EP4348127A1

EP4348127A1 - Water heater

Info

Publication number: EP4348127A1
Application number: EP22731297.2A
Authority: EP
Inventors: Cédrick GRANDBOIS
Original assignee: Enviroheat Het Ltd
Current assignee: Enviroheat Het Ltd
Priority date: 2021-06-04
Filing date: 2022-06-06
Publication date: 2024-04-10
Also published as: GB202108042D0; WO2022254228A1

Abstract

A water heater has a container storing a volume of water and a heater for heating water in the container. Water may flow into and out of the container via an inlet and outlet, the inlet being positioned below the outlet. A mixing arrangement for mixing water in the container is operable to reduce the temperature difference between water at different parts of the container. The heater is arranged to heat water in the container when the water temperature is greater than a first set point and not to heat water when the water temperature is less than a second set point. The mixing arrangement is arranged to mix water in the container when the water temperature is greater than a third set point and not to mix water when the temperature is less than a fourth set point. The water heater may be a domestic water heater.

Description

Water heater

Technical Field of the Invention

The present invention relates to water heaters. More particularly to domestic hot water heaters.

Background to the Invention

Heated water is needed by everyone in their daily life for a wide variety of tasks such as washing, cooking and heating. Almost all modern homes, and commercial and industrial premises, have water heating apparatus to provide hot water to people within them. Heating water consumes a large amount of energy and given the large demand on heated water in modem life there is therefore an ever present need to provide more efficient and effective ways of heating water.

A common way to provide hot water for homes is a hot water cylinder. This is an insulated cylindrical tank. A cold water supply feeds to the bottom of the tank. A thermostatically controlled electric immersion heater is positioned in the tank, usually towards the bottom of the tank but above the cold water inlet and operates to heat water in the tank to a desired temperature. A hot water outlet is provided at the top of the tank from which hot water can be drawn, which is displaced by cold water entering the tank.

Heat transfers to water in the tank from the immersion heater via convection. This leads to a slow mixing of water in the tank which is generally desired so there is a temperature gradient in the tank with hotter water at the top where water is drawn from the tank and cold water towards the bottom of the tank. Reducing mixing of water in the tank enables hot water to continue to be drawn off as cold water enters the tank.

However, limited mixing can lead to hot spots forming around the immersion heater which can cause inefficient heat transfer and thus wasted energy. It also means that not all of the water in a tank is heated, so a larger tank may be required than would otherwise be the case.

It is an object of the present invention to at least partially overcome or alleviate the above problems, and also to provide a water heater with improved efficiency.

Summary of the Invention According to a first aspect of the present invention, there is provided a water heater comprising: a container for storing a volume of water; a heater for heating water stored in the container, wherein the container comprises an inlet via which, in use, water to be heated may flow into the container and an outlet via which, in use, heated water may flow out of the container, the inlet being positioned below the outlet; and a mixing arrangement for mixing water in the container, operable to reduce the temperature difference between water at different parts of the container, wherein the heater is arranged to heat water in the container when the water temperature is less than a first set point and not to heat water when the water temperature is equal to or greater than a second set point, and the mixing arrangement is arranged to mix water in the container when the water temperature is equal to or greater than a third set point and not to mix water when the temperature is less than a fourth set point.

Thus, the water may be mixed to reduce temperature differences in the water and thereby ensure all water in the container is approximately the same temperature. This can increase the efficiency of the water heater in use, as the entire volume of water in the container is heated to the same temperature. This reduces the likelihood that a large volume of cold water forms in the container, which can act as a sink for heat and reduce the efficiency of the water heater. It also allows more usable hot water to be stored in a container of a given size. Furthermore, as the heater typically only senses the temperature of water in one part of the container, when there are fewer temperature differences in the water the measured temperature is more indicative of the overall heat energy stored in the heated water in the container, and therefore the heater can operate more efficiently. In addition, where there is a risk of water freezing in the container, the mixing arrangement reduces the likelihood of ice forming in a section of the container by ensuring the water is mixed. The use of temperature set points to control both the heater and mixing arrangement advantageously enables the water heater to better balance the needs of the user, as described in more detail below.

The outlet may be at or towards a top of the container. The outlet may be positioned within the container. The outlet may be positioned centrally with respect to a horizontal cross-section of the container. The outlet may be fluidly connected to a heated water supply to provide heated water to an end user. The outlet may extend through a side-wall of the container. The outlet may be configured to draw hot water from the top of the container out through a side-wall of the container. The outlet may comprise a pipe- section that is completely contained within the container. The pipe section may comprise a first end and a second end. The first and second ends may be fluidly connected. The first end of the pipe section may connect to the side-wall of the container. The first end may be fluidly connected to the heated water supply via the side-wall of the container. The second end of the pipe section may terminate inside the container. The second end of the pipe section may be positioned to draw hot water directly from the top of the container, for example the second end may be positioned in the top 10%, 7.5%, 5%, 2.5% or 1% of the container. The second end may be positioned centrally with respect to a horizontal cross-section of the container. Where the container has a flat top, the second end may be arranged in a position corresponding or adjacent to the flat top so as to draw hot water from the uppermost point of the container. The second end of the pipe section may be above the first end. Thus, water in the pipe section is insulated by the water in the container before it exits the side-wall reducing heat losses compared to other outlets. In addition as the outlet exits from the side wall, it avoids a thermal bridge forming at the top of the container which is the hottest part, further reducing heat losses. Finally, as the outlet exits from the side-wall of the container rather than the top, the container is more vertically compact and therefore easier to install in some situations.

The inlet may deliver water at or towards a base of the container. The inlet may be at or towards a base of the container. The inlet may comprise a baffle configured to direct water flowing into the container away from the outlet. The baffle may be positioned at or towards a base of the container. Where the container is cylindrical, the inlet may comprise a baffle configured to direct water flowing into the container in a radial direction. This ensures that, in use, unheated water does not pass directly through the container from the inlet to the outlet without being heated and/or mixing with heated water. Furthermore, the thermal expansion of water in the container will lead to the hot water rising to the top of the container and out of the outlet. This ensures that the hottest water in the container flows out the outlet first. The container/water heater may be arranged to allow stratification of temperature in the absence of mixing. The container may be at least part cylindrical. The container may be upright. The container may be elongate. The container may have a domed top and/or a domed base.

The water heater may be a domestic water heater.

The mixing arrangement may comprise any suitable arrangement for reducing temperature differences between water in different parts of the container. The mixing arrangement may comprise a mixing conduit providing a conduit for the flow of water located at or near the top of the container to a position at or near the bottom of the container, and a device for causing water to flow through the mixing conduit so as to mix water in the container. The device may be configured to cause water to flow from a higher point, such as a position at or near the top of the container, to a lower point, such as a position at or near the bottom of the container, via the mixing conduit. The mixing conduit may connect the outlet and the inlet. The device may have a power consumption of no more than 11 watts. The device may be configured to cause water to flow through the mixing conduit at a rate of at least 6 litres per minute and/or no more than 12 or 10 litres per minute. Preferably water may be caused to flow through the mixing conduit at a rate of about 8 litres per minute. The device may be a pump. The pump may be a centrifugal pump. Thus, heated and unheated water may be easily mixed by addition of a mixing conduit without complex or invasive alterations to a conventional water heater.

The mixing conduit may branch into a water supply conduit connected to the inlet. The water supply conduit may be configured to supply unheated water to the inlet. As such, water flowing into the container from the water supply conduit will be combined with water flowing through the mixing conduit before entering the container. Thus, water may be pre-mixed as it enters the container, reducing the requirement for mixing inside the container.

The mixing conduit may branch into a heated water conduit connected to the outlet. The heated water conduit may be configured to carry heated water away from the outlet. Thus, heated water may flow from the outlet into the mixing conduit and the mixing conduit can be easily and non-invasively attached to the water heater. The water heater and/or mixing conduit may be configured to prevent fluid flow in a reverse direction through the mixing conduit. The mixing conduit may comprise a one-way valve. Thus, unheated water is prevented from accessing the outlet via the mixing conduit, this ensures unheated water does not flow to an end user expecting to receive heated water from the outlet.

The water heater may comprise two or more heaters. The heaters may be positioned above one another. The heaters may have the same heating power, or may have different heating powers. The heaters may each have a variable heat power output. In one embodiment, the water heater comprises two heaters: a 1 kW heater; and a 2 kW heater. Thus, different combinations of heaters can be used as required to provide heat energy to the water.

The or each heater may be positioned within the container between the inlet and the outlet. The or each heater may be positioned towards a base of the container, such as in a lower half of the container, but spaced above its base. Preferably, the or each heater is positioned about a third of the height of the container above its base. As such, the heater(s) are positioned to ensure a majority of water in the container is heated effectively without requiring mixing.

The or each heater may be any suitable device for heating water. The or each heater may be configured to heat water directly or indirectly for example, the or each heater may be a heating coil, which could be heated by a gas or oil-fired boiler, a heat pump or some other heat source. The or each heater may be an immersion heater, preferably an electric immersion heater. The or each heater may be an AC and/or a DC immersion heater. Preferably a DC immersion heater may be used in combination with a renewable energy source such as solar PV cells. The or each heater may comprise an alloy. In one example, the or each heater is made of a titanium treated with a nickel- steel super alloy, such as that provided under the trade mark Incoloy and more preferably the nickel-steel super alloy Incoloy 800HT. The nickel-steel super alloy may comprise 30-35 % Nickel by weight. The nickel-steel super alloy may comprise 19-23 % Chromium by weight. The nickel- steel super alloy may comprise 39.5 % Iron by weight. The nickel-steel super alloy may comprise 0.06-0.1 % Carbon by weight. The nickel-steel super alloy may comprise 1.5 % Manganese by weight. The nickel-steel super alloy may comprise 0.045 % Phosphorus by weight. The nickel-steel super alloy may comprise 0.015 % Sulphur by weight. The nickel-steel super alloy may comprise 1 % Silicon by weight. The nickel-steel super alloy may comprise 0.25-0.60 %

Aluminium by weight. The nickel-steel super alloy may comprise 0.25-0.60 %

Titanium by weight. The or each heater may have a surface power output density of at least 10, 15 or 20 W per cm². The or each heater may have a surface power output density of no more than 20, 15, or 10 W per cm². Preferably the surface power density is less than 15 W per cm² and most preferably about 10 W per cm². Thus, electric immersion heaters comprising titanium and a nickel- steel super alloy with appropriate surface power density can be selected to further increase heating efficiency.

The water heater may comprise a temperature sensor configured to output a signal indicative of the temperature of water in the container. The temperature sensor may be a thermocouple or a thermistor. The temperature sensor may be a thermostat. The temperature sensor may be positioned at a point higher than the or each heater over the base of the container. The temperature sensor may be placed no more than 20 cm above the or each heater, preferably the temperature sensor is placed about 15 cm above the uppermost heater. The temperature sensor may be offset from the position of the or each heater in a plane perpendicular to the height of the container. Preferably, the temperature sensor is not placed directly above any heater. Where the container is cylindrical, the temperature sensor may be offset from the or each heater around the circumference of the container. The temperature sensor may be positioned on an opposite side of the or each heater from: the inlet; or an opening in the container that forms part of the inlet. The temperature sensor may be positioned in a recessed pocket within a sidewall of the container. The pocket may penetrate at least 5, 10, 15, 20 or 25 cm into the container, preferably at least 15 cm which can ensure the temperature sensor has access to cooler parts of the container. The water heater may comprise two or more temperature sensors. Thus, the water heater can ensure that water in the container is adequately heated and monitor the effects of mixing.

The water heater may comprise a safety sensor configured to detect when the temperature of water in the container exceeds a safe threshold and prevent heating of water in the container by the or each heater when the temperature exceeds the safe threshold. The safety sensor may prevent mixing of water in the container by the mixing arrangement when the temperature exceeds the safe threshold. The safety sensor may be a thermostat, and it may be arranged to disconnect a power supply to at least the or each heater and the mixing arrangement when the temperature exceeds the safe threshold. The safety sensor may be at or towards a top of the container. The safety sensor may be placed adjacent to the outlet of the container. The safe threshold may be at least 65, 70, 75, or 80 degrees centigrade. The safe threshold may be no more than 100, 90, 80, or 75 degrees centigrade. Preferably, the safe threshold is 75 degrees centigrade. The safety sensor may control a power source of the water heater, the or each heater, and/or the mixing arrangement. The safety sensor may disable the power source if the temperature exceeds the safe threshold. The safety sensor may communicate with the or each heater, and/or the mixing arrangement directly. The safety sensor may override other instructions given to the or each heater, and/or the mixing arrangement. Thus, the safety sensor can act as a back-up to the temperature sensor and ensure that the or each heater is deactivated if the water temperature exceeds the safe threshold. The safety sensor may also prevent mixing of water by the mixing arrangement, advantageously this ensures that the safety sensor detects the hottest water in the container as the hot water rises to the top of the container and is not mixed by the mixing arrangement.

The water heater may comprise a control device configured to control the or each heater. The control device may control the or each heater in dependence of the temperature of water in container.

The control device may be in communication with the temperature sensor. The control device may be configured to control the or each heater and/or the mixing arrangement. The control device may be configured to control the or each heater and/or the mixing arrangement in dependence on the temperature of water in the container as sensed by the temperature sensor. The control device may be in communication with the safety sensor. The control device may be configured to control the or each heater in dependence on the temperature of water in the container as sensed by the safety sensor. According to a second aspect of the present invention there is provided a control device for controlling one or more heaters and a mixing arrangement of a water heater comprising a container for water in dependence on the sensed temperature of water in the container, the control device being configured to cause the or each heater to operate if the temperature of water is less than a first set point, and to turn the or each heater off if the temperature of water is equal to or greater than a second set point, and to cause the mixing arrangement to operate if the temperature of water is equal to or greater than a third set point and to turn the mixing arrangement off if the temperature of water is less than a fourth set point .

Thus, the control device can control the mixing arrangement to ensure water is mixed to reduce temperature differences in the water and thereby ensure all water in the container is approximately the same temperature. This can increase the efficiency of water heating as the entire volume of water in the container is heated to the same temperature. This reduces the likelihood that a large volume of cold water forms in the container, which can act as a sink for heat and reduce the efficiency of heating. In addition, where there is a risk of water freezing in the container, the mixing reduces the likelihood of ice forming in a section of the container. Furthermore, the use of temperature set points to control both the heater and mixing arrangement advantageously enables the control device to better balance the needs of the user, for example, stratification of the water temperature may be permitted during heating to enable faster delivery of hot water when heating the tank from cold, or after a volume of hot water has been drawn off, or stratification may not be permitted to heat all the water in the container and maximise the available hot water.

The control device may be configured to cause at least one heater to operate at a low power output and/or intermittently when the sensed temperature falls below the second set point and to turn the or each heater off if the temperature reaches or exceeds the second set point. Intermittent heating may comprise heating the water in the container with a duty cycle of less than 100%, 75%, 50%, 25% or 10%, preferably 25%. Where there are two or more heaters, low power heating may comprise instructing a subset of the heaters to heat the water in the container. Preferably, low power output heating comprises heating the water in the container with a lkW heating power and a duty cycle of 25%. Thus, the water heater may use low power heating to maintain the temperature of water in the container without using large and unnecessary amounts of power.

The control device may only instruct low power heating of water in the container if the water in the container is not already being heated. The control device may not instruct low power heating of water in the container if the water in the container is being heated at a power greater than low power heating. Thus, low power heating does not interfere with other higher power heating and is only instructed if the water is not already being heated.

The control device may be configured to cause the or each heater to operate at a high power output and/or continuously if the sensed temperature falls below the second set point by a heater control threshold temperature, and to continue to operate until the sensed temperature reaches or exceeds the second set point, and then turn the or each heater off. The first set point may be equal to the second set point minus the heater control threshold temperature. As such the first set point may be equal to or less than the second set point. High power output heating may comprise continuous heating of water in the container. High power heating may comprise instructing the or each heater to heat the water using its maximum power. Where the water heater comprises two or more heaters, high power heating may comprise heating the water with every heater. High power heating may comprise providing heat energy to the water in the container at a higher rate than low power heating. High power heating may comprise heating water in the container at a power of at least 1, 2, 3, 5 or 10 kW, preferably 3 kW. Thus, if the temperature of water in the container falls too far below the second set point, that is below the first set point, high power heating is used to increase the temperature of water in the container back to the second set point.

In both aspects of the invention the or each set point may be any suitable set point. The second set point may be equal to a desired maximum temperature of water flowing out the output. The or each set point may be any suitable value in the range 0- 100 degrees centigrade. Preferably the second set point may be in the range 40-80 degrees centigrade, for example 65 or 62.5 degrees centigrade. The heater control threshold temperature may be set to define an acceptable range of water temperatures. The heater control threshold temperature may be less than 20, 15, 10, or 5 degrees centigrade. The heater control threshold temperature may be at least 2, 5, 10, or 15 degrees centigrade. Preferably the heater control threshold temperature is 10 degrees centigrade. Consequently, the first set point may be no more than 20, 15, 10, or 5 degrees centigrade less than the second set point. The first set point may be at least 2, 5, 10, or 15 degrees centigrade less than the second set point. Preferably the first set point is 5 degrees centigrade less than the second set point, for example 57.5 degrees centigrade. In one embodiment, the first set point and second set point are the same temperature, and the heater control threshold temperature is zero. Thus, the first and second set points and heater control threshold temperature may be used to ensure water is heated to the desired level.

The third set point may be equal to or greater than the fourth set point. The third set point may be no more than 20, 15, 10, or 5 degrees centigrade greater than the fourth set point. The third set point may be within 0.1, 0.2, 0.5, 1, 2 or 5 degrees centigrade of the second set point. The fourth set point may be within 0.1, 0.2, 0.5, 1, 2, or 5 degrees centigrade of the first set point. The third set point may be equal to, greater or less than the second set point. The fourth set point may be equal to or greater, or less than the first set point.

In an embodiment, the third set point is greater than the second set point, for example 62.7 degrees centigrade.

In an embodiment, the fourth set point is greater than the first set point, for example 57.7 degrees centigrade. Advantageously this ensures that heating is closely followed by mixing and vice versa to ensure there is no unnecessary delays in mixing/heating and further that heating and mixing are not done simultaneously at low temperatures which could increase the time for hot water to be available to the user.

The first set point may be equal to the fourth setpoint. The second set point may be equal to the third setpoint. Where this is the case the mixing device and the heater will run alternately to each other, i.e. the mixing device will run only when the heater does not run, and vice versa. In one embodiment, the first, second, third and fourth set points are all the same temperature.

When the control device calls for mixing of water in the water heater it may cause the mixing arrangement to operate continuously or intermittently, for example with a duty cycle of less than 100%, 90%, 75%, 66%, 50%, 33% or 25%, preferably 33%. Thus, mixing can be suitably controlled to ensure that it is appropriate for the circumstances.

The control device may be configured to control the mixing arrangement in response to the operation of the or each heater. The control device may be configured to cause the mixing arrangement to operate if the water in the container is not being heated, and preferably only when the water in the container is not being heated. The control device may be configured to stop the mixing arrangement if the water in the container is being heated. Where water in the container is being heated intermittently, the control device may instruct intermittent mixing of the water in the container. Intermittent mixing of water in the container may comprise instructing mixing of water in the container in periods where the water in the container is not being heated. Thus, the mixing of water in the cylinder during heating is minimised to ensure that the heating process can be most efficient.

The control device may be configured to cause the mixing arrangement to operate if the temperature of water in the container is less than a mixing on threshold temperature which is equal to or less than the (second) set point, but to stop the mixing arrangement if the temperature reaches or exceeds the mixing on threshold. The mixing on threshold temperature may be equal to the third set point. The control device may be configured to delay the operation of the mixing arrangement. The operation of the mixing arrangement may be delayed until the water temperature decreases past the third set point/mixing on threshold temperature. The control device may be configured to stop the mixing arrangement if the temperature of water in the container is equal to or less than a mixing off threshold temperature which is equal to or greater than the (second) set point minus the heater control threshold temperature. The fourth set point may be the mixing off threshold temperature. The mixing on threshold temperature may be at least 1, 2 or 3 degrees centigrade less than the (second) set point. The mixing on threshold temperature may be less than 4, 3, or 2 degrees centigrade less than the (second) set point. Preferably, the mixing on threshold temperature is 3 degrees centigrade less than the (second) set point. The mixing off threshold temperature may be less than the mixing on value. The mixing off threshold temperature may be at least 1, 2 or 3 degrees centigrade more than the (second) set point minus the heater control threshold temperature. The mixing off threshold temperature may be less than 4, 3 or 2 degrees centigrade more than the (second) set point minus the heater control threshold temperature. Preferably, the mixing off threshold temperature is 2 degrees centigrade more than the (second) set point minus the heater control threshold temperature. Thus, water in the container is only mixed when it is within a temperature range defined by the (second) set point, the heater control threshold temperature, and optionally also the mixing on threshold temperature and mixing off threshold temperature. This ensures that all water in the container is heated to a point within this range increasing the efficiency of the water heater.

One or more of the or each set point, heater control threshold temperature, mixing on threshold temperature, and mixing off threshold temperature may depend on the acceptable range of temperature for heated water in the water heater, this will vary considerably depending on the circumstances and application of the heater.

The control device may be configured to determine the rate of change of the measured temperature of water in the container. The control device may be configured to control the mixing arrangement in response to the rate of change of the measured temperature of water in the container. The control device may be configured to stop the mixing arrangement if the sensed temperature is falling with a gradient that exceeds a temperature gradient threshold. The temperature gradient threshold may be at least 0.1, 0.25, 0.5 or 1 degrees centigrade per second. The temperature gradient threshold may be no more than 2, 1, 0.5, or 0.25 degrees centigrade per second. Preferably the temperature gradient threshold is 0.5 degrees centigrade per second. Thus, water is only mixed during low usage conditions that are characterised by gradual cooling of the water. This maximises efficiency in low usage conditions and ensures that in high usage conditions any heated water in the container is available to flow through the outlet rather than being mixed with unheated water.

The control device may be configured to operate in one or more different operating modes. The control device may be configured to select a certain operating mode. The control device may operate according to an operating mode for a specified period of time. The control device may operate according to an operating mode in response to received instructions, information or use characteristics of the water heater. Each operating mode may cause the control device to operate the or each heater and/or the mixing device according to a different control strategy, as described above. For example, one operating mode may comprise high power heating as described above and a different operating mode may comprise low power heating as described above. In a different example, the second set point may be 65 degrees centigrade and in a different operating mode the second set point may be 70 degrees centigrade. One operating mode may comprise turning the water heater off and not heating or mixing the water. Of course, each operating mode may have numerous different features and characteristics and further examples are provided in the detailed description below.

The control device may comprise an internal clock and calendar. The control device may be configured to schedule the selection of different operating modes dependent on the time of day, day of the week, month of the year, and/or the date itself. The control device may be configured to alter the scheduling of different operating modes dependent on information received via the communications module as described below, for example, weather data, energy price information, energy consumption information, energy generation information, and commands from an external device. Thus, control of the water heater can be tailored to suit the needs of each individual user/application.

The control device may comprise a user interface in communication with the control device. The user interface may be configured to output information, for example information indicative of the temperature of the water in the container and/or the state of the water heater. The user interface may be configured to receive control inputs from a user, for example to change the or each set point and/or operating mode of the water heater. The user interface may be any suitable user interface, for example a liquid crystal display, touch screen, computer mouse, keyboard, and/or joystick.

The control device may comprise a communications module configured to communicate with one or more external devices. The communications module may be configured to send operational information about the water heater and control device to the one or more external devices, such as: water temperature information; energy usage information; heater and pump usage information; water usage information; and fault diagnostics information. The communications module may be configured to send notifications to the one or more external devices, for example notifications dependent on the operational information about the water heater as mentioned above. The communications module may be configured to receive information from the one or more external devices, for example information such as: commands to change the operating mode or settings used to control the water heater; software updates; energy price information; energy consumption and availability information; energy patterns; weather and environmental data and forecasts; information relevant to fault diagnostics. Thus, the control device can receive and send critical information to ensure ongoing reliable and efficient operation.

The communications module may be configured to communicate via a wired connection and/or a wireless connection such as WiFi (RTM), Zigbee (RTM), Bluetooth (RTM) or the like. The communications module may be configured to communicate with a network router. The communications module may be configured to communicate to local devices, for example devices that are on the same local area network as the communications module. The communications module may be configured to communicate with remote devices. The communications module may be configured to connect to the internet. The communications module may be configured to communicate with remote devices via the internet. The communications module may be configured to communicate with any suitable type of connected device such as: electronics devices like mobile phones, computers, tablet computers, laptops, and intemet-of-things devices; renewable energy sources like solar PV cells, batteries or wind turbines; and remote servers. Thus, the control device can effectively communicate with a wide range of devices. The control device may be a control device of a water heater according to the first aspect of the present invention.

According to a third aspect of the invention there is provided a method of heating water in a container comprising an inlet via which, in use, water to be heated may flow into the container and an outlet via which, in use, heated water may flow out of the container, the inlet being positioned below the outlet, the method comprising: starting heating of water in the container if the water temperature is less than a first set point; stopping heating water in the container if the water temperature is equal to or greater than a second set point; starting mixing of water in the water container so as to reduce the temperature difference between water at different parts of the water heater when the water temperature is equal to or greater than a third set point; and stopping mixing of water in the water container when the water temperature is less than a fourth set point.

Thus, the water may be mixed to reduce temperature differences in the water and thereby ensure all water in the container is approximately the same temperature. This can increase the efficiency of the method of water heating, as the entire volume of water in the container is heated to about the same temperature. This increases the volume of stored hot water. It also reduces the likelihood that a large volume of cold water forms in the container, which can act as a sink for heat and reduce the efficiency of the heating method. In addition, where there is a risk of water freezing in the container, the mixing reduces the likelihood of ice forming in a section of the container.

The method of heating may be applicable to a water heater according to the first aspect of the present invention, or a control device according to the second aspect of the present invention. The water heater may incorporate any one or more of the features of the water heater of the first aspect of the present invention, or the control device of the second aspect of the present invention as required or desired.

According to another aspect, there is provided a water heater comprising: a container for storing a volume of water; a heater for heating water stored in the container, wherein the container comprises an inlet via which, in use, water to be heated may flow into the container and an outlet via which, in use, heated water may flow out of the container, the inlet being positioned below the outlet; and a mixing arrangement for mixing water in the container, operable to reduce the temperature difference between water at different parts of the container, wherein the mixing arrangement is arranged to mix water in the container when the water is not being heated. Preferably water in the container is mixed only when the water is not being heated. The water heater of this aspect may also include any one or more of the features of the first, second and third aspects described above.

According to another aspect, there is provided a control device for controlling one or more heaters and a mixing arrangement of a water heater comprising a container for water in dependence on the sensed temperature of water in the container, the control device being configured to cause the or each heater to operate if the temperature of water is less than a set point, and to turn the or each heater off if the temperature of water is equal to or greater than the set point, wherein the control device is configured to cause the mixing arrangement to mix water in the container when the or each heater is off. Preferably water in the container is mixed only when the water is not being heated. The water heater of this aspect may also include any one or more of the features of the first, second and third aspects described above.

Detailed Description of the Invention

In order that the invention may be more clearly understood embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, of which:

Figure 1 is a schematic diagram of a first embodiment of a heating cylinder apparatus;

Figure 2 is a schematic cross sectional view of the heating cylinder apparatus of Figure 1 taken along line A-A; Figure 3 is a block diagram showing a method of controlling the heating element of the heating cylinder apparatus of Figure 1;

Figure 4 is a block diagram showing a method of controlling the pump of the heating cylinder apparatus of Figure 1; Figure 5 is a schematic diagram of a second embodiment of a heating cylinder apparatus;

Figure 6 is a block diagram showing the connections between the control device of the heating cylinder apparatus of Figure 5 and external devices; Figure 7 is a block diagram showing a method of controlling the heating element of the heating cylinder apparatus of Figure 5; and

Figure 8 is a block diagram showing a method of controlling the pump of the heating cylinder apparatus of Figure 5.

In Figures 1 and 5, fluid connections between the components are shown as solid lines and electrical connections are shown as dashed lines. Arrows on the solid lines correspond to the direction of fluid flow, in use as described below.

Referring to Figures 1 and 2, a water heater, which in this first embodiment is a heating cylinder apparatus 100, comprises a container configured to contain a volume of water while the water is heated and a mixing arrangement configured to mix water in the container so as to reduce temperature differences in the water. In this embodiment, the container is an insulated domestic water heating cylinder 10 suitable for a domestic hot water supply. In this embodiment, the water heater also comprises a control device 30.

The heating cylinder 10 comprises a heater 11 configured to heat water within the heating cylinder 10. In this embodiment, the heater 11 comprises a first heater 12 and a second heater 13, both of which are electric immersion heaters made of titanium and a nickel-steel super alloy, the heaters having a surface power output density of 10 W per cm². The first heater 12 has a power output of 1 kW, and the second heater 13 has a power of 2 kW. In other embodiments, different types of heaters may be used such as an indirect coil through which water or another fluid is circulated heated by a gas or oil-fired boiler, thermal solar installation, heat pump or other heat source.

In some embodiments, the heating cylinder may also comprise a heating coil from a solar hot water system close to the base of the heating cylinder. This may operate continuously using any available solar power. The temperature of water in the heating cylinder is then supplemented using the heaters 12, 13. In this embodiment, the heating cylinder 10 is positioned such that its central axis is substantially vertical in use. The first heater 12 and second heater 13 are fixed in a common aperture in the sidewall of the heating cylinder 10 and project radially into the volume enclosed by the heating cylinder 10. The first heater 12 is positioned adjacent the second heater 13. The height of the first heater 12 and second heater 13 above a base of the heating cylinder 10 is approximately 33% of the height of the heating cylinder 10. In other embodiments their positions may vary but in general they will be in the lower half of the heating cylinder 10 to ensure at least half the water in the heating cylinder 10 is heated, absent mixing of the water.

The heating cylinder 10 also comprises a temperature sensor 14 configured to measure the temperature of the water within the heating cylinder 10. The temperature sensor 14 is positioned in a pocket that penetrates into the heating cylinder 10 at a point above both the first heater 12 and second heater 13. In this embodiment, the temperature sensor 14 is offset around the circumference of the heating cylinder 10 from the first heater 12 and second heater 13. Furthermore, the temperature sensor 14 is positioned at a height of 0 - 200 mm above the first heater 12 and second heater 13, but in other embodiments the temperature sensor 14 may be at a different height, and its height may depend on the volume of the container/heating cylinder.

The heating cylinder 10 comprises an inlet 15 towards its base. The inlet comprises an opening 17 in a sidewall of the heating cylinder 10, and a baffle 18 positioned within the heating cylinder 10. The opening 17 may be offset around the circumference of the heating cylinder 10 from the first heater 12 and second heater 13 on an opposite side from the temperature sensor 14. The baffle 18 is positioned centrally on the axis of the heating cylinder 10 at a position just above the base of the heating cylinder 10. The baffle 18 is configured to receive water through an aperture (not shown) in the centre of the baffle 18 and direct the water radially with respect to the heating cylinder 10. The inlet 15 also comprises an inlet conduit 19 connecting the opening 17 and the aperture in the baffle 18. In this embodiment, the baffle 18 is a disk, but in other embodiments any suitable baffle 18 may be used. In use, the inlet 15 is configured to allow water to enter the heating cylinder 10, water flows through the opening 17 and inlet conduit 19 to the baffle 18. Water then passes through the aperture in the baffle 18 emerging beneath the baffle 18. As such, water flowing into the heating cylinder 10 is prevented from directly mixing with water in the upper part of the heating cylinder 10 in use.

The inlet 15 is connected to a cold water supply line 2, for example the mains cold water supply for the domestic property.

The heating cylinder 10 also comprises an outlet 16 in a top of the heating cylinder 10. The outlet 16 is configured to allow water to leave the heating cylinder 10. In use, the outlet 16 is fluidly connected to hot water plumbing 1 to provide heated water to an end user, for example in a domestic property.

In some embodiments, the heating cylinder 10 also comprises a safety sensor 40 towards a top of the heating cylinder 10. In this embodiment, the safety sensor 40 is placed adjacent to the outlet 16 on the inside of the heating cylinder. The safety sensor 40 is configured to detect when the temperature of water in the cylinder exceeds a safe threshold. The safe threshold may be 75 degrees centigrade. The safety sensor 40 is configured to disconnect the rest of the heating cylinder apparatus 100 from a power source, ensuring that all elements of the heating cylinder apparatus 100 are deactivated. This is advantageous as it ensures the heater 11 is deactivated and also that the safety sensor 40 senses the hottest water in the heating cylinder 10 as hot water is not circulated by the mixing arrangement. The safety sensor 40 can thereby act as a back-up to the temperature sensor 14 and ensure safe operation of the heating cylinder apparatus 100 if the temperature sensor 14 or control device 30 fails. In other embodiments, the safety sensor 40 communicates with the heater 11 and/or mixing arrangement directly or via the control device 30 to selectively deactivate them.

In this embodiment, the mixing arrangement comprises a pump 20. The pump 20 comprises a pump inlet 21 and a pump outlet 22 and is configured to urge water from the pump inlet 21 to the pump outlet 22. In this embodiment, the pump 20 is an electric centrifugal pump capable of pumping water from the pump inlet 21 to the pump outlet 22 at a rate of about 8 litres per minute with a power consumption of up to 11 watts. The pump inlet 21 is in fluid communication with the outlet 16 via a mixing conduit 23. The mixing conduit 23 connects to the outlet 16 via a branch in the fluid connection between the outlet 16 and hot water plumbing 1. The pump outlet 22 is in fluid communication with the inlet 15 via the mixing conduit 23, the mixing conduit 23 connects to the inlet 15 via a branch in the fluid connection between the inlet 15 and the cold water supply line 2. As such, in use, the pump 20 is configured to urge a flow of water from the outlet 16 to the inlet 15 via the mixing conduit 23, the pump inlet 21 and pump outlet 22.

In this embodiment, a one-way valve 24 is fluidly connected in series in the mixing conduit 23 between the pump outlet 22 and inlet 15/cold water supply line 2. The valve 24 is configured to prevent fluid flowing in a direction from the valve 24 towards the pump outlet 22. In other embodiments, the valve 24 may be located at any suitable location to prevent fluid flow in a direction from the pump outlet 22 towards the pump inlet 21, for example within the pump 20 between the pump outlet 22 and pump inlet 21, or externally in series between the pump inlet 21 and the outlet 16/hot water plumbing 1. The one-way valve 24 thus permits a flow of water from the outlet 16 to the inlet 15 via the pump 20 when the pump 20 is running, and it prevents a reverse flow when the pump 20 is not running. This prevents cold water from the cold water supply line 2 or the bottom of the tank from passing through the pump 20 to the hot water plumbing 1.

In this embodiment, the inlet 15 and outlet 16 each comprise a single opening in the heating cylinder 10 to facilitate fluid connections to: the cold water supply 2 and valve 24; and hot water plumbing 1 and pump inlet 21, respectively. However, in alternative embodiments, the heating cylinder 10 may comprise more than one inlet 15 and outlet 16 respectively to allow dedicated connections to the cold water supply 2, valve 24, hot water plumbing 1, and pump inlet 21 respectively.

As described above, the pump 20 can be used to urge heated water from the outlet 16 through the mixing conduit 23 and back into the heating cylinder 10 through the inlet 15. This has the effect of mixing heated water with unheated water from the cold water supply line 2 as it enters the heating cylinder 10 (when water is flowing into the cylinder from the supply). It also has the effect of mixing warmer water, which tends to rise to the top of the cylinder, with cooler or unheated water close to the base of the heating cylinder 10. Thus, temperature differences of water in the heating cylinder 10 can be reduced and leading to more efficient operation of the heating cylinder 10.

The control device 30 comprises an input to receive information indicative of the temperature of water in the heating cylinder 10 from the temperature sensor 14, and outputs to control operation of the first heater 12, second heater 13 and the pump 20. The control device 30 is configured to control the operation of the first heater 12, second heater 13, and pump 20 in response to the temperature of the water in the heating cylinder 10 as measured by the temperature sensor 14. In this embodiment, the control device 30 is also configured to detect the rate of change of the temperature measured by the temperature sensor 14.

In this embodiment, the control device 30 also comprises a user interface 31 in communication with the control device 30. The user interface 31 is configured to output information indicative of the temperature of the water in the heating cylinder 10 and the state of the heating cylinder apparatus 100, and to receive control inputs from a user. In this embodiment, the user interface 31 comprises a liquid crystal display and a joystick.

The first heater 12, second heater 13, temperature sensor 14, pump 20, control device 30 and user interface 31 are connected to an electric power supply (not shown).

Referring to Figures 3 and 4, the control device 30 is configured to control the first heater 12 and second heater 13 so as to heat the temperature of water in the heating cylinder 10 to achieve a set point, and the pump 20 so as to mix water in the heating cylinder 10 and reduce the temperature difference between water at different parts of the water heater.

Referring to Figure 3, the control device 30 controls the first heater 12 and second heater 13 by first comparing the measured temperature received from the temperature sensor 14 to the set point at step HI. In this embodiment, the set point is 65 degrees centigrade, but in other embodiments it may be set to a different temperature as desired. If the measured temperature is greater than or equal to the set point, the control device 30 moves to step H2, and otherwise moves to step H3.

At step H2, the control device 30 instructs both the first heater 12 and second heater 13 not to heat the water in the heating cylinder 10 as the set point temperature has been achieved.

At step H3, the control device 30 determines if the measured temperature is less than the set point by at least a heater control threshold temperature. In this embodiment, the heater control threshold temperature is 10 degrees centigrade, but in others it may be different. If the measured temperature is less than the set point by at least the heater control threshold temperature, the control device 30 moves to step H4 and otherwise moves to step H5. In this embodiment, the control device 30 would therefore move to step H4 if the measured temperature is less than or equal to 55 degrees centigrade.

At step H4, the control device 30 instructs both the first heater 12 and second heater 13 to heat the water in the heating cylinder 10 continuously at full power. Thus, if the water temperature is below 55 degrees centigrade high power heating is used in an attempt to reach the set point once again.

At step H5, if the first heater 12 and/or second heater 13 are not heating water in the heating cylinder 10, the control device 30 moves to step H6, and otherwise moves to step H7.

At step H6, the control device 30 instructs the first heater 12 to heat water in the heating cylinder with a duty cycle of 25%, for example 15 seconds heating in every minute. Thus, if the measured temperature is between 65 and 55 degrees centigrade and both the first heater 12 and second heater 13 are off, low power heating is used in an attempt to maintain water temperature.

At step H7, no action is taken by the control device 30. This ensures that if high power heating (step H4) is already being used to achieve the set point, it continues to be used until the set point is reached and the heaters 12, 13 are turned off in step H2. In addition, it ensures that if low power heating (step H6) is already being used, it continues to be used until either: the set point is reached and the heaters 12, 13 are turned off in step H2; or, the measured temperature falls below the set point by at least the heater control threshold temperature and high power heating is then instructed in step H4.

After steps H2, H4, H6 or H7, the control device 30 loops back to step HI and repeats the process above.

Referring to Figure 4, at step PI if the first heater 12 and/or second heater 13 are heating water in the heating cylinder, the control device 30 moves to step P2 and otherwise to step P3.

At step P2, the control device 30 instructs the pump 20 not to mix water in the heating cylinder 10. This prevents mixing during heating of water in the heating cylinder.

At step P3, if the measured temperature is greater than or equal to a mixing on threshold temperature, or less than or equal to a mixing off threshold temperature, the control device 30 moves to step P4 and otherwise P5.

In this embodiment, the mixing on threshold temperature is 62 degrees centigrade, 3 degrees centigrade below the set point, and the mixing off threshold temperature is 57 degrees centigrade, 2 degrees centigrade above the set point minus the heater control threshold temperature.

At step P4, the control device 30 instructs the pump 20 not to mix water in the heating cylinder 10. This prevents mixing at temperatures close to and above the set point, and also ensures mixing does not interfere with the heating operations as the temperature reduces past the mixing off threshold temperature.

At step P5, if the water in the cylinder is rapidly cooling, that is the rate of change of the measured temperature is negative and has an absolute value that is greater than a temperature gradient threshold, the control device 30 moves to step P6 and otherwise P7. In this embodiment, the temperature gradient threshold is 0.5 degrees centigrade per second, but in other embodiments it may be different depending on the circumstances and expected water usage.

At step P6, the control device 30 instructs the pump 20 not to mix water in the heating cylinder 10. At step P7, the control device instructs the pump 20 to mix water in the heating cylinder 10.

After steps P2, P4, P6 or P7 the control device 30 returns to step PI.

Thus, water in the container is only mixed when it is within a temperature range defined by the mixing on and mixing off threshold temperatures. This ensures that all water in the container is heated to a point within this range increasing the efficiency of the water heater.

Furthermore, in steps P5-P7 rapid cooling of water in the heating cylinder 10 is detected, which may be due to heavy demand on heated water flowing out the outlet 16. In these circumstances, mixing is prevented to ensure that any heated water in the heating cylinder 10 is available to flow through the outlet 16 rather than being mixed with unheated water.

As described above, in the first embodiment heating and mixing of water in the container 210 is controlled according to first, second, third and fourth set points: the first set point is the “set point” minus the heater control threshold temperature; the second set point is the “set point”; the third set point is the mixing on threshold temperature; and the fourth set point is the mixing off threshold temperature.

Referring to Figure 5, a different water heater is shown and in this second embodiment the water heater is again a heating cylinder apparatus 200. In the second embodiment, the heating cylinder apparatus 200 comprises many of the same features as the first embodiment described above and as such only the differences between them are described. In addition, like numerals are used to denote like features. As with the first embodiment, in the second embodiment, the container is an insulated domestic water heating cylinder 210 suitable for providing a domestic hot water supply.

In this embodiment, the outlet 216 of the heating cylinder is positioned within the heating cylinder 210 adjacent to the top of the heating cylinder 210 but not extending out of the top as with the first embodiment. The outlet 216 is positioned centrally with respect to the horizontal cross-section of the cylinder 210. The outlet 216 is configured to draw hot water from near the top of the heating cylinder 210 and is fluidly connected to hot water plumbing 201 as with the first embodiment. However, in contrast to the first embodiment the outlet 216 of the second embodiment comprises an up-turned pipe section 216a completely contained within the heating cylinder 210. The pipe section 216a delivers hot water from the outlet 216 to the side wall 210a of the heating cylinder 210 where it connects to the hot water plumbing 201. Thus, the hot water in the pipe section 216a is insulated by the hot water within the heating cylinder 210 resulting in a reduction in heat losses compared to the outlet of the first embodiment in which hot water is taken directly out of the heating cylinder 210.

Referring to Figures 5 and 6, in this embodiment, the control device 230 further comprises a communications module 232. In this embodiment, the communications module 232 is configured to communicate with a local solar PV cell 242 via a local area network router 240. The control device 230 can therefore receive information from the solar PV cell 242 to determine how the heating cylinder apparatus 200 should be controlled, for example the solar PV cell 242 may indicate it is generating a surplus of power and the control device 230 may instruct continuous heating to use this available power for example using a dedicated DC heating element.

In this embodiment, the communications module 232 is configured to communicate with a local tablet computer 241 via the router 240. Thus, instantaneous operating statistics and information can be provided to the tablet computer 241 by the communications module 232 and furthermore commands can be received from the tablet computer 241. In addition, notifications can be provided to the tablet computer 241, for example a notification that the set point temperature has been reached.

In this embodiment, the communications module 232 is configured to connect to the internet 250 via the router 240. The communications module 232 is configured to connect to a smart phone 251 via the internet 250. This can allow operating statistics and commands to be sent and received from the smart phone 251 in a similar manner to the tablet computer 241 described above except that the smart phone 251 is not limited to being connected to the same local network as the communications module 232.

In this embodiment, the communications module 232 is also configured to connect to a remote server 252 via the internet 250. The communication module 232 is configured to send and receive data from the remote server 252, for example, software updates, weather data and/or energy price data that could be used to determine when water in the heating cylinder should be heated, fault diagnostics and performance information relating to the heating cylinder apparatus 200, and usage of available local energy sources (such as solar PV cells, batteries or wind turbines) with energy imported from the power grid. This can ensure that the control device 230 can be updated to use more efficient or robust control algorithms and furthermore that in the event of a failure of one of the components of the heating cylinder apparatus 200, the fault can be diagnosed and potentially corrected remotely via the server 252.

As described above by way of example, the communications module 232 is configured to communicate with one or more external devices 241, 242, 251, 252, for example via local networks and/or the internet 250. The communications module 232 is configured to communicate wirelessly with a home network router 240, for example by WiFi (RTM), and connect to other local external devices 241, 242 and/or the internet 250 via the router 240. In other embodiments, other wireless communications standards or wired connections may be used.

As with the first embodiment, the control device 230 of the second embodiment is configured to control the heaters 212, 213 to heat the water in the heating cylinder 210 and achieve a set point, and control the pump 220 to mix water in the heating cylinder 210. In this embodiment, the control device 230 comprises various operating modes that are tailored to certain situations/requirements in the use of the heating cylinder apparatus 200.

Referring to Figures 7 and 8, in a first operating mode the control device 230 is configured to control the first heater 212 and second heater 213 and pump 220 according to first, second, third and fourth set points so as to heat the temperature of water in the heating cylinder 210 and mix water in the heating cylinder 210 and reduce the temperature difference between water at different parts of the water heater.

Referring to Figure 7, in the first operating mode the control device 230 controls the first heater 212 and second heater 213 by first comparing the measured temperature received from the temperature sensor 14 to the second set point at step H21. In this embodiment, the second set point is 65.5 degrees centigrade, but in other embodiments it may be set to a different temperature as desired. If the measured temperature is greater than or equal to the second set point, the control device 230 moves to step H22, and otherwise moves to step H23.

At step H22, the control device 230 instructs both the first heater 12 and second heater 13 not to heat the water in the heating cylinder 210 as the acceptable water temperature defined by second set point temperature has been achieved.

At step H23, the control device 230 determines if the measured temperature is less than the first set point. In this embodiment, the first set point is 57.5 degrees centigrade, but in others it may be different. If the measured temperature is less than the first set point, the control device 230 moves to step H24 and otherwise takes no action and moves to back to step H21, as such if the heaters 212, 213 are heating the water they continue to do so and if they are not they remain off.

At step H24, the control device 230 instructs both the first heater 212 and second heater 213 to heat the water in the heating cylinder 210 continuously at full power. Thus, if the water temperature is below 57.5 degrees centigrade high power heating is used in an attempt to reach an acceptable water temperature.

After steps H22 and H42, the control device 30 loops back to step H21 and repeats the process above.

Referring to Figure 8, in the first operating mode at step P21 the control device 230 compares the measured temperature to the third set point, if the measured temperature is equal to or exceeds the third set point, the control device 230 moves to step P22 and otherwise to step P23. In this embodiment the third set point is 62.7 degrees centigrade.

At step P22, the control device 230 waits until the measured temperature is less than the third set point and then instructs the pump 220 to mix water in the heating cylinder 210.

At step P23, if the measured temperature is less than the fourth set point, the control device 230 moves to step P24 and otherwise takes no action and moves back to P21, as such if the pump 220 is on it remains on and if it is off it remains off. In this embodiment the fourth set point is 57.7 degrees centigrade. At step P24, the control device 30 instructs the pump 220 not to mix water in the heating cylinder 210. This prevents mixing so that it doesn’t interfere with heating and ensures hot water is accessible at the top of the container 210 in the shortest amount of time.

After steps P22 and P24, the control device 230 returns to step P21.

Thus, the first operating mode is a general purpose mode which ensures hot water is available quickly by preventing mixing at low temperatures and also heating the entire volume of water in the container 210 by mixing the water once it reaches acceptable high temperatures.

A second operating mode is configured to maximise the available hot water within the heating cylinder 210. This can be particularly useful to precondition the heating cylinder 210 for a period of heavy usage or to maximise the use of cheap energy or surplus renewable energy. In the second operating mode, the control device 230 is configured to instruct the pump 220 to mix water in the heating cylinder 210 continuously and irrespective of water temperature. This ensures that the variation in the temperature of water within the tank is minimised and that any energy supplied to the heaters 212, 213 is used to efficiently heat water in the tank.

In the second operating mode, the first set point is equal to the second set point and as such the control device 230 is configured to instruct the heaters 212, 213 to continuously heat water in the heating cylinder 210 if the measured water temperature is below the first/second set point and not to heat the water if the temperature is above the first/second set point. In addition, in the second operating mode, the first/second set point may be higher than that used in the other operating modes. This can help ensure that any available energy is used and that the temperature of water in the heating cylinder 210 is maximised in preparation for a period of heavy use. For example, the first/second set point may be set to the safe threshold.

A third operating mode is configured to efficiently maintain an acceptable water temperature in the tank during periods of low hot water usage. The third operating mode is identical to the first operating mode except for the control of the operation of the pump 220. In the third operating mode, the control device 230 is configured to operate the pump 220 using a duty cycle of less than 100%, for example 33%. As such, in a situation where the pump 220 would be instructed to mix water continuously under the first operating mode, in the third operating mode the pump only mixes water intermittently, for example 33% of the time which could be 20 seconds mixing each minute. This is helpful where low water usage is anticipated as in such circumstances only a small amount of water enters the heating cylinder 210 and consequently, only a small amount of mixing is required to maintain water in the heating cylinder 210 at an approximately equal temperature throughout. Therefore, as the pump 220 is operated for less time, there is a corresponding efficiency saving.

Of course, in other embodiments only a subset of the operating modes may be available, or there may be additional operating modes.

In this embodiment, the control device 230 is comprises a clock and calendar 233 that facilitates scheduling of different operating modes and the settings used to control the heating cylinder 210 (e.g. the set point) depending on variables such as the time of day, day of the week, month of the year, or the date itself. In addition, the control device 230 is configured to alter the scheduling of different operating modes and the settings used to control the heating cylinder 210 dependent on information received via the communications module 232, for example, weather data, energy price information, energy consumption information, energy generation information, and commands from a remote device such as a mobile phone.

In one example, the heating cylinder 210 is switched on with the water in the heating cylinder 210 at room temperature. Initially, the heating cylinder is in the third operating mode and as such, heats the water using the heaters 212, 213 until the second set point (62.7 degrees centigrade) is reached. In this mode, the heaters 212, 213 are then switched off and as the water temperature cools, the pump 220 is activated for 20 seconds in every minute according to the third and fourth set points as mentioned above. Once the water temperature falls too low, that is below the first set point, which in this embodiment corresponds to 57.5 degrees centigrade, the heaters 212, 213 are turned back on to maintain the water temperature in the acceptable range. This is especially useful during periods of low use as mentioned above. After a given first time period, which in this example is 1 hour 30 minutes, the control device 230 is configured to turn off both the heaters 212, 213 and pump 220. This may be done when there is no need of hot water to save energy.

In this example, after a second time period has elapsed, which in this example is 11 hours and 5 minutes, the control device 230 switches to the second operating mode. This could be used to maximise a period of reduced energy prices or available local renewable energy, or to prepare the heating cylinder 210 for a period of high hot water demand. In this example, the third operating mode is used for a third time period (30 minutes) and during the third operating mode the first and second set points are changed to 75 degrees centigrade to ensure as much energy as possible is safely transferred to the water in the cylinder.

Next, the control device 230 switches to the first operating mode for a fourth time period (15 hours and 30 minutes), and the set points are returned to their previous values as used in the first time period. This corresponds to a “normal” use mode of the heating cylinder 210 in which intermittent and medium/low hot water demand is present.

In this example, after the fourth time period, the control device 230 once again turns the heating cylinder apparatus 200 including heaters 212, 213 and pump 220 off. The heating cylinder apparatus 200 remains off for a fifth time period of 8 hours and 30 minutes, for example this may be scheduled when there is no anticipated use of hot water.

After the fifth time period, the control device 230 re-activates the first operating mode which then runs for a sixth time period of 11 hours and 35 minutes. Finally, the control device 230 is then scheduled to activate the second operating mode for a seventh time period of 30 minutes. As mentioned above, this could be done to prepare the heating cylinder 210 for a period of very high hot water demand.

As described above, the control device 210 is configured to flexibly schedule and change between the different operating modes as well as to turn the heating cylinder apparatus 200 off depending on various information such as pre-determined instructions and external information. While specific examples are provided above, in other embodiments the order and selection of the different operating modes, set points and other setting used, and time periods that each mode is used for may vary.

The one or more embodiments are described above by way of example only. Many variations are possible without departing from the scope of protection afforded by the appended claims. For example, some embodiments of the invention may use a single heating element or heater to heat water in the heating cylinder 10, or may use more than two heaters. In addition, the example described above used a heating element with effectively four different heating power settings: both first heater 12 and second heater 13 off; first heater 12 on low power setting and second heater 13 off; and first heater 12 on at maximum power setting and second heater 13 on. In other embodiments, there may only be two heating power settings: on; and off. Alternatively, there may be five or more power settings as required.

Claims

1. A water heater comprising: a container for storing a volume of water; a heater for heating water stored in the container, wherein the container comprises an inlet via which, in use, water to be heated may flow into the container and an outlet via which, in use, heated water may flow out of the container, the inlet being positioned below the outlet; and a mixing arrangement for mixing water in the container, operable to reduce the temperature difference between water at different parts of the container, wherein the heater is arranged to heat water in the container when the water temperature is greater than a first set point and not to heat water when the water temperature is less than a second set point and the mixing arrangement is arranged to mix water in the container when the water temperature is greater than a third set point and not to mix water when the temperature is less than a fourth set point.

2. A water heater as claimed in claim 1 wherein the outlet is at or towards a top of the container and the inlet is at or towards a base of the container.

3. A water heater as claimed in any preceding claim wherein the water heater is a domestic water heater.

4. A water heater as claimed in any preceding claim wherein the mixing arrangement comprises a mixing conduit providing a conduit for the flow of water located at or near the top of the container to a position at or near the bottom of the container, and a device for causing water to flow along the conduit from an upper part of the container to a lower part of the container so as to mix water in the container.

5. A water heater as claimed in claim 4 wherein the device for causing water to flow along the conduit is a pump.

6. A water heater as claimed in either claim 4 or 5 wherein the mixing conduit branches into a water supply conduit connected to the inlet.

7. A water heater as claimed in any of claims 4 to 6 wherein the mixing conduit is configured to prevent fluid flow in the reverse direction through the conduit.

8. A water heater as claimed in claim 7 wherein the mixing conduit comprises a one-way valve.

9. A water heater as claimed in any preceding claim wherein the heater is positioned in the container between the inlet and the outlet, and towards a base of the container.

10. A water heater as claimed in any preceding claim wherein the heater is an electric immersion heater comprising titanium treated with a nickel-steel super alloy.

11. A water heater as claimed in any preceding claim wherein the heater is an electric immersion heater with a surface power output density of less than 40 W per cm².

12. A water heater as claimed in any preceding claim comprising two or more heaters.

13. A water heater as claimed in any preceding claim comprising a temperature sensor configured to output a signal indicative of the temperature of water in the container.

14. A water heater as claimed in any preceding claim wherein the outlet may be fluidly connected to the heated water supply via a side-wall of the container.

15. A water heater as claimed in claim 14 wherein the outlet comprises a pipe- section that is completely contained within the container.

16. A water heater as claimed in claim 15 wherein the pipe section comprises a first end and a second end, the first end of the pipe section being connected to the side-wall of the container and wherein the second end of the pipe section is above the first end.

17. A water heater as claimed in any preceding claim wherein the first set point is less than the second set point.

18. A water heater as claimed in any preceding claim wherein the fourth set point is less than the third set point.

19. A water heater as claimed in any preceding claim wherein the third set point is greater than the second set point.

20. A water heater as claimed in any preceding claim wherein the fourth set point is greater than the first set point.

21. A control device for controlling one or more heaters and a mixing arrangement of a water heater comprising a container for water in dependence on the sensed temperature of water in the container, the control device being configured to cause the or each heater to operate if the temperature of water is less than a first set point, and to turn the or each heater off if the temperature of water is equal to or greater than a second set point, and to cause the mixing arrangement to operate if the temperature of water is equal to or greater than a third set point and to turn the mixing arrangement off if the temperature of water is less than a fourth set point.

22. A water heater as claimed in any of claims 1 to 20 comprising a control device as claimed in claim 21.

23. A method of heating water in a container comprising an inlet via which, in use, water to be heated may flow into the container and an outlet via which, in use, heated water may flow out of the container, the inlet being positioned below the outlet, the method comprising: starting heating of water in the container if the water temperature is less than a first set point; stopping heating water in the container if the water temperature is equal to or greater than a second set point; and mixing water in the water heater so as to reduce the temperature difference between water at different parts of the water heater when the water temperature is equal to or greater than a third set point; and stopping mixing of water in the water container when the water temperature is below a fourth set point.

24. A method as claimed in claim 23 comprising using a water heater as claimed in any of claims 1-20 or 22.