GB2603893A

GB2603893A - Controller interface and system for controlling a heating system

Info

Publication number: GB2603893A
Application number: GB2101745.4A
Authority: GB
Inventors: Armstrong Peter; randall Christopher
Original assignee: Mixergy Ltd
Current assignee: Mixergy Ltd
Priority date: 2021-02-09
Filing date: 2021-02-09
Publication date: 2022-08-24
Anticipated expiration: 2041-02-09
Also published as: WO2022171990A1; GB202101745D0; AU2022220245A1; EP4291833A1; US20240093909A1; GB2603893B

Abstract

A controller interface ‘B12’ is disposed between a hot water tank controller ‘B13’ and a heat pump controller ‘B2’ of a heating system in use. The interface comprises a response module configured to receive, from the hot water tank controller, a first signal indicative of a temperature. The response module provides a response signal based on the first signal and a temperature response characteristic and communicates the response signal to the heat pump controller. The controller interface enables interoperability of a heat pump controller and a legacy hot water tank system and hot water tank controller. A hot water tank controller configured to provide a first input signal indicative of a temperature of the controller interface, and a hot water tank having an inlet port and an outlet port to receive a retrofit heat transfer module are also claimed.

Description

I

CONTROLLER INTERFACE AND SYSTEM FOR CONTROLLING A HEATING

SYSTEM

The present disclosure relates to a controller interface between a hot water tank controller and a heat pump controller in a heating system. In particular, the disclosure is relevant to a scenario in which an existing controller of a traditional hot water heating system is integrated with a controller of a heat pump that is retrofitted to an existing water tank. A water tank to which a heat pump is retrofittable is also disclosed.

Background

Heat pumps are becoming an increasingly popular option for the decarbonisation of domestic heating due to their ability to shift multiple units of thermal energy for a single unit of electricity consumption. However, heat-pumps are only capable of transferring heat at a relatively low power output and their efficiency worsens for higher delivery temperatures. Many hot water tanks are installed today for existing gas boilers and electric only systems. If a heating system is upgraded to include a heat-pump, usually a new hot water tank is required with a larger heat exchanger to accommodate the lower temperature heat transfer from the heat pump in comparison to the gas boiler. The larger heat exchanger is also often prohibitively expensive relative to the requirements associated with most incumbent systems. There is a need to provide a water tank that is configured to be operable with a gas boiler and/or electric heater arrangement, which is also suitable for a later retrofit of a heat pump.

Typically, a heat-pump is sold in conjunction with a hot water tank designed to operate with that heat-pump as a single package. In particular, the tank will often be controlled by a temperature sensor inserted through a pocket in the tank into the stored hot water. This temperature sensor is used by the heat-pump to inform the heat-pump's controller when the tank has finished heating. The heat-pump controller will typically control both the space heating provided by the heating system and the provision of hot water from the hot water tank.

In a system in which the water tank is designed to also operate without a heat pump (i.e. before a heat pump is retrofitted), typically the hot water tank will have its own control functionality which is independent the heat pump controller. As such, there may be interoperability challenges associated with the control system associated with the new heat pump system. These problems can lead to situations where a perfectly functioning hot water tank needs to be replaced with undue expense and disruption to the household.

The present disclosure aims to alleviate some or all of the aforementioned problems. Summary of the invention According to a first aspect there is provided a controller interface for interfacing between a hot water tank controller and a heat pump controller, the controller interface comprising: a response module configured to: receive, from a hot water tank controller, a first input signal indicative of a temperature; provide a response signal based on the first input signal and a temperature response characteristic; and communicate the response signal to a heat pump controller.

The controller interface can enable interoperability between a heat pump controller and a legacy hot water tank system and hot water tank controller, thereby enabling use of a legacy hot water tank system that might not otherwise be compatible with a heat pump system.

For robustness the response module may be an electrical circuit and an electrical property of the circuit is configured to vary in dependence on the first input signal and the temperature response characteristic.

For versatility the temperature response characteristic may be programmable, preferably via a user interface.

For interoperability the temperature response characteristic may comprise a temperature-resistance relationship profile.

zo For accuracy the temperature-resistance relationship profile may be modelled on a response of a temperature sensor associated with a heat pump.

For effectiveness the response signal is preferably a resistance of a circuit at the response module.

For versatility the response module may comprise a relay and a pair of potentiometers.

For simplicity the response module may comprise a plurality of fixed value resistors for connection of a subset to a relay.

For accuracy the response module may comprise a transistor configured to operate in dependence on the first input signal.

For ease of control the response module may be configured to vary the response signal between a number of discrete values, preferably between two values; or wherein the response module is configured to vary the response signal in a continuous range of values.

For enhanced interoperability the controller interface may further comprise an auxiliary heater control module configured to: receive, from the heat pump controller, a second input signal associated with an auxiliary heating requirement; and communicate, to the hot water tank controller, an instruction to operate an auxiliary heater in response to the second input signal.

For effectiveness the auxiliary heater control module may comprise a potentiometer and an analogue to digital converter.

The controller interface may be configured to communicate with the hot water tank controller via a digital communication protocol. The controller interface may be configured to communicate with the hot water tank controller via analogue signals.

For convenience the response module may be configured to communicate with the heat pump controller via a sensor cable of the heat pump controller.

For user convenience the controller interface may be further configured to receive a user hot water schedule and to vary the response signal based on the user hot water schedule.

According to another aspect there is provided a hot water tank controller configured to provide a first input signal to the controller interface as aforementioned.

According to another aspect there is provided a system for controlling a heating system comprising: the controller interface as aforementioned; and a hot water tank controller, optionally as aforementioned.

For accuracy the hot water tank controller may be configured to receive temperature measurements from one or more temperature sensors. For versatility the hot water tank controller may be configured to switch on an auxiliary heater.

For user convenience the hot water tank controller may be configured to receive a user hot water schedule and to vary the first input signal based on the user hot water schedule.

The system may further comprise a heat pump controller configured to control a heat pump in dependence on the response signal received from the controller interface.

According to another aspect there is provided a heating system comprising: the system for controlling a heating system as aforementioned; a hot water tank optionally comprising one or more of: an auxiliary heater disposed within the hot water tank; and a temperature sensor configured to measure a temperature of water in the hot water tank and a heat pump configured to heat water in the hot water tank via a heat exchanger.

For ease of retrofit the heating system may further comprise a diverter valve for diverting fluid from the heat pump to or from the heat exchanger, wherein the diverter valve is arranged to energise a pump of the heat exchanger.

According to another aspect there is provided a hot water tank comprising an inlet port and an outlet port arranged to receive a retrofit heat transfer module comprising a plate heat exchanger, wherein the inlet and the outlet are sealed for use in the absence of a retrofit heat transfer module.

According to another aspect there is provided a heating system comprising: the hot water tank as aforementioned; a retrofit heat transfer module comprising: a pump configured to draw water from hot water tank via the outlet port and return water to the tank via the inlet port; and a plate heat exchanger configured to heat water drawn from the second outlet.

For ease of retrofit the heating system may further comprise a heat pump with a diverter valve for diverting fluid to the heat transfer module, wherein the pump is controlled in dependence on the diverter valve.

The heating system may further comprise a hot water tank controller, wherein the pump is controlled in dependence on the hot water tank controller.

According to another aspect there is provide a hot water cylinder control system which can accommodate the retrofit of a future heat transfer module comprising of a plate heat exchanger, circulation pump and connection to a pump control signal either from a tank controller or a heat pump controller wherein the ports are blanked on initial install to await retrofit of heat transfer module.

The pump within the heat transfer module may be energised from a diverter valve which is powered by the heat pump control. The pump within the heat transfer module may be energised from a separate tank control system which operates in conjunction with the heat pump control system.

According to another aspect there is provide a hot water cylinder control system which is able to wrest control of the heating schedule associated with a hot water cylinder via a heat pump control interface by manipulating the apparent temperature readings that would otherwise be presented by a standard temperature sensor.

An additional direct electric detection circuit may be added so that the hot water tank control system is aware of any requirement that the heat pump control system has to use direct electric heating.

A temperature emulation circuit may be provided. The temperature emulation circuit may comprise a relay and potentiometer arrangement wherein discrete switching between resistance values is facilitated. The temperature emulation circuit may comprise an electronically controlled potentiometer which is capable of achieving or emulating a continuous change in resistance value.

A resistance temperature relationship may be programmed remotely into the hot water control system to reflect the heat-pump's anticipated temperature resistance relationship otherwise expected of a conventional temperature sensor which would otherwise be installed.

A direct electric detection circuit may comprise an isolated potentiometer and analogue to digital converter.

The tank controller may infer the point where direct electric heating is necessary via inference of the changing temperature or state of charge of the hot water tank by inspection of a single or plurality of temperature sensors.

The invention may provide a kit comprising the controller interface, system for controlling a heating system or any components of a heating system in any form above. The kit may comprise a set of instructions for assembling the components of the kit to make an apparatus or system described in any form above.

Method aspects/features may be implemented as system aspects/features or as apparatus aspects/features and vice-versa. Any feature in one aspect of the invention may be applied to other aspects of the invention, in any appropriate combination.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 illustrates a layout of a conventional heat pump and hot water tank control arrangement.

Figure 2 illustrates a system for controlling a heating system with tank controller and a separate heat pump controller and a controller interface.

Figure 3 shows, in more detail, a controller interface.

Figure 4 shows, in more detail, an example of a response module. Figure 5 shows, in more detail, another example of a response module.

Figure 6 shows a hot water tank with blanked ports that are ready to accommodate future retrofit of a heat transfer module.

Figure 7 shows a heat transfer module retrofitted to the hot water tank depicted in Figure 6.

Figure 8 shows a heat transfer module retrofitted to the hot water tank depicted in Figure 6.

Figure 1 shows the layout of a typical heating system comprising a heat pump arrangement with a hot water tank A6. In the case of a monobloc system (such as that illustrated), the heat pump Al supplies hot water via flow and return connections A3, A4 to a heat exchanger AO disposed in the hot water tank in order to heat the hot water inside the tank. The hot water tank takes cold water in through an inlet A7 (typically from a mains water supply) towards the bottom of the tank and discharges hot water through an outlet AS towards the top of the tank. A heat pump controller A2 determines the power output from the heat pump on the basis of a user schedule that has been programmed into the heat pump controller by a user. The user schedule specifies a (time-varying) hot water demand and/or a heating demand of the user.

The heat pump controller Al may be configured to receive data from one or more temperature sensors A9 in the hot water tank to ensure there is sufficient hot water to satisfy the user's hot water demand and thereby to inform its control of the power supplied to the heat pump.

The heat pump controller may also be configured to receive data from a one or more room temperature sensors A10 to monitor whether the heat pump is meeting the user's space heating demand. The output of the heat pump is typically routed either to satisfy space heating or hot water provision by a diverter valve A5 which may also be controlled by the heat pump controller.

In the illustrated arrangement, the tank also comprises an auxiliary heater All, for example, an electric heating element, disposed in the water tank. The heat pump controller may be configured to transition from heating water in the water tank from the heat pump to heating the water by the electric heating element All during cold conditions, or in any other scenario in which the heat pump is unable to attain a satisfactory operating temperature.

Figure 2 illustrates an arrangement in which a water tank B6 with an existing water tank controller B13 has been retrofitted with a heat pump B1. The water tank B6 may previously have been operating with a gas boiler (not shown) providing heat to the water in the tank B6. The water tank may comprise a gas boiler heat exchanger (not shown) that was previously coupled to the gas boiler. The water tank comprises an auxiliary heater B11, and one or more temperature sensors B9. The gas boiler and/or the auxiliary heater B11 are configured to be controlled by a tank controller B13. The one or more temperature sensors B9 are in communication with the water tank controller B13.

The auxiliary heater may be, for example, an electrical heater (such as one comprising a direct electrical immersion heating element) for heating water in the tank. This auxiliary heater may have been configured to provide additional heating in the water tank when the tank was operating with the gas boiler. It may be desirable for the user to be able to use the auxiliary heater B11 in a similar way with the new heat pump Bl. The power delivered to the auxiliary heater B11 is controlled by the tank controller B13.

The plurality of temperature sensors B9 are configured to make temperature measurements of the water in the water tank. In the illustrated example, the temperature sensors are arranged in a linear array extending vertically along a side wall of the water tank B6. The temperature measurements made by the temperature sensors B9 are transmitted, via a wired or wireless connection, to the tank controller B13.

The tank controller B13 controls the operation of the auxiliary heater and may be configured to control the operation of the legacy gas boiler. The tank controller B13 may provide a user interface by which a user may program a user schedule which specifies the hot water and/or heating requirements of the user. The tank controller is configured to operate gas boiler and/or the auxiliary heater in dependence on the user schedule. The tank controller receives the temperature measurements from one or more temperature sensors of the hot water tank, so that it can monitor the temperature of the water or the state of charge of the hot water tank and operate the gas boiler and/or auxiliary heater in order to ensure that the water temperature(s) in the tank are adequate to meet the user requirements in accordance with the user schedule.

The heat pump B1 is arranged to provide heat to the water in the hot water tank. The heat pump may have been retrofitted to the hot water tank B6. Fluid is circulated between the heat pump B1 and a heat exchanger BO through which the water in the tank is heated. The heat exchanger BO may be disposed within the hot water tank (as in the examples of Figure 1 and Figure 2), or may be disposed outside the hot water tank (as illustrated in Figure 6 and Figure 7) and heat water drawn from the hot water tank before it is returned in its heated state to the hot water tank.

A heat pump controller B2 is provided and configured to operate the heat pump 31. Typically, the heat pump controller B2 is configured to communicate with the heat pump and one or more temperature sensors of the hot water tank and/or temperature sensors 310 arranged in spaces to be heated by the heating system. A typical heat pump controller may also be configured to control an auxiliary heater in a hot water tank in addition to the heat pump. However, since the temperature sensors B9 and auxiliary heater B11 of the legacy hot water tank B6 are already configured to communicate with the tank controller, it may be advantageous to be able to interface the heat pump controller with the hot water tank controller rather than, or in addition to, having to rewire or replace the temperature sensors and auxiliary heater such that they are operable by the heat pump controller.

A diverter valve B5 is arranged between the heat pump and the hot water tank. The diverter valve is controlled by the heat pump controller to allow the heating system to switch between hot water heating and space heating.

A controller interface 312 provides an interface between the tank controller 313 and the heat pump controller 32. The controller interface is configured to be in communication with both the tank controller and the heat pump controller.

The controller interface 312 receives signals from the tank controller associated with the temperature measurements made by the one or more temperature sensors in communication with the tank controller.

The controller interface 312, from the point of view of the heat pump controller, mimics a temperature sensor associated with the heat pump, for example, the temperature sensor that would typically be installed with a hot water tank that was provided new with the heat pump. Accordingly, the heat pump controller receives the same signal it would have received if it had been connected directly to a temperature sensor, rather than being connected to a controller interface. The controller interface emulates a temperature sensor for the heat pump controller based on a signal received from the tank controller.

More generally, the existing tank controller, the heat pump controller and the controller interface describe together a system for controlling a heating system in which the tank controller is configured to control the operation of a water tank, and the heat pump controller is configured to control the operation of a heat pump, and the controller interface is provided in order for the controllers to be interoperable.

Figure 3 depicts, in more detail, the controller interface 01. The controller interface 01 comprises a response module C2 which receives an input signal C6 from the tank controller associated with a temperature measurement, preferably a temperature measurement of a temperature sensor of the hot water tank. The response module 02 generates a response signal 04 in dependence on this input signal and communicates the response signal to the heat pump controller. The heat pump controller then controls the heat pump in dependence on the received response signal 04. In essence, the controller interface is configured by the response module to 'trick' the heat pump controller to respond as if it were connected to a temperature sensor.

The controller interface may be connected to the tank controller via a control wire. The controller interface is configured to communicate with the tank controller via a digital communication protocol, such as RS485 RS232, MODBUS, CANBUS, I20 or any other suitable communication architecture. In an alternative the controller interface and the tank controller may be connected wirelessly. Alternatively an analogue approach may be used where a continuous voltage is communicated by the tank controller to the controller interface.

The controller interface is configured to communicate with the heat pump controller via a sensor cable of the heat pump controller which is configured to carry a signal from a temperature sensor associated with the heat pump to the heat pump controller.

The response module 02 is preferably an electrical circuit which transforms the input signal from the tank controller in dependence on a temperature response characteristic to produce a response signal to be sent to the heat pump controller. While the response signal may be configured to mimic the signal which might be sent by the heat pump's preferred sensor type (say, A9 in Figure 1), in another example, the temperature response characteristic may comprise simply an indication that an input signal corresponds to a "cold" temperature (i.e. a temperature below a certain threshold) or an indication that the input signal corresponds to a "hot temperature" (i.e. a temperature above or equal to a certain threshold). The response signal may then be an electrical signal which indicates a cold temperature measurement (which might correspond to a signal associated by the heat pump controller with a specific low temperature, e.g. 15°C) or an electrical signal which indicates a hot temperature (which might correspond to a signal associated by the heat pump controller with a hot temperature, e.g. 70°C). The detection of such temperature measurements by the heat pump by cause the heat pump to turn on and off respectively.

The response module may comprise a variable resistor that is able to change its resistance value between two widely separated resistance values (or more generally between discrete resistance values) to exhibit a binary high or low state depending on whether the tank controller requires the heap pump controller to receive a signal indicating the tank is hot or cold. The response signal communicated to the heat pump controller may then be interpreted as would a signal from a temperature sensor indicating a low temperature in the hot water tank (indicating that the heat pump should be switched on to deliver heat to the hot water tank) or as a signal from a temperature sensor indicating a high temperature, indicating that the heat pump may be switched off or dialled down. In particular, the response module C2 may comprise a circuit comprising a relay and pair of potentiometers which switch between two discrete resistance values.

In an alternative, the temperature response characteristic of the response module may comprise a mapping between a temperature indicated by the tank controller in the input signal and a response signal which permits a continuously varying signal, or a signal varying between a plurality of discrete intervals such that the heat pump controller perceives a reflection of the true temperature within the hot water tank. The response signal may then mimic the desired 'apparent resistance' to the heat pump controller such as the heat pump controller would receive from its usual temperature sensor. In such a scenario, the response module 02 may comprise a digitally controlled potentiometer circuit which is capable of approximating a continuous resistance output. 02 may also be implemented by transistor whose gate current (bipolar) or voltage (MOSFET) may be modulated to vary the apparent resistance between its drain-source connections in a continuous fashion. It will be appreciated that such an arrangement is also suitable for implementing the binary "hot/cold" example above and vice versa.

In some instances the heat pump controller may be floating at a potential that is distinct from the tank controller. In such cases suitable isolation circuitry at the interface module is appropriate. Alternatively the requirement for isolation circuitry might avoided by providing an array of fixed-value resistor pairs such that a circuit is formed with an appropriate fixed-value resistor pair, and in operation one or the other fixed-value resistor can be connected to the heat pump controller using a relay switch.

Two exemplary response modules 02 are schematically shown in Figures 4 and 5. In Figure 4 a relay and pair of potentiometers are provided to switch between two discrete resistance values, as described above. In Figure 5 a plurality of fixed resistor pairs is provided, of which two are connected to a switching relay via a patch cable; a jumper wire or selector switch may alternatively provide connection. The fixed resistor pairs in Figure allow for different heat-pump models -which may each require different resistance values -to be catered for. In the example illustrated in Figure 5 an optional a pair of adjustable potentiometers is included to accommodate a heat pump model for which none of the fixed value resistors are suitable.

The controller interface may also comprise an auxiliary heater interface module 03 which may permit the heat pump controller to control an auxiliary heater coupled to the tank controller via the interface.

Typically, the heat pump controller is configured to control the power delivered to an auxiliary heater disposed within a hot water tank to supplement the heating provided by the heat pump via the heat exchanger. The heat pump controller is thus typically provided with an auxiliary heater control cable 05. In the present case, in which an auxiliary heater already exists in the tank coupled to the tank controller it is advantageous for the heat pump to be able to control the auxiliary heater via the controller interface and the tank controller.

The auxiliary heater interface module 03 of the controller interface Cl may thus be in electrical communication with the heat pump controller via the auxiliary heater control cable C5. If the heat pump needs to transition to resistive heating via the heating element within the tank, then the auxiliary heater interface module 03 will detect the appearance of a switched live signal or digital command from the heat pump's auxiliary heater control cable 05. In order to detect the direct electric signal from the heat pump controller, the auxiliary heater interface module 03 may comprise a detection circuit which may comprise an (isolated) potentiometer and analogue to digital converter which is capable of withstanding mains voltages. The controller interface Cl can provide a signal 07 to the tank controller indicating that the auxiliary heater should be switched on. The controller interface Cl may suppress a signal for switching the auxiliary heater on, for example if a user hot water schedule is specified at the controller interface. The tank controller may override the signal and not switch the auxiliary heater on, or it may respond, depending on the control strategy at the tank controller.

In the example shown in Figure 3 the signal 07 concerning the auxiliary heater and the input signal 06 are shown as separate channels. If communication between the controller interface and the tank controller is via a digital communication protocol as described above, then signal C7 and signal C6 can be provided in a common communication link instead.

The controller interface may also comprise a user interface by which a user can program a temperature response characteristic in the user interface. This may allow a user or installer of the interface to program a temperature response characteristic into the response module in dependence on the type of tank controller, temperature sensors, heat pump, auxiliary heaters, and any other relevant information. The controller interface may also permit a user to program a user schedule specifying their heating requirements.

The response signal 04 may reflect the apparent temperature that might be expected within the range of operation associated with the heat pump's usual hot water tank temperature sensor. The heat pump may have been provided with a temperature sensor that is configured specifically for use with the heat pump, but may not be required if the heat pump is retrofitted to an existing hot water tank. A disconnection of the original temperature sensor provided for the heat pump may lead to a fault code being flagged within the heat-pump's control logic. The response signal 04 from the controller interface can replace the expected temperature sensor signal received by the heat pump controller's sensor cable such that the fault-code is not generated. In addition, the actual temperature of the tank may provide useful information to the heat pump controller so that it is running its compressor at an optimal output level. However, since different heat pumps can use different temperature sensor types which exhibit different resistance/temperature relationships, the controller interface may be programmable with a bespoke temperature/resistance relationship to reflect the temperature response characteristic of the original sensor in conjunction with which the heat pump is originally configured to operate.

In use, the controller interface in cooperation with the tank controller and the heat pump controller may enable the tank controller to separately control the hot water tank whilst satisfying the required control logic of the heat pump controller. In order for the tank controller to do so, the heat pump controller may be configured such that hot water is demanded at all times (for example, via a user schedule programmed into the heat pump interface). The tank controller via the interface controller can then provide a signal to the heat pump that causes the heat pump to provide heat, or not. For example, if the user schedule requires water heating and the tank water temperature is low, then the response signal C4 causes the heat pump to provide heat (i.e. a suitable signal emulating a low temperature from a sensor). On the other hand if the user schedule does not require water heating, even if the tank water temperature is low, then the response signal 04 is such that the heat pump does not provide heat (i.e. a suitable signal emulating a high temperature from a sensor). The response signal C4 can in this way cause the heat pump to vary heat provided to the hot water tank. The tank controller may modify the input signal C6 depending on the user schedule, or the controller interface may modify the response signal 04 depending on the user schedule.

In use, typically, the heat pump controller will determine whether to switch from the heat pump to an auxiliary heater on the basis of either (a) a drop in heat pump efficiency (as determined through the sensors and controller logic specific to the heat pump) or (b) failure to attain a sufficient temperature in the hot water tank. If the controller interface has been configured to provide the heat pump controller with an accurate reflection of the actual temperatures associated with the temperature sensor or sensors in the hot water tank, then the heat pump controller may be able to operate as normal. In the case where the temperature response characteristic of the response module is such that it, for example, switches between two widely separated resistances (and does not vary continuously, or in small discrete intervals to provide an accurate reflection of the water temperature), then the operation of the auxiliary heater may need to remain under the control of the tank controller which itself infers when the heat pump controller wishes to transition to the use of the auxiliary heater. The auxiliary heater control module 03 of the controller interface may be responsible for making such an inference. The inference may be based on a signal from the heat pump controller and/or in dependence on the temperature measurements known to the tank controller. The responsibility for operation of the auxiliary heater may therefore be passed on to the tank controller.

Figure 6 illustrates a hot water tank which is configured to operate with a gas boiler and/or an auxiliary heater and is also is configured to receive a retrofit of a heat pump. The hot water tank has a first inlet for drawing cold water into the tank disposed towards the bottom of the tank and a first outlet towards the top end of the tank for drawing out hot water from the tank. Where the tank is configured to be operable in conjunction with a gas boiler, a gas boiler heat exchanger may be provided disposed within the tank to transfer heat from the gas boiler to the water in the hot water tank. Typically, a gas boiler heat exchanger is not suitable to be used with a heat pump, since a heat pump usually requires a larger heat exchanger since the heat pump operates with lower power than a high temperature boiler. The heat exchanger illustrated in Figure 6 is therefore sized to accommodate a high temperature gas boiler. It may not be feasible or desirable to also provide a heat exchanger sized for a heat pump (which may be expensive and occupy, when provided alongside the gas boiler heat exchanger, too great a volume of the hot water tank) when it is not certain that a heat pump will ever be installed.

A user may wish to utilise a water tank with a gas boiler and/or an auxiliary heater initially, and upgrade later to use a heat pump with that same water tank. As such, the hot water tank of Figure 6 is provided with an additional inlet port D1 and outlet port D2, both of which are sealed (also referred to as blanked) by blanking plugs D3, D4. The outlet port is suitable for drawing water out of the hot water tank to be heated external to the tank by a heat pump. The inlet port is suitable for returning the heated water to the tank. This blanked arrangement is ready to accommodate a retrofitted heat pump as depicted in Figure 7. The plugs may be in any form conventionally used to seal such ports. The plugs are intended to be removable but until such time as they are removed, which may be several years, they ensure that the ports remain sealed.

Figures 7 and 8 illustrate heating systems with a retrofit heat transfer module El which has been connected to the previously blanked inlet and outlet port of the hot water tank, which have been unblanked to permit installation of the heat transfer module.

In the example illustrated in Figure 7 a heat pump is connected to the hot water tank of Figure 6 to provide a heating system similar to the one shown in Figure 1. The retrofit heat transfer module El comprises a circulation pump E2 configured to draw water from the hot water tank through the outlet port and return water to the hot water tank through the inlet port. The water drawn from the tank is passed through a heat exchanger (preferably, a plate heat exchanger) of the heat transfer module which is coupled to a heat pump in order to heat the drawn water before it is returned to the hot water tank.

The heat transfer module El is controlled through the auxiliary power supplied to the diverter valve (A5 from Figure 1); the power turns on a pump E2 which circulates water from the hot water tank through the plate heat exchanger E3. The other side of the plate heat exchanger accommodates flow and return connections E5, E6 from the heat pump. In the illustrated example the controller interface and the legacy tank controller are not used, and instead the heat pump controller is suitably connected to a temperature sensor and auxiliary heater.

In an alternative arrangement, illustrated in Figure 8, a heat pump is connected to the hot water tank of Figure 6 to provide a heating system similar to the one shown in Figure 2. In this example the controller interface and the tank controller are used as described with reference to Figures 2 and 3. A heat transfer module El as described above is controlled directly by the hot water tank control (B13 in Figure 2) which is able to energise the circulator pump E2 so that flow through the plate exchanger occurs whilst the flow and return connections are supplied with hot water from the heat pump. An optional temperature sensor E7 is provided so that the tank control system can choose to energise the pump once the heat pump has attained a sufficient temperature.

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

For example, the controller interface is described in the examples provided above as being a separate entity from the hot water tank controller. Alternatively the controller interface may be integrated in the hot water tank controller such that an emulated temperature sensor signal is provided from the hot water tank controller to the heat pump controller.

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

Claims

Claims: 1. A controller interface for interfacing between a hot water tank controller and a heat pump controller, the controller interface comprising: a response module configured to: receive, from a hot water tank controller, a first input signal indicative of a temperature; provide a response signal based on the first input signal and a temperature response characteristic; and communicate the response signal to a heat pump controller.
2. The controller interface of claim 1 wherein the response module is an electrical circuit and an electrical property of the circuit is configured to vary in dependence on the first input signal and the temperature response characteristic.
3. The controller interface of claim 1 or claim 2 wherein the temperature response characteristic is programmable, preferably via a user interface.
4. The controller interface of any preceding claim wherein the temperature response characteristic comprises a temperature-resistance relationship profile.
The controller interface of any preceding claim wherein the temperature-resistance relationship profile is modelled on a response of a temperature sensor associated with a heat pump.
6. The controller interface of any preceding claim wherein the response signal is a resistance of a circuit at the response module.
7. The controller interface of any preceding claim, wherein the response module comprises a relay and a pair of potentiometers.
8. The controller interface of any preceding claim, wherein the response module comprises a plurality of fixed value resistors for connection of a subset to a relay.
9. The controller interface of any preceding claim wherein the response module comprises a transistor configured to operate in dependence on the first input signal.
10. The controller interface of any preceding claim wherein the response module is configured to vary the response signal between a number of discrete values, preferably between two values; or wherein the response module is configured to vary the response signal in a continuous range of values.
11. The controller interface of any preceding claim further comprising an auxiliary heater control module configured to: receive, from the heat pump controller, a second input signal associated with an auxiliary heating requirement; and communicate, to the hot water tank controller, an instruction to operate an auxiliary heater in response to the second input signal.
12. The controller interface of claim 11 wherein the auxiliary heater control module comprises a potentiometer and an analogue to digital converter.
13. The controller interface of any preceding claim wherein the controller interface is configured to communicate with the hot water tank controller via a digital communication protocol or via analogue signals.
14. The controller interface of any preceding claim wherein the response module is configured to communicate with the heat pump controller via a sensor cable of the heat pump controller.
15. The controller interface of any preceding claim wherein the controller interface is further configured to receive a user hot water schedule and to vary the response signal based on the user hot water schedule.
16. A hot water tank controller configured to provide a first input signal indicative of a temperature to the controller interface according to any preceding claim.
17. A system for controlling a heating system comprising: the controller interface according to any of claims 1 to 15; and a hot water tank controller, optionally according to claim 16.
18. The system of claim 17 wherein the hot water tank controller is configured to receive temperature measurements from one or more temperature sensors, optionally wherein the hot water tank controller is configured to switch on an auxiliary heater.
19. The system of claim 17 or claim 18 wherein the hot water tank controller is configured to receive a user hot water schedule and to vary the first input signal based on the user hot water schedule.
20. The system of any of claims 17 to 19 further comprising a heat pump controller configured to control a heat pump in dependence on the response signal received from the controller interface.
21. A heating system comprising: the system for controlling a heating system of claim 20; a hot water tank optionally comprising one or more of: an auxiliary heater disposed within the hot water tank; and a temperature sensor configured to measure a temperature of water in the hot water tank; and a heat pump configured to heat water in the hot water tank via a heat exchanger.
22. The heating system of claim 21 further comprising a diverter valve for diverting fluid from the heat pump to or from the heat exchanger, wherein the diverter valve is arranged to energise a pump of the heat exchanger.
23. A hot water tank comprising an inlet port and an outlet port arranged to receive a retrofit heat transfer module comprising a plate heat exchanger, wherein the inlet and the outlet are sealed for use in the absence of a retrofit heat transfer module.
24. A heating system comprising: the hot water tank of claim 23; a retrofit heat transfer module comprising: a pump configured to draw water from hot water tank via the outlet port and return water to the tank via the inlet port; and, a plate heat exchanger configured to heat water drawn from the second outlet.
25. The heating system of claim 24 further comprising a heat pump with a diverter valve for diverting fluid to the heat transfer module, wherein the pump is controlled in dependence on the diverter valve.
26. The heating system of claim 24 further comprising a hot water tank controller, wherein the pump is controlled in dependence on the hot water tank controller.