Closed heat pump clothes drying washing and drying machine and heat recovery method

Abstract

The invention belongs to the technical field of washing and protecting equipment, and particularly relates to a closed heat pump clothes drying washing and drying machine which comprises a main air duct, a rotating wheel dehumidification device, a dehumidification channel and a bypass air duct. An evaporator, a heat exchanger and a condenser are arranged in the main air duct; the dehumidification channel conducts dehumidification on the dehumidification area, exhausted gas is introduced into the heat exchanger to serve as a heat exchange medium, and the heat exchanger can heat the gas exhausted by the evaporator. In the initial stage of drying, when the bypass air duct is opened, part of return airflow of the return air inlet of the drying roller bypasses the evaporator through the bypass air duct for heat exchange at the heat exchanger, the temperature rise speed is higher, and the drying efficiency is improved. In the later drying stage, when the bypass air duct is closed, air flow of an air return opening of the drying roller completely passes through the evaporator, heat of the dehumidification channel, waste heat of the return air of the roller of the bypass air duct and waste cold of the evaporator are utilized to enable the return air of the roller to be dehumidified once and preheated twice before the return air is recycled into the condenser to be heated, and the dehumidification efficiency is improved; the heat pump load pressure and the energy consumption are reduced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of washing and protecting equipment, and particularly relates to a closed heat pump drying and washing machine and a heat recovery method. BACKGROUND

[0002] The drying technology principle of a general closed drying and washing machine is mainly to use electric heating or a more energy-saving heat pump to generate dry hot air to take away the moisture of clothes, so that the clothes reach a dry state.

[0003] In the prior art, a dehumidification system with a rotating wheel is disclosed, such as the invention application with the application number 202310072139.6 and the patent name of a washing and protecting equipment and a control method. The disclosed rotating wheel dehumidification system is mainly composed of a rotating wheel dehumidification device, a moisture absorption area, a moisture removal area, and a heat source and the like. The working process is roughly as follows: dry air treated by the moisture absorption area is transported to the area to be dehumidified, and the humid air discharged from the area enters the moisture removal area; at the same time, the heat source heats the air into high-temperature air, which enters the moisture removal area of the rotating wheel dehumidification device and becomes high-temperature and high-humidity air, and then is directly discharged to the external environment. However, the following problems exist when the scheme is used: The heat utilization of the existing heat pump drying and washing machine needs to be improved. In the two devices, the evaporator is responsible for cooling and dehumidifying the circulating hot air after the clothes dehumidification is completed, and the condenser is responsible for heating the circulating hot air cooled by the evaporator. In this process, the load of the two devices is large, and the circulating air after the clothes dehumidification still has a lot of heat, and this part of heat is wasted by the evaporator.

[0004] The air inlet temperature rising rate of the existing heat pump drying and washing machine needs to be improved. The circulating hot air only passes through one link of the condenser for temperature rising, and the temperature rising rate is very limited. SUMMARY

[0005] The purpose of the present application is to solve the above-mentioned technical problems, and to provide a closed heat pump drying and washing machine and a heat recovery method, which can achieve faster temperature rising speed in the early stage of drying, can produce more high-temperature and dry circulating hot air when drying clothes, can improve the drying efficiency, can more fully utilize energy in the drying process, can greatly reduce energy waste, and can achieve more energy-saving effect.

[0006] Therefore, the present application provides a closed heat pump drying and washing machine, which comprises: A main air duct is connected to the air inlet and air outlet of the drying drum, and an evaporator, a heat exchanger and a condenser are arranged in the main air duct from the air outlet to the air inlet; A rotary dehumidifying device includes a dehumidifying zone and a dehumidification zone, and the dehumidifying zone is located between the evaporator and the condenser in the main air duct. A dehumidification channel, the dehumidification zone of the rotary dehumidifying device is located in the dehumidification channel, the dehumidification channel is connected to the high-temperature gas to dehumidify the dehumidification zone, and the discharged high-temperature and high-humidity gas is connected to the heat exchanger as a heat exchange medium, and the heat exchanger can heat the gas after the evaporator dehumidification. A bypass air duct includes two states of opening and closing, when the bypass air duct is closed, the air flow of the drying drum air outlet passes through the evaporator, when the bypass air duct is opened, part of the air flow of the drying drum air outlet bypasses the evaporator through the bypass air duct and exchanges heat at the heat exchanger.

[0007] In the technical solution, at the initial stage of drying, the drum back air passes through the evaporator, the temperature is reduced, and the humidity is reduced, and then reaches the heat exchanger and mixes with another drum back air entering the bypass air duct, and the remaining heat of part of the drum back air is used for preheating to increase the temperature. At the same time, the rotary dehumidifying device receives high-temperature gas from the dehumidification channel in the dehumidification zone, and gradually releases water under the influence of high temperature to form high-temperature and high-humidity hot air into the heat exchanger as a heat exchange medium. The drum back air passes through the heat exchanger and exchanges heat with the high-temperature and high-humidity gas discharged from the dehumidification zone into the heat exchanger, and the temperature is increased again, and then the drum back air passes through the dehumidification zone of the rotary dehumidifying device, and the humidity is greatly reduced, and then the drum back air enters the condenser for heat exchange and temperature rise to obtain high-temperature and dry drum inlet air. In this process, the drum back air is preheated twice before entering the condenser, and the drying efficiency is greatly improved. The high-temperature and high-humidity hot air in the heat exchanger exchanges heat with the relatively cold drum back air passing through the evaporator through the heat exchange wall to form condensate, and the waste heat of the evaporator is utilized. The bypass air duct is opened at the initial stage of drying, which can increase the temperature faster at the initial stage of drying. The bypass air duct is closed at the middle and late stages of drying, which can improve the dehumidification efficiency.

[0008] The heat of the dehumidification channel, the remaining heat of the drum back air of the bypass air duct and the waste heat of the evaporator make the drum back air pass through dehumidification and preheating twice before recycling into the condenser for heating. The bypass air duct is opened at the initial stage of drying, which can increase the temperature faster at the initial stage of drying. When drying clothes, it can produce more high-temperature and dry circulating hot air, and the drying efficiency is improved. The bypass air duct is closed at the middle and late stages of drying, which can improve the dehumidification efficiency and reduce the load pressure of the heat pump system, reduce energy consumption, make the application of energy more sufficient during the drying process, greatly reduce the waste of energy, and be more energy-saving.

[0009] Further, the dehumidification channel is connected to the outside environment.

[0010] In the technical solution, the air in the dehumidification channel is introduced from the outside.

[0011] Further, the first fan is arranged in the dehumidification channel and close to the air inlet end of the dehumidification channel, and the first fan provides power for the air in the dehumidification channel to move towards the dehumidification area.

[0012] Further, the heat source is arranged in the dehumidification channel and used to heat the air introduced from the outside into the dehumidification channel.

[0013] Further, the heat source is arranged between the first fan and the dehumidification area.

[0014] Further, the inlet of the heat exchange pipe of the heat exchanger is communicated with the air outlet end of the dehumidification channel.

[0015] Further, the second fan is arranged in the main air duct and provides power for the air in the main air duct.

[0016] Further, one end of the bypass air duct is communicated with the air return port of the drying drum, and the other end is communicated with the air inlet of the heat exchanger.

[0017] Further, the heat recovery method of the closed heat pump clothes dryer comprises the following steps. The high-temperature and high-humidity gas discharged from the dehumidification area in the dehumidification channel is introduced into the heat exchanger as a heat exchange medium to preheat the gas after the evaporator is cooled and dehumidified. The bypass air duct is arranged to be opened and closed, and part of the return air gas in the air return port of the drying drum is guided to the space between the evaporator and the heat exchanger in the main air duct to preheat the gas after the evaporator is cooled and dehumidified. The method comprises the following steps. S1: Start the drying program: put the clothes to be dried into the drying drum, and make the air in the main air duct start to flow. S2: Initial drying stage: when it is determined that the initial drying stage, the rotating speed of the first fan is adjusted to the high speed value set in the program, the output power of the heat source is adjusted to the high power value set in the program, the bypass air duct is opened, and the system temperature rising rate is accelerated. S3: Late drying stage: when it is determined that the late drying stage, the rotating speed of the first fan is adjusted to the low speed value set in the program, the output power of the heat source is adjusted to the low power value set in the program, the bypass air duct is closed, and the system power consumption is reduced. S4: Drying end: when it is determined that the clothes are dried, the rotating wheel of the rotating dehumidification device, the first fan and the heat source are all stopped, and the program is ended.

[0018] Further, the determination parameter of the initial drying stage at least includes the condenser temperature rising rate detected by the temperature sensing bag.

[0019] Further, the determination parameter of the initial drying stage at least includes the condenser temperature rising rate detected by the temperature sensing bag.

[0020] The beneficial effects of the present application are: The heat of the dehumidification channel, the waste heat of the drum return air of the bypass air duct, and the waste cold of the evaporator are used to make the drum return air pass through dehumidification and preheating twice before being recycled into the condenser for heating. The bypass air duct is opened in the initial drying stage, so that the temperature rising rate in the pre-drying temperature rising stage is faster. In the process of drying clothes, more high-temperature dry circulating hot air can be produced, and the drying efficiency is improved. In the middle and later stages of drying, the bypass air duct is closed, which can improve the dehumidification efficiency, reduce the load pressure of the heat pump system, and reduce energy consumption. In the drying process, the application of energy is more sufficient, the waste of energy is greatly reduced, and the energy saving is more. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The schematic diagram of the present application; Figure 2 The flow chart of the heat recovery method of the present application; The marks in the figure are: 1, main air duct; 2, air inlet; 3, return air outlet; 4, drying drum; 5, evaporator; 6, heat exchanger; 7, condenser; 8, rotary dehumidification device; 9, dehumidification zone; 10, dehumidification zone; 11, dehumidification channel; 12, bypass air duct; 13, first fan; 14, heat source; 15, second fan. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present application will be described clearly in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art belong to the scope of protection of the present application.

[0023] In the description of the present application, it should be noted that the terms used herein are merely for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. For the purpose of description, the dimensions of the various parts shown in the drawings are not drawn to scale. The techniques, methods, and devices known to those of ordinary skill in the relevant art can not be discussed in detail, but should be considered part of the specification when appropriate. In all examples shown and discussed herein, any specific value should be interpreted as merely exemplary and not as a limitation. Thus, other examples of the exemplary embodiments can have different values. It should be noted that like reference numerals and letters refer to like items in the following drawings, and thus, once an item is defined in one drawing, it need not be discussed further in subsequent drawings.

[0024] It should be noted that the terms "first", "second", and the like in the description and claims of the application are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the use of such terms as "first" and "second" are arbitrary labels and are used for purposes of distinguishing between the elements being referred to, and therefore, it is to be understood that the "first" and "second" elements can be interchangeable and that the embodiments of the application can operate in other sequences than those described or illustrated herein. Moreover, the terms "first", "second", and the like are not necessarily used consistently throughout the description and claims, and are used in the context of the specific application in which they are used.

[0025] It should be noted that in the description of the present application, the orientation or positional relationships indicated by the terms such as "front, back, up, down, left, right", "horizontal, vertical, perpendicular, horizontal", and "top, bottom" are generally based on the orientation or positional relationships shown in the drawings, and are merely for the convenience of describing the present application and simplifying the description. Without being contrary, these orientation terms do not indicate or imply that the devices or elements referred to must have a particular orientation or be constructed and operated in a particular orientation, and therefore should not be understood as limiting the scope of protection of the present application. The orientation terms "inner, outer" refer to the inner and outer relative to the contour of the parts themselves.

[0026] It should be noted that in this application, the terms "comprising", "including", or any other variant thereof are intended to cover a non-exclusive inclusion, such that processes, methods, articles, or apparatuses that comprise a list of elements are not limited to those elements, but can also include other elements not expressly listed, or can also include elements inherent in such processes, methods, articles, or apparatuses. Without further limitation, an element defined by the statement "comprising a" does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes the element. In addition, it should be pointed out that the scope of the methods and apparatuses in the embodiments of the present application is not limited to performing functions in the order shown or discussed, but can also include performing functions in a substantially simultaneous manner or in reverse order according to the functions involved, for example, the described method can be performed in an order different from that described, and various steps can also be added, omitted, or combined. In addition, the features described with reference to certain examples can be combined in other examples.

[0027] As shown in Figure 1 A closed heat pump clothes drying and washing machine comprises: A main air duct 1, the two ends of which are respectively connected to the air inlet 2 and the air return 3 of the drying drum 4, and an evaporator 5, a heat exchanger 6 and a condenser 7 are sequentially arranged in the main air duct 1 from the air return 3 to the air inlet 2; A rotary dehumidification device 8, which comprises a dehumidification zone 9 and a dehumidification zone 10, and the dehumidification zone 9 is located between the evaporator 5 and the condenser 7 in the main air duct 1; A dehumidification channel 11, the dehumidification zone 10 of the rotary dehumidification device 8 is located in the dehumidification channel 11, the dehumidification channel 11 introduces high-temperature gas to dehumidify the dehumidification zone 10, and the discharged high-temperature and high-humidity gas is introduced into the heat exchanger 6 as a heat exchange medium, and the heat exchanger 6 can heat the gas after the evaporator 5 dehumidification; A bypass air duct 12, which comprises two states of opening and closing, when the bypass air duct 12 is closed, the air flow of the air return 3 of the drying drum 4 passes through the evaporator 5 entirely, when the bypass air duct 12 is opened, part of the air return flow of the air return 3 of the drying drum 4 bypasses the evaporator 5 through the bypass air duct 12 and exchanges heat at the heat exchanger 6.

[0028] The dehumidification channel 11 is communicated with the outside environment. The air in the dehumidification channel 11 is introduced from the outside. A first fan 13 is arranged in the dehumidification channel 11 and is arranged close to the air inlet end of the dehumidification channel 11. The first fan 13 provides power for the air in the dehumidification channel 11 to move towards the dehumidification zone 10. A heat source 14 is arranged in the dehumidification channel 11 and is used to heat the air introduced from the outside into the dehumidification channel 11. The heat source 14 is not limited to electric heating, microwave, heat pump and other heating methods. The heat source 14 is arranged between the first fan 13 and the dehumidification zone 10.

[0029] When the dehumidification program starts, the temperature sensing bag starts to detect the temperature rising rate of the condenser 7, the drum inlet air temperature and the drum return air temperature. When the drying process just starts, the temperature of the condenser 7 rises quickly and the temperature rising rate is large. The program judges that it is in the initial stage of drying. The rotary dehumidification device 8 starts to rotate and the bypass air duct 12 is opened. Under the drive of the second fan 15, the high-temperature and high-humidity drum return air after the clothes in the drying drum 4 are dried enters the evaporator 5 and the bypass air duct 12 at the air inlet of the evaporator 5 respectively. The temperature and humidity of the drum return air are reduced after passing through the evaporator 5. Then the drum return air reaches the heat exchanger 6 and is mixed with another drum return air entering from the bypass air duct 12. The heat of the drum return air discharged from the bypass air duct 12 is used to preheat and increase the temperature of the air from the evaporator 5.

[0030] In the dehumidification channel 11, the first fan 13 operates to absorb fresh air. The fresh air is heated by the heat source 14. The fresh air is dehumidified by the dehumidification zone 10 of the rotary dehumidification device 8. The rotary dehumidification device 8 gradually releases water under the influence of high temperature to form high-temperature and high-humidity hot air which enters the heat exchanger 6. The high-temperature and high-humidity hot air in the heat exchanger 6 exchanges heat with the relatively cold drum return air from the evaporator 5 through the heat exchange wall to form condensate. The relatively cold drum return air from the evaporator 5 is preheated by the heat exchanger 6. The temperature is increased again, which is beneficial to the recycling of the residual cold of the evaporator 5. Subsequently, the drum return air passes through the dehumidification zone 9 of the rotary dehumidification device 8 and the humidity is greatly reduced. Then the drum return air enters the condenser 7 to exchange heat and increase the temperature. The drum inlet air is obtained. In this process, the drum return air is preheated twice and dehumidified twice before entering the condenser 7. The drying efficiency is greatly improved.

[0031] When the temperature sensing bag detects that the temperature rising rate of the condenser 7 is reduced to the program setting value and the temperature difference between the drum return air and the inlet air is less than the program setting value, the system judges that the drying process has reached the later stage. The power consumption of the rotary dehumidification device 8 is reduced by reducing the rotating speed of the first fan 13 and the output power of the heat source 14 in the dehumidification zone 10 and closing the bypass air duct 12. When the system judges that the clothes are successfully dried, the rotary dehumidification device 8, the first fan 13 and the heat source 14 all stop running. The program runs.

[0032] The bypass air duct 12 is opened in the initial stage of drying, so that the temperature rising speed is faster in the temperature rising stage of the initial stage of drying. In the middle and later stages of drying, the bypass air duct 12 is closed, so that the dehumidification efficiency is improved.

[0033] The drum return air is dehumidified once and preheated twice before being recycled into the condenser 7 for heating by using the heat of the dehumidification passage 11, the waste heat of the drum return air of the bypass air duct 12 and the waste cold of the evaporator 5. The temperature rising speed is faster in the temperature rising stage of the initial stage of drying by opening the bypass air duct 12. The circulating hot air with higher temperature can be produced in the process of drying clothes, so that the drying efficiency is improved. In the middle and later stages of drying, the bypass air duct 12 is closed, so that the dehumidification efficiency is improved, the load pressure of the heat pump system is reduced, the energy consumption is reduced, the energy is more fully used in the drying process, the energy waste is greatly reduced and the energy saving is improved.

[0034] The heat exchange pipe inlet of the heat exchanger 6 is communicated with the air outlet end of the dehumidification passage 11.

[0035] The second air fan 15 is arranged in the main air duct 1 and provides power for the air in the main air duct 1.

[0036] One end of the bypass air duct 12 is communicated with the return air outlet 3 of the drying drum 4, and the other end is communicated with the air inlet of the heat exchanger 6.

[0037] The heat recovery method of the closed heat pump drying and washing machine: The heat exchanger 6 is arranged in the main air duct 1, the high-temperature and high-humidity gas discharged from the dehumidification zone 10 in the dehumidification passage 11 is introduced into the heat exchanger 6 as a heat exchange medium, and the gas after the evaporator 5 is cooled and dehumidified is preheated; The bypass air duct 12 is arranged to be opened and closed, and when the bypass air duct 12 is opened, part of the return air gas of the return air outlet 3 of the drying drum 4 is directly guided to the evaporator 5 and the heat exchanger 6 in the main air duct 1 to bypass the cooling of the evaporator 5, so as to preheat the gas after the evaporator 5 is cooled and dehumidified in the initial stage of drying; The method comprises the following steps: S1: starting the drying program: putting the drying object into the drying drum 4, and starting the air flow in the main air duct 1; S2: initial stage of drying: when it is determined that it is the initial stage of drying, the rotating speed of the first air fan 13 is adjusted to the high speed value set in the program, the output power of the heat source 14 is adjusted to the high power value set in the program, the bypass air duct 12 is opened, and the system temperature rising speed is increased; S3: later stage of drying: when it is determined that it is the later stage of drying, the rotating speed of the first air fan 13 is adjusted to the low speed value set in the program, the output power of the heat source 14 is adjusted to the low power value set in the program, the bypass air duct 12 is closed, and the system power consumption is reduced; S4: drying end: when the clothes are determined to be dried, the runner of the runner dehumidification device 8, the first fan 13 and the heat source 14 are all stopped, and the program is ended.

[0038] The determination parameters of the early drying stage at least include the condenser 7 temperature rising rate detected by the temperature sensing bag.

[0039] The determination parameters of the late drying stage at least include the condenser 7 temperature rising rate detected by the temperature sensing bag and the difference between the drum inlet air temperature and the drum outlet air temperature.

[0040] The control flow of the heat recovery method is shown in the following figure. Figure 2 When the condenser 7 temperature rising rate is greater than the program setting value, it is determined that the drying process is in the early drying stage, the first fan 13 speed is adjusted to the high speed program setting value, the heat source 14 output power is adjusted to the high power program setting value, the bypass air duct 12 is opened, the runner dehumidification device 8 is operated at high load, and the system temperature rising rate is accelerated. When the temperature sensing bag detects that the condenser 7 temperature rising rate is less than the program setting value, the difference between the drum inlet air temperature and the drum outlet air temperature is detected again. If the difference is less than the program setting value, it is determined that the drying process is in the late drying stage, the first fan 13 speed is adjusted to the low speed program setting value, the heat source 14 output power is adjusted to the low power program setting value, the bypass air duct 12 is closed, the runner dehumidification device 8 is operated at low power, and the system power consumption is reduced. Then the clothes drying data is collected. If the clothes drying is successful, it indicates that the drying process is about to end, the runner is stopped, the first fan 13 and the heat source 14 are all stopped, the runner dehumidification device 8 is closed, and the program is ended.

[0041] The embodiments of the present application are described above in combination with the drawings. In the case of no conflict, the embodiments and the features in the embodiments can be combined with each other, the present application is not limited to the above specific embodiments, the above specific embodiments are only illustrative, not limited, and the person skilled in the art can make many forms under the inspiration of the present application without departing from the scope of the present application and the protection scope of the claims.

Claims

1. A closed-loop heat pump clothes dryer / washer, characterized in that... ,include: The main air duct (1) is connected to the air inlet (2) and the air return outlet (3) of the drying drum (4) at both ends. An evaporator (5), a heat exchanger (6) and a condenser (7) are arranged in the main air duct (1) from the air return outlet (3) to the air inlet (2). Rotary dehumidifier (8), the rotary dehumidifier (8) includes a dehumidification zone (9) and a dehumidification zone (10), the dehumidification zone (9) is located between the evaporator (5) and the condenser (7) in the main air duct (1); Dehumidification channel (11), the dehumidification zone (10) of the rotary dehumidifier (8) is located in the dehumidification channel (11). High temperature gas is introduced into the dehumidification channel (11) to dehumidify the dehumidification zone (10), and the discharged high temperature and high humidity gas is introduced into the heat exchanger (6) as a heat exchange medium. The heat exchanger (6) can heat up the gas after the evaporator (5) has been cooled and dehumidified. The bypass ventilation duct (12) has two states: open and closed. When the bypass ventilation duct (12) is closed, all the airflow from the return air inlet (3) of the drying drum (4) passes through the evaporator (5). When the bypass ventilation duct (12) is open, part of the return airflow from the return air inlet (3) of the drying drum (4) passes through the bypass ventilation duct (12) and bypasses the evaporator (5) to exchange heat at the heat exchanger (6).

2. A closed-loop heat pump clothes dryer / washer according to claim 1, characterized in that, The air inlet of the dehumidification channel (11) is connected to the external environment.

3. A closed-loop heat pump clothes dryer / washer according to claim 2, characterized in that, The dehumidification channel (11) is equipped with a first fan (13), which is located near the air inlet of the dehumidification channel (11). The first fan (13) provides power to the air in the dehumidification channel (11) so that the air moves toward the dehumidification zone (10).

4. A closed-loop heat pump clothes dryer / washer according to claim 3, characterized in that, A heat source (14) is provided inside the dehumidification channel (11) to heat the air introduced from the outside into the dehumidification channel (11).

5. A closed-loop heat pump clothes dryer / washer according to claim 4, characterized in that, The heat source (14) is located between the first fan (13) and the dehumidification zone (10).

6. A closed-loop heat pump clothes dryer / washer according to any one of claims 1-5, characterized in that, The heat exchange tube inlet of the heat exchanger (6) is connected to the air outlet of the dehumidification channel (11).

7. A closed-loop heat pump clothes dryer / washer according to any one of claims 1-5, characterized in that, One end of the bypass ventilation duct (12) is connected to the return air inlet (3) of the drying drum (4), and the other end is connected to the air inlet of the heat exchanger (6).

8. A method for heat recovery in a closed-loop heat pump washer-dryer, characterized in that, Using the closed-loop heat pump washer-dryer as described in any one of claims 1-5: A heat exchanger (6) is installed in the main air duct (1). The high temperature and high humidity gas discharged from the dehumidification zone (10) in the dehumidification channel (11) is introduced into the heat exchanger (6) as a heat exchange medium to preheat the gas after the evaporator (5) has been cooled and dehumidified. A bypass ventilation duct (12) that can be opened and closed is set up. When the bypass ventilation duct (12) is opened, part of the return air gas from the return air inlet (3) of the drying drum (4) bypasses the cooling of the evaporator (5) and is directly guided to the space between the evaporator (5) and the heat exchanger (6) in the main air duct (1). This is used to preheat the gas after cooling and dehumidifying the evaporator (5) in the early stage of drying. Includes the following steps: S1: Start the drying program: Place the items to be dried into the drying drum (4) to allow the air in the main air duct (1) to begin flowing; S2 Drying Initial Stage: When it is determined to be the drying initial stage, the speed of the first fan (13) is adjusted to the high speed value set by the program, the output power of the heat source (14) is adjusted to the high power value set by the program, the bypass ventilation duct (12) is opened, and the system heating rate is accelerated. S3: Drying stage: When it is determined to be the drying stage, the speed of the first fan (13) is adjusted to the low speed value set by the program, the output power of the heat source (14) is adjusted to the low power value set by the program, the bypass ventilation duct (12) is closed, and the system power consumption is reduced. S4: Drying complete: When the clothes are determined to be dry, the rotor of the dehumidifier (8), the first fan (13) and the heat source (14) all stop running, and the program runs out.

9. A heat recovery method for a closed-loop heat pump washer-dryer according to claim 8, characterized in that, The initial drying parameters include at least the condenser (7) heating rate detected by the temperature sensor.

10. A heat recovery method for a closed-loop heat pump washer-dryer according to claim 8, characterized in that, The parameters for determining the later stage of drying include at least: the heating rate of the condenser (7) detected by the temperature sensor and the difference between the inlet air temperature and the outlet air temperature of the drum.

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