Condensation dryer with heat pump and recirculation unit, and method for its operation.

Description

[0001] The invention relates to a condensation dryer with a heat pump and recirculation component, as well as a method for its operation. The invention particularly relates to a condensation dryer with a drum for laundry items to be dried, a supply air duct, an exhaust air duct from which a recirculation duct branches off, which opens into the supply air duct upstream of a drum inlet, a fan, a heat pump with a condenser arranged in the supply air duct, an evaporator arranged in the exhaust air duct, a throttle and a compressor, as well as a control device and a heating device; and a preferred method for its operation.

[0002] Tumble dryers are generally operated as vented or condenser dryers. Condenser dryers, which operate by condensing the moisture evaporated from the laundry by warm process air, allow for energy recovery from the heated process air, for example, through the use of a heat pump. The condensate produced in the condenser dryer is collected and either pumped out or disposed of by manually emptying a collection container.

[0003] In vented dryers, however, the moisture-laden air from passing through a laundry drum is generally expelled from the dryer. Heat recovery often does not occur.

[0004] However, exhaust air dryers with heat recovery are known. For example, publication DE 30 00 865 A1 describes a tumble dryer with heat recovery. The tumble dryer consists of a container that holds and moves the laundry, into which a supply air stream heated by a heating element flows, while the moist, warm air is discharged as exhaust air through an outlet. A heat exchanger is arranged in front of the heating element in the supply air stream, through which the moist, hot exhaust air from the container flows.

[0005] The publication DE 197 31 826 A1 describes a tumble dryer with a heat recovery system (e.g. a heat pump), in which the largely closed air circuit can exchange the circulating air with the room air through two openings at two predetermined locations in order to maintain the drying and condensation temperature at the predetermined values.

[0006] The publication EP 2037034 B1 describes an exhaust air dryer with a heat pump and a cleaning device for the evaporator.

[0007] Exhaust air dryers with heat recovery are also described in the publications US 2012 / 0030960 A1 and DE 10 2008 055 087 A.

[0008] The publication DE 40 23 000 C2 describes a tumble dryer with a heat pump circuit in which an air supply opening is arranged in the process air duct between the condenser and the evaporator, which can be closed with a controllable closing device.

[0009] Publication DE 43 06 217 B4 describes a program-controlled tumble dryer with a laundry drum in which the process air is conveyed through the drum by a fan in a closed process air duct equipped with closure devices. The tumble dryer also has a heat pump circuit consisting of an evaporator, compressor, and condenser designed to precipitate the moisture in the process air from the drum. The closure devices are arranged so that the flow of the process air depends on a process phase.

[0010] In an exhaust air dryer with a heat pump, heat is extracted from the exhaust air from the drying chamber, usually a drum, by the heat pump's evaporator, which then returns it to the supply air via the condenser. Because the exhaust air dryer is an open system, unlike a condensation dryer with a closed process air circuit, both latent heat and sensible heat are recovered. This means that an exhaust air dryer with heat recovery can consume less energy than a condensation dryer, even if its condensation efficiency is less than 50%, for example.

[0011] Depending on the heat pump's efficiency, heat is extracted from the heat pump's surroundings. However, a higher condensation efficiency would be desirable for more efficient operation.

[0012] In order to increase the condensation efficiency above 80% with an open air duct, the state of the art describes additional heat exchangers in the refrigeration circuit - desuperheaters or subcoolers. In a closed system, the continuously introduced compressor power leads to increasing heating of the dryer. If this power input is not balanced with energy loss, for example due to component heating, radiation, convection, or leakage, the system can overheat, thereby reducing the efficiency of the heat pump. One known countermeasure is the use of actively cooled additional heat exchangers in the refrigeration circuit or air-to-air heat exchangers in the process air. Since in an open system the temperature of the supply air from an installation room remains virtually constant and is not higher than the ambient temperature, overheating does not occur under typical installation conditions of the condensation dryer.The constant low temperature level ensures high efficiency of the heat pump.

[0013] In contrast, an exhaust air dryer can have the disadvantage of a negative impact on the overall energy balance of the installation location, as the generally warmer indoor air is exchanged several times with cooler outside air. Open air duct systems with condensation efficiencies greater than 80% eliminate this disadvantage, as the exhaust air does not need to be ducted out of the installation room.

[0014] It is also known that the energy efficiency of an exhaust air dryer can be improved by using a recirculation system. In this system, the process air, which is laden with moisture from the laundry in the drying chamber, is partially recirculated to the drying process via the heating device.

[0015] The publication DE 103 49 712 A1 describes a method for drying laundry in a tumble dryer with a program control device, a drying chamber and a process air duct in which a fan for conveying the dry air through the drying chamber and a heating device are arranged, wherein the process air duct is designed with a fresh air supply and an exhaust air discharge and wherein means for separating the dry air flow into an exhaust air portion and a recirculation air portion are arranged in the process air duct.

[0016] Publication DE 34 46 468 A1 describes a method for drying laundry in a tumble dryer with a drivable laundry drum, a fan, a heater arranged in the flow path of the drying air, and a cooled condenser through which the drying air is passed after exiting the laundry drum. The drying air is split into two partial air streams after exiting the laundry drum. One partial air stream is fed to the condenser, and the other is remixed with the partial air stream exiting the condenser, bypassing the condenser.

[0017] Publication DE 34 19 743 C2 describes a tumble dryer with a drum, a heating unit equipped with an air supply connection, and an exhaust air connection. Various additional units that determine the dryer's operating mode can be connected between the heating unit's air supply connection and the exhaust air connection. In one embodiment of the dryer, a recirculation section is interposed between the air supply connection and the exhaust air connection, which contains an air control device, allowing the dryer's air supply to exhaust air ratio to be varied.

[0018] Publication DE 10 2007 042969 A1 describes a dryer with a drying chamber for objects to be dried, a process air duct containing a heater for heating the process air and a fan for directing the heated process air from a supply air inlet through the drying chamber to an exhaust air outlet, as well as at least one heat exchanger. The heat exchanger is arranged between the drying chamber and the exhaust air outlet. A recirculation duct branches off from the process air duct behind the drying chamber, through which a portion of the process air can be directed to the heater. The at least one heat exchanger can be formed by an evaporator and a condenser of a heat pump.

[0019] The publication DE 10 2009 002482 A1 discloses a dryer with a drying chamber for objects to be dried, a process air duct, a heater for heating the process air and a first fan, a program controller, a heat exchanger and a humidity sensor arrangement for measuring humidity signals as a measure of a humidity of the process air, wherein first means for evaluating the humidity signals measured by the humidity sensor arrangement and second means for influencing actuators for the operation of the dryer are present in the program controller and are configured in such a way that a predetermined numerical range for the relative humidity stored in the program controller can be maintained in a drying process by influencing the actuators.It is also disclosed that for controlling a drying process, the relative humidity can be measured in order to control the proportions of recirculating air and exhaust air in such a way that the relative humidity is kept within a predetermined numerical range.

[0020] The publication DE 10 2016 210265 A1 discloses a method for operating a condensation dryer with a process air duct, in which process air is moved in a circuit by means of a fan, a heater, a drum with laundry items placed therein, and a control device, wherein a heat exchanger for condensing water from warm, moist process air and at least one humidity sensor are arranged in the process air duct, wherein a drying process comprises the following steps: (a) Measuring a relative humidity H rel of the process air using the humidity sensor; (b) Measuring a temperature TP of the process air using a temperature sensor; (c) Determining an absolute water load LW of the process air from the relative humidity H rel taking into account the temperature TP , wherein a relationship stored in the control device between a maximum water load LW max< and the temperature TP is used; (d) Tracking the temporal progression of the water load LW; (e) Using the temporal progression of the water load LW to determine a residual moisture RW in the laundry items; (f) Comparing the residual moisture RW with a predetermined residual moisture RW set< ; and (g) Ending the drying process when the predetermined residual moisture RW set< is reached or undershot.

[0021] The publication DE 10 2018 203158 A1 discloses an appliance for drying laundry, comprising at least one open process air system with at least one drying chamber accommodating laundry to be dried and at least one heat pump thermally coupled to the process air system, which has at least one evaporator serving as a heat sink for process air discharged from the drying chamber and at least one condenser serving as a heat source for process air to be supplied to the drying chamber, wherein the evaporator and the condenser are arranged laterally next to each other and offset in height from each other,wherein either, on the one hand, a section of a first process air line connecting the drying chamber to the evaporator runs above the condenser and a section of a second process air line connecting the condenser to the drying chamber runs below the evaporator, or, on the other hand, a section of the first process air line runs below the condenser and a section of the second process air line runs above the evaporator.

[0022] Publication DE 10 2005 041145 A1 discloses a tumble dryer in which the warm air used to dry laundry is heated using a heat pump heating system, the heat pump heating system including a compressor with variable power. Preferably, the tumble dryer includes a control device that controls or regulates the power of the compressor depending on the settings made by the user of the tumble dryer.

[0023] Against this background, the object of the present invention was to provide a condensation dryer with an open air system and a heat pump for heat recovery that is highly energy efficient. A portion of the warm, moist process air from the drum is to be used as recirculated air. Furthermore, the object of the present invention was to provide a method for its operation.

[0024] This object is achieved according to this invention by a condensation dryer and a method for its operation having the features of the respective independent patent claims. Preferred embodiments of the condensation dryer according to the invention and of the method according to the invention are listed in the corresponding dependent patent claims. Preferred embodiments of the condensation dryer according to the invention correspond to preferred embodiments of the method according to the invention, and vice versa, even if this is not explicitly stated herein.

[0025] The subject of the invention is thus a condensation dryer with a drum for receiving laundry items to be dried, a supply air duct, an exhaust air duct, from which a recirculation duct branches off, which opens into the supply air duct in front of a drum inlet, a fan, a heat pump with a condenser arranged in the supply air duct, an evaporator arranged in the exhaust air duct, a throttle and a compressor, as well as a control device and a heating device, wherein the condensation dryer is designed such that, in a drying program carried out therein, warm, moist process air from the drum flows in an exhaust air duct section delimited downstream by the evaporator essentially in the same direction as supply air in an inlet area of ​​the supply air duct containing the condenser, and the process air leaving the drum has a relative humidity F rel< for which F rel< min ≤ F rel< ≤ F rel< max applies,where F rel< min is a predetermined minimum value and F rel< max is a maximum value of the relative humidity achievable in the drying program, and the exhaust air duct part and the condenser have a common wall which has a plurality of holes forming the recirculation duct.

[0026] It has been found that increasing the relative humidity of the process air at the drum outlet improves the drying efficiency and / or drying speed of a condenser dryer. The air condition at the drum outlet is influenced by the air flow rate, the temperature inside the drum and the relative humidity of the process air at the drum inlet, the air flow through the drum, as well as the laundry load and type of laundry.

[0027] Relative humidity is an indirect measure of the sensible heat content of the process air. Although in an open air system with a heat pump, as used in the condensation dryer according to the invention, the sensible heat is also recovered as energy, thereby increasing the drying rate, this proportion should be small relative to the latent heat to achieve high condensation efficiency.

[0028] The dimensions of an additional heat exchanger to achieve the condensation efficiency, e.g., a subcooler, can then be smaller. In any case, the efficiency of the condensation dryer increases with the present invention.

[0029] By adding the air with a higher water content, the water content of the process air increases before and after the condenser. The relative humidity at the drum inlet increases, as does that of the process air at the drum outlet.

[0030] In a preferred embodiment of the condensation dryer according to the invention, the recirculating air duct opens into the supply air duct after the condenser in the flow direction of the supply air.

[0031] In a more preferred embodiment of the condensation dryer according to the invention, the recirculating air duct opens into the supply air duct in the flow direction of the supply air before or at the condenser, thus leading to an increased air flow through the condenser.

[0032] According to the invention, it is preferred that a flow measuring device be arranged in the supply air duct, both upstream and downstream of the condenser. This allows the proportion of added recirculated air from the drum to be determined.

[0033] In the condensation dryer according to the invention, the exhaust air duct section and the condenser share a common wall, which has a plurality of holes forming the recirculation duct. It is again preferred that the plurality of holes be located in an inlet area of ​​the condenser.

[0034] The shape and number of holes are not limited, provided that the plurality of these holes can achieve a desired proportion of recirculation according to the invention.

[0035] In any case, a condensation dryer is preferred in which the plurality of holes is designed to interact with the fan to create an air volume flow through the condenser during a drying program carried out in the condensation dryer such that it consists of 15 to 50% by volume, preferably 20 to 40% by volume, of recirculated air. The resulting significant increase in the air volume flow through the condenser compared to the evaporator also leads to an improvement in the efficiency of the heat pump. While efficiency remains unchanged, the heat exchangers, in particular an additional heat exchanger, can be made smaller. However, if the air volume flow through the condenser is not increased, the volume flow of the supply and exhaust air is reduced, with the result that the noise level of the condensation dryer decreases while maintaining the same efficiency.

[0036] According to the invention, an increase in the proportion of recirculated air can be achieved, for example, by increasing the fan power and thus the fan's conveying capacity. This increase in fan power leads to an increase in the negative pressure in the supply air duct and an increase in the positive pressure in the exhaust air duct. This increases the pressure difference for the passage of process air from the drum or the exhaust air duct into the supply air duct, particularly in the inlet area of ​​the condenser.

[0037] The number, positioning, and size of the holes are generally fixed and therefore cannot be changed. However, the condensation dryer can advantageously have a device that allows control of the total effective opening area of ​​the plurality of holes. For example, such a device can be designed to completely or partially cover some holes, whereby the cover can also be realized, for example, with a partially air-permeable foam that impedes the passage of air. Another covering option is the use of an adjustable blind.

[0038] In an advantageous embodiment of the condensation dryer according to the invention, the heat pump contains an additional cooler, also known as a subcooler. This allows the heat pump's operation to be better controlled and, in particular, prevents overheating.

[0039] However, the present invention specifically makes it possible to avoid the use of an additional cooler. This is the case if the proportion of process air in the recirculation duct, which in embodiments of the invention directly enters the condenser, is sufficiently large. In an alternative, more preferred embodiment of the invention, the heat pump therefore does not contain an additional cooler.

[0040] According to the invention, a condensation dryer is also preferred in which a relationship between a fan speed u and a ratio r between an air flow velocity vc in the condenser and an air flow velocity vε in the evaporator is stored in the control device. This enables better control of the recirculation air component in the condensation dryer according to the invention.

[0041] Finally, a condensation dryer is also preferred in which a humidity sensor is arranged at the drum outlet to determine the relative humidity F rel< of the process air leaving the drum. While it is possible to implement the invention based on empirical values ​​for the relative humidity and its dependence on various parameters, measuring the relative humidity F rel< leads to more accurate results. The additional use of a temperature sensor at the drum outlet is advantageous.

[0042] Adjustable closure devices can be installed in the individual ducts, such as the supply air duct, the recirculation air duct, and the exhaust air duct, to improve the control of the air flows, and in particular the proportion of supply air in an air flow through the condenser. Adjustable closure devices can be used, for example, as dampers that can be opened to different widths independently or independently of one another.

[0043] The dryer preferably comprises an electric heating device so that process air can be heated by both the condenser and the electric heating device. Since the energy required for drying decreases with the increasing degree of dryness of the laundry items to be dried in the condensation dryer, it is expedient to regulate the heating device accordingly, i.e., to reduce its heating power as the degree of dryness increases. Furthermore, in the condensation dryer of the present invention, if the evaporator inlet temperature is too high, the proportion of recirculated air can be reduced depending on the temperature.

[0044] By using a recirculation duct or by passing the hot, moisture-laden recirculated air through the recirculation duct to the heater, the air temperature in front of the heater is generally raised. However, due to the increased airflow over the heater, the drum inlet temperature can remain within an acceptable range.

[0045] To accelerate the heating of the process air after the condensation dryer is switched on, the amount of supply air in the supply air duct can be controlled, for example using adjustable closure devices, so that in an initial phase of a drying program the supply of supply air is stopped and only recirculated air is used as process air.

[0046] According to the invention, it is preferred if exhaust air, supply air and / or refrigerant are each passed through the corresponding heat exchangers in a cross-current or counter-current process.

[0047] The evaporator of the heat pump is located in the exhaust air duct to extract heat from the warm, moist air from the drum, which generally flows into an installation room via the exhaust air duct.

[0048] In a condensation dryer equipped with a heat pump, the warm, moisture-laden process air is cooled primarily in the heat pump's evaporator, where the transferred heat is used to evaporate a refrigerant used in the heat pump circuit. The heat pump's refrigerant, which evaporates as a result of the heating, is fed via a compressor to the heat pump's condenser, where heat is released due to the condensation of the gaseous refrigerant. This heat is used to heat the process air or the supply air before it enters the drying chamber.

[0049] In the dryer according to the invention, the fan is preferably arranged directly after the condenser or directly before the condenser.

[0050] The invention also relates to a method for operating a condensation dryer with a drum for receiving laundry items to be dried, a supply air duct, an exhaust air duct, from which a recirculation duct branches off, which opens into the supply air duct in front of a drum inlet, a fan, a heat pump with a condenser arranged in the supply air duct, an evaporator arranged in the exhaust air duct, a throttle and a compressor, as well as a control device and a heating device, wherein the condensation dryer is designed such that, in a drying program carried out therein, warm, moist process air from the drum flows in an exhaust air duct section delimited downstream by the evaporator, essentially in the same direction as supply air in an inlet area of ​​the supply air duct containing the condenser, and the process air leaving the drum has a relative humidity F rel<for which F rel< min ≤ F rel< ≤ F rel< max applies, where F rel< min is a predetermined minimum value and F rel< max is a maximum value of the relative humidity achievable in the drying program, and the exhaust air duct part and the condenser have a common wall which has a plurality of holes which form the recirculation duct, wherein the fan is controlled by the control device such that the process air leaving the drum has a relative humidity F rel< for which F rel< min ≤ F rel< ≤ F rel< max applies.,

[0051] The expression "flows substantially in the same direction" is intended to take into account the fact that the recirculation air portion, i.e. the portion of the process air that flows through the plurality of holes as an embodiment of the circulation duct used according to the invention in embodiments of the invention, is transverse or even vertical to this direction and therefore influences the flow in the exhaust air and recirculation duct.

[0052] In a preferred embodiment of the method according to the invention, the fan is controlled by the control device such that an air volume flow through the condenser consists of 15 to 50 volume%, preferably 20 to 40 volume%, of recirculated air.

[0053] According to the invention, a method is further preferred in which a ratio r between an air flow velocity vc in the condenser and an air flow velocity vε in the evaporator is greater than 1, preferably greater than 1.2.

[0054] Finally, the process according to the invention is preferably carried out after the process air leaving the drum has reached a predetermined minimum temperature. At this point, a very high relative humidity (Frei) is generally present at the drum outlet, preferably even a maximum relative humidity (F rel< max ). The invention then enables the maintenance of such a high relative humidity. The process according to the invention is thus preferably carried out during a main drying phase.

[0055] However, during the course of a drying program, the relative humidity F rel< of the process air leaving the drum decreases, particularly after the main drying phase, in which most of the moisture content of the laundry is removed, has ended. Therefore, an increase in the relative humidity F rel< at the drum outlet can be very advantageously achieved even in such a final phase of a drying program following the main drying phase, for example, by increasing the fan speed u.

[0056] As already stated, the laundry load also influences the relative humidity F rel< of the process air. Therefore, it is advantageous to determine the drum load with laundry items in a conventional manner. A relationship between the load and F rel< min or F rel< max can then be stored in the control system, allowing these values ​​to be adjusted more precisely.

[0057] The condensation dryer according to the invention and the method according to the invention have the advantage that the condensation dryer can operate in an energy-efficient manner with a high condensation efficiency. In particular, the efficiency and / or noise level of the condensation dryer according to the invention can be improved by using an open air system, a heat pump for heat recovery, and an additional portion of the process air that is diverted after the drum outlet and recirculated as recirculated air before or after the condenser.

[0058] Further details of the invention will become apparent from the following description of non-limiting embodiments of the condensation dryer according to the invention and a method using this condensation dryer. Reference is made to the Figures 1 to 7 . Fig. 1shows a perspective view of a prior art condensation dryer with a heat pump, where no supply air duct is used for partial recirculation of process air from the drum. Fig. 2 shows a vertical section through the condensation dryer of Fig. 1 , which shows the air flow through the supply air duct, drum and exhaust air duct. Fig. 3 shows a vertical section through a condensation dryer according to the invention according to a first embodiment, in which part of the process air from the drum is fed via a recirculation duct to a condenser in the supply air duct. Fig. 4 shows how Fig. 3 a vertical section through the condensation dryer according to the invention according to a first embodiment, in which part of the process air from the drum is fed via a recirculation duct to a condenser in the supply air duct. In contrast to Fig. 3For reasons of clarity, there are no arrows here to show the flow of air in the condensation dryer. Fig. 5 shows a diagram showing the flow of process air through the condenser, the drum, the evaporator and a subcooler according to a second embodiment of the condensation dryer according to the invention (thick arrows), wherein the thin arrows show the flow of a refrigerant through the components of the heat pump used. Fig. 6 shows a diagram showing the flow of process air through the condenser, the drum, the evaporator and a subcooler according to a third embodiment of the condensation dryer according to the invention (thick arrows), wherein the thin arrows show the flow of a refrigerant through the components of the heat pump used. Fig. 7shows a perspective top view of a lower part of a condensation dryer used according to the invention, in which in particular a common wall separating the condenser from the exhaust air duct can be seen, which has a plurality of holes in an inlet area of ​​the condenser which can function as a recirculation duct.

[0059] Fig. 1shows a perspective view of a prior art condensation dryer 1 with a heat pump, of which the condenser 8 and the evaporator 9 can be seen here. This condensation dryer does not use a supply air duct for the partial recirculation of process air from the drum 2. The air flow through the condensation dryer is illustrated by the arrows. The light arrow indicates supply air from a room in which the condensation dryer is installed, which is conveyed in the supply air duct 3 due to the use of a fan (not shown here). This supply air is heated in the condenser 8, and the then heated process air is then passed on to and into the drum 2. The then warm, moist process air leaves the drum 2 at the drum outlet 18. The process air has the comparatively highest temperature here, which is shown by the black arrows.The warm, humid process air is cooled by condensation (not shown here) of the moisture in the evaporator 9 and transported through the exhaust air duct 4 into a room housing the condensation dryer 1. 17 denotes a subcooler in the heat pump circuit.

[0060] Fig. 2 shows a vertical section through the condensation dryer 1 of Fig. 1 , in which the air flow through supply air duct 3, drum 2 and exhaust air duct 4 is shown. The same reference numerals have the same meaning here as in Fig. 1 . 7 means a blower.

[0061] Fig. 3shows a vertical section through a condensation dryer 1 according to the invention according to a first embodiment, in which a portion of the process air from the drum 2 is fed via a recirculation duct 5 to a condenser 8 in the supply air duct 3. The recirculation duct 5 is located here in an inlet section 13 of the supply air duct 3. 12 denotes an exhaust air sub-duct in which the process air flows essentially in the same direction as in the supply air duct, i.e., in particular, in the condenser 8. 7 denotes a fan, and 17 a subcooler. The splitting thick arrow illustrates how a portion of the warm, moist process air from the drum 2 is fed into the condenser 8 as recirculation air after the drum outlet 18 in the area of ​​the condenser 8.

[0062] Fig. 4 shows how Fig. 3a vertical section through the condensation dryer 1 according to the invention according to a first embodiment, in which part of the process air from the drum 2 is fed via a recirculation duct 5 to a condenser 8 in the supply air duct 3. In contrast to Fig. 3 For reasons of clarity, there are no arrows showing the flow of air in the condensation dryer 1. Other reference symbols have the same meaning as in Fig. 3 .

[0063] Fig. 5shows a diagram illustrating the flow of process air through the condenser 8, the drum 2, the evaporator 8, and a subcooler 17 according to a second embodiment of the condensation dryer 1 according to the invention (thick arrows), with the thin arrows indicating the flow of a refrigerant through the components of the heat pump used. The refrigerant is guided in the refrigerant circuit, which here additionally has a throttle 10 and a compressor 11. The curved thick arrow here shows that a portion of the process air from the drum 2, after the condenser 8, is recirculated into the supply air duct (not shown here) containing the condenser 8.

[0064] Fig. 6shows a diagram depicted by thick arrows showing the flow of process air through the condenser 8, the drum 2, the evaporator 9 and a subcooler 17 according to a third embodiment of the condensation dryer 1 according to the invention, wherein the thin arrows show the flow of a refrigerant through the components of the heat pump used. The refrigerant is guided in the refrigerant circuit, which here additionally has a throttle 10 and a compressor 11. The curved thick arrow shows that a portion of the process air from the drum 2 is discharged compared to Fig. 5 According to the invention, it is preferably returned before or at the condenser 8 into the supply air duct (not shown here) containing the condenser 8.

[0065] Fig. 7shows a perspective top view of a lower part of a condensation dryer used according to the invention, in which in particular a common wall 14 separating the condenser 8 from the exhaust air duct (not shown here) can be seen, which has a plurality of holes 15 in an inlet area 16 of the condenser 8. 13 denotes an inlet part of the supply air duct (also not shown here). List of reference symbols

[0066] 1 Condensation dryer 2 Drum for holding laundry items to be dried 3 Supply air duct 4 Exhaust air duct 5 Recirculation duct 6 Drum inlet 7 Fan 8 Condenser 9 Evaporator 10 Throttle 11 Compressor 12 Exhaust air duct section 13 Inlet area (of the supply air duct) 14 Common wall of condenser and recirculation duct section 15 Numerous holes (in the common wall) 16 Condenser inlet area 17 Additional cooler, subcooler (in the heat pump) 18 Outlet (for process air from the drum), drum outlet

Claims

1. Condenser tumble dryer (1) having a drum (2) for receiving laundry items to be dried, a supply air channel (3), an exhaust air channel (4), a recirculated air channel (5) branching off therefrom and discharging into the supply air channel (3) upstream of a drum inlet (6), a blower (7), a heat pump (8, 9, 10, 11) having a condenser (8) which is arranged in the supply air channel (3), an evaporator (9) which is arranged in the exhaust air channel (4), a throttle (10) and a compressor (11), as well as a control facility and a heating facility, wherein the condenser tumble dryer (1) is designed such that, in a drying program carried out therein, moist warm process air flows out of the drum (2) in an exhaust air channel part (12) defined downstream by the evaporator (9), substantially in the same direction as the supply air in an inlet region (13) of the supply air channel (3) containing the condenser (8), characterised in that the process air leaving the drum (2) has a relative air humidity Frel, to which Frelmin ≤ Frel ≤ Frelmax applies, wherein Frelmin is a predetermined minimum value and Frelmax is a maximum value of the relative air humidity which can be achieved in the drying program, and the exhaust air channel part (12) and the condenser (8) have a common wall (14) which has a plurality of holes (15) which form the recirculated air channel (5).

2. Condenser tumble dryer (1) according to claim 1, characterised in that the recirculated air channel (5) discharges into the supply air channel (3) in the direction of flow of the supply air downstream of the condenser (8).

3. Condenser tumble dryer (1) according to claim 1, characterised in that the recirculated air channel (5) discharges into the supply air channel (3) in the direction of flow of the supply air upstream of or at the condenser (8).

4. Condenser tumble dryer (1) according to claim 3, characterised in that in each case a flow measuring facility is arranged in the supply air channel (3) upstream and downstream of the condenser (8).

5. Condenser tumble dryer (1) according to one of claims 1 to 4, characterised in that the plurality of holes (15) is located in an inlet region (16) of the condenser (8).

6. Condenser tumble dryer (1) according to one of claims 1 to 5, characterised in that the plurality of holes (15) is configured in a drying program carried out in the condenser dryer (1) in cooperation with the blower (7) to form an air volume flow through the condenser (8), such that it consists of 15 to 50% by volume, preferably 20 to 40% by volume, of recirculated air.

7. Condenser tumble dryer (1) according to one of claims 1 to 6, characterised in that it has an apparatus which permits a total effective opening surface of the plurality of holes (15) to be controlled.

8. Condenser tumble dryer (1) according to one of claims 1 to 7, characterised in that the heat pump (8, 9, 10, 11) contains an additional cooler (17).

9. Condenser tumble dryer (1) according to one of claims 1 to 8, characterised in that a relationship between a rotational speed u of the blower (7) and a ratio r between an air flow speed vc in the condenser (8) and an air flow speed vE in the evaporator (9) is stored in the control facility.

10. Condenser tumble dryer (1) according to one of claims 1 to 9, characterised in that a humidity sensor is arranged at the outlet (18) of the drum (2) for determining the relative air humidity Frel of the process air leaving the drum (2).

11. Method for operating a condenser tumble dryer (1) having a drum (2) for receiving laundry items to be dried, a supply air channel (3), an exhaust air channel (4), a recirculated air channel (5) branching off therefrom and discharging into the supply air channel (3) upstream of a drum inlet (6), a blower (7), a heat pump (8, 9, 10, 11) having a condenser (8) which is arranged in the supply air channel (3), an evaporator (9) which is arranged in the exhaust air channel (4), a throttle (10) and a compressor (11), as well as a control facility and a heating facility, wherein the condenser tumble dryer (1) is designed such that, in a drying program carried out therein, moist warm process air flows out of the drum (2) in an exhaust air channel part (12) defined downstream by the evaporator (9), substantially in the same direction as the supply air in an inlet region (13) of the supply air channel (3) containing the condenser (8), and the process air leaving the drum (2) has a relative air humidity Frel, to which Frelmin ≤ Frel ≤ Frelmax applies, wherein Frelmin is a predetermined minimum value and Frelmax is a maximum value of the relative air humidity which can be achieved in the drying program, and the exhaust air channel part (12) and the condenser (8) have a common wall (14) which has a plurality of holes (15) which form the recirculated air channel (5), wherein the blower (7) is controlled by the control facility such that the process air leaving the drum (2) has a relative air humidity Frel, to which Frelmin ≤ Frel ≤ Frelmax applies.

12. Method according to claim 11, characterised in that the blower (7) is controlled by the control facility such that an air volume flow through the condenser (8) consists of 15 to 50% by volume, preferably 20 to 40% by volume, of recirculated air.

13. Method according to claim 11 or 132, characterised in that a ratio r between an air flow speed vc in the condenser (8) and an air flow speed vE in the evaporator (9) is greater than 1, preferably greater than 1.2.

14. Method according to one of claims 11 to 13, characterised in that it is carried out after the process air leaving the drum (2) has reached a predetermined minimum temperature.