GB2353346A

GB2353346A - Control system for a water heater

Info

Publication number: GB2353346A
Application number: GB9914513A
Authority: GB
Inventors: Patrick Joseph Hart
Original assignee: ECO THERM
Current assignee: ECO THERM
Priority date: 1999-06-23
Filing date: 1999-06-23
Publication date: 2001-02-21
Also published as: GB9914513D0

Abstract

A water heater system suitable for use in controlling the volume of heated water in a hot water storage cylinder 2 comprises a cold water inlet 4, a hot water outlet 8, a single heater 12, a first temperature sensor 16 located in an upper portion of the cylinder, a second temperature sensor 18 located in a lower portion of the cylinder and a control means 22 for controlling the heater depending on whether the upper or lower temperature sensor is selected, wherein a user of the system may select between the first sensor 16 so that a small volume of water is heated or the second sensor 18 so that substantial volume of water is heated to a predetermined temperature. The heater 12 may be in the form of an immersion type electrical heater or comprise a heat exchanger coil portion of a central heating system located within the storage cylinder. The temperature sensors may be in the form of thermostats or thermisters.

Description

2353346 -1WATER HEATER The present invention relates to a water heater and

in particular a domestic water heater and to a control system for use therewith.

Conventional domestic water heater/storage vessels are generally in the form of a preferably insulated storage cylinder provided with a cold water inlet and a hot water outlet. The storage cylinder is generally provided with some form of heating means such as for example an internal electric immersion heater or an internal heat exchanger coil which is supplied with hot water from a central heating boiler. Such conventional storage cylinders use a thermostat, usually placed at the lower portion of the cylinder so that when the heating means has heated the water within the storage vessel down to the position of the thermostat the thermostat causes the heating means to switch off. Such systems will be generally known to plumbers, central heating engineers and others skilled in the art.

Such conventional storage cylinders can have a capacity of in excess of 100 litres and it will be appreciated that heating such a large volume of water and storing it at an elevated temperature for domestic use consumes large amounts of energy and is thus costly.

It will be appreciated that where only small amounts of hot water are used then there is significant waste of energy in maintaining such a large volume of water at an elevated temperature. Moreover changes in demography resulting in a substantial increase in the number of people living alone or two person occupancy of houses and smaller family sizes mean that there is less demand for such large volumes of hot water to be stored. Additionally the volumes of hot water required can vary from time to time during the day where in a family home, for example, only a small volume may be required in the morning whereas larger volumes may be required in the evening, for example for bathing requirements.

Energy saving control circuit system and apparatus for use with hot water the storage cylinders have been proposed before. For example, Stipe in US 4737615 discloses a complex arrangement involving a water heater having upper and lower electric heating elements and control circuitry so that the lower heating element may assist the upper heating element where the entire contents of the hot water tank is required. European Patent Publication No. 038318 also discloses a complex arrangement involving first and second pumps.

It will be appreciated that replacing a large volume conventional storage cylinder with a smaller volume storage -3cylinder would be an expensive undertaking for any household. It will also be appreciated that replacing equipment with that of the type disclosed in the abovenoted patent publications would be expensive. Accordingly there exists a demand to provide a simple and inexpensive means of converting existing hot water storage cylinders (or for modifying a new hot water cylinder) in such a way that either the entire contents can be heated or only a portion heated, selectively by a householder.

It is an object of the present invention to realise this demand and to minimise or avoid one or more of the disadvantages mentioned above.

The present invention provides a water heating system suitable for use in controlling the volume of heated water in a hot water storage cylinder system which comprises a hot water storage container having a cold water inlet means and a heated water outlet means; a single heating means formed and arranged for heating water stored in said container; a first temperature sensing means located at an upper portion of said container and formed and arranged for sensing when a first volume of heated water at the top of said container reaches a predetermined temperature; and a second temperature sensing means located at a lower portion of said container formed and arranged for sensing when a second substantial volume of water in said container has reached said pre-determined temperature; and control means coupled to said first and second sensing means and said heating means for receiving signals from said first and second sensing means and for switching on and/or off said heating means in response to said signals received from said first and second sensing means and means for selectively switching between said first and second temperature sensing means whereby a user in use of the system may select between a first small volume of water being heated or a second substantial volume of water being heated to said pre10 determined temperature.

Thus with a water heating system according to the present invention, small or large volumes of heated water may be heated as required and useful savings in energy consumption 15 achieved.

Preferably said hot water storage container is in the form of a more or less conventional storage cylinder of the type found in many households and as will be known to those skilled in 20 the art.

Any suitable single heating means may be used though preferably there is used a conventional immersion type electric heating element again of the type generally found in 25 households and as will be known to those skilled in the art. Alternatively where said hot water storage container/ cylinder L -5is part of a central heating system, said single heating means comprises the heat exchanger coil located within said storage container/ cylinder. Again such arrangements will be known to those skilled in the art and will be the same as many domestic central heating and hot water systems found commonly in many households across the country.

Any suitable form of temperature sensing means may be used though preferably there is used a thermostat desirably a thermistor. A particular advantage of using a thermistor is that it may be simply bonded or otherwise secured to the exterior of a conventional hot water storage container/cylinder without the requirement for modification thereof so long as it is in thermal connection with the contents of the container/cylinder.

As it will be appreciated that the above system is suitable for retrofitting to existing waterheater/central heating systems which will of course already have a temperature sensing means in the form of a thermostat at a lower end of the container/ cylinder, fitting of the first upper temperature sensing means, particularly a thermistor, is straightforward and inexpensive.

In its simplest form the said control means may comprise switch means formed and arranged for switching between said -6 first and second sensing means. Preferably though there is used a control means having electronic circuitry formed and arranged to process signals received from said sensing means and for switching on and off said heating means.

Preferably said control means is situated adjacent said container /vessel though preferably it is remotely located, in for example a kitchen or other suitable position within a house, whereby a user may readily and remotely switch between the first and second temperature sensing means and thus remotely select between a large or smaller volume of water to be heated.

Desirably said control means is provided with means for selecting the water temperature in such a way that a user is able to choose between the volumes of water and the temperature thereof. Such an arrangement may be particularly suitable in for example a small guesthouse where a number of baths and hence a large volume of hot water may be used early in the morning such hot water being mixed with mains or storage cold water. Additionally the control means may be provided with means of timing the duration the system is in use. Thus for example, the system may be set so that a large volume of water is heated to an elevated temperature first thing in the morning to allow for showers etc. and then switched off after a predetermined period and then at -7lunchtime switched back on so as to heat a small volume of water f or cooking and washing purposes and then in the evening switched on again to heat a large volume of water for baths etc.

A third temperature sensing means may be provided at a medial portion on said storage container/ cylinder to permit heating of a medium body of water equating to approximately half the storage capacity of the container/cylinder.

Further preferred features and advantages of the present invention will appear from the following detailed description given by way of an example of the preferred embodiment illustrated with reference to the accompanying drawings in which: Fig. 1 is a schematic diagram of a water heating system according to the present invention; Fig. 2 shows a storage cylinder for use with the system shown in Fig. 1; and Figs. 3-6 are graphs showing the test results on a water heating system according to the invention.

A water heating system, generally indicated by reference number 1, is shown schematically in Fig. 1. The system 1 comprises a hot water storage cylinder 2 (see also Fig. 2) which has a cold water inlet pipe 4 at it lower end 6 and a -8hot water outlet pipe 8 at it top end 10. A single heating means in the form of an electric immersion heater 12 is located in an upper central portion 14 of the cylinder 2(see Fig. 2). A first thermistor 16 is located approximately one third of the way clown the cylinder 2 and a second thermistor 18 is located at the lower portion 6 of the cylinder. A diverter switch 20 for controlling whether the upper or lower thermistor 16,18 is operational is provided. Each of the thermistors is an electrical connection with a control unit 22 for switching on and off the heater 12. The temperature of the water within the cylinder 2 is detected at the position of the thermistors 16, 18 on the cylinder 2.

When it is required to heat only a small volume of water then the switch 20 is positioned to bring the upper thermistor 16 into operation and thus once the upper thermistor 16 detects the presence of heated water at its position on the cylinder 2 it causes the control unit 22 to switch off the immersion heater 12. When it is required to heat substantially all the water contained within the cylinder 2 the diverter switch 20 is switched so as to bring the lower thermistor 18 into the circuit and thereby the immersion heater 12 will continue to heat more or less all of the water in the cylinder 2 until the thermistor causes the heater 12 to switch off by the control unit.

-9In order to assess the energy savings that may be achieved with the water heating system 1 according to the invention, a series of test were undertaken. These tests will be described below and with reference to Figs. 3-6 of the accompanying 5 drawings. Example A water heating system 1 similar to that shown in Fig. 2 was tested to provide data on the efficiency of the water heating system 1 of the present invention in comparison to a conventional water heating storage system.

A test rig 24 was assembled comprising an insulated hot water cylinder 2 fitted internally with an electric immersion heater 12 and having mounted on the sides first and second thermostats 16,18 respectively located at the lower and upper positions 6, 10 respectively of the cylinder 2. Cold water was fed into the base of the cylinder 2 via a motorised valve 26 through the cold water inlet 4 connected to a time switch (not shown) within a control unit 22. Hot water, heated by the immersion heater 12, was drawn from the top of the cylinder 2 through the hot water outlet pipe 8 to be collected in a measuring tank (not shown) before being dumped into a drain.

The electricity consumption of the heater 12 was measured using a conventional electricity meter. In addition, five thermocouples (28-36) were located at various vertically -10distanced points on the outer surf ace of the cylinder 2 to access stratification levels and mixing effects. The temperatures measured by the thermocouples (28-36) were recorded using a Squirrel data logger. The test rig was located in a heated laboratory (ambient temperature in the range 20 'C to 25 'C), which is a similar environment to that of a hot water cylinder in a domestic situation e.g. in a boiler cupboard.

The electric immersion heater 12 was used to heat the water in the cylinder 2 instead of the more usual heat exchanger coil as it is easier to record accurate energy consumption (electricity) using an immersion heater. Additionally, the water temperature distribution within the cylinder 2 obtained using an immersion heater is very similar to that with a coil type heater. Both types of heater give an almost uniform temperature distribution in the water above the heater indicating that the water is fully mixed.

Test Procedure Four tests (1 - 4) were performed using the test rig 24 as described above:

1. Upper thermostat 16 used to sense water temperature, low draw off rate.

2. Upper thermostat 16 used to sense water temperature, high draw-off rate. 3. Lower thermostat 18 used to sense water temperature, high drawoff rate.

4. Lower thermostat 18 used to sense water temperature, high draw-off rate.

Each test lasted for 48 hours. The draw-off pattern for each of the tests was identical and was as follows:

(a) 0900, start test with cylinder 2 full of cold water.

(b) 1200, draw off of heated water [301 (low draw-off) or 601 (high drawof f) 1.

(c) 1800, draw-off of heated water, as above.

(d) 0600, draw-off of heated water, as above.

(e) 1200, draw-off of heated water, as above.

(f) 1800, draw-off of heated water, as above.

(g) 0600, draw-off of heated water, as above.

(h) 0900, end test.

The thermostat was set at approximately 600C for each of the four tests. over the test period there were six draw-offs (bg) of. heated water corresponding to a total of either 1801 (litres) (low draw-off) or 3601 (litres) (high draw-off) of heated water, equivalent to 901 or 1801 per day. The cylinder 2 capacity was approximately 1201 and the daily hot water -12demand was therefore about 75% and 150% of the cylinder 2 capacity.

The draw-off of heated water was performed by manually adjusting the flow from a cold header tank to give either 21/minute or 41/minute and setting the time switch of the control circuit 22 to open the motorised valve 26 for 15 minutes to refill the cylinder 2 with cold water.

Domestic hot water consumption is normally about 451/head so the two drawoffs are substantially equivalent to a two-person household and fourperson household respectively.

During each test, a sample temperature profile record was obtained using a thermocouple located at each of the five points (28-36) on the vessel 2 and the electricity consumption with time was noted.

The same thermostat was used in all four tests and was moved to upper or lower positions 6 and 10 in the cylinder 2 according to the requirements of the particular test. Strapon thermostats were not used as they did not have sufficient current capacity.

-13Results The energy consumption of the immersion heater 12 for each of the f our tests are summarised below:

Test 1. 14.2 kWh (upper thermostat, low draw-off of heated water) Test 2. 23.6 kWh (upper thermostat, high draw-off of heated water) Test 3. 28.2 kWh (lower thermostat, high draw-off of heated water) Test 4. 19.1 kWh (lower thermostat, low draw-off of heated water) Comparing Test 1 with Test 4, (both low draw-off), there was an energy saving (26%) through use the upper thermostat 16 instead of the lower thermostat 18. Comparing Test 2 with Test 3, (both high draw-off), there was a similar saving in the amount of electricity consumed in absolute terms, however there was a lesser saving in percentage terms (16%).

The key to the temperature records obtained from the thermocouples is as follows: Channel 1: temperature at the outlet pipe 10 of the cylinder 2; Channel 2: temperature at the level of the upper thermostat 16; Channel 3: temperature half way between the upper and lower thermostats 16,18; -14Channel 4: temperature at the level of the lower thermostat 18; and Channel 5: temperature of the electric cable 38 in electrical connection with the immersion heater 12.

The thermocouple sensors 28-34 were located on the outside surface of the cylinder 2. The purpose of recording the temperature of the cable 38 with thermocouple 36 was to detect when the immersion heater 12 was ION' (the cable 38 heated slightly when a current flowed through it).

The main reason for the difference in energy consumption can be deduced by examining the graphs from Tests 2 and 3 (Figs. 4, 5). It may be seen that during the 12 hour periods between heated water drawof f s (in the centre of both graphs), the immersion heater, when the lower thermostat 18 (Test 3) was used, was switched on four times (shown as spikes, on Channel 5), while the immersion heater 12 remained off for the full 12 hours where the upper thermostat 16 (Test 2) was used.

A similar pattern of temperature changes can be seen by comparing the results of Tests 1 and 4 (see Figs. 3, 6) it can also be seen in all four tests that the water temperatures at all levels in the cylinder 2 are generally close together, indicating a low level of stratification and a high degree of mixing. The main exception is during a draw- -15of f period, where cold water was introduced into the bottom of the cylinder 2 at about 1800 hrs, which had a depressing effect on all the water temperatures (except at the hot water pipe 12). This indicated that mixing occurred due to the inf lux of cold water. The influx of cold water triggered the thermostat to activate the heater 12, which then quickly reheated the water to its preselected temperature.

In conclusion, it has been shown that the water heating system

1 of the present invention can provide sufficient hot water for use in domestic 2-4 person households with energy consumption savings of up to 26% over convention water heating systems. Even when a high flow-rate of heated water is drawnoff from the cylinder 2 (Test 2), the water temperature at the hot water outlet 8 (recorded by a thermocouple 28, Channel 1, Fig. 4) dips only very slightly during a 15 minute draw-of f of 601, with energy consumption savings of 16.3% over a conventional water heating system.

The scope of the present invention is intended to encompass those modifications and/or additions to the present invention that would be apparent to one skilled in the art of water heating systems.

Claims

1 A water heating system suitable for use in controlling the volume of heated water in a hot water storage cylinder system which comprises a hot water storage container having a cold water inlet means and a heated water outlet means; a single heating means formed and arranged for heating water stored in said container; a first temperature sensing means located at an upper portion of said container and formed and arranged for sensing when a first volume of heated water at the top of said container reaches a pre-determined temperature; and a second temperature sensing means located at a lower portion of said container formed and arranged for sensing when a second substantial volume of water in said container has reached said pre-determined temperature; and control means coupled to said first and second sensing means and said heating means for receiving signals from said first and second sensing means and for switching on and/or off said heating means in response to said signals received from said first and second sensing means and means for selectively switching between said first and second temperature sensing means whereby a user in use of the system may select between a first small volume of water being heated or a second substantial volume of water being heated to said predetermined temperature.

-172. A water heating system as claimed in claim 1 wherein said hot water storage container is in the form of a conventional storage cylinder.

3. A water heating system as claimed in claim 1 or claim 2 wherein said single heating means is in the f orm of an immersion type electrical heating element.

4. A water heating system as claimed in claim 1 or claim 2 wherein said single heating means comprises a heat exchanger coil portion of a central heating system located within said storage container/cylinder.

5. A water heating system as claimed in any one of claims 1 to 4 wherein said temperature sensing means is in the f orm of a thermostat.

6. A water heating system as claimed in any one of claims 1 to 4 wherein said temperature sensing means is in the form of a thermister.

7. A water heating system as claimed in any one of claims 1 to 6 wherein said control means comprises switch means formed and arranged for switching between said first and second sensing means.

-188. A water heating system as claimed in any one of claims 1 to 7 wherein said control means has electronic circuitry formed and arranged to process signals received from said sensing means and for switching on and off said heating means. 5 9. A water heating system as claimed in any one of claims 1 to 8 wherein said control means is remotely located from said water heating system.

10. A water heating system as claimed in any one of claims 1 to 9 wherein said control means is provided with means for timing the duration the system is in operation.

11. A water heating system as claimed in any one of claims 1 to 10 wherein there is provided a third temperature sensing means provided at a medial portion on said storage container/cylinder to permit heating of a medium body of water equating to approximately half the storage capacity of said container/cylinder.

12. A water heating system substantially as described hereinbefore and with particular reference to Figs. 1 and 2 of the accompanying drawings.