Hot water supply system

Abstract

A hot water supply system (HWSS) (400) includes a cabinet that is a substantially sealed enclosure. The cabinet contains an insulated thermal energy reservoir (406) for connection (414, 416) to a heat pump (not shown). Water from the cold water inlet (408) is directed through a valve (418, 422) to the energy store or auxiliary heater (420). Under the control of a controller (430), the valves and auxiliary heaters are controlled by power semiconductor devices (424, 426) and (428) themselves. The heat dissipated by the power semiconductor device is diverted by baffles (426, 428) and / or fans (434) to reduce the temperature difference between the energy store (406) and the air around the energy store, thereby reducing energy loss.

Description

Technical Field

[0001] The present invention relates to a hot water supply system (HWSS), and more particularly, to a hot water supply system used in conjunction with a heat pump using a heat energy storage device. Background Art

[0002] Households and small commercial premises typically meet their hot water needs through gas boilers or furnaces. Either the water is heated and stored in some kind of tank, or the water is heated on demand when a hot water tap (cock) is opened within the premises. With increasing concerns about the environmental damage caused by burning fossil fuels, attention has turned to alternative technologies for providing hot water, such as heat pumps.

[0003] Heat pumps use refrigeration technology to extract heat from a lower temperature source and transfer that heat to a higher temperature source. For example, a heat pump can extract heat from air at, say, 15 degrees Celsius and heat water to a temperature of, say, 50 degrees Celsius. Such a heat pump is called an air source heat pump, although water source heat pumps and ground source heat pumps are also available and work on the same principle. Although operating a heat pump requires energy (usually electrical energy), the efficiency of a heat pump can be up to four times or more that of, for example, an electric heater.

[0004] However, heat pumps are not suitable for providing instant hot water, such as when a user turns on a tap. Specifically, heat pumps have limitations in terms of startup speed and startup frequency. It may take more than a minute for a heat pump to turn on, perform self-checks, and actually provide hot water. This is unacceptable for a user who wants hot water for handwashing for 20 seconds. Additionally, a heat pump typically cannot be started more than six times per hour and may be unavailable during periods such as defrost cycles.

[0005] To address these issues, the present applicant has developed a heat storage device as described in a UK patent application filed on 7 February 2021. The heat storage device uses a phase change material, such as paraffin wax, to store energy in a highly space-saving manner by utilizing a material that changes from solid to liquid (and vice versa) at relevant temperatures. A heat pump is used to heat an energy storage unit containing the phase change material to the temperature at which the material changes from solid to liquid. This phase change absorbs a large amount of energy, which can then be recovered when a single tap is opened without starting the heat pump. Using a phase change material makes the energy storage unit very compact, i.e., for its size, it can store a large amount of energy. Cold water from the mains supply is fed through the energy storage unit to provide a smaller quantity of hot water (e.g., sufficient for a shower). The heat pump is started to meet long-term hot water demands, but even in this case, the energy storage unit is used to provide hot water until the heat pump is fully operational.

[0006] One difficulty with such a device is heat loss from the energy storage unit. Such devices typically operate at around 50 °C (i.e. approximately 30 °C higher than the ambient temperature in most households). The demand for hot water is often very intermittent, with peaks in the morning and evening and little demand during the day and at night. This means that the energy storage unit is prone to heat loss over a relatively long period of time. Of course, the storage unit is insulated, but the amount of insulation that can be included in the hot water supply system, which is typically sized to replace an existing gas boiler, is limited. Summary of the Invention

[0007] The object of the present invention is to improve this problem.

[0008] According to a first aspect of the present invention, there is provided a hot water supply system located in a cabinet, the hot water supply system comprising:

[0009] a thermal energy storage unit for storing energy received from a heat pump, the energy storage unit comprising a first layer of insulating material;

[0010] a heat pump supply connection and a heat pump return connection, the heat pump supply connection and the heat pump return connection being connected to the thermal energy storage unit;

[0011] a cold water inlet and a hot water outlet, the cold water inlet being coupled to the energy storage unit and the hot water outlet being coupled to the thermal energy storage unit;

[0012] a controller;

[0013] a heat generating component; and

[0014] an air flow guiding device arranged to guide air from near the heat generating component to near the thermal energy storage unit, thereby reducing the temperature difference between the energy storage unit and the air surrounding the energy storage unit.

[0015] The arrangement of the hot water supply system within the cabinet is designed to maintain the internal temperature within the housing, particularly the internal temperature around the energy storage unit, above the ambient temperature. By reducing the temperature difference between the thermal energy storage unit and the surrounding air (within the cabinet), heat loss from the energy storage unit will be reduced. The thermal energy storage unit preferably comprises a phase change material in order to store energy in a space-saving manner.

[0016] The internal temperature of the cabinet will increase due to heat loss from the energy storage unit, but also due to heat dissipated by other heat generating components such as power electronics for controlling auxiliary heaters. Thyristors or triacs are also typically used to start and stop the heat pump, control electrically controlled valves, etc. These devices are preferably provided with heat sinks.

[0017] The air flow guiding device preferably includes at least one baffle. One or more baffles can be positioned to utilize the convection within the cabinet.

[0018] Alternatively or additionally, the air flow guiding device can include at least one duct.

[0019] According to a preferred embodiment, the air flow guiding device includes at least one fan. The fan is preferably under the control of a controller, and the controller starts and stops the fan in response to the output of a temperature sensor.

[0020] According to another preferred embodiment, a second fan is arranged to distribute cooling air to the heat generating devices. This will provide a safety feature if the heat generating devices become overheated.

[0021] The second fan can rely on the cooling air from the cold water inlet, and the cold water inlet can be provided with at least one vane in the air path from the second fan.

[0022] Alternatively or additionally, the cooling air is obtained from outside the cabinet.

[0023] In many embodiments, the heat generating devices include power semiconductor devices. These devices are preferably provided with heat sinks.

[0024] To minimize the heat loss from the energy storage, the cabinet is preferably substantially airtight. The cabinet also preferably includes a layer of insulating material.

[0025] To better manage the air flow within the cabinet, the cabinet is preferably provided with holes towards its bottom, and the holes can be opened and closed under the control of a controller. To further manage the air flow within the cabinet, the cabinet can be provided with holes towards its top, and the holes can be opened and closed under the control of a controller.

[0026] To best manage the resources stored in the energy storage, the HWSS is preferably provided with at least a first electrically controlled valve and a second electrically controlled valve. The first electrically controlled valve is arranged to control the water flow through the energy storage, and the second electrically controlled valve is arranged to control the water flow through the auxiliary heater. To perform this control, the controller is arranged to determine the relative flow rates of the water through the energy storage and the auxiliary heater. The controller is preferably also arranged to start and stop the heat pump. Description of the Drawings

[0027] The present invention will now be described by way of example with reference to the accompanying drawings, in which:

[0028] Figure 1 A schematic diagram of an HWSS to which embodiments of the present invention can be applied is shown;

[0029] Figure 2 A perspective view of an HWSS cabinet according to an embodiment of the present invention is shown;

[0030] Figure 3 shows a graphical representation of a HWSS according to an embodiment of the present invention; and

[0031] Figure 4 shows a graphical representation of another embodiment of the HWSS. DETAILED DESCRIPTION

[0032] Figure 1 Schematically illustrates a facility according to a first aspect of the present disclosure. The facility 100 includes a hot water supply system (HWSS) within a building represented by block 110 and a heat pump 120 (which will typically be located outside the building), the heat pump 120 being arranged to heat the water in the HWSS 110. The HWSS includes at least one outlet 130, such as a faucet or shower outlet. The HWSS also includes an energy storage device (ESA) 140 that contains a large amount of phase change material (PCM). A processor 150 (which may also be referred to as a system controller) is arranged to provide a signal to the heat pump 120 based on the opening of an outlet (such as outlet 130) of the hot water system, where appropriate.

[0033] The large amount of phase change material has a sufficient latent heat capacity to heat a predetermined amount of water to a predetermined temperature within an interval from the opening of the outlet of the hot water supply system to at least the start of the heat pump heating the water in the hot water supply system. Phase change materials (such as paraffin wax having a phase change temperature of 50 °C) are suitable, but alternative and suitable combinations of materials will be apparent to those skilled in the art.

[0034] The HWSS 110 is supplied with water to be heated, for example, from a cold water supply 160, and at least one flow sensor 170 is included in the flow path between the supplier of the water to be heated and at least one outlet 130. Preferably, the heat pump is arranged to heat the water in the HWSS by a closed-loop arrangement, which is schematically indicated by a pipe system 190, and the supplier of the water to be heated is directly connected to the HWSS, as shown by the pipe system 200. The flow sensor 170 may be located on the supply side of the hot water system or on the outlet side of the entire system. The HWSS is provided with at least one temperature sensor 210. If only a single temperature sensor 210 is provided, this temperature sensor should be in the flow path between the energy storage device 140 and at least one outlet 130.

[0035] The HWSS 110 also includes an on-demand auxiliary water heater 220 in the flow path between the energy storage device 140 and at least one outlet 130. When an on-demand water heater 220 is included in the HWSS, a temperature sensor is preferably included in the flow path between the energy storage device and the on-demand water heater, and a temperature sensor is included between the on-demand water heater and at least one outlet 130. The on-demand water heater 220 is preferably an electric heater.

[0036] The processor 150 is coupled to the flow sensor 170, the memory 151, each temperature sensor 210, and the heat pump. Additionally, one or more sensing devices in the ESA are preferably coupled to the processor such that the processor is aware of the state of the ESA. The processor 150 is also connected to the on-demand water heater 220.

[0037] For a preferred configuration in which the heat pump heats the water in the HWSS via a closed-loop arrangement, a heat exchanger (not shown) receives the liquid heated by the heat pump on one side and the water to be heated in the HWSS on the other side. Preferably, the heat exchanger forms part of the ESA. Preferably, the heat exchanger includes some or all of a large amount of phase change material.

[0038] As Figure 1 shown, due to its size, the heat pump is typically located outside the building housing the HWSS. The heat pump, whether installed outside or inside the building, typically takes 30 to 60 seconds to start providing heat after receiving a start signal. This is because the internal processor of the heat pump typically has to check several components and subsystems, and also because of the inherent lag in starting the compressor and pump of the heat pump, etc. Even after the heat pump starts, there is of course an inevitable delay before the heat from the heat pump reaches the HWSS. Similarly, it takes some time to transfer heat between the hot liquid supplied by the heat pump and the water to be heated in the HWSS through any heat exchanger. Additionally, the heat pump is typically also configured to avoid starting more than 6 times per hour (this depends on the manufacturer, but the data is similar between manufacturers), and the processor 150 of the system will be aware of this constraint applicable to the connected heat pump and will also know its own history of sending start commands - and incorporate this information into its decisions regarding the management of the various heat sources available to it.

[0039] The processor 150 of the HWSS is configured to provide a start signal to the heat pump based on a signal received from the flow sensor 170. As described above, the facility is configured such that there is a time interval between providing the start signal to the heat pump and heating the water in the hot water system by the heat pump. This means that, in the absence of hot water storage or some other hot water source, turning on a faucet or shower supplied by the HWSS requires waiting a long time, well over a minute, for hot water to flow out of the outlet. This is frustrating for the user and a significant waste of water. The wait for hot water can be shortened by using an on-demand water heater until the hot water exits the heat pump. However, with this arrangement, assuming that most instances of hot water usage from the faucet (as opposed to the shower) are less than 60 to 90 seconds, most of the hot water used will come from the on-demand water heater (electric or gas-powered), and thus the green energy benefits of the heat pump will be largely lost.

[0040] The processor 150 can modulate the power output of the electrical component 220 based on a value received from the temperature sensor 210 to achieve the correct target temperature at the outlet 130.

[0041] The ESA is provided as a means of bridging the gap between the hot water demand (i.e., turning on the faucet or shower control) and the delivery of hot water heated by the heat pump. The system is preferably configured such that the ESA is filled with energy from the heat pump. Using the temperature information from the temperature sensor 210 and the flow information from the flow sensor 170, the processor 150 is configured to preferentially use the ESA to heat the water supplied through the outlet 130. In this way, the processor 150 minimizes its use of the on-demand water heater 220.

[0042] Accordingly, the processor is configured to provide a start signal to the heat pump based on a signal received from the flow sensor, the facility is arranged such that there is a time interval between providing the start signal to the heat pump and heating the water in the hot water system by the heat pump, the energy storage device contains a large amount of phase change material having a latent heat capacity sufficient to heat at least a predetermined amount of water in the hot water system to the target temperature until the water in the hot water system is heated by the heat pump so that hot water can be supplied from the controllable outlet during the interval between sending the start signal and heating the water in the hot water system by the heat pump. The target temperature can be set based on the preferences of the system user but is typically between, say, 40 to 45 degrees Celsius. The predetermined amount can be based on the desired duration of supplying water at a certain flow rate, which is selected based on the normal flow rate of the outlet of the HWSS having the highest flow rate or a lower flow rate that is considered sufficient and acceptable. The system and the processor are preferably configured to allow these two variables (temperature and amount) to be adjusted within preset limits (the preset limit values may be adjusted during system installation).

[0043] Information from the flow sensor 170 can tell the processor 150, for example, whether the outlet that has been opened is a shower outlet or a washbasin outlet. If the processor 150 determines that the shower outlet has been opened, the processor 150 will send a start signal to the heat pump because it is worth starting the heat pump within the few minutes that a shower typically takes. Conversely, if the flow rate information supplied to the processor 150 indicates that the washbasin faucet has been opened, the processor will determine not to send a start signal to the heat pump because it is unlikely that the heat pump can provide hot water before the washbasin faucet is closed again.

[0044] The processor 150 can be associated with a logic system (such as a machine learning algorithm) that enables the processor to learn the behavior of the occupants of the premises served by the HWSS, so as to be able to create a database from which the processor 150 can reliably predict the amount and duration of hot water demand / usage based on the time of day, day of the week, outlet used, etc. This can be enhanced, for example, by providing additional flow sensors associated with different outlets of the HWSS, some or all of these flow sensors, and preferably at least capable of easily distinguishing outlets with short-term hot water demand (such as bathroom washbasins) from outlets with long-term hot water demand (such as showers and kitchen sinks). Additionally, by providing one or more flow sensors in the cold water supply, cold water usage corresponding to flushing the toilet can be identified, from which, for example, an urgent demand for hot water for a short supply for handwashing can be inferred. The system processor 150 is preferably provided with a logic system in order to control all kinds of heating devices (ESA, instantaneous water heater, and heat pump) in the most efficient, economical, and effective way.

[0045] It can be considered that the ESA 140, heat exchanger, processor 150, instantaneous water heater 220, and flow sensor 170 and temperature sensor 210 together constitute an interface unit 250 that interfaces between the heat pump 120 and the hot water system 110 in the building. Figure 1 This interface unit for heating only the water in the hot water system in the building is shown, but it should be understood that in many parts of the world, space heating is required in many buildings, and using a heat pump for this space heating is attractive.

[0046] Typically, even current combination boilers used in small homes are large enough to provide 24 kW and more of hot water, which is equivalent to shower or bath flow rates, but typical space heating energy demands are much lower (usually around 4 kW). If a system is designed where domestic hot water (DHW) and space heating are both provided only by a heat pump, a 24 kW heat pump would need to be specified to meet the DHW demand, but for typical 1 - to 3 - bedroom apartments and homes, such a system would be impractically large as these apartments and homes mostly require space heating and use hot water only intermittently.

[0047] Figure 2 A perspective view of the HWSS 200 according to an embodiment of the present invention is shown. The HWSS is contained within a cabinet 202. The cabinet has pipe connections for the supply pipe 204 and the return pipe 206 of a heat pump (not shown) on its sides. Heat from the heat pump is used to heat water from the cold main 208 to provide a hot water output 210. The cabinet 202 is completely airtight except for a small hole 212 in one corner of its bottom. Since the air temperature (and thus the air volume) within the cabinet may vary, a hole may be required, but the hole is designed to be as small as possible to minimize heat loss within the cabinet.

[0048] Although the figure shows the locations of various pipe fittings, those skilled in the art will understand that these pipe fittings can be located at other points on the cabinet. Although the small hole is located on the bottom of the cabinet, it can be located on one of the other panels, or even omitted, as long as when the small hole is present, it is oriented towards the bottom of the cabinet.

[0049] Figure 3 A front schematic view of the HWSS 300 located within a six - sided rectangular cabinet 302 is shown, with the front panel of the cabinet 302 removed to illustrate the embodiment. The cabinet has an insulation layer 304 and is airtight except for a small hole 312 in the bottom panel. The heat or energy storage apparatus (ESA) 306 has a send connector 314 for receiving a heating fluid from the heat pump and a return connector 316 for returning the fluid to the heat pump (not shown). In an indirect sense, the ESA is heated by a heat exchanger within the ESA. The HWSS has a cold water inlet 308 from a water tank or the mains water and a hot water outlet 310. Heat from the ESA can be transferred to the water from the cold water inlet using another heat exchanger within the ESA.

[0050] The cold water inlet is connected to a temperature sensor 318 that provides a temperature value to a controller 320. The controller is also informed of the energy storage level in the ESA and can determine whether the ESA can adequately heat the water from the cold water inlet. If the answer is no, the controller can activate an auxiliary heater 322 via a power semiconductor device 324, such as a triac or thyristor. The device 324 preferably has a heat sink to transfer the heat dissipated in the device to the surrounding air. The auxiliary heater is an electric heater arranged between the output of the ESA and the hot water outlet of the HWSS. The power semiconductor device 324 is located below the ESA 306. Any heat dissipated by the semiconductor device will warm the surrounding air, which will be sucked upward by convection. Thus, the warm air is sucked around the ESA, reducing the temperature difference between the ESA and the surrounding air and thereby reducing heat loss from the surrounding air. One or more baffles or ducts can be arranged to direct the warm air.

[0051] Figure 4 Another embodiment of the HWSS 400 according to the present invention is shown. The cabinet 402 includes a send path 414 and a return path 416 for a heat pump (not shown), as well as a cold water inlet 408 and a hot water outlet 410. The send and return from the heat pump are connected to the ESA 406, which is provided with an insulating layer or sheath 404. Energy is provided by the heat pump and stored in the ESA, and the stored energy can be transferred to the water from the cold water inlet 408 as previously described. The cabinet includes a layer of insulating material 456.

[0052] Figure 4 The arrangement in the embodiment in Figure 3 differs from the arrangement in

[0053] The heater 420 and the valve are controlled by respective power electronics 424 disposed near a pair of baffles 426, 428 that direct air (arrow H) upward from the power electronics toward the ESA 406. Baffle 426 may be omitted and the side of the cabinet used to direct the airflow, although this may dissipate heat through the cabinet wall. Front and rear baffles (not shown) may also be provided. As an alternative or supplement to one or more baffles, one or more ducts may be used. The power electronics are all preferably provided with heat sinks. The temperature sensor 438 determines the temperature of the power electronics and reports it to the controller 430. Other heat-generating components of the system may be arranged in positions similar to those of the power electronics.

[0054] Although convection can be used to convey air within the cabinet, it is preferred that a heating fan 434 be provided near the power electronics to direct the air within the cabinet above the devices and between the baffles 426, 428. The heating fan itself will be driven by one of the power electronics 424 under the control of the controller 430. The fan 434 may be activated when the controller 430 determines that there is excess heat in the devices 424 that can usefully be redistributed near the ESA 406 (e.g., by reference to the temperature sensors 438, 452).

[0055] An additional fan (cooling fan 436) may optionally be provided. Although most power electronics are capable of operating at 80 °C and are not likely to overheat, the fan 436 may be activated if the controller determines that these devices are too hot. Also, in these devices 424, the fan will have its own power electronics. The fan 436 has two possible sources of relatively cool air for cooling the semiconductor devices. First, an actuator 442 may be used to open a hole 440 in the bottom wall of the cabinet. This allows ambient air to be drawn into the cabinet through the fan 436. To ensure sufficient air enters the cabinet, an actuator 446 may be used to open a hole 444 at the top of the cabinet. Second, the fan may be arranged to blow air across the cold water inlet 408. Due to the flow of cold tap water, the pipe is typically cooler than the ambient air temperature. The pipe may be provided with vanes 448 to allow the cold pipe to extract more heat from the air driven by the fan 436.

[0056] The controller 430 is provided with inputs from various sensors to allow appropriate decisions regarding air management within the cabinet. Sensor 432 detects the temperature of the incoming cold water, and sensor 450 detects the temperature of the outgoing hot water. The controller uses these values to determine whether to activate the auxiliary heater 420 and the relative flow rates through the energy storage and the auxiliary heater. The controller is also provided with the temperature of the air within the cabinet (preferably adjacent to the ESA) by sensor 452, and the temperature of the power semiconductor devices by sensor 438. The output from the controller is connected (not shown) to the power semiconductor device 424 to operate the valves, heaters, and fans.

[0057] The controller may be provided with external information such as weather forecasts, and may also be programmed to record the behavior of the air within the cabinet in response to various actions. These actions may include the amount of hot water pumped, the activation of fans 434 and 436, the opening of holes 440 and 444, etc. The controller can then use this record in future situations to determine whether to activate a fan, for how long, and at what speed.

[0058] The controller is also arranged to provide start and stop signals to a heat pump (not shown). The controller may be arranged to activate the heat pump when it determines that the energy storage is depleted and unable to meet the demand for hot water. This may occur when the water flow through sensor 454 indicates that the user is showering or bathing.

Claims

1. A hot water supply system, the hot water supply system being located in a cabinet and comprising: A thermal energy storage, the thermal energy storage being configured to store energy received from a heat pump, the energy storage comprising a first insulating material layer; A heat pump supply connection and a heat pump return connection, the heat pump supply connection and the heat pump return connection being connected to the thermal energy storage; A cold water inlet and a hot water outlet, the cold water inlet being coupled to the energy storage, the hot water outlet being coupled to the thermal energy storage; A controller; A heat generating component; And An air flow guiding device, the air flow guiding device being arranged to guide air from near the heat generating component to near the thermal energy storage, thereby reducing the temperature difference between the energy storage and the air around the energy storage.

2. The hot water supply system according to claim 1, wherein the air flow guiding device comprises at least one baffle.

3. The hot water supply system according to claim 1 or 2, wherein the air flow guiding device comprises at least one duct.

4. The hot water supply system according to claim 1, 2 or 3, wherein the air flow guiding device comprises at least one fan.

5. The hot water supply system according to claim 4, further comprising a second fan, the second fan being arranged to distribute cooling air to the heat generating device.

6. The hot water supply system according to claim 5, wherein the cooling air is sourced from the cold water inlet.

7. The hot water supply system according to claim 6, wherein the cold water inlet is provided with at least one vane in the air path from the second fan.

8. The hot water supply system according to claim 6 or 7, wherein the cooling air is obtained from outside the cabinet.

9. The hot water supply system according to any one of the preceding claims, wherein the heat generating device comprises a power semiconductor device.

10. The hot water supply system according to claim 8, wherein the power semiconductor device is provided with a heat sink.

11. The hot water supply system according to any one of the preceding claims, wherein the cabinet is substantially airtight.

12. The hot water supply system according to any one of the preceding claims, wherein the cabinet comprises an insulating material layer.

13. The hot water supply system according to any one of the preceding claims, wherein the cabinet is provided with holes facing its bottom, the holes being capable of being opened and closed under the control of the controller.

14. The hot water supply system according to any one of the preceding claims, wherein the cabinet is provided with holes facing its top, the holes being capable of being opened and closed under the control of the controller.

15. The hot water supply system according to any one of the preceding claims, further comprising at least a first electrically controlled valve and a second electrically controlled valve, the first electrically controlled valve being arranged to control the water flow through the energy storage, the second electrically controlled valve being arranged to control the water flow through the auxiliary heater.

16. The hot water supply system according to claim 14, wherein the controller is arranged to determine the relative flow rates of water through the energy storage and the auxiliary heater.

17. The hot water supply system according to any one of the preceding claims, wherein the controller is arranged to start and stop the heat pump.

18. The hot water supply system according to any one of the preceding claims, wherein the thermal energy storage includes a phase change material for storing energy.

Images