Water heating system and device

Abstract

A heating system is provided. The heating system includes: a heat pump; a circuit of heat transfer fluid to transfer heat to or from the heat pump; a water 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. 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.

Description

[0001] Water Heating System and Device

[0002] The present invention relates to a system for heating water, in connection with a heat pump as heat source. 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] Heat pumps including both ground source heat pumps and air source heat pumps are becoming an increasingly popular option for space heating. Heat pump systems can include a buffer vessel that can serve as a heat reservoir. A buffer vessel can store heat and release it when opportune, for instance for a defrosting cycle of the heat pump, or to reduce on / off cycling of a heat pump as a dwelling is heated around its particular control set point temperature and hysteresis margin. Disadvantages of accommodating a buffer vessel include the requirement for additional space that may not be conveniently available, and also the addition of complexity in installing a heat pump system.

[0004] The present disclosure aims to alleviate some or all of the aforementioned problems.

[0005] According to a first aspect there is provided a heating system including: a heat pump; a circuit of heat transfer fluid to transfer heat to or from the heat pump; a water 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, preferably in dependence on a temperature distribution in the water tank. By enabling provision of heat to or drawing of heat from different portions of the tank performance of the tank as a heat buffer can be optimised.

[0006] The controller may be configured to control the selector arrangement in dependence on at least a temperature in the upper portion of the water tank and a temperature in the lower portion of the water tank. The controller may be configured to determine whether to transfer heat to the upper portion of the water tank or to the lower portion of the water tank or to both in dependence on at least a temperature in the upper portion of the water tank and a temperature in the lower portion of the water tank. The controller may be configured to determine whether to transfer heat from the upper portion of the water tank or from the lower portion of the water tank or from both in dependence on at least a temperature in the upper portion of the water tank and a temperature in the lower portion of the water tank. The controller may be configured to control the selector arrangement to cause heat transfer from the lower portion of the water tank if a temperature in the lower portion of the water tank is above a temperature threshold; and to transfer heat from the upper portion of the water tank if a temperature in the lower portion of the water tank is below a temperature threshold and a temperature in the upper portion of the water tank is above the temperature threshold. The controller may be configured to control the selector arrangement to cause heat transfer to the upper portion of the water tank if a temperature in the upper portion of the water tank is below a temperature threshold; and to transfer heat to the lower portion of the water tank if a temperature in the upper portion of the water tank is above a temperature threshold and a temperature in the lower portion of the water tank is below a (different or same) temperature threshold.

[0007] The heating system may include a means of sensing a tank status, the tank status being indicative of a quantity of thermal energy stored in the tank and / or a temperature distribution in the tank. The tank status is preferably indicative of a distribution of thermal energy stored in the tank. The heating 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. This can enable particularly efficient and favourable resolution of temperature distribution in the water tank.

[0008] The controller may be configured to determine a quantity of heat above a temperature threshold in the lower portion of the water tank and / or the upper portion of the water tank, preferably in dependence on a temperature distribution in the water tank. This can enable particularly effective optimisation of performance and heat buffering. The controller is preferably configured to cause the selector arrangement to direct heat to or draw heat from the upper heat transfer means or the lower heat transfer means in dependence on the quantity of heat above a temperature threshold in the lower portion of the water tank and / or the upper portion of the water tank. This can enable diversion of heat to or from a portion of the tank that is particularly effective for an intended use. The temperature threshold may be: a minimum temperature for user hot water supply; a minimum temperature for water sterilisation; a minimum temperature for space heating; or a minimum temperature for heat pump defrosting. The controller may be configured to determine that a temperature of the upper portion of the tank is below a threshold; and cause the selector arrangement to direct heat to the upper heat transfer means. The controller may be configured to determine that a temperature of the upper portion of the tank is above a first threshold; determine that a temperature of the lower portion of the tank is below a second threshold; determine that the heat pump is in the on state; and cause the selector arrangement to direct heat to the lower heat transfer means. The controller may be configured to determine that the heat pump requires a defrost cycle; determine that a quantity of heat above a temperature threshold in the lower portion of the water tank is above a threshold; and cause the selector arrangement to draw heat from the lower heat transfer means. The controller may be configured to determine that a request for sterilization of the water tank has been received; and cause the selector arrangement to direct heat to the lower heat transfer means.

[0009] The upper and lower portions of the water tank may be defined by location of upper and lower heat transfer means (preferably being a portion of the water tank affected by the upper or lower heat transfer means respectively), or they may be defined by a baffle arranged between the upper and lower heat transfer means.

[0010] 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 coil configured to transfer heat between the heat transfer fluid and 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 coil or to both.

[0011] The upper heat transfer coil preferably has a flow path from top to bottom, such that the heat transfer fluid enters the upper heat transfer coil at a top of the upper heat transfer coil, and exits the upper heat transfer coil at a bottom of the upper heat transfer coil. This can enable particularly effective heat transfer. The lower heat transfer coil preferably has a flow path from bottom to top, such that the heat transfer fluid enters the lower heat transfer coil at a bottom of the upper heat transfer coil, and exits the lower heat transfer coil at a top of the upper heat transfer coil. This can enable particularly effective heat transfer.

[0012] The heating system may further comprise a heat exchanger and the circuit of heat transfer fluid may be arranged to transfer heat between the heat pump and the heat exchanger. The heating 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 return valve arrangement 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. The circuit of water may further comprise a pump. The circuit of water from the tank to the heat exchanger and back to the tank may further comprise an upper draw branch arranged to draw water from an upper portion of the water tank. The upper draw branch is preferably arranged to draw water from a top of the tank. The upper draw branch may include a part of a hot water outlet from the tank. The circuit of water from the tank to the heat exchanger and back to the tank may further comprise a lower draw branch arranged to draw water from a lower portion of the water tank. The circuit of water from the tank to the heat exchanger and back to the tank may further comprise a draw control means configured to control flow from the upper draw branch and the lower draw branch. The controller may be further configured to control the draw control means for heat transfer from the upper portion of the water tank or the lower portion of the water tank or both. The draw control means may be a controllable first pump in the upper draw branch and a controllable second pump in the lower draw branch. The draw control means may be a draw valve arrangement configured to direct flow via the upper draw branch or the lower draw branch.

[0013] The controller may be configured to determine that a heat pump requires a defrost cycle; determining that a quantity of heat above a temperature threshold in the lower portion of the water tank is above a threshold; and cause the draw control means to allow flow from the lower draw branch. The controller may be configured to determine a temperature of the upper portion of the tank is below a threshold; and cause the draw control means to allow flow from the upper draw branch. The controller may be configured to determine that a temperature of the upper portion of the water tank is below a first threshold; and cause the draw control means to allow flow from the upper draw branch and the selector arrangement to allow flow to the upper return branch. The controller may be configured to determine that a temperature of the upper portion of the water tank is above the first threshold and a demand for hot water is received; and cause the draw control means to allow flow from the lower draw branch, and the selector arrangement to allow flow to the upper return branch. The controller may be configured to determine that a temperature of the upper portion of the water tank is above a second threshold; a temperature of the lower portion of the water tank is below a third threshold; no demand for hot water is received; and the heat pump state is on; and cause the draw control means to allow flow from the lower draw branch only, and the selector arrangement to allow flow to the lower return branch. The controller may be configured to determine that a quantity of heat above a temperature threshold in the lower portion of the water tank is above a fourth threshold and a defrost condition of the heat pump is received; and cause the draw control means to allow flow from the lower draw branch. The controller may be configured to determine that a temperature of the lower portion of the water tank is below a fifth threshold and a sterilization condition is received; and cause the selector arrangement to allow flow to the lower return branch only.

[0014] The heating system may further comprise a space heating system.

[0015] The water tank may further comprise a destratification pump. The destratification pump is preferably arranged to transfer water between the upper portion of the water tank and the lower portion of the water tank. The controller may be configured to activate the destratification pump in dependence on a temperature distribution in the water tank. This can enable particularly efficient management of the heat distribution in the tank for more effective heat transfer and heat buffering.

[0016] The water tank may comprise at least one baffle. Preferably at least one baffle is positioned between the lower and the upper portions of the water tank. Optionally at least one baffle is positioned within the lower portion of the water tank. The at least one baffle is preferably positioned above a further water inlet. This can assist thermal stratification in the tank. The at least one baffle may divide the water tank into an upper portion and a lower portion. The baffle can assist the upper portion of the heat tank and the lower portion of the heat tank being held at different temperatures, in particular enabling accumulation of more heat in the lower portion of the tank than would be the case in the absence of the baffle.

[0017] The lower portion may be at least 30 litres and / or less than 100 litres. The lower portion may be half of the water tank’s volume or less and / or a fifth of the water tank’s volume or more.

[0018] The water tank may comprise at least one electric heating element. The water tank may comprise at least two electric heating elements. An upper electric heating element may be positioned in the upper portion of the tank, and a lower electric heating element is positioned in the lower portion of the tank. The controller may be configured to activate at least one electric heating element in dependence on a temperature distribution in the water tank. This can enable boosting of a temperature in a portion of the tank beyond what might be available from the heat pump. It can also enable particularly rapid heating of a portion of the tank.

[0019] The water tank may be for storing hot water at ambient pressure or for storing pressurized hot water, optionally potable water or mains pressurized water or water for supply to a user.

[0020] According to another aspect there is provided a method for controlling a heating system comprising selection of heat transfer to or from an upper portion of a water tank or a lower portion of the water tank or both, preferably in dependence on a temperature distribution in the water tank. By enabling provision or drawing of heat from different portions of the tank performance of the tank as a heat buffer can be optimised. The method may comprise determining a quantity of heat above a temperature threshold in the lower portion of the water tank and / or the upper portion of the water tank, preferably in dependence on a temperature distribution in the water tank. This can enable particularly effective optimisation of performance and heat buffering. The selection of heat transfer to or from an upper portion of a water tank or a lower portion of the water tank or both may be in dependence on the quantity of heat above a temperature threshold in the lower portion of the water tank and / or the upper portion of the water tank. The heating system may be as aforementioned. The method may include aforementioned actions performed by a controller.

[0021] According to another aspect there is provided a controller for use in a heating system, optionally as aforementioned. The controller is preferably configured to control heat transfer to an upper portion of a water tank or a lower portion of the water tank or both.

[0022] The controller may be configured to receive as input data from at least one temperature sensor, preferably an array of temperature sensors, and to determine a temperature distribution in the water tank and / or a quantity of heat above a temperature threshold in the lower and / or upper portion of the water tank. The controller may be configured to receive as input information from a plurality of temperature sensors fixed to the water tank.

[0023] The controller may be configured to output control signals for a configuration for drawing heat from the water tank and supplying the heat to a heat pump in response to an input indicating a demand to defrost the heat pump. Heat may be supplied to water from the lower portion and / or water from the upper portion of the water tank by heating the water in a heating circuit external to the water tank. Heat may be supplied to water from the lower portion and / or water from the upper portion of the water tank by heating the water within the water tank.

[0024] The controller may be configured to receive as input a power status of the heat pump.

[0025] According to another aspect there is provided a water tank comprising a baffle arranged to divide the water tank into an upper portion and a lower portion. This can enable the upper portion of the heat tank and the lower portion of the heat tank to be held at different temperatures. The lower portion may be at least 30 litres. The lower portion may be less than 100 litres. The lower portion may be half of the water tank’s volume or less. The lower portion may be a fifth of the water tank’s volume or more. The water tank may be for a heating system as aforementioned. The lower portion of the water tank may be for defrosting a heat pump.

[0026] According to another aspect there is provided a heating system including: a water tank for storing hot water; a space heating system comprising a circuit of heat transfer fluid and a heat exchange means for receiving heat from the water tank; and a controller configured to control the transfer of heat from the water tank to the heat exchange means for dynamic adjustment of a target temperature of heat transfer fluid in the space heating system. This can enable particularly high efficiency of the heating system while accommodating user convenience. The controller may be configured to temporarily increase a target temperature of heat transfer fluid in the space heating system to boost user perception of space heating. The increased target temperature may be in a range of 70-90 degrees Celsius, e.g. 75 degrees Celsius. The controller may be configured to reduce a target temperature of heat transfer fluid in the space heating system following a temporary boost request. The reduced target temperature may be in a range of 40-60 degrees Celsius, e.g. 55 degrees Celsius. The heating system may further be as aforementioned.

[0027] According to another aspect there is provided a user interface for a controller as aforementioned comprising a means for user input of a request for a temporary boost to space heating. The user interface may comprise a means for presenting to a user a suggestion for a temporary boost to space heating, optionally wherein the suggestion is dependent on weather data and / or on user location data.

[0028] According to another aspect there is provided a heating system including: a heat source; a circuit of heat transfer fluid to transfer heat to or from the heat source; a tank for storing hot liquid; an upper heat transfer means configured to transfer heat from the heat source to an upper portion of the tank; a lower heat transfer means configured to transfer heat from the heat source to a lower portion of the tank; a selector arrangement configured to route heat from or to the heat source 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 tank or the lower portion of the tank or both, preferably in dependence on a temperature distribution in the tank. By enabling provision or drawing of heat from different portions of the tank performance of the tank as a heat buffer can be optimised and adapted for specific uses.

[0029] The heating system may include one or more of:

[0030] • a heat pump as heat source;

[0031] • a space heating system;

[0032] The tank may include one or more of:

[0033] • two or more heat transfer coils arranged in or at the tank as upper and lower heat transfer means;

[0034] • a heat exchanger to receive heat from the heat source (preferably a plate heat exchanger) and a circuit of liquid from the tank to the heat exchanger and back to the tank to transfer heat between the tank and the heat exchanger, with an upper and lower return branch in the circuit of liquid and / or an upper and lower draw branch in the circuit of liquid as upper and lower heat transfer means;

[0035] • one or more baffles, preferably arranged to divide the water tank into an upper portion and a lower portion;

[0036] • a destratification pump arranged to transfer water between the upper portion of the tank and the lower portion of the tank;

[0037] • a thermostatic mixing valve at an outlet of the tank;

[0038] • one or more electrical heating elements arranged in the tank; and

[0039] • a temperature sensor, preferably an array of temperature sensors arranged to sense temperatures at different heights of the tank.

[0040] The tank may be for storing pressurised potable water or for unpressurised thermal store liquid.

[0041] Features of the heating system may be as aforementioned.

[0042] According to another aspect there is provided a controller for a heating system as aforementioned. According to another aspect there is provided a heating system including: a water tank for storing hot water; a conduit providing a flow path from an upper portion of the water tank to a lower portion of the water tank; a destratification pump arranged to pump fluid from an upper portion of the water tank to a lower portion of the water tank; and a controller configured to control the destratification pump in dependence on a temperature distribution in the water tank. By enabling flow of fluid from different portions of the tank performance of the tank as a heat buffer can be optimised, and in particular provision of heat at lower temperatures.

[0043] The heating system may further comprise a means of sensing or inferring a temperature distribution in the water tank. The means of sensing or inferring a temperature distribution in the water tank may comprise one or more temperature sensors. The means of sensing or inferring a temperature distribution in the water tank may comprise an array of temperature sensors.

[0044] The water tank may be arranged to receive heat from and / or provide heat to a heat pump. The controller may be configured to receive information from the heat pump and to activate the destratification pump in dependence on the information from the heat pump. The controller may be configured to activate the destratification pump in response to a defrost request from the heat pump. The controller may be configured to activate the destratification pump when the temperature distribution in the water tank indicates a sufficient stored heat to allow defrosting of the heat pump.

[0045] The heating system may further comprise a heat exchanger configured to transfer heat between a heat pump and the water tank. The heat exchanger may comprise a heat transfer coil configured to transfer heat between a heat transfer fluid and water in the water tank. The heat exchanger may be internal to the water tank. The heat exchanger may be external to the water tank. The heating system may further comprise a circuit of water from the water tank to the heat exchanger and back to the water tank to transfer heat between the water tank and the heat exchanger. The circuit of water from the tank to the heat exchanger and back to the water tank may comprise a heat exchange pump arranged to draw water from a lower portion of the water tank to an upper portion of the water tank. The destratification pump may be arranged in a branch bypassing the heat exchange pump. One or more non-return valves may be arranged to prevent flow from the destratification pump to the heat exchange pump and / or from the heat exchange pump to the destratification pump. The destratification pump may be arranged to pump fluid from an upper portion of the water tank to a lower portion of the water tank via the heat exchanger. The controller may be configured to activate the destratification pump when the temperature distribution in the water tank indicates that a quantity of energy stored in the water tank exceeds a threshold. An average temperature of water in the water tank may exceed 60 degrees Celsius. The controller may further be configured to activate the destratification pump in dependence on a signal from a thermostat.

[0046] The water tank may be for holding water at atmospheric pressure or for holding pressurized water. The water tank may be for holding potable water.

[0047] The water tank may comprise at least one baffle. The baffle may be arranged in a lower portion of the water tank. The baffle may be as aforementioned. A portion of the water tank below the baffle may comprise less than half the tank volume and / or less than 100 litres. A portion of the water tank below the baffle may comprise at least 30 litres. A portion of the water tank below the baffle may comprise a fifth of the tank volume or more.

[0048] The water tank may comprise at least one electric heating element.

[0049] The heating system may further comprise a heat pump.

[0050] The heating system may comprise an upper heat transfer means configured to transfer heat from a 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; and 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. The controller may be further 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. The heating system may be as aforementioned.

[0051] According to another aspect there is provided a method of operating a heating system, the method comprising: determining a temperature distribution in a water tank for storing hot water; and controlling a destratification pump arranged to pump fluid from an upper portion of the water tank to a lower portion of the water tank in dependence on a temperature distribution in the water tank. The heating system may be as aforementioned.

[0052] According to another aspect there is provided a heating system including one or more of: a heat pump; • a circuit of heat transfer fluid to transfer heat to or from the heat pump;

[0053] • a water tank for storing hot water;

[0054] • one or more heat transfer means configured to transfer heat from the heat pump to the water tank;

[0055] • a controller;

[0056] • a means of determining a temperature distribution in the water tank;

[0057] • a destratification pump.

[0058] The features of the heating system may be as aforementioned.

[0059] 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.

[0060] 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.

[0061] Any apparatus feature as described herein may also be provided as a method feature, and vice versa.

[0062] Any feature in one aspect of the invention may be applied to other aspects of the invention, in any appropriate combination. In particular, method aspects may be applied to apparatus aspects, and vice versa. 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.

[0063] 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. As used herein, means plus function features may be expressed alternatively in terms of their corresponding structure, such as a suitably programmed processor and associated memory.

[0064] As used herein, the terms ‘heat’ and ‘thermal energy’ are interchangeable.

[0065] 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:

[0066] Brief Description of the Drawings

[0067] Figure 1 A is a schematic of a first example of a heating system;

[0068] Figure 1 B is a schematic of a variant of the heating system of Figure 1A;

[0069] Figure 2 is a schematic of a second example of a heating system;

[0070] Figure 3 is a schematic of a third example of a heating system in a first configuration;

[0071] Figure 4 is a schematic of a third example of a heating system in a second configuration;

[0072] Figure 5 is a schematic of a third example of a heating system in a third configuration;

[0073] Figure 6 is a schematic of a third example of a heating system in a fourth configuration;

[0074] Figure 7A is a graph showing the temperature of water in a water tank at different heights within the tank during a first mode of operation of an example of a heating system;

[0075] Figure 7B is another graph showing the temperature of water in a water tank at different heights within the tank;

[0076] Figure 8 is a graph showing the temperature of water in a water tank at different heights within the tank during a second mode of operation of an example of a heating system;

[0077] Figure 9 is a graph showing another example of the temperature of water in a water tank at different heights within the tank;

[0078] Figure 10 is a graph showing another example of the temperature of water in a water tank at different heights within the tank;

[0079] Figure 11A is a graph showing another example of the temperature of water in a water tank at different heights within the tank; Figure 11 B is a graph showing another example of the temperature of water in a water tank at different heights within the tank; and

[0080] Figure 12 is a schematic of a water tank and a graph showing another example of the temperature of water in a water tank at different heights within the tank;

[0081] Figure 13 a schematic of a fourth example of a heating system;

[0082] Figure 14A is a schematic of a water tank and a graph showing an example of the temperature of water in a water tank at a first time; and

[0083] Figure 14B is a graph showing the temperature of water in a water tank at a second time.

[0084] Detailed Description

[0085] Figure 1A shows a schematic of a first example of a heating system. The heating system comprises a heat pump 110, a circuit of heat transfer fluid 120, a water tank 150, a water tank outlet system 160, and a space heating system 190.

[0086] The circuit of heat transfer fluid 120 comprises a heat pump outlet pipe 121 , a plate heat exchanger 140 comprising a heat exchanger first intake 122, and a heat exchanger outlet pipe 123. The heat exchanger outlet pipe 123 is connected to valve arrangement 124. The valve arrangement is connected to the space heating system 190 and bypass pipe 125. Bypass pipe 125 and the space heating system connect to heat pump inlet pipe 126.

[0087] The water tank 150 comprises an inlet 155 for receiving water to replenish the tank, e.g. pressurised mains water.

[0088] The water tank outlet system 160 comprises a hot water outlet 162 for a user to draw hot water from the tank. The hot water outlet 162 may also serve as upper draw branch for providing water from the top of the tank to the heat exchanger 140. A hot water pump 164 is arranged to pump water from the hot water outlet 162 to the heat exchanger 140. A lower draw branch 166, a buffer pump 168, a buffer valve 170, a lower return branch 172, and heat exchanger second intake 174. The hot water outlet 162 is connected to an upper portion of the water tank, such that water may flow out of the water tank through the hot water outlet. The hot water pump 164 controls the flow rate of water through the hot water outlet. The lower draw branch 166 is connected to a lower portion of the water tank, such that water may be drawn out of the water tank through the lower draw branch. The buffer pump 168 controls the flow rate of water through the lower draw branch. The buffer valve 170 prevents flow of water through the lower draw branch back into the water tank, and permits the flow of water through the lower draw branch out of the water tank. The hot water outlet 162 and the lower draw branch 166 both connect to the heat exchanger second intake.

[0089] The space heating system comprises radiators 195.

[0090] Figure 1 B shows a variant of the heating system of Figure 1A. In addition to the features discussed with reference to Figure 1A, an upper return branch 176 is included. The upper return branch 176 can serve to provide heated water from the heat exchanger 140 to an upper portion of the tank 150, instead of to a lower portion of the tank via the lower return branch 172. A three-port valve 178 is included to permit selection of the upper return branch 176 or the lower return branch 172.

[0091] In a first stage of operation, the heat pump may be switched on. In the on state, the heat pump heats a heat transfer fluid. This fluid is then pumped through heat transfer circuit 120. At the heat exchanger 140, the heat transfer fluid in the heat exchanger first intake 122 is in thermal contact with the water in the heat exchanger second intake 174.

[0092] In a first configuration of the water tank outlet system 160, the buffer pump is off and the hot water pump is on, causing water from the hot water outlet to flow through the heat exchanger second intake. Since the hot water outlet is positioned in an upper portion of the tank, the water leaving the tank through this outlet is at a higher temperature compared to the rest of the tank, due to hot water being less dense and so naturally rising to the top of a water tank. The water from the hot water outlet may therefore be at a higher temperature than the heat transfer fluid. In this case, heat is transferred from the water in the heat exchanger second intake to the heat transfer fluid in the heat exchanger first intake. The heat transfer fluid may then flow through the space heater system, providing heat to the surroundings, before flowing back into the heat pump.

[0093] Advantageously, in this configuration the water tank may provide additional heat to the heat transfer fluid, allowing the space heating system to heat up the surroundings faster than would be possible in reliance on the heat pump alone.

[0094] In a second configuration of the water tank outlet system 160, the buffer pump is on and the hot water pump is off, causing water from the lower draw branch to flow through the heat exchanger second intake. If the water in the buffer region has been heated to a higher temperature than the heat transfer fluid, then heat will again be transferred from the water in the heat exchanger second intake to the heat transfer fluid in the heat exchanger first intake. Advantageously, in this configuration, the water tank also provides additional heat to the heat transfer fluid, allowing the space heating system to heat up the surroundings faster than would be possible in reliance on the heat pump alone.

[0095] In a second stage of operation, the heat pump may still be on, but the valve arrangement in the heat transfer circuit may be set such that the heat transfer fluid passes through the bypass pipe rather than the space heater system. This stage of operation may follow the first stage of operation. After the first stage of operation, the surroundings of the space heater system may have sufficient heat, and it may not be desirable to heat this system further.

[0096] In this stage of operation, the heat transfer fluid may be hotter than the water at the hot water outlet and / or the lower draw branch. The heat transfer fluid in the heat exchanger first intake may therefore transfer heat energy to water from the water tank in the heat exchanger second intake. When the water tank outlet system is in the first configuration, the heat energy can be transferred to water from the hot water outlet. When the water tank outlet system is in the second configuration, the heat energy can be transferred to water from the lower draw branch.

[0097] Heat pumps deteriorate faster if subjected to more thermal cycling, so reducing the number of on-off cycles the heat pump undergoes in a given period can extend the lifetime of the heat pump. Advantageously, this second stage of operation allows heat energy generated by a heat pump to be stored in a water tank. This prolongs the period for which the heat pump may be switched on while efficiently storing the thermal energy, therefore prolonging the life of the heat pump.

[0098] In a third stage of operation, the heat pump may be switched off. Heat transfer fluid is still pumped through the circuit 120. The heat transfer fluid therefore comes into thermal contact with the water from the water tank outlet system in the heat exchanger second intake. If the water in the heat exchanger second intake is hotter than the heat transfer fluid, then heat will be transferred to the heat transfer fluid. The heat transfer fluid may therefore still provide heat to the space heating system even while the heat pump is switched off, provided sufficient hot water is present in the tank.

[0099] Advantageously, the use of hot water from the water tank to heat the heat transfer fluid allows a period during which the heat pump is switched off to be extended without resulting in any undesirable change in the temperature of the surroundings. For example, if the temperature of the surroundings meets a temperature setpoint, the heat pump may be switched off, and then when the temperature of the surroundings falls below a threshold then the water tank outlet system may be used to provide heat to the space heating system via the heat transfer fluid.

[0100] In a fourth stage of operation, the heat pump may be switched off, and the valve arrangement in the heat transfer circuit may be set such that the heat transfer fluid passes through the bypass pipe rather than the space heater system. The heat transfer fluid is still pumped through the circuit 120, and so comes into thermal contact with the water from the water tank outlet system in the heat exchanger second intake. In this stage of operation, the water in the heat exchanger second intake is hotter than the heat transfer fluid. The heat exchanger therefore allows heat to be transferred from the water tank outlet system to the heat transfer fluid. The heat transfer fluid then flows back through the heat pump. This allows heat to be transferred to the heat pump.

[0101] A problem with heat pumps used for long periods is that frost may form on the outside of the pipes at the cold sink. Frost reduces the rate of heat transfer from the pipes to the cold sink, which means that the pump efficiency is reduced. Advantageously, the fourth stage of operation transfers heat energy to the heat pump, which may be used to defrost the outside of the heat pump.

[0102] In an example the destratification pump 164 is switched on and hot water from the top of the tank pumped to the lower portion of the tank via the heat exchanger, providing heat to the heat transfer fluid for defrosting the pump. The lower portion of the tank may then still be warm enough to provide heat defrosting. The baffle 112 can serve to reduce tank-wide mixing such that the lower portion of the tank can contain moderately warm water pumped from the top portion of the tank. Once hot water at the top of the tank is depleted then the pump 168 can be switched on and moderately warm water be pumped from the lower portion of the tank to the heat exchanger and back to the lower portion of the tank, thus providing further heat for defrosting purposes.

[0103] The water tank may optionally comprise upper heating element and lower heating element. The water tank may also further comprise upper baffle and lower baffle.

[0104] Figure 2 shows a schematic of a second example of a heating system. The heating system comprises a heat pump 110, a circuit of heat transfer fluid 220, and a water tank 150 with a cold water inlet 255 and a hot water outlet 260 for a user to draw hot water.

[0105] The circuit of heat transfer fluid 220 comprises a heat pump outlet pipe 221 , an upper heat transfer coil 225, and a lower heat transfer coil 230. Upper heat transfer coil 225 and lower heat transfer coil 230 may be pipes external to the water tank, but with thermal contact with the water tank, and / or may be pipes running through the water tank. The heat pump outlet pipe connects to the upper heat transfer coil via upper valve 232. The upper valve is further connected to an upper bypass pipe 234. When the upper valve is in a first position, heat transfer fluid flows through the upper heat transfer coil. When the upper valve is in a second position, heat transfer fluid flows through the upper bypass pipe.

[0106] The upper heat transfer coil 225 and the upper bypass pipe both connect to lower valve 240. Lower valve 240 is connected to the lower heat transfer coil 230 and a lower bypass pipe 242. When the lower valve is in a first position, heat transfer fluid flows through the lower heat transfer coil. When the lower valve is in a second position, heat transfer fluid flows through the lower bypass pipe. The lower bypass pipe and the lower heat transfer coil are both connected to a heat pump inlet pipe 244.

[0107] In embodiments, the circuit of heat transfer fluid may be connected to a space heating system.

[0108] In a first heating mode, the heat pump may be switched on. In the on state, the heat pump heats a heat transfer fluid. This fluid is then pumped through heat transfer circuit 220. In a first configuration, the upper valve may be in the first position, such that heat transfer fluid flows through the upper heat transfer coil, and the lower valve may be in the second position, such that heat transfer fluid does not flow through the lower heat transfer coil, and instead flows through the lower bypass pipe back to the heat pump inlet pipe. This configuration is shown in Figure 3, with arrows indicating flow paths and flow directions.

[0109] The heat transfer fluid in the upper heat transfer coil is in thermal contact with the water in an upper portion of the water tank. Since hot water is less dense than cooler water, the water in the upper portion of the water tank may be warmer than water in a lower portion of the water tank. In this case, the upper heat transfer coil may allow heat to be transferred from the water tank to the heat transfer fluid, even if the average temperature of the water in the water tank is similar to or even below the temperature of the heat transfer fluid, as long as the temperature of the upper portion of the water tank in thermal contact with the upper heat transfer coil is greater than the temperature of the heat transfer fluid.

[0110] Advantageously, this allows heat transfer fluid to be heated to a desired temperature even when the heat pump alone is not capable of achieving this temperature, or when it is undesirable to cause the heat pump to heat the fluid to this temperature, and even when the average temperature of the water tank is not high enough to allow the transfer of sufficient thermal energy to the heat transfer fluid. For example, a user may desire a heating system to quickly heat up a home. Significantly more energy is required to increase the temperature of the home than is required to keep the temperature of the home at a steady state. It is therefore desirable to be able to provide heat transfer fluid at a high temperature for a short period of time, as the home is heated to the desired temperature. The present invention allows heat transfer fluid heated by a heat pump to be further heated by hot water from the upper portion of a water tank, which allows the home to be heated to the desired temperature more quickly. Heat pump efficiency decreases for higher temperature output, meaning that the coefficient of performance is lower when higher temperatures are required. The first heating mode advantageously allows heat transfer fluid to be heated by a combination of the heat pump and the water tank, allowing the heat pump to operate with a higher coefficient of performance and so increased energy efficiency.

[0111] In a second configuration, the upper valve may be in the second position, such that heat transfer fluid flows through the upper bypass pipe, and the lower valve may be in the first position, such that heat transfer fluid flows through the lower heat transfer coil to the heat pump inlet pipe. This configuration is shown in Figure 4, with arrows indicating flow paths and flow directions.

[0112] The heat transfer fluid in the lower heat transfer coil is in thermal contact with the water in a lower portion of the water tank. The water in the lower portion of the water tank may be at a higher temperature than the heat transfer fluid in the lower heat transfer coil. If this is the case, heat will be transferred from the water in the water tank to the heat transfer fluid. This may be desirable where, for example, a user desires to heat their home and also draw hot water from the water tank. In this case, it is desirable for the water at a hot water outlet of the water tank to be at a high temperature and not to be cooled by heat transfer fluid. However, water in the lower portion of the water tank may have sufficient heat to be able to heat the heat transfer fluid. Advantageously, this allows water at a high temperature to be drawn off, while water at a lower temperature is used to heat the heat transfer fluid. This configuration may also be desirable when a home has reached a steady temperature state, and a user sets the system to maintain the temperature of the home. For maintenance of the home temperature at a temperature setpoint, it is necessary for heat transfer fluid to be circulated at a lower temperature than the temperature of heat transfer fluid required to reach the temperature setpoint. It may therefore be desirable to provide a smaller boost to the temperature of heat transfer fluid during steady state operation. Advantageously, the second configuration allows a smaller boost to the temperature of the heat transfer fluid to be provided. In a third heating mode, the heat pump may be on, and the upper valve and lower valve may be in the second position, such that no heat transfer occurs between the heat transfer fluid and the water tank. This may be desired when the home has already reached a steady state temperature, and it is desired to maintain this temperature, as heat from the heat pump alone may be sufficient for this purpose. This configuration is shown in Figure 5.

[0113] In a fourth heating mode, the heat pump may be on, and both the upper valve and lower valve may be in the first position, such that heat transfer occurs between the heat transfer fluid and water in both the upper and lower portions of the water tank. When the temperature of the water tank is greater than the temperature of the heat transfer fluid, this stage may be desirable to provide a greater area of thermal contact between the heat transfer fluid and the water tank, for example to provide additional heat to the heat transfer fluid when it is desired to increase the temperature of a home. This configuration is shown in Figure 6.

[0114] The system may also operate in a charging mode, which may be used when the temperature of the water in the upper and / or the lower portion of the water tank has fallen below the temperature of the heat transfer fluid. In a first charging mode, the heat pump is on, and the upper valve is in the first position, while the lower valve is in the second position. This configuration is shown in Figure 3. When the temperature of the water in the upper portion of the water tank is lower than the temperature of the heat transfer fluid, this results in heat transfer from the heat transfer fluid to the water in the upper portion of the water tank. This allows heat from a heat pump to be stored in the water in the upper portion of the water tank. Advantageously, this may be used to raise the temperature of the water in the upper portion of the water tank quickly to the required temperature threshold, for example when demand has caused the water in the upper portion of the water tank to drop below the required temperature threshold. This may be done much faster than would be done by merely heating the base of the water tank.

[0115] In a second charging mode, the heat pump is on, the upper valve is in the second position, and the lower valve is in the first position. This configuration is shown in Figure 4. When the temperature of the water in the lower portion of the water tank is lower than the temperature of the heat transfer fluid, this results in heat transfer from the heat transfer fluid to the water in the lower portion of the water tank. This allows heat from a heat pump to be stored in the water in the lower portion of the water tank. The temperature profile of a water tank may be uniform or may vary significantly with height. When the lower portion of a water tank is cooler than the upper portion of a water tank, the lower portion of the water tank may be used to store additional heat even when the upper portion of the water tank is at a maximum target temperature for the water tank.

[0116] In a third charging mode, the heat pump may be on and the upper and lower valves may both be in the first position. When both the upper and lower portions of the water tank are at a temperature below the temperature of the heat transfer fluid, this configuration allows transfer of heat energy to the water tank.

[0117] One example use of the charging mode may be to store excess energy that has become available to the system. For example, a home may be connected to a domestic photovoltaic energy generation system, or a wind turbine. These energy generation systems can be unreliable in output, and may sometimes produce a large surplus of electricity where this is not needed, and at other times may not produce sufficient electricity. Electricity grids can also suffer energy surplus at certain times, which it may be beneficial to absorb. The charging mode allows a surplus of electricity to be stored as thermal energy in the water tank, which may then be used at a later time.

[0118] Another use of the charging mode may be to lengthen the heat pump operation cycle. Thermal cycling accelerates heat pump degradation. Extending the duration for which a heat pump may be on and usefully producing heat by allowing heat energy to be stored in a water tank allows the on portion of a heat pump cycle to be extended. Advantageously, this may reduce the thermal cycling the heat pump is subjected to, and therefore extend the life of the heat pump.

[0119] The system may further operate in a discharging mode. In this mode, the heat pump is switched off. A first discharging mode is operable with the configuration shown in Figure 3, a second discharging mode is operable with the configuration shown in Figure 4, and a third discharging mode is operable with the configuration shown in Figure 6. When the temperature of the water in the upper and / or the lower portions of the water tank is greater than the temperature of the heat transfer fluid, these modes allow the heat transfer fluid to be heated using the latent heat of the water rather than the heat pump. Advantageously, this allows a heating system to provide heat while the heat pump is switched off. This may be used to extend a heat pump operation cycle, and so reduce ageing of the heat pump, without affecting performance of the system.

[0120] Additionally, the system may operate in a sterilization mode. In this mode, the heat pump is on, and the temperature of the heat transfer fluid is greater than the temperature of the upper portion and / or the lower portion of the water tank. Where a water tank stores potable water, it may be necessary to periodically raise the temperature above a threshold to prevent the growth of pathogens. This may be done using the configurations shown in Figures 3, 4 and 6 to transfer heat energy from the heat transfer fluid to the water tank.

[0121] The system may further operate in a defrost mode. In this mode, the heat pump is off, and the temperature of the heat transfer fluid is lower than the temperature of the upper portion and / or the lower portion of the water tank. Where the cold sink of a heat pump is exposed to air containing moisture, this may condense on the cold sink and freeze to create frost. Such frost acts to insulate the cold sink and so reduces the efficiency of heat transfer into the cold sink, therefore reducing the efficiency of the heat pump. It is therefore desirable to defrost a heat pump periodically. This may be done using the configurations shown in Figures 3, 4 and 6 to transfer heat energy to the heat transfer fluid from the water tank, where the water in the upper and / or the lower portions of the water tank has sufficient thermal energy to transfer to the heat transfer fluid to allow effective defrosting. Advantageously, periodic defrosting allows the heat pump to operate with a greater energy efficiency.

[0122] In the first defrosting mode, the upper valve is in the first position and the lower valve is in the second position. This allows a heat pump to be defrosted even if the average energy of the water tank is not sufficient, as long as the energy in the upper portion of the water tank is sufficient.

[0123] In the second defrosting mode, the upper valve is in the first position and the lower valve is in the second position. This allows a heat pump to be defrosted using energy from the lower portion while allowing the temperature of the upper portion of the tank to remain roughly unchanged, ensuring that sufficient hot water is available to be drawn off even during heat pump defrosting.

[0124] The water tank shown in Figures 1-6 may comprise additional features. For example, the water tank may comprise at least one heating element 114. In one embodiment, the water tank comprises two heating elements, wherein one is positioned in the lower portion of the water tank and one is positioned in the upper portion of the water tank.

[0125] In one embodiment, the water tank comprises at least one baffle 112. A baffle acts to reduce mixing between water above the baffle and water below the baffle. A baffle may be positioned just above a cold inlet 155, 255 to the tank. This may result in inflowing cold water replenishing water in the tank (e.g. following a draw event of hot water) being baffled to reduce inadvertent flows in the tank that may disrupt thermal stratification in the tank. Another baffle may be positioned between the upper portion of the tank and the lower portion of the tank. This may result in a greater difference being achievable between the temperature of water in the upper portion of the tank and the lower portion of the tank. Advantageously, the ability to control the temperatures of the upper and lower portions of the water tank virtually independently increases the flexibility of the system. Increasing a temperature in a lower portion of the tank may be beneficial in order to accumulate heat above a particular threshold, e.g. for defrosting purposes, which may outweigh the benefit of maintaining the lower portion of the tank as cool as possible for optimally effective heat transfer in the lower portion and high coefficient of performance of the heating system. In one embodiment, a lower and upper baffle plate may be positioned within the lower portion of the tank. In one embodiment, the lower and upper baffle plates enclose a volume of at least a fifth of the water tank’s total volume. In one embodiment, the lower and upper baffle plates enclose a volume of less than one half of the water tank’s total volume.

[0126] Conveniently the water tank can comprise a means of sensing a tank status that is indicative of a quantity of thermal energy stored in the tank and / or a temperature distribution in the tank. Such a tank status can quantify a heat stored in the water tank (optionally above a minimum temperature threshold), or a temperature distribution of water in the tank, or a temperature profile of water in the tank. This can permit selection of a heating regime in the tank in dependence on a particular temperature distribution of water in the tank for optimal heating and heat energy storage, also in dependence on the intended uses of the heat (e.g. domestic hot water supply, space heating, sterilisation, heat pump defrosting). In some examples, the means of sensing a tank status comprises a plurality of temperature sensors 116. These 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 means of determining a temperature distribution in the tank may include as few as one temperature sensor and infer 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 fluid 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.

[0127] For additional versatility the water tank may comprise a destratification pump. This transfers water between the top and bottom of the water tank. For example, the destratification pump may remove water from the upper portion of the tank and pump this water into the lower portion of the tank. In another example, the destratification pump may remove water from the lower portion of the tank and pump this water into the upper portion of the tank. The destratification pump may be switched on to even out the temperature profile of the tank. For example, the destratification pump may be switched on when it is desired that all of the water in the water tank be heated above a threshold temperature. The threshold temperature may be a threshold above which the water is sterilized. In another example, the destratification pump may be switched on to even out the temperature profile of the tank, e.g. in order to have a larger quantity of water at a lower temperature for a particular purpose (e.g. space heating).

[0128] In some examples the water tank may comprise a thermostatic mixing valve on the hot water outlet, which allows the hot water output from the water tank to be mixed with cold water to achieve a desired water output temperature.

[0129] In some examples the valve arrangement consists of two three-port valves, each individually actuable, for convenience electrically actuable e.g. by way of a motor (also known as motorised valves). The valve arrangement may be controlled by a controller.

[0130] In some examples the heat transfer fluid is water or an aqueous solution. The heat transfer fluid may treated with corrosion inhibitors and / or antifreeze.

[0131] Advantageously in the water tank of Figures 2-6 the heat transfer fluid flows through the upper heating coil from the top of the upper heating coil to the bottom of the upper heating coil. This can promote stratification of the water tank, allowing the heat transfer fluid to transfer the maximum energy at the top of the upper heating coil, to ensure that water at a hot water outlet at the top of the water tank is most quickly heated to the target temperature.

[0132] Advantageously in the water tank of Figures 2-6 the heat transfer fluid flows through the lower heating coil from the bottom of the lower heating coil to the top of the lower heating coil. This can maximise the heat transfer between the heat transfer fluid and the water in the lower portion of the water tank. Figure 7A shows a temperature profile 700 of water in the water tank. The temperature profile may be measured by an array of sensors, or it may be inferred from data such a flow rate at an inlet, flow rate at an outlet, and / or a temperature measurement. A model of temperature distribution in the tank may assist in inferring a temperature profile in the tank. As the height of water in the tank increases, the temperature of the water also increases. In this example temperature profile, the temperature of the water in the upper portion of the tank is fairly uniform, while the temperature in the lower portion of the tank is less uniform. In the illustrated example this is a result of the lower coil receiving heat (indicated with arrows) and transferring it to the tank as described with reference to Figure 4, and in the well-stratified tank the hot (less dense) water has accumulated at the top of the tank. Such a temperature profile may be formed by different means, for example by input of heat by an upper or lower electrical heating element and / or heat transfer from a heat transfer fluid via a heat exchanger and an upper or lower return branch, and / or by input of heat from both an upper and lower heating coil.

[0133] Figure 7A shows three temperature thresholds which are of relevance to the performance of the heating system. The first temperature threshold, Td, is a defrost temperature threshold. This is a minimum temperature at which the heat transfer fluid may defrost the heat pump. The second temperature, Ts, is a space heating threshold temperature, which is the current temperature at which the heat transfer fluid must be when entering a space heating system. The third temperature, Th, is a domestic hot water temperature, which is a minimum temperature for hot water drawn from the tank via the hot water outlet for use in a home. In an example Tdis around 40 °C, Tsis around 50 °C and This around 65 °C, but a wide range of temperatures may be selected for these values depending on user preference, system configuration, environment, season, and other factors.

[0134] The temperature of the upper portion of the tank is maintained above Thso that water in this portion of the tank is hot enough to be drawn off for use in the home. The water in the lower portion of the tank falls below this threshold Th.

[0135] Figure 7B shows the same tank as shown in Figure 7A with the same temperature profile 700, however here heat in not being transferred to the tank, but instead heat is being drawn from the tank for transfer to the heat pump. This may be useful to defrost the heat pump. The shaded area 710 in Figure 7B is indicative of a quantity of heat stored in the lower portion of the water tank that may be received by the lower coil to raise the temperature of the heat transfer fluid above the defrost temperature threshold Td. The quantity of heat indicated by the area 610 determines a quantity of heat that can usefully be provided for defrosting. Water below Tdis not warm enough to serve for defrosting. Water above the upper horizontal upper boundary 712 of the shaded area 710 would be sufficiently hot for defrosting purposes, but is not well available by way of the lower coil 230. The upper boundary 712 is defined by an upper baffle position in the tank (e.g. in the examples illustrated in Figures 1A and 1 B), and / or by the locations of the heat transfer coils. In this example, area 710 is large enough to provide a sufficient quantity of heat to defrost the heat pump. For the illustrated tank the flow regime discussed with reference to Figure 4 is appropriate (indicated with arrows) in order to draw heat from a lower part of the tank and provide it to the heat pump. The hot water in the upper part of the tank can remain undisturbed by the defrosting operation and available for user domestic hot water provision or for space heating.

[0136] Figure 8 shows a different temperature profile. In this example, the quantity of heat stored in the lower portion of the tank above the defrost temperature threshold Td, illustrated by the shaded portion 810, is insufficient for successful defrosting of the heat pump to take place. In this instance it is appropriate to draw heat from the upper part of the tank where sufficient hot water is available, rather than from the lower part of the tank. For the illustrated tank the flow regime discussed with reference to Figure 3 is appropriate (indicated with arrows) in order to draw heat from an upper part of the tank and provide it to the heat pump. In the tank described with reference to Figures 1A and 1B the upper draw branch can provide suitably hot water to the heat exchanger instead of the lower draw branch in this scenario.

[0137] Figure 9 shows an another temperature profile, for example as might be observed after a quantity of heat has been drawn from the upper portion of the tank illustrated in Figure 8. In this example, the temperature of water in the upper portion of the tank is insufficient for hot water delivery for domestic use. The temperature of the upper portion of the tank is also below the space heating threshold temperature Ts. In this scenario heat is provided to the tank, e.g. from the heat pump if available. In the example a flow regime discussed with reference to Figure 3 is shown for transfer of heat to the upper portion of the tank via upper coil 225; this 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. Once an upper portion of the tank has been heated to provide enough sufficiently hot water (or the upper part of the tank is too hot to permit efficient heat transfer from the upper coil), gradual, more efficient heating heat of the remained of the tank can be provided by way of the lower coil (as described with reference to Figure 4), or heat may alternatively be provided via both the upper and lower coil (as described with reference to Figure 6).

[0138] Figure 10 shows a further example temperature profile. In this case, the temperature of the upper portion of the tank is significantly above Th. When it is desired to use the heat pump to store energy in the water tank, the upper portion of the tank may be too hot to allow for efficient transfer of heat from the heat transfer fluid to the water in the tank. It may therefore be desired to provide heat to both the upper and lower portions of the tank (as illustrated in this example with a flow regime as discussed with reference to Figure 6), or alternatively only to the lower portion of the tank (as discussed with reference to Figure 4).

[0139] Figures 11A and 11 B show exemplary temperature profiles before and after providing heat to the lower portion of the water tank. In Figure 11 A, the temperature of the lower portion is fairly uniform. For example, it may be at a temperature at which cold water is taken in to the water tank from a cold water inlet. The temperature of the water in the upper portion of the water tank varies gradually from below the space heating temperature Tsat the boundary between the lower and upper portions of the water tank, to above Th.

[0140] Figure 11 B shows the water tank temperature profile after providing heat to the lower portion for a period of time. The temperature profile is essentially shifted downwards, such that the gradual transition between water below Tsand water above Thhappens in the lower portion of the water tank rather than in the upper portion of the water tank. Compared to the temperature profile in Figure 11 A there is enough energy stored in the lower portion of the water tank above Tsthat heat could now be drawn from the lower portion e.g. via a lower coil for the purpose of space heating, while maintaining the heat stored in the upper portion for e.g. domestic hot water use.

[0141] Figure 12 shows the water tank temperature profile for a tank where further heat has been provided to an upper portion of the tank with an upper electric heating element 114. This can permit the upper portion of the tank to be heated to a temperature higher than might be available from the heat pump by way of the upper coil in the illustrated tank example. Boosting the thermal energy by the electric heating element can enable the tank to provide heat e.g. for space heating, for instance for quickly reheating a home on arrival of a resident before permitting the temperature in the heat transfer circuit to drop again for more efficient operation. Boosting the thermal energy by the electric heating element can also permit the tank to accept additional surplus electricity, be it from an electricity grid, from a domestic photovoltaic system, or from another electricity source.

[0142] Figure 13 shows a tank 150 with a destratification pump 900. A destratification line connects the hot outlet 260 and the cold inlet 255 to the tank. The destratification pump is arranged in the destratification line to pump fluid from the hot outlet 260 to the cold inlet 255. A non-return valve 902 is included in the destratification line to prevent flow backflow from the cold inlet to the hot outlet. The de-stratification pump can help control and optimise the temperature distribution in the tank for several purposes, e.g. to ensure that 1) a sterilising temperature is achieved at the bottom of the tank and 2) full volumetric thermal capacity of the tank is made use of considering the stratification of heat around coils that would occur during heating and 3) to improve a heat transfer coefficient between stored hot water in tank and heat transfer coils.

[0143] Figures 14A and 14B illustrate an example where destratification by virtue of operation of the destratification pump 900 is beneficial. Figure 14A shows a heat tank temperature profile prior to a sterilization process; in the lower portion of the tank some regions are below a sterilization temperature Tst. Providing further heat via the lower coil may not or only slowly bring the temperatures in the lowest regions sufficiently high, while in the upper portion of the tank a risk of overheating may arise. Figure 14B shows a heat tank temperature profile following operation of the destratification pump. This results in heat from the top of the tank being transferred to the bottom of the tank, resulting in a temperature profile that is fairly uniform and above the sterilization temperature Tst throughout the tank. Advantageously, this allows the water to be sterilized, which means the water in the hot water tank may be kept as a potable water source. In an example Tst is around 60 °C, but temperatures of least 50 degrees Celsius (more preferably at least 60 degrees Celsius) may be used for sterilisation generally.

[0144] Various other modifications will be apparent to those skilled in the art.

[0145] For instance, the illustrations in Figures 7A to 14B show examples of tanks with upper and lower coils for providing heat to or drawing heat from an upper or lower portion of the tank. Alternatively the tanks described with reference to Figures 1A and 1 B can provide the same functionality by way of selection of upper or lower draw branch and upper or lower return branch for the external heat exchanger. This can permit providing of heat to or drawing of heat from an upper or lower portion of the tank to achieve the same operation.

[0146] Many of the illustrations show examples of tanks in the form of water cylinders. Water cylinders are typically unvented tanks for containing mains pressurised water. A pressurised tank can distribute hot water throughout a building without needing any pumps. 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. The tank may however be in another form. The tank may be a vented tank for containing water at ambient pressure. The water contained in the tank may include additives.

[0147] 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.

[0148] 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.

[0149] 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.

[0150] Where the upper portion of the tank is referred to herein (e.g. for drawing heat from, or for providing heated water to), it should be appreciated that this may include near the top 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 a lower portion of the tank is referred to (e.g. for providing heat to, or for pumping water to be heated from), it should be appreciated that this may include near the bottom of the tank, a bottom portion of the tank, a part of the tank that is not an upper portion of the tank, or 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.

[0151] An upper feature as referred to herein is preferably above a lower feature in the tank, with the tank in such orientation as it is intended to be installed for use. An upper feature is preferably in an upper portion of the tank. A lower feature as referred to herein is preferably below an upper feature of the tank, with the tank in such orientation as it is intended to be installed for use. A lower feature is preferably in a lower portion of the tank.

[0152] 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. Reference numerals appearing in the claims are by way of illustration only and shall have no limiting effect on the scope of the claims.

[0153] The term ‘comprising’ as used in this specification and claims preferably means ‘consisting at least in part of’.

Claims

Claims1. A heating system including: a heat pump; a circuit of heat transfer fluid to transfer heat to or from the heat pump; a water 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.

2. A heating system according to claim 1 , further comprising a means of sensing or inferring a temperature distribution in the tank.

3. A heating system according to claim 2, wherein the means of sensing comprises one or more temperature sensors, preferably an array of temperature sensors arranged to sense temperatures at different heights of the tank.

4. A heating system according to any preceding claim, wherein the controller is configured to determine a quantity of heat above a temperature threshold in the lower portion of the water tank and / or the upper portion of the water tank, preferably in dependence on a temperature distribution in the water tank.

5. A heating system according to claim 4, wherein the controller is configured to cause the selector arrangement to direct heat to or draw heat from the upper heat transfer means or the lower heat transfer means in dependence on the quantity of heat above a temperature threshold in the lower portion of the water tank and / or the upper portion of the water tank.

6. A heating system according to claim 4 or 5, wherein the temperature threshold is a minimum temperature for user hot water supply; a minimum temperature for water sterilisation; a minimum temperature for space heating; or a minimum temperature for heat pump defrosting.

7. A heating system according to any preceding claim, wherein the controller is configured to determine that a temperature of the upper portion of the tank is below a threshold; and cause the selector arrangement to direct heat to the upper heat transfer means.

8. A heating system according to any preceding claim, wherein the controller is configured to determine that a temperature of the upper portion of the tank is above a first threshold; determine that a temperature of the lower portion of the tank is below a second threshold; determine that the heat pump is in the on state; and cause the selector arrangement to direct heat to the lower heat transfer means.

9. A heating system according to any preceding claim, wherein the controller is configured to determine that the heat pump requires a defrost cycle; determine that a quantity of heat above a temperature threshold in the lower portion of the water tank is above a threshold; and cause the selector arrangement to draw heat from the lower heat transfer means.

10. A heating system according to any preceding claim, wherein the controller is configured to determine that a request for sterilization of the water tank has been received; and cause the selector arrangement to direct heat to the lower heat transfer means.

11. A heating system according to any preceding claim, wherein: the upper heat transfer means is 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 is a lower heat transfer coil configured to transfer heat between the heat transfer fluid and a lower portion of the water tank; and the selector arrangement is 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 coil or to both.

12. A heating system according to claim 11 , wherein the upper heat transfer coil has a flow path from top to bottom, such that the heat transfer fluid enters the upper heat transfer coil at a top of the upper heat transfer coil, and exits the upper heat transfer coil at a bottom of the upper heat transfer coil.

13. A heating system according to claim 11 or 12, wherein the lower heat transfer coil has a flow path from bottom to top, such that the heat transfer fluid enters the lower heat transfer coil at a bottom of the upper heat transfer coil, and exits the lower heat transfer coil at a top of the upper heat transfer coil.

14. A heating system according to any one of claims 1 to 10, wherein:the heating system further comprises a heat exchanger and the circuit of heat transfer fluid is arranged to transfer heat between the heat pump and the heat exchanger; the heating system further comprises 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 is an upper return branch in the circuit of water that is arranged to return water to the upper portion of the water tank; and the lower heat transfer means is a lower return branch in the circuit of water that is arranged to return water to the lower portion of the water tank.

15. A heating system according to claim 14, wherein the selector arrangement is a return valve arrangement 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.

16. A heating system according to claim 14, wherein the selector arrangement is 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.

17. A heating system according to any one of claims 14 to 16 wherein the circuit of water further comprises a pump.

18. A heating system according to any one of claims 14 to 17, wherein the circuit of water from the tank to the heat exchanger and back to the tank further comprises: an upper draw branch arranged to draw water from an upper portion of the water tank; a lower draw branch arranged to draw water from a lower portion of the water tank; and a draw control means configured to control flow from the upper draw branch and the lower draw branch, wherein the controller is further configured to control the draw control means for heat transfer from the upper portion of the water tank or the lower portion of the water tank or both.

19. A heating system according to claim 18, wherein the draw control means is a controllable first pump in the upper draw branch and a controllable second pump in the lower draw branch.

20. A heating system according to claim 18, wherein the draw control means is a draw valve arrangement configured to direct flow via the upper draw branch or the lower draw branch.

21. A heating system according to any one of claims 18 to 20, wherein the controller is configured to determine that a heat pump requires a defrost cycle; determining that a quantity of heat above a temperature threshold in the lower portion of the water tank is above a threshold; and cause the draw control means to allow flow from the lower draw branch.

22. A heating system according to any one of claims 18 to 21 , wherein the controller is configured to determine a temperature of the upper portion of the tank is below a threshold; and cause the draw control means to allow flow from the upper draw branch.

23. A heating system according to any one of claims 18 to 22, wherein the controller is configured to determine that a temperature of the upper portion of the water tank is below a first threshold; and cause the draw control means to allow flow from the upper draw branch and the selector arrangement to allow flow to the upper return branch.

24. A heating system according to any one of claims 18 to 23, wherein the controller is configured to determine that a temperature of the upper portion of the water tank is above the first threshold and a demand for hot water is received; and cause the draw control means to allow flow from the lower draw branch, and the selector arrangement to allow flow to the upper return branch.

25. A heating system according to any one of claims 18 to 24, wherein the controller is configured to determine that a temperature of the upper portion of the water tank is above a second threshold; a temperature of the lower portion of the water tank is below a third threshold; no demand for hot water is received; and the heat pump state is on; and cause the draw control means to allow flow from the lower draw branch only, and the selector arrangement to allow flow to the lower return branch.

26. A heating system according to any one of claims 18 to 25, wherein the controller is configured to determine that a quantity of heat above a temperature threshold in the lower portion of the water tank is above a fourth threshold and a defrost condition of the heat pump is received; and cause the draw control means to allow flow from the lower draw branch.

27. A heating system according to any one of claims 18 to 26, wherein the controller is configured to determine that a temperature of the lower portion of thewater tank is below a fifth threshold and a sterilization condition is received; and cause the selector arrangement to allow flow to the lower return branch only.

28. A heating system according to any preceding claim, further comprising a space heating system.

29. A heating system according to any preceding claim, wherein the water tank further comprises a destratification pump, wherein the destratification pump transfers water between the upper portion of the water tank and the lower portion of the water tank.

30. A heating system according to claim 29, wherein the controller is configured to activate the destratification pump in dependence on a temperature distribution in the water tank.

31. A heating system according to any preceding claim, wherein the water tank comprises at least one baffle.

32. A heating system according to claim 31 , wherein at least one baffle is positioned between the lower and the upper portions of the water tank.

33. A heating system according to claim 31 or 32, wherein at least one baffle is positioned within the lower portion of the water tank.

34. A heating system according to claim 33, wherein the at least one baffle positioned within the lower portion of the water tank is positioned above a further water inlet.

35. A heating system according to any preceding claim, wherein the water tank comprises at least one electric heating element.

36. A heating system according to claim 35, wherein the water tank comprises at least two electric heating elements, wherein an upper heating element is positioned in the upper portion of the tank, and a lower heating element is positioned in the lower portion of the tank.

37. A heating system according to claim 35 or 36, wherein the controller is configured to activate at least one electric heating element in dependence on a temperature distribution in the water tank.

38. A heating system according to any preceding claim, wherein the water tank is for storing hot water at ambient pressure or for storing pressurized hot water, optionally potable water or mains pressurized water or water for supply to a user.

39. A controller for use in a heating system, optionally according to any preceding claim, the controller configured to control heat transfer to or from an upper portion of a water tank or a lower portion of the water tank or both in dependence on a temperature distribution in the water tank.

40. The controller of claim 39 further configured to receive as input data from at least one temperature sensor, preferably an array of temperature sensors, and to determine a temperature distribution in the water tank and / or a quantity of heat above a temperature threshold in the lower and / or upper portion of the water tank.41 . The controller of claim 39 or 40 further configured to output control signals for a configuration for drawing heat from an upper portion of the water tank or a lower portion of the water tank or both and supplying the heat to a heat pump in response to an input indicating a demand to defrost the heat pump.

42. The controller of any of claims 39 to 41 further configured to receive as input a power status of the heat pump.

43. A water tank comprising a baffle, wherein the baffle divides the water tank into an upper portion and a lower portion, such that the upper portion of the heat tank and the lower portion of the heat tank may be held at different temperatures.

44. The water tank of claim 43, wherein the lower portion is at least 30 litres and / or less than 100 litres.

45. The water tank of claim 43 or 44, wherein the lower portion is half of the water tank’s volume or less and / or a fifth of the water tank’s volume or more.

46. A heating system including: a water tank for storing hot water; a space heating system comprising a circuit of heat transfer fluid and a heat exchange means for receiving heat from the water tank; and a controller configured to control the transfer of heat from the water tank to the heat exchange means for dynamic adjustment of a target temperature of heat transfer fluid in the space heating system.

47. A heating system according to claim 46 wherein the controller is configured to temporarily increase a target temperature of heat transfer fluid in the space heating system to boost user perception of space heating.

48. A heating system according to claim 46 or 47 wherein the controller is configured to reduce a target temperature of heat transfer fluid in the space heating system following a temporary boost request.

49. A user interface for a controller according to any one of claims 46 to 48, comprising a means for user input of a request for a temporary boost to space heating.

50. A user interface according to claim 49 comprising a means for presenting to a user a suggestion for a temporary boost to space heating, optionally wherein the suggestion is dependent on weather data and / or on user location data.51 . A method for controlling a heating system comprising selection of heat transfer to or from an upper portion of a water tank or a lower portion of the water tank or both, preferably in dependence on a temperature distribution in the water tank.

52. A method according to claim 51 comprising determining a quantity of heat above a temperature threshold in the lower portion of the water tank and / or the upper portion of the water tank, preferably in dependence on a temperature distribution in the water tank.

53. A method according to claim 51 or 52 wherein selection of heat transfer to or from an upper portion of a water tank or a lower portion of the water tank or both is in dependence on the quantity of heat above a temperature threshold in the lower portion of the water tank and / or the upper portion of the water tank.

54. A heating system including: a water tank for storing hot water; a conduit providing a flow path from an upper portion of the water tank to a lower portion of the water tank; a destratification pump arranged to pump fluid from an upper portion of the water tank to a lower portion of the water tank; and a controller configured to control the destratification pump in dependence on a temperature distribution in the water tank.

55. A heating system according to claim 54, further comprising a means of sensing or inferring a temperature distribution in the water tank.

56. A heating system according to claim 55, wherein the means of sensing or inferring a temperature distribution in the water tank comprises one or more temperature sensors.

57. A heating system according to claim 56, wherein the means of sensing or inferring a temperature distribution in the water tank comprises an array oftemperature sensors.

58. A heating system according to any one of claims 54 to 57, wherein the water tank is arranged to receive heat from and / or provide heat to a heat pump, and wherein the controller is further configured to receive information from the heat pump and to activate the destratification pump in dependence on the information from the heat pump.

59. A heating system according to claim 58, wherein the controller is configured to activate the destratification pump in response to a defrost request from the heat pump.

60. A heating system according to claim 58 or 59, wherein the controller is configured to activate the destratification pump when the temperature distribution in the water tank indicates a sufficient stored heat to allow defrosting of the heat pump.61 . A heating system according to any one of claims 54 to 60, further comprising a heat exchanger configured to transfer heat between a heat pump and the water tank.

62. A heating system according to claim 61 wherein the heat exchanger comprises a heat transfer coil configured to transfer heat between a heat transfer fluid and water in the water tank.

63. A heating system according to claim 61 or 62, wherein the heat exchanger is internal to the water tank.

64. A heating system according to claim 61 or 62, wherein the heat exchanger is external to the water tank, and wherein the heating system further comprises a circuit of water from the water tank to the heat exchanger and back to the water tank to transfer heat between the water tank and the heat exchanger.

65. A heating system according to claim 64, wherein the circuit of water from the tank to the heat exchanger and back to the water tank comprises a heat exchange pump arranged to draw water from a lower portion of the water tank to an upper portion of the water tank.

66. A heating system according to claim 65, wherein the destratification pump is arranged in a branch bypassing the heat exchange pump, preferably with a nonreturn valve arranged to prevent flow from the destratification pump to the heat exchange pump and / or from the heat exchange pump to the destratification pump.

67. A heating system according to claim 66, wherein the destratification pump is arranged to pump fluid from an upper portion of the water tank to a lower portion of the water tank via the heat exchanger.

68. A heating system according to any one of claims 54 to 67, wherein the controller is configured to activate the destratification pump when the temperature distribution in the water tank indicates that a quantity of energy stored in the water tank exceeds a threshold, preferably wherein the average temperature of water in the water tank exceeds 60 degrees Celsius.

69. A heating system according to any one of claims 54 to 68, wherein the controller is further configured to activate the destratification pump in dependence on a signal from a thermostat.

70. A heating system according to any one of claims 54 to 69, wherein the water tank is for holding water at atmospheric pressure or for holding pressurized water.71 . A heating system according to any one of claims 54 to 70, wherein the water tank is for holding potable water.

72. A heating system according to any one of claims 54 to 71 , wherein the water tank comprises at least one baffle.

73. A heating system according to claim 72, wherein the baffle is arranged in a lower portion of the water tank, optionally wherein a portion of the water tank below the baffle comprises less than half the tank volume and / or less than 100 liters.

74. A heating system according to any one of claims 54 to 73, wherein the water tank comprises at least one electric heating element.

75. A heating system according to any one of claims 54 to 74, further comprising a heat pump.

76. A heating system according to any one of claims 54 to 75, comprising an upper heat transfer means configured to transfer heat from a 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; wherein the controller is further 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.

77. A method of operating a heating system, the method comprising: determining a temperature distribution in a water tank for storing hot water; and controlling a destratification pump arranged to pump fluid from an upper portion of the water tank to a lower portion of the water tank in dependence on a temperature distribution in the water tank.

78. A method according to claim 77, wherein the heating system is according to any one of claims 54 to 76.

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