COMBINED HEAT & POWER Aldenham revisited – CHP system fits the bill
Reliability, affordability and improved sustainability were Aldenham School’s key requirements when planning to refurbish the plant room serving one of its boarding houses. And the CHP and boiler system installed over a year ago is successfully putting ticks in all the boxes. Mark Gibbons, Baxi’s national manager renewables, checks in with the school’s bursar to find out more
A
year since installing a combined heat and power (CHP) and boiler system in one of its boarding houses, independent school Aldenham has reported a
35-40% fall in gas consumption and an additional £4,500 of on-site generated electricity going back into the building. A similar CHP and boiler system, recently installed in the plant room of a second boarding house, is already showing a parallel trend in total energy savings. So successful is the solution proving that the School is planning to refurbish a third boarding house plant room with a CHP system during the summer shutdown period.
Karl Mahon, bursar and clerk to the Governors at the Aldenham Foundation, puts its success down to the collaborative partnership it has formed with its heating and hot water solutions provider, Baxi.
The partnership began a few years ago, when Aldenham School first identified that the three floor-standing boilers at Paull’s House, one of its five boarding houses, were reaching end of life. “We had a number of requirements when the time came to refurbish the heating system,” said Karl. “First and foremost, we needed to implement a new solution that would reliably and efficiently meet the heating and hot water demand in the building. We have 60 children staying there in the evening so ensuring that the building is warm and comfortable with plentiful hot showers and hot water for catering was clearly a top priority.
“Sustainability was another important factor,” he continued. “Across the education sector, there is an increasing focus on reducing carbon emissions as we move towards our carbon neutral goals. However, pragmatism also has a part to play. Faced with inflated energy prices, we must find ways of mitigating the soaring costs where possible. Sustainability, reliability and affordability were therefore our main considerations.” Like many independent schools, Aldenham has a stock of older existing buildings. In fact, at Paull’s House, parts of the building date right
16 BUILDING SERVICES & ENVIRONMENTAL ENGINEER APRIL 2023
back to the 16th Century. When exploring the options, Karl and his estates manager Tony Albon looked into heat pumps as a possible solution but had to rule them out due to the building fabric at Paull’s House and the upfront cost. Understanding the complexity of the retrofit challenge, Karl was keen to form a partnership with a heat expert to build mutual trust and integrity. “The upfront capital expenditure relating to heating and hot water refurbishments is a challenge for the independent school sector, especially with the rises in energy prices, catering costs and salaries,” Karl said. “But this is a critical service, and we have to prioritise it. That’s why it’s absolutely essential to get it right and ensure we have a system that will deliver payback within the next five years or so and last a good number of years longer.”
The Baxi team had lengthy discussions with Karl and Tony to understand the exact requirements at Paull’s House before presenting the feasible options. This included the need to connect the new system to the neighbouring science block that was being refurbished. Multiple site visits were carried out to ensure that the proposed solution would be an energy-efficient system tailored around the needs of the buildings. When Baxi proposed a CHP and boiler solution, they immediately put Karl and Tony in touch with a school using a similar system to understand how the system worked and the real world benefits it was delivering. “The Baxi team were happy for us to visit the school without them and ask all the questions we liked,” said Karl. “We were impressed with their confidence in the solution they had put forward as well as the extremely positive feedback from the school.” The Remeha R-Gen SenerTec Dachs CHP unit provides a thermal output of up to 14.7kW and an electrical output of 5.5kWe. The unit is controlled according to the heat demand, while the internal microprocessor controller tracks the electrical output to match the thermal output. Three Potterton Commercial Sirius three WH stainless steel boilers, which operate alongside the CHP to meet peak load, boast a wide 9:1
modulation ratio for improved efficiency and boiler longevity. The boilers boast high gross seasonal efficiency of up to 97.3% with ultra- low NOx emissions under 24 mg/kW to minimise impact on the environment. The boilers are supplied with the latest Siemens controls and state-of-the-art PCB to enable enhanced control options for energy-efficient operation. Both the CHP unit and the boilers are future
proof to the projected introduction of a blend of 20% hydrogen into the UK’s natural gas supply. “The CHP and boiler system seemed the
perfect solution, meeting our need for reliability and improved sustainability, thanks to the more energy-efficient heating and hot water from a hydrogen-blend ready system, while delivering proven cost savings,” continued Karl. “Once we had the go-ahead from the Governors, the Baxi team worked closely with our heating contractors, supporting them with the design and installation phases. Their engineers then carried out the pre- commissioning and final commissioning to ensure that the system worked right first time.” Accurate sizing of the CHP unit was critical to maximise the energy and carbon saving benefits. Big buildings don’t necessarily need big CHP units, as Paull’s House demonstrates. The CHP was handed over in December 2021 and the system has been performing trouble-free and better than anticipated ever since. “The 5.5kWe CHP has been running flat out, 24 hours a day, 365 days a year, improving the efficiency of the system and meeting the needs of the building,” Karl added. “A year into operation, we are seeing a 35- 40% decrease in annual gas consumption with an added £4,500 of electricity being put back into the building, further reducing total energy costs in the building. What’s more, the second CHP installation at McGill’s is showing the same energy-saving trend. “Our fixed term energy contract ended in
March, so we are bracing ourselves for the increase in energy prices that are expected to rise by as much as three times this month. We are therefore delighted with the efficiencies of the CHP system and the associated reduction in energy usage.”
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