GB2446159A

GB2446159A - Pre-heater for central heating and hot water supply systems

Info

Publication number: GB2446159A
Application number: GB0701744A
Authority: GB
Inventors: Christopher Charles Farrell
Original assignee: Zenex Technologies Ltd
Current assignee: Zenex Technologies Ltd
Priority date: 2007-01-30
Filing date: 2007-01-30
Publication date: 2008-08-06
Anticipated expiration: 2027-01-30
Also published as: GB0701744D0; GB2446159B

Abstract

The pre-heater 60 for a heating system includes a heating device 62 adapted to heat a fluid within a pipe 64 prior to the fluid being heated by a boiler. The pre-heater can be used to warm water or another fluid entering a boiler. The heating device may include a heating element in direct contact with the outer surface of the pipe. The heating element may be partially embedded into a flexible substrate and formed into a meandering path. A heat exchanger, microwave or ohmic heating source may alternatively be used for the heating device.

Description

P108497GB/SAB

A HEATER FOR CENTRAL HEATING AND HOT WATER SUPPLY SYSTEMS

FIELD OF THE INVENTION

The present invention relates to an apparatus for and method of enhancing the performance of a central heating system or a hot water supply system.

BACKGROUND OF THE INVENTION

Modem central heating and hot water supply systems frequently incorporate gas-fired or oil-fired condensing boilers. As is well known, the exhaust gases in such boilers contain moisture that can condense to release latent heat which may be used to provide additional heating.

During periods of high demand such as starting of a central heating system to provide space heating, the temperature of the heat exchange fluid at the output of the boiler may be below a target temperature and the boiler is operated at full power to achieve the target temperature in a minimum time period. The gas/oil and air flow rates are then adjusted to their maximum levels with the result that the exhaust gases pass through the heat exchanger at an increased rate. This leads to a reduction in the proportion of moisture that condenses and a corresponding reduction in the efficiency of the boiler. Accordingly a significant proportion of the energy expended by a central heating system during the course of a typical day is expended in the first hour of operation. Some estimates suggest that around 30% of the total daily energy use of the system occurs in the first hour of heating following a cold start.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a pre-heater for a heating system comprising a heating device adapted to heat a fluid within a pipe prior to the fluid being heated by a boiler.

It is thus possible to reduce the temperature rise that needs be imparted by the boiler, either in space heating mode or warm water supply mode (that is supplying water for washing, baths and so on).

According to a second aspect of the present invention there is provided an apparatus for heating a fluid comprising a boiler and a pre-heater, wherein the fluid is heated by the pre-heater prior to being heated by the boiler.

According to a third aspect of the present invention there is provided a method of enhancing the efficiency andlor power output of a fluid heating system comprising pre-heating a fluid before it enters a boiler.

RJEF DESCRIPTION OF THE FIGURES

The present invention will further be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of a combined central heating and hot water supply system having a pre-heater and constituting an embodiment of the present invention; Figure 2 schematically illustrates a first embodiment of a pre-heater; Figure 3 schematically illustrates a second embodiment of the pre-heater; Figure 4 is a plan view of a third embodiment of the pre-heater prior to fitting around a pipe of a central heating or hot water supply system; Figure 5 is a cross-section view of the pre-heater of Figure 4 taken on Section X-X of Figure 4 afler fitting the pre-heater around a pipe of a central heating or hot water supply system; Figure 6 schematically illustrates a power supply system for an embodiment of an electrically-resistive pre-heater; and Figure 7 schematically illustrates a further embodiment of the pre-heater.

DESCRIPTION OF PREFERRED EMBODiMENTS OF TILE INVENTION Figure 1 schematically illustrates a combined central heating and hot water supply system 1. For the purposes of illustration, boiler 2 provides heat for both central heating and hot water supply purposes. However, it should be understood that the boiler 2 may provide heat for only one of these purposes. Boiler 2 may be of the condensing or non-condensing type. Furthermore boiler 2 may burn gas, oil or any other combustible material. The boiler 2 comprises a combustion chamber 4 containing a heat exchanger 6 and a burner 8. The boiler 2 also comprises a pump 10, a multi-port valve 12, a supply outlet 14 and a return inlet 16 for a heat exchange fluid in the central heating system. A further heat exchanger 18 is selectively connectable in series with the heat exchanger 6 by the multi-port valve 12, so as to warm water for washing, bathing and the like. The further heat exchanger 18 is generally internal to a combination boiler, but can be provided in a hot water cylinder. A first space heater 20 has an inlet 22 and an outlet 24. A second space heater 26 has an inlet 28 and an outlet 30. The space heaters may, for example, be radiators and are connected in parallel. A supply path 32 is formed between the boiler outlet 14 and the space heater inlets 22 and 28. A return path 34 for the central heating system is formed between the space heater outlets 24 and 30 and the boiler inlet 16. A first pre-heater 36 is located at a convenient position along the return path 34 of the central heating system.

For hot water provision cold water enters the hot water supply system from the water mains supply at a cold water inlet 42, and hot water exits the hot water supply system from a hot water outlet 44. The hot water outlet 44 may, for example, be a hot water tap or a shower head. As shown in Figure 1, a second pre-heater 46 may be located at a convenient position between the cold water inlet 42 and the further heat exchanger 18. Alternatively, the second pre-heater 46 may be located at a convenient position along a return path 48 of the hot water supply system. The heat exchanger 6 within the boiler 2, the space heaters 20 and 26, the further heat exchanger 18 and the pipes connecting them contain the heat exchange fluid which is typically water. In Figure 1, the multi-port valve 12 is shown located in the return paths for the central heating and hot water supply systems; however, it may alternatively be located in the corresponding supply paths 32 and 38.

When only the central heating system is in use, the return path 48 of the hot water supply system is closed by the multi-port valve 12 and the heat exchange fluid does not circulate around the further heat exchanger 18. When only the hot water system is in use, the return path 34 of the central heating system is closed by the multi-port valve 12 and the heat exchange fluid does not circulate around the space heaters. When both the central heating and the hot water supply systems are in use, the multi-port valve 12 is adjusted so that the heat exchange fluid can circulate in a time multiplexed manner through both the further heat exchanger 18 and the space heaters. In use, combustion occurs at burner 8 thus heating the heat exchange fluid as it passes through the heat exchanger 6. The heat exchange fluid is pumped by the pump 10 so that heat exchange fluid passes through the space heaters 20 and 26 andior the further heat exchanger 18, and returns to the boiler 2.

The heat exchange fluid is cooled as it traverses the space heaters andlor the further heat exchanger. Pre-heater 36 when in use supplies heat to the cooled heat exchange fluid in the return path 34 of the central heating system before it enters the boiler 2 at return inlet 8.

Similarly pre-heater 46 can be used to supply heat to the cold mains water before it enters the further heat exchanger 18.

Pre-heating the heat exchange fluid in the case of the central heating system, or the cold water supply in the case of the hot water supply system, enhances the performance of the respective system by enhancing the efficiency andlor the effective output power. For example, in the case when only the central heating system is in use, the heat exchange fluid flow rate and the thermal load are fixed, the pre-heater is switched off and the boiler 2 is operated at full power, it may be assumed that the heat exchange fluid at the supply outlet 6 reaches a target temperature at the end of a heating period which varies in accordance with the air temperature. When the pre-heater is switched on, and the heat exchange fluid flow rate and thermal load remain fixed, the heat exchange fluid may be heated to the same target temperature either by operating the boiler 2 at a power level below the maximum power level for the same target time period, or by operating the boiler 2 at its maximum power level for a period of time less than the heating period. In the former case, the efficiency of the overall heating process is improved because the boiler operates more efficiently at a power level below its maximum power level (because the combustion products spend more time in contact with the heat exchanger 6 or the boiler may operate in a condensing mode). In the latter case, the efficiency of the overall heating process is improved because the boiler 2 is operated at maximum power for a reduced time.

Alternatively, the pre-heater may be switched on and the boiler 2 may be operated at its maximum power level for the heating period with the result that the heat exchange fluid at the supply outlet may be heated to a higher target temperature in excess of the original target temperature. In this case, the pre-heater simply boosts or augments the output power of boiler 2. This may be especially useful if boiler 2 is, for example, marginally under-powered for a particular installation, or is in use on a particularly cold day. Pre-heating the cold water from the mains supply using pre-heater 46 may enhance the performance of the hot water supply system in much the same ways as the central heating system performance is enhanced by pre-heating the heat exchange fluid as already outlined above.

In the descriptions of the pre-heater embodiments that follow, the pre-heater may correspond to the pre-heater 36 of the central heating system or the pre-heater 46 of the hot water supply system. The fluid in each case may be the heat exchange fluid of the central heating system or the water of the hot water system.

Figure 2 schematically illustrates a first embodiment of a pre-heater 50 corresponding to pre-heater 36 or 46. The pre-heater 50 comprises an electrically-resistive heating element 52 contained within a pipe 54. Heating element 52 is in direct thermal contact with, but electrically isolated from, the fluid. For example, the heating element 52 may be coated with a thin layer of electrically insulating material such as PTFE or PVC. The heating element 52 is formed into a helical coil about an axis that is aligned substantially parallel with the direction of the fluid flow. In use, heat is generated when an electric current is passed through the heating element 52.

Figure 3 schematically illustrates a second embodiment of a pre-heater 60 corresponding to pre-heater 36 or 46. Pre-heater 60 comprises an electrically-resistive heating element 62 wrapped around and in thermal contact with the outer surface of a thermally-conductive pipe portion 64. As shown in Figure 3, the heating element 62 may be wrapped around pipe portion 64 so as to form a helical coil. An electric current is passed through the heating element 62 thus generating heat. Heat is transferred to the fluid via the thermally-conductive pipe portion 64 as the fluid flows through pipe portion 64. The heating element 62 may be coated with a thin layer of electrically insulating material such as PTFE or PVC.

Figure 4 shows a pre-heater 70 which is easily retrofitted to existing installations and which comprises an electrically-resistive heating element 72 and a flexible electrically-insulating substrate 76. The heating element 72 is formed into a meandering path and may be at least partially embedded into the substrate 76 so as to form something like an electric blanket. The heating element 72 may be orientated in any arbitrary manner with respect to the direction of fluid flow. In the embodiment shown in Figure 4, for example, the heating element is oriented such that the majority of the length of the heating element 72 is perpendicular to the direction of fluid flow. However the heating element can alternatively be aligned such that the majority of the length of the heating element 72 is parallel to the direction of fluid flow. As shown in Figure 5, the heating element 72 of the electric blanket pre-heater 70 is, in use, fitted around and in thermal contact with the outer surface of a thermally-conductive pipe portion 74. The width of the electric blanket W is preferably large enough so that, when fitted around pipe portion 74, the electric blanket substantially encircles it. Figure 5 is a cross-section taken on X-X as indicated on Figure 4.

An electric current is passed through the heating element 72 thus generating heat. Heat is transferred to the fluid as the fluid flows through pipe portion 74 via the thermally-conductive pipe portion 74.

The electrically-resistive heating elements of any of the foregoing embodiments of the pre-heaters 36 or 46 may be operated by passing an electric current through them. For example, as depicted in Figure 6, the heat-exchange element 62 of the pre-heater 60 may be supplied with an electric current from a variety of sources. Such a current may, for example, be supplied from a mains socket 80 via a transformer-rectifier 82 or alternatively from at least one battery 84. In the latter case, this provides for the possibility that a renewable energy source such as a wind turbine generator 86 or a photovoltaic solar panel array 88 may be used to charge the or each battery 84. By way of illustration, modern central heating systems typically have a fluid flow rate of approximately 0.4 litres/s.

Assuming the heat exchange fluid is water, then to raise 0.4 litres of water each second by I C requires approximately 1.68 kW of power. Deep-cycle 12 V batteries are commercially available with capacities of 150 Ab. Such batteries are capable of delivering 1.8 kW of power for 1 hour. Thus assuming that the charging and discharging operations of such a battery are 100% efficient then, a 150 Ah deep cycle battery is capable of delivering sufficient power to pre-heat the water in the return path of a central heating system by 1 C for 1 hour or by 2 C for half an hour and so on. Furthermore, commercially available wind turbines with a swept area having a 2 m diameter are capable of generating 200 W at 12 V DC in moderate wind speeds of 15 knots. Photovoltaic solar panels are also capable of delivering approximately 20 W/m2 on average over the course of a day at a latitude of approximately 47 N. Thus a 10 m2 photovoltaic solar panel array is also capable of delivering 200 W on average during the course of a day. Thus if such a wind turbine or such a photovoltaic solar panel array were to charge a 150 Ah battery for 9 hours, then it would replenish the electrical energy expended in heating the water in the return path of a central heating system by I C for 1 hour. To provide protection against over-heating, pre-heater 60 may be switched on or off by a switch 90 in response to the temperature of the fluid as sensed by a temperature sensor 92. Temperature sensor 92, may, for example, be a thermistor either mounted inside the pipe portion 64 in direct thermal contact with the fluid, or mounted in thermal contact with the outer surface of the thermally-conductive pipe portion 64. The switch 90 may also be operated in response to a signal generated by a timer 94 thus allowing for the pre-heater 60 to be operated during a first part of a day and the at least one battery 84 to be charged during a second part of the day.

In alternative embodiments of the pre-heaters 36 or 46, the fluid may be heated using an alternative method. For example, microwaves or acoustic waves could be used to heat the fluid.

In further alternative embodiments of pre-heaters 36 or 46, the pre-heater heating element may comprise a heat exchanger which is analogous to the electrically-resistive heating element pre-heater embodiments of Figures 2 to 5, but wherein heat is provided via the heat exchanger heating element which contains a further heat exchange fluid that is heated remotely by a heat source. For example, Figure 7 schematically illustrates a pre-heater comprising a heat exchanger heating element 102 wrapped around and in thermal contact with the outer surface of a thermally conductive pipe portion 104. The heat exchanger 102 contains a further heat exchange fluid which is isolated from the fluid in the central heating system, and which is heated by a heat source such as a solar panel array 106 or a ground source heat exchanger 108 to a temperature greater than that of the fluid at the location of the heat exchanger 102. A pump 110 circulates the further heat exchange fluid to and from the heat exchanger 102 via pipes 112 and 114 respectively. To provide protection against over-heating, the pre-heater of Figure 7 may be switched on or off by a valve 116 in response to the temperature of the fluid as sensed by a temperature sensor 118. The temperature sensor 118, may, for example, be a thermistor either mounted inside pipe portion 104 and in direct thermal contact with the fluid, or may be mounted in thermal contact with the outer surface of the thermally-conductive pipe portion 104. The valve 116 may also be operated in response to a signal generated by a timer 120 thus allowing for the pre-heater of Figure 7 to be operated during a part of a day.

Claims

A pre-heater for a heating system comprising a heating device adapted to heat a fluid within a pipe prior to the fluid being heated by a boiler.
2, A pre-heater for a heating system as claimed in claim I, wherein the heating device comprises a heating element that is in direct contact with the outer surface of the pipe, and the pipe is a thermally-conductive pipe.
3. A pre-heater for a heating system as claimed in claim 2, wherein the heating element is at least partially embedded into a flexible substrate.
4. A pre-heater for a heating system as claimed in claim 2 or 3, wherein the heating element is formed into a meandering path and, in use, is wrapped around the outer surface of the thermally-conductive pipe.
5. A pre-heater for a heating system as claimed in claim 2 or 3, wherein the heating element is wrapped around the outer surface of the thermally-conductive pipe a plurality of times so as to form a coil having an axis aligned with the length of the pipe.
6. A pre-heater for a heating system as claimed in claim 2, 3 4 or 5, wherein the heating element is an electrically-resistive heating element and wherein an electric current is passed through the heating element to generate heat.
7. A pre-heater for a heating system as claimed in claim 2, 3, 4 or 5 wherein the heating element is a heat exchanger that contains a further fluid that is heated by a heat source.
8. A pre-heater as claimed in claim 1, wherein the heating device comprises a microwave source for directing microwave energy into the fluid.
9. An apparatus for heating a fluid comprising a boiler and a pre-heater, wherein the fluid is heated by the pre-heater prior to being heated by the boiler.
10. An apparatus for heating a fluid as claimed in claim 9, wherein the pre-heater comprises a heating element.
11. An apparatus for heating a fluid as claimed in claim 10, wherein the heating element is in thermal contact with the outer surface of the thermally-conductive pipe.
12. An apparatus for heating a fluid as claimed in claim 11, wherein the heating element is at least partially embedded into a flexible substrate.
13. An apparatus for heating a fluid as claimed in claim 12, wherein the heating element is formed into a meandering path in the substrate, such that, in use it is wrapped around the outer surface of the pipe.
14. An apparatus for heating a fluid as claimed in claim 11 or 12, wherein the heating element is wrapped around the outer surface of the thermally-conductive pipe a plurality of times so as to form a coil having an axis aligned with the length of the pipe.
15. An apparatus for heating a fluid as claimed in claim 10, wherein the heating element is in direct thermal contact with the fluid.
16. An apparatus for heating a fluid as claimed in any of claims 9 to 15, wherein the heating element is an ohmic heating element.
17. An apparatus for heating a fluid as claimed in claim 16, wherein electrical energy is supplied to the pre-heater from a mains supply.
18. An apparatus for heating a fluid as claimed in claim 16 or 17, wherein electrical energy is supplied to the pre-heater from at least one battery.
19. An apparatus for heating a fluid as claimed in claim 18, wherein electrical energy is supplied to the pre-heater from the at least one battery during a first part of a day and the battery is charged during a second part of the day.
20. An apparatus for heating a fluid as claimed in claims 18 or 19 wherein the at least one battery is charged using electrical energy from a mains supply.
21 An apparatus for heating a fluid as claimed in claims 1 8, 19 or 20, wherein the at least one battery is charged using electrical energy generated from a renewable energy source.
22. An apparatus for heating a fluid as claimed in any of claims 9 to 15, wherein the pre-heater comprises a heat exchanger that contains a fluid that is heated by a heat source.
23. An apparatus for heating a fluid as claimed in any of claims 9 to 22, wherein the system is a central heating system, and/or a hot water supply system.
24. An apparatus for heating a fluid as claimed in any of claims 9 to 23, wherein the fluid is water.
25. A method of enhancing the efficiency and/or power output of a fluid heating system comprising pre-heating a fluid before it enters a boiler.
26. The method of claim 25, wherein the energy used to pre-heat the fluid is provided from the mains electricity supply or is generated by a renewable energy source.