Warm water supply system

Abstract

The hot water supply system (HWSS) (400) generally includes a cabinet enclosed by a housing. The cabinet includes a heat insulating energy storage unit (406) connected (414, 416) to a heat pump (not shown). Water from the cold water inlet (408) is guided to the energy storage unit or the auxiliary heater (420) by valves (418, 422). The valves and the auxiliary heater are controlled by power semiconductor devices (424, 426) and (428) under the control of a controller (430). The heat dissipation by the power semiconductor devices is redirected by baffles (426, 428) and / or a fan (434) to reduce the temperature difference between the energy storage unit (406) and the surrounding air, thereby suppressing energy loss.

Description

Technical Field

[0001] The present invention relates to a hot water supply system (HWSS), particularly a hot water supply system used together with a heat pump utilizing a thermal energy storage mechanism.

Background Art

[0002] In households and small commercial facilities, the required conditions for hot water are often met by gas combustion boilers or heating furnaces. The hot water is either heated or stored in some kind of tank, or heated on demand when a hot water tap is opened within the facility. With growing concerns about environmental damage caused by the combustion of fossil fuels, attention has been focused on alternative technologies for supplying hot water, such as heat pumps.

[0003] A heat pump uses refrigeration technology to extract heat from a low-temperature source and transfer that heat to a high-temperature source. For example, a heat pump can extract heat from air at 15 degrees Celsius and heat water to 50 degrees Celsius. Such a heat pump is called an air-source heat pump, but there are also water-source heat pumps and ground-source heat pumps, which operate on the same principle. Although energy (usually electricity) is required to operate a heat pump, the efficiency of a heat pump can be more than four times that of, for example, an electric stove.

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, a heat pump is not suitable for instant hot water supply, such as when a user turns on a tap. Specifically, there are limitations on how fast a heat pump can start up and how frequently it can operate. It may take more than a minute for a heat pump to turn on, perform a self-check, and actually produce hot water. This is unacceptable for a user who wants to use hot water for only 20 seconds to wash their hands. Furthermore, a heat pump usually cannot be operated more than six times per hour and may not be available during defrost cycles, etc.

[0005] To address these problems, the applicant has developed a heat storage mechanism as described in a UK patent application filed on 7 February 2021. This uses a phase change material such as paraffin wax, a material that changes from solid to liquid (and vice versa) at a relevant temperature, to store energy in a very space-efficient way. A heat pump is used to heat the energy storage unit containing the phase change material up to the temperature at which the material changes from solid to liquid. This phase change absorbs a large amount of energy, and then the energy can be recovered without operating the heat pump when a single tap is opened. By using a phase change material, the energy storage unit becomes very compact, i.e., it can store a large amount of energy for its size. Cold water from the main water pipe is supplied through the energy storage unit to supply a small amount of warm water (e.g., enough for a shower). Long-term warm water demand is met by operating the heat pump, but even in this case, the energy storage unit is used for warm water supply until the heat pump is fully operational.

[0006] The drawback of this mechanism is the heat loss from the energy storage unit. This typically operates at around 50°C, i.e., around 30°C higher than the ambient temperature in most homes. The demand for warm water has peaks in the morning and evening but is quite intermittent throughout the day and night because there is little demand. This means that the energy storage unit is prone to heat loss over a relatively long period. Although the storage unit is insulated, there is usually a limit to the amount of insulation that can be incorporated into a hot water system designed as an alternative to an existing gas boiler.

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

Means for Solving the Problem

[0008] According to a first aspect of the present invention, there is provided a hot water supply system disposed within a cabinet, the hot water supply system comprising: a thermal energy storage unit for storing energy received from a heat pump, the thermal energy storage unit including a first heat insulating layer; a heat pump supply connection and a heat pump return connection connected to the thermal energy storage unit; a cold water inlet coupled to the energy storage unit and a hot water outlet coupled to the thermal energy storage unit; a controller; a heat generating component; and airflow guiding means arranged to guide air from the vicinity of the heat generating component to the vicinity of the thermal energy storage unit, thereby reducing the temperature difference between the thermal energy storage unit and the air surrounding the thermal energy storage unit.

[0009] The arrangement of the hot water supply system within the cabinet is intended to maintain the internal temperature within the housing, particularly in the vicinity of the energy storage unit, higher than 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 is reduced. The thermal energy storage unit preferably comprises a phase change material for storing energy in a space-efficient manner.

[0010] The internal temperature of the cabinet is increased by heat loss from the energy storage unit, but also by heat dissipated by other heat generating components such as power electronics devices used to control auxiliary heaters. SCRs or triacs are also typically used for starting and stopping the heat pump, controlling electric control valves, etc. These devices preferably comprise a heat sink.

[0011] The airflow guiding means preferably comprises at least one baffle. One or more baffles can be arranged to utilize convection within the cabinet.

[0012] Alternatively, or additionally, the airflow guiding means comprises at least one duct.

[0013] According to a preferred embodiment, the airflow guiding means comprises at least one fan. The fan is preferably under the control of a controller that operates and stops the fan in response to the temperature sensor output.

[0014] According to another preferred embodiment, a second fan is arranged to distribute the cooling air to the heat generating device. This provides a safety function in case the heat generating device gets too hot.

[0015] The second fan can rely on the cooling air from the cold water inlet, and the cold water inlet can comprise at least one vane in the path from the second fan or in the air.

[0016] Alternatively, or additionally, the cooling air is supplied from outside the cabinet.

[0017] In many embodiments, the heat generating device includes a power semiconductor device. These devices preferably comprise a heat sink.

[0018] To minimize heat loss from the energy storage unit, the cabinet is preferably substantially airtight. The cabinet also preferably comprises a heat insulating layer.

[0019] To manage the airflow inside the cabinet more appropriately, the cabinet preferably comprises an opening on the side of its bottom, and this opening can be opened and closed under the control of the controller. To further manage the airflow inside the cabinet, the cabinet can comprise an opening on the side of its top, and this opening can be opened and closed under the control of the controller.

[0020] To optimally manage the resources stored in the energy storage unit, the HWSS preferably includes at least a first electric control valve arranged to control the flow of water through the energy storage unit and a second electric control valve arranged to control the flow of water through the auxiliary heater. To perform this control, the controller is configured to determine the relative flow rates of water through the energy storage unit and the auxiliary heater. The controller is preferably also configured to operate or stop the heat pump.

[0021] Next, the present invention will be illustratively described with reference to the following attached drawings.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0023] Detailed Description Figure 1 schematically shows a facility according to a first aspect of the present disclosure. The facility 100 includes a building-internal hot water supply system (HWSS) represented by a box 110, and a heat pump 120 configured to heat the water of the HWSS 110 (generally installed outside the building). The HWSS includes at least one outlet 130 such as a faucet or a shower outlet. The HWSS further includes an energy storage arrangement (ESA) 140 containing a mass of phase change material (PCM). A processor 150, sometimes also called a system controller, is configured to provide a signal to the heat pump 120 as appropriate based on the opening of an outlet such as the outlet 130 of the hot water system.

[0024] The mass of phase change material has a latent heat capacity sufficient to heat a predetermined amount of water to a predetermined temperature from when the outlet of the hot water supply system opens until at least the heat pump starts heating the water in the hot water supply system. A phase change material such as paraffin having a phase transition temperature of 50°C is suitable, but alternative materials or suitable combinations of materials will be apparent to those skilled in the art.

[0025] In the HWSS 110, for example, the water to be heated is supplied from a cold water supply section 160, and at least one flow transducer 170 is included in the flow path between the supply 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 schematically shown by a pipe 190, and the supply of the water to be heated is directly connected to the HWSS as shown by a pipe 200. The flow transducer 170 may be provided on the supply side of the hot water system or on the outlet side of the whole system. The HWSS includes at least one temperature transducer 210. If only a single temperature transducer 210 is provided, this should be in the flow path between the energy storage mechanism 140 and at least one outlet 130.

[0026] The HWSS 110 also includes an instantaneous auxiliary water heater 220 in the flow path between the energy storage mechanism 140 and at least one outlet 130. When the instantaneous water heater 220 is included in the HWSS, it is preferable to include a temperature transducer in the flow path between the energy storage mechanism and the instantaneous water heater, and it is also preferable to include a temperature transducer between the instantaneous water heater and at least one outlet 130. The instantaneous water heater 220 is preferably an electric heater.

[0027] The processor 150 is coupled to the flow rate transducer 170, the memory 151, each temperature transducer 210, and the heat pump. Further, it is preferable that one or more sensing mechanisms in the ESA are coupled to the processor so that the processor recognizes the state of the ESA. The processor 150 is also connected to the instantaneous water heater 220.

[0028] In a preferred configuration where the heat pump heats the water in the HWSS by a closed-loop arrangement, a heat exchanger (not shown) receives the liquid heated by the heat pump on one side and the water in the HWSS to be heated on the other side. Preferably, the heat exchanger forms part of the ESA. Preferably, the heat exchanger includes some or all of a mass of phase change material.

[0029] As shown in FIG. 1, due to its size, a heat pump is usually installed outside the building that houses the HWSS. Whether installed outside or inside the building, it usually takes 30 to 60 seconds from receiving a start signal to starting heat supply. This is because the internal processor of the heat pump needs to check a plurality of components and subsystems, and there is also a time lag inherent in starting components such as the compressor and the pump of the heat pump. Even after the heat pump starts, there is of course an inevitable delay until the heat from the heat pump reaches the HWSS. Similarly, it takes a certain amount of time for heat to be transferred between the high-temperature liquid supplied from the heat pump and the water heated by the HWSS via a heat exchanger. Furthermore, the heat pump is usually configured to avoid starting more than six times per hour (the numerical values are the same among manufacturers although they may vary depending on the manufacturer), and the system's processor 150 recognizes this constraint applied to the connected heat pump and also keeps track of its own history of sending start instructions, and reflects this information in decisions regarding the management of various available heat sources.

[0030] The processor 150 of the HWSS is configured to supply a start signal to the heat pump based on the signal received from the flow sensor 170. As described above, the present facility is configured such that a time interval occurs between the provision of the start signal to the heat pump and the heating of the water in the hot water system by the heat pump. For this reason, when there is no hot water storage tank or other hot water source, even if the faucet or shower supplying hot water by the HWSS is turned on, a long waiting time of more than one minute occurs until hot water comes out of the outlet. This is not only unsatisfactory for the user but also a great waste of water. By using the instantaneous water heater until the time when hot water arrives from the heat pump, the waiting time for hot water can be shortened. However, in such an arrangement, considering that in most cases the use of hot water from the faucet (in contrast to the shower) is less than 60 to 90 seconds, most of the hot water used will be supplied from the instantaneous water heater (either electric or gas type), and the green energy advantage of providing the heat pump will be almost lost.

[0031] Based on the value received from the temperature sensor 210, the processor 150 can adjust the output of the electrical element 220 and achieve the correct target temperature at the water outlet 130.

[0032] The ESA is provided as a means to bridge the gap between the demand for hot water (i.e., the opening of the faucet or shower control device) and the supply of hot water heated by the heat pump. The system is preferably configured such that the ESA is charged with the energy from the heat pump. The processor 150 is configured to preferentially use the ESA to heat the water supplied through the outlet 130 using the temperature information from the temperature sensor (210) and the flow rate information from the flow sensor 170. In this way, the processor 150 minimizes the use of the instantaneous water heater 220.

[0033] Accordingly, the processor is configured to provide a start signal to the heat pump based on the signal received from the flow sensor, the mechanism is arranged such that a time interval occurs between providing the start signal to the heat pump and the water in the hot water system being heated by the heat pump, the energy storage mechanism contains a mass of phase change material having a latent heat capacity sufficient to heat a predetermined amount of water in the hot water system to the target temperature at least until the water in the hot water system is heated by the heat pump, and enables the supply of hot water from a controllable outlet during the interval between the transmission of the start signal and the heating of the water in the hot water system by the heat pump. The target temperature can be set based on the preferences of the user of the system, but generally ranges from 40 to 45 °C. The predetermined amount can be based on the desired water supply time at a flow rate selected based on either the normal flow rate used at the outlet of the HWSS having the maximum flow rate, or a relatively low flow rate considered appropriate and acceptable. The system and the processor are preferably configured to be able to adjust these two variables (temperature and amount) within a preset range (the preset range can be adjusted during the installation of the system).

[0034] The information from the flow sensor 170 can convey to the processor 150, for example, whether the open outlet is a shower outlet or a sink outlet. If the processor 150 determines that the shower outlet is open, since it is expected that it is worth starting the heat pump for the number of minutes that a shower usually takes, the processor 150 transmits a start signal to the heat pump. Conversely, if the flow rate information supplied to the processor 150 suggests that the faucet of the sink is open, since it is unlikely that the heat pump can supply hot water before the faucet of the sink is closed again, the processor determines not to transmit a start signal to the heat pump.

[0035] Processor 150 can be associated with logic, such as a machine learning algorithm, that enables it to learn the behavior of the occupants of a facility served by the HWSS, thereby enabling the creation of a database that allows the processor 150 to reliably predict the amount and duration of hot water demand / usage depending on the time of day, day of the week, water outlet used, etc. Such an approach can be enhanced, for example, by further providing flow sensors associated with different water outlets of the HWSS (some or all, preferably at least, to be able to quickly distinguish between outlets with short-term hot water demand such as a hand-washer in the cloakroom and outlets with long-term hot water demand such as a shower or kitchen sink). Additionally, by providing one or more flow sensors in the cold water supply, it may be possible to identify the use of cold water for toilet flushing and, for example, infer an impending demand for a short-term hot water supply for handwashing therefrom. The system processor 150 preferably comprises logic for controlling all the various heating resources (ESA, instantaneous water heater, and heat pump) in the most effective, economical, and efficient way.

[0036] ESA 140, the heat exchanger, processor 150, instantaneous water heater 220, and flow transducer 170 and temperature transducer 210 can all be considered to constitute an interface unit 250 that interfaces between the heat pump 120 and the building domestic hot water system 110. Although FIG. 1 shows such an interface unit that only heats the water for the building domestic hot water system, it will be understood that in many regions of the world, there is a need for space heating in many buildings and it may be attractive to use a heat pump for such space heating.

[0037] Generally, current combi-boilers, which are also used in small-scale housing, are large enough to supply hot water of 24 kW or more corresponding to the flow rate of a shower or a bathtub. However, the energy demand for general space heating is much lower, usually about 4 kW. If a system is designed to supply both domestic hot water (DHW) and space heating only by a heat pump, it is necessary to specify a 24 kW heat pump to meet the requirements of DHW. However, such a system would be unrealistically large for typical one- to three-bedroom apartments or houses where only space heating and intermittent hot water use are required in most cases.

[0038] Figure 2 is a perspective view of the HWSS200 according to an embodiment of the present invention. The HWSS is housed within a cabinet 202. On the side of the cabinet, there are piping connections for the flow pipe 204 and the return pipe 206 of a heat pump (not shown). The heat from the heat pump is used to heat the water from the cold main pipe 208 and provide a hot water output 210. The cabinet 202 has a completely airtight structure except for a small opening 212 at one corner of the bottom. The opening may be necessary because the air temperature (and thus the air volume) inside the cabinet may change. However, the opening is designed to be as small as practically possible to minimize the heat loss from inside the cabinet.

[0039] Although the figure shows the positions of various pipe joints, those skilled in the art will understand that these may be arranged at other locations in the cabinet. The small opening is located on the bottom surface of the cabinet, but it may be arranged on any of the other panels or may be omitted.

[0040] Figure 3 is a front perspective view of the HWSS 300 disposed within a six-sided rectangular cabinet 302, with the front panel removed for purposes of illustration. The cabinet has a thermal insulation layer 304 and is airtight except for a small opening 312 in the bottom panel. The heat or energy storage mechanism (ESA) 306 has a feed coupling 314 that receives fluid heated from a heat pump and a return coupling 316 for returning the fluid to a heat pump (not shown). The ESA is indirectly heated by a heat exchanger within the ESA. The HWSS has a cold water inlet 308 and a hot water outlet 310 from a tank or a main water supply pipe. Heat from the ESA can be transferred to the water from the cold water inlet using another heat exchanger within the ESA.

[0041] The cold water inlet is connected to a temperature sensor 318, which provides a temperature value to a controller 320. The controller is also informed about the degree of energy storage in the ESA and can determine whether the ESA can sufficiently 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 a thyristor. The device 324 preferably has a heat sink for transferring the heat dissipated within the device to the surrounding air. The auxiliary heater is an electric heater disposed between the output of the ESA and the hot water outlet of the HWSS. The power semiconductor device 324 is disposed under the ESA 306. The heat dissipated by the semiconductor device warms the surrounding air that is drawn upward by convection. Thus, the warm air is drawn to surround the ESA, reducing the temperature difference between the ESA and the surrounding air and thereby reducing the heat loss therefrom. One or more baffles or ducts can also be arranged to direct the warmed air.

[0042] Figure 4 shows another embodiment of the HWSS400 according to the present invention. The cabinet 402 includes a supply 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 supply and return from the heat pump are connected to the ESA 406 with a heat insulation layer or jacket 404. Energy is supplied from the heat pump and stored in the ESA, and the stored energy is transferred to the water from the cold water inlet 408 as described above. The cabinet includes a heat insulation layer 456.

[0043] The configuration of the embodiment of FIG. 4 is different from that of FIG. 3, particularly in providing two different water paths through the HWSS. The first path goes from the cold water inlet 408 through the temperature sensor 432 and valve 418 to the ESA, and the second path goes from the cold water inlet through the valve 422 to the auxiliary heater 420. The controller 430 uses the temperature information from the sensor 432 to determine the range for operating the auxiliary heater and the relative flow of water through the ESA and the auxiliary heater. The controller includes a plurality of inputs from sensors such as the sensor 432 and a plurality of outputs 460 for driving the power electronics devices described later.

[0044] The heater 420 and the valve are controlled by respective power electronics devices 424 arranged adjacent to a pair of baffles 426, 428 that direct air (arrow H) from the power electronics device upward toward the ESA 406. The baffle 426 can be omitted and the side of the cabinet can be used to direct the air flow, but in this case, heat may be dissipated through the wall of the cabinet. Baffles may be provided on the front and back (not shown). One or more ducts may be used instead of or in addition to one or more baffles. The power electronics devices preferably all include heat sinks. The temperature sensor 438 measures the temperature of the power electronics and reports this to the controller 430. Other heat generating components of the system can also be arranged in the same position as the power electronics devices.

[0045] Convection can also be used to move the air within the cabinet, but it is preferred to provide the heating fan 434 adjacent to the power electronics device to direct the air from within the cabinet onto and between the device and the baffles 426, 428. The heating fan itself is driven by one of the power electronics devices 424 under the control of the controller 430. The fan 434 can be activated when the controller 430 determines that there is sufficient heat in the device 424 to usefully redistribute it in the vicinity of the ESA 406 (see, for example, the temperature sensors 438, 452).

[0046] An optional additional fan, a cooling fan 436, may be provided. Most power electronics devices are operable at 80° C. and have a low likelihood of overheating, but the fan 436 can be activated if the controller determines that the device is too hot. Again, the fan will have its own power electronics device within the device 424. There are two possible sources of cooling air for cooling the semiconductor device by the fan 436. First, an opening 440 provided in the bottom wall of the cabinet can be opened using the actuator 442. Thereby, ambient air is drawn into the cabinet by the fan 436. The opening 444 at the top of the cabinet may be opened using the actuator 446 so that sufficient air enters the cabinet. Second, the fan can be arranged to blow air onto the cold water inlet 408. The tube is normally cooler than the ambient air temperature due to the flow of cold mains water. Vanes 448 may be provided on the tube so that the cold tube extracts more heat from the air driven by the fan 436.

[0047] The controller 430 is provided with inputs from various sensors to enable appropriate judgment 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 warm water. The controller uses these values to determine whether to activate the auxiliary heater 420 and the relative flow rates through the energy storage unit 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 device by sensor 438. The output from the controller is connected (not shown) to the power semiconductor device 424 to activate valves, heaters, and fans.

[0048] The controller may be provided with external information such as weather forecasts and may be programmed to record the behavior of the air within the cabinet in response to various operations. These operations include the amount of warm water drawn, the operation of fans 434 and 436, the opening of apertures 440 and 444, etc. This record may be used by the controller in the future to determine whether to operate the fans, for how long, and at what speed.

[0049] The controller is also configured to provide start and stop signals to a heat pump (not shown). The controller may be configured to activate the heat pump when it is determined that the energy storage is insufficient to meet the demand for warm water. This may occur when the water flow through sensor 454 indicates that the user is taking a shower or filling the bathtub with hot water.

Claims

1. A hot water supply system installed inside a cabinet, a thermal energy storage unit for storing the energy received from a heat pump, the thermal energy storage unit including a first heat insulation layer, a heat pump supply connection and a heat pump return connection connected to the thermal energy storage unit, a cold water inlet coupled to the energy storage unit and a hot water outlet coupled to the thermal energy storage unit, a controller, a heat generating component, and an air flow guiding means arranged to guide air from the vicinity of the heat generating component to the vicinity of the thermal energy storage unit, thereby reducing the temperature difference between the energy storage unit and the air surrounding the energy storage unit. A hot water supply system comprising the above.

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

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

4. The hot water supply system according to any one of claims 1 to 3, wherein the air flow guiding means comprises at least one fan.

5. The hot water supply system according to claim 4, further comprising a second fan 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 obtained from the cold water inlet.

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

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

8. The hot water supply system according to any one of claims 1 to 7, wherein the heat generating device comprises a power semiconductor device.

9. The hot water supply system according to claim 8, wherein the power semiconductor device comprises a heat sink.

10. The hot water supply system according to any one of claims 1 to 9, wherein the cabinet is substantially airtight.

11. The hot water supply system according to any one of claims 1 to 10, wherein the cabinet comprises a heat insulation layer.

12. The hot water supply system according to any one of claims 1 to 11, wherein the cabinet comprises an opening on the side of its bottom that can be opened and closed under the control of the controller.

13. The hot water supply system according to any one of claims 1 to 12, wherein the cabinet is provided with an opening on the upper side thereof that can be opened and closed under the control of the controller.

14. The hot water supply system according to any one of claims 1 to 13, further comprising at least a first electric control valve arranged to control the water flow through the energy storage unit and a second electric control valve arranged to control the water flow through the auxiliary heater.

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

16. The hot water supply system according to any one of claims 1 to 15, wherein the controller is configured to operate and stop the heat pump.

17. The hot water supply system according to any one of claims 1 to 16, wherein the thermal energy storage unit comprises a phase change material for storing energy.

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