EP3074566A1

EP3074566A1 - Heat pump type laundry dryer with improved operational safety and energy efficiency and method for operating the same

Info

Publication number: EP3074566A1
Application number: EP13796111.6A
Authority: EP
Inventors: Selcuk KARAGOZ; Bora Abdik; Onur Ozdemir; Ersin BEDIR
Original assignee: Arcelik AS
Current assignee: Arcelik AS
Priority date: 2013-11-29
Filing date: 2013-11-29
Publication date: 2016-10-05
Also published as: WO2015078523A1

Abstract

The present invention relates to a method for operating a heat-pump type laundry dryer (1). The method for operating a heat-pump type laundry dryer (1) according to the present invention comprises: a step of turning off the compressor (6) by a protective switch when the protective switch detects an abnormal state of the compressor (6); a step of obtaining the refrigerant temperature T1 and/or the process air temperature T2 or the process air humidity H; a step of determining a first rate R1 of a change in the temperature T1 and/or a second rate R2 of a change in the temperature T2 or a third rate R3 of a change in the humidity H; and a step of operating the motor of the laundry drum, the process air circuit and the refrigerant circuit based on the temperature T1 and/or the temperature T2 or the humidity H respectively in combination with the first rate R1 and/or the second rate R2 or the third rate R3 which are used to judge whether the compressor (6) is in the abnormal state, wherein the compressor (6) is cooled by the second fan (9) in accordance with the judgment.

Description

HEAT PUMP TYPE LAUNDRY DRYER WITH IMPROVED OPERATIONAL SAFETY AND ENERGY EFFICIENCY AND METHOD FOR OPERATING THE SAME

The present invention relates to a heat pump type laundry dryer and a method for operating a heat-pump type laundry dryer. The present invention particularly relates to a method for improving operational safety and energy efficiency of a heat pump type laundry dryer.
The heat pump technology constitutes a relatively energy-efficient method of drying laundry. A heat pump type laundry dryer typically consists of a closed process air circuit and a refrigerant circuit which are arranged so as to mutually exchange heat. The process air circuit includes a duct for circulating process air through a laundry drum by means of a fan. The refrigerant circuit includes an evaporator, a compressor, a condenser, and an expansion valve such as a capillary in serial connection for circulating a refrigerant. The evaporator and the condenser are particularly arranged in heat exchange with the process air within the circulation duct for respectively dehumidifying and subsequently heating the process air. The heat absorbed by the evaporator when dehumidifying the process air is subsequently partly transferred back to the process air by means of the condenser. Thereby, a drying performance of the laundry dryer is increased.
In general, the drying process depends on several factors. For instance, the rate of heat transferred to the process air by the condenser depends on the rate of heat transferred to the refrigerant by the compressor and the rate of heat transferred to the refrigerant by the evaporator during a condensation of the humid process air. When the heat exchange at the condenser diminishes, the overall temperature of the refrigeration circuit starts to increase. Consequently, the compressor eventually operates in an abnormal state which is generally detrimental to the laundry dryer. Relatively high environmental temperatures or clogging of any lint filters arranged in the process air duct are some of the factors which can easily give rise to an abnormal operational state of the laundry dryer.
Several techniques have been developed to prevent a laundry dryer from malfunctioning in an abnormal state. For instance, a conventional heat pump type laundry dryer is typically provided with a fan for cooling the compressor when an abnormal state occurs. In this conventional technique, a temperature of the refrigerant or alternatively a temperature of the process air is monitored by a temperature sensing unit according to a commonly used algorithm shown in Fig. 3, which is executed by a control unit of the conventional heat pump type laundry dryer. In this conventional technique, when the monitored temperature exceeds an upper threshold temperature, the compressor is turned off to prevent malfunctioning of the compressor and the fan is turned on to accelerate cooling of the compressor. Furthermore, the cooling process is typically continued until the temperature drops below a lower threshold temperature.
WO 2013/050262 A1 discloses a heat pump type laundry dryer which has first temperature sensor arranged in the air duct and a second temperature sensor arranged on a refrigerant line. The heat pump type laundry dryer also includes a cooling fan for cooling the compressor. A control unit thereof monitors the temperate of the process air and the temperature of the refrigerant, and subsequently operates the cooling fan, for example, when the refrigerant temperature exceeds an upper limit temperature.
A heat pump type laundry dryer may also eventually operate in an abnormal state when increasingly more current is drawn by the compressor due to low-voltage in the mains. Therefore, a conventional heat pump type laundry dryer is usually provided with a protective switch, in particular an over-current switch or alternatively a thermal switch which respectively deactivate the compressor when an overcurrent or overheating is detected by protective switch itself.
There might be instances where, for example, a protective switch deactivates the compressor even though the temperature monitored in accordance with the aforementioned conventional algorithm does not exceed beyond the limit temperature. In such instances, the control unit will not be aware of the deactivation of the compressor, since a protective switch generally functions independently of the control unit. Consequently, the control unit will continue to operate the laundry dryer without taking any protective measures against the abnormal state of the compressor. To avoid such instances, the control unit may be equipped with an additional circuit for monitoring the protective switch. However, this would increase the overall cost of the laundry dryer.
An objective of the present invention is to provide a heat pump type laundry dryer and a method for operating a heat pump laundry dryer which overcomes the aforementioned problems of the prior art and which enables a safe and energy-efficient operation of the laundry dryer.
This objective has been achieved by the method of operating a heat pump type laundry dryer according to the present invention as defined in claim 1, and the heat pump type laundry dryer according to the present invention as defined in claim 13. Further achievements have been attained by the subject-matters respectively defined in the dependent claims.
The method for operating a heat-pump type laundry dryer according to the present invention comprises: a step of turning off the compressor by the protective switch when the protective switch detects an abnormal state of the compressor; a step of obtaining the refrigerant temperature T1 and/or the process air temperature T2 or the humidity H; a step of determining a first rate R1 of a change in the temperature T1 and/or a second rate R2 of a change in temperature T2 or a third rate R3 of a change in the humidity H; and a step of operating the motor of the laundry drum, the process air circuit and the refrigerant circuit based on the temperature T1 and/or the temperature T2 or humidity H respectively in combination with the first rate R1 and/or the second rate R2 or the third rate R3 which are used to judge whether the compressor is in the abnormal state, wherein the compressor is cooled by a compressor cooling fan in accordance with the judgment.
In an embodiment, a first threshold rate Rth1 and/or a second threshold rate Rth2 or a third threshold Rth3 are used to judge whether the heat-pump type laundry dryer is in an abnormal state. It is judged that the compressor is in an abnormal state if at least one of the first rate R1, the second rate R2 and the third rate R3 exceeds a respective one of the first threshold rate Rth1, the second threshold rate Rth2 and the third threshold rate Rth3. In this embodiment, the compressor cooling fan is turned on so as to rotate at a predetermined speed if it is judged that compressor is in an abnormal state.
In another embodiment, the process air fan is turned off if it is judged that compressor is in an abnormal state.
In another embodiment, the drum motor is also turned off or a rotation speed thereof is reduced if it is judged that compressor is in an abnormal state.
In another embodiment, a sign of the first rate R1 and/or a second rate R2 or a third R3 are monitored to judge whether the heat-pump type laundry dryer (1) is still in an abnormal state or has recovered to a normal state. In this embodiment, it is judged that that the compressor (6) is still in an abnormal state if at least one of the first rate R1, the second rate R2 and the third rate R3 has a positive value. In this embodiment, the compressor cooling fan is turned off if it is judged that compressor has recovered to a normal state.
In an alternative embodiment, instead of judging whether the compressor is still in an abnormal state, the compressor is cooled by the compressor cooling fan for a predetermined duration or until a temperature T1 and/or a temperature T2 drops below a lower threshold temperature.
By the method of the present invention, the control unit is enabled to immediately initiate cooling of the compressor by means of the compressor cooling fan when the compressor has been turned off by a protective switch but the refrigerant temperature and the process air temperature as being observed have not yet increased beyond any critical temperatures. Thereby, the compressor recovers to a normal state within a relatively shorter time in comparison to a case where the compressor cooling fan is activated not until before the refrigerant temperature or the process air temperature exceeds a respective critical temperature. Hence, the drying process is prevented from unnecessarily prolonging. Moreover, there might be instance where after deactivation of the compressor by the protective switch the refrigerant temperature and the process air temperature do not sufficiently increase so as to exceed a respective critical temperature either due radiative cooling of the compressor or due to an unfavorable location of the temperature sensors. Thereby, the method of the present invention improves operational safety of the heat pump type laundry dryer. By the method of the present invention, the energy efficiency of the heat pump type laundry dryer is also improved through deactivating the drum motor and process air fan when the compressor is judged as being in an abnormal state.
Additional advantages of the heat pump type laundry dryer according to the present invention and the method for operating the heat pump type laundry dryer according to the present invention will become apparent with the detailed description of the embodiments with reference to the accompanying drawings in which:
Figure 1 – is a schematic view of a heat pump type laundry dryer according to an embodiment of the present invention,
Figure 2 – is a flowchart showing the steps of a method of operating the heat pump type laundry dryer according to an embodiment of the present invention,
Figure 3 – is a flowchart partly showing the steps of a conventional method of operating a heat pump type laundry dryer.
The reference signs appearing on the drawings relate to the following technical features.

Laundry dryer (Heat pump type)
Drum
Duct
First fan
Evaporator
Compressor
Condenser
Expansion valve
Second fan
Control unit
First sensing unit
Second sensing unit

The heat-pump type laundry dryer (1) comprises: a drum (2) for receiving laundry to be dried, a motor (not shown) for rotating the drum (2), a process air circuit including, a duct (3) which is arranged to discharge process air into the drum (2) and to draw process air out of the drum (2) and a first fan (4) which is arranged to circulate the process air in the duct (3) through the drum (2), a refrigerant circuit including an evaporator (5), a compressor (6), a condenser (7), and an expansion valve (8) or capillary which are connected in series to circulate a refrigerant, and a second fan (9) which is arranged to cool the compressor (6), wherein the evaporator (5) is arranged to dehumidify the process air in the duct (3), and wherein the condenser (7) is arranged to heat the dehumidified process air in the duct (3); a control unit (10) for operating each of the motor, the process air circuit and the refrigerant circuit, a first sensing unit (11) and/or a second sensing unit (12), wherein the first sensing unit (11) is arranged to measure a temperature T1 of the refrigerant and to output a first signal indicative of the temperature T1 to the control unit (10), and wherein the second sensing unit (12) is arranged to measure a temperature T2 and/or a humidity H of the process air and to output a second signal indicative of the temperature T2 or the humidity H to the control unit (10) and a protective switch (not shown) for detecting an abnormal state of the compressor (6) (Fig. 1).
The method for operating the heat-pump type laundry dryer (1) according to the present invention comprises: a step of turning off the compressor (6) by the protective switch when the protective switch detects an abnormal state of the compressor (6); a step (S1a) of obtaining based on the first signal and/or the second signal, the temperature T1 and/or the temperature T2 or the humidity H; a step (S1b) of determining, based on the first signal, a first rate R1 of a change in the temperature T1, and/or determining, based on the second signal, a second rate R2 of a change in temperature T2 or a third rate R3 of a change in the humidity H; and a step of operating the motor, the process air circuit and the refrigerant circuit based on the temperature T1 and/or the temperature T2 or the humidity H respectively in combination with the first rate R1 and/or the second rate R2 or the third rate R3 which are used to judge whether the compressor (6) is in the abnormal state. In the method according to the present invention the compressor (6) is cooled by the second fan (9) in accordance with the judgment based on the first rate R1 = ΔT1/Δt and/or the second rate R2 = ΔT2/Δt or the third rate R3 = ΔH/Δt, where Δ signifies a change in the respective measured parameter, i.e., T1, T2 or H, and t signifies a respective time interval (Fig. 2).
According to the present invention any sudden rise in the refrigerant temperature T1 and/or process air temperature T2 or process air humidity H is respectively monitored through the first rate R1 and/or the second rate R2 or the third rate R3 (Fig. 2). The aforementioned sudden rise is indicative of an abnormal state of the compressor (6). Thereby, the control unit (10) is enabled to initiate cooling of the compressor (6) by means of the second cooling fan (9) even when the refrigerant temperature T1 or process air temperature T2 has not increased beyond a first threshold temperature Tth1 and a second threshold temperature Tth2 (Fig. 3). Thus, the heat-pump type laundry dryer (1) can be more safely operated. Moreover, the control unit (10) is also enabled to immediately initiate cooling of the compressor (6) by means of the second cooling fan (9) i.e., considerably well before the refrigerant temperature T1 or the process air temperature T2 has respectively increased beyond a first threshold temperature Tth1 or a second threshold temperature Tth2 (Fig. 3). Thereby, the compressor (6) can be returned to a normal state within a relatively shorter time. Hence, the drying process is prevented from unnecessarily prolonging.
In an embodiment, a first threshold rate Rth1 and/or a second threshold rate Rth2 or a third threshold Rth3 are used to judge whether the heat-pump type laundry dryer (1) is in an abnormal state (Fig. 2). In this embodiment, the operation step includes: a step (S2a) of comparing the first rate R1 and/or the second rate R2 or the third rate R3 respectively with a first threshold rate Rth1 and/or a second threshold rate Rth2 or a third threshold rate Rth3; a first step (S2b) of judging that the compressor (6) is in an abnormal state if at least one of the first rate R1, the second rate R2 and the third rate R3 exceeds a respective one of the first threshold rate Rth1, the second threshold rate Rth2 and the third threshold rate Rth3; and a step (S3a) of turning on or increasing a rotation speed of the second fan (9) if the judgment in the first judgment step (S2b) is affirmative. Thereby, the compressor (6) can be more reliably protected against overheating.
In another embodiment, the operation step further includes: a step (S3b) of turning off the first fan (4) if the judgment in the second judgment step (S2b) is affirmative (Fig. 2). Thereby, the first fan (4) is prevented from unnecessarily consuming electrical energy when the compressor (6) is in an abnormal state. In addition, since the first fan (4) is turned off, the process air is prevented from reducing a temperature difference between the evaporator (5) and the condenser (4). Thereby, the drying process can be effectively resumed when the compressor (6) recovers to a normal state.
In another embodiment, the operation step further includes: a step (S3c) of turning off or reducing the rotation speed of the motor if the judgment in the second judgment step (S2b) is affirmative (Fig. 2). Thereby, the motor is prevented from unnecessarily consuming electrical energy when the compressor (6) is in an abnormal state. In this embodiment, the rotation speed of the motor can be alternatively reduced instead of being completely stopped.
In another embodiment, a sign of the first rate R1 and/or a second rate R2 or a third R3 is monitored to judge whether the heat-pump type laundry dryer (1) is still in an abnormal state or has recovered to a normal state. In this embodiment, the operation step further includes: a step of monitoring (S4a) a sign of the first rate R1 and/or the second rate R2 or the third rate R3 if the judgment in the first judgment step (S2b) is affirmative; a second step (S4b) of judging that the compressor (6) is still in an abnormal state if at least one of the first rate R1, the second rate R2 and the third rate R3 has a positive value; and a step (S5a) of turning off or reducing a rotation speed of the second fan (9) if the judgment in the second judgment step (S4b) is negative (Fig. 2).
In another embodiment, the operation step further includes: a step (S5b) of turning on the first fan (4) if the judgment in the second judgment step (S4b) is negative (Fig. 2).
In another embodiment, the operation step further includes: a step (S5c) of turning on or increasing a rotation speed of the motor if the judgment in the second judgment step (S4b) is negative (Fig. 2).
In another embodiment, the operation step further includes: a step (S6a) of comparing the temperature T1 with a first threshold temperature Tth1 or comparing the temperature T2 with a second threshold temperature Tth2; a third step (S6b) of judging that the compressor (6) is in an abnormal state if the temperature T1 exceeds the first threshold Tth1 or if the temperature T2 exceeds the second threshold Tth1; a step (S7) of turning on the second fan (9) if the judgment in the third judgment step (S6b) is affirmative; and a step (S9) of turning off the second fan (9) if the judgment in the third judgment step (S6b) is negative (Fig. 3).
In another embodiment, the operation step further includes: a step (S8a) of comparing the temperature T1 with a first threshold temperature Tth1´ or comparing the temperature T2 with a second threshold temperature Tth2´ if the judgment in the third judgment step (S6b) has been affirmative, wherein the first threshold temperature Tth1´ is lower than first threshold temperature Tth1, and wherein the second threshold temperature Tth2´ is lower than the second threshold temperature Tth2; a fourth step (S8b) of judging that the compressor (6) is still in an abnormal state if the temperature T1 exceeds the first threshold temperature Tth1´ or if the temperature T2 exceeds the second threshold temperature Tth1´; a step (S7) of keeping the second fan (9) turned on if the judgment in the fourth judgment step (S8b) is negative; and a step (S9) of turning off the second fan (9) if the judgment in the fourth judgment step (S8b) is affirmative (Fig. 3).
In another alternative embodiment, the first threshold temperature Tth1´ and the second threshold temperature Tth1´ are not used. In this alternative embodiment, the second fan (9) is kept turned on for a predetermined duration and subsequently turned off (Fig. 3).
In another embodiment, the compressor (6) is turned off by the protective switch when the protective switch detects an abnormal temperature of the compressor (6). In this embodiment, the protective switch is a thermal switch (not shown) in particular a thermostat or the like.
In another embodiment, the compressor (6) is turned off by the protective switch when the protective switch detects an abnormal electrical current supplied to the compressor (6). In this embodiment, the protective switch is an over-current switch (not shown) or the like.
In the heat-pump type laundry dryer (1) according to the present invention the control unit (10) is configured to operate the motor, the process air circuit and the refrigerant circuit in accordance with the method steps as defined in any one of the above described embodiments (Figs. 2 and 3).
In another embodiment, the protective switch is a thermal switch which is adapted to deactivate the compressor (6) when the thermal switch detects an abnormal temperature of the compressor (6).
In alternative embodiment, the protective switch is an over-current switch which is adapted to deactivate the compressor (6) when the over-current switch detects an abnormal electrical current supplied to the compressor (6).
The program according to the present invention comprises computer-readable codes for causing a computer-implemented heat-pump type laundry dryer (1) to execute the method steps defined in any one of the above embodiments (Figs. 2 and 3).
By the method of the present invention, an operational safety of the heat pump type laundry dryer (1) has been improved without incurring additional costs. By the method of the present invention, an energy efficiency of the heat pump type laundry dryer (1) has also been improved.

Claims

A method for operating a heat-pump type laundry dryer (1) comprising a drum (2) for receiving laundry, a motor for rotating the drum (2), a process air circuit including a duct (3) arranged to discharge process air into the drum (2) and to draw process air out of the drum (2), and a first fan (4) arranged to circulate the process air in the duct (3) through the drum (2), a refrigerant circuit including an evaporator (5), a compressor (6), a condenser (7), and an expansion valve (8) connected in series to circulate a refrigerant, and a second fan (9) arranged to cool the compressor (6), wherein the evaporator (5) is arranged to dehumidify the process air in the duct (3), and wherein the condenser (7) is arranged to heat the dehumidified process air in the duct (3), a control unit (10) for operating the motor, the process air circuit and the refrigerant circuit, a first sensing unit (11) and/or a second sensing unit (12), wherein the first sensing unit (12) is arranged to measure a temperature T1 of the refrigerant and to output a first signal indicative of the temperature T1 to the control unit (10), and wherein the second sensing unit (12) is arranged to measure a temperature T2 or a humidity H of the process air and to output a second signal indicative of the temperature T2 or the humidity H to the control unit (10) and a protective switch for detecting an abnormal state of the compressor (6), the method comprising the steps of:

- turning off the compressor (6) by the protective switch when the protective switch detects an abnormal state of the compressor (6),

- obtaining based on the first signal and/or the second signal, the temperature T1 and/or the temperature T2 or the humidity H (S1a),

- determining, based on the first signal, a first rate R1 of a change in the temperature T1, and/or determining, based on the second signal, a second rate R2 of a change in the temperature T2 or a third rate R3 of a change in the humidity H (S1b) and

- operating the motor, the process air circuit and the refrigerant circuit based on the temperature T1 and/or the temperature T2 or the humidity H respectively in combination with the first rate R1 and/or the second rate R2 or the third rate R3 which are used to judge whether the compressor (6) is in said abnormal state, wherein the compressor (6) is cooled by the second fan (9) in accordance with the judgment.
The method according to claim 1, characterized in that the operation steps of:

- comparing the first rate R1 and/or the second rate R2 or the third rate R3 respectively with a first threshold temperature Rth1 and/or a second threshold temperature Rth2 or a third threshold temperature Rth3 (S2a),

- judging that the compressor (6) is in an abnormal state if at least one of the first rate R1, the second rate R2 and the third rate R3 exceeds a respective one of the first threshold temperature Rth1, the second threshold temperature Rth2 and the third threshold temperature Rth3 (S2b) and

- turning on or increasing a rotation speed of the second fan (9) if the judgment in the first judgment step (S2b) is affirmative (S3a).
The method according to claim 2, characterized in that the operation step of:

- turning off the first fan (4) if the judgment in the second judgment step (S2b) is affirmative (S3b).
The method according to claim 2 or 3, characterized in that the operation step of:

- turning off or reducing the rotation speed of the motor if the judgment in the second judgment step (S2b) is affirmative (S3c).
The method according to any one of claims 2 to 4, characterized in that the operation steps of:

- monitoring a sign of the first rate R1 and/or the second rate R2 or the third rate R3 if the judgment in the first judgment step (S2b) is affirmative (S4a),

- judging that the compressor (6) is still in an abnormal state if at least one of the first rate R1, the second rate R2 and the third rate R3 has a positive value (S4b) and

- turning off or reducing a rotation speed of the second fan (9) if the judgment in the second judgment step (S4b) is negative (S5a).
The method according to claim 5, characterized in that the operation step of:

- turning on the first fan (4) if the judgment in the second judgment step (S4b) is negative (S5b).
The method according to claim 5 or 6, characterized in that the operation step of:

- turning on or increasing a rotation speed of the motor if the judgment in the second judgment step (S4b) is negative (S5c).
The method according to any one of claims 1 to 7, characterized in that the operation steps of:

- comparing the temperature T1 with a first threshold temperature Tth1 or the temperature T2 with a second threshold temperature Tth2 (S6a),

- judging that the compressor (6) is in an abnormal state if the temperature T1 exceeds the first threshold temperature Tth1 or if the temperature T2 exceeds the second threshold temperature Tth2 (S6b),

- turning on the second fan (9) if the judgment in the third judgment step (S6b) is affirmative (S7) and

- turning off the second fan (9) if the judgment in the third judgment step (S6b) is negative (S9).
The method according to claim 8, characterized in that the operation steps of:

- comparing the temperature T1 with a first threshold temperature Tth1´ or the temperature T2 with a second threshold temperature Tth2´ if the judgment in the third judgment step (S6b) is affirmative, wherein the first threshold temperature Tth1´ is lower than first threshold temperature Tth1, and wherein the second threshold temperature Tth2´ is lower than the second threshold temperature Tth2 (S8a),

- judging that the compressor (6) is still in an abnormal state if the temperature T1 exceeds the first threshold temperature Tth1´ or if the temperature T2 exceeds the second threshold temperature Tth2´ (S8b),

- keeping the second fan (9) turned on if the judgment in the fourth judgment step (S8b) is negative (S7) and

- turning off the second fan (9) if the judgment in the fourth judgment step (S9) is affirmative (S9).
The method according to any one of claims 1 to 9, characterized in that the operation step of:

- turning off the compressor (6) by the protective switch when the protective switch detects an abnormal temperature of the compressor (6).
The method according to any one of claims 1 to 9, characterized in that the operation step of:

- turning off the compressor (6) by protective switch when the protective switch detects an abnormal electrical current supplied to the compressor (6).
A heat-pump type laundry dryer (1) comprising a drum (2) for receiving laundry, a motor for rotating the drum (2), a process air circuit including a duct (3) arranged to discharge process air into the drum (2) and to draw process air out of the drum (2) and a first fan (4) arranged to circulate the process air in the duct (3) through the drum (2), a refrigerant circuit including an evaporator (5), a compressor (6), a condenser (7), and an expansion valve (8) connected in series to circulate a refrigerant, and a second fan (9) arranged to cool the compressor (6), wherein the evaporator (5) is arranged to dehumidify the process air in the duct (3), and wherein the condenser (7) is arranged to heat the dehumidified process air in the duct (3), a control unit (10) for operating the motor, the process air circuit and the refrigerant circuit, a first sensing unit (11) and/or a second sensing unit (12), wherein the first sensing unit (11) is arranged to measure a temperature T1 of the refrigerant and to output a first signal indicative of the temperature T1 to the control unit (10) and wherein the second sensing unit (12) is arranged to measure a temperature T2 and/or a humidity H of the process air and to output a second signal indicative of the temperature T2 or the humidity H to the control unit (10), a protective switch for detecting an abnormal state of the compressor (6), the heat-pump type laundry dryer (1) being characterized in that the control unit (10) is configured to operate the motor, the process air circuit and the refrigerant circuit in accordance with the method steps defined in any one of claims 1 to 11.
The method according to claim 12, characterized in that the protective switch is either a thermal switch adapted to deactivate the compressor (6) when the thermal switch detects an abnormal temperature of the compressor (6) or an over-current switch adapted to deactivate the compressor (6) when the over-current switch detects an abnormal electrical current supplied to the compressor (6).
A program comprising computer-readable codes for causing a computer-implemented heat-pump type laundry dryer (1) to execute the method steps defined in any one of claims 1 to 11.