Low Energy House

Low Energy House - Micro CHP Units - Combined Heat and Power

Micro Combined Heat and Power or Micro CHP units are emerging as a new product for central heating markets. The aim is to replace a central heating boiler with a device of similar physical size that provides some electricity as well as heat and has a potential to reduce carbon emissions

Micro CHP Units

Micro CHP Unit - Image Provided by Baxi EcogenCombined heat and power (CHP), or cogeneration is the process of generating both electrical power and useful heat from a single source. Large Scale CHP suitable for commercial applications, has been available for some time. The latest development includes micro CHP which is essentially a gas boiler, similar in size to a normal wall hung boiler, which generates electricity for use in the home while providing heating and hot water.

Micro CHP - Engine Types

Micro CHP units can be based on several different technologies including: Internal Combustion Engines, Free Piston Stirling Engines, Steam Engines, Micro-turbines and Fuel Cells. The most popular Micro CHP systems use Free Piston Sterling Engines that produce heat, in the home or small businesses, and generate electricity as a by-product.

The timing of high heat demand does not always coincide with the timing of high electricity demand so the surplus electricity is sold to the National Grid via an approved export meter.

Micro CHP Technology

Manufacturers are engaged in the development of a variety of technologies for Micro CHP including Internal Combustion, Free Piston Stirling Engine (FPSE) and Fuel Cells. The Micro CHP units that are currently available use FPSE technology because it has been tried and tested in other applications, including cryogenic cooling in the Apollo space missions, and is at the most advanced stage of development. The challenge has been to take this sophisticated technology and adapt it for a Micro CHP device, achieving the desired high performance and reliability at an affordable price.

Micro CHP Micro CHP Unit (Cutaway) - Image Provided by Baxi EcogenThermal and Power Output

The unit ignites in response to an initial heat demand of up to 6 kilowatts. The Free Piston Stirling Engine generates 6 kilowatts of heat and 1 kilowatt of electricity by driving a displacer and magnetic piston up and down between a generator coil. If the heat demand goes above 6 kilowatts, the supplementary burner will fire up and can produce an additional 18 kilowatts of thermal output.  As heat demand falls in the home, the unit modulates down as low as 4 kilowatts, while still generating electricity.

Micro CHP Fuel

Micro CHP units operate on natural gas and testing in the laboratory, under extreme conditions, has shown that they offer a long service life. A Free Piston Stirling Engine is an external combustion engine which makes it fuel flexible and it can be adapted to operate on biogas, LPG or Biomass with excellent efficiencies and reliability. 

Micro CHP Maintenance

There are relatively few moving parts and it has been designed to require no external lubrication, making it extremely low maintenance.

The gas connections and flow and return water pipes connect just like a conventional boiler and the installation must be made by an installer who is on the Gas Safe Register