A waste heat recovery system and method for a dishwasher

Abstract

The application discloses a kind of waste heat recovery system and waste heat recovery method of dish washer, waste heat recovery system includes: heat exchanger, the drain of dish washer is connected with the wastewater inlet of heat exchanger, the wastewater outlet of heat exchanger is connected with sewer;Wastewater inlet is equipped with first temperature sensor, first temperature sensor is used to detect the temperature of wastewater discharged by dish washer and is recorded as first temperature;Water storage tank, clean water is stored in water storage tank, water storage tank is connected with the clean water inlet of heat exchanger, the clean water outlet of heat exchanger is connected with water storage tank, water storage tank is also connected with the water inlet of dish washer;Second temperature sensor is equipped in water storage tank, second temperature sensor is used to detect the temperature of clean water in water storage tank and is recorded as second temperature;Controller, controller is electrically connected with heat exchanger, water storage tank, first temperature sensor and second temperature sensor.The waste heat of dish washer wastewater is fully recovered in the application, the heat energy in wastewater can be efficiently utilized, and high-temperature wastewater can also be avoided to scald sewer.

Description

TECHNICAL FIELD

[0001] The present application relates to a residual heat recovery system and method for a dishwasher. BACKGROUND

[0002] In a conventional dishwasher, the high-temperature wastewater is discharged into the sewer, and the heat energy is lost, resulting in waste of energy. The heat energy contained in the high-temperature wastewater is not fully utilized.

[0003] At the same time, the temperature limit of the sewer is about 60℃, and the high-temperature wastewater (70-80℃) may cause the temperature of the sewer pipe to be too high when directly discharged into the sewer, resulting in problems such as deformation, aging, and blockage of the pipe. This has a negative impact on the reliability and service life of the sewer pipe. SUMMARY

[0004] The present application aims to overcome the problem of high temperature of the wastewater discharged from the dishwasher in the prior art, which may damage the sewer pipe, and to provide a residual heat recovery system and method for a dishwasher.

[0005] The present application solves the above technical problems by the following technical solutions:

[0006] In one aspect, the present application provides a residual heat recovery system for a dishwasher, which comprises:

[0007] a heat exchanger, a wastewater inlet of the dishwasher is connected to a wastewater inlet of the heat exchanger, and a wastewater outlet of the heat exchanger is connected to a sewer; the wastewater inlet is provided with a first temperature sensor for detecting the temperature of the wastewater discharged from the dishwasher and recording as a first temperature;

[0008] a water storage tank, the water storage tank stores clean water, the water storage tank is connected to a clean water inlet of the heat exchanger, a clean water outlet of the heat exchanger is connected to the water storage tank, and the water storage tank is also connected to a water inlet of the dishwasher; the water storage tank is provided with a second temperature sensor for detecting the temperature of the clean water in the water storage tank and recording as a second temperature;

[0009] a controller, the controller is electrically connected to the heat exchanger, the water storage tank, the first temperature sensor, and the second temperature sensor;

[0010] the water storage tank is used to send the clean water to the heat exchanger, the heat exchanger is used to exchange heat between the wastewater discharged from the dishwasher and the clean water, and the clean water after heat exchange is sent back to the water storage tank;

[0011] The controller is configured to start the heat exchanger to exchange heat between the clean water and the waste water when the first temperature is greater than a first preset temperature, wherein the second temperature is less than the first temperature during the heat exchange.

[0012] In the present application, when the temperature of the dishwasher waste water is higher than the temperature limit of the sewer pipe, directly discharging the waste water into the sewer pipe can scald the sewer pipe. The present application sets a first temperature sensor to detect the temperature of the waste water, and starts the heat exchange when the temperature of the waste water is higher than a first preset temperature, so as to exchange heat between the high-temperature waste water and the cold water in the water storage tank, which can preheat the cold water, recycle the heat energy, and cool the high-temperature waste water, thereby avoiding scalding the sewer pipe. Preferably, in the present application, the second temperature is less than the first temperature by 3℃ when the heat exchange is started. At this time, starting the heat exchange can achieve a better heat exchange effect.

[0013] Preferably, a waste water tank is further arranged between the heat exchanger and the sewer pipe, the waste water outlet of the heat exchanger is connected with the water inlet of the waste water tank, the waste water tank is connected with the waste water inlet of the heat exchanger through a first water pump, and the water outlet of the waste water tank is connected with the sewer pipe through a control valve.

[0014] Preferably, the water inlet of the waste water tank is provided with a third temperature sensor, the heat exchanger stops working when the second temperature is not less than the first temperature, the waste water tank is used for storing the waste water, the third temperature sensor is used for detecting the temperature of the waste water in the waste water tank and recording as a third temperature, the control valve is used for discharging the waste water into the sewer pipe when the third temperature is lower than the first preset temperature, the waste water tank is used for storing the waste water when the second temperature is not less than the third temperature, and the controller is used for controlling the first water pump to pump the waste water into the heat exchanger to exchange heat with the clean water when the third temperature is greater than the first preset temperature, wherein the second temperature is less than the third temperature during the heat exchange.

[0015] In the present application, when the waste water enters the waste water tank, the temperature of the waste water is detected, and when the temperature of the waste water is higher than a first preset temperature, there is a risk of scalding the sewer pipe. At this time, if the temperature of the waste water is higher than the temperature of the clean water in the water tank, the first water pump is started to pump the waste water into the heat exchanger to exchange heat with the clean water, and the heat exchange stops when the temperature of the clean water is not less than the temperature of the waste water. If the temperature of the clean water is not less than the temperature of the waste water at this time, the heat exchange is not performed, and the waste water is stored in the waste water tank. When the temperature of the waste water is less than the first preset temperature, the control valve is opened to discharge the waste water into the sewer pipe. In the present application, the heat exchange stops when the temperature of the clean water is not less than the temperature of the waste water, at this time, the temperature difference between the temperature of the water in the water storage tank and the temperature of the waste water is not large, and even higher than the temperature of the waste water, and the heat exchange effect is not obvious, so the heat exchange is not performed, and the waste water is stored in the waste water tank at this time.

[0016] Preferably, the water storage tank is also connected with a tap water pipeline, and the water storage tank is used to store the clean water accessed from the domestic water outlet.

[0017] Preferably, the water storage tank is connected with the heat exchanger through a second water pump, and the second water pump is used to pump the clean water into the heat exchanger when the waste heat recovery system needs heat exchange.

[0018] Preferably, the water storage tank is provided with a heat preservation layer.

[0019] Preferably, the water storage tank is connected with the water inlet of the dishwasher through a second valve, and the second valve is opened when the dishwasher needs hot water and is closed when the dishwasher needs cold water.

[0020] Preferably, the tap water outlet is connected with the water inlet of the dishwasher through a first valve, and the first valve is opened when the dishwasher needs cold water and is closed when the dishwasher needs hot water.

[0021] Preferably, the controller is also used to judge whether the dishwasher is in a working state when the first temperature is less than a first preset temperature, and if the dishwasher is in the working state, judge whether the first temperature is greater than the second temperature, and start the heat exchanger to perform heat exchange between the waste water and the clean water when the first temperature is greater than the second temperature.

[0022] In the present application, for waste water less than the first preset temperature, there is still some heat, and when there is a temperature difference between the waste water temperature and the water temperature in the water tank, i.e. the waste water temperature is greater than the clean water temperature, the waste water temperature has recycling value, and heat exchange can be performed to further recycle the heat energy in the waste water, so as to realize recycling of the water temperature not higher than the first preset temperature.

[0023] Preferably, when the first temperature is less than the first preset temperature and the dishwasher is not in the working state, the heat exchanger stops the heat exchange. At this time, since the dishwasher no longer needs hot water, the heat exchange can be stopped, and the first temperature is less than the first preset temperature, so the pipeline will not be scalded, and thus the waste water can be safely discharged.

[0024] The present application also provides a waste heat recovery method of a dishwasher, which is realized by using the waste heat recovery system as described above, and the waste heat recovery method comprises the following steps:

[0025] detecting the temperature of the waste water discharged from the dishwasher and recording the temperature as a first temperature, and detecting the temperature of the clean water in the water storage tank and recording the temperature as a second temperature;

[0026] judging whether the first temperature is greater than a first preset temperature;

[0027] when the first temperature is greater than the first preset temperature, starting the heat exchanger to exchange heat between the clean water and the waste water, wherein the first temperature is greater than the second temperature when the heat exchange is performed.

[0028] Preferably, in the step of judging whether the first temperature is greater than the first preset temperature, if the first temperature is less than the first preset temperature, the following steps are performed:

[0029] judging whether the dishwasher is in operation;

[0030] if the dishwasher is in operation, judging whether the second temperature is less than the first temperature, and if the dishwasher is not in operation, stopping the heat exchanger and discharging the waste water into the sewer;

[0031] if the second temperature is less than the first temperature, starting the heat exchanger to exchange heat between the clean water and the waste water, and if the second temperature is not less than the first temperature, stopping the heat exchanger and discharging the waste water into the sewer.

[0032] Preferably, when the waste heat recovery system comprises a waste water tank, the waste heat recovery method further comprises:

[0033] detecting a temperature of the waste water in the waste water tank and recording the temperature as a third temperature;

[0034] judging whether the third temperature is greater than the first preset temperature;

[0035] when the third temperature is greater than the first preset temperature, starting the heat exchanger to exchange heat between the clean water and the waste water, wherein the second temperature is less than the third temperature when the heat exchanger is working, and when the second temperature is not less than the third temperature, the heat exchanger is not working and the waste water is stored in the waste water tank; and when the third temperature is less than the first preset temperature, discharging the waste water into the sewer.

[0036] Preferably, if the dishwasher is in operation, the following steps are further included:

[0037] when the dishwasher is in operation, judging whether the dishwasher needs hot water;

[0038] when the dishwasher needs hot water, the clean water in the water storage tank that has been exchanged heat is introduced into the dishwasher, and when the dishwasher does not need hot water, tap water is introduced into the dishwasher.

[0039] The positive progress effect of the present application is that by detecting the temperature of the wastewater to determine whether to start the heat exchanger, multiple benefits are achieved. First, by monitoring the wastewater temperature in real time and according to the set temperature threshold, potential damage and damage to the sewer caused by high-temperature wastewater can be avoided. Second, through the detection of wastewater temperature and the corresponding heat exchanger starting mechanism, the scheme can achieve the full recovery of heat energy in the wastewater. By using the wastewater temperature as the basis for starting the heat exchanger, the heat energy in these wastewater can be effectively captured and recycled for heating clean water in the water storage tank. This method of recycling heat energy can significantly reduce the demand for external energy, thereby achieving the goal of energy saving. Finally, the waste heat recovery system of the present application has wide adaptability and can be adapted to dishwashers with different washing programs. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 is a schematic diagram of the waste heat recovery system of embodiment 1 of the present application.

[0041] Figure 2 is a flowchart of the waste heat recovery method of the dishwasher of embodiment 2 of the present application.

[0042] Figure 3 is a flowchart of the wastewater treatment of the dishwasher of embodiment 2 of the present application.

[0043] Figure 4 is a flowchart of the water valve control of embodiment 2 of the present application.

[0044] BRIEF DESCRIPTION OF DRAWINGS:

[0045] dishwasher 1

[0046] heat exchanger 2, first temperature sensor 21

[0047] water storage tank 3, second temperature sensor 31

[0048] first water pump 4

[0049] wastewater tank 5, third temperature sensor 51

[0050] control valve 6

[0051] sewer 7

[0052] second water pump 8

[0053] first valve 9

[0054] second valve 10

[0055] tap 11 DETAILED DESCRIPTION

[0056] The application will be further described in the following by way of examples without limiting the application to the examples described.

[0057] Example 1

[0058] The present example provides a waste heat recovery system of a dishwasher, as shown in the figure, the preheating recovery system in the present example is arranged outside the dishwasher 1, i.e. is separate from the dishwasher 1. The waste heat recovery system comprises a heat exchanger 2, a water storage tank 3, a first water pump 4, a waste water tank 5, a second water pump 8, and a controller (not shown in the figure). Figure 1

[0059] The drain of the dishwasher 1 is connected to the waste water inlet of the heat exchanger 2, the waste water outlet of the heat exchanger 2 is connected to the water inlet of the waste water tank 5, the water outlet of the waste water tank 5 is connected to the sewer 7 through the control valve 6; the waste water tank 5 is connected to the waste water inlet of the heat exchanger 2 through the first water pump 4; the clean water outlet of the heat exchanger 2 is connected to the water storage tank 3 through the water outlet pipe, and the water storage tank 3 is connected to the clean water inlet of the heat exchanger 2 through the second water pump 8.

[0060] The water storage tank 3 is connected to the tap 11, and is also connected to the water inlet of the dishwasher through the second valve 10, and the tap 11 is connected to the water inlet of the dishwasher through the first valve 9.

[0061] In the present example, the waste water inlet of the heat exchanger 2 is provided with a first temperature sensor 21, the water storage tank 3 is provided with a second temperature sensor 31, and the water inlet of the waste water tank 5 is provided with a third temperature sensor 51. The controller is electrically connected to the heat exchanger 2, the water storage tank 3, the first temperature sensor 21, the second temperature sensor 31, and the third temperature sensor 51.

[0062] The first temperature sensor 21 is used to detect the temperature of the waste water discharged from the dishwasher 1 to the heat exchanger 2, and is recorded as the first temperature; the second temperature sensor 31 is used to detect the temperature of the clean water in the water storage tank 3, and is recorded as the second temperature; and the third temperature sensor 51 is used to detect the temperature of the waste water in the waste water tank 5, and is recorded as the third temperature.

[0063] ​When the first temperature is greater than the first preset temperature, and the second temperature is less than the first temperature, the controller starts the heat exchanger 2 to perform heat exchange. In the embodiment, the first preset temperature is 55℃, and the wastewater above this temperature is easy to scald the sewer pipe made of PVC (Polyvinyl chloride). It should be noted that the embodiment is only an example, and the first preset temperature is the temperature limit of the sewer pipe material. Above the temperature limit, there is a risk of scalding the sewer pipe. Below the temperature limit, it is a safe temperature. The 55℃ mentioned in the embodiment does not represent a limitation on the scheme. Those skilled in the art can set the value of the first preset temperature according to the different sewer pipe materials. When the first temperature is greater than the second temperature, that is, there is a temperature difference between the wastewater and the clean water, so the heat exchanger 2 can take away the heat of the wastewater to preheat the clean water, and at the same time, the wastewater is cooled to avoid scalding the sewer. At the same time, the water storage tank 3 in the embodiment is provided with a heat preservation layer, which can be heat preserved to further retain the temperature of the preheated clean water, and the energy is recycled to fully save resources. In the embodiment, when the second temperature is less than the first temperature by 3℃, a significant heat exchange effect can be achieved.

[0064] When the second temperature is not less than the first temperature, the heat exchange is stopped. At this time, the temperature difference between the wastewater and the clean water is not obvious, and the heat exchange effect is poor. The wastewater is discharged into the wastewater tank 5 for storage.

[0065] At this time, if the third temperature is less than the first preset temperature, that is, the wastewater in the wastewater tank is within the safe temperature range, the control valve 6 is opened to discharge it into the sewer 7. If the third temperature is greater than the first preset temperature, there is still a risk of scalding the sewer 7. Therefore, it is judged whether the third temperature is greater than the second temperature. If it is greater, the first water pump 4 and the heat exchanger 2 are started to pump the wastewater into the heat exchanger 2 to exchange heat with the clean water, further reducing the temperature of the wastewater, until the second temperature is not less than the third temperature, and the heat exchange is stopped. At this time, the wastewater returns to the wastewater tank 5 again, and it is judged whether the third temperature is greater than the first preset temperature. This cycle continues until the third temperature is reduced to below the first preset temperature. It should be noted that when the third temperature is greater than the first preset temperature, the second temperature is not less than the third temperature, and the wastewater stays in the wastewater tank 5. It is cooled naturally, or the heat exchange is started again when the second temperature is less than the third temperature. In this way, it can be ensured that the wastewater discharged from the wastewater tank 5 is less than the first preset temperature, and the risk of overheated wastewater scalding the sewer 7 is minimized.

[0066] In this embodiment, if the first temperature is less than the first preset temperature, the wastewater can also be recovered, specifically as follows: when the first temperature is less than 55℃, if the dishwasher 1 is still working, it is possible that hot water is still needed, at this time, although the wastewater is in the safe temperature range, the heat in it still has the value of recovery, at this time, the second temperature is less than the first temperature, the heat exchanger 2 is started to perform heat exchange. At this time, when the dishwasher 1 is not working, the heat exchange is stopped, because if the dishwasher 1 stops working, the next time the dishwasher 1 is started can be after several hours, it is not meaningful to recover the heat of the wastewater at this temperature. In other embodiments, if the dishwasher 1 stops working, the heat can also be continued to be recovered, because the storage tank 3 has a heat preservation layer, which can be heat preserved to a certain extent to avoid heat loss. In addition, in this embodiment, under this working condition, if the second temperature is not less than the first temperature, there is no need for heat exchange, and the wastewater is directly discharged, because at this time the wastewater will not damage the sewer 7, and there is no heat exchange value, and it can be directly discharged.

[0067] In addition, in this embodiment, when the dishwasher 1 needs hot water, the second valve 10 is opened, the first valve 9 is closed, and the preheated clean water from the storage tank 3 is introduced into the dishwasher 1. When the dishwasher 1 does not need hot water, the first valve 9 is opened, the second valve 10 is closed, and the tap water is directly introduced into the dishwasher 1.

[0068] The waste heat recovery system of this embodiment determines whether to start the heat exchanger 2 by detecting the temperature of the wastewater through the first temperature sensor 21. Through the detection of the temperature of the wastewater and the corresponding starting mechanism of the heat exchanger 2, the temperature of the wastewater can be reduced, so as to avoid damaging the sewer, and the heat energy in the wastewater can be fully recovered. By using the temperature of the wastewater as the basis for starting the heat exchanger 2, the heat energy in the wastewater can be effectively captured and recovered and used to heat the clean water in the storage tank 3. This method of recycling heat energy can significantly reduce the demand for external energy, thereby achieving the goal of energy saving.

[0069] Embodiment 2

[0070] As shown in the flowchart of Figures 2-4 This embodiment provides a waste heat recovery method using the waste heat recovery system in embodiment 1, which comprises the following steps:

[0071] Detect the temperature of the wastewater discharged by the dishwasher 1 and record it as the first temperature, and detect the temperature of the clean water in the storage tank 3 and record it as the second temperature;

[0072] Determine whether the first temperature is greater than the first preset temperature, wherein the first preset temperature is 55℃;

[0073] When the first temperature is greater than the first preset temperature 55℃, the heat exchanger 2 and the second water pump 8 are started to perform heat exchange between the clean water and the wastewater, wherein the first temperature is greater than the second temperature when the heat exchange is performed.

[0074] In this embodiment, the wastewater is directly discharged into the sewer 7 when the temperature of the wastewater is greater than 55°C, which is easy to cause damage, therefore, in this working condition, if the temperature of the wastewater is higher than the temperature of the clean water, the heat exchanger 2 is started to exchange heat, which can reduce the temperature of the wastewater and recycle the heat energy, which is a resource recycling. The water in the water storage tank 3 is circulated into the heat exchanger 2 by the circulating pump, which can realize the circulation heat exchange and improve the heat exchange effect. It should be noted that the first preset temperature 55°C in this embodiment is only an example, the first preset temperature is the temperature limit of the sewer pipe material, and the temperature higher than the temperature limit will have the risk of scalding the sewer pipe, and the temperature lower than the temperature limit is the safe temperature, and the 55°C in this embodiment does not represent the limitation of the present application, and the first preset temperature can be set according to the different sewer pipe materials.

[0075] If the first temperature is less than the first preset temperature 55°C, the following steps are performed:

[0076] It is judged whether the dishwasher 1 is in the working state;

[0077] If the dishwasher 1 is in the working state, it is judged whether the second temperature is less than the first temperature; if the dishwasher 1 is not in the working state, the heat exchanger 2 stops working, and the wastewater is discharged into the sewer;

[0078] If the second temperature is less than the first temperature, the heat exchanger 2 is started to exchange heat between the wastewater and the clean water; if the second temperature is not less than the first temperature, the heat exchanger 2 stops working, and the wastewater is discharged into the sewer 7.

[0079] In this embodiment, if the temperature of the wastewater is lower than 55°C, which is the safe water temperature, but there is still heat energy in the water, if the temperature of the clean water is lower than the temperature of the wastewater, heat exchange and recycling can also be performed. In this embodiment, the heat exchange is started when the second temperature is less than the first temperature minus 3°C, and the heat exchange effect is more obvious at this temperature difference.

[0080] When the waste heat recovery system includes the wastewater tank 5, the waste heat recovery method further includes:

[0081] The temperature of the wastewater in the wastewater tank 5 is detected and recorded as the third temperature;

[0082] It is judged whether the third temperature is greater than the first preset temperature;

[0083] When the third temperature is greater than the first preset temperature, the first water pump 4 and the heat exchanger 2 are started to exchange heat between the wastewater and the clean water, wherein the second temperature is less than the third temperature when the heat exchanger works, when the second temperature is not less than the third temperature, the heat exchanger does not work, and the wastewater is stored in the wastewater tank 5; when the third temperature is less than the first preset temperature, the wastewater is discharged into the sewer 7.

[0084] In the embodiment, the heat-exchanged wastewater enters the wastewater tank 5, and the temperature sensor in the wastewater tank 5 is used to re-detect the wastewater temperature. If the wastewater temperature is still higher than 55℃, the wastewater cannot be discharged. According to the comparison between the wastewater temperature and the clean water temperature, if the wastewater temperature is high, the heat exchange is started to cool the wastewater; if the wastewater temperature is low, the wastewater is stored in the wastewater tank 5 and is kept until the temperature is reduced to below 55℃, or until the clean water temperature is reduced to below the wastewater temperature, and then the heat exchange is performed.

[0085] The waste heat recovery method provided in the embodiment further comprises water valve control.

[0086] When the dishwasher 1 is working, it is determined whether the dishwasher 1 needs hot water.

[0087] If the dishwasher 1 needs hot water, the second valve 10 is opened, the first valve 9 is closed, and the heat-exchanged clean water in the water storage tank 3 is introduced into the dishwasher 1.

[0088] If the dishwasher 1 does not need hot water, the second valve 10 is closed, and the first valve 9 is opened, and cold water is introduced into the dishwasher 1.

[0089] In the embodiment, when the dishwasher 1 needs hot water, the preheated water in the water storage tank 3 is introduced into the dishwasher 1 by controlling the valves, and the cold water from the water inlet 11 does not enter the dishwasher 1. When the dishwasher does not need hot water, the cold water from the water inlet 11 directly enters the dishwasher 1 by controlling the valves. When the dishwasher 1 stops working, the above valve control is stopped.

[0090] Although the specific embodiments of the present application are described above, those skilled in the art should understand that this is only an example, and the protection scope of the present application is defined by the appended claims. Those skilled in the art can make various changes or modifications to the embodiments without departing from the principles and essence of the present application, and these changes and modifications all fall within the protection scope of the present application.

Claims

1. A waste heat recovery system for a dishwasher, characterized in that, The waste heat recovery system includes: The dishwasher's drain outlet is connected to the wastewater inlet of the heat exchanger, and the heat exchanger's wastewater outlet is connected to the sewer. The wastewater inlet is equipped with a first temperature sensor, which is used to detect the temperature of the wastewater discharged by the dishwasher and record it as the first temperature. A water storage tank stores purified water. The water storage tank is connected to the purified water inlet of the heat exchanger, and the purified water outlet of the heat exchanger is connected to the water storage tank. The water storage tank is also connected to the water inlet of the dishwasher. A second temperature sensor is provided inside the water storage tank. The second temperature sensor is used to detect the temperature of the purified water in the water storage tank and record it as the second temperature. The controller is electrically connected to the heat exchanger, the water storage tank, the first temperature sensor, and the second temperature sensor. The water storage tank is used to send the purified water into the heat exchanger, and the heat exchanger is used to exchange heat between the wastewater discharged from the dishwasher and the purified water, and to send the purified water after heat exchange back to the water storage tank. The controller is used to start the heat exchanger to exchange heat between the purified water and the wastewater when the first temperature is greater than the first preset temperature, wherein the second temperature is less than the first temperature during the heat exchange. The controller is also used to determine whether the dishwasher is in working state when the first temperature is less than the first preset temperature; if the dishwasher is in working state, it determines whether the first temperature is greater than the second temperature; when the first temperature is greater than the second temperature, it starts the heat exchanger to exchange heat between the wastewater and the purified water. The first preset temperature is determined based on the temperature resistance limit of the sewer pipe material; A wastewater tank is also provided between the heat exchanger and the sewer. The wastewater outlet of the heat exchanger is connected to the inlet of the wastewater tank. The wastewater tank is connected to the wastewater inlet of the heat exchanger via a first water pump. The outlet of the wastewater tank is connected to the sewer via a control valve. A third temperature sensor is provided at the inlet of the wastewater tank. When the second temperature is not less than the first temperature, the heat exchanger stops working, and the wastewater tank is used to store the wastewater. The third temperature sensor is used to detect the temperature of the wastewater in the wastewater tank and record it as the third temperature. The control valve is used to discharge the wastewater into the sewer when the third temperature is lower than the first preset temperature. The wastewater tank is used to store the wastewater when the second temperature is not less than the third temperature; The controller is used to control the first water pump to pump the wastewater into the heat exchanger to exchange heat with the purified water when the third temperature is greater than the first preset temperature, wherein the second temperature is less than the third temperature during the heat exchange.

2. The waste heat recovery system as described in claim 1, characterized in that, The water storage tank is also connected to a tap water pipe, and is used to store purified water supplied by the tap water inlet. And / or, the water storage tank is connected to the heat exchanger via a second water pump, the second water pump being used to pump the purified water into the heat exchanger when the waste heat recovery system needs heat exchange; And / or, the water storage tank is provided with an insulation layer; And / or, the water storage tank is connected to the water inlet of the dishwasher via a second valve, the second valve being opened when the dishwasher needs hot water and closed when the dishwasher needs cold water; And / or, the tap water inlet is connected to the water inlet of the dishwasher via a first valve, the first valve being open when the dishwasher needs cold water and closed when the dishwasher needs hot water.

3. The waste heat recovery system as described in any one of claims 1-2, characterized in that, When the first temperature is lower than the first preset temperature and the dishwasher is not in operation, the heat exchanger stops the heat exchange.

4. A method for waste heat recovery from a dishwasher, characterized in that, The waste heat recovery method is implemented using the waste heat recovery system as described in any one of claims 1-3, and the waste heat recovery method includes: The temperature of the wastewater discharged from the dishwasher is detected and recorded as the first temperature; Determine whether the first temperature is greater than the first preset temperature; When the first temperature is greater than the first preset temperature, the heat exchanger is activated to exchange heat between the purified water and the wastewater. If the first temperature is lower than the first preset temperature, it is determined whether the dishwasher is in working condition. If the dishwasher is in working condition, it is determined whether the first temperature is greater than the second temperature. When the first temperature is greater than the second temperature, the heat exchanger is started to exchange heat between the wastewater and the purified water. The first preset temperature is determined based on the temperature resistance limit of the sewer pipe material; When the waste heat recovery system includes a wastewater tank, the waste heat recovery method further includes: The temperature of the wastewater in the wastewater tank is detected and recorded as the third temperature; Determine whether the third temperature is greater than the first preset temperature; When the third temperature is greater than the first preset temperature, the heat exchanger is activated to exchange heat between the wastewater and the purified water. When the heat exchanger is working, the second temperature is less than the third temperature. When the second temperature is not less than the third temperature, the heat exchanger is not working and the wastewater is stored in the wastewater tank. When the third temperature is less than the first preset temperature, the wastewater is discharged into the sewer.

5. The waste heat recovery method as described in claim 4, characterized in that, The step of detecting the temperature of the wastewater discharged from the dishwasher and recording it as the first temperature further includes: detecting the temperature of the purified water in the water storage tank and recording it as the second temperature; And / or, in the step of activating the heat exchanger when the first temperature is greater than the first preset temperature to exchange heat between the purified water and the wastewater, the first temperature is greater than the second temperature during the heat exchange. And / or, when the first temperature is lower than the first preset temperature, If the dishwasher is not in operation, the heat exchanger stops working and discharges the wastewater into the sewer. If the second temperature is not less than the first temperature, the heat exchanger stops working and the wastewater is discharged into the sewer.

6. The waste heat recovery method as described in claim 5, characterized in that, If the dishwasher is in operation, the following steps are also included: When the dishwasher is working, determine whether the dishwasher needs hot water; When the dishwasher needs hot water, the purified water that has undergone heat exchange in the water storage tank is introduced into the dishwasher; when the dishwasher does not need hot water, tap water is introduced into the dishwasher.

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