GB2294315A

GB2294315A - Combined heat and power sources

Info

Publication number: GB2294315A
Application number: GB9419943A
Authority: GB
Inventors: Keith Terrence Moss
Original assignee: Post Office
Current assignee: Post Office
Priority date: 1994-10-04
Filing date: 1994-10-04
Publication date: 1996-04-24
Also published as: GB9419943D0

Abstract

A combined heat and power source comprises an engine 1, an alternator 3, heat exchangers 6, 12 to transfer heat from the body and the exhaust 11 of the engine to an output heat exchanger 9, 15 and valve and/or pumps 8, 14 to control the flow of the heat exchanger fluid. An electrical heating element 17 is also provided at the output heat exchanger and this serves to supplement or replace the waste engine heat and/or to provide heating for the engine. The combined power source operates within a predetermined efficiency range which is maintained by providing heating via the electrical heating element in relation to power demands and by selectively employing the power source to provide heat and power. <IMAGE>

Description

COMBINED HEAT AND POWER SOURCE The present invention relates to a combined heat and power source and more particularly to the application of such a source to the heating of individual premises.

In cold or temperate climates, surplus or otherwise wasted heat from electricity power stations is sometimes tapped for use in providing very large quantities of continuous heat and/or hot water outside the power station. In some arrangements, this excess heat is used industrially or domestically for a large number of premises. Combined heat and power sources are not solely restricted to large scale applications. Relatively small scale combined heat and power sources, usually powered by diesel engines or small gas turbines, may be employed to supplement and/or to replace external power supplies within individual premises or adjacent groups of premises, for example individual groups of commercial, industrial or residential buildings.Where such sources are utilised, maximised efficiently of matching of supply and demand, with minimal waste of fuel, for both electrical and thermal power is highly desirable. The heat and electrical power requirements in such premises are largely dependent upon the time of day and/or ambient conditions. In commercial applications, for example, where the working day may run from 8am to 6pm, the required electrical power outside the working hours is normally very low in relation to the peak demands of the day, whereas the requirement for heat may be dependent on other factors rather than simply the working hours. During relatively cold ambient temperatures, it is likely that the requirement for heat will be greatest immediately preceding the start of each working day in order to provide acceptable ambient early morning conditions.

The present invention seeks to provide an improved combined-heat and power source in which heat and electrical power outputs are better coordinated to improve overall efficiency and cost effectiveness in relation to externally provided power sources. The present invention also seeks to reduce the need for supplementary heating and to give better operation of the combined heat and power sources by extending their operational life and by reducing maintenance costs.

According to the present invention, there is provided a combined heat and power source comprising electrical and heat power generating parts, for supplying power to respective outputs, in which waste heat from the electrical power generating part serves to provide generated heat power and in which the generated electrical power is controllably converted into heat to supplement the generated heat power in such manner as to maintain the efficiency of the combined source in a predetermined range.

The predetermined range may be narrow and centred on the maximum fuel efficiency of the loaded motive means.

Preferably the electrical power generating parts comprise combustion driven motive means and alternator means and the waste heat power includes the exhaust heat from the motive means and preferably also the waste heat from its body.

Preferably the waste heat is made available at a heat output by heat exchanging means at the power source, by fluid means which transfers the exchange heat and by further heat exchanging means at the output. The device may be connected to an external electrical supply which may be controllable to provide heat, preferably at the output or, alternatively, at the power source. The motive means may be an internal combustion engine.

Reference will now be made, by way of example only, to the accompanying drawings in which: Figure 1 shows a combined heat and power source; and Figure 2 shows a flow diagram for the operation of the apparatus in Figure 1.

Figure 1 shows a combined heat and power source which provides electrical power from an alternator 3 and heating at a heat output 10. The combined source comprises a motive unit 1, with an output 2 linked to the alternator 3, and an exhaust 11. The motive unit 1 may be an internal combustion engine or gas turbine or any other motion inducting means. The alternator may be any apparatus adaptable to utilise the motion of the motive means to generate electrical power. The motive unit 1 includes a jacket or cooling arrangement 4 through which a fluid 5 flows via a valve and/or pump arrangement 8 to a heat exchanger and/or a radiator 6.

The exhaust heat from the motive unit 1 passes through an exhaust gas heat exchanger 12 which communicates the heat to the heat output 10 through a fluid 13 via a valve and/or pump arrangement 14 and a further heat exchanger 15 provided at the heat output 10.

In addition, transfer to heat from the heat exchanger and/or radiator 6 for the motive unit 1 to the output 10 from a secondary side of the heat exchanger 6 through a fluid 7 via a valve and/or pump arrangement 8 to a further heat exchanger 9 at the output 10. The fluids 5, 7 and 13 may be water with an anti-freeze solution or oil. The heat transferred between the body of motive unit 1 in particular and the heat output may take place in either direction, either to provide heat to the output as described above or to provide warming heat to the body of the motive unit 1 for speedy optimum operation of cold motive units. The heat exchanging means at the heat output 10 may pool exchanged heat or may extract heat in sequence for the medium to be heated, for ambient example air or cold water.

The waste heat from the motive unit 1, alternatively, may be communicated directly to the output 10 without the use of the heat exchangers 6, 9, 12 and 15, the fluids 7 and 13 and the arrangements 8 and 14. Indeed, a simple valve may control the flow of exhaust gases to a heat exchanger to convert directly cold water or ambient air into heated water or air. This may also be the case with the waste heat generated from the body of the motive unit 1.

The heat output 10 is also provided with heating elements 17 which may be connected either to an external power source or to the alternator 3. These electrical heating elements 17 are provided to supplement the heat collected from the motive unit 1 and/or to provide heat thereto during start-up of the motive unit 1. A control device 16 enables the generated electrical power to be fed to the heating elements 17 to supplement and/or replace the externally supplied power.

In order to implement the combined heat and power source of the present invention at particular premises, the heat and power requirements of such premises must be first determined to provide data for the operation of the power source. If only electrical power is required during certain periods of the day, it may be advantageous to connect the electrical supply to the premises to an external supply rather than to the power source of the invention, since excess heat is, of course, to be wasted.

If, alternatively, the heating requirements are high as when the ambient temperatures are low, the electrical power requirements, which would affect the total heat output of the source, and the heat needed to warm the premises are desirably determined. In this connection, various temperature sensors may be provided to determine, in conjunction with timing devices, for example, the requirements of the premises to be supplied. To make best use of the heat and power source may necessitate the implementation of computer control device, with software taking account of the historical record of heating requirements for the premises and/or being able to interpret on-line information relating to the weather, for example.

Referring to Figure 2, this flow diagram shows an example of the operation of the apparatus shown in Figure 1. If the premises do not require heat, the externally supplied electrical current is disconnected from the electrical heating element 17 in the heat output 10 and, likewise, the generated electrical power is disconnected from the heating element 17. If, however, the premises do require heat, heat is transferred from the power source via the heat exchangers 6, 9, 12 and 15 to the output 10.

If, in addition, there is spare electrical capacity, whereby the motive unit 1 is under-utilised and running inefficiently, the heating element 17 is then connected controllably via the device 16 to the alternator 3 to provide additional heating. The motive unit 1 then provides heat directly from waste heat and indirectly from the generated electricity, with the operation of the motive unit 1 being maintained at a fuel efficient level, taking into account loading. If the heating is required to be at a high level and the demand for electrical power is low, the heating element 17 in the heating source 10 operates to provide a high output.Conversely, if the demand for electrical power is high, the supply to the heating element 17 is reduced, with care being taken to ensure that the meeting of unexpected demands in electrical power are not jeopardised; With computer control in addition to manual control and input, the expected electrical power demands may be logged and, accordingly, the operation of the heating element 17 varied automatically. Also, the power output for the whole source, the ambient temperature of parts of the premises, the electrical power consumption and the fuel input rate for the motive unit 1 may be monitored, allowing the cost of operating the system and its operation to be determined continuously and compared to that of externally provided power for selection of the most cost efficient. For example, the shutting down of heating element 17 may be started a few minutes before a high electrical power demand is expected to take account of expected increases in waste heat or the power source may be shut down near the end of the. working day to take account of feedback delays in monitoring heated areas.

Claims

CLAIMS:

1. A combined heat and power source comprising electrical and heat power generating parts for supplying power to respective outputs and in which waste heat from the electrical power generating part serves to provide generated heat power for the heat power generating part, with the generated electrical power being controllably converted into heat to supplement the generated heat power in such manner as to maintain the efficiency of the combined source when operating in a predetermined range by maintaining a generally constant load therefor.

2. A combined heat and power source according to claim 1, wherein the electrical power generating part comprises combustion driven motive means and alternator means and the waste heat is provided by the exhaust gas heat from the motive means.

3. A combined heat and power according to claim 2, wherein the waste heat source includes the heat from the body of the motive means.

4. A combined heat and power source according to claim 1, 2 or 3, wherein the waste heat is communicated to the heat output by heat exchanging means provided at the combined power source and at the output, with fluid means to transfer the exchanged heat therebetween.

5. A combined heat and power source according to any preceding claim, wherein the combined power source is connected to an external electricity supply controllable to provide heat at the output heat exchanging means.

6. A combined heat and power source according to claim 4 or 5, wherein the output heat exchanging means extracts heat in sequence from the generated heat to the medium to be heated.

7. A combined heat and power source according to claim 4, 5 or 6, wherein electrical heating means is provided at the output of the heat exchanging means.

8. A combined heat and power source according to any one of claims 2 to 7, wherein heat from the output heat exchanging means provides heat for the motive means.

9. A combined heat and power source substantially as herebefore described, with reference to and as shown in Figures 1 and 2 of the accompanying drawings.