise energy costs and carbon emissions, the operation strategy of the on-site energy system should consider:

• Half hourly electricity price fluctuations (selling price, buying and distribution charges)
• Weather conditions
• On-site renewable energy generation
• Estimates of carbon dioxide emissions and
• Opportunities for energy conversion on-site, and the optimal management of energy storage systems considering the synergies between different energy systems

Currently, there are no tools available to quantify the potential gains of optimising the operation of these energy supply systems. The gap between sophisticated academic research and the simple approaches required by site energy mangers hinders the potential benefits of local multi energy systems from being realised.

A research project was undertaken by researchers at Cardiff University in partnership with the UK Cabinet Office and the estate office energy managers at Queen Elizabeth Hospital (QEH), Kings Lynn and University of Warwick (UoW) to address this gap. The project was funded by the Centre for Energy Systems Integration.

The researchers developed a decision tool to evaluate operation improvement opportunities at a public sector site and demonstrated it through a simple interactive user interface. Mathematical techniques to simplify the complex optimisation problem were developed. The tool captures different objectives of an energy manager in the public sector estate (e.g. cost minimisation, carbon emission reduction) and generates key performance indicators (KPIs) that enable useful comparisons. Two case study sites, QEH and UoW were used to demonstrate the decision tool.

The study demonstrated a carbon emissions saving potential of around 15%, total energy savings of around 10% and cost savings of around 17% possible from optimising the operation of the energy system at Queen Elizabeth Hospital, Kings Lynn (QEH). These results are based on perfect foresight and optimised operation of the energy assets. The study also illustrates the dichotomy between the two competing objectives, cost optimisation and carbon savings that suggest alternate strategies for control of on-site energy assets.

Public sector energy supply systems must evolve rapidly if they are to make the contribution to the de-carbonisation of the UK that is needed. This study has shown that there are significant possibilities for reduction in CO2 emissions and cost from improved operation of energy management systems (EMS) in hospitals and on university campuses. It can safely be assumed that similar opportunities exist widely throughout the public sector.