EP2843118A1

EP2843118A1 - Heat-pump laundry treatment apparatus and method of operating a compressor

Info

Publication number: EP2843118A1
Application number: EP13181947.6A
Authority: EP
Inventors: Paolo Driussi
Original assignee: Electrolux Appliances AB
Current assignee: Electrolux Appliances AB
Priority date: 2013-08-28
Filing date: 2013-08-28
Publication date: 2015-03-04
Anticipated expiration: 2033-08-28
Also published as: PL2843118T3; EP2843118B1

Abstract

The invention relates to a method of operating a compressor (14) in a laundry treatment apparatus, in particular laundry dryer or washer-dryer, wherein the laundry treatment apparatus comprises a heat-pump system having a compressor (14) adapted to circulate a refrigerant (6) through the heat-pump system during a laundry drying operation and wherein the laundry treatment apparatus comprises a control unit (51) controlling the operation of the laundry treatment apparatus. In case that the operation of the compressor (14) is suspended, the operation of the compressor (14) is restarted upon receiving a restarting signal. The value of power or current (I_comp) supplied to the compressor (14) after restarting the compressor operation is monitored and the compressor operation is maintained or suspended again in dependency of the monitored value of power or current (I_comp). Further the invention relates to a laundry treatment apparatus adapted to implement the method.

Description

The invention relates to a method of operating a compressor in a heat-pump laundry treatment apparatus, in particular a heat-pump laundry dryer or a heat-pump washer-dryer. Further the invention relates to a laundry treatment apparatus having a control unit adapted to control the operation of the laundry treatment apparatus.
EP 1 541 745 B1 discloses a heat pump laundry dryer comprising a heat pump system including a compressor which is adapted to circulate a refrigerant through the heat-pump system. Furthermore, the laundry dryer comprises a drum having therein laundry, and a process air path for guiding process air or drying air to the rotary drum. The dryer also comprises a blower for blowing the drying air to the process air path independent of the rotation of the drum and the operation of the compressor. After stopping the compressor operation and when resuming a drying operation, the compressor is restarted only after waiting the lapse of a predetermined period since the time of stopping the compressor. A controller is used for controlling operation of the dryer, in particular for operating the blower and the compressor.
It is an object of the invention to provide a method of operating a heat-pump laundry treatment apparatus in such a manner that its heat-pump system operation is economic or improved, and to provide a laundry treatment apparatus implementing the improved operation.
The invention is defined in independent claims 1 and 15, respectively. Particular embodiments are set out in the dependent claims.
According to the invention, a heat pump laundry treatment apparatus comprises a heat-pump system having a compressor which is adapted to circulate a refrigerant through the heat-pump system during a laundry drying operation. Furthermore, the heat pump laundry treatment apparatus comprises a control unit controlling the operation of the heat pump laundry treatment apparatus. The heat pump laundry treatment apparatus - in the following description also denoted in brief "apparatus" - is in particular configured as a heat pump laundry dryer or a heat pump washing machine having a drying function (washer-dryer).
In case that the compressor operation is suspended, the method of operating the compressor comprises at least the following:

the compressor operation is restarted upon receiving a restarting signal,
after restarting the compressor operation, the value of (electrical) power or current supplied to the compressor is monitored, and
the compressor operation is maintained or suspended again in dependency of the monitored value of the power or current.

In this regard, it is noted that the operation mode "suspended" does include also the operation mode "stopped". Basically this means that in these cases the compressor is in the status "OFF", i.e. not active.
Monitoring the value of power or current and switching the operation mode (maintaining and suspending) of the compressor is preferably made by a control unit. Particularly, this unit is part of the control unit controlling the (overall) operation of the apparatus.
Suspension of the compressor operation may depend on predetermined conditions. Preferably, the compressor operation will be suspended, if the drying cycle/drying operation is suspended and/or if a safety threshold temperature of the heat-pump system is exceeded (e.g. compressor temperature or refrigerant temperature, particularly refrigerant temperature at the compressor outlet). Compressor operation may also be suspended upon user interaction, for example by pressing a pause button or if the user opens a loading opening for adding or removing parts of the laundry to be dried.
In a preferred embodiment the compressor operation is restarted irrespective of considering any predetermined time delay after suspending or stopping the compressor operation. Avoiding such time delays in the restart procedure contributes to a quick successful restart of the compressor operation.
In an embodiment maintaining and suspending again the restarted compressor operation is made depending on a predetermined value of the power or current. I.e., the restarted compressor operation is maintained (continued), if the monitored value of the power or current is lower than the predetermined value, and the compressor operation is suspended again, if the monitored value of the monitored power or current is equal or higher than the predetermined value.
Preferably, the value of power or current supplied to the compressor after restarting the compressor operation is monitored for a predetermined delay time period and/or is monitored at a predetermined delay time after restarting the compressor operation. The decision/determination to maintain or suspend again the compressor operation is made in dependency of this monitored value. Considering the predetermined delay time period and/or the predetermined delay time ensures easily a correct evaluation of the compressor's performance status in comparison to its nominal performance whereby achieving the nominal performance value is necessary to maintain the compressor operation after its restart. Particularly, the delay time period or delay time is defined in the range of milliseconds lower than one second or some seconds (e.g. two seconds).
As already mentioned, the compressor operation is restarted upon receiving a restarting signal. This means that upon receiving a restarting signal the status of the compressor is switched "ON". Particularly, the restarting signal is initiated manually by a user giving a start signal to a control switch, control panel or the like, and/or by the control unit. Preferably the control unit initiates the restarting signal if predetermined conditions and/or circumstances are fulfilled. For example, the control unit detects resumption/restart of a suspended drying operation and subsequently initiates the restarting signal.
In case of suspending again the compressor operation (after having received the restarting signal), the compressor operation is preferably restarted a second time after expiry of a predetermined suspension time period. This suspension time period is set accordingly. E.g., the suspension time period is predefined as some seconds, particularly two seconds.
In order to realize a facile procedure for a successful restart of the compressor operation it is preferred to maintain the second-time restarted compressor operation also in dependency of the monitored value of power or current of the compressor.
Particularly, the second-time restarted compressor operation is maintained and suspended according to the condition for the first time of restart of the compressor operation. If the compressor operation is suspended again after the second time of restart, the compressor operation is preferably restarted (and suspended again if necessary) further times as long as the needed nominal operation conditions have been achieved.
Thereby, after suspending the compressor operation the restarted standard operation of the compressor can be achieved by a sequence or loop of switching (ON and OFF) the compressor operation status. This switching is repeated as long as the compressor is operating again by a power or current absorption corresponding to nominal conditions, particularly lower than the predetermined value of power or current. Considering the aforementioned predetermined (delay) time/time period and the predetermined suspension time period, a successful restart of the compressor operation is achievable even after a few retrials to restart successfully the compressor, particularly already some seconds after the first-time restart of the compressor.
Preferably the predetermined delay time period (and/or predetermined delay time) and the predetermined suspension time period have equal values. The values can be predetermined in the range of milliseconds lower than one second or in the range of some seconds (e.g. two seconds). Thus, the restarting procedure supports a quick successful restart of the compressor operation.
In a preferred embodiment the apparatus comprises a cooling fan for cooling a component of the heat-pump system, in particular and preferably the compressor. The cooling fan is adapted to convey cooling air over one component and (if applicable) also over other heat-pump system components. The cooling air may be conveyed through or over the compo-nent(s) wherein the cooling fan may be arranged upstream or downstream of the heat-pump system component. Operating the cooling fan offers an efficient support in achieving the nominal conditions of the heat-pump system, particularly of the compressor, which are needed for a quick successful restart of the compressor operation after suspending the compressor operation.
Preferably a unit for controlling the operation of the cooling fan is adapted such that the conveyance capacity (which can also be denoted as cooling capacity) of the cooling fan varied or adjusted depending on operation conditions of the apparatus. Particularly, the cooling fan is controlled by the already mentioned control unit controlling the overall operation of the apparatus.
In case that the compressor operation is suspended, the method of operating the cooling fan comprises at least the following modes:

if the cooling fan is active at the time of suspending the compressor operation, the cooling fan operating is maintained at the same conveyance rate or its conveyance rate is increased, and
if the cooling fan is not active at the time of suspending the compressor operation, the cooling fan for conveying cooling air to the at least one heat-pump system component is activated.

Thereby, after suspension of the compressor operation, the cooling fan is active or will be activated. This cooling routine allows cooling at least a portion/component of the heat-pump system after suspending compressor operation. Such component may be any part of the heat-pump system, in particular the compressor or an auxiliary condenser. Consequently, this cooling routine increases the probability in successfully restarting the heat-pump system, in particular for successfully restarting the compressor. In particular the chance for restarting the compressor is improved by using a cooling fan operation. A quick successful restart of the compressor operation is supported by the cooling fan operation, even after a very short time period after ending a previous drying operation (the compressor is stopped at the end of the previous drying operation) and/or after a short time period when the compressor operation has been suspended in a running (but presently suspended) drying process.
In a further embodiment of suspending the compressor operation, the cooling fan operation (particularly having the increased conveyance rate) remains for a predetermined period after the suspension of the compressor operation. In one embodiment, continuation of fan operation for the predetermined (time) period is independent of any other or of additional conditions. E.g. operating the fan for the predetermined time period is started immediately after detecting the suspension of the compressor operation. In other embodiments, this time period is running dependent on predefined additional conditions. For example, the predetermined period is running if predefined temperature conditions of the refrigerant and/or the compressor are fulfilled.
Particularly, the cooling fan operation after suspending the compressor operation is controlled by temperature detection and comparison with a temperature threshold value. For example, the cooling fan operation

is maintained as long as a temperature of the compressor is above a predetermined temperature threshold value, and/or
is maintained for a predetermined operation period after the event that a temperature of the compressor is equal to or is below a predetermined temperature threshold value. Considering the predetermined operation period it is possible to maintain the cooling fan operation even if the compressor temperature is below the temperature threshold value. This cooling extension supports implementing the cooling routine.

Regarding the predetermined temperature threshold value, preferably the predetermined threshold value can be different - depending on the operation mode of the heat-pump system/compressor. Particularly, two different threshold values can be defined as follows:

a first temperature threshold value that is used during the operation of the compressor for operating the cooling fan when the compressor temperature is above the first temperature threshold value, and
a second temperature threshold value that is lower than the first temperature threshold value (and used preferably during suspension of the compressor operation).

Controlling the fan operation using the two different temperature threshold values provides a further possibility to extend cooling operation during suspension of the compressor. The second temperature threshold value used during suspension of the compressor is lower than the first temperature threshold value used during compressor operation (not suspended) and consequently the cooling fan is switched inactive (status "OFF") during compressor suspension not until the temperature of the compressor is lower than the second temperature threshold value.
If the temperature threshold value corresponds to the lowered second temperature threshold value during heat-pump system/compressor suspension, it is preferred to change this value again to the higher first temperature threshold value when the heat-pump system/compressor is resumed (i.e. restarted) again. This change can be made as soon as the resumption (i.e. restart) is detected or alternatively when a predetermined time interval has expired after the resumption.
In a preferred embodiment the compressor suspension is cancelled in order to resume (i.e. restart) the compressor operation and this resumption is combined with maintaining the cooling fan operation (i.e. active cooling fan) or maintaining the cooling fan operation at the increased conveyance rate for a predetermined delay operation period after resuming the compressor operation. Thereby cooling of the compressor (and other heat-pump system components, if applicable) is maintained for a predetermined delay period after resuming compressor operation. Consequently efficient heat-pump performance can be achieved very fast after resuming compressor operation. Particularly compressor operation is resumed when or at the time when a suspended drying operation is resumed.
When the predetermined delay operation period is expired then preferably the cooling fan operation is changing (i.e. resuming) to a standard operation as it is used during normal drying operation. The standard operation of the fan may provide that the fan is off or is on and blowing with a predetermined conveyance rate in dependency of the operation conditions (e.g. temperature of the refrigerant and/or compressor) during the standard drying operation.
Usually the apparatus (particularly laundry dryer or washer-dryer) comprises a laundry storing compartment and a door covering an opening for loading/unloading the laundry storing compartment wherein the door is closed during a drying operation. If the door is opened the control operation is preferably as follows: The drying operation and the compressor operation are suspended, whereas the cooling fan is kept active at the same conveyance rate or its conveyance rate will be increased. However, if the cooling fan is not active at the time of suspending the drying operation and the compressor operation, the cooling fan will be activated.
This control operation can be easily provided when the motor driving the laundry storing compartment and the motor driving the cooling fan are independently controllable components of the apparatus. Particularly, the laundry storing compartment is configured as a rotatable drum driven by a drum motor and the cooling fan is driven by a fan motor that can be controlled independent of the operation of the drum motor, i.e. the fan motor is capable to be operated independently of the drum motor. Thus, the cooling routine can be implemented independently from user actions during operation of the apparatus.
In a further embodiment the compressor operation is maintained for a predetermined operation period when the drying operation is suspended. Thereby a potential suspension of compressor operation is delayed for a predetermined operation period after suspension of the drying operation. Likewise, a cooling fan operation is preferably maintained within the predetermined operation period (preferably with an increased fan speed). Extension by this predetermined operation period is beneficial for the heat-pump system efficiency because it is more efficient to avoid any change in the heat-pump system's operation mode (operating or suspending) when the drying operation is suspended only for a short time. This "short time suspension" is made e.g. in case the user opens the door of the laundry storing compartment only short-time to add a laundry piece into the laundry storing compartment and a door safety switch suspends the drying operation. Other possibilities to suspend the drying operation could be made by pressing an extra button and/or repressing a drying start button which results in a suspension (pause) of drying operation.
In general, suspending drying operation means at least stopping rotation of the drum-like laundry storing compartment and/or stopping a process air blower.
In a further embodiment the operation status of the cooling fan

is maintained during operation of the compressor in the predetermined operation period after suspension of the drying operation, and/or
is maintained, if the drying operation is resumed within the predetermined operation period.

It is noted that the operation status of the cooling fan may be "OFF" (i.e. not active/deactivated) or "ON" (i.e. active/activated).
Preferably, the described cooling routine is applied to cool at least the refrigerant compressor of the heat-pump system in order to increase the probability of an immediate successful restart of the compressor upon a respective request (particularly receiving a restarting signal), even when there was only a short time period since compressor suspension. This target can be supported e.g. by controlling and/or reducing temperatures of the compressor shell or casing during the drying cycle's and/or compressor's suspension mode. Furthermore, cooling the compressor during the suspension mode contributes to a faster re-balancing of pressure differences within the heat-pump system, thus allowing a faster successful restart of the compressor after its suspension.
Additionally and/or alternatively, the at least one component of the heat-pump system to be cooled according to the cooling routine is an auxiliary heat exchanger or condenser adapted to cool the refrigerant at a location external to the process air channel. Thus, the cooling fan is able to support appropriate refrigerant temperatures for an efficient drying air performance.
According to another aspect of the invention a laundry treatment apparatus is provided which comprises: a heat pump system having a compressor for circulating the heat pump refrigerant during a laundry drying operation, and a control unit. The control unit is adapted to control the apparatus' operation according to any of the above methods and/or is adapted to control the operation of the compressor such that, in case that the compressor operation is suspended,

restarting the operation upon receiving a restarting signal,
after restarting the compressor operation, monitoring the value of power or current supplied to the compressor, and
maintaining or suspending again the compressor operation in dependency of the monitored value of the power or current.

Preferably the control unit of the laundry treatment apparatus is adapted to implement any of the method steps described above or in the following description individually or in any arbitrary combination. Additionally or alternatively the laundry treatment apparatus is further configured according the above or following elements and features individually or in any combination thereof.
A laundry treatment apparatus configured in this way and/or with a control unit implementing such method steps provides the advantages as described above and/or below. In particular the apparatus provides a more efficient or improved operation of the heat pump system.
Reference is made in detail to preferred embodiments of the invention, examples of which are illustrated in the accompanying figures, which show:

Fig. 1: a schematic view of a laundry treatment apparatus,
Fig. 2: a schematic view of some components of the laundry treatment apparatus,
Fig. 3: a flow diagram showing an implementation example of a compressor restart method,
Fig. 4: a flow diagram showing an embodiment of a compressor cooling method that may be implemented as an supplement to the compressor restart method of Fig. 4,
Fig. 5: a flow diagram showing another embodiment of a compressor cooling method, and
Fig. 6: a flow diagram showing still another embodiment of a compressor cooling method.

Fig. 1 shows a schematically depicted laundry treatment apparatus 2 (denoted in brief "apparatus") which in this embodiment is a heat pump tumble dryer. The tumble dryer 2 comprises a heat pump system 4, including a closed refrigerant loop 6 which comprises in the following order of refrigerant flow B: a first heat exchanger 10 acting as evaporator for evaporating the refrigerant and cooling process air, a compressor 14, a second heat exchanger 12 acting as condenser for cooling the refrigerant and heating the process air, and an expansion device 16 from where the refrigerant is returned to the first heat exchanger 10. Together with the refrigerant pipes connecting the components of the heat pump system 4 in series, the heat pump system 4 forms the refrigerant loop 6 through which the refrigerant is circulated by the compressor 14 as indicated by arrow B.
The process air flow within the treatment apparatus 2 is guided through a compartment 18 of the home appliance 2 for receiving articles to be treated, e.g. a drum 18. The articles to be treated are textiles, laundry 19, clothes, shoes or the like. The process air flow is indicated by arrows A in Fig. 1 and is driven by a process air blower 8. The process air channel 20 guides the process air flow A outside the drum 18 and includes different sections, including the section forming the battery channel 20a in which the first and second heat exchangers 10, 12 are arranged. The process air exiting the second heat exchanger 12 flows into a rear channel 20b in which the process air blower 8 is arranged. The air conveyed by blower 8 is guided upward in a rising channel 20c to the backside of the drum 18. The air exiting the drum 18 through the drum outlet (which is the loading opening 21 of the drum and which is covered by a door 24) is filtered by a fluff filter 22 arranged close to the drum outlet in or at the channel 20. The optional fluff filter 22 is arranged in a front channel 20d forming another section of channel 20 which is arranged behind and adjacent the front cover of the dryer 2.
The condensate formed at the first heat exchanger 10 is collected and guided to a condensate collector 30 which is connected to an extractable condensate drawer 40 via a drain pipe 46, a drain pump 36 and a drawer pipe 50. The collected condensate can be pumped from the collector 30 to the drawer 40 which is arranged at an upper portion of the apparatus 2 from where it can be comfortably withdrawn and emptied by a user.
As shown in Fig. 2, a control unit 51 is disposed in the cabinet of the apparatus 2 to control several components in order to achieve efficient cooling of the compressor 14. The control unit 51 controls a cooling fan 54. This cooling fan 54 is driven by a fan motor 56. The cooling fan 54 blows cooling air C towards the compressor 14 for cooling. Alternatively or additionally, the cooling fan 54 sucks cooling air over the compressor 14 and/or is capable to additionally cool other components of the heat-pump system 4, e.g. an auxiliary heat exchanger arranged outside of the process air channel 20 and/or electronic components of the apparatus 2. The activated cooling fan 54 generates the cooling air flow C indicated in Fig. 2 for cooling the compressor 14 preferably according to cooling routines described below.
Furthermore, the control unit 51 is adapted to control a compressor motor 59 which is driving the compressor 14. The compressor 14 is operated or activated by the control unit 51 in response to predefined signals according to overall operation of the apparatus 2 and according to a restarting routine (for restarting the compressor) to be described in detail. When the compressor 14 is activated, the status of the compressor 14 is set to "ON". When the compressor 14 is not active (i.e. suspended or stopped), the status of the compressor 14 is "OFF". As can be seen in Fig. 2, the control unit 51 monitors the value of electric current I_comp supplied to the compressor 14. Monitoring this value is important during the restarting routine.
Preferably the control unit 51 is at the same time the control unit for controlling and monitoring the overall operation of the apparatus 2. For example and as shown in Fig. 2, the control unit 51 receives a temperature signal from a temperature sensor 41 which is for example arranged at the outlet of the second heat exchanger 12 (condenser) and which is indicative of the refrigerant temperature T_refrig at that position.
The cooling fan 54 is operated or activated by the control unit 51 in response to predefined signals according to overall operation of the apparatus 2 and according to the cooling routine to be described in detail. When the cooling fan 54 is activated, which means that cooling air C is blown towards or sucked from the compressor 14, the status of the cooling fan 54 is set to "ON". When the cooling fan 54 is not active or deactivated, the status of the cooling fan 54 is "OFF".
A compressor temperature sensor 60 is arranged at the compressor 14 to detect the temperature T_comp of the compressor 14. The control unit 51 compares the signals of this compressor temperature sensor 60 with a defined temperature threshold value to control the cooling operation of the heat-pump system 4. The compressor temperature sensor 60 can be arranged in a suitable position at or in or on a casing of the compressor 14.
The control by the control unit 51 for restarting the compressor 14 according to a restarting routine or method will be explained by the flow diagram according to Fig. 3. The section of the operation of the dryer 2 shown in Fig. 3 is starting (step S1) under a status where the operation of the compressor 14 is suspended, i.e. the status of the compressor motor 59 is inactive and the compressor 14 is "OFF". In this regard, the term "suspension" includes e.g. a pause of the compressor operation during a running drying cycle or stopping the compressor operation at the end or after the end of a drying cycle.
The operation of the compressor 14 is restarted, i.e. its status will be switched to "ON" in step S2, as soon as a restarting signal is received by the control unit 51. This restarting signal is preferably initiated by a user giving a start signal or ending a pause and/or by the control unit 51 itself. In this regard, it is noted that the compressor operation is able to be restarted independent of any predetermined time delay after suspension of the compressor operation. Subsequent to the step S2, the value of electric current I_comp supplied to the compressor 14 is monitored by the control unit 51 (step S3) at least for a predetermined delay time period t_delay-t. If the predetermined delay time period t_delay-t is expired (step S4), the monitored value of electric current I_comp is compared with a predetermined threshold value of current I_thresh (step S5). Depending on the result of this comparison the compressor operation is maintained (kept active) or suspended again. The restarted compressor operation is maintained, if the monitored value of current I_comp is lower than the predetermined threshold value of current I_thresh, i.e. the compressor 14 remains in the status "ON" (step S6).
If the monitored value of current I_comp is equal to or is higher than the predetermined threshold value of current I_thresh according to the comparison in step S5, the compressor operation is suspended again, i.e. the compressor 14 is switched into the status "OFF" (step S7). According to subsequent step S8, the compressor 14 remains in this status "OFF" during a predetermined time, i.e. during a set predetermined suspension time period t_susp (step S8). After expiry of this predetermined suspension time period t_susp the compressor operation is restarted automatically a second time, i.e. the compressor 14 is switched into the status "ON" (step S9). The latter status corresponds to the status according to step S2 and the restarting routine is transit to step S3 and subsequent steps. This means that the second-time restarted compressor operation again is generally maintained depending on the value of current I_comp of the compressor 14. In other words, the second-time restarted compressor operation is maintained and suspended according to the condition for the first time of restart of compressor operation.
According to this restarting routine it is possible to successfully restart the normal operation of the compressor 14 at any time after its suspension by a sequence of switching the status of the compressor 14 between "ON" and "OFF" - as long as the starting current I_comp is at or above the threshold I_thresh. If not successful the first time, the restarting routine repeats steps S7 till step S9 until the suspended compressor 14 is running again in its normal operation by remaining the status "ON" according to step S6 (the starting compressor current falls below I_thresh).
The predetermined delay time period t_delay-t and/or the predetermined suspension time period t_susp is/are preferably within the range of milliseconds lower than one second or within the range of some seconds. Particularly, the predetermined delay time period t_delay-t and the predetermined suspension time period t_susp are equal. For example, the delay time period t_delay-t and/or the suspension time period t_susp are predetermined as two seconds.
Figs. 4 to 6 represent embodiments of a cooling routine or method controlled by the control unit 51 for cooling the compressor 14. These embodiments may be implemented independent of the compressor restarting routine (exemplified in the embodiment of Fig. 3) or may be implemented in combination as further embodiment(s) of the compressor restarting routine while the compressor operation is suspended or when the suspension of the compressor cancelled.
The exemplary embodiment for a compressor cooling routine shown in Fig. 4 as a portion of the operation of the dryer 2 is starting (step S10) under a standard operation mode. In this regard, the status of the compressor 14 is "ON", i.e. the compressor 14 is in operation. The cooling fan 54 is in the standard operation mode "STANDARD", i.e. the cooling fan 54 is either in the state "ON" with a predetermined conveyance rate or in the state "OFF" according to the standard operation mode.
In step S20 it is verified, if a drying operation is suspended. If this is the case, the compressor 14 remains in operation until expiry of a predetermined operation period t_op (step S30). This extension of the compressor operation as compared to the drying operation by step S30 provides the chance that a restart of the drying operation is initiated and suspension of the drying operation is cancelled without stopping the compressor at all. In this 'best' case the operation of the heat pump system is not or minimally affected (normally the process air blower is stopped which results in increase of condenser temperature (here at numeral 12) and decrease of evaporator temperature (here at numeral 10). No compressor 14 restart or waiting period processing with a temporal delay of the overall drying process is necessary here. It is to be noted that step S30 is optional and with suspension of the drying process the compressor operation may be suspended directly (S20 to S40).
In the embodiment of Fig. 4 and at step S30, after expiry of this time period t_op (YES) the compressor operation is suspended, i.e. the compressor 14 is in the state "OFF" (step S40). In the embodiment of Fig. 4 (as compared to Fig. 5), during the suspension of the compressor the temperature threshold for activating/deactivating the cooling fan 54 is set to T_thresh = T_thresh-2 by step S50, while during the STANDARD operation - which is applied in the non-suspended drying operation - the threshold T_thresh = T_thresh-1 with T_thresh-1 > T_thresh-2. This effects cooling of the compressor 14 during compressor suspension to a temperature which is lower than the temperature during the periods where the compressor is operating (active). By cooling to a lower temperature, the likelihood of successful compressor start is increased and/or shortening the pause time before the compressor restart is achieved which both also result in shorter interruption times in case of compressor suspension during a running (but temporally suspended) drying process.
In step S60 the cooling fan 54 is set to active (state "ON"), which either means that the cooling fan operation is maintained at the same conveyance rate (r_convey = maintained) or the conveyance rate is increased (r_convey = increased). Or, if prior to step S60 the state of the cooling fan 54 was previously not active (state "OFF") the cooling fan 54 is activated (state "ON") for conveying cooling air by step S60).
Step S70 verifies, whether the detected refrigerant temperature T _refrig is less than or equal to the threshold temperature T_thresh set in S50. In case of 'No', the cooling of the compressor 14 by the fan 54 is continued with the conditions set in S60. In case of 'Yes', in step S80 the temperature threshold is set back to the higher value T_thresh = T_thresh-1. Basically by the loop of steps S70, S60, the cooling fan operation is maintained as long as the detected refrigerant temperature T _refrig is above the defined temperature threshold value T_thresh. In order to implement an extension of the cooling fan operation, the temperature threshold value T_thresh corresponds to a second temperature threshold value T_thresh-2 used during suspension of the compressor 14 (step S50). This second temperature threshold value T_thresh-2 is lower than a first temperature threshold value T_thresh-1 used during operation of the compressor 14 and the heat-pump system 4 for operating the cooling fan 54 when the refrigerant temperature T _refrig is above the first temperature threshold value T_thresh-1.
If the detected refrigerant temperature T _refrig is equal to or lower than the defined temperature threshold value T_thresh (step S70) the temperature threshold T_thresh is changed (S80) and the operation of the cooling fan 54 is suspended, i.e. is changed to the state "OFF" (step S90).
After step S90 the drying process suspension processing routine continues with other steps - compare e.g. Fig. 6. For example with the drying process suspended, the compressor operation suspended and the fan operation stopped (OFF) the control unit 51 waits for a drying operation restart command (cancellation of suspension) and performs a compressor and drying process restart routine in dependency of the then existing conditions. Fig. 6 gives an embodiment for restarting the compressor 14 as soon as (e.g. drying operation suspension is cancelled and thus) compressor suspension is cancelled.
An alternative routine to temporally extend or expand the cooling operation during the suspended compressor operation is provided by step S100 in Fig. 5 (instead of steps S50 and S80 in Fig. 4). In step S70, the detected refrigerant temperature T_refrig is compared with the standard temperature threshold value T_thresh (corresponding to T_thresh_1 in the routine according to Fig 4). If the detected refrigerant temperature T_refrig is higher than the temperature threshold value T_thresh, the cooling fan operation is maintained (according to step S60). Even if the detected refrigerant temperature T_refrig is lower than or equal to the temperature threshold value T_thresh in step S70 the cooling fan operation is maintained for a predetermined operation period or predetermined time period t_pred by the delay implemented by step S100. After expiry of the predetermined operation period or predetermined time period t_pred (and after the detected refrigerant temperature T_refrig dropped below the threshold T_thresh), the operation of the cooling fan 54 is suspended, i.e. its operation mode is changed to the state "OFF" (step S90) as already described along the routine in Fig. 4.
Alternatively, the control routine according to the steps S50 - S90 or according to the steps S60 - S 100 is implemented by substituting the refrigerant temperature T _refrig by the compressor temperature T_comp.
The flow diagram in Fig. 6 provides another section of the compressor cooling control routine. In case the status of the compressor 14 is "OFF" (i.e. the compressor operation is suspended) according to step S120, it is verified, if this suspension is cancelled (step S130). If not cancelled, the compressor 14 remains suspended (step 120). If the suspension is cancelled (e.g. due to resuming drying operation), the operation of the compressor 14 is resumed and consequently the state of the compressor 14 is "ON" (step S140). In this case and according to step 150, the operation of the cooling fan 54 is activated (stat_fan = ON) or maintained (stat_fan = ON, r_convey = maintained) or the cooling fan is operated at the increased conveyance rate (stat_fan = ON, r_convey = increased) until a predetermined delay operation period t_delay-op is expired (step S160). After expiry of the predetermined delay operation period t_delay-op the state of the cooling fan 54 is changed to "STANDARD". In the standard mode the "OFF"-state or "ON"-state (with a defined conveyance rate) is controlled according to the conditions of the standard control routine.
The routine of Fig. 6 can be implemented in combination with the routines of Figs. 4 and 5 and vice versa. E.g. and as mentioned above, this routine is implemented as (drying operation +) compressor operation restart routine after step S90 (Figs. 4 and 5).
The routines or methods for compressor cooling shown in Figs. 4 to 6 may be combined with the compressor restart routine shown in Fig. 3. For example the continuation of compressor cooling according to the routine shown in Fig. 6 is the next step following to step S6 in Fig. 3 or the routine of Fig. 6 is initiated in parallel to execution of step S6. Alternatively or additionally the compressor cooling routine of Fig. 4 or 5 is executed in parallel to the routine of Fig. 3 - preferably therein at step S1 (stat_comp = OFF) and/or each time the compressor restart routine of Fig. 3 is executing step S7.

Reference Numeral List

2	tumble dryer	60	compressor temperature sensor
4	heat pump system		compressor temperature sensor
6	refrigerant loop	A	process air flow
8	blower	B	refrigerant flow
10	first heat exchanger	C	cooling air flow
12	second heat exchanger	I_comp	monitored value of current
14	compressor	I_thresh	predetermined value of current
16	expansion device		predetermined value of current
18	drum	r_convey	conveyance rate
19	laundry	stat_fan	status of cooling fan
20	process air channel	stat_comp	status of compressor
20a	battery channel	S1 - S170	control steps
20b	rear channel	t_delay-op	predetermined delay operation period
20c	rising channel		predetermined delay operation period
20d	front channel	t_delay-t	predetermined delay time period
21	loading opening		predetermined delay time period
22	filter element	t_op	predetermined operation period
24	door		predetermined operation period
30	condensate collector	t_pred	predetermined time period
36	drain pump	t_susp	predetermined suspension time period
40	condensate container		predetermined suspension time period
41	refrigerant temperature sensor	T_comp	compressor temperature
	refrigerant temperature sensor	T_refrig	refrigerant temperature
46	drain pipe	T_thresh	temperature threshold value
50	drawer pipe	T_thresh-1	first temperature threshold value
51	control unit		first temperature threshold value
54	cooling fan	T_thresh-2	second temperature threshold value
56	fan motor		second temperature threshold value
59	compressor motor

Claims

Method of operating a compressor (14) in a laundry treatment apparatus, in particular laundry dryer (2) or washer-dryer, wherein the laundry treatment apparatus comprises:
a heat-pump system (4) having a compressor (14) adapted to circulate a refrigerant through the heat-pump system (4) during a laundry drying operation, and

a control unit (51) controlling the operation of the laundry treatment apparatus (2), wherein the method comprises:
suspending the operation of the compressor (14),

restarting the operation of the compressor (14) upon receiving a restarting signal,

monitoring the value (I_comp) of power or current supplied to the compressor (14) after restarting the compressor operation, and

in dependency of the value (I_comp) of the power or current
maintaining the compressor operation, or
suspending again the compressor operation.
Method according to claim 1, wherein the compressor operation is restarted independent of any predetermined time delay after suspension of the compressor operation.
Method according to claim 1 or 2, wherein
the compressor operation is maintained, if the monitored value (I_comp) of the power or current is lower than a predetermined value (I_thresh), and
the compressor operation is suspended again, if the value of the monitored power or current (I_comp) is equal to or is higher than the predetermined value (I_thresh).
Method according to claim 1, 2 or 3, wherein the value (I_comp) of power or current supplied to the compressor (14) after restarting the compressor operation is monitored for a predetermined delay time period (t_delay-t) or is monitored at a predetermined delay time after restarting the compressor operation, before determining whether the compressor operation is maintained or suspended again.
Method according to any of the previous claims, wherein receiving the restarting signal is initiated by one or more of:
a user giving a start signal or ending a pause, and

the control unit (51).
Method according to any of the previous claims, further comprising:
in case of suspending again the compressor operation, a predetermined suspension time period (t_susp) is set, and

the compressor operation is restarted a second time after expiry of the predetermined suspension time period (t_susp).
Method according to claim 6, wherein the second-time restarted compressor operation is maintained depending on the value of power or current (I_comp) of the compressor (14).
Method according to claim 6 or 7, wherein the second-time restarted compressor operation is maintained and suspended according to the condition for the first time of restart of the compressor operation.
Method according to any of the preceding claims, wherein the predetermined delay time period (t_delay-t) or the predetermined delay time, and the predetermined suspension time period (t_susp) have equal values.
Method according to any of the preceding claims, wherein the laundry treatment apparatus (2) comprises a cooling fan (54) operated for cooling the compressor (14) by conveying cooling air (C) over the compressor (14).
Method according to claim 10, wherein in case the compressor operation is suspended, the method further comprises:
if the cooling fan (54) is active at the time of suspending the compressor operation (14), maintaining the cooling fan (54) operating at the same conveyance rate (r_convey) or increasing the conveyance rate (r_convey) of the cooling fan (54), and

if the cooling fan (54) is not active at the time of suspending the compressor operation, activating the cooling fan (54) for conveying cooling air (C) to the compressor (14).
Method according to claim 11, further comprising: maintaining the cooling fan operation for a predetermined period (t_pred) after suspending the compressor operation.
Method according to claim 11 or 12, wherein after suspending the compressor operation the method further comprises:
maintaining the cooling fan operation as long as a temperature (T_comp) of the compressor (14) is above a temperature threshold value (T_thresh), or

maintaining the cooling fan operation for a predetermined operation period (t_pred) after the event that a temperature (T_comp) of the compressor (14) is at or is below a temperature threshold value (T_thresh).
Method according to claim 13, wherein the temperature threshold value (T_thresh) is
a first temperature threshold value (T_thresh-1) that is used during the compressor operation for operating the cooling fan (54) when the compressor temperature (T_comp) is above the first temperature threshold value (T_thresh-1), or
a second temperature threshold value (T_thresh-2) that is lower than the first temperature threshold value (T_thresh-1) and is used during suspension of the compressor operation for operating the cooling fan (54).
Laundry treatment apparatus, in particular laundry dryer (2) or washer-dryer, wherein the laundry treatment apparatus comprises:
a heat-pump system (4) having a compressor (14) adapted to circulate a refrigerant through the heat pump system (4) during a laundry drying operation, and

a control unit (51) controlling the operation of the laundry treatment apparatus (2), wherein the control unit (51) is adapted to control the operation of the laundry treatment apparatus (2) according to any of the previous method claims.