GB2253268A

GB2253268A - Water heating and space heating apparatus

Info

Publication number: GB2253268A
Application number: GB9202526A
Authority: GB
Inventors: George Hepburn
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-02-06
Filing date: 1992-02-06
Publication date: 1992-09-02
Anticipated expiration: 2012-02-06
Also published as: GB2253268B; GB9202526D0

Abstract

A water heating and space heating system 10 includes a heat store in the form of a tank 12 containing a relatively large volume of water and two sets of electrical water heating elements 14, 16. A wet space heating system including a plurality of radiators 18 is in fluid communication with the tank 12 through tank outlet and return ports 20, 22; 24. A heat exchanger 26 is located in an upper portion of the tank and has a cold water inlet 28 and a hot water outlet 30 for feeding hot water faucets 32. The two sets of electrical heating elements 14, 16 are provided in lower and upper portions of the tank 12 respectively to heat the entire volume of water or to heat only an upper portion of the tank 12 in times of reduced demand or when energy consumption is to be minimised. A third heating element 17 may be provided in the heat exchanger 26. The tank 12 and heat exchanger 26 may be pressurised to store water at above the normal boiling point temperature. A motorised value 56 directs return water to the upper return inlet 24 when the upper heating element 16 only is in use to limit circulation within the tank. <IMAGE>

Description

IMPROVEMENTS IN WATER HEATING AND SPACE HEATING APPARATUS AND METHODS This invention relates to improvements in apparatus and methods for water heating and space heating. In particular, but not exclusively, the invention relates to an improved water and space heating system in which electric elements are used as a primary heat source.

One of the most popular forms of space heating for domestic and commercial applications is wet heating systems in which hot water is circulated from a boiler through radiators located throughout the space 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.

In many situations it is not possible or is inconvenient to utilise a gas, oil or solid fuel fired boiler and in these situations electricity may be used to provide space and water heating. Electrical space heating may be provided using radiant element heaters, though these are generally considered to be expensive to run.

Many homes are provided with "storage heaters" which draw low tariff power, usually during the night and early morning, to heat material, typically in the form of bricks, which then gives off heat during the day. Such heaters suffer the disadvantage that they are less controllable than other systems and cannot be used to produce instantaneous heat in, for example, a rarely used room where the heater has not had the opportunity to warm up during the previous low tariff period. Also, electric storage heaters tend to be heavy and bulky. Electric water heating typically takes the form of one or more electrical heating elements located in a water tank.

Again, heating water using such elements tends to be relatively expensive when compared with other fuels.

It is one object of the present invention to provide a water and space heating system which is suited for heating using an intermittent supply of energy, such as low tariff electricity, to provide a steady supply of heat for heating water and for space heating.

In one embodiment of the present invention a water heating and space heating system includes a heat store in the form of a tank containing a relatively large volume of water, electrical heating elements for heating the water in the tank, a wet space heating system including a plurality of radiators in fluid communication with the tank through tank outlet and return ports, and a heat exchanger located in an upper portion of the tank and having a cold water inlet and a hot water outlet for feeding a hot water supply. Two sets of electrical heating elements are provided, one set in an upper portion of the tank and another set in a lower portion of the tank.The lower set of elements may be utilised to heat the entire volume of water, while the upper set of elements may be utilised to heat only an upper portion of the tank in times of reduced demand or when energy consumption is to be minimised.

The system is particularly suited for utilising low tariff electricity made available to the consumer outside peak demand periods which typically occur around morning and evening meal times. During the period when low tariff electricity is available the volume of water in the tank, which is highly insulated, is heated to a relatively high temperature by the lower set of elements, and if the water in the tank is stored at above atmospheric pressure the water may be heated to, for example, 1100C. Water for space heating is drawn from the tank and mixed with return water from the space heating system to bring the water temperature to around 800C before being pumped through the radiators. The consumable hot water available from the heat exchanger is mixed with cold water to reduce the water temperature to around 550C before being supplied to the hot taps.If the temperature of the water in the tank falls below a predetermined level during a period when low tariff electricity is not available the upper set of elements are utilised to provide sufficient heating to allow a continued supply of hot water and space heating.

When the low tariff electricity becomes available once more the lower set of elements heat the water and bring the water temperature back up to 1100C.

In accordance with one aspect of the present invention there is provided water heating apparatus including: heat store means in the form of a tank for containing a volume of water; and heating means for heating the water in the tank including a first heating element located in a lower portion of the tank and a separately operable further heating element located in an upper portion of a tank.

The apparatus may form part of a hot water supply system including a heat exchanger located in the tank having a cold water inlet and hot water outlet for feeding the hot water supply.

The apparatus may form part of a space heating system including at least one radiator in fluid communication with the tank through tank outlet and return ports.

The lower heating element may be used to heat the entire volume of water during periods when low tariff energy is available, whereas the upper heating element may be used outwith low tariff periods and may be arranged such that heating the water in the tank using the upper heating element leaves the water in the lower portion of the tank substantially undisturbed. The upper heating element may also be utilised when heat demand is low, for example, during the summer months.

Where the apparatus forms part of a space heating system the tank may include upper and lower return ports for connection to alternate returns from the space heating radiators, and the returns provided with valve means for at least shutting off flow to the lower return port.

Typically, the valve means will direct return flow through the upper return port when only the upper heating element is operating, to minimise disturbance to the water in the lower portion of the tank.

The tank may be sealed for maintaining the pressure of the volume of water at above atmospheric pressure, to permit the water to be heated to temperatures above 1000C without boiling. Further, the heat exchanger may contain water at above ambient pressure.

A further heating element may also be provided within the heat exchanger, for use in conjunction with the upper heating element.

In accordance with a further aspect of the present invention there is provided a method of heating a store of water for use in heating comprising the steps: providing a volume of water contained in a tank to form a heat store; and selectively heating either the entire volume of water to a temperature higher than that necessary to meet the direct heating requirements of the store using a heating element located in a lower portion of the volume, or heating only a portion of the volume of water to a temperature at or around the temperature necessary to meet the direct heating requirements of the store.

If the store of water is to be used to provide a supply of hot tap water the method includes the further step of passing cold water through a heat exchanger located in the volume of water to heat the water to provide a supply of hot water.

If the store of water is to be used to provide heat for space heating the method includes the further step of utilising the volume of water as a source of hot water for a wet space heating system.

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 schematic representation of a water heating and space heating system in accordance with one embodiment of the present invention; Figure 2 is a sectional view of a heat exchanger of the system of Figure 1; and Figure 3 is a schematic representation of a water heating and space heating system in accordance with a further embodiment of the present invention.

Reference is fist made to Figure 1 of the drawings, which illustrates a water heating and space heating system 10 in accordance with one embodiment of the present invention.

The system includes a heat store in the form of a well insulated tank 12 containing a relatively large volume of water. For domestic applications a 250 - 600 litre tank may be utilised. The water is heated by means of one of three electrical heating element units 14, 16, 17. The tank 12 provides the source of hot water for a space heating system represented in Figure 1 by a single radiator 18 which communicates with the tank 12 through a tank outlet port 20 and two return ports 22, 24. A heat exchanger 26, typically of 20 - 40 litres capacity, is provided in an upper portion of the tank 12 and is connected in line with a cold water inlet 28 and a hot water outlet 30 which feeds the hot water supply, represented in Figure 1 by a hot tap 32.

The tank 12 and space heating system are sealed and contain water at a pressure of around 0.5 bar. Minor variations in pressure are accommodated by a pressure vessel 34 which includes a pressure gauge from which the pressure of the system may be read and also includes a safety valve 36 which can release pressure should some element of the system fail resulting in the water pressure rising above a predetermined safe level, for example 3 bar. A relief valve 38 is also provided on the tank 12, the valves 36, 38 also being provided with tundishes (not shown) with suitable drains to carry off any water which escapes through the valves. The pressurization of the tank 12 and space heating system allows the water in the tank 12 to be heated to a relatively high temperature, typically around 1100C, without boiling.

The system 10 is intended to rely mainly on low tariff electricity which is available during off-peak periods. During this time a specially adapted meter will supply electricity to the lower heating unit 14 to maintain the temperature of the water in the tank at a predetermined level. In this example the heating unit 14 includes five heating elements 40 of a combined rating of 15 kW and is provided with a thermostat 42 set at 1100C, and a high limit thermostat 44 set at 1150C, and which must be manually re-set.

When heating is required in the building provided with the system 10 a pump 46 draws water from the tank outlet port 20 and into the space heating circuit. Before passing into the circuit the hot water passes through a mixer valve 48 where the hot water (1100C) is mixed with return water from the radiators (typically at around 600C), the valve 48 including a temperature sensor and flow control such that the water supplied to the radiators 18 is around 800C. In normal operation the remainder of the return water passes through the lower return port 22 into the tank 12 adjacent the main heating unit 14. The port 22 is provided with a non return valve 50. This arrangement provides for good circulation of the water in the tank 12 and results in a minimal temperature gradient across the height of the tank 12.

The returning water may also flow through an auxiliary return 52 and enter the tank through the upper return port 24 which enters the tank 12 substantially level with the upper heat unit 16. In normal operation water is free to pass through the auxiliary return 52 and enter the tank through the upper return port 24 and this further facilitates proper circulation of water within the tank 12. However, when the water within the tank 12 is not being heated by the main heat unit 14 the consumer may wish to minimise circulation within the tank 12. The situation may occur during peak load periods where low tariff power is not available for the main heating unit 14 and the consumer wishes to use the smaller upper heat unit 16, which in this example is provided with three heating elements 54, of a combined rating of 9 kW.By utilising the upper heat units 16 and returning the water from the space heating system through the upper return port 24 the amount of circulation in the lower portion of the tank 12 may be minimised such that a temperature gradient may develop and the heat unit 16 is effectively only heating the water in the upper portion of the tank 12, such that the tank 12 is effectively operating as a flow boiler.

Control of the flow of return water to the tank is controlled by a motorised valve 56.

The system is intended to use the minimum amount of high tariff electricity by utilising the store of heat created during low tariff periods through use of the lower heating unit 14. The water is heated to 1100C and during the peak period the water temperature is permitted to fall to around 800C, the fall in temperature being accommodated by varying the proportion of return water mixed with the heating system supply at the mixer valve 48. If the temperature of the water in the tank should fall below 800C, one of the elements of the upper heating unit 16 is switched on. Similarly, a fall in temperature below 750C results in two elements being switched on, and a fall below 700 results in all three elements being utilised.

Once the peak period has passed the three elements of the upper heating unit 16 are isolated and the five elements of the lower heating unit 14 used to bring the temperature of the water up to 1100C.

Switching of power supplies between the heating units 14, 16 may be controlled by any suitable means, such as providing a timed switch which controls the supply of power to the lower heating unit 14 and a normally on connector for the upper heating unit 16, such that when power to the lower unit 14 is switched off, the connector is switched on to supply power to the upper unit 16.

The supply of cold water for the heat exchanger 26 comes directly from the mains supply via a stop cock 58, a filter 59 and pressure valve 60, set at 3 bar, and also a non return valve 62 which prevents inadvertent contamination of the mains supply. The cold water inlet 28 is in the form of a tube which extends into one side of the heat exchanger 26, as illustrated more clearly in Figure 2 of the drawings. The heat exchanger 26 is cylindrical in form and has various tubes 63 extending between the upper and lower walls 64, 66 to facilitate circulation of heating water through the heat exchanger 26. The hot water outlet 30 is located on the other side of the heat exchanger 26 adjacent the upper wall 64. The heated water is then passed through a mixer valve 68 where the hot water is mixed with cold water, supplied through a by-pass pipe 70, in controlled proportion to bring the water temperature down to the desired level for supply to the taps, typically 550C. The mixer valve 68 also serves to reduce the pressure of the water.

A third heating unit 17 is provided in the centre of the heat exchanger 26 and may be utilised in conjunction with the upper heating unit 16 outside low tariff periods when the temperature of water in the tank 12 falls below the heat supply temperature.

Expansion of the water within the heat exchanger 26 and associated pipe work is accommodated by means of an expansion vessel 72.

It is preferred that the tank 12 and heat exchanger 26 are fabricated from suitable stainless steel, though other materials, such as the traditional copper, may also be used. The capacities of the tank and heat exchanger and the rating of the heating elements may be selected depending on the application of the system and the relative lengths of the periods when low tariff and high tariff power is available.

Reference is now made to Figure 3 of the drawings which shows a further embodiment of the present invention. The system of Figure 3 is substantially similar to the first described embodiment as shown in Figure 1, similar elements of the system of Figure 3 being identified with the same reference numbers prefixed with 1. In the embodiment of Figure 3 the tank 112 and the radiators 118 are not sealed and the tank 112 is provided with a vent 80. Water supply to the tank 112 is provided from a feed tank 82 which is mounted above the tank 112 to provide a head, the feed pipe 84 entering the tank 112 and an inlet 86 at a lower portion of the tank 112.

This system will typically operate at a lower temperature than the first described embodiment, the water in the tank 112 being heated to around 950C by the lower heating unit 114 during low tariff periods.

From the above description it will be evident that these embodiments of the invention provide systems which allow consumers to obtain the bulk of their electricity required for heating and hot water during low tariff periods. This is also advantageous to electricity generators and suppliers as the variations in demand for electricity between peak periods and off-peak periods will be reduced.

It will be clear to those of skill in the art that the above described embodiments are merely exemplary of the present invention and that various modifications and improvements may be made without departing from the scope of the invention: for example, a system may be provided which will only provide a supply of hot tap water, or a supply of hot water for space heating; the heating units may utilise a source of energy other than electricity and may be in the form of gas elements; and the capacity rating and operating temperatures of the system may vary widely, depending on application.

Claims

1. Water heating apparatus including: heat store means in the form of a tank for containing a volume of water; and heating means for heating the water in the tank including a first heating element located in a lower portion of the tank and a separately operable second heating element located in an upper portion of the tank.

2. The apparatus of claim 1, further including a heat exchanger located in an upper portion of the tank above the second heating element the tank, the heat exchanger having a cold water inlet and hot water outlet for feeding a hot water supply.

3. The apparatus of claim 1 or 2, wherein the tank includes outlet and return ports for connection to a wet space heating system.

4. The apparatus of any one of the preceding claims, wherein the tank is sealed for maintaining the pressure of the volume of water at above ambient pressure.

5. The apparatus of any one of claims 2 to 5, wherein the heat exchanger is adapted to contain water at above ambient pressure.

6. The apparatus of any one of claims 2 to 5, further including a first mixer valve downstream of the heat exchanger hot water outlet for mixing heated water from the heat exchanger with cooler water before supplying the water to a faucet.

7. The apparatus of claim 6, wherein the first mixer valve includes an expansion valve.

8. The apparatus of claims 2 to 5, wherein a further heating element is provided in the heat exchanger.

9. A water heating and space heating system including: a heat store in the form of a tank containing a volume of water; heating means for heating the water in the tank including a first heating element located in a lower portion of the tank, and a separately operable second heating element located in an upper portion of the tank; at least one radiator in fluid communication with the tank through tank outlet and returns ports; and heat exchange means located in the tank and having a cold water inlet and a hot water outlet for feeding a hot water supply.

10. The system of claim 9, further including a connection for extending between the radiator return port and the outlet port, the connection being provided with a mixing valve.

11 The system of claim 9 or 10, wherein the tank includes upper and lower return ports for connection to alternate radiator returns and further includes valve means for at least shutting off flow to the lower return port.

12. A method of heating a store of water for use in heating comprising the steps: providing a volume of water contained in a tank to form a heat store; and selectively heating either the entire volume of water to a temperature higher than that necessary to meet the direct heating requirements of the store using a heating element located in a lower portion of the volume, or heating only a portion of the volume of water to a temperature at or around the temperature necessary to meet the direct heating requirements of the store using a heating element located in an upper portion of the volume of water.

13. The method of claim 12 further comprising the step of passing cold water through a heat exchanger located in the volume of water to heat the cold water to provide a supply of hot water.

14. The method of claim 12 or 13 further comprising the step of utilising volume of water to provide a source of hot water for a wet space heating system.

15. The method of claim 12, 13 or 14, wherein the volume of water is maintained at above ambient pressure to permit heating off the water to relatively high temperatures without boiling.

16. The method of claim 13, 14 or 15, wherein the supply of water to the heat exchanger is at above ambient pressure

17. The method of claim 13, 14, 15 or 16, wherein the supply of hot water from the heat exchanger is mixed with cold water before being made available for use.

18. The method of claim 14, 15, 16 or 17, wherein return water from the wet space heating system is mixed with the hot water taken directly from the heated volume of water before being passed to the space heating system.

19. The method of any one of claims 14 to 18, wherein return water from the space heating system is directed into a lower portion of the tank when the first heating element is operating and into an upper portion of the tank when the second heating element is operating.

20. Water heating apparatus substantially as described and illustrated herein with reference to Figures 1 and 2 or Figure 3.