COMBINED HEAT & POWER
Tackling school energy challenges with CHP
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Co-generating CHP systems can provide an effective solution for schools with high domestic hot water demands, helping mitigate rising energy costs and improving the energy efficiency of their estates. Mark Gibbons, CHP national sales manager at Baxi Commercial Solutions, looks at a case in point
riving improved sustainability is increasingly a priority for environmentally-minded school estates managers as they look to reduce energy consumption and ensure optimal comfort levels in their buildings while cutting site emissions. But improving the way school buildings are heated can be challenging, especially in older, historic premises where the technically and financially feasible options are currently limited. Such was the undertaking facing Tony Albon, head of estates at Aldenham School in Elstree, one of the UK’s finest independent schools. Founded as a traditional boarding school in 1597, Aldenham today offers both day and boarding options for girls and boys on its original expansive estate.
The school is constantly updating its facilities, including, most recently, the heating system at Paull’s House, one of Aldenham’s five boarding houses where students live and work outside of the classroom and sports field.
“When the ageing gas boilers at Paull’s House
reached end of life, we were keen to explore solutions other than replacement to make a greater contribution to the school’s wider sustainability commitments,” Tony explained. “Our key requirements were to improve outcomes for students and staff through a more efficient and reliable system, and simultaneously reduce the associated running costs and greenhouse gas emissions associated with heating,” he continued. “But we were working with an extremely old building in which parts of the fabric date back to the 16th Century. So, we decided to call in the heat experts for advice.” Tony and Karl Mahon, Aldenham’s bursar, held lengthy discussions with the Baxi Commercial Solutions team to gain a thorough understanding of their exact requirements. Included within this was the need to connect the new system to the neighbouring science block that was also being refurbished. Detailed site visits were carried out to ensure that the proposed solution would be an energy-efficient system tailored around the needs of the buildings.
Paull’s House is made of solid brick and has high air filtration, factors which ruled out use of renewable technologies on this occasion. Several alternative options were evaluated, including Combined Heat and Power (CHP). Ultimately, this was considered the most viable solution at Paull’s House due to its ability to meet the heating and large domestic hot water requirements more efficiently, reducing energy bills, and simultaneously produce on-site electricity via the CHP. CHP produces useful heat and electricity at the point of use in a single, highly efficient process. Rather than rejecting ‘waste’
heat to atmosphere like traditional power stations, CHP captures it and feeds it into the building’s heating network to produce useful thermal energy. This energy can then be used to provide primary space heating and/or pre-heat for domestic hot water within the building. By simultaneously generating heat and onsite power, the system can typically achieve total fuel efficiency of 85-90%, double that of conventional technology. That means primary energy savings of up to 30% and an emissions reduction of around 20%, compared with traditional generation. “The Baxi team really took the time to explain the proposed solution,” said Tony. “Mark Gibbons arranged visits to a couple of sites where similar Baxi CHP systems had been installed so that we could gain a better understanding of how the technology worked. It was great to be able to see the CHP in situ, hear the building owners’ own experiences and come away with an accurate, realistic idea of the energy saving benefits.”
After completing a feasibility survey and a final assessment of the heating and hot water demand at Paull’s House, a Remeha R-Gen SenerTec Dachs G5.5 CHP was selected, supported by three Potterton Commercial Sirius three 110kW wall hung condensing boilers. The mini-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. The three Potterton Commercial Sirius three WH stainless steel boilers, which operate alongside the CHP to meet peak load, boast a wide
16 BUILDING SERVICES & ENVIRONMENTAL ENGINEER APRIL 2022
9:1 modulation ratio for improved efficiency and boiler longevity. The high gross seasonal efficiency of up to 97.3% reduces energy consumption while ultra-low NOx emissions under 24 mg/kW 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. The project contractors were Keeble
Environment Services Ltd. “We’ve had a very good experience working with Baxi,” Tony added. “The CHP team has been by our side throughout the project. They helped our contractors at the design stage, providing useful schematics and monitoring the planning of the system install. They then continued to support our contractors throughout the installation period, offering expert advice and helpful tips to smooth the process. And of course, their CHP engineers carried out the all-important commissioning for optimal operation and maximum efficiency.” The CHP was handed over in December 2021 and the system has been performing trouble-free and even better than anticipated ever since. “We have had no problems whatsoever,” confirmed Tony. “Looking ahead, it’s reassuring to know that Baxi’s specialist team will be carrying out all future maintenance and servicing. This, along with the training they are providing us, will ensure that the CHP continues to deliver as designed. “We are looking forward to monitoring the performance of the CHP, analysing the energy savings and calculating the return on investment. We have great plans for further projects with Baxi Commercial Solutions.”
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