EP3425109B1

EP3425109B1 - Method of operating a heat pump laundry dryer or heat pump washing machine having drying function

Info

Publication number: EP3425109B1
Application number: EP17180174.9A
Authority: EP
Inventors: Ornella BRANDOLISIO; Lorenzo Corso; Fabio GARZENA; Roberto Ragogna
Original assignee: Electrolux Appliances AB
Current assignee: Electrolux Appliances AB
Priority date: 2017-07-07
Filing date: 2017-07-07
Publication date: 2022-05-04
Anticipated expiration: 2037-07-07
Also published as: EP3425109A1; AU2018203683B2; PL3425109T3; CN109208290A; AU2018203683A1; CN109208290B

Description

The present invention relates to a method of operating a laundry drying machine, such as a heat pump laundry dryer or a heat pump washing machine having drying function.
In particular, this invention relates to a method of operating a laundry drying machine having drying function in order to carry out a drying cycle on a laundry loaded by a user.
The duration time of the drying phase is a function of the clothes textile properties: synthetic clothes dry faster than cotton clothes; lighter and thinner ones are faster at drying than stiffer and thicker ones; the dimension and shape also affect the drying.
In an automatic drying cycle, moisture contained in the laundry load is measured or estimated for determining when such drying cycle is to be ended because the laundry load has reached a desired level of dryness.
The laundry moisture is generally determined, or estimated, by means of a conductimetric sensor wherein two or more spaced apart electrodes, when touched by wet laundry, generate a signal which is representative of the laundry moisture.
Other ways can be used for determining or estimating the laundry moisture content such as monitoring an electrical parameter (Voltage, current, phase) of an electric motor driving the drum. All such ways for determining or estimating the laundry moisture content hardly give information about how the moisture is distributed among the pieces of laundry within the drum. For example, at about the end of a drying cycle, a wide piece of laundry like a bed sheet, which is particularly dried, may be in frequent or constant contact with the above mentioned electrodes thereby providing a control unit of the laundry drying machine with a signal indicating that the overall laundry load is dried, while a core portion of the laundry load within the drum may still be partly wet.
This problem is magnified in the case whereby the clothes of the laundry are composed of mixed textile fabrics (e.g. a mixture of cotton, silk, wool etc.), different dimensions and sizes or different weight.
There is therefore a problem of ensuring that the whole laundry mass contained within the drum is uniformly dried at the end of a drying cycle, thereby avoiding as much as possible moisture concentration on some areas of the said mass.
EP2415927A2 discloses a heat pump device connecting a compressor, a heat radiator, an expansion mechanism, and a heat absorber by using a pipe through which a refrigerant circulates, a temperature measuring unit that is disposed in a pipe connecting the heat radiator, and a wind circuit through which air of the heat pump device flows inside from an air inlet at the heat absorber and flows outside from an air outlet at the heat radiator, are included. Further, a drain pan receiving condensed water produced by heat exchange between the air in the wind circuit and air in heat absorber is further included, and the temperature measuring unit is disposed under a boundary position where water of the drain pan overflows.
WO2015082011A1 discloses a method for controlling a drying cycle in a laundry drying machine of the type comprising a heat pump system having a refrigerant circuit for a refrigerant and comprising a drying air circuit for conveying a volume flow of drying air in a laundry drum suitable for receiving laundry to be dried. The refrigerant circuit comprises: a compressor with a variable rotation speed; a first heat exchange for a thermal coupling between the drying air circuit and the refrigerant circuit and a second heat exchanger for a further thermal coupling between the drying air circuit and the refrigerant circuit. The method comprises an optimization procedure comprising the step of controlling the rotation speed or the power of the compressor during a plurality of time intervals of the drying cycle. The optimization procedure comprises the steps of: determining an efficiency parameter related to the amount of water removed from the laundry during a first time interval; determining an efficiency parameter related to the amount of water removed from the laundry during a second time interval; comparing the efficiency parameter determined during the second time interval with the efficiency parameter determined during the first time interval; adjusting the rotation speed or the power of the compressor in a third time interval according to the result of said comparison.
EP2811064A1 discloses a method for operating a laundry treatment apparatus, in particular a heat pump dryer or washing machine having dryer function, and a laundry treatment apparatus having a heat pump system, wherein the apparatus comprises a heat pump system and a laundry treatment chamber for treating laundry using process air, and wherein the heat pump system comprises: a first heat exchanger for heating a refrigerant fluid, a second heat exchanger for cooling the refrigerant fluid, an expansion device, a refrigerant loop, in which the refrigerant fluid is circulated through the first and second heat exchangers and the expansion device, and a compressor for circulating the refrigerant fluid through the refrigerant loop, the method comprising: detecting at least one temperature signal, and, in dependency of the at least one detected temperature signal, selecting at least one predetermined temperature threshold value for switching the compressor ON and/or OFF.
A purpose of the present invention is to provide a method of operating a laundry drying machine, such as a heat pump laundry dryer or a heat pump washing machine having drying function, which offers a solution to the drawbacks described above.
Another purpose of the present invention is to provide a method of operating a laundry drying machine, such as a heat pump laundry dryer or a heat pump washing machine having drying function, which reduces the quantity of over-dried clothes and randomly wet clothes after the drying phase.
A further purpose of the present invention is to provide a method of operating a laundry drying machine, such as a heat pump laundry dryer or a heat pump washing machine having drying function, that reduces the quantity or dimensions of wet zones on a large sheet (e.g. bed linen) during the drying, creating an evenness in the moisture distribution throughout the entire sheet.
Still, a further purpose of the present invention is to provide a method of operating a laundry drying machine, such as a heat pump laundry dryer or a heat pump washing machine having drying function that reduces the formation of creases and wrinkles in the clothes during the drying phase.
The air flow through the drum of a heat pump tumble dryer, the clothes and the heat exchangers (evaporator and condenser) is ideally in a closed loop. Hot dry air from the condenser of the heat pump system is preferably pumped into the inlet of the drum of the tumble dryer; the hot air absorbs moisture from the wet clothes as the drum rotates.
The humid air is discharged at the outlet of the drum and directed towards the evaporator of the heat pump system, where the air is cooled and dehumidified by the evaporator, which in turn takes heat from the humid air, thus condensing the water vapor in the humid air into liquid and this liquid is exhausted from the air flow circuit.
The dehumidified air is then passed across the condenser of the heat pump system where it is re-heated and sent back into the drum, thereby continuing the cycle over and over during the drying phase.
According to the present invention, as it will be described below, the compressor is driven in a way that advantageously provides for a distribution of moisture among the laundry mass during a drying cycle such that, at the end of that cycle, said mass results to be uniformly dried.
Therefore, clothes with moisture lower than that of other pieces of laundry will be sources from which pieces of drier laundry can absorb moisture thereby promoting the achievement of a point of equilibrium of the moisture content among the laundry. Process air driven across the laundry promotes the moisture transfer among pieces of laundry acting as a medium to equilibrate the moisture content of different cloth materials of the laundry load, giving a better uniformity and evenness. Depending on the laundry type, also wrinkles and creases can be reduced.
The present invention takes advantage of this phenomenon during the drying process, alternating between time periods with compressor switched on and ones with compressor switched off, and/or between time periods wherein the compressor operates at different levels of energy, in order to maximize the drying evenness.
In at least a first drying phase, the compressor is left on, till a desired temperature or time or laundry moisture level or a combination of at least two of said conditions according to the program selected is achieved.
In subsequent drying phases (preferably a second drying phase and a third drying phase) the "on/off" or "high/low supplied energy" alternating of the compressor is used, after which said program may move to a laundry cooling phase.
By "phase", it is meant the period assigned to a particular section or a step of the drying process.
By "process", or "drying process", it is meant the total period from start of operating the machine to the end.
By "laundry treatment process" it is meant the overall process, comprising both the drying process and possible other optional end phases, such as a cooling phase or an anticrease phase.
In order to avoid a longer cycle duration due to the activation/deactivation of the compressor or its operation at different levels of energy, the compressor driving management can be linked to the laundry load dryness level.
Thus, the object of the present invention is implementing a method of operating a laundry drying machine, such as a heat pump laundry dryer or a heat pump washing machine having drying function, in order to carry out a laundry treatment process on a laundry load comprising a drying cycle.
The laundry drying machine implementing such method comprises:

a control unit controlling the operation of the laundry drying machine,
a laundry treatment chamber for treating laundry using process air,
a process air circuit for circulating the process air,
a heat pump system having a refrigerant loop, in which the refrigerant fluid is circulated through a first and a second heat exchanger in thermal communication with the process air,
a compressor for circulating the refrigerant fluid through the refrigerant loop.

The method of the invention comprises the following steps:

driving the compressor by means of the control unit according to a first driving sequence in a first portion of the drying cycle;
driving the compressor by means of the control unit according to a second driving sequence in a second portion of the drying cycle different from the first portion;

laundry load amount;
moisture content of laundry load;
temperature of laundry load;
temperature of the process air;
temperature and/or humidity of the environment where the laundry drying machine is placed;
laundry treatment program selected by a user;
laundry treatment process or drying process time;
a preset value of energy consumption;

This allows moisture circulating from wet clothes to drier ones, in order to obtain a substantially uniform moisture level in the laundry load.
According to the invention, the second driving sequence may preferably provide for driving the compressor intermittently for a first time period in correspondence of a first level of energy, for a second time period in correspondence of a second level of energy, for a third time period in correspondence of a third level of energy, for a fourth time period in correspondence of a fourth level of energy.
In this way, the energy consumption may be modulated depending on the time duration of the respective time period, maximizing the energy saving.
For example, according to the invention, a time period corresponding to the lower levels of energy may be substantially equal to or longer than the time period corresponding to the upper levels of energy.
This allows advantageously to distribute moisture among the laundry load for a longer time.
Alternatively, according to the invention, a time period corresponding to the upper levels of energy may be substantially longer than a time period corresponding to the lower levels of energy.
This allows advantageously to decrease the overall laundry moisture level, mostly in the initial stages, speeding up the process.
Furthermore, according to the invention, the first level and the third level may be substantially equal to each other, and the second level and the fourth level may be substantially equal to each other.
This could lead to a compromise, between uniformity of the laundry moisture and a short time duration of the process.
Moreover, according to the invention, the second driving sequence is followed by a third driving sequence in a third portion of the drying cycle different from the first portion and the second portion, wherein the compressor is driven intermittently between a lower level of energy and an upper level of energy, the time periods corresponding to lower levels of energy of the third driving sequence being longer than the time periods corresponding to lower levels of energy of the second driving sequence.
According to the invention, the second driving sequence is selected among a plurality of available driving sequences on the basis of one or more of the parameters of the first list.
In other words, there is a plurality of preset driving sequences, which are chosen at the beginning of the cycle or already included in the program selected, or chosen time by time, basing on the parameters detected according to the first list. According to the invention, there could be also two different driving sequences controlled with different parameters of the first list.
Additionally, a condition of end of drying process, to be controlled during the drying process, may be defined depending on at least one parameter of the following second list:

laundry moisture equal or below a minimum threshold value,
temperature of drying air exiting the laundry treatment chamber equal or above a maximum threshold value,
elapsed time equal or above a maximum threshold value,
the activation of an alarm indicating a machine component failure or a machine malfunctioning (i.e. bad use or misuse by the user).

The condition of end of drying process may be in fact a function of one or more of the parameters of the second list; for example: the function could provide that, if the laundry moisture value is equal or below a threshold value, the elapsed time shall be detected and, if a value has been reached, the drying process shall end.
In this case, according to the invention, the step of setting the at least one condition of end of drying process may preferably occur before starting to drive the compressor according to one of the first or second driving sequences.
More particularly, the following steps may be preferably repeated in sequence until at least one parameter of the second list is met:

setting parameters of the first list to be controlled in a driving sequence,
selecting the driving sequence among a plurality of available driving sequences,
setting a condition for ending the driving sequence.

In detail, when at least one parameter of the second list is met, a final laundry treating step may be performed.
For example, the final laundry treating step may comprise a cooling phase, wherein laundry may be moved within the laundry treatment chamber and/or a cooling air flow may be provided to said laundry load. Additionally, according to the invention, the lower level of energy may be obtained by switching OFF the compressor, and the upper level of energy may be obtained by switching ON the compressor.
Similarly, in the first driving sequence the compressor may remain always switched ON.
The invention also relates to a laundry drying machine having a control unit programmed for carrying out the method of the invention.
Further characteristics and advantages of the present invention will be apparent from the following detailed description of preferred but not exclusive embodiments of a method of operating a laundry drying machine, such as a heat pump laundry dryer or a heat pump washing machine having drying function according to the claim 1 attached.
Detailed characteristics of the method of operating a laundry drying machine, such as a heat pump laundry dryer or a heat pump washing machine having drying function according to the present invention are quoted in the corresponding dependent claims.
Further characteristics and advantages of the present invention will result from the description of two forms of preferred execution but not exclusive of a method of operating a laundry drying machine, such as a heat pump laundry dryer or a heat pump washing machine having drying function according to the present invention, illustrated by a non-limitative example with accompanying drawings, in which:

Figure 1 illustrates a schematic view of the tumbler dryer,
Figure 2a illustrates a first embodiment of the method of the invention applied to a simplified control with few parameters on a simple system,
Figure 2b illustrates a second embodiment of the method of the invention applied to a multiparametric control on a multifunctional system.

BRIEF DESCRIPTION OF DRAWINGS

With reference to the figures, the reference numeral 10 generally designates a laundry drying machine.
The laundry drying machine comprises: a control unit 11 adapted to supply energy to a compressor 17 during at least a first drying phase P1 and a second drying phase P2, a laundry treatment chamber 12, a process air circuit 13, for circulating a process air A, a heat pump system 14 comprising a first and second heat exchangers 16a,16b in thermal communication with the process air A.
Said first heat exchanger (evaporator) 16a takes heat and therefore cools down said process air A and said second heat exchanger (condenser) 16b gives heat to the process air A.
A refrigerant loop 15 circulates a refrigerant fluid R within said heat pump system 14.
A compressor 17 increases the pressure and the corresponding saturation temperature (boiling point) of the refrigerant vapor to a level of pressure at which the refrigerant R can condense by rejecting its heat through said condenser.
The heat exchanger (evaporator) 16a receives heat, therefore cooling down said process air A, while said second heat exchanger (condenser) 16b gives heat to the process air A.
In the following, two different embodiments will be described, wherein the compressor is respectively of a variable speed type or of a fixed speed type.
At least a first drying phase P1 and a second drying phase P2 each comprise a sequence type.
By "sequence type" or "driving sequence" it is meant a series of duty cycles which are performed in a phase P1, P2, P3 or P4. For example, there could be a constant duty cycle series or a variable duty cycle series.
By "duty cycle" it is meant the percentage of the duration of time or time period in which said compressor 17 is on (or at a higher energy level) to the cycle time.
By "cycle time" it is meant the duration of time or time period in which said compressor 17 is on (or at a higher energy level) added to the duration of time when said compressor 17 is off (or at a lower energy level) during a single cycle.
By "cycle" it is meant a single time duration when said compressor 17 is off (or at a lower energy level) followed by a single time duration or time period when said compressor 17 is on (or at a higher energy level).
The wording "drying cycle" is used in the present specification as a synonym of "drying process", as defined above.
Therefore, the duty cycle is then calculated as: $\begin{array}{l} duty cycle = time compressor (17) on/ (cycle time) * \\ 100 % . \end{array}$
For example, in both embodiments of figures 2a and 2b, said first drying phase P1 has a duty cycle of almost 100%. This is because, except for the first low energy level A11, which lasts much less than the overall drying phase P1, the compressor 17 is on (or at a higher energy level) throughout the phase, i.e. time compressor 17 on (or at a higher energy level) substantially equals cycle time. This can be calculated as: $[duty cycle = about 1 * 100 % = almost 100 %] .$
At least said second drying phase P2 provides for driving the compressor 17 intermittently between a lower level of energy and an upper level of energy.
Preferably, said heat pump system 14, in addition, comprises an expansion valve 18 and/or compressor 17 cooling fan CF. Said process air circuit 13 is provided by process air conduit 19 connected to the heat exchangers 16a, 16b and a drum 20 in the laundry treatment chamber 12 in such a way that the process air flows through said drum 20, the laundry load L and said heat exchangers 16a,16b is in a closed loop.
Said drum 20 is preferably rotated by a drum motor M1 about the axis of its opening and a drying fan DF actuated by a motor (preferably M1). In a simple embodiment, both said drum and said drying fan DF may be operated by the same motor M1.
The laundry drying machine uses the method explained below to even the moisture of said laundry load L such that, at the end of the drying process each cloth of the laundry load L comes out having a moisture level comparable to the others, irrelevant of their size, texture, weight or other properties that can affect the rate at which they dry.
By moisture level it is meant the percentage of water present in the laundry load L in said laundry treatment chamber 12 while with humidity level it is meant the percentage of water vapor present in the process air A.
In a first embodiment of a laundry drying machine, with compressor 17 activation fixed shown in fig 2a, said control unit 11 is adapted to drive said fixed compressor 17, according to said first drying phase P1.
In figure 2a the following curves are shown:

Curve E, indicating the energy level supplied to the compressor;
Curve t, indicating the elapsed time;
Curve H, indicating the laundry load moisture.

At the beginning of the drying process, all the clothes are substantially equally wet, there is no need to transfer moisture from one cloth to the other, therefore said compressor 17 is substantially always on within said first drying phase P1.
The internal of said laundry treatment chamber 12 is equipped with a moisture and/or humidity sensing device, able to detect or estimating the laundry moisture or the humidity of drying air leaving the drum.
The sequence type of said first drying phase P1 and at least the lower and upper level of energy of a second drying phase may be defined, on the basis of these parameters: laundry load amount detection, environmental temperature and/or humidity of the environment where the laundry machine is placed, moisture content of laundry load, temperature of laundry load, temperature of process air, laundry treatment process time (i.e. drying process time), a preset value of energy consumption admitted for the machine operation and the program selected. Basing on the same parameters, the end condition(s) of at least said first drying phase P1 is(are) imposed, selected among a plurality of possible end conditions (time period, moisture level, humidity level, temperature, etc).
Also the whole second drying phase P2 may be defined basing on the above listed parameters.
Preferably, in this first embodiment, for said first drying phase P1, a first time limit t1 is set as the end condition, i.e. at the end of such time limit t1 said first drying phase P1 ends. During said first drying phase P1, the laundry load moisture level drops slightly with time because the whole machine has to heat up and the heat pump has to end its transitory period.
Said second drying phase P2 starts at the end of said first drying phase P1. The sequence type of said second drying phase P2 is selected based on the time limit t1 of the first drying phase P1 and the program selected.
A first level H1 of laundry moisture is set as the end condition of said second drying phase P2.
Preferably, according to this embodiment, said second drying phase P2 has a sequence type comprising a series of constant duty cycles of 50% with constant time period.
By "time period" it is meant the duration of time for which said compressor 17 is off (or at a lower energy level) or duration of time for which said compressor is on (or at a higher energy level) in a single cycle. For example, in every cycle time of the sequence type of said second drying phase P2, said compressor is switched off for a time period of 5 minutes; then switched on for another time period of 5 minutes. Said compressor alternates between the on/off, but maintaining same time period of 5 minutes.
When the first laundry moisture level H1, which is preset as the end condition of said second phase P2, is reached (e.g. is detected by a conductimetric signal), said second drying phase P2 comes to an end; then a third drying phase P3 begins.
The third drying phase P3 has also an end condition; preferably, a second laundry moisture level H2, lower than that of said first laundry moisture level H1, is selected as the end condition for the third drying phase P3.
Preferably, said third drying phase P3 has a sequence type comprising a series of constant duty cycles of 50% with variable time periods.
For example, for a first cycle time, said compressor is switched off for a period of 2 minutes and then switched on for another 2 minutes. For a second cycle time, said compressor is switched off for 5 minutes and switched on for another 5 minutes and then the first and second cycle time repeat. In other words, the duty cycle is constant; however, the cycle times are different. The first and second cycle times repeat till the second laundry moisture level H2 for said third drying phase P3 is obtained. Said first, second and third drying phases have preferably same upper energy level and same lower energy level.
Preferably, when said second laundry moisture level H2 is achieved, said third drying phase ends; a fourth phase P4, for example, a laundry cooling phase, starts.
Based on the laundry moisture level, a second time limit t2 may be set as the end condition of said fourth phase.
By "time limit", it is meant a duration of time set for a particular entire phase (eg. P1, P2, P3, P4).
When said second time limit t2 is reached, said fourth phase P4 comes to an end.
During said fourth phase P4, the temperature in the laundry treatment chamber 12 reduces gradually, till the time limit is reached.
The drying process comes to an end when the predetermined end condition of the drying process is met. Preferably, in this embodiment, when the desired laundry moisture level is attained. An end condition of the drying process is constantly monitored during the whole drying process, because it could be met in any instant of time.
In a second embodiment, shown in figure 2b, a variable speed compressor is provided and it is driven between two energy levels of different amount. Said compressor 17 is not completely switched off, but regulated by increasing or reducing the amount of energy supplied to it. This is done, for example, by regulating the speed of the compressor 17.
A variable speed process fan may be also provided, and preferably it works independently from the compressor 17, e.g. when the speed of the compressor 17 is lowered, the fan could be operated in order to lower the temperature inside the chamber 12, or it could be switched off, depending on the requirements.
In figure 2b the following curves are shown:

Curve E, indicating the energy level supplied to the compressor;
Curve t, indicating the elapsed time;
Curve H, indicating the laundry load moisture;
Curve T, indicating the temperature of process air A leaving the drum;
Curve S, indicating the speed of the process fan.

For example, in the present embodiment, the process fan is operated at a first speed S1, during the first drying phase P101, at a second speed S2, during the second drying phase P102, at a third speed S3, during the third drying phase P103, at a fourth speed S4, during the fourth phase P104. In particular, the highest speed is the fourth one S4, i.e. while the compressor is at its lowest energy level and a decrease in temperature can be obtained, and - except for the speed S0 corresponding to the first low energy level A111, which lasts much less than the overall drying phase P101 - the lowest speed is the first one S1, when the compressor is supplied with the higher energy level of phase P101.
Preferably, the second speed S2 is higher than the third speed S3.
In this case, said first drying phase P101 is dependent on the load moisture, the program selected and the environmental temperature. A first sequence type, at least one condition that ends said first drying phase P101 and at least one end condition for the drying process are selected based on these same parameters. Said at least one end condition for the drying process is selected from a plurality of available end of process conditions.
Preferably, said drying process end conditions may be defined depending on at least one of the following:
laundry moisture below a minimum threshold value, temperature of process air A (drying air) exiting the laundry treatment chamber above a maximum threshold value, elapsed time above a maximum threshold value, the activation of an alarm indicating a machine component failure or a machine malfunctioning.
At the beginning of the drying process (also corresponding to the beginning of said first drying phase P101), when said compressor 17 is activated, it moves from a first lower energy level A111 of the first drying phase to a first upper energy level A112 of the first drying phase P101.
Preferably, a first temperature T101 of process air leaving the drum is set as the end condition for said first drying phase P101. Said second drying phase P102 starts when the temperature T101 is attained.
Said second drying phase P102 is selected based on the said first temperature T101 and the program selected according to said drying phase P101.
Based on this information, a second sequence type and at least one condition that, once met, causes the end of said second drying phase P102 are selected.
Said second sequence type, preferably, has a series of constant duty cycles of 50% and a constant time period throughout the second drying phase P102.
The speed of said compressor 17 is reduced such that the first upper energy level A112 of said first drying phase P101 falls to a second lower energy level A121.
Said second lower energy level A121 is higher than the first lower energy level A111. This second lower energy level A121 is maintained for a time period preferably of 5 minutes and then said compressor 17 speed is increased.
The energy level of said compressor 17 moves to a second upper energy level A122 higher than that of first upper energy level A112. In said second drying phase P102, the temperature of drying air leaving the drum slightly increases, whilst the laundry moisture level reduces.
The cycle repeats till the desired end condition is met.
For example, said second drying phase P102 comes to an end when at least a predetermined first laundry moisture level H101 and a predetermined time limit t101 for said second drying phase P102 are obtained and said third drying phase P103 begins.
A third sequence type of said third drying phase P103 is selected based on the first laundry moisture level H101 and the time limit t101 and laundry load weight at end of second drying phase P102.
Based on these same conditions, at least one condition that ends said third drying phase P103 is selected among a plurality of possible end conditions. Preferably, a second laundry moisture level H102 is set as the end condition to be fulfilled for said third drying phase P103 to end.
Preferably said third path has a third sequence type with series of variable duty cycles.
Preferably the third lower energy level and third upper energy level are lower than the second lower energy level and the second upper energy level respectively. The third lower energy level A131 corresponds to the first lower energy level A111. The third upper energy level A132 corresponds to the first upper energy level A112.
A fourth upper energy level A134 of said third drying phase P103 corresponds to the second lower energy level A121.
The temperature of process air leaving the drum in said third drying phase further increases whilst the laundry moisture level decreases.
Preferably, said third drying phase P103 comes to an end when the second laundry moisture level H102, set based on the above-mentioned conditions for said third drying phase P103, is achieved.
A fourth phase P104 (for example, a cooling phase) is selected based on the said second laundry moisture level H102 selected according to said third drying phase P103.
Based on this condition, the machine selects a fourth sequence type for said fourth phase P104 and at least one condition that ends said fourth phase P104. Preferably, a second temperature T102 of process air leaving the drum is set as the end condition for said fourth phase P104.
During said fourth phase P104, the temperature of process air leaving the drum reduces till the predetermined temperature T102 for said fourth phase P104 is obtained.
End of the drying process occurs when the at least one of the above-listed end conditions (e.g. laundry load is below a predetermined moisture level or process air leaving the drum is below a predetermined temperature imposed). An optional phase may also be selected for anti-crease or anti-wrinkles.
In the nutshell, with a variable speed compressor 17, the compressor speed is adjusted, preferably based on the temperature information.
With a fixed speed compressor 17, the on/off may be managed through a hysteresis control on the process air temperature. For example, based on the outlet's NTC, the air flow can be adjusted using variable process fan speed.
Moreover, as previously mentioned, embodiments indicated with variable compressor speed can also be implemented on a machine with fixed compressor speed and vice versa.
For example, the start and end conditions on a variable compressor machine can be implemented on a machine with fixed compressor and vice versa.
Another example: the duty cycles implemented on a variable speed compressor machine can be implemented on a fixed speed compressor machine and vice versa.
The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims; all the details may further be replaced with other technically equivalent elements.
In practice, materials used, as well as the contingent shapes and dimensions, may be any according to the requirements and the state of art.
Where the constructional characteristics and techniques mentioned in the following claims are followed by reference signs or numbers, such signs and reference numbers have been applied with the sole purpose of increasing the intelligibility of the claims and consequently, they do not constitute in any way limiting the interpretation of each element identified, purely by way of example, by such signs and reference numbers.

Claims

Method of operating a laundry drying machine (10), such as a heat pump laundry dryer or a heat pump washing machine having drying function, in order to carry out a laundry treatment process on a laundry load (L) comprising a drying cycle,
wherein the laundry drying machine (10) comprises:
a control unit (11) controlling the operation of the laundry drying machine (10),

a laundry treatment chamber (12) for treating laundry using process air (A),

a process air circuit (13) for circulating the process air (A),

a heat pump system (14 ) having a refrigerant loop (15), in which the refrigerant fluid (R) is circulated through a first and a second heat exchanger (16a,16b) in thermal communication with the process air (A),

a compressor (17) for circulating the refrigerant fluid (R) through the refrigerant loop (15), and wherein the method comprises the following steps:
- driving the compressor (17) by means of the control unit (11) according to a first driving sequence in a first portion (P1) of the drying cycle;

- driving the compressor (17) by means of the control unit (11) according to a second driving sequence in a second portion (P2) of the drying cycle different from the first portion;

characterized in that

said method comprises the step of detecting, before said second portion (P2) of the drying cycle, one or more parameters of the following first list:
- laundry load (L) amount;

- moisture content of laundry load (L);

- temperature of laundry load (L);

- temperature of the process air (A);

- temperature and/or humidity of the environment where the laundry drying machine (10) is placed;

- laundry treatment program selected by a user;

- laundry treatment process or drying process time;

- a preset value of energy consumption;

wherein said second driving sequence is selected, on the basis of said one or more parameters detected according to said first list, among a plurality of available driving sequences providing for driving the compressor (17) intermittently between a lower level of energy and an upper level of energy wherein the lower and upper level of energy and a condition for ending the second driving sequence are defined in such a way to allow moisture to circulate from wet clothes to drier ones, in order to obtain a substantially uniform moisture level in the laundry load, depending on one or more parameters of said first list.
Method according to claim 1, characterized in that the second driving sequence provides for driving the compressor (17) intermittently for a first time period in correspondence of a first level of energy, for a second time period in correspondence of a second level of energy, for a third time period in correspondence of a third level of energy, for a fourth time period in correspondence of a fourth level of energy.
Method according to claim 2, characterized in that a time period corresponding to the lower levels of energy is substantially equal to or longer than the time period corresponding to the upper levels of energy.
Method according to claim 2, characterized in that a time period corresponding to the upper levels of energy is substantially longer than a time period corresponding to the lower levels of energy.
Method according to any of claims 2-4, characterized in that the first level and the third level are substantially equal to each other, and in that the second level and the fourth level are substantially equal to each other.
Method according to any of the claims 2-5, characterized in that the second driving sequence is followed by a third driving sequence in a third portion (P3) of the drying cycle different from the first portion (P1) and the second portion (P2), wherein the compressor (17) is driven intermittently between a lower level of energy and an upper level of energy, the time periods corresponding to lower levels of energy of the third driving sequence being longer than the time periods corresponding to lower levels of energy of the second driving sequence.
Method according to claim 1, characterized in comprising two different driving sequences controlled with different parameters of the first list.
Method according to any of claims 1-7, characterized in that a condition of end of drying process, to be controlled during the drying process, is defined depending on at least one parameter of the following second list:
- laundry moisture equal or below a minimum threshold value,

- temperature of drying air exiting the laundry treatment chamber (12) equal or above a maximum threshold value,

- elapsed time equal or above a maximum threshold value,

- the activation of an alarm indicating a machine component failure or a machine malfunctioning.
Method according to claim 8, characterized in that the step of setting the at least one of end of drying process conditions occurs before starting to drive the compressor (17) according to one of the first or second driving sequences.
Method according to claim 9, characterized in that the following steps are repeated in sequence until at least one parameter of the second list is met:
- setting parameters of the first list to be controlled in a driving sequence,

- selecting the driving sequence among a plurality of available driving sequences,

- setting a condition for ending the driving sequence.
Method according to any of claims 9-10, characterized by comprising the following step:
- when at least one parameter of the second list is met a final laundry treating step is performed.
Method according to claim 11, characterized in that the final laundry treating step comprises a cooling phase, wherein laundry is moved within the laundry treatment chamber (12) and/or a cooling air flow is provided to said laundry load (L).
Method according to any of claims 1-12, characterized in that the lower level of energy is obtained by switching OFF the compressor (17), and the upper level of energy is obtained by switching ON the compressor (17).
Method according to any of the claims 1-13, characterized in that in the first driving sequence the compressor (17) remains always switched ON.
A laundry drying machine (10) having a control unit (11) programmed for carrying out the method according to any claim 1 to 14.