The Disenco HomePowerPlant is a micro-Combined Heat and Power (m-CHP) appliance, based upon a kinematic Stirling engine design. The Stirling engine uses helium as its working gas and utilises an external heat source, to provide the energy for the motive force. The Stirling engine drives a generator to produce 3 kW of mains voltage electricity, it is capable of exporting this electricity back to the utility grid via the UK’s G83 connection protocol. It is anticipated that the Disenco HomePowerPlant will generate, on average, up to 50% of a typical domestic users electrical needs and between 60 to 70% of peak load demands and all of its heat and hot water consumptions.
Unlike an internal combustion engine where combustion takes place inside the cylinder at low efficiencies, Stirling engines are external combustion engines operating at high efficiencies. The cycle is sealed and contains a constant volume of working gas commonly air, hydrogen or in our case helium. The cycle works by expanding and contracting the volume of gas caused by temperature differentials at either end of the engine and hence the engine has a hot and a cold end. The heating and cooling is supplied to the engine externally. The current heat source is provided by an external gas fired burner, transmitting heat through a heat exchanger to the volume of gas in the engine. Cooling is supplied by water cooled heat exchangers.
The Disenco HomePowerPlant uses a beta (b) type Stirling engine. This type of engine has a power piston and a displacer piston within the same cylinder. The displacer piston has only sliding contact with the cylinder and its purpose is to move gas back and forth between the hot and cold end of the engine. When the gas is in the hot end of the engine the gas expands to push the power piston down, due to the fact that both pistons are connected to the same crank with an offset (phase angle). The displacer piston con rod passes through the power piston via a gas tight seal arrangement. The displacer piston then moves to shuttle the gas to the cold end of the engine where the gas contracts. Due to the momentum of the flywheel on the crank the power piston compresses the gas. The displacer then moves to shuttle the gas back to the hot end of the engine where the cycle starts again when the power piston is pushed down. In both instances the gas passes through a regenerator, the regenerator is a thermodynamic sponge which is located between the hot and cold end of the engine, as the working gas passes through, heat energy is temporarily transferred to and from the regenerator.
In the Power stroke, the heated gas increases its pressure and pushes the power piston along the cylinder. The displacer piston now moves to shuttle the gas to the cold end of the cylinder. The cooled gas is now compressed by the flywheel momentum. This takes less energy since the working gas is cooled its pressure decreases. Power piston has compressed the gas, the displacer piston has moved so that majority of the working gas is adjacent to the hot heat exchanger (heat source).
Heat produced by the combustion process may be to: Preheat the incoming air/fuel mix, Generation electricity and heat the water circuit.
The water circuit extracts excess heat as follows:
Heat transfer to the outer skin of the combustion chamber, through an enclosed water jacket.
Through heat transferred to the Stirling engine, via a water jacket over the generator.
From a heat exchanger built into the engine’s heater head.
From the combustion products exiting the combustion chamber, via a two stage water/gas heat exchanger, after which the exhaust gases exit the appliance via a flue.
Heat recovered to water circuit is transferred to an external water thermal store for use in domestic heating.
12-18kW of thermal heat will be available for domestic heating needs, which combined with water storage gives upto 25kW of thermal.
Finally in the process the rotary motion of the stirling engine drives a permanent magnet synchronous generator that produce upto 3kW of electrical output. This power output is managed by our own power electronics to provide clean electricity in whatever form, frequency and voltage the client may require.
