Water heating system and device

Abstract

A system for heating water is provided. The system includes a tank for holding hot water. The system includes an external heating device to provide heat to water of the tank with a circuit of heat transfer fluid to transfer heat to or from the external heating device. The system may include a heat exchange coil in the circuit of heat transfer fluid, the heat exchange coil arranged to provide heat to water in the tank. The system includes a plate heat exchanger arranged external to the tank for transferring heat from the circuit of heat transfer fluid to water of the tank. The system includes a flow path from the tank to the heat exchanger and back to the tank, and a pump arranged to pump water in the flow path. The system may include a flow selector for routing the circuit of heat transfer fluid to or from the heat exchange coil or the plate heat exchanger. The system may include a controller for controlling the flow selector in dependence on a demand for immediate hot water from the tank.

Description

[0001] Water Heating System and Device

[0002] The present invention relates to a system for heating water, in connection with an external heat source such as a heat pump. Such a system may lend itself to use in domestic or commercial water heating systems where it is necessary or desirable to have a stored quantity of heated water for immediate use.

[0003] A conventional heating system comprises a tank containing water that may be drawn by a user. The water in the tank may be heated by an immersed electrical heater or indirectly by an external heat source (usually a gas-fired boiler or heat pump). Heat may then be extracted from the tank for domestic or industrial purposes. Maximising efficiency of heat storage in the tank and heat transfer from the external heat source to the tank is necessary to reduce operating costs and the time required to achieve a required temperature of water in the tank.

[0004] Present heating systems employ a coiled copper heat exchanger mounted coaxially in a cylindrical tank connected to an external heat source by a pump forming a secondary heat loop. When used without a direct heating method, this indiscriminate heating of water in the tank can result in long heat up times and eventually excessive quantities of hot water, increasing the operating cost of the system.

[0005] Furthermore, refilling of the tank during use can result in unwanted mixing between hot and cold water, thereby reducing the temperature of water drawn off for use.

[0006] Finally, the improvement of hot water tanks can result in an excessive number of pipes and apertures in the body of the tank thereby increasing the cost and complexity of the device.

[0007] The present disclosure therefore aims to provide improvements for heating systems.

[0008] According to a first aspect of this disclosure there is provided a system for heating water including a tank for holding hot water and a tank outlet conduit for discharging hot water from the tank to a user. An external heating device may provide heat to water of the tank. A heat exchanger may be arranged external to the tank for transferring heat from the external heating device to water of the tank. A flow path from the tank to the heat exchanger and back to a top of the tank may be provided. A pump may be arranged to pump water in the flow path. A controller may control flow in the flow path. The flow path may include at least a portion of the tank outlet conduit. The flow path and the tank outlet conduit may share a common tank opening.

[0009] The flow path including a portion of the tank outlet conduit or sharing a common tank opening with the tank outlet conduit can permit efficient use of conduits, reduction of number of openings in the tank, ease of installation, and low cost of manufacture. The portion of the tank outlet conduit may in use receive flow in either direction. The portion of the tank outlet conduit may in use receive flow into the tank at a first time and flow out of the tank at a second time.

[0010] A diffuser may be arranged at an outlet of the flow path into the tank. The diffuser can reduce mixing of water within the tank, in particular in case heat is elsewise provided to the tank near the outlet of the flow path into the tank (e.g. by an electric immersion heater).

[0011] Means of sensing or inferring a temperature distribution in the tank may be included, preferably an array of temperature sensors arranged to sense temperatures at different heights of the tank. This can enable nuanced control of the provision of heat to the tank.

[0012] The system may include a flow sensing device configured to determine whether the tank outlet conduit is discharging water from the tank to a user. The controller may be configured to prevent flow in the flow path to a top of the tank when the tank outlet conduit is discharging water from the tank to a user. The system may include a flow sensing device configured to determine whether the tank outlet conduit is discharging water from the tank in response to a user hot water demand. The controller may be configured to prevent flow in the flow path to a top of the tank when the tank outlet conduit is discharging water from the tank in response to a user hot water demand. The system may include a flow sensing device configured to determine whether the tank outlet conduit is discharging hot water from the tank to a user. The controller may be configured to prevent flow in the flow path to a top of the tank when the tank outlet conduit is discharging hot water from the tank to a user. This can enable prioritising of use of the shared portion of the tank outlet conduit discharging hot water from the tank to a user without adverse effects on either mode of use. The flow sensing device may be a flow sensor at the cold-water feed to the tank. The flow sensing device may be a flow meter or a temperature senor at the tank outlet conduit, preferably at a portion not shared with the flow path.

[0013] For efficient heating the flow path may be from a bottom of the tank. To reduce convective flow in the tank the system may further comprise a baffle for baffling flow between the bottom of the tank and the rest of the tank. The flow path may comprise an upper return branch from the heat exchanger to the top of the tank and a lower return branch from the heat exchanger to a bottom of the tank. This can enable more sophisticated heating of water in the tank, and in particular quick heating of a smaller quantity at the top of the tank or slower more efficient heating of the entire volume of the tank.

[0014] The system may comprise a three-port valve controllable by the controller and configured to route water from the heat exchanger either to the upper return branch or to the lower return branch. The system may comprise a first pump in the lower return branch and a second pump in the upper return branch, the first and second pumps controllable by the controller to route water from the heat exchanger either to the upper return branch or to the lower return branch.

[0015] The system may include a flow orifice restriction in the upper return branch. This can be beneficial for a low flow rate in the upper return branch.

[0016] The controller may be configured to precede flow to the upper return branch with a period of flow to the lower return branch. This can permit enable particularly robust control. The controller may be configured to initiate flow to the lower return branch at a first flow rate and to decrease flow to a second, lower flow rate before transitioning flow to the upper return branch. This can permit enable particularly robust control.

[0017] The system may include at least one valve arranged to prevent water flowing in the flow path or in a portion of the flow path while the tank outlet conduit is discharging hot water from the tank to a user. The system may include at least one valve arranged to prevent water flowing in the flow path or in a portion of the flow path while the tank outlet conduit is discharging hot water from the tank in response to a user hot water demand The valve may be a non-return valve or a controllable valve. This can prevent unintended bypass flows when hot water is drawn from the system.

[0018] The pump may be a variable speed pump controllable by the controller.

[0019] The system may an electric immersion heater, preferably arranged in an upper portion of the tank.

[0020] According to another aspect there is provided a system for heating water including: a tank for holding hot water; an external heating device to provide heat to water of the tank with a circuit of heat transfer fluid to transfer heat to or from the external heating device; a heat exchange coil in the circuit of heat transfer fluid, the heat exchange coil arranged to provide heat to water of the tank; a plate heat exchanger arranged external to the tank for transferring heat from the circuit of heat transfer fluid to water of the tank; a flow path from the tank to the heat exchanger and back to the tank and a pump arranged to pump water in the flow path; a flow selector for routing the circuit of heat transfer fluid to or from the heat exchange coil or the plate heat exchanger; and a controller for controlling the flow selector in dependence on a demand for immediate hot water from the tank.

[0021] The system can permit efficient use of heat from an external heat source. The flow selector is preferably a three-port valve.

[0022] The system may be as aforementioned. The system may include features of the system as aforementioned.

[0023] According to another aspect there is provided a system for heating water including: a hot water tank and a heat pump; a hot water tank controller and a heat pump controller; a temperature sensor for providing a control input to the heat pump controller; and a bypass switch configured to: receive, from the hot water tank controller, bypass activation signal; in first configuration provide a connection connecting the temperature sensor to the heat pump controller; in second configuration disconnect the temperature sensor from the heat pump controller; and select the first or second configuration in dependence on the bypass activation signal.

[0024] The system can enable effective coordination between controllers.

[0025] The system may be as aforementioned. The system may include features of the system as aforementioned.

[0026] The bypass switch may comprise a bypass resistor that in the second configuration is connected to the heat pump controller. The bypass resistor may be a fixed value resistor. In the second configuration an open circuit may be formed. In the second configuration a short circuit may be formed. The bypass resistor may be a variable resistor. The bypass resistor may be variable in dependence on an input from the hot water tank controller. According to another aspect there is provided a system for heating water including: a hot water tank and a heat pump; a flow selector for routing heat from the heat pump to an upper portion of the hot water tank or to a lower portion of the hot water tank; and a hot water tank controller configured to control heating water of the hot water tank and a heat pump controller configured to control heat output of the heat pump; wherein the hot water tank controller is configured to: receive a signal indicating a demand for immediate hot water, and in response to the signal control the flow selector to route heat from the heat pump to the lower portion of the hot water tank for an initial period of time before routing heat from the heat pump to the upper portion of the hot water tank for satisfying the demand for immediate hot water.

[0027] The system can enable effective system stabilisation under the influence of separate controllers. By virtue of initial operation with routing of heat to the lower portion of the tank the system being controlled has a large thermal mass and a gradual thermal response, permitting stable system initialisation and adjustment to the intended system setting, namely routing of heat to the upper portion of the tank for satisfying the demand for immediate hot water.

[0028] The system may be as aforementioned. The system may include features of the system as aforementioned.

[0029] The system for heating water may include a flow path from the tank to a heat exchanger arranged external to the tank and back to a top of the tank. The system for heating water may include a flow path from the tank to a heat exchanger arranged external to the tank and back to a bottom of the tank. A pump may be arranged in the flow path to pump water in the flow path. The system may comprise a tank outlet conduit for discharging hot water from the tank to a user. The system may comprise a tank outlet conduit for discharging hot water from the tank in response to a user hot water demand. The heat exchanger may be for transferring heat from a heat transfer fluid of the heat pump to water of the tank. The system may comprise a heat exchange coil in a circuit of heat transfer fluid, the heat exchange coil arranged to provide heat to water in the tank. The heat pump may include a circuit of heat transfer fluid to transfer heat to or from the heat pump. The system may comprise a flow selector for routing a circuit of heat transfer fluid to the heat exchange coil or the plate heat exchanger.

[0030] The initial period of time may be a period of time until a portion of water from the hot water tank is heated to a threshold temperature. Optionally the initial period may be a period of time until a portion of heat transfer fluid from the heat pump is heated to a threshold temperature.

[0031] The system may comprise a flow path with an upper return branch from the heat exchanger to the top of the tank and a lower return branch from the heat exchanger to a bottom of the tank. The controller may be configured to precede flow to the upper return branch with a period of flow to the lower return branch. The controller may be configured to initiate flow to the lower return branch at a first flow rate and to decrease flow to a second, lower flow rate before transitioning flow to the upper return branch.

[0032] According to another aspect there is provided a system for heating water including: a heat pump; a circuit of heat transfer fluid to transfer heat to or from the heat pump; a tank for storing hot water; an upper heat transfer means configured to transfer heat from the heat pump to an upper portion of the water tank; a lower heat transfer means configured to transfer heat from the heat pump to a lower portion of the water tank; a selector arrangement configured to route heat from or to the heat pump to or from: the upper heat transfer means; the lower heat transfer means; or both; and a controller; wherein the controller is configured to control the selector arrangement for heat transfer to or from the upper portion of the water tank or the lower portion of the water tank or both in dependence on a temperature distribution in the water tank.

[0033] The system may further comprise a means of sensing or inferring a temperature distribution in the tank.. The means of sensing may comprise one or more temperature sensors, preferably an array of temperature sensors arranged to sense temperatures at different heights of the tank.

[0034] The upper heat transfer means may be an upper heat transfer coil configured to transfer heat between the heat transfer fluid and the upper portion of the water tank. The lower heat transfer means may be a lower heat transfer device configured to transfer heat between the heat transfer fluid and water from a lower portion of the water tank. The selector arrangement may be a valve arrangement in the circuit of heat transfer fluid arranged to route the heat transfer fluid to the upper heat transfer coil or the lower heat transfer device or to both.

[0035] The system may further comprise a heat exchanger and the circuit of heat transfer fluid is arranged to transfer heat between the heat pump and the heat exchanger. The system may further comprise a circuit of water from the tank to the heat exchanger and back to the tank to transfer heat between the tank and the heat exchanger. The upper heat transfer means may be an upper return branch in the circuit of water that is arranged to return water to the upper portion of the water tank. The lower heat transfer means may be a lower return branch in the circuit of water that is arranged to return water to the lower portion of the water tank. The selector arrangement may be a three-port valve in the circuit of water from the tank arranged to route the water to the upper return branch or the lower return branch or to both. The selector arrangement may be a controllable first pump in the upper return branch and a controllable second pump in the lower return branch selectable to pump the water via the upper return branch or the lower return branch or both.

[0036] The system may be as aforementioned. The system may include features of a system as aforementioned.

[0037] According to another aspect there is provided a controller for a system for heating water, wherein the controller is adapted to: receive an indication of whether a tank outlet conduit is discharging water from a tank to a user or in response to a user hot water demand; and prevent flow in a flow path to a top of the tank when the tank outlet conduit is discharging hot water from the tank to a user or in response to a user hot water demand. The flow path is from the tank to a heat exchanger arranged external to the tank and back to a top of the tank. A pump may be arranged in the flow path to pump water in the flow path. The tank is for holding hot water. The tank outlet conduit may be for discharging hot water from the tank to a user. The tank outlet conduit may be for discharging hot water from the tank in response to a user hot water demand. The heat exchanger is for transferring heat from an external heating device to water of the tank. The flow path preferably includes at least a portion of the tank outlet conduit.

[0038] The system for heating water may be as aforementioned. The system for heating water may include features of a system for heating water as aforementioned.

[0039] The controller can enable use of the tank outlet conduit for dual purposes of drawing hot water from the tank; and providing hot water to the tank at different times. Enabling twofold uses of the tank outlet conduit can permit efficient use of conduits, reduction of number of openings in the tank, ease of installation, and low cost of manufacture.

[0040] The controller may be adapted to receive from a flow sensing device the indication of whether the tank outlet conduit is discharging water from the tank to a user or in response to a user hot water demand. The flow sensing device may be a flow sensor at the cold- water feed to the tank. The flow sensing device may be a flow meter at the tank outlet conduit. The flow sensing device may be a temperature senor at the tank outlet conduit. The flow path may comprise an upper return branch from the heat exchanger to the top of the tank and a lower return branch from the heat exchanger to a bottom of the tank. The controller may be configured to route water from the heat exchanger to the lower return branch when the tank outlet conduit is discharging water from the tank to a user or in response to a user hot water demand.

[0041] According to another aspect there is provided a controller for a system for heating water, wherein the controller is adapted to: receive a signal indicating a demand for immediate hot water from a hot water tank, and in response to the signal to control a flow selector to route heat from a heat pump to a lower portion of the hot water tank for an initial period of time before routing heat from the heat pump to an upper portion of the hot water tank for satisfying the demand for immediate hot water.

[0042] The controller can enable effective system stabilisation under the influence of separate controllers. By virtue of initial operation with routing of heat to the lower portion of the tank the system being controlled has a large thermal mass and a gradual thermal response, permitting stable system initialisation and adjustment to the intended system setting, namely routing of heat to the upper portion of the tank for satisfying the demand for immediate hot water.

[0043] The initial period of time may be a period of time until a portion of water from the hot water tank is heated to a threshold temperature. Optionally the initial period may be a period of time until a portion of heat transfer fluid from the heat pump is heated to a threshold temperature.

[0044] The system may comprise a flow path with an upper return branch from the heat exchanger to the top of the tank and a lower return branch from the heat exchanger to a bottom of the tank. The controller may be configured to precede flow to the upper return branch with a period of flow to the lower return branch. The controller may be configured to initiate flow to the lower return branch at a first flow rate and to decrease flow to a second, lower flow rate before transitioning flow to the upper return branch.

[0045] The system for heating water may be as aforementioned. The system for heating water may include features of a system for heating water as aforementioned.

[0046] The system for heating water may include a flow path from the tank to a heat exchanger arranged external to the tank and back to a top of the tank. The system for heating water may include a flow path from the tank to a heat exchanger arranged external to the tank and back to a bottom of the tank. A pump may be arranged in the flow path to pump water in the flow path. The flow selector may be for routing fluid to the top of the tank or to the bottom of the tank. The system may comprise a tank outlet conduit for discharging hot water from the tank to a user or in response to a user hot water demand. The heat exchanger may be for transferring heat from a heat transfer fluid of the heat pump to water of the tank. The system may comprise a heat exchange coil in a circuit of heat transfer fluid. The heat exchange coil may be arranged to provide heat to water in the tank. The heat pump may include a circuit of heat transfer fluid to transfer heat to or from the heat pump. The flow selector may be for routing a circuit of heat transfer fluid to the heat exchange coil or the plate heat exchanger.

[0047] According to another aspect there is provided a computer program and a computer program product for carrying out any of the methods described herein and / or for embodying any of the apparatus features described herein. According to another aspect there is provided a non-transitory computer readable medium having stored thereon a program for carrying out any of the methods described herein and / or for embodying any of the apparatus features described herein. According to another aspect there is provided a computer program product comprising software code for carrying out any method as herein described. Features implemented in hardware may generally be implemented in software, and vice versa. Any reference to software and hardware features herein should be construed accordingly.

[0048] The invention also provides a signal embodying a computer program for carrying out any of the methods described herein and / or for embodying any of the apparatus features described herein, a method of transmitting such a signal, and a computer product having an operating system which supports a computer program for carrying out any of the methods described herein and / or for embodying any of the apparatus features described herein.

[0049] According to another aspect there is provided a valve for use with a heating system comprising: a body through which fluid is allowed to flow and a moveable restriction to the fluid flow, wherein in a first position the restriction provides a predetermined restriction to the fluid flow, and upon increasing the fluid flow rate through the valve beyond a predetermined value, the restriction moves to a second position in which the restriction provides a smaller restriction to the fluid flow than the first position. Advantageously this may allow for a fine control of fluid flow rate though a heating system when operating with a wide range of external heating devices.

[0050] The restriction may comprise an orifice plate held in place by a spring. The orifice plate may be a disc with a hole through its thickness, the disc being configured to move along the body of the valve. Movement of the orifice plate may be controlled by the spring, such that fluid flow through the valve causes a force to act on the orifice plate in a direction opposite to the force of the spring on the orifice plate.

[0051] The valve may further comprise a spring seat configured to retain the spring whilst allowing fluid to flow through the valve. The spring seat may be a body mounted internally to the valve with holes extending through its thickness, thereby providing a solid surface against which the spring can press whilst the holes allow for fluid to pass through the spring seat. The number and diameter of the holes may be chosen to minimise any further flow restriction or may be chosen to provide a predetermined flow restriction.

[0052] The valve may further comprise an additional flow restriction in the body of the valve. The flow restriction may comprise an additional stationary orifice plate.

[0053] The moveable valve restriction may be in the first position when the heating system is coupled to a low-powered external heating device. The moveable valve restriction may be in the second position when the heating system is coupled to a high-powered external heating device.

[0054] According to another aspect there is provided a system for heating water as aforementioned further comprising a valve as aforementioned.

[0055] According to another aspect there is provided a system for heating water including: a tank for holding hot water; a heat exchanger arranged external to the tank for transferring heat from an external heating device to water of the tank; a flow path from the tank to the heat exchanger and back to a top of the tank; a pump arranged to pump water in the flow path; and a valve as aforementioned arranged in the flow path.

[0056] The flow path may comprise an upper return branch for returning water back to the top of the tank and a lower return branch for returning water back to a bottom of the tank. The valve may be arranged in the upper return branch.

[0057] The system for heating water may include features of a system for heating water as aforementioned. Any apparatus feature as described herein may also be provided as a method feature, and vice versa.

[0058] Any feature in one aspect of the invention may be applied to other aspects of the invention, in any appropriate combination. Furthermore, any, some and / or all features in one aspect can be applied to any, some and / or all features in any other aspect, in any appropriate combination.

[0059] It should also be appreciated that particular combinations of the various features described and defined in any aspects of the invention can be implemented and / or supplied and / or used independently.

[0060] Description of the drawings

[0061] These and other aspects of the present invention will become apparent from the following exemplary embodiments that are described with reference to the following figures in which:

[0062] Figure 1 shows an embodiment of a system comprising a tank, external heating device, and periphery devices;

[0063] Figure 2 shows another embodiment of a system comprising a tank, external heating device, and periphery devices;

[0064] Figure 3 shows another embodiment of a system comprising a tank, external heating device, and periphery devices;

[0065] Figure 4 shows another embodiment of a system comprising a tank, external heating device, and periphery devices;

[0066] Figure 5 shows another embodiment of a system comprising a tank, external heating device, and periphery devices;

[0067] Figures 6a and 6b are schematics for a bypass switch;

[0068] Figure 7 shows a control schematic for a system comprising a tank, external heating device, and periphery devices;

[0069] Figure 8 shows temperature and flow rate graphs for a system comprising a tank, external heating device, and periphery devices;

[0070] Figures 9a and 9b show a diagram of a valve for use in a heating system; and

[0071] Figure 10 shows an embodiment of a system comprising a tank, external heating device, and periphery devices. Specific Description

[0072] The present disclosure relates to a heating system 1-1 , 1-2, 1-3, 1-4, and 1-5 comprising a tank 100, an external heating device 110 configured to provide heat to water (or another fluid) stored in the, an electric immersion heater 140, a thermocline sensor 180, a cold- water inlet, and a control unit configured to control the electronic devices that form the heating system. The heating system may be controlled such that the external heating device 110 provides a heat input to the water stored in the tank 110, or the water provides heat to the external heating device 110 (for instance of the external heating device 110 is a heat pump that requires defrosting).

[0073] Figure 1 shows a heating system 1-1 in which there is provided a tank 100 which may be filled with water (or another fluid). The water can be heated and can then either be drawn by a user to provide hot water; or the water in the tank can be used to receive, store or provide heat. The tank can act as both a boiler and a thermal store. Where hot water is drawn by a user this can in some examples result in dispensing of hot water to a user. In other examples hot water is drawn by a user for provision e.g. to a space heating system in response to a user demand.

[0074] The tank is in the form of a cylinder with domed ends. This form is favourable for stress distribution and particularly well suited for a tank for containing pressurised water. The tank is preferably intended for containing mains pressurised water. Such a tank is ordinarily unvented. A pressurised tank can distribute hot water throughout a building without needing any pumps. This is particularly convenient for providing hot water to a user. The tank 100 is connected to the cold-water inlet for receiving e.g. mains pressurised cold water, and a tank outlet conduit 178 e.g. for providing heated water to a user.

[0075] The tank 100 is fitted with a baffle 102 near its base. The baffle 102 is configured to restrict the movement of the water in the tank between the volume below the baffle and the main volume of the tank, thereby reducing convection in the tank and assisting with stratification of the temperature of the water. In the well-stratified tank hot (less dense) water has accumulated at the top of the tank The baffle 102 may be shaped according to the desired restriction characteristics (which may for instance depend upon the fluid used in the tank, the volume and other dimensions of the tank, the external heat source etc.).

[0076] In an upper region of the tank 100 there is located an electrical immersion heater 140 (also referred to as heater or electric immersion heating element). The immersion heater 140 is a simple heating element, configured to increase the temperature of the water in the tank 100 when provided with electrical power. The immersion heater 140 is controlled and feeds back to a control unit 130 (also referred to as controller or tank controller).

[0077] The system may further feature a thermocline sensor 180 or similar temperature detecting device. The thermocline sensor 180 is configured to measure the quantity of thermal energy stored in the tank 100 and / or a temperature distribution in the tank and feeds this information back to the control unit 130. The thermocline sensor 180 is typically an array of temperature sensors arranged to sense temperatures at different heights of the tank. This can enable particularly efficient and favourable resolution of temperature distribution in the tank. The thermocline sensor 180 may for instance be fixed to an outer surface of the tank or immersed inside the tank. An array of temperature sensors may be arrayed at different heights along the tank, e.g. vertically along the wall of the water tank or inside the tank, such that the array of sensors detects the temperature of the water in the tank at a plurality of heights. This may be used to determine a heat profile graph showing how the temperature of the water in the water tank varies with height. The vertical temperature distribution is particularly informative, as due to thermal stratification in the tank horizontal temperature distributions are typically less significant. Other means of determining a temperature distribution of water in the tank may be used alternatively or additionally. For instance, the thermocline sensor may include as few as one temperature sensor and inference of a temperature distribution from a model of temperature distribution in the tank. Inferring a temperature distribution from a model of temperature in a tank can be improved with measurements such as a flow rate measurement of water into and / or out of the tank and temperature data from outside the tank, such as at a cold inlet and at a hot inlet. Other means of determining a temperature distribution of water in the tank may include thermal imaging or density sensing or other suitable techniques.

[0078] The system further includes a feed pipe 122 arranged to draw water from the tank 100 below the baffle 102. The feed pipe 122 is arranged to provide water from the tank to a heat exchanger 120.

[0079] The heat exchanger 120 is preferably a plate heat exchanger, although it will be appreciated that other types of heat exchanger (such as a shell and tube heat exchanger) may be used as well. The heat exchanger 120 takes water from the tank 100 via the feed pipe 122 and heat transfer occurs between the water from the tank 100 and a heat transfer fluid from an external heat source 110.

[0080] The external heat source 110 is located remotely from the tank 100 and is configured to provide a thermal energy input into the tank 100. The external heat source 110 may provide thermal energy from a number of sources; the external heat source 110 may be a gas or other fossil fuel fired boiler, a heat pump, a solar array, or an electrical heater. The external heat source 110 is connected via a self-contained or secondary fluid loop 112 to the heat exchanger 120. In one mode of operation the secondary fluid is heated by the external heat source 110 and pumped to the heat exchanger 120 where it transfers thermal energy to the water from the tank. The secondary fluid in turn loses thermal energy and is returned to the external heat source 110 to begin the cycle again.

[0081] The circuit of water from the tank can continue from the heat exchanger 120 to a lower return branch 160 or an upper return branch 171. The lower return branch 160 re-enters the tank 100 and terminates below the baffle 102 for returning water back to a lower part of the tank. The upper return branch 171 returns the water to the top of the tank 100. A circuit of water from the tank to the heat exchanger and back to the tank is formed to transfer heat between the tank and the heat exchanger.

[0082] The upper return branch can permit particularly rapid heating of the upper portion of the tank in order to ensure that hot water is rapidly available e.g. for domestic hot water provision. Slower and more efficient heating heat of the entirety of the tank can be provided by way of the lower return branch. In some examples heat may be provided to the tank via both the upper and lower return branch simultaneously. By reversing the flow direction of the second pump, hot water can be provided from the top of the tank to the heat exchanger so as to provide heat from the tank to the external heat source 110.

[0083] In the example illustrated in Figure 1 each return branch 160, 171 includes a pump 164, 174 The return branches 160, 171 may each include an optional non-return valve 162, 172 (also referred to as a one-way valve).

[0084] A first pump 164 is configured to circulate the water, first drawing through the feed pipe 122, through the heat exchanger 120 and finally discharging back into the tank 100 below the baffle 102 via the lower return branch 160 with the optional non-return valve 162.

[0085] A second pump 174 is connected to the outlet of the heat exchanger 120 and returns the water via the upper return branch 171 and an optional second non-return valve 172 to the top of the tank 100. An optional diffuser 170 may be mounted on the outlet of the upper return branch at the top of the tank 100 to reduce the quantity of mixing that occurs as the water is reintroduced back into the tank 100. An optional orifice restriction 173 is included in the upper return flow branch 171 to ensure that low enough flow rates can be delivered at low pump speeds. This can enable low flow rates in the upper return branch so that the water can receive more heat at the heat exchanger and be provided to the top of the tank suitably hot.

[0086] The upper return branch 171 includes a portion of the tank outlet conduit 178. This means a single pipe with a suitable junction may be used to perform both the return of water from the heat exchanger 120 and to draw water from the tank 100 for use.

[0087] In order to accommodate both draw of hot water from the tank and return of heated water to the top of the tank via the same tank outlet conduit, a number of features may be included that can assist in sensing whether a hot water draw event is occurring, and permit control of the return of heated water to suspend that process for the duration of the hot water draw event. These features can include a flow sensing device in the tank outlet conduit, a flow sensor at the cold-water feed to the tank, and a controller adapted to control flow in the upper return branch in dependence on detection of a draw event. These features are described in more detail.

[0088] A flow sensing device 176 is optionally mounted in the tank outlet conduit 178 downstream of the junction with the upper return branch 171. The flow sensing device 176 senses if water is drawn from the tank 100 and feeds this information back to the control unit 130. The flow sensing device 176 can for example sense flow magnitude or it can sense a temperature permitting inference that water is being drawn from the tank 100 by detecting a rise in temperature. This information may then be fed back to the control unit 130. In a variant the flow sensing device 176 is replaced by or supplemented with a flow sensor 152 at the cold-water feed 150. The flow sensor 152 can sense magnitude of flow in the cold- water feed; when cold water is being drawn into the tank this indicates that a hot water draw from the tank is occurring from the tank. This information may then be fed back to the control unit 130.

[0089] The control unit 130 is connected to the various electronic devices that form part of the heating system 1-1. In the figure shown, dashed lines show exemplary connection from the control unit to its controlled devices including the pumps 164 174, the thermocline sensor 180, the immersion heater 140, the flow sensing device 176, and the flow sensor 152. These devices may receive and feedback to the control unit 130 to improve the control of the heating system 1-1. The control unit 130 may also control the external heat source 110. In a first operating mode, the external heat source 110 provides a heat input to the tank 100. water is drawn from the tank 100 via the feed pipe 122 and passes into the heat exchanger 120. The external heat source 110 heats a secondary fluid (also referred to as a heat transfer fluid) that is transferred to the secondary side of the heat exchanger 120 and heat is transferred to the water in the heat exchanger 120.

[0090] The first pump 164 draws the water from the heat exchanger 120 and returns it to the tank via the lower return branch 160 into the base of the tank 100.

[0091] Alternatively, the second pump 174 draws the water from the heat exchanger 120 and discharges it via the upper return branch 171 into the top of the tank 100, optionally through a diffuser 170 to reduce the quantity of mixing in the tank 100 as the water is returned. This is particularly beneficial when the immersion heater 140 is turned on to provide additional heat input to the tank 100.

[0092] The pumps 164 174 may also be run together to balance the water returning to the top and base of the tank via each return path. This may also be used to smooth out any instabilities in the system during heating.

[0093] The pumps 164 174 are controlled by the control unit 130, and their flow and pressure performance may be varied to alter the flow rate of water passing through the pumps. This allows for a desired set-point temperature to be more easily achieved in the tank 100 during the heating procedure. The desired temperature may for instance be the temperature of the water to be drawn off for use (via the diffuser 170).

[0094] In some scenarios - e.g. during supply of heat from the immersion heater 140 -flow via the upper return branch could introduce colder water in water drawn by a user, thereby reducing the system efficiency. To prevent the second pump 174 from pumping water into the tank outlet conduit 178 during a user draw event the first and second pumps are controlled by the control unit 130 to prevent water flow in the upper return branch 171. The control unit 130 detects a signal from the flow sensing device 176 and / or the flow sensor 152 indicating water is being drawn off and turns off the second pump 174 to prevent cold water mixing with hot water drawn from the tank 100. The controller may active the first pump 164 instead to divert water to the bottom of the tank for the duration of the draw event. In some examples the system may further include a temperature sensor in the upper return branch 171 upstream of the junction with the tank outlet conduit 178, so that controller may determine whether water in the upper return branch 171 is at least as hot as the water in the top of the tank in which case the second pump may continue to operate rather than being interrupted during a user hot water draw event. In some examples the controller may determine whether water being drawn off is hot or not. If the water being drawn off is not hot then the controller may cause the second pump to continue to operate rather than being interrupted during a user hot water draw event.

[0095] The non-return valves 162 172 can optionally assist in preventing a bypass flow from occurring when water is drawn from the tank 100. These only allow water to flow in one direction, meaning that any water drawn at the tank outlet conduit 178 has to be drawn from the top of the tank 100 via the optional diffuser 170. This ensures that the hottest water is drawn for use. The non-return valves 162, 172 may be replaced with suitable shutoff valves that can be controlled by the controller to open or shut the upper return branch to permit water from the top of the tank 100 to be drawn via the tank outlet conduit 178.

[0096] In a second operating mode, the external heat source 110 is a heat pump and receives heat from the tank 100 to defrost or prevent freezing of the evaporator.

[0097] Water is drawn from the feed pipe 122 and passes into the heat exchanger 120. Secondary fluid from the external heat source 110 is circulated and passes through the secondary side of the heat exchanger 120.

[0098] In this operating mode the water is warmer than the secondary fluid, therefore heat transfers from the water to the secondary fluid. This warmer secondary fluid may then be used by the external heat source 110 to defrost or prevent freezing of any components.

[0099] The water is then returned to the tank 100 preferably via the lower return branch as previously described.

[0100] In a variant the fluid circuit with the upper branch is operated in the reverse direction, that is, the second pump is controlled to draw water from the top of the tank, provide it to the heat exchanger, and return it to the bottom of the tank via the feed pipe 122. This can be useful in scenarios where the water at the bottom of the tank is not warm enough for a defrost operation, but the water at the top of the tank is.

[0101] Figure 2 shows another embodiment of the heating system 1-2 in which a single pump 224 and a three-port valve 290 are used to route water through the feed 122 and return branches 160 171.

[0102] The single pump 224 is provided upstream of the junction between the upper and lower return branches 160, 171 , preferably between the heat exchanger and the inlet of the feed 122, but it may alternatively be provided between the heat exchanger and the junction between the return branches.

[0103] At the junction between the upper and lower return branches 160, 171 the three-port valve 290 is provided to direct flow either into the upper or lower return branch 160, 171. The three-port valve 290 is electronically controllable to operate a valve in the valve body to connect two of the three ports together.

[0104] In this heating system 1-2, the three-port valve 290 is used to route water from the feed pipe 122 and pump 224 and heat exchanger 120 to either the lower return branch 160 or the upper return branch 171. The three-port valve 290 is controlled by the control unit 130 that sets its position (and thus the pipes that are connected) to route water according to the mode of operation.

[0105] The modes of operation of this heating system 1-2 are the same as described with reference to Figure 1 and heating system 1-1 , where the controller controls the three-port valve 290 for selection of the upper or lower return branch rather than one or the other pump.

[0106] Figure 3 shows another embodiment of the heating system 1-3 with an indirect heating coil 304, similar to the type used in traditional water tanks.

[0107] In this embodiment, the feed pipe 122 connects to a pump 224, then to the heat exchanger 120, and finally to the return pipe 260 that is arranged to return water to the bottom of the tank, similar to the lower return branch described above. In this example there are no branches in the fluid circuit from the tank to the heat exchanger and back to the tank. The flow of water is controlled by varying the performance of the pump 224.

[0108] The secondary fluid loop 112 between the external heating device 110 and heat exchanger 120 includes a branch 114 for connected to the heat exchange coil 304. The feed pipe from the external heating device 110 carrying secondary fluid passes into a three-port valve 390 which connects either to one side of the heating coil 304 and one side of the heat exchanger 120.

[0109] The heat exchange coil 304 comprises a coiled copper (or similar heat conducting material) tube mounted inside and near the top of the tank 100. The specific dimensions of the heat exchange coil 304 may be altered to suit a variety of parameters, for instance the volume of the tank 100, the tank 100 dimensions, the desired outlet water temperature etc. The heat exchange coil 304 dimensions are preferably chosen to maximise the rate of heat transfer from the secondary fluid passing through the coils to the water in contact with the coils.

[0110] The outlet of the heat exchange coil 304 connects to the return side of the secondary fluid loop between the external heating device 110 and the heat exchanger 120. This completes the secondary fluid loop, allowing the secondary fluid to be directed to the heat exchanger 120 or the heating coil 304.

[0111] The heating system 1-3 illustrated in Figure 4 permits use of a tank that already has a coil provided, for instance for retrofitting a heat pump as heating device 110 to a heating system previously using a gas boiler as heating device. Heating the upper portion of the tank with the heat exchange coil 304 may be less efficient than with the external heat exchanger and upper return branch as described with reference to Figures 1 and 2. It can enable particularly stable control, as typically a larger volume of water is heated with the heat exchange coil 304 than with the upper return branch, and the system response to control settings is slower.

[0112] In the direct heating mode, the three-port valve 390 connects the external heating device 110 to the heat exchanger 120. The pump 224 draws water from the feed pipe 122, passes it to the heat exchanger 120 where it is heated by the secondary fluid from the external heating device 110. The heated water is then pumped back into the tank via the return pipe 260.

[0113] In the indirect heating method, the three-port valve 390 connects the external heating device 110 to the indirect heating coil 304. The heated secondary fluid passes through the indirect heating coil 304, transfers its heat to the water, then returns to the return side of the secondary fluid loop. The cooled secondary fluid is then reheated by the external heating device 110.

[0114] A number of advantages afforded by the systems described above are summarised as follows:

[0115] • heat transfer between a tank and an external heat source (such as a heat-pump or gas boiler) enabled:

[0116] • high efficiency of heat transfer between the tank and the external heat source;

[0117] • ability to rapidly attain a useful temperature within the top volume of the cylinder to reduce the wait time required to the point where useable hot water is available; • bi directional energy flow between the tank and the external heat source so that the system can provide heat from the external heat source to the tank or from the tank back to the external heat source for the purposes of defrosting in the case of a heat pump, or heat from the cylinder back to the flow and return circuits for the purposes of providing space heating; and

[0118] • the ability to enable the same system to provide rapid heating from the top down via an optional direct electric immersion heating element.

[0119] Features of the variant with two pumps described above with reference to Figure 1 and the variant with the three-port valve described above with reference to Figure 2 include:

[0120] • A plate heat exchanger exchanges heat between the external heat source and the tank.

[0121] • Pump 1 draws water from the plate heat exchanger and discharges back to the bottom of the tank.

[0122] • Pump 2 draws water from the plate heat exchanger and discharges back to the top of the tank via the hot outlet, an optional diffuser is provided for on the top outlet to minimise mixing e.g. when the immersion heater is providing heat.

[0123] • Optional non-return valves are in place to ensure that bypass flows do not result when hot water is drawn from the system.

[0124] • An optional flow measurement device can determine when a hot water draw event occurs, permitting the control algorithm to shut down the upper return branch and (optionally) redirect the flow to the lower return branch during a hot water draw event. This can facilitate heating and hot water draw off without compromising outlet temperature, that is, avoiding putting cold water to the outlet of the system, which may otherwise occur e.g. during heating with the immersion heater.

[0125] • The flow measurement device may be a temperature sensor on the hot water outlet which would detect a sudden change in temperature indicating a hot water draw event.

[0126] • Pumps can be variable speed controlled to achieve a desired set-point temperature during top-up.

[0127] • Pumps 1 and 2 could run concurrently to smooth out any control instabilities during top-up mode via outboard indirect heat source.

[0128] • An optional orifice restriction included in the upper return flow branch can ensure that low enough flow rates can be delivered at low pump speeds. Figure 4 illustrates an arrangement similar to the system shown in Figure 2 with an additional feature for particularly effective interfacing with a heat pump 410 as heating device.

[0129] A temperature sensor 402 is associated with control of the heat pump 110, and the heat pump controller 430 is adapted to control operation of the heat pump based on data from the temperature sensor (e.g. increasing heat output when a measured temperature is below a setpoint). To coordinate control of the heat pump with control of the devices for heating the water tank devices (e.g. pumps 164, 174, 224, valves 290, 390) the controller 130 for the tank can mimic an output from the heat pump’s temperature sensor. In some instances this is inconvenient, e.g. if the heat pump controller requires from the temperature sensor more than a simple binary input (indicating either that a setpoint is met or that heating is required); or if the sensor data format is non-standard. In this case the approach illustrated in Figure 4 can be beneficial. Instead of merely mimicking the temperature sensor for the heat pump controller, the heat pump’s own temperature sensor 402 is integrated with the tank. The data from the temperature sensor 402 is routed to the heat pump controller via a bypass switch 404. The bypass switch 404 is controlled by the tank controller 130. The bypass switch 404 permits the tank controller 130 to select whether the data from the temperature sensor 402 is provided onward to the heat pump controller, or whether instead an alternative is provided to the tank controller (and the data from the temperature sensor suppressed). The bypass switch can include a bypass resistor 406. The bypass resistor 406 can be suitably selected to provide to the heat pump controller a desired alternative (e.g. indicating either that a setpoint is met or that heating is required). The bypass resistor 406 may for instance be a specific fixed value resistor, or and open circuit or short circuit depending on the control arrangement preferred by the heat pump controller. In some examples the bypass resistor may be variable in dependence on an input from the tank controller. Figures 6a and 6b show schematics for a bypass switch 404 in different configurations. The bypass switch 404 includes a relay controlled by the tank controller 130 for selecting whether the heat pump controller 430 is connected to the temperature sensor 402 or to the bypass resistor 406. Figure 6a shows a heating mode in which controller 130 energises the relay in the bypass switch 404 connecting the heat pump controller 430 to the temperature sensor 402. Figure 6b shows a shut off mode in which the controller 130 de-energies the relay in the bypass switch 404 connecting the heat pump controller 430 to the bypass resistor 406.

[0130] This can permit the tank controller 130 to override a control input to the heat pump controller causing the heat pump controller to adapt control of the heat pump. For instance if the temperature in the top of the tank is high the heat pump controller 430 might respond by reducing heat output at the heat pump. The tank controller 130 may however override this in order to heat the remainer of the tank, and only revert to a state causing the heat pump controller 430 to reduce heat output at the heat pump once e.g. a minimum temperature is sensed nearer the bottom of the tank by the thermocline sensor 180. As illustrated in Figure 4, the temperature sensor 402 from the heat pump is installed at the tank 100 such that it measures a temperature in an upper region of the tank, by immersion or at a surface of the tank. In an alternative the temperature sensor 402 is installed elsewhere in the tank peripherals, for instance in the path of the water between the tank and the heat exchanger 120. The temperature sensor 402 can usefully be installed downstream of the heat exchanger 120. This can permit meaningful control by the heat pump controller.

[0131] Figure 5 illustrates an arrangement similar to the system shown in Figure 4, albeit with the temperature sensor 402 integrated into the path of the water between the tank and the heat exchanger 120 at an outlet from the heat exchanger 120, rather than at the tank 100. This arrangement allows for control of the heat pump based on the temperature of the water heated by the heat exchanger rather than a tank water temperature. The sensor may for instance be integrated into the heat exchanger or into the outlet from the heat exchanger to determine the water temperature.

[0132] Figure 7 illustrates a control scheme for a top up mode, where heat is provided to the top of the tank, e.g. to rapidly heat up a smaller volume of water for immediate use. The described control scheme is designed to achieve particularly stable control.

[0133] Careful control management can be especially important in a heating system where a heating device controller controls heat output from the heating device based on a sensed temperature at the tank (or e.g. at an external heat exchanger or an external fluid loop), and the tank controller 130 controls operation of the top up heating (e.g. diverting flow to the upper return branch described with reference to Figures 1 and 2 and adopting a low pump rate to heat the water to a higher temperature). As the aim is rapid heating of a small volume of water, the control parameters can change rapidly, and it can occur that between the heating device controller and the tank controller system instabilities can be introduced. For instance if a small volume in the tank is heated to a high temperature the heating device controller may reduce the heat output as a high temperature is achieved, whereas the tank controller may require further heat to enable heating of a larger quantity of water. The tank controller can enable more stable and smoother operation of the heating system by initialising operation with a system having a slow response time before shifting operation to a system with a faster response time. Such a control scheme is discussed in more detail as follows.

[0134] Once the top-up mode is initiated a first phase of operation is provided in a ‘full circulation’ control state, as illustrated in the upper system schematic in Figure 7 (with arrows indicating flow paths). In this state, the lower return branch is active, returning flow to the bottom of the tank. The pump starts at a high flow rate before being gradually reduced as the temperature of the control loop increases through PID control. The large thermal mass provides a very stable control response. This state persists if a draw event is detected.

[0135] Next, operation is provided in a ‘top-up’ control state, as illustrated in the upper system schematic in Figure 7. Once a system loop temperature (that is, a temperature of secondary fluid following heating by the external heating device) reaches a ‘top-up target threshold’ the controller switches the flow to the upper return branch returning flow to the top of the tank. In this state, PID control is applied to the temperature of water emerging from the plate heat exchanger into the tank. If a draw event is detected then the controller immediately reverts the system back to the ‘Full Circulation’ control state.

[0136] By initiating the operation in configuration with a slow thermal response, and permitting the secondary fluid circuit to stabilise at a desired operational state, before switching to the desired configuration with a faster thermal response more stable control of the heating top- up can be enabled.

[0137] The control scheme is illustrated in Figure 7 with reference to the system variant with a three-port valve, but it can be applied to the other system variants described above.

[0138] Figure 8 shows a number of graphs illustrating the implementation of the control system described in Figure 7. The bottom graph shows a pump flow rate against time (e.g. for pump 164 or 174, or for pump 224) as set by the tank controller 130 to provide a higher or lower flow rate of water from the tank through the heat exchanger 120. The middle graph shows a flow path selection (e.g. by activation of one or another pump 164, 174 or by control of a three-way valve 290, 390) against time as set by the tank controller 130 to provide heat to one or another region of the tank. The top graph shows an observed temperature over time of water from the tank through the heat exchanger 120 at an outlet of the heat exchanger 120 (solid line); and of secondary fluid following heating by the external heating device (a heat pump in the illustrated schematic). The graphs illustrate an example of operation of the heating system from an initial state where the water drawn from the tank is in a ‘cold’ state, and the secondary fluid discharged from the heating device is also in a ‘cold’ state, and an immediate demand for hot water is to be satisfied. As described above, the operation is initiated in configuration with a relatively high pump flow rate, and the flow of water from the tank is returned to the bottom of the tank. A relatively slow thermal response is observed, as the secondary fluid discharged from the heating device gradually warms up and the water drawn from the tank becomes gradually warmer downstream of the heat exchanger. The pump flow rate is gradually decreased as the secondary fluid discharged from the heating device becomes warmer and the water downstream of the heat exchanger increases in temperature. Once the water downstream of the heat exchanger reaches a suitable temperature for providing hot water to a user, the controller causes the flow of water from the tank to be returned to the top of the tank (or in the example illustrated in Figure 3 the controller causes the secondary fluid to be directed to the heat exchange coil in the upper part of the tank). The tank controller adjusts the pump flow rate to maintain a suitable temperature for providing hot water to a user at the water downstream of the heat exchanger, and the heat pump controller adjusts the output of heat to maintain a temperature of the secondary fluid following heating by the heat pump. In the system state after the initiation the thermal time constants are relatively small but as only smaller temperature changes occur over time the system can be controlled and remain stable. In the top graph a horizontal arrow indicates a thermal time constant of a system including both a system loop (that is, the circuit of secondary fluid of the heat pump) and the body of water in the tank, including the heat exchanger and the water in the external flow path. Another horizontal arrow indicates a time delay in the thermal response of the water discharged from the heat exchanger compared to the secondary fluid entering the heat exchanger; this time delay is due to the thermal mass of the heat exchanger. Another horizontal arrow indicates a thermal time constant of the system loop (that is, the circuit of secondary fluid of the heat pump) and the heat exchanger (only), under system setting such that (cold) water is drawn from the bottom of the tank, pumped through the heat exchanger at a relatively low pump rate so as to heat the water to a relatively high temperature, and routed to the top of the tank to provide immediately available relatively hot water for a user demand.

[0139] Figure 9a shows a valve 500 for use in a heating system 1-5 in a first position. The valve 500 comprises a body for installation in a fluid flow of a heating system 1-5. From the inlet to the outlet of the valve 500 there is a shuttle seat, a shuttle 502, a spring 504, a spring seat 506, and an orifice restriction place 510.

[0140] The shuttle 502 is a disc located in the body of the valve 500 and is able to move longitudinally along the axis of the valve 500. The external diameter of the shuttle 502 may be chosen to be slightly smaller than the inner diameter of the valve 500 body, allowing the shuttle 502 to slide along the longitudinal axis of the valve 500 without becoming stuck.

[0141] A shuttle orifice 508 in the centre of the shuttle 502 permits fluid flow through the valve 500. The shuttle orifice 508 may be a simple hole in the centre of the shuttle 502 or may feature additional features (such as a bevel or sharp edge) to control the intake or discharge coefficients to the orifice to optimise fluid flow.

[0142] The shuttle 502 is held in place in the valve 500 by the spring 504, the opposite end of which is attached to a spring seat 506. The spring 504 is a coiled spring and configured to be compressed in normal use.

[0143] The spring seat 506 is a body mounted inside the valve 500 which permits fluid flow through spring seat 506 whilst supporting the spring 504 and the shuttle 502. This may be achieved by one or a number of holes through the spring seat 506 body.

[0144] An orifice restriction 510 may be included in the valve 500 which comprises a body with a smaller orifice than the valve 500 diameter, restricting the flow of fluid through the valve 500. The orifice restriction 510 may have additional features to control to intake and discharge coefficient to regulate the flow restriction in the valve 500.

[0145] The fluid enters the valve 500 from the direction of shuttle 502 towards the spring 504, spring seat 506, and orifice restriction 510. Due to the shuttle orifice 508 the fluid is able to pass through the shuttle 502 but incurs a pressure drop in doing so, causing a resultant force to act on the shuttle 502 towards the spring 504.

[0146] In the state shown in figure 9a, the force of the fluid flow against the shuttle 502 is less than the force of the spring 504. The spring 504 therefore pushes the shuttle 502 against a stop, causing all fluid to flow through the shuttle orifice 508.

[0147] Figure 9b shows the valve 500 in a second state in which the fluid flowrate has increased through the valve 500. As the flowrate of fluid increases, so too does the dynamic pressure of the fluid acting against the shuttle 502. Once the fluid pressure force exceeds the spring 504 force, the shuttle 502 begins to move against the spring 504. As the spring 504 is compressed, it exerts a greater force back on the shuttle 502 (due to its spring constant). The movement of the shuttle 502 also opens a bypass around the shuttle 502 (shown in the figure as arrows moving towards the edges of the shuttle 502) meaning not all the fluid flow through the valve 500 now passes through the valve orifice 502. This reduces the pressure force acting against the shuttle 502. The shuttle 502 therefore comes to rest at a position above its stop, towards the spring 504 and spring seat 506.

[0148] The valve 500 parameters may be adjusted as necessary to cause the shuttle 502 to open the bypass flow at a predetermined flow rate (for instance by altering the stiffness of the spring, the size of the shuttle orifice 508 or the distance between the spring seat 506 and shuttle 502).

[0149] Figure 10 shows the heating system 1-5 with the valve 500 installed in the upper return branch 171.

[0150] When thermal energy is being input to the heating system 1-5 using a low powered device (such as a small heat pump operating at around 5kW or less) the first 164 and second 174 pumps are likely to be operated at a low speed in a top-up mode to permit greater heat transfer from the external heating device 110. The valve 500 therefore remains in the state shown in figure 9a as the flowrate of fluid through the valve 500 is too low to overcome the pressure of the spring 504 against the shuttle 502, meaning the shuttle 502 remains pressed against its seat. This means all fluid flow from the heat exchanger 120 must pass through the shuttle orifice 508.

[0151] In some examples the minimum operating speed of the pumps 164, 174 is too great for optimal heat top up of the heating system 1-5. In this case the small shuttle orifice 508 allows for a greater range of flow control at low fluid flowrates as a greater pressure is required from the pumps to achieve the same flowrate, moving the pumps into a better operating envelope.

[0152] When a large external heat input is being provided (such as a gas boiler operating at around 30kW), the small shuttle orifice 508 would excessively restrict the flow of fluid through the valve 500 and by extension the heat exchanger 120. When the flow exceeds a predetermined value, the valve 500 moves to the state shown in figure 9b, opening the bypass flow around the shuttle 502. This reduces the flow restriction in the valve 500, allowing for a greater flowrate through the valve 500.

[0153] The valve 500 therefore allows for a greater dynamic range of precise flow rate control when operating the heating system 1-5 with a wide range of external heat devices 110. Whilst the valve 500 has been shown in use with heating system 1-5, it will be appreciated that the valve 500 could be used with any of the heating systems 1-1 1-2 1-3 1-4 described herein.

[0154] Various other modifications will be apparent to those skilled in the art. For example, while the detailed description has considered a vessel such as a hot water tank, the disclosures herein could similarly be used with other fluids that are heated.

[0155] Where the top of the tank is referred to herein (e.g. for drawing hot water from, for providing heated water to, or for locating a heat exchange coil), it should be appreciated that this may include near the top of the tank, an upper portion of the tank, a top portion of the tank, a top half, third or quarter of the tank (by volume or by height), with the tank in such orientation as it is intended to be installed for use. Where the bottom of the tank is described (e.g. for letting in cold water, for pumping water to be heated from), it should be appreciated that this may include near the bottom of the tank, in a lower portion of the tank, or in a bottom half, third or quarter of the tank (by volume or by height), with the tank in such orientation as it is intended to be installed for use.

[0156] Many of the illustrations show examples of tanks in the form of water cylinders. A water cylinder is a tank in the form of a cylinder with domed ends. This form is favourable for stress distribution and particularly well suited for a tank for containing pressurised water. Water cylinders are typically unvented tanks for containing mains pressurised water. The tank may however be in another form.

[0157] Generally the tank may be for storing pressurized water or for storing water at ambient pressure, optionally potable water or mains pressurized water or water for supply to a user or water for supply in response to a user hot water demand. A pressurised tank can distribute hot water throughout a building without needing any pumps. The tank may be an unvented tank for containing mains pressurised water. The tank may be a vented tank for containing water at ambient pressure. The water contained in the tank may include additives.

[0158] Typically a target temperature for providing hot water from the tank is in the range 40-90 degrees Celsius, e.g. 75 degrees Celsius. A target temperature may be in a range of 50- 70 degrees Celsius, e.g. 55 degrees Celsius or around 60 degrees Celsius. A suitable target temperature for hot water in the tank may be selected depending on user preference, intended use for the hot water (e.g. for space heating or for dispensing to user), tank configuration and other factors. Typically cold water is provided to the tank at a temperature in the range of 10-20 degrees Celsius, depending on the water source and e.g. season and other factors, and may in some scenarios be higher or lower. A heat source such as a heat pump can provide heat transfer fluid at a temperature e.g. in a range of 50-90 degrees Celsius, e.g. 80 degrees Celsius or 65 degrees Celsius.

[0159] While good results have been achieved with a tank capable of providing heat to or drawing heat from an upper or lower portion of the tank, more than two heat transfer zones may be accommodated. For example, if three heat exchange coils are included in the upper, central and lower portion of the tank those portions may be selectively heated or heat drawn (similarly if three draw branches and three return branches are included with the external heat exchanger arrangement). This may be appropriate for particularly large tanks, for example. The tank may include further heat exchangers, inside or outside the tank, for drawing or providing heat at different locations in the tank.

[0160] Many of the illustrations show examples of heat transfer coils arranged inside the tank. Coils may alternatively be arranged outside the tank at the tank wall. Some of the examples show a plate heat exchanger arranged outside the tank. A plate heat exchanger may alternatively be arranged inside the tank, e.g. with a submersible pump to drive flow, or with a conduit section outside the tank to accommodate a pump outside the tank.

[0161] Where the terms ‘above’ and ‘below’, ‘upper’ and ‘lower’ are used herein, these are meant with the tank in such orientation as it is intended to be installed for use.

[0162] It will be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope of the invention.

[0163] Reference numerals appearing in the claims are by way of illustration only and shall have no limiting effect on the scope of the claims.

Claims

Claims1 . A system for heating water including: a tank for holding hot water; an external heating device to provide heat to water of the tank with a circuit of heat transfer fluid to transfer heat to or from the external heating device; a heat exchange coil in the circuit of heat transfer fluid, the heat exchange coil arranged to provide heat to water in the tank; a plate heat exchanger arranged external to the tank for transferring heat from the circuit of heat transfer fluid to water of the tank; a flow path from the tank to the heat exchanger and back to the tank and a pump arranged to pump water in the flow path; a flow selector for routing the circuit of heat transfer fluid to or from the heat exchange coil or the plate heat exchanger; and a controller for controlling the flow selector in dependence on a demand for immediate hot water from the tank.

2. The system of claim 1 , wherein the flow selector is a three-port valve.

3. The system of any preceding claim, further comprising: a tank outlet conduit for discharging hot water from the tank in response to a user hot water demand; the controller being further adapted to control flow in the flow path; wherein the flow path from the tank to the heat exchanger and back to the tank includes at least a portion of the tank outlet conduit or wherein the flow path and the tank outlet conduit share a common tank opening.

4. A system for heating water including: a tank for holding hot water and a tank outlet conduit for discharging hot water from the tank in response to a user hot water demand; an external heating device to provide heat to water of the tank; a heat exchanger arranged external to the tank for transferring heat from the external heating device to water of the tank; a flow path from the tank to the heat exchanger and back to a top of the tank and a pump arranged to pump water in the flow path; anda controller for controlling flow in the flow path; wherein the flow path includes at least a portion of the tank outlet conduit or wherein the flow path and the tank outlet conduit share a common tank opening.

5. The system of any preceding claim, further comprising a diffuser arranged at an outlet of the flow path into the tank, the diffuser configured to reduce mixing of water within the tank.

6. The system of any preceding claim, further comprising a means of sensing or inferring a temperature distribution in the tank, preferably an array of temperature sensors arranged to sense temperatures at different heights of the tank.

7. The system of any preceding claim, further comprising a flow sensing device configured to determine whether the tank outlet conduit is discharging water from the tank in response to a user hot water demand; and the controller is configured to prevent flow in the flow path to a top of the tank when the tank outlet conduit is discharging water from the tank in response to a user hot water demand.

8. The system of claim 7, wherein the flow sensing device is a flow sensor at the cold- water feed to the tank.

9. The system of claim 7, wherein the flow sensing device is a flow meter or a temperature senor at the tank outlet conduit, preferably at a portion not shared with the flow path.

10. The system of any preceding claim, wherein the flow path is from a bottom of the tank; optionally further comprising a baffle for baffling flow between the bottom of the tank and the rest of the tank.11 . The system of any preceding claim, wherein the flow path comprises an upper return branch from the heat exchanger to the top of the tank and a lower return branch from the heat exchanger to a bottom of the tank.

12. The system of claim 11 , further comprising a three-port valve controllable by the controller and configured to route water from the heat exchanger either to the upper returnbranch or to the lower return branch.

13. The system of claim 11 , further comprising a first pump in the lower return branch and a second pump in the upper return branch, the first and second pumps controllable by the controller to route water from the heat exchanger either to the upper return branch or to the lower return branch.

14. The system of any of claims 11 to 13, further comprising a flow orifice restriction in the upper return branch.

15. The system of any of claims 11 to 14, wherein the controller is configured to precede flow to the upper return branch with a period of flow to the lower return branch.

16. The system of claim 15, wherein the controller is configured to initiate flow to the lower return branch at a first flow rate and to decrease flow to a second, lower flow rate before transitioning flow to the upper return branch.

17. The system of any preceding claim, further comprising at least one valve arranged to prevent water flowing in the flow path or in a portion of the flow path while the tank outlet conduit is discharging hot water from the tank in response to a user hot water demand.

18. The system of any preceding claim, wherein the pump is a variable speed pump controllable by the controller.

19. The system of any preceding claim, further comprising an electric immersion heater.

20. A controller for a system for heating water according to any preceding claim, wherein the controller is adapted to: receive an indication of whether the tank outlet conduit is discharging water from the tank in response to a user hot water demand; and prevent flow in the flow path to a top of the tank when the tank outlet conduit is discharging hot water from the tank in response to a user hot water demand; and / or receive an indication of a demand for immediate hot water from the tank; and control the flow selector to route the circuit of heat transfer fluid to the heat exchange coil.

21. A controller according to claim 20, adapted to receive from a flow sensing device the indication of whether the tank outlet conduit is discharging water from the tank in response to a user hot water demand, optionally wherein the flow sensing device is a flow sensor at the cold-water feed to the tank or a flow meter at the tank outlet conduit or a temperature senor at the tank outlet conduit.

22. A controller according to claim 20 or 21 , wherein the flow path comprises an upper return branch from the heat exchanger to the top of the tank and a lower return branch from the heat exchanger to a bottom of the tank, and the controller is adapted to route water from the heat exchanger to the lower return branch when the tank outlet conduit is discharging water from the tank in response to a user hot water demand.

23. A system for heating water including: a hot water tank and a heat pump; a hot water tank controller and a heat pump controller; a temperature sensor for providing a control input to the heat pump controller; and a bypass switch configured to: receive, from the hot water tank controller, bypass activation signal; in first configuration provide a connection connecting the temperature sensor to the heat pump controller; in second configuration disconnect the temperature sensor from the heat pump controller; and select the first or second configuration in dependence on the bypass activation signal.

24. A system according to claim 23, wherein the bypass switch comprises a bypass resistor that in the second configuration is connected to the heat pump controller, optionally wherein the bypass resistor is a fixed value resistor, further optionally wherein in the second configuration an open circuit or a short circuit is formed; or wherein the bypass resistor is a variable resistor, preferably variable in dependence on an input from the hot water tank controller.

25. A system according to claim 22 or 23, wherein the temperature sensor is installed:i) at the tank such that it measures a temperature in an upper region of the tank; ii) at a flow path external to the tank for water of the tank; iii) at a heat exchanger external to the tank for receiving heat from the heat pump; or iv) at a flow path external to the tank for water of the tank and downstream of a heat exchanger in the flow path for receiving heat from the heat pump.

26. A system for heating water including: a hot water tank and a heat pump; a flow selector for routing heat from the heat pump to an upper portion of the hot water tank or to a lower portion of the hot water tank; and a hot water tank controller configured to control heating water of the hot water tank and a heat pump controller configured to control heat output of the heat pump; wherein the hot water tank controller is configured to: receive a signal indicating a demand for immediate hot water, and in response to the signal control the flow selector to route heat from the heat pump to the lower portion of the hot water tank for an initial period of time before routing heat from the heat pump to the upper portion of the hot water tank for satisfying the demand for immediate hot water.

27. A valve for use with a heating system, comprising: a body through which fluid is allowed to flow; and a moveable restriction to the fluid flow; wherein in a first position the restriction provides a predetermined restriction to the fluid flow; and upon increasing the fluid flow rate through the valve beyond a predetermined value, the restriction moves to a second position in which the restriction provides a smaller restriction to the fluid flow than the first position.

28. A valve according to claim 27, wherein the restriction comprises an orifice plate held in place by a spring.

29. A valve according to claim 28, further comprising a spring seat configured to retain the spring whilst allowing fluid to flow through the valve.

30. A valve according to any of claims 27 to 29, further comprising an additional flow restriction in the body of the valve.

31. A system according to any of claims 1 to 19 or 23 to 26, further comprising a valve according to any of claims 27 to 30.

32. A system for heating water including: a tank for holding hot water; a heat exchanger arranged external to the tank for transferring heat from an external heating device to water of the tank; a flow path from the tank to the heat exchanger and back to a top of the tank; a pump arranged to pump water in the flow path; and a valve according to any of claims 27 to 30 arranged in the flow path.

33. A system according to claim 32, wherein the flow path comprises an upper return branch for returning water back to the top of the tank and a lower return branch for returning water back to a bottom of the tank, wherein the valve is arranged in the upper return branch.

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