GB2534298A - Micro combined heat and power unit - Google Patents

Abstract

A micro combined heat and power (mCHP) unit 10 comprises an internal combustion (ic) engine 12 driving an electric generator (14, figure 4). An internal fluid circuit 22 for central heating fluid conveys the fluid so that it extracts heat from a series of components in order of increasing expected normal operating temperature. The coolest component may be the generator (14, figure 4), and the series may comprise the engine crank case (oil sump) 36, cylinder block, cylinder head and exhaust heat exchanger 28, with the exhaust manifold being the hottest component.

Description

MICRO COMBINED HEAT AND POWER UNIT

FIELD OF THE INVENTION

The present invention relates to a micro combined heat and power unit. 5 BACKGROUND OF THE INVENTION Micro combined heat and power (mCHP) units have recently been developed for domestic buildings or small/medium commercial business units. mCHP technology is an example of co-generation where energy is provided in several forms.

Typical mCHP units use a generator to convert fuel into electrical energy, which can be used in a building. A by-product of generating the electricity is the generation of heat. In a normal generator set up, this heat would be wasted. However, in mCHP units, it is common to capture energy from this heat, e.g. for use in heating the building. This greatly improves the overall efficiency of the unit in terms of energy input vs useful energy output.

mCHP units in domestic or small/medium commercial buildings typically generate more heat energy than electrical energy and are controlled primarily by heat demand. The useful heat energy is typically provided in the form of hot water, which is utilised by either a central heating system and/or hot water for cooking, cleaning, bathing etc. If the heat and electricity requirements of the building are consistent with the ratio of heat and electricity output from the unit then all is well. However, if the electrical demand fluctuates significantly, as is often the case, the mCHP unit may often he in a state where it produces more electrical energy than required (e.g. for a given heat demand).

A major benefit of mCHP units is that this excess electrical energy can be exported to the national electrical grid, e.g. for sale to the relevant utility company.

mCHP units typically include an engine-driven electrical generator and a heat exchanger for converting waste heat energy from the engine to useful heat energy in a working fluid (typically water for a central heating system).

A variety of engines (e.g. Sterling-type engines and IC engines) have been suggested or developed for use in mCHP units, and these may run on a variety of fuels. Natural gas is particularly suitable since many homes and small/medium sized office buildings are already connected to a supply of natural gas. A variety of other gaseous fuels may similarly be used, such as propane, methane, hydrogen or LPG. Liquefied fuels are also suitable, particularly for units incorporating an internal combustion engine-driven electrical generator.

There is a need for further improvement in mCHP technology, e.g. to address issues related to one or more of the service life, packaging, noise and vibration, and efficiency of mCHP units.

SUMMARY OF THE INVENTION

A first aspect of the invention provides a micro combined heat and power (mCHP) unit according to claim 1.

In embodiments according to the first aspect of the invention: - the unit may include an internal combustion engine for driving the generator; and/or - the unit may include a first heat exchanger configured to transfer waste heat energy from the engine and/or the generator to useful heat energy in a working fluid, and a second heat exchanger configured to transfer the heat of combustion from the burner exhaust to useful heat energy in the working fluid; and/or - the engine may be an IC engine, and wherein the IC engine and/or the fuel burner are operable using gaseous fuel, preferably natural gas, propane, methane or LPG; and/or -the engine and the fuel burner may each be operable using the same fuel type; and/or - the unit may further comprise a control valve for controlling a supply of fuel to the engine and/or the fuel burner; and/or - the unit may further comprise a diverter valve for controlling the flow of the working fluid through the first and/or second heat exchangers; and/or - the unit may further comprise a controller connected to the control valve and/or to the diverter valve; and/or -the working fluid may be water, preferably for a central heating system; and/or - the first heat exchanger may include a conduit for transporting the working fluid through and/or around the engine, such that during operation the working fluid is heated and the engine is cooled; and/or -the first heat exchanger may include a conduit for transporting the working fluid through and/or around the generator, such that during operation the working fluid is heated and the generator is cooled; and/or - the unit may further comprise a conduit for transporting the working fluid through an exhaust system of the IC engine, the exhaust system including a heat exchanger such that during operation the working fluid is heated and the exhaust system is cooled; 15 and/or - the unit may further comprise a pump for pumping the working fluid from an inlet to an outlet of the unit; and/or - the generator may he an alternator; and/or - the unit may further comprise a rectifier for converting AC output by the alternator 20 to DC, and an inverter for converting DC output by the rectifier to AC at a predetermined frequency; and/or -the fuel burner may be operable independently of the engine driven electric generator; and/or - the unit may further comprise a cabinet, which houses the engine, generator, fuel 25 burner and heat exchanger arrangement(s), and may further comprise a wall mounting for mounting the unit to a wall; and/or - the first heat exchanger may be configured to transfer useful heat energy from the working fluid to raise the temperature of the engine prior to operation of the engine; and/or - the controller may be configured to start the engine when the temperature of the engine is at or above the predetermined level; and/or - the first heat exchanger may be configured to transfer heat between an oil sump of the engine and the working fluid; and/or - the first heat exchanger may be configured to transfer heat between an engine block of the engine and the working fluid; and/or -the first heat exchanger may be configured to transfer heat between an exhaust system of the engine and the working fluid; and/or - the first heat exchanger may he configured to transfer heat between a conduit, which passes around the outside of the engine, and the working fluid; and/or - a controller may be connected to one or more temperature sensors within or adjacent the engine; and/or - the unit may include an electrical heating element for heating the working fluid; and/or - the electrical heating element may be powered by electrical energy generated by the generator; and/or -the electrical heating element may he disposed within a circuit for conveying the working fluid through the mCHP unit; and/or - the electrical heating element may be an emersion heater; and/or - the working fluid circuit may include a heat exchanger within an exhaust system of the engine, and the heating element may be disposed within said heat exchanger; 25 and/or - the working fluid circuit may include a conduit which passes around the engine, and the heating element may be disposed within said conduit; and/or - the healing element may be energised to pre-heat the engine prior to operation; and/or -the unit may be configured so that the working fluid passes through an oil sump of the engine, and the heating element may be energised to heat oil in the sump; and/or - the unit may include a heat exchanger configured to transfer waste heat energy from the engine exhaust to useful heat energy in a working fluid, wherein the heat exchanger may comprise a first section and a second section, the first section having a working fluid inlet and a working fluid outlet, and the second section having a working fluid inlet and a working fluid outlet, an exhaust conduit is arranged to convey the engine exhaust from the engine through the first section and then through the second section of the heat exchanger, and a working fluid conduit is arranged to convey the working fluid from the working fluid outlet of the second section of the heat exchanger towards the working fluid inlet of the first section of the heat exchanger; wherein the first and second sections of said heat exchanger may be attached or integrally formed; and/or wherein the first section of the heat exchanger may have a higher operating temperature than the second section of the heat exchanger; and/or wherein the operating temperature of the second section of the heat exchanger may be sufficiently low to cause condensation of steam in the exhaust; and/or wherein the first and second heat exchanger sections may have a plate-like, or tubular, construction to direct the working fluid therethrough; and/or wherein the heat exchanger may further comprise thermal insulation between the first and second sections; and/or wherein the working fluid conduit may be arranged to convey the working fluid through the engine between exiting the working fluid outlet of the second section of the heat exchanger and entering the working fluid inlet of the first section of the heat exchanger; and/or wherein the unit further comprises a second working fluid conduit arranged to convey the working fluid through the generator and towards the working fluid inlet of the second section of the heat exchanger.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects and features of the invention will be apparent from the claims and the following description of embodiments, made by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic assembly view of an mCHP unit; Figure 2 is a schematic view of part of the mCHP unit of Figure 1, showing the engine exhaust gas heat exchanger in detail; Figure 3 is a schematic view showing the mCHP unit of Figure 1 connected to a multiple flue passing through a wall of a building in which the mCHP unit is installed; Figure 3a is a cross sectional view through the multiple flue of Figure 3 along line a-a; Figure 4 is a perspective side view of a twin spark plug engine assembly for use in an mCHP unit; Figure 5 is a perspective view of an anti-vibration device of the kind shown in Figure 4; Figure 6 is a schematic view of an oil recirculation system for an IC engine for use in 15 an mCHP unit; Figure 7 is a diagram indicating key elements in a power regulation circuit for use with an mCHP unit; Figure 8 is schematic view from the end of an mCHP unit incorporating the engine assembly of Figure 4, showing some of the internal features; Figure 9 is a schematic perspective view from the end of the mCHP unit as shown in Figure 8; Figure 10 is a schematic perspective view of the mCHP unit as shown in Figures 8 and 9 but viewed from a different angle.

DETAILED DESCRIPTION OF EMBODIMENTS

Figure 1 shows a schematic layout for key components of an mCHP unit 10. The unit 10 has an internal combustion engine 12, an alternator (e.g. as shown at 14 in Figure 4) arranged to be driven by the engine 12, and a gas burner 16 which forms part of a gas booster boiler 18. The engine 12, alternator 14, and burner 16 are disposed within an enclosure, e.g. wall or floor mounted cabinet/housing, indicated generally at 20.

The alternator 14 produces electrical energy when the engine 12 is running. A water circuit 22 runs around the engine 12, for transferring waste heat energy from the engine 12 to useful heat energy in water flowing through the circuit. In the embodiment depicted in Figure 1, the water circuit 22 is coupled to a central heating system (i.e. external to the housing 20). The central heating system is indicated generally at 24.

The water circuit 22 is additionally plumbed in parallel to the gas booster boiler 18 with a three way valve 26, for selectively controlling the flow of water through an exhaust/water heat exchanger 28 and/or the gas booster boiler 18.

The water circuit 22 includes a "cool" water inlet 30 for connection to the central heating system 24, a water pump 32, a water conduit 34 which passes through an oil sump 36 of the engine 12, a water conduit 38 connected between the water conduit 34 and the exhaust/water heat exchanger 28, and a water conduit 40 connected between the heat exchanger 28 and the valve 26.

In parallel, a water conduit 42 is branched from the water conduit 38 and connected to an inlet 44 of the gas booster boiler 18. A water conduit 46 is connected between an outlet 48 of the gas booster boiler 18 and the valve 26. Valve 26 is coupled by water conduit 50 to another three way valve 52 arranged to control the flow of water to either continue around the water circuit 22 or to exit the water circuit 22 via an outlet 54 coupled to the central heating system 24.

Although not visible in Figure 1, the water circuit 22 additionally flows through the engine 12 as will he described in detail with reference to Figure 2.

It will he appreciated that whilst the mCHP unit 10 is shown connected to a central heating system 24, it could alternatively or additionally be connected to a hot water cylinder for supplying hot water for cooking, cleaning, bathing etc. in the building in which the unit 10 is installed.

The internal combustion engine 12 is operable using mains natural gas or LPG. However, the same, or a similar, internal combustion engine may be adapted to run on a wider variety of gaseous or liquid fuels, as will he appreciated by those skilled in the art.

The engine 12 is coupled to the alternator 14 such that when the engine 2 is running, the alternator 14 generates electrical energy. The engine 12 is a four stroke overhead valve internal combustion (IC) engine, which produces most of its output energy over about 45° of crank shaft rotation, every 2 crank revolutions. This has the potential for quite large crank shaft speed cyclic variations. If the speed variations are transmitted to the alternator 14, then this would lead to distortion of the AC wave form of the electrical output, and also result in engine rocking and vibration.

To combat this, a smooth coupling is provided between the engine 12 and the alternator 14. Essentially, the smoothing coupling stores energy during the power stroke of the engine 12, and releases it in a controlled manner to the alternator 14 over the remaining time before the next power stroke. The smoothing coupling therefore enables the AC wave form of the alternator electrical output to be bought closer to sinusoidal form, and in turn reduces engine rocking, vibration, and cyclic speed variations.

The AC electrical output of the alternator 14 is rectified and inverted to provide a constant AC output of a predetermined frequency corresponding to mains electrical power. This may he, for example, 50 or 60 kHz depending on the country of use. The electrical output from the unit 10 may therefore be used to power electrical appliances within the building, or exported to the national electricity grid, e.g. as described below with reference to Figure 8.

Most of the heat from the engine 12 is transferred to useful heat energy in the water circuit 22 when the engine 12 is running. Relatively cool water is fed from the central heating system 24 of the building in which the mCHP unit 10 is installed via inlet 30 to the water pump 32. This relatively cool water is passed through the water conduit 34 which is disposed in the oil sump 36 of the engine 12.

When the engine 12 is running, oil 56 in the sump 36 is fed by oil pump 58 through oil filter 60 to the engine 12. Oil which drains back from the engine 12 into the sump 36 therefore heats up until the engine 12 reaches a steady operating temperature. The thermal energy of the oil 56 in the sump 36 is transferred through the walls of the water conduit 34 to heat the water in the water circuit 22.

Water in the water circuit 22 then proceeds via water conduit 38 where it enters the exhaust/water heat exchanger 28. The exhaust/water heat exchanger 28 will be described in detail below with respect to Figure 2 but essentially transfers waste heat energy from the engine exhaust to further raise the temperature of the water in water circuit 22.

The water which exits the exhaust/water heat exchanger 28 is transferred by water conduit 40 to valve 26. When the engine is running, valve 26 controls the flow of hot water from water conduit 40 to water conduit 50. During normal operation of the mCHP unit 10, valve 52 directs the hot water from water conduit 50 to the outlet 54 which is connected to the central heating system 24. The hot water flows through the central heating system 24 and this heat is used to heat the occupied space in the building such that relatively cool water returns from the central heating system at inlet 30.

As can be seen, the mCHP unit 10 uses fuel supplied to the engine 12 to provide both electrical energy and useful heat energy output. The IC engined mCHP unit 10 produces useful heat energy and electrical energy in the ratio of approximately 3:1. That is, for every 3kW of heat produced, 1kW of electricity is produced. If the requirements of the building using the heat and electricity are in this proportion then all is well. However, many buildings typically experience relatively large fluctuations in electrical energy usage.

A major benefit of mCHP units is that excess electrical energy can be exported to the national electricity grid and the mCHP unit operator is compensated by the utility 30 company for a net export of electrical energy. However, some central governments arc limiting the amount of electrical energy that can be exported to the national electricity grid by a domestic installation. If the mCHP unit produces heat and electricity in the ratio of 3:1 and the cap on the amount of electrical energy that can be exported is, for example, 2kW then the practical limit on the heat output of the unit would be around 6kW. However, this is unlikely to be sufficient for most domestic applications at certain times of the year.

Therefore, the mCHP unit 10 includes the additional gas booster boiler 18 with the gas burner 16 such that it becomes possible to operate the mCHP unit 10 to produce more heat when required, without increasing the electrical output. This boost heat facility widens the appeal of the mCHP unit 10 and allows the unit to replace a standard domestic boiler instead of being installed in addition to it, thus saving space, cost and complexity.

The gas booster boiler 18 is plumbed in parallel to the water circuit 22. Valve 26 is operable to control the flow of water in the water circuit 22 such that it flows through the exhaust/water heat exchanger 28 and/or through the gas booster boiler 18. When the boiler 16 is operating water flows via water conduit 38, which is connected to inlet 44 of the gas booster boiler 18, and heated water flows from outlet 48 via water conduit 46 through valve 26 to water conduit 50.

The gas booster boiler 18 is of known type and familiar to those skilled in the art. By firing the gas booster boiler 18, the heat output of the mCHP unit 10 can be boosted without increasing the electrical output. A mCHP unit having only an internal combustion engine with a heat output rating of, say, 6kW can he boosted with an additional 15 to 20kW of heat output by the addition of the gas booster boiler 18.

The exhaust/water heat exchanger 28 further includes an electrical heater (immersion heater) 62. The electrical heater 62 can therefore he used to convert electrical energy into heat energy in the water flowing in the water circuit 22. The electrical heater 62 is, in the embodiment depicted in Figure 1. situated in a water jacket of the exhaust/water heat exchanger 28. However, it will be appreciated that the electrical heater 62 could be disposed at a variety of other positions around the water circuit 22 within the mCHP unit 10. The electrical immersion heater 62 is of known type and so will not be described in further detail here. The electrical heater is coupled to a controller for controlling the operation of the electrical heater 62.

The gas booster boiler 18 and the electrical heater 62 are adapted to perform a variety of functions. These functions are generally complimentary and so in some instances, it may not be necessary to provide both the gas booster boiler 18 and the electrical heater 62 within the same mCHP unit. However, in the preferred implementation shown in Figure 1, both boiler 18 and electrical heater 62 are provided in addition to the engine-driven alternator 14.

When the engine 12 is running to drive the alternator 14 the ratio of the amount of heat energy to the amount of electrical energy produced is dependent upon the engine speed but is generally approximately 3:1. If the requirements for the building in which the unit 10 is installed and using the electricity and heat generated by the mCHP unit 10 are in this proportion then all is well. However, there arc several benefits in being able to produce more heat than required by using some of the electrical output and converting it to heat in the system.

A further, and equally important use, for the electrical heater 62 or the boiler 18 is to preheat the engine 12 and engine oil 56 before start up of the engine 12 from a cold start, so as to minimise where on the engine moving parts. This is made possible, because the electrical heater 62 or boiler 18 is adapted to heat water in the water circuit 22, which passes through the oil sump 36 by means of water conduit 34.

Although not shown in Figure 1, the water circuit 22 also passes through the engine block of engine 12, as mentioned previously.

When the engine 12 is running at normal operating temperature, flow of water around the water circuit 22 which passes through the engine block is arranged to cool the engine and heat the water. By a reverse process, when the engine 12 is not running, hot water flowing around the water circuit 22 can he used to heat the engine 12 before start up so as to minimise wear on the engine moving parts.

A yet further use for the electrical water heater 62, or boiler 18, is to heat the oil 56 in the oil tank 36 when the engine 12 is not running so as to induce any condensation in the oil 56 to evaporate. Condensation can form in the oil 56 since the engine 12 has a normal operating temperature of around 90-100 degrees Celsius, whilst the oil in the tank 36 will be around 60-70 degrees when the engine is operating. Therefore, the speed at which condensation evaporates from the oil is limited. The process for heating the oil 56 by exchange of heat energy from water flowing in the water circuit 22 through water conduit 34, which is in contact with oil 56 in the sump 36, is substantially the same process as that described above.

Prior to start up of the engine 12 from cold, valve 52 can be positioned so as to shut off flow of water from outlet 54 to the central heating system 24. In this way. water in the water circuit 22 pumped by water pump 32 can flow through the exhaust/water heat exchanger 28 where it is heated by the electrical heater 62 and/or through the booster boiler 18 (depending on the operating status of the boiler 16 and the position of valve 26) and returned via conduit 50 to the water pump 32. Water continues to flow around the water circuit 22 until the engine 12 and/or the oil 56 has reached a desired temperature.

When the engine 12 is running, valve 52 may be positioned so as to direct water in water conduit 22 from outlet 54 through the central heating system 24 and back through inlet 30. In this way, the electrical heater 62 and/or boiler 18 is operable to provide a boost heat function so as to provide additional heat energy to the building above that recovered from the waste heat from the engine 12.

The gas burner 16 of the gas booster boiler 18 is connected to a controller for controlling the supply of fuel to the gas burner 16. The controller for the electrical heater 62 and the gas burner 16 may he a single controller, or may be separate controllers. Either or both of these controllers may receive feedback from one or more sensors within the mCHP unit 10. For example, the or each controller may be connected to one or more temperature sensors disposed in the oil sump 36 and/or the engine 12. Additionally, or alternatively, the or each controller may be connected to a sensor disposed within the oil sump 36 for sensing accumulation of condensation in the oil 56.

The gas booster boiler 18 is essentially a heat exchanger for transferring the heat of combustion from the burner exhaust generated by the gas burner 16 into useful heat energy in the water which flows through the gas booster boiler 18 as part of the water circuit 22.

The valve 26 is a diverter valve for controlling the flow of water through the exhaust/water heat exchanger 28 and/or the gas booster boiler 18. The valve 26 is operatively coupled to a controller for controlling the position of the valve 26.

In an embodiment, the engine 12 is operable using the same fuel as the gas burner 16. This has significant advantages in reducing the number of separate fuel supplies necessary for operating the mCHP unit 10. However, it will be appreciated that the burner 16 for the booster boiler 18 may be adapted to run on a different gaseous fuel or indeed a liquid fuel as appropriate. The fuel for the burner 16 of the booster boiler 18 may be different from that used by the engine 12.

One or more control valves (not shown) may be provided for controlling the supply of fuel to the burner 16 and the engine 12. This may be a single control valve or may be a separate control valve for each of the burner 16 and the engine 12. The or each control valve is connected to a controller for controlling operation of the or each control valve. The or each controller for the diverter valve 26 and for the or each control valve for the burner 16 and engine 12 may be operatively coupled such that water flows in the relevant portion of the water circuit 22 according to whether the engine 12 and/or the burner 16 are in operation.

Figure 2 illustrates part of the mCHP unit 10 and shows the exhaust/water heat exchanger 28 in greater detail. The heat exchanger 28 includes a first "hot" section 64 and a second "cool" condensing section 66 which in this embodiment are separated by thermal insulation 68. The hot section 64 has a water inlet 70 and a water outlet 72. The condensing section 66 has a water inlet 74 and a water outlet 76. An exhaust conduit 78 is arranged to convey hot exhaust gas 80 from the engine 12 through the hot section 64 and then through the condensing section 66 of the heat exchanger 28.

The exhaust/water heat exchanger 28 is connected to the water circuit 22 as follows.

Water is pumped by the water pump 32 via water conduit 22 to the inlet 74 of the condensing section 66. The water flows through the condensing section 66 and around the exhaust conduit 78 which passes therethrough and then exits via outlet 76. A water conduit 82 is connected to the outlet 76 of the condensing section 66 and is arranged to convey the water towards the inlet 70 of the hot section 64 of the exhaust/water heat exchanger 28.

In the embodiment shown in Figure 2, the water conduit 82 does not convey the water directly to the inlet 70 of the hot section 64 of the heat exchanger 28. Instead, the water conduit 82 is arranged to convey the water from the outlet 76 so as to pass through the engine 12 and then out via a further water conduit 84 to the inlet 70. However, it will be appreciated that water conduit 82 may be connected directly between outlet 76 and inlet 70. Water which enters the hot section 64 of the heat exchanger 28 via inlet 70 flows through the hot section 64 of the heat exchanger 28 and around the exhaust conduit 78 and then exits via outlet 72 which is connected to water conduit 40 of the circuit 22.

For the mCHP unit 10 to achieve good efficiency, it is important that the maximum amount of heat is extracted from the exhaust of the engine 12. To extract the heat from the exhaust gases they are passed through heat exchanger 28 in which the heat is transferred from the exhaust gas to cooling water in the water circuit 22. How well the heat is extracted from the exhaust gases is a function of the difference in the temperature of the exhaust gas and the cooling water.

The heal exchanger 28 is configured so as to maximise the difference in temperature of the exhaust gas and the cooling water by the arrangement of the heat exchanger 28 and the path of the cooling water through the heat exchanger 28. This design ensures that the steam content of the engine exhaust 80 condenses in the heat exchanger 28 over as wide a working range as possible, thus liberating the latent heat of vaporisation which exchanges more heat energy into the water circuit 22. The condensing of the steam in the exhaust gas 80 takes place in the condensing section 66.

The hot section 64 and the condensing section 66 of the heat exchanger 28 are shown in Figure 2 as a single unit with thermal insulation 68 between the hot section 64 and the condensing section 66 so as to improve the thermal performance of the heat exchanger 28. However, in an alternative embodiment, the hot section 64 and the condensing section 66 may be two discrete heat exchanger units which together form the heat exchanger 28. Each heat exchanger section 64, 66 may he of conventional type and may, for example, have a plate-like, or tubular construction to direct the water through the section.

In the embodiment shown in Figure 2, water from the central heating system 22 is directed through the oil sump 36 before being directed via water conduit 38 in to the condensing section 66 of the heat exchanger 28. In an alternative embodiment, the relatively cool water from the central heating system 24 may be conveyed directly to the condensing section 64.

In a yet further alternative embodiment, the alternator 14 may be water cooled and the relatively cool water from the central heating system 24 may be directed first through the water cooled alternator before being directed in to the condensing section 64 of heat exchanger 28. Passing the water through the water cooled alternator first has benefits in that for maximum electrical efficiency, the alternator 14 should be operated at the lowest temperature possible. However, there may he a trade off between the electrical efficiency of the alternator 14 and the thermal efficiency of the heat exchanger 28.

Also, in the embodiment depicted in Figure 2, the water conduit 82 is arranged to convey cooling water through the engine 12 after exiting the condensing section 66 and before entering the hot section 64 of the heat exchanger 28. This cooling water may pass through other components in the mCHP unit 10. In particular, the water may pass through the engine 12 crank case, cylinder barrel and/or cylinder head after leaving the condensing section 66 but before entering the hot section 64 of heat exchanger 28.

In exemplary embodiments, the mCHP unit 10 incorporates a circuit for transporting the working fluid from a central heating system of a building. through an internal fluid circuit within the mCHP unit 10, and back to the central heating system of the building, wherein waste heat energy from the engine and/or the heat of combustion from the fuel burner is converted into useful energy in the working fluid within the internal fluid circuit, and wherein the internal fluid circuit is arranged so that cool water enters the circuit from the central heating system, is arranged to pass through or adjacent a relatively cool component within unit for recovering heat energy from said relatively cooled component, before passing through or adjacent a series of successively less cold components within the unit (the series comprising at least two components, the first having an expected normal operating temperature colder than the second and so on throughout the series) in order to recover heat energy from said series of successively less cold components. In effect, the coolest component is cooled first (i.e. with the coolest water, e.g. just after it returns to the unit from the radiators in the central heating system), and then the next coolest component, and so on, until the working fluid gets to the hottest component. This arrangement and methodology has been found to provide for an advantageous net heat transfer effect within the unit, and will be applicable to units not incorporating a boost burner or fuel burner.

By way of example, an exemplary flowpath for the working fluid would begin with the coolest water passing first through or adjacent the alternator 14, before passing through or adjacent the following series of components (starting with the coolest first): the engine sump, the coolest part of the exhaust heat exchanger, the cylinder block of the engine, the cylinder head and the exhaust manifold. Under normal operating conditions, the effect of this flow path would ensure that the water exiting the circuit was hotter than before it entered the circuit.

It will be understood that the exhaust from the engine has a very high temp range (from say 900 degree C at the exit of the cylinder head to 60 degree C as it exits the heat exchanger). Hence, in exemplary embodiments, the exhaust gas heat exchanger is split into a number of parts, so that each part can communicate with the water circuit at a position in series to give best overall heat transfer.

Figure 3 illustrates the mCHP unit 10 connected to a multiple balanced flue 86, which passes through a wall 88 of a building in which the mCHP unit 10 is installed, and thereby connect the mCHP unit 10 with ambient air outside the building. A cross section through the flue 86 along line a-a is shown in Figure 3a.

As shown in Figure 3a, the multiple balanced flue 86 has an outer conduit 90, a first inner conduit 92 generally concentrically arranged within the outer conduit 90, and a second inner conduit 94 disposed within the outer conduit 90 and integrally formed with the outer wall of the first inner conduit 92.

A space 96 between the outer conduit 90 and the first inner conduit 92 is arranged to convey the incoming ambient air from outside the building towards the mCHP unit 10 for use in the combustion process by the engine 12 and/or the burner 16.

A space 98 hounded by the first inner conduit 92 is arranged to convey exhaust from the burner 16 of the gas booster (auxiliary) boiler 18 to the ambient air outside the building in which the mCHP unit 10 is installed.

A space 100 bounded by the second inner conduit 94 is arranged to convey exhaust from the engine 12 to ambient air outside the building in which the mCHP unit 10 is installed.

The IC engine 12 exhaust will typically be at a higher pressure than the gas booster boiler exhaust, and will also have an inevitable tendency to pulse and carry slightly more contaminants. It is therefore preferable to keep the two exhaust streams separate so as to prevent mixing of the exhaust from the engine 12 with exhaust from the burner 16 within the flue 86.

Keeping the two exhaust streams separate eliminates, or at least reduces, pressure cross talk or interference which may cause fuelling and instability problems in control of the gas booster boiler 18. By keeping the two exhaust streams separate both within the mCHP unit 10 and within the flue 86 it also avoids any tendency to back-feed gas into the boiler heat. exchanger 28 from the internal combustion engine 12 and vice versa.

For good thermal efficiency of the overall system, the conduit 94 which carries the engine flue is in direct thermal contact with the incoming air supply 104 thus giving good heat exchange between outgoing flue gas and the incoming air supply. As can clearly be seen in Figure 3a, the conduit 94 is significantly smaller than the conduit 92 and so a large proportion of the outer surface of the conduit 92 is in direct contact with the incoming air supply 38 which again provides good thermal efficiency due to the heat exchange between the outgoing boiler exhaust and the incoming air supply 38.

In the embodiment described above with reference to Figures 3 and 3a, the conduit 94 which carries the engine flue is generally straight and runs parallel to the conduit 92 which carries the auxiliary boiler exhaust flue. However, several alternative arrangements are envisaged. For example, the conduit 94 need not be integrally formed with the conduit 92. A plurality of the conduits 94 may be provided arranged spaced around the conduit 92. The or each conduit 94 may be spirally. as opposed to linearly, arranged around the conduit 92. One or more of these alternatives may provide improved heat transfer which may need to be offset against the increased cost of production more complex flue arrangement.

In a yet further alternative embodiment, the incoming air for (he burner 16 and the engine 12 need not he conveyed along a common conduit. Instead, separate conduits may he provided for the incoming air for each of the burner 16 and the engine 12. In the case of separate air conduits, each air conduit may have one or other of the engine flue and exhaust flue conduits concentrically or otherwise disposed therein.

It will he understood that separation of condensate from the flue gases in an mCHP unit can he a problem. In a wall mounted mCHP unit, the problem is less of an issue, because a condensate separator can be mounted within the unit and the unit can be configured to ensure that any condensate collected by the separator is allowed to drain away to a convenient place under gravity. However, to overcome the problem in a floor mounted units, a pump may be required in some instances, in order to ensure that any condensate is moved away from the separator.

As mentioned above, the IC engine 12 exhaust will typically be at a higher pressure than the gas booster boiler exhaust, and this pressure can he used to push the engine exhaust to an elevated location, e.g. via a flue extending from the unit to atmosphere at a location above the engine. This may be particularly the case for the flue system shown in Figures 3 and 3a, where the engine exhaust is carried by a relatively small diameter conduit. In exemplary embodiments, a condensate separator is mounted in the flue at an elevated location relative to the engine and exhaust heat exchanger, for separation away from the unit. The pressure from the engine and the small diameter exhaust gas conduit ensures that the exhaust containing condensate is pushed up to the high level separator. There, any collected condensate can be allowed to drain away under gravity. This arrangement obviates the need for a pump to deal with condensate issues for floor mounted mCHP units or other mCHP units where there is insufficient head to enable a unit-contained separator to allow collected condensate to drain away under gravity.

Referring now to Figures 4 and 5, a modified engine/generator assembly 200 for use in an embodiment of the invention is shown in more detail. An alternator 14 is connected to an output of the IC engine 212. It will be understood that the assembly may be responsible for generating considerable vibration during operation. In order to reduce the level of vibration, an anti-vibration device 202 is attached to the assembly 200.

The anti-vibration device 202 consists of an elongate member or arm 204, one end of which is attached (e.g. via a clamp arrangement 205 and bolts 206) to the assembly (in this case, a crank case 211 of the IC engine 212). The opposite end of the arm 204 is arranged in free space (i.e. is not grounded to another part of the MCHP unit 10). A weight 208 is provided at the end of the arm 204. The anti-vibration device 202 serves as a cantilever leaf spring, and is configured to flex, and thereby allow the weight 208 to move, e.g. backwards and forwards, relative to the assembly 200.

The arm 204 is tubular (i.e. steel tube) in exemplary embodiments, but may he of solid construction in other embodiments, or a flat leaf spring.

By tuning the anti-vibration device 202, e.g. by changing the mass of the weight, and/or the position of the weight 208, and/or by changing the length and/or configuration of the arm 204, it is possible to influence the frequency at which the device will vibrate during operation of the assembly 200.

Accordingly, by matching that frequency with the vibration characteristics of the assembly 200, it will be possible to cancel vibration effects of the assembly and in turn reduce the overall transmitted vibration to the rest of the MCHP unit, e.g. of the 30 kind shown in Figure 1.

In exemplary embodiments, it may be preferred to mount the device 202 on another part of the assembly 200, e.g. on the alternator casing 213.

The device 202 provides an anti vibration mechanism that is cheap and easy to manufacture, and avoids the need for a working fluid (and associated seals) to provide a damping effect.

For the IC engine MCHP unit 10 to be commercially successful, it needs to be capable of operating successfully with long service intervals. The assembly of Figure 4 incorporates two spark plugs 301, 302 per cylinder of the engine 212. A controller 304 (ECU) is programmed to fire the spark plugs 301, 302 alternately. When incorporated in an IC engine-driven mCHP unit, the engine 212 has been shown to significantly increase the typical service period for the mCHP unit 10. The controller 304 is programmed to monitor the spark plug performance, e.g. to detect if one of the spark plugs 301, 302 wears out or fails. In such instances, the controller 304 is programmed to switch the ignition to the other spark plug 301, 302 continuously. The controller 304 is configured to raise an alarm (e.g. a visual and/or audible alarm on the MCHP unit 10) or via a wireless or wired link to a remote user/service agent, indicating that the unit needs servicing/repairing.

An IC engine-driven mCHP unit incorporating an engine having two spark plugs per cylinder has been found to benefit from an extended service life, in particular when the engine is operable to use the two spark plugs, but with only one firing at a time, alternately, one plug for each combustion event.

In exemplary embodiments, the ECU 304 is used to control all engine functions, including the ignition system. Sensors (not shown), e.g. hall effect type sensors, are used to determine crankshaft position in order to time the ignition spark. In order to operate the two spark plugs per cylinder, the ECU 304 outputs to two separate ignition circuits, one for each spark plug 301, 302. Software in the ECU 304 decides which spark plug 301, 302 to fire and monitors the spark plug condition (e.g. using known engine technology).

It will be understood that the units described herein include a fuel control system for controlling the supply of fuel to the engine 12 when the engine is intended to be running. Fuel control systems for engines are known and will not be described here.

It will he understood that IC engine-driven mCHP units require oil in order to maintain adequate lubrication of the engine during use. Over a long period of use, this may raise service issues. In particular, the oil capacity of a standard IC engine sump may he insufficient to accommodate the oil usage required to enable the unit to run for a desirably long period between services.

In order to address this problem, a system of oil replenishment has been devised, an 10 example of which is shown in Figure 6.

An IC engine for use in an mCHP unit, e.g. of the kind shown in Figure 1, is indicated at 412. The engine 412 includes a housing 401 which defines an oil sump 402. An auxiliary oil tank 403 (for holding an auxiliary supply or reservoir of oil) is located in communication with sump 402. An oil supply conduit 404 is arranged for conveying oil from the oil tank 403 to the sump 401 and an oil outlet conduit 405 is arranged for conveying oil from the sump 402 to the oil tank 403. An oil pump 406 is provided in the oil supply conduit 404, for pumping oil from the oil tank 403 to the engine housing 401. An oil filter 407 is provided upstream of the oil pump 406, for filtering oil as it travels from the tank 403 to the engine housing 401.

The oil tank 403 provides an auxiliary supply of oil for the engine 412 and is intended to be mounted with the engine 412 inside an mCHP unit (e.g. located within the same overall housing or cabinet for the mCHP unit).

The pump 406 may be controlled to pump oil to the engine housing 401 (e.g. constantly or in accordance with a predetermined schedule dependent upon the demand on the engine 412) when the engine 412 is in use.

The oil outlet conduit 405 defines an overflow weir 408 on the sump 402, so that excess sump oil may flow out of the sump 402 towards the oil tank 403, e.g. as a result of supply of oil being provided to the sump 402 from the supply conduit 404.

The oil supply conduit 404 opens into the engine housing 401 at a location above the level of the weir 408.

The position of the weir 408 deteit tines the oil level in the sump 402 of the engine 412, and the flow of oil from the auxiliary supply ensures that a sufficient volume of oil is present in the system for a desired period between services. The flow of oil in the system helps with oil cooling (especially if the supply is constant). Re-circulating the oil through the oil filter 407 assists in keeping the engine oil clean.

An advantage of mCHP units (e.g. of the kind described herein) is that they can often be used to export (excess) electrical output into an electricity distribution grid.

However, depending on the installation, there is usually a limit imposed by the electrical grid operators as to the maximum electrical output that is allowed to be exported to the grid.

Typically, the electrical output from the mCHP unit to the grid will be a function of the mCHP electrical output minus the electrical load of the building to which the mCHP is connected. Hence, there may be instances in which the output of the mCHP unit exceeds the maximum output allowed to the grid, e.g. if the electrical load of the building is low.

Clearly, for a maximum return from the mCHP unit, the electrical output of the mCHP unit to the grid needs to be kept at the maximum limit as often as possible.

In an ideal situation, the sum of the building load and the value of allowable electrical export to the grid will exceed the output from the electrical output from the mCHP unit. However, if the building load is low, the available output to grid will increase and may potentially exceed the allowable limit.

Accordingly, a system for regulating the electrical output of an mCHP unit has been devised, in order to monitor the level of electrical output from the mCHP unit to the grid and to reduce the electrical output of the mCHP unit if the maximum allowable output to the grid is reached.

Figure 7 shows an embodiment of such a system, indicated generally at 500.

The system 500 includes an mCHP unit 510 configured for generating electrical energy and including means for converting waste heat produced during the generation of the electrical energy into useful energy in a working fluid (e.g. for use in a central heating system). The mCHP unit 510 may be in accordance with any of the embodiments described herein, or other known forms of mCHP unit.

The unit 510 includes an inverter arrangement or power electronics 502 to enable the unit 510 to transfer generated electrical energy to a power distribution hoard 504 in a suitable format, e.g. for powering a lighting circuit 506 or other building power circuits 508 for a building 512.

The mCHP unit 510 is also connected to a power distribution grid 514, for exporting power to the grid 514. However, the grid 514 has an export limit, e.g. 2kW.

A power sensor 516 (e.g. within the unit 510) is arranged to monitor the power output from the unit 510, the power consumption by the power distribution board 504, and the power output to the grid 514. If the power sensor 516 indicates that the maximum allowable output to the grid 514 is reached (e.g. due to a reduction in demand on the power distribution board 504), a controller 518 (e.g. an ECU in the unit 510) is configured to modify the operation of the unit 510, or to modify the use of the output from the unit 510.

In one embodiment, the unit 510 includes an engine-driven electric generator (e.g. of the kind described herein) and the controller 518 is configured to moderate the operation of the engine (e.g. to turn it down) in order to reduce the output from the unit 510.

In another embodiment, the controller 518 is arranged in communication with an electrical heater on the unit (e.g. of the kind described herein for heating the working fluid circuit within the unit), which can be used to convert electrical energy from the generator into heat energy within the working fluid in the unit 510. Hence, if the grid export limit is exceeded, the controller can he used to switch on the electrical heater, and thereby reduce the power output from the unit 510. This would provide a very fast response, without needing to moderate the engine output.

In addition or alternatively, the controller may be arranged in communication with one or more auxiliary electrical devices 520, external to unit 510 and not powered via the distribution hoard, in order to divert power to the one or more auxiliary electrical devices if the grid export limit is exceeded, thereby reducing the power output from the unit 510. Again, this would provide a fast response, without needing to moderate the engine output.

It may be preferable to combine two or more of the above options, in order to provide an optimal solution for avoiding breach of the grid export limit.

Referring now to Figures 8 to 10, there is shown an mCHP unit 210 incorporating the 10 engine assembly 200 from Figure 4 and a boost boiler arrangement 250 (which may be of the kind described herein, e.g. with reference to Figure 1).

The unit 210 takes the form of a cabinet 252 which defines a common housing for the assembly 200 and the boost boiler arrangement 250. The cabinet 252 is primarily intended to be mounted on a wall in a building, e.g. via a bracket 254 on a rear wall of the cabinet 252.

As can be seen, the engine assembly 200 is mounted at a position below the boost boiler arrangement 250. More particularly, the engine assembly 200 is mounted on a support structure 256 supported off a base wall 258 of the cabinet 252 by feet 260, which include springs 262 for damping vibration of the support structure 256 and assembly 200 during running of the engine 212.

The anti-vibration device 202 is arranged to extend vertically within the cabinet, wherein the distal end of the arm 204 is uppermost, i.e. with the weight 208 held above the level of the engine 212.

The boost boiler arrangement 250 is suspended from the roof 264 of the cabinet 252.

In this embodiment, the engine 212 has a single cylinder with twin spark plugs 301, 302 (e.g. as in the illustrated embodiment Figure 4). The cylinder is arranged at an angle to the vertical.

A heat exchanger assembly 268 for the engine 212, e.g. of the kind described with reference to Figure 2, is mounted on top of the engine assembly 200.

Part of a flue 270, e.g. forming part the flue system described with reference to Figures 3 and 3a, is shown extending from the roof of the cabinet 252, for transferring engine and boiler exhaust away from the unit 210.

It will be understood that the mCHP unit 210 is of a kind having an alternator 14 as an electric generator for generating electrical energy, an IC engine 212 for driving the alternator 14, wherein the heat exchanger assembly 268 is arranged for transferring waste heat energy from the engine and/or the alternator into useful heat energy in a working fluid passing through a water circuit within the unit (e.g. of the kind described with reference to Figures 1 and 2), for use in a central heating system. An electrical immersion heater (not shown) may be included in water circuit, e.g. as described with reference to Figures 1 and 2). The boost boiler arrangement 250 provides a heat boost function, e.g. as described with reference to Figure 1. The anti-vibration device is arranged for reducing the level of vibration from the engine assembly 200 during use of the engine. Control systems for the ignition and fuelling of the engine and/or for controlling the flow of working fluid through the unit 210, and/or for controlling any other systems or functions described herein with reference to Figures 1 to 7, may be included within the unit 210. Other features described herein with reference to Figures 1 to 7may be incorporated within the unit 210.

It will he understood that the units described herein include a fuel control system for controlling the supply of fuel to the engine 12 when the engine is intended to be running. Fuel control systems for engines are known and will not be described here.

The mCHP units described herein are advantageous in many respects. Where a fuel burner is incorporated, it becomes possible to generate additional useful heat energy e.g. for times when the heat demand exceeds the heat available from the engine-driven generator alone. The boost heat facility provided by the burner widens the appeal of the unit and allows the unit to replace a standard boiler instead of being in addition to it, which saves space, cost and complexity. Other aspects and features of the units described herein address issues of efficiency, and or noise and or packaging, and other issues related to the improvement of conventional mCHP technology.

Although described with reference to an IC engine assembly of a kind suitable for use in an mCHP unit having boost burner 18, it will be understood that the anti-vibration device of Figures 4 and 5 is equally suited for use in noise/vibration reduction in engine-driven mCHP units which do not incorporate a boost burner 18. Similarly, the twin-spark plug ignition system employed in the IC-engine assembly of Figure 4 is also applicable to mCHP units which do not include a boost burner. The oil recirculating system described with reference to Figure 6 is applicable to IC-engine driven mCHP units with or without a fuel burner, and to engines having multiple or single spark plugs per cylinder.

Although the invention has been described above with reference to one or more embodiments, it will he appreciated that various changes or modifications may he made without departing from the scope of the invention as defined in the appended claims.

Claims (9)

1. Claims 1. A micro combined heat and power (mCHP) unit comprising: an electric generator for generating electrical energy, an engine for driving the generator, and a heat exchanger arrangement for transferring waste heat energy from the engine and/or the generator into useful heat energy in a working fluid, the unit further comprising an internal fluid circuit for conveying the working fluid from a central heating system of a building, through the mCHP unit, and back to the central heating system of the building, wherein waste heat energy from the engine is converted into useful energy in the working fluid within the internal fluid circuit, by allowing relatively cool water to enter the internal fluid circuit from the central heating system, and to he conveyed through or adjacent a relatively cool component within unit for recovering heat energy from said relatively cooled component, before passing through or adjacent a series of successively less cold components within the unit, in order to recover heat energy from said series of successively less cold components, one after another.
2. 2. A micro combined heat and power (mCHP) unit comprising: an electric generator for generating electrical energy, an engine for driving the generator, and a heat exchanger arrangement for transferring waste heat energy from the engine and/or the generator into useful heat energy in a working fluid, the unit further comprising an internal fluid circuit for conveying the working fluid from a central heating system of a building, through the mCHP unit, and back to the central heating system of the building, wherein circuit comprises a flowpath through or adjacent a series of components of the unit arranged ascending order of expected normal operating temperature, with the coolest first, so that the working fluid, when conveyed through the circuit, cools the coolest of said components first, then the next coolest component in the series, and so on, until the working fluid gets to the hottest component in the series.
3. 3. The mCHP according to claim 1 or claim 2, wherein the series of components comprises at least two components, the first having an expected normal operating temperature being colder than the second and so on throughout the series.
4. 4. The mCHP unit according to any preceding claim, wherein the coolest component in the series is the generator.
5. 5. The mCHP unit. according to claim 4, wherein the generator is an alternator.
6. 6. The mCHP unit according to any preceding claim, wherein the hottest component in the series is an exhaust manifold last.
7. 7. The mCHP unit according to any preceding claim, wherein the exhaust gas heat exchanger is split into a number of parts, so that each part can communicate with the working fluid at a position in series to give best overall heat transfer
8. 8. The mCHP according to any preceding claim, wherein the unit is a floor mounted cabinet or housing.
9. 9. The mCHP unit according to any preceding claim, wherein the engine is an internal combustion engine.