GB2312493A

GB2312493A - Boiler for space heating and domestic hot water

Info

Publication number: GB2312493A
Application number: GB9708302A
Authority: GB
Inventors: George J Hepburn
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-04-24
Filing date: 1997-04-24
Publication date: 1997-10-29
Anticipated expiration: 2017-04-24
Also published as: GB2312493B; GB9708302D0; GB9608597D0

Abstract

A heating system comprises a first vessel 10 containing a first reservoir of heated water for use as a hot water supply and a second vessel 12, within the first vessel 10, containing a second reservoir of heated water serving as a source of hot water for wet space heating. A water heater 14 heats the water in the second vessel 12 which then serves to heat the water in the first vessel 10. A control system (46) maintains the temperature of the water in the second vessel 12 within a restricted temperature range above the temperature required for space heating. The water heater 14 in the second vessel 12 has electric heating elements. The first vessel 10 may be directly heated by electric heater 24 and/or solar heat exchanger 26, so that domestic hot water can be produced in "summer" mode.

Description

HEATING SYSTEM This invention relates to heating systems and in particular to systems for providing wet space heating and a domestic hot water supply.

Wet space heating is in common use in many domestic and commercial applications and involves circulation of hot water from a boiler through radiators located throughout the area to be heated. At present, the majority of these systems are gas, oil or solid fuel fired. The heated water from the boiler also provides the heat source for the hot water supply, the heated water being carried from the boiler and passed through a coil located within a hot water heating and storage tank.

Recently, electrically powered wet space heating systems have been developed and marketed, such as the Dual Heat (trade mark) electric combination boiler produced by Redring Electric Limited, of Peterborough, England. This system is similar to that described in UK Patent Application GB-A-2 253 268. In this system electric heating elements heat a relatively large volume of water contained within an insulated tank and from which hot water is drawn for space heating. The domestic hot water supply is provided by passing water through a heat exchanger located within the tank. In general, systems such as these run on low tariff electricity and running costs are comparable with those of gas, oil and solid fuel fired systems. As the system is likely to be linked to a low tariff electricity supply there will be periods, typically of two hours, during times of peak electricity demand, when there will be no electricity supplied to the system. The large volume of heated water in the system is intended to retain sufficient energy to provide space heating through this period, however it is inevitable that the water temperature will drop such that the output of the space heating system will fall, particularly in the winter months when heating demand is high. Also, once the volume of relatively hot water stored in the heat exchanger has been used, any further demand for domestic hot water from the system will likely only provide relatively cool water.

Once the electricity supply to the system is restored the provision of a relatively large volume of water serving as a heat store for the wet space heating portion of the system leads to a relatively lengthy "warm up" period before full heating and domestic hot water outputs are available once more.

It is among the objects of embodiments of the present invention to obviate or mitigate these disadvantages.

According to the present invention there is provided a heating system comprising: a first vessel for containing a first reservoir of heated water for use as a hot water supply; a second vessel, within the first vessel, for containing a second reservoir of heated water serving as a source of hot water for use in wet space heating; means for heating the water in the second vessel such that the heated water in the second vessel serves to heat the water in the first vessel; and control means for maintaining the temperature of the water in the second vessel within a restricted temperature range above the temperature required for space heating.

According to another aspect of the present invention there is provided a space and water heating method comprising the steps: providing a first vessel containing a first reservoir of water for use as a domestic hot water supply; providing a second vessel within the first vessel and containing a second reservoir of water for use in space heating; heating the water in the second vessel such that the heated water in the second vessel serves to heat the water in the first vessel; and maintaining the temperature of the water in the second vessel within a temperature range above that required for space heating.

As the water in the second vessel is heated to a temperature in excess of that required for space heating requirements, typically in the region of 95 - 970C whereas space heating requires water at a temperature of 75 - 800C, the water in the first vessel will thus also be heated to a temperature in excess of that required for domestic hot water supply, typically 500C. The high water temperatures minimise the volume of heated water that is drawn from the vessels, and also minimises the risk of harmful bacteria, such as Legionella, growing within the first vessel.

Maintaining the water temperature in the second vessel within a relatively high temperature range permits the volume of water in the second vessel to be minimised. In the preferred embodiment the second vessel has a volume of only 14 litres (3 gallons), such that the total volume of water in a typical wet heating system using small bore piping and small volume radiators may be as low as 28 litres (6 gallons); this allows the system to provide maximum output space heating within a relatively short period (typically five minutes) following a shutdown. The maintenance of the temperature of the water in the second vessel within a restricted range also stabilises the demand for heated water from the vessel.

Preferably, the control means modulates the output of the heating means in response to the temperature of the water in the second vessel. Most preferably, the control means reduces the output of the heating means as an upper limit temperature is reached. This prevents the occurrence of large temperature variations which are evident in conventional thermostat controlled boilers where, for example, electric heating elements may continue to provide a substantial heating effect after the power supply to the elements has been shut off. The provision of appropriate control means permits the water in the system to be maintained at a relatively high temperature (95 - 970C) without the risk that the water in the second system will reach boiling point; in current systems, safety concerns limit the maximum thermostat shut-off temperature to around 850C. The control means may include a control unit such as an appropriate microprocessor linked to thyristors for controlling the heating elements.

Preferably also, the control means also controls the switching on of power to the heating means when this includes a plurality of electric heating elements. This may be achieved by switching on each individual element under the control of a timer, such that the elements are switched on at timed intervals. This prevents the occurrence of large surges in electricity demand, which may otherwise disrupt the power supply to other appliances linked to the same supply, and may even blow fuses or cause trip switches to open.

Preferably also, the first reservoir of water is larger than the second reservoir. Typically, the second reservoir is around 6% of the volume of the first reservoir. Most preferably, the vessels collectively contain a relatively large volume of water which serves as a heat store and may be, for example, heated using low tariff energy during certain periods in the day for use in space heating and as a hot water supply throughout the day.

The heating means may be in the form of a boiler sited remotely from the second vessel, for example an electric, gas, oil or solid fuel boiler, though most preferably the heating means is located within the second vessel, and thus within the first vessel. In the preferred embodiment, the heating means includes one or more electric heating elements located within the second vessel. This provides a very compact and easily installed heating system, as the boiler" and hot water store are combined within a single unit. For typical domestic applications the heating means will have an output of 9 - 15 kW. Most preferably, the walls of the second vessel are relatively thin to facilitate heat transfer to the water in the first vessel.

Further, it is preferred that heating elements are located adjacent the walls of the second vessel to allow direct heating of the water in the first vessel. It is also preferred that the heating elements have a relatively large surface area, to prevent the water in contact with the element surfaces from boiling.

To permit heating of the water in the first vessel when space heating is not required, or to accelerate heating of the water in the first vessel, additional heating means may be provided for directly heating the water in the first vessel, typically including one or more electric heating elements. Further, in the preferred arrangement, alternative heating means are provided for the first vessel, for example means for connection to a supply of solar heated water.

Preferably also, flow and return conduits are provided for fluid communication between the second vessel and the space heating system, the flow and return conduits being linked via a mixing valve whereby the water passing into the space heating system is a mix of the hotter water from the second vessel and the cooler water returning from the system, the relative proportions thereof being selected to provide a predetermined water temperature. Thus, in the majority of situations, only a relatively small volume of heated water needs to be drawn from the second vessel to maintain the wet heating system water temperature at a desired level. Further, it may be possible to provide space heating for an extended period without requiring activation of the heating means, for example during periods when low tariff energy is not available, as the relative proportions of hotter and cooler water may be adjusted as the temperature of the water in the second vessel falls.

The flow conduit will typically draw water from the hotter upper portion of the second vessel, while the return conduit will exit into the lower portion of the second vessel.

Preferably also, a domestic hot water supply conduit extends from an upper portion of the first vessel and includes a mixer valve whereby the domestic hot water supply is a mix of the hotter water from the first vessel and unheated water, to provide a domestic hot water temperature of around 50 - 550C. It is thus possible to provide a hot water supply for an extended period without requiring activation of the heating means, as the relative proportions of hotter and cooler water adjusts as the temperature of the water in the first vessel falls. This aspect of the system also allows hot water to be obtained from the preferred system relatively quickly after a shutdown; the large volume of water in the first vessel is likely to cool below 500C only after an extended period, and it is only necessary for the water temperature to rise to 500C, well below the normal operating temperature, before "hot" water becomes available.

In certain embodiments of the invention, the system may be provided with an electricity supply controller which identifies available low tariff energy supplies and is adapted to draw power from the least expensive supply available at a particular point in time.

According to a further aspect of the present invention there is provided a heating system comprising: a first vessel for containing a first reservoir of heated water for use as a hot water supply; a second vessel, within the first vessel, for containing a second reservoir of heated water serving as a source of hot water for use in wet space heating; and means for heating the water in the second vessel such that the heated water in the second vessel serves to heat the water in the first vessel, said heating means being located within the second vessel.

According to a still further aspect of the present invention there is provided a space and water heating method comprising the steps: providing a first vessel containing a first reservoir of water for use as a domestic hot water supply; providing a second vessel within the first vessel and containing a second reservoir of water for use in space heating; providing means for heating the second reservoir of water, said means being positioned within the second vessel; and heating the water in the second vessel such that the heated water in the second vessel serves to heat the water in the first vessel.

These further and still further aspects of the present invention may be provided in combination with the first described aspects of the invention and in combination with selected ones of the preferred features thereof.

These and other aspects of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a plan view of part of a heating system in accordance with a preferred embodiment of the present invention; Figure 2 is an elevational view of the heating cylinder of Figure 1, part of which is shown in section on line 2 - 2 of Figure 1; and Figure 3 is an elevational view of the cylinder of Figure 1.

The drawings illustrate an insulated copper heating cylinder 10 forming part of a heating system in accordance with a preferred embodiment of the present invention. The cylinder is of relatively large volume (200 - 300 litres) and, in use, contains a first reservoir of heated potable water for use as a domestic hot water supply, as will be described. Located within the cylinder 10 is a smaller stainless steel cylinder 12 (15 cm diameter, 14.25 litres volume) containing a smaller second, separate reservoir of heated water which acts as a source of heated water for a wet space heating system. The smaller cylinder 12 accommodates a series of electrical heating elements 14 (typically 9 - 12 kw maximum output) which, as will be described, provide the primary heating for the system. The cylinder 12 and the elements 14 thus form part of a small electric boiler within the larger cylinder 10.

The larger cylinder 10 includes a cold water supply conduit 16 which may be linked to the main water supply.

The output of the conduit is pressure controlled, using an appropriate pressure valve (not shown), such that water is supplied to the cylinder 10 at a pressure of 2 - 3 bar.

The conduit will also be provided with a strainer, a nonreturn valve, an expansion vessel and a pressure relief valve. Further, the open end of the conduit 16 at the lower end of the cylinder 10 is angled such that the flow of water into the cylinder 10 tends to create movement of water in the bottom of the cylinder, preventing the creating of "dead-zones". Domestic hot water may be drawn from the upper end of the cylinder 10 through a supply conduit 18 linked to a mixer valve 20 such that the relatively hot water at from the cylinder 10 (typically at 90 - 950C) may be mixed with unheated water at similar pressure supplied through conduit 22 (linked to conduit 16) to provide a water temperature better suited to a domestic hot water supply (typically 50 to 550C).

As noted above, the primary heating source for the system is the heating elements 14 located within the smaller cylinder 12. However, for use in "summer" mode, when space heating is not required, an electrical heating element 24 provided in the lower portion of the cylinder 10 may be activated to provide a domestic hot water supply.

In addition, the cylinder 10 may accommodate an additional heat exchanger 26 linked to, for example, a solar heating system.

The upper end of the cylinder 10 is provided with a collar 28 which supports a metal plate 30 from which the heating elements 14 depend and extend into the cylinder 12.

The collar 28 is formed by the upper end of the cylinder 12 and is brazed to the cylinder 10. A "steady" strap 32 stabilises the lower end of the cylinder 12. In this embodiment, several heating elements are utilised, the elements having a large surface area to prevent the water in contact with the element surfaces from boiling. To facilitate heat transfer from within the cylinder 12, the wall of the cylinder 12 is relatively thin. Further, a number of the U-shaped elements are positioned circumferentially around the cylinder close to the cylinder wall.

The cylinder 12 is linked to the wet space heating system (not shown) by appropriate flow and return conduits 34, 36. The flow conduit 34 is linked to a mixing valve 38 in communication with the return conduit 36 such that the water supplied to the space heating system (typically at 75 - 800C) is generally a mix of the water drawn from the cylinder 12 (at 95 - 970C) and the cooler return water (at 65 - 700C). A suitable circulating pump 40 is provided on the flow conduit 34, and as may be seen from Figure 1 is mounted on the cylinder 10 to minimise the volume occupied by the system.

A rectangular casing 42 is provided on the front of the cylinder 10 and accommodates a suitable expansion vessel 44 for this unvented system, and also a control system 46 linked to temperature sensors located within each of the cylinders 10, 12 via appropriate amplifiers and comparators. The casing accommodates all of the valves and the like forming part of the system such that the cylinder 10 may be supplied to an installer in assembled form requiring only connection to a cold water supply, a domestic hot water conduit, space heating flow and return conduits and the electricity supply.

In use, in normal "winter" mode, the elements 14 are activated to heat the water within the smaller cylinder 12.

This volume of heated water then acts as a source of hot water for the wet heating system. In this mode the larger volume of water within the cylinder 10 is heated by the radiated heat from the water within the smaller cylinder 12 and will provide a hot water supply once the water temperature has risen to around 50 C.

The electronic control 46 modulates the supply of electricity to the elements 14, using a microprocessor controller linked to a series of thyristors to maintain the temperature of the water in the cylinder 12 within a 0.50C range. As the temperature of the water reaches the upper limit temperature the heating output of the elements is reduced such that the residual heating effect provided by the elements 14, after power is shut off on the water reaching the upper limit temperature, is minimal. This avoids the possibility that the water temperature will continue to rise, possibly to a potentially dangerous level, after the power is shut off.

When switching on the elements 14, the control system 46 ensures that the full heating demand is not drawn instantaneously; each element 14 is linked to a timer such that the elements are switched on at five second intervals.

In "summer" mode, when space heating is not required, the heating element 24 located within the larger cylinder 10 is utilised to heat the water in the cylinder 10 directly and thus provide a domestic hot water supply.

One of the main advantages of the system described above is that space heating will be available within a relatively short period after activating the internal boiler, even after prolonged shutdown of the entire system.

This is due, in part, to the relatively small volume of water within the cylinder 12 and the rest of the wet heating system. The system will also provide a generous supply of hot water, allowing a household to have a number of hot baths in quick succession.

Depending upon the application and local regulations and practices, the system may be used in vented or unvented form. Also, the materials used to build the system and the capacity and output of the system may be selected to suit particular applications and operating conditions.

The system described above has the heating elements 14 located within the smaller cylinder 12. However, in other systems water heating may take place remotely from the cylinders 10, 12, for example in a remotely sited electric, oil, gas or solid fuel fired boiler linked by suitable flow and return conduits to the cylinder 12.

It will be clear to those of skill in the art that the above-described embodiment is merely exemplary of the present invention, and that various modifications and improvements may be thereto without departing from the scope of the invention. For example, the vessels of the system may be formed from any suitable materials, including copper and stainless steel.

Claims

1. A heating system comprising: a first vessel for containing a first reservoir of heated water for use as a hot water supply; a second vessel, within the first vessel, for containing a second reservoir of heated water serving as a source of hot water for use in wet space heating; and means for heating the water in the second vessel such that the heated water in the second vessel serves to heat the water in the first vessel, said heating means being located within the second vessel.

2. The system of claim 1, wherein the heating means includes one or more electrical heating elements.

3. The system of claim 2, wherein heating elements are located adjacent the walls of the second vessel to allow direct heating of the water in the first vessel.

4. The system of any of claims 2 or 3, wherein the heating elements have a relatively large surface area, to prevent the water in contact with the element surfaces from boiling.

5. The system of any of the preceding claims, wherein the walls of the second vessel are relatively thin to facilitate heat transfer to the water in the first vessel.

6. The system of any of the preceding claims, wherein an additional heating means is provided for directly heating the water in the first vessel.

7. The system of claim 6, wherein the additional heating means includes one or more electric heating elements.

8. The system of claim 6 or 7, wherein alternative heating means are provided for the first vessel.

9. The system of claim 8, wherein said alternative heating means include means for connection to a supply of solar heated water.

10. The system of any of the preceding claims, wherein the first reservoir of water is larger than the second reservoir.

11. The system of claim 10, wherein the second reservoir is less than 25% of the volume of the first reservoir.

12. The system of claim 11, wherein the second reservoir is less than 15 of the volume of the first reservoir.

13. The system of claim 12, wherein the second reservoir is less than 10k of the volume of the first reservoir.

14. The system of claim 13, wherein the second reservoir is around 6% of the volume of the first reservoir.

15. The system of any of the preceding claims, further including control means for maintaining the temperature of the water in the second vessel within a temperature range above the temperature required for space heating.

16. The system of claim 15, wherein the control means modulates the output of the heating means in response to the temperature of the water in the second vessel.

17. The system of claim 15 or 16, wherein the control means is operable to reduce the output of the heating means as an upper limit temperature is approached.

18. The system of claim 17, wherein the control means includes a microprocessor linked to thyristors for controlling the heating means.

19. The system of any of claims 15 to 18, wherein the control means controls the supply of power to individual heating elements.

20. The system of claim 19, wherein the control means includes a timer and power is supplied to the individual elements under the control of the timer, such that the elements are switched on at timed intervals.

21. The system of any of the preceding claims, wherein flow and return conduits are provided for fluid communication between the second vessel and the space heating system, the flow and return conduits being linked via a mixing valve whereby, in use, the water passing into the space heating system is a mix of hotter water from the second vessel and cooler water returning from the space heating system, the relative proportions thereof being selected to provide a predetermined water temperature.

22. The system of claim 21, wherein the flow conduit is arranged to draw water from the hotter upper portion of the second vessel, while the return conduit is arranged to exit into the lower portion of the second vessel.

23. The system of any of the preceding claims, wherein a domestic hot water supply conduit extends from an upper portion of the first vessel and includes a mixer valve whereby the domestic hot water supply is a mix of hotter water from the first vessel and unheated water.

24. The system of any of the preceding claims, further comprising an electricity supply controller for identifying available low tariff energy supplies and drawing power from the least expensive supply available at a particular point in time.

25. The system of any of the preceding claims, wherein the system is unvented.

26. A space and water heating method comprising the steps: providing a first vessel containing a first reservoir of water for use as a domestic hot water supply; providing a second vessel within the first vessel and containing a second reservoir of water for use in space heating; providing means for heating the second reservoir of water, said means being positioned within the second vessel; and heating the water in the second vessel such that the heated water in the second vessel serves to heat the water in the first vessel.

27. The method of claim 26, wherein the water in the second vessel is heated by one or more electric heating elements.

28. The method of claim 26 or 27, wherein the water in the second vessel is heated to a temperature in excess of 900C.

29. The method of claim 28, wherein the water in the second vessel is heated to a temperature in the region of 90 - 970C.

30. A heating system comprising: a first vessel for containing a first reservoir of heated water for use as a hot water supply; a second vessel, within the first vessel, for containing a second reservoir of heated water serving as a source of hot water for use in wet space heating; means for heating the water in the second vessel such that the heated water in the second vessel serves to heat the water in the first vessel; and control means for maintaining the temperature of the water in the second vessel within a temperature range above the temperature required for space heating.

31. The system of claim 30, wherein the heating means includes one or more electric heating elements located within the second vessel.

32. The system of claim 30, wherein the heating means includes a boiler sited remotely from the second vessel.

33. A space and water heating method comprising the steps: providing a first vessel containing a first reservoir of water for use as a domestic hot water supply; providing a second vessel within the first vessel and containing a second reservoir of water for use in space heating; heating the water in the second vessel such that the heated water in the second vessel serves to heat the water in the first vessel; and maintaining the temperature of the water in the second vessel at a temperature above that required for space heating.

34. The method of claim 33, wherein the water in the second vessel is heated to a temperature in excess of 90at.

35. The method of claim 34, wherein the water in the second vessel is heated to a temperature in the region of 90 - 97or.

36. A water and space heating method substantially as described herein.

36. A water and space heating system substantially as described herein and as illustrated in the accompanying drawings.

37. A water and space heating method substantially as described herein.

Amendments to the claims have been filed as follows 1. A heating system comprising: a first vessel for containing a first reservoir of heated water for use as a hot water supply; a second vessel, within the first vessel, for containing a second reservoir of heated water serving as a source of hot water for use in wet space heating; means for heating the water in the second vessel such that the heated water in the second vessel serves to heat the water in the first vessel, said heating means being located within the second vessel; and control means for maintaining the temperature of the water in the second vessel within a temperature range above the temperature required for space heating.

12. The system of claim 11, wherein the second reservoir is less than 15% of the volume of the first reservoir.

13. The system of claim 12, wherein the second reservoir is less than 10% of the volume of the first reservoir.

15. The system of any of the preceding claims, wherein the control means modulates the output of the heating means in response to the temperature of the water in the second vessel.

16. The system of any of the preceding claims, wherein the control means is operable to reduce the output of the heating means as an upper limit temperature is approached.

17. The system of claim 16, wherein the control means includes a microprocessor linked to thyristors for controlling the heating means.

18. The system of any of the preceding claims, wherein the control means controls the supply of power to individual heating elements.

19. The system of claim 18, wherein the control means includes a timer and power is supplied to the individual elements under the control of the timer, such that the elements are switched on at timed intervals.

20. The system of any of the preceding claims, wherein flow and return conduits are provided for fluid communication between the second vessel and the space heating system, the flow and return conduits being linked via a mixing valve whereby, in use, the water passing into the space heating system is a mix of hotter water from the second vessel and cooler water returning from the space heating system, the relative proportions thereof being selected to provide a predetermined water temperature.

21. The system of claim 20, wherein the flow conduit is arranged to draw water from the hotter upper portion of the second vessel, while the return conduit is arranged to exit into the lower portion of the second vessel.

22. The system of any of the preceding claims, wherein a domestic hot water supply conduit extends from an upper portion of the first vessel and includes a mixer valve whereby the domestic hot water supply is a mix of hotter water from the first vessel and unheated water.

23. The system of any of the preceding claims, further comprising an electricity supply controller for identifying available low tariff energy supplies and drawing power from the least expensive supply available at a particular point in time.

24. The system of any of the preceding claims, wherein the system is unvented.

25. A space and water heating method comprising the steps: providing a first vessel containing a first reservoir of water for use as a domestic hot water supply; providing a second vessel within the first vessel and containing a second reservoir of water for use in space heating; providing means for heating the second reservoir of water, said means being positioned within the second vessel; and heating the water in the second vessel to a temperature above that required for spacing heating and such that the heated water in the second vessel serves to heat the water in the first vessel.

26. The method of claim 25, wherein the water in the second vessel is heated by one or more electric heating elements.

27. The method of claim 25 or 26, wherein the water in the second vessel is heated to a temperature in excess of 90"C.

28. The method of claim 27, wherein the water in the second vessel is heated to a temperature in the region of 90 - 970C.

29. A heating system comprising: a first vessel for containing a first reservoir of heated water for use as a hot water supply; a second vessel, within the first vessel, for containing a second reservoir of heated water serving as a source of hot water for use in wet space heating; means for heating the water in the second vessel such that the heated water in the second vessel serves to heat the water in the first vessel; and control means for maintaining the temperature of the water in the second vessel within a temperature range above the temperature required for space heating.

30. The system of claim 29, wherein the heating means includes one or more electric heating elements located within the second vessel.

31. The system of claim 29, wherein the heating means includes a boiler sited remotely from the second vessel.

32. A space and water heating method comprising the steps: providing a first vessel containing a first reservoir of water for use as a domestic hot water supply; providing a second vessel within the first vessel and containing a second reservoir of water for use in space heating; heating the water in the second vessel such that the heated water in the second vessel serves to heat the water in the first vessel; and maintaining the temperature of the water in the second vessel at a temperature above that required for space heating.

33. The method of claim 32, wherein the water in the second vessel is heated to a temperature in excess of 900C.

34. The method of claim 33, wherein the water in the second vessel is heated to a temperature in the region of 90 - 970C.

35. A water and space heating system substantially as described herein and as illustrated in the accompanying drawings.