Combined care and energy efficiency

15 March 2004

Mini CHP units are being installed in UK care homes as a low energy cost, low emissions option

axi Technologies UK is installing six DACHS mini CHP units at ‘Extra Care’ sheltered housing schemes being built in NE England by Gleeson Construction Services for Hanover Housing. Two of them have been commissioned very recently, with the balance to be phased in over the coming months.

The CHP units were selected by project consulting engineer BES as a major component in a series of environmental sustainability measures introduced for these schemes. The inclusion of CHP was required by the local government’s brief as part of its corporate environmental policy. Similar units are already operating at a number of sites in the UK, most of them multi-tenanted accommodation with centralised heating systems.

Derek Griffiths, MD of BES, commented “CHP is an efficient way of ... meeting thermal and electrical demands in many applications. The Dachs units ... were selected due to the potential reduction in CO2 emissions, contributing to Durham county council’s commitment to environmental sustainability. The outputs of the units are a good match with the landlord’s anticipated electrical and thermal base loads.”

Durham county council’s ‘Extra Care’ schemes were developed in partnership with social landlord Hanover Housing and consist of blocks of 36 or 45 self-contained flats with a range of on-site facilities specifically designed for older and disabled people.

The Dachs units, producing 12 kW of heat and generating 5.5 kW of electricity, will act as the lead heating appliance in each system, working alongside high efficiency condensing boilers to provide the winter balance. Heat generation cannot be modulated (except to a limited extent by water storage) and therefore the CHP units are sized to match the base heating load. The electricity generated will be used predominantly for ‘landlord load’ use, mainly in the plant room, communal areas and for lighting.

In addition to the boilers, the systems will include alternatives to traditional heating

solutions such as solar panels, used in this case to partly serve the domestic hot water load. Rain water harvesting will also be adopted at one of the sites. Full metering including a heat metering package has been installed to monitor performance on a permanent basis.


Dachs was originally developed by Baxi subsidiary SenerTec GmbH, a specialist in the application of internal combustion technology to CHP applications. The company, widely credited with developing the mini-CHP market in Europe, has with its partner network installed over 8000 units around the continent, predominantly in Germany, working as stand-alone heating and electricity generators or in tandem with hot water boilers.

Care or sheltered properties are considered to be ideal applications for this technology in the UK, possessing constant electrical and thermal loads that support continuous operation of the mini-CHP units. The demand for its energy saving and therefore environmentally friendly features is a growing aspect of the UK market, primarily as a response to CO2 emissions targets. Dachs is claimed to reduce primary energy needs by around 30 % compared to supply by centralised power generation and conventional gas fired boiler plant.

Key features

The unit was first launched in the UK in 2003 following Baxi’s acquisition of SenerTec. A typical opeating overall efficiency would be79%, leading to significant CO2 emissions reductions compared to centralised power generation or gas fired boiler plant. “A single unit can save up to 15 tonnes of CO2 per annum, equivalent to a 48 % emissions reduction.” says Baxi marketing manager Yan Evans. It also offers the end user a degree of self-sufficiency.

The basic modules can be installed in single and multi-unit packages of up to six units, with liquid and gaseous fuel options. There is a further option, fitting an exhaust condenser, that can add up to

3 kW to the heat output, depending on the water circuit return temperature. Although the primary energy is the heat output, helping to reduce the amount of fuel used by other heating appliances at the property, electrical generation costs are also claimed to be lower, in suitable applications, than the terms such organisations (care homes etc) would be offered by a local electricity supply company.


Mini CHP salient features

Internal view of the mini CHP unit Internal view of the mini CHP unit
Schematic of a typical system Schematic of a typical system

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