CHP and Boilers for St Aidan's Refurbishment


Baxi Commercial Division has recently supplied Potterton Commercial boilers and a Baxi-SenerTec multi-module Dachs mini-CHP system for a refurbishment of the heating system at St Aidan's College, Durham University. Situated at the top of Windmill Hill with excellent views of Durham City, the college was designed by renowned architect, Sir Basil Spence who was famously responsible for the new Coventry Cathedral. The college is built in the form of a hand, with parallel accommodation corridors that enclose a spacious, landscaped garden. The main body of the building - the 'palm' of the hand - houses a gymnasium, music room, shop, bar, offices and Junior Common Room. When the existing heating system reached the end of its operational life, the University was keen to ensure that the replacement equipment should employ renewable energy and low carbon technologies.

The Baxi Commercial Division equipment, selected by consulting engineers TG Armstrong & Partners, fulfilled this requirement admirably as the new system not only provides space heating for the College in an energy-efficient manner but, at the same time, generates electrical power. The Dachs mini-CHP system comprises three units, each with an electrical output of 5.5kW and, due to their exhaust gas condensers, a heating output of up to 15.5kW per unit. All are connected to a single buffer vessel which is recommended in installations where heat demand is variable. The constant demand that the vessel provides keeps the units running, maintaining the electricity supply as well as avoiding wear and tear on the engine due to unnecessary shutdowns. Acting as lead appliance, the modular CHP engines are designed to match the College's thermal base load to maximize the potential run hours and to increase the overall efficiency of the engines by reducing the number of starts per day and to increase the amount of energy generated. The engines were installed alongside traditional gas fired boilers, bringing energy and carbon savings to the University.

Supplementing the combined heat and power system are three Potterton Commercial 440kW NXR4 sectional cast iron boilers, each with eleven sections. The heating pipework distribution within the plantroom consists of a primary heating circuit which supplies the College's hot water system, as well as separately controlled heating circuits which feed perimeter radiators and underfloor heating. All the equipment was installed in the basement plant room and given the modular format of plant supplied, there were no access or handling issues. The flue for the Dachs system required careful integration with the boiler flues and the existing chimney In order to ensure correct operation.

The NXR range of sectional, cast-iron boilers is exceptionally robust and incorporates a specially designed heat exchanger with multiple flue-ways and fins coupled with a large chamber which ensures environmentally sound combustion, reducing both CO and NOx emissions. Boilers in the range achieve up to 89% gross seasonal efficiency, 98% net.

For ultimate peace of mind, the heat exchanger carries a lifetime guarantee. Features of the range include high/low and fully modulating match tested burners with oil, natural gas, LPG and dual fuel options, an integrated control panel with a BEMS interface and optional sequence and zone controls. The NXR4 models installed at St Aidan's College are fitted with fully modulating natural gas burners and are controlled by the site Building Management System, enabling time control and priority operation of the boilers, with the CHP system operating as lead boiler in all circumstances.


Martin Huitson, Durham University's Senior Mechanical Services Engineer, has expressed his approval of the new CHP installation since, in its first year of operation it achieved 87% of its predicted energy production despite initial operational 'bedding-in' issues. Totals produced were 73,357 kWh of electricity and 171,185kW of heat. Martin commented: "In year two, from October 2011 to the beginning of February 2012, the system has generated 42% of the energy predicted, so we are off to a positive start."

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