Method for determining the residual moisture in a heat pump dryer and heat pump dryer suitable for this purpose

Abstract

The invention relates to a method for operating a dryer 1 with a drum 3 for receiving laundry items to be treated, a drive motor 18 for the drum 3, a process air duct 2 for guiding process air in which process air is moved by means of a blower 6, which is connected at a first end 8 to an air outlet opening of the drum 3 and at a second end 12 to an air inlet opening 9 of the drum 3, a control unit 10, a heat pump arranged in the process air duct 2 with an evaporator 4, a condenser 5, an expansion unit 14 and a compressor 13, wherein a first thermometer 28 for measuring the inlet temperature T1 and a second thermometer 29 for measuring the outlet temperature T2 are arranged at the refrigerant inlet 19 of the evaporator 4, wherein the control unit 10 is configured to convert superheat SH,The invention relates to the determination of the residual moisture H of the laundry items, which can be calculated as the difference T2-T1, and wherein the dryer 1 has at least one sensor 26, 27 for determining measured values ​​of the process air, and the control unit 10 is configured to link the measured values ​​of the process air and / or calculated values ​​derived therefrom with model parameters determined from a predictive model in order to determine the residual moisture, wherein the method in a drying process comprises the following steps: (a) measuring the inlet temperature T1 at the refrigerant inlet 19 of the evaporator 4 and the outlet temperature T2 at the refrigerant outlet 20 of the evaporator 4; (b) calculating the superheat SH as the difference T2-T1; and (c) determining the residual moisture of the laundry items from the superheat SH using the control unit 10. The invention also relates to a heat pump dryer suitable for carrying out this method.

Description

[0001] The invention relates to a method for determining the final residual moisture in a heat pump dryer and to a heat pump dryer suitable for this purpose.The invention relates in particular to a method for operating a dryer with a drum for receiving laundry items to be treated, a drive motor for the drum, a process air duct for guiding process air in which process air is moved by means of a blower, wherein the process air duct is connected at a first end to an air outlet opening of the drum and at a second end to an air inlet opening of the drum, a control unit, a heat pump arranged in the process air duct with an evaporator, a condenser, an expansion unit and a compressor, wherein a first thermometer for measuring the inlet temperature T1 and a second thermometer for measuring the outlet temperature T2 are arranged at the refrigerant inlet of the evaporator, and a heat pump dryer suitable for carrying out this method.

[0002] Condensation drying processes rely on the evaporation of moisture from laundry using warm process air and the subsequent dehumidification of this process air through condensation on a heat exchanger. In this drying process, cool process air is generally passed over a heater, such as the condenser of a heat pump, by a fan. The warm, dry process air then enters the drum, which serves as the drying chamber and contains the laundry. The warm, dry process air absorbs the moisture from the laundry. The warm, moist process air is then transferred from the drum to a heat exchanger for dehumidification, for example, an air-to-air heat exchanger or the evaporator of a heat pump.The warm, humid process air is cooled, causing the water it contains to condense and be collected in a condensate tray, which is generally located below the heat exchanger. Once a certain fill level is reached, the condensed water is typically pumped (also called a "condensate pump") into a storage tank (also called a "condensate reservoir") or into a wastewater drain.

[0003] The drying process generally continues until a specific residual moisture content is reached in the dried laundry. The moisture level is typically determined by measuring the electrical resistance of the laundry. For this purpose, a varying number of electrodes are usually positioned at different locations within the dryer. These electrodes measure the laundry's resistance using either direct or alternating current. As the residual moisture in the laundry decreases, its resistance also decreases. This resistance is measured and correlated with the residual moisture content. The drying process is then usually terminated when a predetermined resistance value is reached, which serves as the so-called cut-off value, particularly for the heating of the process air.These cut-off values ​​depend on the load size and the initial moisture content (also referred to as the "initial residual moisture" of the damp laundry items coming out of a washing machine) of the laundry items, since, for example, with the same moisture content, the relative humidity of the process air is higher for larger loads. It should also be considered that with a high initial moisture content, it can take longer for drying to become effective even inside the laundry items. Therefore, to improve the drying process, procedural steps are often carried out to determine the initial state, i.e., in particular, the load size and initial moisture content of the laundry items. Based on this information, the cut-off limit can then be adjusted. Methods are also known that use several measured variables, such as...Energy, in particular the total energy used so far for drying, electrical power, temperature and elapsed time, are correlated to improve the accuracy of the prediction.

[0004] A heat pump is characterized by two heat exchangers: a heat sink, where heat is absorbed, a heat source, where heat is released, and a pump unit, which transfers heat from the heat sink to the heat source, possibly with a temperature change. In a condensing dryer equipped with a compressor-type heat pump, the cooling of the warm, moisture-laden process air essentially takes place in the heat sink of the heat pump, also known as the evaporator. The transferred heat is used to evaporate a refrigerant circulating in the pump unit, which is designed as a closed loop. The refrigerant, evaporated due to the heating process, is fed via a compressor in the pump unit to the heat source, which acts as a condenser for the refrigerant. Heat is released there as the gaseous refrigerant condenses.Behind the condenser, the now liquid refrigerant is expanded in a throttle of the pumping unit, which reduces its internal pressure, and finally returns to the evaporator.

[0005] According to the design of the refrigeration circuit in a heat pump dryer, the refrigerant is superheated on the low-pressure side (in the evaporator) after complete evaporation. The temperature difference between the temperature of the superheated vapor and the evaporation temperature is called superheat (SH). The SH changes when the heat absorption in the refrigerant changes. This occurs when the energy input to the evaporator changes, particularly when the energy in the air from the drum changes.

[0006] The phenomenon of refrigerant superheating in a heat pump has long been known, for example from EP 2 468 945 B1 and EP 2 745 760 A1, as has its significance for heat pump control. It is particularly well known that the superheating during operation of a heat pump changes fundamentally due to its specific characteristics. EP 2 468 945 B1 describes how the air heating capacity at the condenser is always higher than the air cooling capacity at the evaporator. This is because the condenser must also dissipate the heat generated by the refrigerant compression system itself. This leads to a continuous increase in the temperature of the air directed to the drum and a continuous increase in the refrigerant pressure and temperature on the pressure side of the refrigerant compressor.On the one hand, this behavior is useful at the beginning of the drying cycle, as it accelerates the start-up phase; on the other hand, it becomes very detrimental once the hot air generator reaches steady-state operation at full power. EP 2 468 945 B1 also describes maintaining the outlet temperature from the evaporator within a predetermined temperature range by adjusting the flow rate or by pre-cooling the refrigerant.

[0007] DE 10 2017 207601 A1 describes a method for operating a laundry drying device. During a drying process, measurements of process air are taken. To determine the moisture content of the laundry to be dried, the measured values ​​and / or calculated variables are linked with model parameters determined from a predictive model. Different groups of model parameters are used for different moisture ranges. The measured values ​​can include relative humidity, temperature, and / or pressure. The calculated variables can include moisture difference, temperature difference, water load, and / or enthalpy.

[0008] Against this background, the object of the present invention was to provide an improved method for operating a heat pump dryer, which in particular enables its control by determining the residual moisture of the laundry items to be treated in a more precise manner, so that the termination of a drying process or the switching off of the heat pump dryer can be carried out as precisely as possible based on this criterion. A further object of the invention was to provide a suitable heat pump dryer for this purpose.

[0009] The solution to this problem is achieved according to this invention by a method for operating a heat pump dryer and a heat pump dryer suitable for carrying out this method, comprising the features of the respective independent claims. Preferred embodiments of the method and the heat pump dryer according to the invention are listed in the respective dependent claims. Preferred embodiments of the method correspond to preferred embodiments of the heat pump dryer according to the invention, and vice versa, even if this is not explicitly stated herein.

[0010] The invention thus relates to a method for operating a dryer comprising a drum for receiving laundry items to be treated, a drive motor for the drum, a process air duct for guiding process air in which process air is moved by means of a blower, wherein the process air duct is connected at a first end to an air outlet opening of the drum and at a second end to an air inlet opening of the drum, a control unit, a heat pump arranged in the process air duct with an evaporator, a condenser, an expansion unit, e.g.a controllable expansion valve, and a compressor, wherein a first thermometer for measuring the inlet temperature T1 is arranged at the refrigerant inlet of the evaporator and a second thermometer for measuring the outlet temperature T2 is arranged at the refrigerant outlet of the evaporator, wherein the control unit is configured to determine a residual moisture H of the laundry items from a superheat SH, which can be calculated as the difference T2-T1 and preferably is, and wherein the dryer has at least one sensor for determining measured values ​​of the process air and the control unit is configured to link the measured SH values ​​as well as measured values ​​of the process air and / or calculated values ​​therefrom with model parameters determined from a predictive model in order to determine the residual moisture, wherein the method in a drying process comprises the following steps: . (a) Measurement of the inlet temperature T1 at the refrigerant inlet of the evaporator and the outlet temperature T2 at the refrigerant outlet of the evaporator; (b) Calculation of the superheat SH as the difference T2-T1; and (c) Determination of the residual moisture of the laundry items from the superheat SH using the control unit.

[0011] According to the invention, it is particularly preferred that the residual moisture of the laundry items resulting from overheating SH is determined by evaluating the curve of SH that decreases over time.

[0012] The drying efficiency of a dryer is primarily determined by the accuracy of its moisture sensing. Therefore, it is crucial to determine the residual moisture content as accurately as possible, especially towards the end of the drying process.

[0013] This invention is based on the correlation between the residual moisture H in the laundry items and the superheat (SH) of the refrigerant in the evaporator.

[0014] The superheat (SH) is a very sensitive parameter in the refrigeration cycle. It reacts, for example, to changes in the humidity of the process air. Towards the end of the drying process, the process air transports less and less water from the laundry to the evaporator. This decrease in latent energy in the form of water vapor leads to a measurable change in the superheat (SH). This change correlates directly at the end of the drying process with the decrease in water transport in the drum from the laundry to the process air via evaporation, and thus from the process air to the evaporator, where the water vapor condenses. The SH decreases because the specific enthalpy of the process air decreases due to the reduced amount of water, which results in a lower amount of energy being supplied to the evaporator from the process air per unit of time.

[0015] Preferably, the method according to the invention is carried out such that the superheat SH is continuously measured during the drying process, at least over a predetermined period Δt set, and if it is determined that the measured superheat SH is essentially constant during the period Δt set, the measured SH is used as a reference value (threshold value) SH ref for determining the residual moisture. Preferably, the speed of the blower and / or the speed of the compressor is constant during the period Δt set. If SH ref falls below the threshold, a final drying phase can advantageously be started, which is suitable for ending the overall drying process in order to achieve a final residual moisture content of 0% as precisely as possible.

[0016] Determining the drum load with laundry items should preferably be done during a drying process in order to adapt the drying process to the load, as different quantities of laundry items behave differently.

[0017] The moisture level of the laundry, i.e., the humidity or residual moisture, changes during a drying process because surface water evaporates first, followed by pore and capillary water from the fabric. Depending on the initial moisture level and the fabric type, the moisture level changes throughout the drying process. Therefore, continuous and precise monitoring of the moisture level is advantageous for gentle and energy-efficient drying, as well as for accurately controlling the final residual moisture to a predetermined value, such as "iron dry."

[0018] The drying process is thus influenced by the proportions of surface water and water present inside the laundry items, the latter being removed from the items relatively slowly. Therefore, the drying process also depends on the load size.

[0019] For the requirement In any case, if the residual moisture H set< is to be taken into account, it is advantageous if the load quantity of laundry items in the drum and / or the initial moisture content of the laundry items can be considered.

[0020] In a preferred embodiment of the method according to the invention, a load W of laundry in the drum is therefore taken into account for determining the predetermined residual moisture H set<, whereby a relationship between the load W and the residual moisture H set< stored in the control unit is used.

[0021] The load size and / or initial moisture content can be set by the user or, preferably, determined by the dryer. Various methods are possible for this. A determined load size refers to the dry mass of the laundry placed in the drum to be dried. However, at the beginning of the drying process, laundry items have a moisture content, based on their dry mass, of approximately 60%, for example, after washing and spinning at 1200 rpm. Furthermore, different load sizes behave differently in a drying process. For instance, a drying process with a full load may take longer than one with a half load. Similarly, the duration of the individual phases in the drying process can vary.

[0022] The method for determining the drum load W with laundry items is not limited according to the invention. For example, the load can be set by user input. In general, however, the drum load is determined by the dryer, for example by weighing the drum and / or by evaluating the motor current and / or electrical power of the electric drive motor.

[0023] Preferably, the drum load is determined by evaluating the motor current and / or the electrical power of the electric drive motor. For example, if the power supplied to the electric drive motor is kept constant, the dependence of the motor current on the load of the electric drive motor can be used to determine the drum load. In particular, the current profile can be monitored over a given period, for example, during drum startup. The load can then be inferred from the dependence of the electric drive motor's torque on the drum load and from the dependence of the torque on the motor current.

[0024] A method preferred according to the invention is therefore one in which the drive motor is a BLDC electric motor and its drive power is evaluated with regard to loading the drum with laundry items.

[0025] Preferably, in addition to the process steps (a) to (c) mentioned therein, the method according to the invention includes the process steps (d) Comparing the determined residual moisture H with a predetermined residual moisture H set< ; and (e) Terminating the drying process when the predetermined residual moisture H set< is reached or falls below.

[0026] Through process control, the superheat SH can be kept at a constant value, for example, using an expansion valve or by regulating this temperature difference with a variable-speed compressor. In such cases, a control deviation (e = actual value - setpoint) could be considered an indirect measure or substitute for the SH. Changes in SH or the control deviation can, via a suitable algorithm, provide information about the residual moisture in the laundry. The signal (values) from the algorithm could be used to supplement the measurement of the conductance signal or to directly utilize the process control variable (residual moisture in the laundry).

[0027] Generally, a surface temperature (SH) of 0 K or just above is particularly energy-efficient. An SH greater than 0 K may be necessary to prevent liquid refrigerant from coming into contact with the compressor. Therefore, an SH greater than 0 K acts as a safety factor to ensure that no liquid refrigerant reaches the compressor.

[0028] To improve the evaluation of SH, further measurements can be carried out during the drying process and used as part of a multivariate analysis: (a) Measuring the relative humidity Hrel of the process air using the humidity sensor; (b) Measuring the temperature TP of the process air using a temperature sensor; (c) Determining the absolute water content LW of the process air from the relative humidity Hrel, taking into account the temperature TP, whereby a relationship between a maximum water content Lmax and the temperature TP, preferably stored in the control unit, is used; (d) Monitoring the time course of the water content LW; (e) Using the time course of the water content Lw to determine a residual moisture content H in the laundry items; (f) Comparing the residual moisture content H with a predetermined residual moisture content Hset; and (g) Terminating the drying process when the predetermined residual moisture content Hset is reached or falls below the predetermined residual moisture content Hset.

[0029] As already mentioned, the water loading can be determined via the power consumption of a variable-speed (BLDC) electric motor.

[0030] The process according to the invention generally begins simultaneously with the initiation of a drying program. In this program, an electric heater, which is usually also used, and the blower are generally switched on to direct heated process air into the drum for drying damp laundry items.

[0031] In a preferred embodiment of the method according to the invention, a temperature sensor and a humidity sensor are arranged in the process air duct both upstream and downstream of the drum, wherein, for multivariate analysis in conjunction with the measured SH, the relative humidity Hrel is measured as relative humidity Hrel before and as relative humidity Hrel after the drum; the temperature TP of the process air is measured as temperature TPrel before and as temperature TPrel after the process air after the drum; and from the relative humidity Hrel after and Hrel before, taking into account the temperatures TPrel after and TPrel before, an absolute water content Lw of the process air downstream of the drum and an absolute water content Lw before the drum are calculated, and from this a difference ΔLw = Lw after < _ Lw before is calculated.The temporal course of the difference ΔL W of the water load LW can be tracked; and the temporal course of the difference ΔL W of the water load LW of the process air can be additionally used to determine the residual moisture RW in the laundry items by evaluating the SH.

[0032] The temperature and humidity sensors used are not limited as long as they can measure the temperature or relative humidity of the process air. However, sensors capable of simultaneously measuring both temperature and relative humidity are advantageously used. In a preferred embodiment of the invention, a dual sensor is used as both the temperature and humidity sensor, enabling simultaneous measurement of the temperature (TP) and relative humidity (Hrel) of the process air. Even more preferred is the use of a triple sensor, which can additionally determine the pressure (PP) of the process air.

[0033] In the determination of residual moisture according to the invention via the absolute water content of the process air, the influence of the air pressure is advantageously taken into account.

[0034] In a preferred embodiment of the method according to the invention, at least one pressure sensor is therefore provided in the process air duct, which measures the pressure PP of the process air, which is then used to determine the water loading LW, whereby a relationship stored in the control unit between the pressure PP, a maximum water loading LW max< and the temperature TP is used.

[0035] Preferably, a triple sensor is used as the pressure sensor, which can also simultaneously measure the relative humidity H rel and the temperature TP.

[0036] A drying process in the dryer according to the invention is also influenced in particular by an airflow of the process air, since the size of the airflow determines how long a certain amount of air can be in contact with damp laundry items.

[0037] In a preferred embodiment of the method according to the invention, the airflow AP of the process air is therefore set or measured and taken into account for determining the predetermined residual moisture H set<, whereby a relationship between the airflow AP and the residual moisture H set< stored in the control unit is used. A rotational speed or power consumption of the blower can be considered as a measure of the airflow AP of the process air. However, an actual airflow of the process air can also be measured by a flow meter and then considered as the airflow AP of the process air.

[0038] According to the invention, the measured SH values, as well as the measured values ​​of the process air and / or calculated parameters derived therefrom, are linked to model parameters determined from a predictive model, preferably using different groups of model parameters for different humidity ranges. Due to the different groups of model parameters, the accuracy in determining the degree of humidity can be flexibly adapted to different phases of a drying process – and in particular to target values ​​that may change during a drying process.

[0039] Linking measured values ​​and / or calculated values ​​derived from them with predefined model parameters can include linking only measured values, only calculated values, or any combination of at least one measured value and at least one calculated value with predefined model parameters. A calculated value can be a quantity derived from or calculated from one or more measured values ​​from a sensor or sensors. For example, a calculated value can be a mathematical product or quotient of at least one directly measured value and / or a quantity calculated by applying at least one mathematical function (square root, power, exponent, logarithm, etc.) to at least one measured value. Furthermore, a calculated value can be formed by differentiating and / or averaging several measured values ​​(from one or more sensors).

[0040] A moisture range refers in particular to a range of moisture levels in the laundry.

[0041] In a preferred embodiment of the invention, each input parameter (i.e., a measured value or a calculated quantity) is linked to a corresponding model parameter. Furthermore, it is preferred that the measured values ​​are acquired continuously, particularly at a constant acquisition rate.

[0042] A "model parameter" can be understood, in particular, as a value—e.g., determined experimentally and / or numerically—that is used to link with at least one measured value in order to determine the moisture level of the laundry. Several model parameters can be grouped in a vector ("parameter vector") or in a matrix ("parameter matrix"). A single model parameter can be a constant, a variable, or a formula. The at least one model parameter used in the process can, for example, result from a prior "training" of the associated—especially multivariate—prediction model, perhaps performed at the factory. Thus, those model parameters (values) are used that previously showed the best agreement between the calculated moisture value and, for example, a directly measured moisture value.

[0043] According to the invention, it is preferred that the moisture level is calculated by vector multiplication of a vector of measured values ​​or calculated variables ("measurement vector") with a parameter vector. The parameter vectors can be stored in the laundry drying device.

[0044] Furthermore, a preferred embodiment involves assigning successively narrower moisture ranges to the different groups, with the accuracy of determining the moisture level increasing the narrower the moisture range used. In other words, the model parameters of a first group can be used for a first moisture range, the model parameters of a second group for a second moisture range, and so on. Since a successively narrower moisture range, relative to the drying progress, can determine or predict the moisture level of the laundry more accurately than the preceding moisture range. Successively narrower moisture ranges can be understood to be, in particular, moisture ranges that are applied sequentially for increasingly narrower or narrower moisture ranges.

[0045] One possible approach is to calculate the moisture level using a "hierarchical" use of the model parameter groups. This means that at the beginning of a drying process, the first group of model parameters is used, which has sufficient accuracy for its initial moisture range. Then, from a predetermined first transition value, the second group of model parameters is used, which has higher accuracy for its second moisture range.

[0046] According to the invention, it is particularly preferred that the predictive models are generated or have been generated using multivariate algorithms. These algorithms can, in particular, determine the maximum variance in the measured values ​​or calculated variables during a drying process (e.g., using PCA and / or PLS). The predictive models can be in the form of matrices that are multiplied by measurement vectors. The predictive models or the algorithms can be adapted or trained based on experimental drying processes. In particular, a model can recognize a dynamic behavior of the measured values ​​or calculated variables that is determined by the physical drying process and the drying sequence.

[0047] Preferably, the model parameters of all groups are calculated using the same basic model, and input parameters (i.e., measured values ​​and / or calculated variables) from the respective humidity ranges are used to adapt the basic model for different groups. This allows for a particularly low effort in determining the model parameters. In particular, the input parameters temperature, water loading, specific enthalpy, relative humidity, and the differences between pressure, humidity, temperature, water loading, and specific enthalpy can be provided individually or in any combination for adapting the basic model.

[0048] Using input parameters from the respective humidity ranges to adapt the basic model for different groups can involve using only input parameters from the respective humidity ranges. Alternatively, input parameters from larger areas than the respective humidity range can be used. In particular, input parameters extending beyond the respective humidity range down to 0% can be used.

[0049] The adaptation or training of the model, and thus the calculation of the model parameters for a specific humidity range, can advantageously be carried out by training or adapting a (not yet adapted) basic model or its algorithms using experimentally determined input parameters suitable for this humidity range. The adaptation can include defining parameters of the algorithms. In principle, the model parameters of a group can be determined based on an adapted model or on the basis of a combination of several adapted models.

[0050] In general, different basic models can be used for at least two different humidity ranges, which, for example, use different types of algorithms.

[0051] It is also preferred that the measured values ​​include, in addition to the superheat SH, at least relative humidity, temperature, and / or pressure. Measuring these parameters allows for a particularly precise prediction of the moisture content of the laundry. Specifically, the moisture content can also be calculated using only the relative humidity and temperature, or possibly only the temperature.

[0052] In one embodiment, the calculated parameter includes a moisture difference, a temperature difference, a water load, and / or an enthalpy. These parameters enable a particularly precise prediction of the laundry's moisture level. The differences can be derived, for example, from measurements taken before and after the drum.

[0053] To calculate or predict the moisture content of laundry items, combinations of measured values ​​and calculated parameters derived from one another can also be used. For example, in one variant, the moisture content can be calculated based on the following input parameters: superheat (SH); temperature or temperature difference; relative humidity or humidity difference; and water load or water load difference, where the water load can be calculated from the temperature and relative humidity. Instead of or in addition to the water load, enthalpy can be used, which can also be calculated from temperature, relative humidity, and, if applicable, pressure or differences thereof.

[0054] In another embodiment, the determined moisture level of the laundry is compared to a target value, where the target value corresponds to a point on a moisture level curve of a characteristic drying process. If the moisture level determined by the models is within a tolerance range associated with the target value, the drying process is stopped. This has the advantage of further reducing the influence of disturbances such as winders. Alternatively, the drying process can be stopped when the determined moisture level reaches a corresponding target value.

[0055] The invention further relates to a dryer comprising a drum for receiving laundry items to be treated, a drive motor for the drum, a process air duct for guiding process air in which process air is moved by means of a blower, wherein the process air duct is connected at a first end to an air outlet opening of the drum and at a second end to an air inlet opening of the drum, a control unit, a heat pump comprising an evaporator, a condenser, an expansion unit and a compressor, wherein a first thermometer for measuring the inlet temperature T1 and a second thermometer for measuring the outlet temperature T2 are arranged at the refrigerant inlet of the evaporator, and the control unit is configured to calculate, from a superheat SH, which can be calculated as the difference T2-T1 and is preferably calculated from this,to determine the residual moisture H of the laundry items, and wherein the dryer has at least one sensor for determining measured values ​​of the process air and the control unit is set up to link the measured SH values ​​as well as measured values ​​of the process air and / or calculated variables therefrom with model parameters determined from a predictive model in order to determine the residual moisture.

[0056] Preferably, the at least one sensor for determining measured values ​​of the process air comprises a temperature sensor and / or a humidity sensor. Preferably, a dual or triple sensor is used as the temperature and humidity sensor, capable of simultaneously measuring the temperature TP and the relative humidity H rel of the process air. Preferably, a triple sensor is used as both the temperature and humidity sensor, which, in addition to the temperature TP and the relative humidity H rel, can also measure the air pressure PP of the process air.

[0057] Finally, according to the invention, a dryer is also preferred which has a conductivity sensor in the drum and in which the control unit is set up to determine the residual moisture in order to link the moisture value measured with the moisture sensor in the drum with model parameters determined from a prediction model.

[0058] As already mentioned, it is advantageous to evaluate the current and / or power consumption of an optionally used BLDC electric motor, for example, with regard to the drum load. Furthermore, the change in the residual moisture of the laundry during the drying process can be observed. In a preferred embodiment of the dryer, the control unit is therefore configured to infer the moisture content H of the laundry in the drum from the measured current of the drive motor.

[0059] In a further preferred embodiment of the dryer according to the invention, it has a controllable expansion valve in the heat pump and the control unit is set up to keep the superheat SH within a predetermined temperature range ΔT SH by controlling the expansion valve.

[0060] According to the invention, a condensation dryer is preferred in which a temperature sensor and a humidity sensor are arranged in the process air duct before and / or after the drum.

[0061] In general, in the condensation dryer according to the invention, a condensate pump is arranged in a condensate tray or a condensate channel connected to the condensate tray. The condensate tray is generally connected via a so-called condensate channel to a container for the temporary storage of the condensate, i.e., a condensate tank, or to a wastewater line for the disposal of the condensate.

[0062] The dryer according to the invention preferably has an electric or a gas heater, with an electric heater being preferred. The heater serves to warm the process air before it is introduced into the drum of the heat pump dryer, especially at the beginning of a drying process.

[0063] The dryer according to the invention is in particular a clothes dryer per se or a washer-dryer. A washer-dryer is, in this context, a combination appliance that has a washing function for washing laundry and a drying function for drying damp laundry.

[0064] The dryer according to the invention advantageously preferably has an optical and / or acoustic display device for different states of the heat pump dryer. An optical display device is preferably used. The display device can, for example, provide information about the operation of the dryer by displaying text or by illuminating different colored LEDs, for example, about the progress of the absolute water load LW and / or the residual moisture H of the laundry items, about the superheat SH, about the load quantity, the phase of the drying process, for example, heating phase, steady-state phase, transient phase, or the remaining drying time of a drying process.

[0065] The method and heat pump dryer of the invention offer several advantages. In particular, the invention allows for improved control of the desired residual moisture content of laundry items during the drying process, thus optimizing the termination of the drying process. In embodiments of the invention, laundry properties such as load and moisture level can be precisely determined by evaluating the superheat (SF). Improved moisture sensing in the laundry items is achieved through the use of easily determined temperature signals. The invention offers the possibility of using the measured superheat in combination with existing conductivity technology, or with alternative methods for determining the residual moisture in the laundry, e.g., through algorithms from multivariate data analysis as mentioned herein, in which the superheat signal is combined with the conductivity signals.In embodiments of the invention, measured values ​​of the process air, such as temperature, relative humidity, and pressure, can also be advantageously used. In embodiments of the invention, the individual phases of a drying process, and in particular the control of a drying process to achieve a predetermined residual moisture content of the laundry items, are possible for each individual load of laundry in the drum. The inventive method and dryer thus allow for an individual, energy-efficient, and gentle drying process adapted to the user's requirements.

[0066] The relationship between the dryness level of the laundry, i.e., residual moisture, and the difference in water load can, according to the present invention, serve as an improved switch-off criterion for heating the process air and thus for terminating the drying process. This switch-off criterion generally depends on the load and the process air volume flow rate, but is almost independent of the initial residual moisture, with these influencing factors being taken into account in embodiments of the invention.

[0067] Furthermore, this method is robust and inexpensive to implement. It is largely independent of the position or entanglement of the laundry in the drum. In addition, the method is fast and can deliver calculated moisture levels practically in real time. The same applies to the dryers described herein that are suitable for carrying out this method.

[0068] Further details of the invention are described below with reference to the attached Figures 1 to 5 explained, of which Fig. 1 a dryer according to an unrestricted embodiment of a dryer according to the invention; Fig. 2 a the area of ​​the evaporator of the heat pump used in the dryer according to the invention; Fig. 3 the course of superheating (SH) during a drying process; Fig. 4 the course of the measured water loading (evap in) of the process air at the inlet of the process air duct into the evaporator during a drying process; and Fig. 5 the calculated course of the specific enthalpy of the process air during a drying process show.

[0069] The Figure 1Figure 1 shows a vertical section through an embodiment of a dryer 1 according to the invention, which is designed as a condensation dryer with a heat pump comprising a condenser and an evaporator. Fig. 1 The long arrows indicate the flow direction of the process air. The short arrows with unfilled arrowheads indicate the flow direction of the refrigerant in the heat pump.

[0070] The in Fig. 1 The dryer 1 shown contains a drum 3 rotatable about a horizontal axis 12 as a drying chamber for holding damp laundry items (not shown here), as well as a heat pump 4, 5, 13, 14, comprising an evaporator 4, a condenser 5, a compressor 13 and a throttle valve 14. Laundry carriers 25 are attached inside the drum 3 for moving laundry items during drum rotation.

[0071] The process air is guided through the drum 3 in the process air duct 2 by means of a blower 6. In the embodiment shown here, in addition to heating the process air by the heat pump, it is also possible to heat the process air by an electric heating device 21, which can be switched on, for example, for particularly rapid heating of the process air. The heated air is directed into the drum 3 from the rear, i.e., from the side of the drum 3 opposite a door 22 that closes the filling opening, through its perforated base. The heated process air thus enters the drum 3, where moisture is extracted from the damp laundry items (not shown in the figure).

[0072] The warm, moist process air leaves the drum 3 via a lint filter 16 inside the door 22, is deflected downwards, and flows in the process air duct 2 to the evaporator 4 of the heat pump, where it is cooled. In the evaporator 4, a refrigerant circulating in the heat pump circuit 4, 5, 13, 14 is evaporated and fed via a compressor 13 to the condenser 5, where the refrigerant returns to its liquid state, releasing heat to the cooled and dehumidified process air flowing in the process air duct 2. The refrigerant, now in liquid form, is directed back to the evaporator 4 via a throttle valve 14, thus closing the refrigerant circuit. In the evaporator 4, the moisture absorbed from the laundry by the process air condenses as a result of the cooling and is collected in a condensate tray 7, from which it can be pumped out for storage or disposal (not shown here). 23 means condensation.

[0073] Dryer 1 is controlled by a control unit 10, which can be operated by the user via a control unit 24. Dryer 1 also has an evaluation unit 11 integrated into the control unit 10, which evaluates the measured values ​​from the sensors.

[0074] The heat pump dryer 1 is suitable for carrying out the method according to the invention, wherein in particular the control unit 10 is set up for carrying out the method according to the invention.

[0075] An optical and / or acoustic display device 17 enables the display of a remaining drying time with regard to a residual moisture value selected by the user, for example iron-dry, or the display of the determined load or other states of the dryer or the display of the status of the drying process, for example in a color-differentiated form.

[0076] At the in Figure 1In the embodiment shown, the blower 6 and the drum 3 are driven by a common drive motor 18, which in this embodiment is a brushless direct current (BLDC) motor.

[0077] Two triple sensors 26, 27, namely one triple sensor 27 at the first end 8 of process air duct 2 and one triple sensor 28 at the second end 9 of process air duct 2, are connected to the control unit 8, in particular to the evaluation unit 11 contained therein. The triple sensors 27, 28 can each measure the relative humidity, temperature, and air pressure of the process air and thus provide the measured values ​​that are advantageous for the method according to the invention, so that the residual moisture H of the laundry items and, in particular, the load of laundry items in the drum 3 can be determined.

[0078] In the drum 3, a conductivity sensor 15 is located on a laundry carrier 25 for the additional determination of the laundry moisture.

[0079] Fig. 2 Figure 2 shows the area of ​​the evaporator 4 of the heat pump used in a dryer according to the invention. A first thermometer 28 for measuring the refrigerant temperature T1 is arranged at the refrigerant inlet 19, and a second thermometer 29 for measuring the refrigerant temperature T2 is arranged at the refrigerant outlet 20. The evaporator 2 is in contact with the process air duct 2 to dehumidify the warm, moist process air contained therein. The thick solid arrows indicate the flow direction of the process air, and the thin dashed arrows indicate the flow direction of the refrigerant.

[0080] Fig. 3This shows the course of superheating (SH) during a drying process. It is clearly visible that SH initially rises, then falls towards the end of the drying process, i.e., with increasing time. This declining portion of the SH curve is particularly useful for determining residual moisture. This portion is highlighted by a dotted tangent.

[0081] Fig. 4 shows the course of the measured water loading (evap in) of the process air at the inlet of the process air duct into the evaporator during a drying process.

[0082] According to the change in Fig. 3 As shown in the curve, the curve of the water load also drops here, which is highlighted by a dotted straight line.

[0083] Fig. 5shows the calculated course of the specific enthalpy of the process air during a drying process and thus corresponds in particular to the course of the SH curve in Fig. 3 . REFERENCE MARK LIST

[0084] 1 Heat pump dryer 2 Process air duct 3 Drum 4 Evaporator (of the heat pump) 5 Condenser (of the heat pump) 6 Blower 7 Condensate tray 8 First end of the process air duct 9 Second end of the process air duct 10 Control unit 11 Evaluation unit in the control unit 12 Horizontal (rotary) shaft 13 Compressor (of the heat pump) 14 Expansion unit, expansion (throttle) valve 15 Conductivity sensor in the drum 16 Lint filter 17 Display device, optical and / or acoustic evaluation unit 18 Drive motor for blower and drum, BLDC motor 19 Refrigerant inlet at the evaporator 20 Refrigerant outlet at the evaporator 21 (Electric) heating device 22 Door 23 Condensate 24 Operating unit 25 Laundry agitator 26 First triple sensor (temperature, relative humidity, pressure) 27 Second triple sensor (temperature, relative humidity, pressure) 28 First thermometer (in the refrigerant circuit before the evaporator) 29 Second thermometer (in the refrigerant circuit after the evaporator)

Claims

1. Method for operating a dryer (1) with a drum (3) for accommodating laundry items to be treated, a drive motor (18) for the drum (3), a process air channel (2) for guiding process air, in which process air is moved by means of a fan (6), which is connected at a first end (8) to an air outlet opening of the drum (3) and at a second end (12) to an air inlet opening (9) of the drum (3), a controller unit (10), a heat pump arranged in the process air channel (2) with an evaporator (4), a condenser (5), an expansion unit (14) and a compressor (13), wherein a first thermometer (28) for the measurement of the input temperature T1 is arranged at the coolant inlet (19) of the evaporator (4) and a second thermometer (29) for the measurement of the output temperature T2 is arranged at the coolant outlet (20) of the evaporator (4), characterised in that the controller unit (10) is configured to determine a residual humidity H of the laundry items from an overheating SH that can be calculated as a difference T2-T1, and wherein the dryer (1) has at least one sensor (26,27) for ascertaining measurement values of the process air and the controller unit (10) is configured to link the measured SH values as well as the measurement values of the process air and / or calculation variables calculated therefrom with model parameters determined from a prediction model, in order to determine the residual humidity, wherein the method comprises the following steps in a drying process: (a) measurement of the input temperature T1 at the coolant inlet (19) of the evaporator (4) and the output temperature T2 at the coolant outlet (20) of the evaporator (4); (b) calculation of the overheating SH as a difference T2-T1; and (c) determination of the residual humidity of the laundry items from the overheating SH by means of the controller unit (10).

2. Method according to claim 1, characterised in that the overheating SH during the drying process is measured continuously at least over a predefined period of time Δtset and, if it is established that the measured overheating SH is substantially constant during the period of time Δtset, then the measured SH is used as reference value SHref for the determination of the residual humidity.

3. Method according to claim 2, characterised in that the rotational speed of the fan (6) and / or the rotational speed of the compressor (13) is constant during the period of time Δtset.

4. Method according to one of claims 1 to 3, characterised in that the drive motor (18) is a BLDC electric motor and its drive power is evaluated with regard to a loading of the drum (3) with laundry items.

5. Method according to one of claims 1 to 4, characterised in that the sensor (26,27) comprises a temperature sensor and a humidity sensor, and a dual sensor (26,27), which is able to measure the temperature TP and the relative humidity Hrel of the process air simultaneously, is used as temperature sensor and humidity sensor.

6. Method according to one of claims 1 to 5, characterised in that it additionally comprises the method steps (d) comparison of the determined residual humidity H with an upper limit value of the residual humidity Hset; and (e) termination of the drying process when reaching or falling below the predefined residual humidity Hset.

7. Dryer (1) with a drum (3) for accommodating laundry items to be treated, a drive motor (18) for the drum (3), a process air channel (2) for guiding process air, in which process air is moved by means of a fan (6), wherein the process air channel (2) is connected at a first end (8) to an air outlet opening of the drum (3) and at a second end (12) to an air inlet opening (9) of the drum (3), a controller unit (10), and a heat pump arranged in the process air channel (2) with an evaporator (3), a condenser (5), an expansion unit (14) and a compressor (13), wherein a first thermometer (28) for the measurement of the input temperature T1 is arranged at the coolant inlet (19) of the evaporator (3) and a second thermometer (29) for the measurement of the output temperature T2 is arranged at the coolant outlet (20) of the evaporator (3), and the controller unit (10) is configured to determine a residual humidity of the laundry items from an overheating SH that can be calculated as a difference T2-T1, and wherein the dryer (1) has at least one sensor (26,27) for ascertaining measurement values of the process air and the controller unit (10) is configured to link the measured SH values as well as the measurement values of the process air and / or calculation variables calculated therefrom with model parameters determined from a prediction model, in order to determine the residual humidity.

8. Dryer (1) according to claim 7, characterised in that the at least one sensor (26,27) comprises a temperature sensor and / or a humidity sensor for ascertaining measurement values of the process air.

9. Dryer (1) according to claim 8, characterised in that a dual sensor or triple sensor, which is able to measure the temperature TP and the relative humidity Hrel of the process air simultaneously, is used as temperature sensor and humidity sensor (26,27).

10. Dryer (1) according to one of claims 8 to 9, characterised in that it has a conductivity sensor (15) in the drum (3) and the controller unit (10) is configured for determining the residual humidity, in order to link the humidity value measured using the humidity sensor in the drum with model parameters determined from a prediction model.

11. Dryer (1) according to one of claims 8 to 10, characterised in that the controller unit (10) is configured to infer a moisture content H of the laundry items in the drum (3) from the measured current of the drive motor (18).

12. Dryer (1) according to one of claims 8 to 11, characterised in that it has a regulatable expansion valve (14) in the heat pump and the controller unit (10) is configured to keep the overheating SH in a predefined temperature range ΔTSH through the regulation of the expansion valve (14).

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