CN116616667A - Waste heat recovery system and waste heat recovery method of dishwasher - Google Patents

Abstract

The invention discloses a waste heat recovery system and a waste heat recovery method of a dishwasher. The waste heat recovery system includes: a heat exchanger, the drain outlet of the dishwasher is connected to the waste water inlet of the heat exchanger, and the waste water outlet of the heat exchanger is connected to the sewer connection; the waste water inlet is provided with a first temperature sensor, and the first temperature sensor is used to detect the temperature of the waste water discharged from the dishwasher and recorded as the first temperature; the water storage tank stores clean water in the water storage tank, and the water storage tank and the heat exchanger The clean water inlet is connected, the clean water outlet of the heat exchanger is connected with the water storage tank, and the water storage tank is also connected with the water inlet of the dishwasher; a second temperature sensor is arranged in the water storage tank, and the second temperature sensor is used to detect the temperature in the water storage tank. The temperature of the clean water is recorded as the second temperature; the controller is electrically connected with the heat exchanger, the water storage tank, the first temperature sensor and the second temperature sensor. The invention fully recovers the waste heat of the dishwasher waste water, can efficiently utilize the heat energy in the waste water, and can prevent the high-temperature waste water from scalding a sewer.

Description

Waste heat recovery system and waste heat recovery method of dishwasher

technical field

The invention relates to a waste heat recovery system and a waste heat recovery method of a dishwasher.

Background technique

After the traditional dishwasher discharges high-temperature wastewater into the sewer, the heat energy will be lost, resulting in a waste of energy. The thermal energy contained in high temperature wastewater has not been fully utilized.

At the same time, the temperature resistance limit of the sewer is around 60°C. When high-temperature wastewater (70-80°C) is directly discharged into the sewer, the temperature of the sewer pipe may be too high, causing problems such as pipe deformation, aging, and blockage. This has a negative impact on the reliability and service life of the sewer pipes.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the defects in the prior art that the washing wastewater of the dishwasher is too high in temperature and easily damage the sewer pipe, and provide a waste heat recovery system and a waste heat recovery method of the dishwasher.

The present invention solves the above technical problems through the following technical solutions:

One aspect of the present invention provides a waste heat recovery system for a dishwasher, the waste heat recovery system includes:

A heat exchanger, the drain of the dishwasher is connected to the waste water inlet of the heat exchanger, and the waste water outlet of the heat exchanger is connected to the sewer; the waste water inlet is provided with a first temperature sensor, and the first The temperature sensor is used to detect the temperature of the waste water discharged from the dishwasher and recorded as the first temperature;

A water storage tank, storing clean water in the water storage tank, the water storage tank is connected to the clean water inlet of the heat exchanger, the clean water outlet of the heat exchanger is connected to the water storage tank, and the water storage tank is also connected to the water storage tank The water inlet of the dishwasher is connected; the water storage tank is provided with a second temperature sensor, and the second temperature sensor is used to detect the temperature of the clean water in the water storage tank and recorded as the second temperature;

a controller, 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 clean water into the heat exchanger, and the heat exchanger is used to exchange heat between the waste water discharged from the dishwasher and the clean water, and exchange all the waste water after the heat exchange. Said clean water is sent back to said water storage tank;

The controller is used to activate the heat exchanger to perform heat exchange between the purified 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.

In the present invention, when the temperature of the waste water from the dishwasher is higher than the temperature resistance limit of the sewer pipe, directly discharging the waste water into the sewer pipe is likely to scald the sewer pipe. The present invention detects the waste water temperature by setting the first temperature sensor, and starts heat exchange when the waste water temperature is higher than the first preset temperature, and performs heat exchange between the high-temperature waste water and the cold water in the water storage tank, which can preheat the cold water, that is, The heat energy can be recycled, and the high-temperature wastewater can be cooled, so as to avoid scalding the sewer pipes. Preferably, in the present invention, the heat exchange is started when the second temperature is lower than the first temperature -3°C. At this time, starting the heat exchange can achieve a better heat exchange effect.

Preferably, a waste water tank is also provided between the heat exchanger and the sewer, the waste water outlet of the heat exchanger is connected to the water inlet of the waste water tank, and the waste water tank is connected to the waste water tank through the first water pump. The waste water inlet of the heat exchanger is connected, and the water outlet of the waste water tank is connected with the sewer through a control valve.

Preferably, the water inlet of the waste water tank is provided with a third temperature sensor, and the heat exchanger stops working when the second temperature is not lower than the first temperature, and the waste water tank is used to store the waste water , the third temperature sensor is used to detect the waste water temperature in the waste water tank, and recorded as the third temperature, and the control valve is used to set the temperature of the waste water in the waste water tank when the third temperature is lower than the first preset temperature The waste water is discharged into the sewer; the waste water tank is used to store the waste water when the second temperature is not less than the third temperature; the controller is used to store the waste water when the third temperature is greater than the first preset temperature , controlling the first water pump to pump the waste water into the heat exchanger to exchange heat with the clean water, wherein the second temperature is lower than the third temperature during the heat exchange.

In the present invention, the wastewater temperature is detected when the wastewater enters the wastewater tank. When the wastewater temperature is higher than the first preset temperature, there is a risk of scalding the downpipe. At this time, if the wastewater temperature is higher than the temperature of the clean water in the tank, the first A water pump pumps the waste water into the heat exchanger to exchange heat with the clean water until the temperature of the clean water is not lower than the temperature of the waste water and stops the heat exchange. If the temperature of the clean water is not lower than the temperature of the waste water at this time, no heat exchange is performed, and the waste water is stored in the waste water tank for standing. When the waste water temperature is lower than the first preset temperature, the control valve is opened, so that the waste water is discharged into the sewer pipe. In the present invention, the heat exchange is stopped when the temperature of the purified water is not lower than that of the waste water. At this time, the temperature difference between the water temperature in the water storage tank and the waste water temperature is not large, even higher than the waste water temperature, and the heat exchange effect is not obvious, so no heat exchange is performed. At this point the waste water is stored in the waste water tank.

Preferably, the water storage tank is also connected to the tap water pipeline, and the water storage tank is used to store clean water that is connected from the domestic water outlet.

Preferably, the water storage tank is connected to 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 to exchange heat; In the present invention, the circulating heat exchange of purified water can be realized through the second water pump, and the heat exchange effect can be improved.

Preferably, an insulation layer is provided inside the water storage tank;

Preferably, the water storage tank is connected to the water inlet of the dishwasher through a second valve, the second valve is opened when the dishwasher needs hot water, and the second valve is opened when the dishwasher needs cold water. said second valve is closed;

Preferably, the tap water port is connected to the water inlet of the dishwasher through a first valve, the first valve is opened when the dishwasher needs cold water, and the first valve is opened when the dishwasher needs hot water. The first valve is closed.

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

In the present invention, for waste water below the first preset temperature, which still contains a certain amount of heat, when there is a temperature difference between the waste water temperature and the water temperature in the water tank, that is, when the waste water temperature is greater than the clean water temperature, the waste water temperature still has recovery value , heat exchange can be performed to further recover the thermal energy in the waste water, so as to realize the recovery of the water temperature not higher than the first preset temperature.

Preferably, when the first temperature is lower than a first preset temperature and the dishwasher is not in a 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 at the same time, the first temperature is lower than the first preset temperature, so the pipe will not be scalded, so it can be discharged safely.

The present invention also provides a waste heat recovery method for a dishwasher, the waste heat recovery method is realized by using the above waste heat recovery system, and the waste heat recovery method includes:

Detecting the temperature of the waste water discharged from the dishwasher and recording it as the first temperature, detecting the temperature of the clean water in the water storage tank and recording it as the second temperature;

judging whether the first temperature is greater than a first preset temperature;

When the first temperature is greater than the first preset temperature, start the heat exchanger to perform heat exchange between the purified water and the waste water, wherein the first temperature is greater than the second temperature.

Preferably, in the step of judging whether the first temperature is greater than a first preset temperature, if the first temperature is lower than the first preset temperature, the following steps are performed:

judging whether the dishwasher is in working condition;

If the dishwasher is in the working state, it is judged whether the second temperature is lower than the first temperature, if the dishwasher is not in the working state, the heat exchanger stops working, and the waste water is discharged into the sewer;

If the second temperature is lower than the first temperature, start the heat exchanger to exchange heat between the waste water and the clean water; if the second temperature is not lower than the first temperature, the The heat exchanger stops working and the waste water is discharged into the sewer.

Preferably, when the waste heat recovery system includes a waste water tank, the waste heat recovery method further includes:

Detect the temperature of the waste water in the waste water tank, and record it as the third temperature;

judging whether the third temperature is greater than the first preset temperature;

When the third temperature is greater than the first preset temperature, start a heat exchanger to exchange heat between the waste water and the clean water, wherein the second temperature is lower than the The third temperature, when the second temperature is not lower than the third temperature, the heat exchanger does not work, and the waste water is stored in the waste water tank; when the third temperature is lower than the first When the temperature is preset, the waste water is discharged into the sewer.

Preferably, if the dishwasher is in working condition, 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 heat-exchanged clean water in the water storage tank is passed into the dishwasher; Pass tap water into the bowl machine.

The positive and progressive effect of the present invention is that whether to start the heat exchanger is determined by detecting the temperature of the waste water, thereby realizing multiple benefits. First, by monitoring the wastewater temperature in real time and according to the set temperature threshold, potential damage and damage to the sewer pipes caused by high-temperature wastewater can be avoided. Secondly, through the detection of the wastewater temperature and the corresponding start-up mechanism of the heat exchanger, this scheme can realize the full recovery of heat energy in the wastewater. By using the temperature of the wastewater as the basis for the activation of the heat exchanger, the thermal energy in this wastewater can be efficiently captured and recovered to be used to heat the clean water in the storage tank. This method of thermal energy recycling can significantly reduce the need for external energy, thereby achieving energy conservation goals. Finally, the use of the waste heat recovery system of the present invention has wide adaptability and can be adapted to dishwashers with different washing procedures.

Description of drawings

FIG. 1 is a schematic diagram of a waste heat recovery system according to Embodiment 1 of the present invention.

Fig. 2 is a flow chart of the waste heat recovery method of the dishwasher according to Embodiment 2 of the present invention.

Fig. 3 is a flow chart of the wastewater treatment of the dishwasher according to Embodiment 2 of the present invention.

Fig. 4 is a flow chart of water valve control in Embodiment 2 of the present invention.

Explanation of reference signs:

Dishwasher 1

Heat exchanger 2, first temperature sensor 21

Water storage tank 3, second temperature sensor 31

First water pump 4

Waste water tank 5, third temperature sensor 51

Control valve 6

Sewer 7

Second water pump 8

First Valve 9

Second valve 10

Water outlet 11

Detailed ways

The present invention is further illustrated below by means of examples, but the present invention is not limited to the scope of the examples.

Example 1

This embodiment provides a waste heat recovery system for a dishwasher. As shown in FIG. 1 , the preheat recovery system in this embodiment is arranged outside the dishwasher 1 , that is, it is designed separately from the dishwasher 1 . The waste heat recovery system includes 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).

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, and 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. Connect 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 with the water storage tank 3 through the water outlet pipe, and the water storage tank 3 is connected with the clean water inlet of the heat exchanger 2 through the second water pump 8 connect.

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

In this embodiment, 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 with 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 .

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; 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.

When the first temperature is higher than the first preset temperature and the second temperature is lower than the first temperature, the controller activates the heat exchanger 2 for heat exchange. In this embodiment, the first preset temperature is 55° C., and waste water higher than this temperature is likely to scald the sewer pipe made of PVC (Polyvinyl chloride, polyvinyl chloride). It should be noted that this embodiment is only an example. The first preset temperature is the temperature resistance limit of the sewer pipe material. If it is higher than the temperature resistance limit, there will be a risk of scalding the sewer pipe. If it is lower than the temperature resistance limit, it is a safe temperature. The 55°C mentioned in this embodiment does not represent a limitation to this solution, and those skilled in the art can set the value of the first preset temperature as required according to different materials of the downpipe. When the first temperature is greater than the second temperature, that is, there is a temperature difference between the waste water and the clean water, so the heat of the waste water can be taken away by the heat exchanger 2 to preheat the clean water, and at the same time, the waste water is cooled to avoid scalding the sewer. At the same time, the water storage tank 3 in this embodiment is provided with an insulating layer, which can be used for heat preservation, further retains the temperature of the preheated clean water, and recycles energy to fully save resources. In this embodiment, when the second temperature is lower than the first temperature -3°C, an obvious heat exchange effect can be produced.

When the second temperature is not less than the first temperature, the heat exchange is stopped. At this time, the temperature difference between the waste water and the clean water is not obvious, and the heat exchange effect is not good. The waste water is passed into the waste water tank 5 for storage.

At this time, if the third temperature is lower than the first preset temperature, that is, the waste water in the waste water tank is within the safe temperature range, then 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 a risk of scalding the sewer 7, so it is judged whether the third temperature is greater than the second temperature, if greater, the first water pump 4 and the heat exchanger 2 are started, and the waste water pump enter the heat exchanger 2 to exchange heat with clean water, further reduce the temperature of the waste water, and stop the heat exchange until the second temperature is not less than the third temperature. At this time, the waste water returns to the waste water tank 5, and then judges whether the third temperature is greater than the first preset temperature, and so on until the third temperature drops below the first preset temperature. It should be noted that if the third temperature is greater than the first preset temperature and the second temperature is not less than the third temperature, the waste water will stay in the waste water tank 5 and wait for it to cool naturally, or wait until the second temperature is lower than the third temperature again. start the heat exchange again. In this way, it can be ensured that the waste water discharged from the waste water tank 5 is all waste water lower than the first preset temperature, so as to prevent the overheated waste water from scalding the sewer 7 to the greatest extent.

In this embodiment, if the first temperature is lower than the first preset temperature, the waste water can also be recovered, specifically as follows, when the first temperature is lower than 55°C, if the dishwasher 1 is still working, it may still be Hot water is needed. At this time, although the waste water is in a safe temperature range, the heat in it still has the value of recovery. At this time, the second temperature is lower than the first temperature, and the heat exchanger 2 is started for heat exchange. Wherein, when the dishwasher 1 is not working, the heat exchange is stopped, because if the dishwasher 1 stops working, it may be several hours after the next startup of the dishwasher 1, and it is not meaningful to recover the heat of the waste water at this temperature. In other embodiments, if the dishwasher 1 stops working, it can continue to recover heat, because there is an insulating layer in the water storage tank 3, which can keep warm and avoid heat loss to a certain extent. In addition, in this embodiment, under this working condition, if the second temperature is not lower than the first temperature, there is no need for heat exchange, and the waste water is directly discharged, because the waste water will not damage the sewer 7 at this time, and has no heat exchange value , can be discharged directly.

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 is passed into the dishwasher 1 from the water storage tank 3 . When the dishwasher 1 does not need hot water, the first valve 9 is opened, the second valve 10 is closed, and tap water is directly fed into the dishwasher 1 .

The waste heat recovery system of this embodiment detects the temperature of the waste water by the first temperature sensor 21 to determine whether to start the heat exchanger 2, and through the detection of the waste water temperature and the corresponding start-up mechanism of the heat exchanger 2, the waste water can be cooled down, thereby avoiding damage to the sewer , and can fully recover the heat energy in the wastewater. By using the waste water temperature as the basis for starting the heat exchanger 2 , the thermal energy in the waste water can be effectively captured and recovered and used to heat the clean water in the water storage tank 3 . This method of thermal energy recycling can significantly reduce the need for external energy, thereby achieving energy conservation goals.

Example 2

As shown in the flowcharts of Figures 2-4, this embodiment provides a waste heat recovery method realized by using the waste heat recovery system in Embodiment 1, and the method includes the following steps:

Detect the temperature of the waste water discharged from the dishwasher 1 and record it as the first temperature, detect the temperature of the clean water in the water storage tank 3, and record it as the second temperature;

judging whether the first temperature is greater than a first preset temperature, wherein the first preset temperature is 55°C;

When the first temperature is higher than the first preset temperature of 55°C, the heat exchanger 2 and the second water pump 8 are started to exchange heat between the clean water and the waste water, wherein the first temperature is higher than the second temperature during the heat exchange.

In this embodiment, when the waste water temperature is higher than 55°C, it is easy to cause damage if it is directly discharged into the sewer 7. Therefore, under this working condition, if the waste water temperature is higher than the clean water temperature, the heat exchanger 2 is started to exchange heat, which can reduce waste water. Temperature, and secondly, heat energy can be recovered, which is the recycling of resources. Wherein, the water in the water storage tank 3 is passed into the heat exchanger 2 through the circulating pump, so that the circulating heat exchange can be realized and the heat exchange effect can be improved. It should be noted that the first preset temperature of this embodiment is 55°C as an example only. The first preset temperature is the temperature resistance limit of the sewer pipe material. If the temperature is higher than the temperature resistance limit, there will be a risk of scalding the sewer pipe. The temperature resistance limit is a safe temperature. The 55°C mentioned in this embodiment does not represent a limitation to this solution. Those skilled in the art can set the value of the first preset temperature according to the different materials of the downpipe.

If the first temperature is 55°C lower than the first preset temperature, the following steps are performed:

Determine whether the dishwasher 1 is in working condition;

If the dishwasher 1 is in the working state, it is judged whether the second temperature is lower than the first temperature; if the dishwasher 1 is not in the working state, the heat exchanger 2 stops working, and the waste water is discharged into the sewer;

If the second temperature is lower than the first temperature, start the heat exchanger 2 to exchange heat between the waste water and the clean water;

In this embodiment, if the wastewater temperature is lower than 55°C, it is safe water temperature, but there is still heat energy in the water at this time, if the purified water temperature is lower than the wastewater temperature, heat exchange recovery can also be performed. In this embodiment, it is preferable to start the heat exchange when the second temperature<the first temperature-3°C, and the heat exchange effect of this temperature difference is more obvious.

When the waste heat recovery system includes the waste water tank 5, the waste heat recovery method also includes:

Detect the waste water temperature in the waste water tank 5, and record it as the third temperature;

judging whether the third temperature is greater than the first preset temperature;

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

In this embodiment, the waste water after heat exchange enters the waste water tank 5, and the temperature sensor in the waste water tank 5 is used to re-detect the waste water temperature. If the waste water temperature is still higher than 55°C, it cannot be discharged. If the waste water temperature is high, heat exchange is started to cool the waste water; if the waste water temperature is low, the waste water is stored in the waste water tank 5 and left to stand until its temperature drops below 55°C; or when the purified water temperature is lowered again Heat exchange is performed at the temperature of the wastewater.

The waste heat recovery method provided in this embodiment also includes water valve control:

When the dishwasher 1 is working, it is judged whether the dishwasher 1 needs hot water;

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 passed into the dishwasher 1 .

If the dishwasher 1 does not need hot water, close the second valve 10, open the first valve 9, and feed cold water into the dishwasher 1.

In this embodiment, when the dishwasher 1 needs hot water, the preheated water in the water storage tank 3 enters the dishwasher 1 by controlling the valve, and the cold water from the tap water port 11 does not enter the dishwasher 1 . When the dishwasher does not need hot water, the cold water from the water outlet 11 directly enters the dishwasher 1 by controlling the valve. When the dishwasher 1 stops working, the above valve control is stopped.

Although the specific implementation of the present invention has been described above, those skilled in the art should understand that this is only an example, and the protection scope of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principle and essence of the present invention, but these changes and modifications all fall within the protection scope of the present invention.

Claims (10)

1. A waste heat recovery system for a dishwasher, characterized in that the waste heat recovery system comprises: A heat exchanger, the drain of the dishwasher is connected to the waste water inlet of the heat exchanger, and the waste water outlet of the heat exchanger is connected to the sewer; the waste water inlet is provided with a first temperature sensor, and the first The temperature sensor is used to detect the temperature of the waste water discharged from the dishwasher and recorded as the first temperature; A water storage tank, storing clean water in the water storage tank, the water storage tank is connected to the clean water inlet of the heat exchanger, the clean water outlet of the heat exchanger is connected to the water storage tank, and the water storage tank is also connected to the water storage tank The water inlet of the dishwasher is connected; the water storage tank is provided with a second temperature sensor, and the second temperature sensor is used to detect the temperature of the clean water in the water storage tank and recorded as the second temperature; a controller, 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 clean water into the heat exchanger, and the heat exchanger is used to exchange heat between the waste water discharged from the dishwasher and the clean water, and exchange all the waste water after the heat exchange. Said clean water is sent back to said water storage tank; The controller is used to activate the heat exchanger to perform heat exchange between the purified 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. 2. The waste heat recovery system according to claim 1, characterized in that, a waste water tank is also provided between the heat exchanger and the sewer, and the waste water outlet of the heat exchanger is connected to the waste water tank. connected to the water inlet, the waste water tank is connected to the waste water inlet of the heat exchanger through the first water pump, the water outlet of the waste water tank is connected to the sewer through a control valve, and the water inlet of the waste water tank is provided with a third Temperature Sensor, When the second temperature is not less than the first temperature, the heat exchanger stops working, and the waste water tank is used to store the waste water; The third temperature sensor is used to detect the waste water temperature in the waste water tank, and recorded as the third temperature, and the control valve is used to set the Waste water is discharged into said sewer. 3. The waste heat recovery system according to claim 2, wherein the waste water tank is used to store the waste water when the second temperature is not less than the third temperature; The controller is used to control 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 heat exchange When the second temperature is lower than the third temperature. 4. The waste heat recovery system according to claim 1, characterized in that, the water storage tank is also connected to the tap water pipeline, and the water storage tank is used to store clean water connected to the tap water outlet, And/or, the water storage tank is connected to 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 to exchange heat; 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 through a second valve, the second valve is opened when the dishwasher needs hot water, and the second valve is opened when the dishwasher needs cold water. said second valve is closed; And/or, the tap water port is connected to the water inlet of the dishwasher through a first valve, the first valve is opened when the dishwasher needs cold water, and the first valve is opened when the dishwasher needs hot water. The first valve is closed. 5. The waste heat recovery system according to claim 1, wherein the controller is further used to determine whether the dishwasher is in a working state when the first temperature is lower than a first preset temperature, and if If the dishwasher is in working condition, it is judged whether the first temperature is higher than the second temperature, and when the first temperature is higher than the second temperature, the heat exchanger is started to convert the wastewater and the cleaning Water for heat exchange. 6. The waste heat recovery system according to any one of claims 1-5, wherein when the first temperature is lower than the first preset temperature and the dishwasher is not in a working state, the The heat exchanger stops the heat exchange. 7. A waste heat recovery method for a dishwasher, characterized in that the waste heat recovery method is realized by using the waste heat recovery system according to any one of claims 1-6, and the waste heat recovery method comprises: Detecting the temperature of the waste water discharged from the dishwasher and recording it as the first temperature; judging whether the first temperature is greater than a first preset temperature; When the first temperature is greater than the first preset temperature, the heat exchanger is activated to exchange heat between the clean water and the waste water. 8. The waste heat recovery method according to claim 7, wherein the step of detecting the temperature of the waste water discharged from the dishwasher and recording it as the first temperature further comprises: detecting the temperature of the clean water in the water storage tank. temperature, and recorded as the second temperature; And/or, when the first temperature is greater than the first preset temperature, start the heat exchanger, and perform heat exchange between the clean water and the waste water, when performing the heat exchange the first temperature is greater than the second temperature; And/or, in the step of judging whether the first temperature is greater than a first preset temperature, if the first temperature is lower than the first preset temperature, perform the following steps: judging whether the dishwasher is in working condition; If the dishwasher is in working condition, it is judged whether the second temperature is lower than the first temperature; if the dishwasher is not in working condition, the heat exchanger stops working, and the waste water is discharged into the sewer; If the second temperature is lower than the first temperature, start the heat exchanger to exchange heat between the waste water and the clean water; if the second temperature is not lower than the first temperature, the The heat exchanger stops working and the waste water is discharged into the sewer. 9. The waste heat recovery method according to claim 7, wherein when the waste heat recovery system includes a waste water tank, the waste heat recovery method further comprises: Detect the temperature of the waste water in the waste water tank, and record it as the third temperature; judging whether the third temperature is greater than the first preset temperature; When the third temperature is greater than the first preset temperature, start a heat exchanger to exchange heat between the waste water and the clean water, wherein the second temperature is lower than the The third temperature, when the second temperature is not lower than the third temperature, the heat exchanger does not work, and the waste water is stored in the waste water tank; when the third temperature is lower than the first When the temperature is preset, the waste water is discharged into the sewer. 10. The waste heat recovery method according to claim 8, characterized in that, if the dishwasher is in working condition, it further comprises the following steps: When the dishwasher is working, it is judged whether the dishwasher needs hot water; When the dishwasher needs hot water, the heat-exchanged clean water in the water storage tank is passed into the dishwasher; Access to tap water.