St John's CHP Energy Centre & Energy Efficiency Improvements

During the tender stage, we identified issues with the aging internal flues of the boiler house which posed risks of interruption to the steam supply to the hospital. We suggested that these flues should be replaced with new stainless steel flues to extend the lifespan and increase the reliability of the scheme.

The Health Board was keen to utilise its existing assets to improve efficiencies so we analysed the systems around the hospital to identify opportunities to maximise savings. We identified that there was significant heat that was emitted from the laundry area which was otherwise going to waste, and so we provided a solution that would capture this wasted heat to generate some of the heating and hot water for the hospital. We designed a system that would divert the high temperature condensate return into a new 300kW plate heat exchanger to transfer the waste heat emitted from the laundry area and convert it into low temperature hot water which would then be distributed around the hospital’s heating system. This provides significant carbon and financial savings for the scheme, with this innovation along generating financial savings of £26,249 per year.

The Health Board desired a solution that would be adaptable in the future to include new technologies that were less reliant on fossil fuels. We ensured the solution was flexible with the possibility to replace the CHP engine at the end of life to accommodate renewable systems in later years.

We wanted to ensure the client was part of the project at every step and so took some of the NHS Lothian team to visit the Jenbacher factory in Austria to witness the CHP factory testing prior to its shipping to Scotland for installation at the hospital. This allowed them to see the engine up close and running at full electrical output to enhance their understanding and guarantee the quality of the product.

St John’s is a major hospital with constant operation and so a key priority was to ensure that there would be no disruption to the energy supply and little disturbance to normal hospital operations during construction. We therefore took the decision to remove and deliver major plant over two weekends when there would be a reduced number of staff and out patients, keeping accessibility restrictions to a minimum.

The first weekend saw the first aged boiler removed and the delivery of two 5MW steam boilers, and the second weekend saw the removal of the remaining two aged boilers and the delivery of the 6.7MW boiler and 1.5MW CHP engine. Completing the work in stages was beneficial for two reasons: firstly, it allowed us to quickly install key plant in short time periods which reduced any inconvenience to the hospital; and secondly, it ensured that there was no down time in energy supply as there was always at least two boilers running at any time.

We have entered into an energy performance contract with the Health Board which guarantees the savings of the project for a period of 25 years. This will see savings of 2,649 tonnes of carbon* and a reduction of £644,000 in energy costs each year.

*Carbon savings calculated using factors at the time of project bid.