Micro CHP launch

Recognised as a ‘Centre of Competence’ by parent company the Bosch Group, Worcester’s product development department based at its head office in Warndon, has been tasked with developing micro CHP (combined heat and power generation) appliances for the domestic market.

Martyn Bridges, director of marketing and technical support at Worcester, explains: “Like a boiler, a micro CHP appliance heats a heating and hot water system, but at the same time also generates electricity. A CHP unit is sometimes called ‘energy recycling’ because the same energy is used twice – once for hot water and once for electrical energy.

“There are various methods and technologies which can be employed to generate electrical energy within a domestic heating appliance. Worcester has chosen the free piston Stirling engine, as the ‘engine’ is totally maintenance free for the life of the appliance and requires no extra or special skills to install, commission or service over that of a condensing boiler.

“A CHP appliance works by using a free piston Stirling engine sealed inside an air-tight cylinder filled with an operating gas. Heat is applied, in this case, by a high-efficiency natural gas burner, however it could be oil or even solar one day, and circulated. This is then cooled at the bottom by the circulation of primary heating water, which in turn becomes hot and is conveyed to the heating system. The temperature difference moves a displacer piston up and down and this linear motion drives a ‘power piston’ up and down.

“The power piston consists of a series of magnets which move up and down between copper windings. It is this action which generates the electricity. The principle allows the engine to produce 7kW of heat and 1kW of electricity. Included within the appliance is a ‘booster’ boiler assembly for times when the home requires ‘extra’ heat or when a rapid response is necessary.

“The benefit of a Stirling engine is that it generates electrical energy and heat exactly where it is needed, so that no energy is lost during transportation. An electricity-generating Stirling heating system is also very environmentally friendly, as the heat released in the electricity-generating process is almost entirely used for space and hot water heating.

“It is believed that the Government is planning to introduce legislation that states the UK’s energy providers must buy-back excess electricity from homeowners at a more-attractive rate than the normal price of electricity. This scheme has already been implemented in Germany, where the energy providers are required to buy excess electricity back at double the price homeowners would have paid for “grid” electricity. In the UK, depending on the various tariffs, it currently costs approximately 14p per kWh for an hour of electricity, meaning that if the UK follows Germany the Government will be buying back electricity at 28p for every kWh of electricity homeowners created and didn’t use.

“Realistically, in the future I expect that CHP units will be the most likely boiler change. Current building regulations are more geared towards new build properties, ensuring technologies such as solar panels and air source heat pumps are fitted as best practice. However, with existing properties it’s slightly more difficult, so in my opinion the best way to improve the energy-efficient rating of an existing property is to improve the efficiency of the appliances and controls. Condensing boilers have really helped, but I do think CHP units could become a very possible regulation in the future. The principle of a boiler that generates its own electricity, as well as reduces the strain on coal-fired and gas-fired stations, is definitely part of the Government’s thinking in order to decentralise electricity supplies.

“To be given this product to develop for the domestic market on behalf of the Bosch Group is a fantastic achievement and we are delighted at the challenge presented to our business in this exciting technology area. The first generation CHP unit we’re designing is currently in its production stages and larger in size than a regular boiler at the moment. However, once the prototype has been finely tuned the principle is that the unit will be of a similar size to our wall-hung boilers. Electrically they are more complicated for the installer to fit, so we also plan to put extensive training programmes into place. Heavy trialling is set to take place throughout 2008 and 2009 and the unit expected to be available for sale in 2011.”

Date published: 20th February, 2009

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