Mark Gibbons, CHP National Sales Manager at Baxi Commercial Solutions, explains how a Combined Heat and Power system is simultaneously reducing electricity costs and improving heating efficiency at Aldenham School…

A Baxi Commercial Solutions Combined Heat and Power (CHP) system is successfully meeting the requirement for more reliable and sustainable heating and hot water at one of the UK’s finest independent schools.

Improving the way school buildings are heated can be a huge challenge, especially in historic buildings like Paulls House, one of five boarding houses at Aldenham School in Elstree, which dates back to 1597. While driving improved sustainability is increasingly a priority for many school estates managers, the technically and financially feasible options can often be limited in older, poorly insulated stock.

Paull’s House Plant Room

“When the ageing gas boilers at Paulls House reached end of life, we were keen to explore solutions other than replacement to make a greater contribution to theschools wider sustainability commitments,” explained Tony Albon, Aldenham’s Head of Estates.

“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 parts of the fabric date back to the sixteenth century. So, we decided to call in the heat experts for advice.”

The Baxi Commercial Solutions team, led by Key Accounts Director Neville Small, held lengthy discussions with Tony and Karl Mahon, Aldenham’s Bursar, 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 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 leaky and made of solid brick, so renewable technologies had to be ruled out as they perform most effectively in well-insulated premises. CHP was considered the most viable option due to its ability to meet the heating and hot water requirements more efficiently and simultaneously produce on-site electricity at lower costs, thereby further reducing energy bills.

Sirius WH boilers

CHP Benefits

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, the CHP National Manager, 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, Mark recommended installing a Remeha R-Gen SenerTec Dachs 5.5 CHP supported by three Potterton Commercial Sirius three 110kW wall hung condensing boilers.

The selected 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 9:1 modulation ratio for improved efficiency and boiler longevity. The high gross seasonal efficiency of up to 97.3% reduces energy consumption and low NOx of under 24.6mg/kW minimises 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.

“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 specialist CHP engineers carried out the all-important commissioning for optimal operation and maximum efficiency.”

Both the CHP unit and the ultra-low NOx stainless-steel boilers are compatible with the proposed introduction of 20% hydrogen into the gas network, enhancing the sustainability of the installation.

The collaboration has resulted in the best possible solution for the School, meeting all our objectives,” Tony added.

Baxi’s specialist team will be carrying out all future maintenance and servicing as well as providing training to ensure that the CHP continues to deliver as designed.

Our boarding students have commented on the improved comfort levels in Paull’s House, as have the teachers in the science block,” Tony continued.

“Sustainability was another driver, and we anticipate an annual reduction in electricity costs of around £3,500 from the on-site generation and a saving of over 6,000 kg of carbon. It’s a fantastic result – we have great plans for further projects with this partnership.”

For more information on the Remeha R-Gen CHP range, visit

For more information on Potterton Commercial Sirius three wall hung boilers, visit