Heat pump type laundry dryer and method for controlling the same

Abstract

The present invention relates to a heat-pump type laundry dryer comprising a drum, a process air circuit, a refrigerant circuit which has a compressor and a control unit for conducting the drying process. The laundry dryer of the present invention further comprising: a fan for cooling the compressor and a sensor for sensing the process air temperature T_air, wherein the control unit sets a first threshold temperature T_th 1 which is equal to or smaller than 55° C., sets a second threshold temperature T_th 2 which is less than T_th 1 and initiates, prior to the termination of the drying process a cooling process in which the fan is turned ON when T_air reaches T_th 1 and the fan is turned OFF when T_air drops below T_th 2.

1 . A heat-pump type laundry dryer comprising: a drum for receiving the laundry, a process air circuit for conveying dehumidified heated process air through the drum, a refrigerant circuit for dehumidifying the process air and heating the dehumidified process air, wherein the refrigerant circuit has a refrigerant compressor and a control unit for conducting the drying process of the laundry, characterized in that a fan for cooling the compressor and a sensor for sensing the process air temperature T_air, wherein the control unit is configured to set a first threshold temperature T_th 1  which is equal to or smaller than 55° C., to set a second threshold temperature T_th 2  which is less than T_th 1  and to initiate, prior to the termination of the drying process a cooling process in which the fan is turned ON when T_air reaches T_th 1  and the fan is turned OFF when T_air drops to T_th 2 . 
     
     
         2 . The heat-pump type laundry dryer according to  claim 1 , characterized in that the control unit is further configured to initiate the cooling process when a predetermined drying program has been selected by the user or a predetermined duration has elapsed since the drying process was commenced. 
     
     
         3 . The heat-pump type laundry dryer according to  claim 1 , characterized in that a sensor for sensing the refrigerant temperature T_rfg, wherein the control unit is further configured to set a third threshold temperature T_th 3 , to set a fourth threshold temperature T_th 4  which is equal to smaller than T_th 3  and to initiate an auxiliary cooling process prior to the initiation of the cooling process or after the initiation of the cooling process when T_air has not yet reached T_th 1 , wherein in the auxiliary cooling process the fan is turned ON when T_rfg exceeds T_th 3  and the fan is turned OFF when T_rfg drops below T_th 4 . 
     
     
         4 . The heat-pump type laundry dryer according to  claim 1 , characterized in that the process air circuit comprises an air filter which is located immediately downstream of the drum, wherein the sensor for sensing the process air temperature T_air is located in the vicinity of the air filter. 
     
     
         5 . A method for controlling a heat-pump type laundry dryer, the method comprising:
 a step of starting the drying process in which the laundry is dried by process air, the method being characterized by further comprising:   a step of setting a first threshold temperature T_th 1  which is equal to or smaller than 55° C. and a second threshold temperature T_th 2  which is less than T_th 1 ;   a step of initiating a cooling process prior to the termination of the drying process, wherein the cooling process comprising:   a step of sensing the process air temperature T_air, turning a compressor cooling fan ON when the process air temperature T_air reaches T_th 1  and turning the compressor cooling fan OFF when the process air temperature T_air drops to T_th 2 .   
     
     
         6 . The control method according to  claim 5 , characterized in that in the initiating step the cooling process is initiated when a predetermined drying program has been selected by the user or a predetermined duration has elapsed since the drying process was commenced. 
     
     
         7 . The control method according to  claim 5 , the method further comprising:
 a step of initiating an auxiliary cooling process prior to the initiation of the cooling process, or after the initiation of the cooling process when T_air has not yet reached T_th 1 , wherein the auxiliary cooling process comprising:   a step of setting a third threshold temperature T_th 3  and a fourth threshold temperature T_th 4  which is equal to or less than T_th 3  and a step of sensing the refrigerant temperature T_rfg, turning the compressor cooling fan ON when the refrigerant temperature T_rfg exceeds T_th 3  and turning the compressor cooling fan OFF when the refrigerant temperature T_rfg drops below T_th 4 .   
     
     
         8 . The heat-pump type laundry dryer according to  claim 2 , characterized in that a sensor for sensing the refrigerant temperature T_rfg, wherein the control unit is further configured to set a third threshold temperature T_th 3 , to set a fourth threshold temperature T_th 4  which is equal to smaller than T_th 3  and to initiate an auxiliary cooling process prior to the initiation of the cooling process or after the initiation of the cooling process when T_air has not yet reached T_th 1 , wherein in the auxiliary cooling process the fan is turned ON when T_rfg exceeds T_th 3  and the fan is turned OFF when T_rfg drops below T_th 4 . 
     
     
         9 . The heat-pump type laundry dryer according to  claim 2 , characterized in that the process air circuit comprises an air filter which is located immediately downstream of the drum, wherein the sensor for sensing the process air temperature T_air is located in the vicinity of the air filter. 
     
     
         10 . The heat-pump type laundry dryer according to  claim 3 , characterized in that the process air circuit comprises an air filter which is located immediately downstream of the drum, wherein the sensor for sensing the process air temperature T_air is located in the vicinity of the air filter. 
     
     
         11 . The control method according to  claim 6 , the method further comprising:
 a step of initiating an auxiliary cooling process prior to the initiation of the cooling process, or after the initiation of the cooling process when T_air has not yet reached T_th 1 , wherein the auxiliary cooling process comprising:   a step of setting a third threshold temperature T_th 3  and a fourth threshold temperature T_th 4  which is equal to or less than T_th 3  and a step of sensing the refrigerant temperature T_rfg, turning the compressor cooling fan ON when the refrigerant temperature T_rfg exceeds T_th 3  and turning the compressor cooling fan OFF when the refrigerant temperature T_rfg drops below T_th 4 .