WO2015165487A1

WO2015165487A1 - Heat pump laundry dryer

Info

Publication number: WO2015165487A1
Application number: PCT/EP2014/058587
Authority: WO
Inventors: Francesco Cavarretta; Stefano Zandona'
Original assignee: Electrolux Appliances Aktiebolag
Priority date: 2014-04-28
Filing date: 2014-04-28
Publication date: 2015-11-05
Also published as: EP3137674A1; CN106255780B; EP3137674B1; AU2014392299A1; CN106255780A

Abstract

The present invention relates to a laundry dryer (1) of the type comprising a heat pump system (20) having a refrigerant circuit (30) where a refrigerant (R) flows and comprising a drying air circuit (10) in communication with a laundry container (9) suited for receiving laundry to be dried using drying air (A). The refrigerant circuit (30) comprises: a first heat exchanger (21) for heating the drying air (A) and cooling the refrigerant (R); a second heat exchanger (23) for cooling the drying air (A) and heating the refrigerant (R); a refrigerant expansion device (22) arranged in the refrigerant circuit (30) between the first heat exchanger (21) and the second heat exchanger (23), and a compressor (24) arranged in the refrigerant circuit (30) between the second heat exchanger (23) and the first heat exchanger (21). The compressor (24) comprises a compressor chamber (260) for the refrigerant (R) and a lubricant (L). The ratio of the amount (Q) of lubricant (L) to the volume (Vd) of the compressor chamber (260) is comprised between 5 and 15 ml/cc.

Description

HEAT PUMP LAUNDRY DRYER

The present invention concerns the field of laundry drying techniques.

In particular, the present invention refers to a laundry dryer equipped with a heat pump system.

BACKGROUND ART

Laundry treating machines capable of carrying out a drying process on laundry, hereinafter simply indicated as laundry dryers, generally comprise a drying chamber for accommodating therein the laundry to be dried. A heated and dehumidified drying medium, typically air, is guided through the drying chamber. Upon passing through the drying chamber and laundry, the heated and dehumidified drying air takes up humidity and at the same time cools down. The drying air then exits the drying chamber, thereby discharging humidity from the drying chamber and the laundry.

In order to improve the energy efficiency of such laundry dryer, it is known to use heat pumps. In this way, residual heat from the drying air exiting the drying chamber can be extracted therefrom and transferred again to the drying air before it re-enters the drying chamber.

Therefore, the drying air is cooled down and dehumidified and then heated up in the heat pump system and finally reinserted again into the drying chamber.

The heat pump system typically comprises a refrigerant flowing in a closed-loop refrigerant circuit constituted by a condenser, an expansion device, an evaporator and a compressor. The condenser heats up the drying air while the evaporator cools and dehumidifies the drying air leaving the drying chamber. The refrigerant flows in the refrigerant circuit where it is compressed by the compressor and expanded in the expansion device.

According to the known technique, compressors utilized in said refrigerant circuit typically comprise a compression mechanism section wherein the refrigerant is compressed.

Known compression mechanisms comprise moving parts, such as rotary shafts, bearings, pistons, etc., which force the refrigerant to be compressed into an airtight chamber. The moving parts are advantageously driven by an electric motor opportunely connected thereto. Compressors typically used in heat pump system are rotary or scroll compressors, either hermetic or semihermetic.

The compressor opportunely comprises a proper quantity of lubricant, such as oil. The lubricant promotes a safe hydrodynamic lubrication inside the compressor by creating a thin film between the moving parts (rotary shafts, bearings, pistons, etc.).

Furthermore, the lubricant flowing inside the compressor removes heat from the compressor motor. The lubricant thus acts as cooling lubricant.

In the heat pump system of known type, part of said lubricant from inside the compressor is discharged to the outside and flows along the closed-loop refrigerant circuit together with the refrigerant. It is important that said discharged lubricant returns to the compressor along the closed-loop refrigerant so that a proper quantity of lubricant is advantageously maintained inside the compressor.

Furthermore, due to the solubility of the refrigerant into the lubricant, a portion of refrigerant is absorbed into the lubricant. This portion of refrigerant absorbed into the lubricant is not used for its purpose (heat transfer). The drying efficiency of the laundry dryer is therefore reduced.

An effective way for helping the lubricant to return inside the compressor is placing the compressor at a lower level with respect the other components of the heat pump system. In this case, the lubricant advantageously returns to the compressor by gravity.

Nevertheless, in the heat pump laundry dryers of known type the heat pump system is typically confined in a small area in the basement of the same laundry dryer. The compressor and the other components of the heat pump system are therefore arranged at substantially the same level.

A first drawback of the known heat pump system is therefore constituted by the fact that the lubricant does not return to the compressor by gravity.

The correct quantity of lubricating is not maintained inside the compressor and the compressor life and/or reliability of the compressor is therefore reduced.

Furthermore, a quantity of lubricant is trapped along the refrigerant circuit. This quantity of lubricant may be deposited on the internal surfaces of the condenser and/or the evaporator. The presence of lubricant oil on said surfaces, reduces the thermal conductivity (or increase the thermal resistivity) of the condenser and/or the evaporator, thus reducing the heat transfer between the refrigerant and the drying air and hence reducing the drying efficiency of the laundry dryer.

The heating efficiency of the condenser for the drying air is therefore reduced. Analogously, the dehumidifying effect of the evaporator for the drying air exiting the drying chamber is reduced. The drying cycle may last longer than desired and/or the drying effect of the laundry may not be acceptable.

Furthermore, the quantity of lubricant trapped along the refrigerant circuit may accumulate in particular zones along the refrigerant circuit, for example in curves of piping connecting the components of the heat pump system. Such lubricant accumulation zones are detrimental for the heat pump functioning and therefore for the drying efficiency.

Another drawback of the known heat pump system is constituted by the fact that, due to the partial solubility of the refrigerant into the lubricant oil, a portion of lubricant oil remains separated from the refrigerant. This portion of lubricant oil may return to the compressor thanks to the dragging action of the refrigerant on the same lubricant oil. The dragging action depends on the speed of the refrigerant along the refrigerant circuit. Nevertheless, the speed of the refrigerant at the condenser typically has the lowest value along the refrigerant circuit. This may cause a certain difficulty for the refrigerant to drag the lubricant, which may accumulate at the condenser. Again, the presence of lubricant at the condenser, reduces the thermal conductivity (or increase the thermal resistivity) of the condenser, thus reducing the heat transfer between the refrigerant and the drying air and hence reducing the drying efficiency of the laundry dryer.

The aim of the present invention is therefore to solve the noted drawbacks.

It is one object of the present invention to provide laundry dryers for drying articles of the type comprising a heat pump system having an increased reliability.

It is another object of the present invention to provide laundry dryers for drying articles of the type comprising a heat pump system having an increased efficiency.

DISCLOSURE OF INVENTION

The applicant has found that by providing a laundry dryer of the type comprising a heat pump system having a refrigerant circuit where a refrigerant flows and comprising a drying air circuit in communication with a laundry container suited for receiving laundry to be dried using drying air, the refrigerant circuit comprising: a first heat exchanger for heating said drying air; a second heat exchanger for cooling said drying air; a refrigerant expansion device arranged between the first heat exchanger and the second heat exchanger, and a compressor arranged between the second heat exchanger and the first heat exchanger, said compressor comprising a compressor chamber for the refrigerant and a lubricant, by providing said compressor with lubricant so that the ratio of the amount of said lubricant to the volume of the compressor chamber is comprised between 5 and 15 ml/cc, it is possible to obtain a laundry dryer having an increased reliability and/or efficiency compared to the laundry dryers of known type.

In a first aspect the present invention relates, therefore, to a laundry dryer of the type comprising a heat pump system having a refrigerant circuit where a refrigerant flows and comprising a drying air circuit in communication with a laundry container suited for receiving laundry to be dried using drying air, said refrigerant circuit comprising:

a first heat exchanger for heating said drying air and cooling said refrigerant; a second heat exchanger for cooling said drying air and heating said refrigerant; a refrigerant expansion device arranged in said refrigerant circuit between said first heat exchanger and said second heat exchanger, and

a rotary or a scroll compressor arranged in said refrigerant circuit between said second heat exchanger and said first heat exchanger, said compressor comprising a compressor chamber for said refrigerant and a lubricant;

wherein the ratio of the amount of said lubricant to the volume of said compressor chamber is comprised between 5 and 15 ml/cc.

More preferably, said ratio is comprised between between 5 and 10 ml/cc.

In a preferred embodiment of the invention, said first and/or said second heat exchanger further comprises a heat exchanger module, said module including:

- an inlet header to direct a flow of the refrigerant into the module;

- an outlet header to discharge the refrigerant from the module; and

- a plurality of heat exchange layers fluidly connecting the inlet to the outlet header to enable the refrigerant to flow from the inlet to the outlet header and/or vice versa; the layers being stacked one above the others in a predetermined stacking direction and each layer including a plurality of channels.

Preferably, the heat exchange layers are substantially parallel one to the others. More preferably, the channels of the plurality are substantially parallel one to the others.

In a preferred embodiment of the invention, the heat exchange layers are formed by a single tube including the plurality of channels and the tube comprises U- shaped bends in order to form the stacked layers, i.e. the tube bending on itself several times to form the stacked layers.

Said channels have a hydraulic diameter smaller or equal than 5 mm, preferably smaller or equal than 3 mm, more preferably smaller or equal than 1 mm.

In further preferred embodiments of the invention, said first and/or said second heat exchanger includes a plurality of channels to enable the refrigerant to flow, wherein the channels have a hydraulic diameter smaller than 5 mm.

According to an embodiment of the invention, the hydraulic diameter of each of the channel, where the hydraulic diameter DH is defined as

DH=4*A/P

where A is the cross sectional area of the channel and P is the wetted perimeter of the cross-section of the channel, is smaller or equal than 5 mm, i.e. DH < 5 mm, more preferably DH < 3 mm, even more preferably DH < 1 mm.

In a preferred embodiment of the invention, the amount of the refrigerant in the refrigerant circuit is smaller or equal than 300gr.

In this case, preferably, the ratio of the amount of lubricant to the amount of the refrigerant in the refrigerant circuit loop is comprised between 0,2 and 0,5 ml/gr.

In further preferred embodiments of the invention, the amount of the refrigerant in the refrigerant circuit is bigger than 300gr.

In this case, preferably, the ratio of the amount of lubricant to the amount of the refrigerant in the refrigerant circuit loop is smaller than 0,25 ml/gr.

In preferred embodiments of the invention, the rotary compressor is a rolling- piston compressor.

Preferably, the refrigerant is one of the refrigerants of the group comprising: HydroFluoroCarbons (HFC), HydroFluoroHolefins (HFOs) or Hydrocarbons (HC). More preferably, the refrigerant is one of the refrigerants of the group comprising: R134a; R407C; R290; R441a.

In a preferred embodiment of the invention, the drying air circuit is a closed-loop drying air circuit.

According to a preferred embodiment of the invention, the compressor is driven at a variable rotational speed. Preferably, the compressor is driven by means of an inverter motor.

In preferred embodiments of the invention, the heat pump system further comprises a cooling fan unit for the compressor.

Preferably, the compressor comprises an electric motor. More preferably, said electric motor comprises winding formed by aluminium wires.

Opportunely, the refrigerant expelled from the compressor chamber is apt to cool down the compressor, preferably is apt to cool down the electric motor of the compressor, more preferably to cool down the winding of the motor. BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will be made clearer by reading the following detailed description of exemplary and non- limitative embodiments thereof, referring to the following drawing figures, wherein:

- Figure 1 shows a perspective view of a laundry dryer with a heat pump system according to a preferred embodiment of the invention;

- Figure 2 illustrates a schematic diagram of the laundry drying machine of Figure 1;

- Figures 3 and 4 show cross-sectional views of a rolling piston compressor;

- Figure 5 shows a cross-sectional view of a compressor usable in the heat pump system of a laundry drying machine according to a preferred embodiment of the invention;

- Figure 6 is a perspective view of a portion of an embodiment of the laundry drying machine of Figure 1 with the casing removed;

- Figures 7a and 7b are a schematic front view and top view, respectively, of an embodiment of the heat exchanger module of the laundry drying machine of figures 1 or 2;

- Figures 8a and 8b are a schematic front view and top view, respectively, of a further additional embodiment heat exchanger module of the laundry drying machine of figures 1 or 2;

- Figure 9 is a cross-sectional view of an element of the detail of fig. 6;

- Figure 10 is a perspective view in section of an element of figure 6.

DETAILED DESCRIPTION OF THE INVENTION Figure 1 shows a laundry dryer 1 according to an embodiment of the present invention. It is pointed out that the present invention has proved to be particularly successful when applied to a front-loading laundry dryer with a rotatable laundry container; however it is clear that the present invention can be applied as well to a top-loading laundry dryer.

Figures 1 and 2 illustrate a laundry dryer 1 with a heat pump system 20 according to a preferred embodiment of the present invention.

The laundry dryer 1 preferably comprises, though not necessarily, a substantially parallelepiped-shaped outer boxlike casing 2 which is preferably structured for resting on the floor. More in detail, casing 2 generally includes a basement 44, visible in Figure 6. The laundry dryer 1 defines an horizontal plane (X", Y") which is substantially the plane of the ground on which the laundry dryer 1 is situated, and a vertical direction Z" perpendicular to the plane (X", Y").

A laundry container comprising a rotatably drum 9 is provided within the casing 2. A front door 8, pivotally coupled to the front upright side wall 2a, is provided for allowing access to the drum interior region to place laundry to be dried therein.

The drum 9 is advantageously rotated by a drum motor 27, preferably an electric motor, which preferably transmits the rotating motion to the shaft of the drum 9, advantageously by means of a belt/pulley system. In a different embodiment of the invention, the drum motor can be directly associated with the shaft of the drum 9.

The laundry dryer 1 is provided with a drying air circuit 10, as illustrated in Figure 2, which is structured to circulate inside the drum 9 a drying medium A, such as air, in particular comprising ambient air, as schematically illustrated with dashed line in Figure 2.

The drying air A circulates over and through the laundry located inside the drum 9 to dry the laundry.

The drying air circuit 10 is also structured for drawing moist air from the drum 9 and cooling down the moist air leaving the drum 9 so to extract and retain the surplus moisture. The dehumidified air is then heated up to a predetermined temperature preferably higher than that of the moist air arriving from the drum 9. Finally the heated, dehumidified air is conveyed again into the drum 9, where it flows over and through the laundry stored inside the rotatable drum 9 to rapidly dry the laundry, as said above.

The drying air circuit 10 forms, therefore, a closed-loop for the drying air A. Laundry dryer 1 with drying air A forming a closed-loop belongs to laundry dryers known as condense laundry dryers.

An air conveyance device 12 is preferably arranged along the drying air circuit 10 for generating the volume flow of drying air A.

The air conveyance device 12 preferably comprises a fan. In a preferred embodiment of the invention, the fan 12 comprises an electric motor 45.

In further preferred embodiments, the fan 12 and the drum 9 may be preferably driven by the same electric motor. This may advantageously reduce the cost and/or the size of the laundry dryer. On the contrary, two electric motors 27, 45, as described above, may be advantageously driven and controlled independently so that the fan 12 and the drum 9 may be controlled independently.

The air conveyance device 12 is preferably arranged upstream of the drum 9. In different embodiments, nevertheless, the air conveyance device 12 may be arranged in any place along the drying air circuit 10.

Preferably, and more particularly, the drying air circuit 10 then comprises a dehumidifying unit 23 arranged downstream of the drum 9 and a heater unit 21 arranged downstream of the dehumidifying unit 23 and upstream of the drum 9. It is underlined that in the present application the terms "upstream" and "downstream" are referred to the flowing direction of the air, heated air and/or moist air, during the standard functioning of the laundry dryer; for example saying that the fan is arranged upstream of the drum means that in the standard functioning of the laundry dryer the air firstly passes through the fan and then flows into the drum; saying that the dehumidifying unit is arranged downstream of the drum means that in the standard functioning of the laundry dryer the air firstly circulates inside the drum and then passes through the dehumidifying unit. In the dehumidifying unit 23 the moist air leaving the drum 9 condenses and cools down and the water generated therein is preferably collected in a removable water container 14, visible in Figure 1, arranged below the dehumidifying unit 23.

In the preferred embodiment here described, the dehumidifying unit 23 is the evaporator of the heat pump system 20 and the heating unit 21 is the condenser of said heat pump system 20.

Therefore, the evaporator 23 cools down and dehumidifies the moist air coming from the drum 9 and then the condenser 21 heats up the dehumidified air coming from the evaporator 23. The heated air is then conveyed again into the drum 9. In further embodiments, the drying air circuit may not form a closed-loop. In this case, for example, the drying air may be conveyed to a condenser from outside, then conveyed into the drum, from the drum conveyed to the evaporator and finally expelled to the outside (as happens in laundry dryers known as vented laundry dryers).

The heat pump system 20 with its evaporator 23 and condenser 21, therefore, interacts with the drying air circuit 10. In fact, the drying air circuit 10 and the heat pump system 20 are thermally coupled by the condenser 21 and the evaporator 23.

In particular, the heat pump system 20 comprises a refrigerant circuit 30 forming a closed-loop circuit where a refrigerant R flows.

The refrigerant circuit 30 comprises a compressor 24, a first heat exchanger 21, i.e. the condenser 21 in the preferred embodiment here described, an expansion device 22 and a second heat exchanger 23, i.e. the evaporator 23 in the preferred embodiment here described. The compressor 24, the condenser 21, the expansion device 22 and the evaporator 23 are connected in series to form said closed-loop refrigerant circuit 30.

In the following the heat exchangers are named either condenser and evaporator or first and second heat exchanger, respectively.

The refrigerant R flows in the refrigerant circuit 30 wherein is compressed by the compressor 24, condensed in the condenser 21, expanded in the expansion device 22 and then vaporized in the evaporator 23.

In particular, the refrigerant R coming from the evaporator 23 at a compressor inlet 24a is compressed by the compressor 24 and expelled through a compressor outlet 24b towards the condenser 21.

In different embodiments, the refrigerant is advantageously a gas, such as C0₂, which maintains its gaseous state along all the closed-loop circuit. In this type of heat pump system the gas temperature changes while passing through the first heat exchanger and the second heat exchanger. In this case, the first heat exchanger and the second heat exchanger act, respectively, as a gas cooler and a gas heater.

Generally, the first heat exchanger 21 defines a thermal coupling between the drying air circuit 10 and the refrigerant circuit 30 wherein the temperature of the drying air A increases (heating) and the temperature of the refrigerant R decreases (cooling).

Analogously, the second heat exchanger 23 defines a further thermal coupling between the drying air circuit 10 and the refrigerant circuit 30 wherein the temperature of the drying air A decreases (cooling) and the temperature of the refrigerant R increases (heating).

A compressor control unit 26 is also preferably provided for controlling the compressor 24. In particular, the compressor control unit 26 is provided for controlling the rotational speed Cs of the compressor 24. The compressor control unit 26 for controlling the rotational speed Cs of the compressor 24 can be part of a central processing unit, not illustrated.

The compressor 24 may be rotated at a fixed rotational speed or, in different preferred embodiments, it may be driven at a variable rotational speed.

It should to be noted that with rotational speed Cs of the compressor 24 it is meant the rotational speed of a driving motor which is part of the compressor 24. In a preferred embodiment of the invention, the compressor 24 comprises an electric motor and the compressor control unit 26 comprises an inverter, which is advantageously used when a variable rotational speed is required.

The electric motor of compressors, as known, comprises windings formed by wires that are arranged in coils, typically wrapped around a portion of the stator included in the electric motor. In a preferred embodiment of the invention, the wires are made of aluminium.

A cooling fan unit 70 or blower unit is preferably arranged close to the compressor 24 to remove heat from the compressor 24, i.e. from the heat pump system 20, during a drying operation. The cooling air flow, which is an ambient air flow in the embodiment, is actively driven by the cooling fan unit 70 and is taking heat from (the surface of) the compressor 24. The fan unit 70 comprises a blower or fan which is driven by a fan motor controlled by the central processing unit of the laundry dryer 1.

An interface unit 15 is preferably arranged on the top of the casing 2. The interface unit 15 is preferably accessible to the user for the selection of the drying cycle and insertion of other parameters, for example the type of fabric of the load, the degree of dryness, etc.. The interface unit 15 preferably displays machine working conditions, such as the remaining cycle time, alarm signals, etc. For this purpose the interface unit 15 preferably comprises a display 13. In further embodiments, the interface unit may be differently realized, for example remotely arranged in case of a remote-control system.

Further, the laundry dryer 1 may comprise several kinds of sensor elements, which are not shown in the figures. For example, the sensor elements may be provided for detecting the temperature, the relative humidity of the drying air A and/or the electrical impedance at suitable positions of the laundry dryer 1, the pressure and/or the temperature of the refrigerant, etc..

The central processing unit above mentioned is advantageously connected to the various parts of the laundry dryer 1, or peripheral units or sensor elements, in order to ensure its operation.

The compressor 24 used in the heat pump system 20 according to the present invention preferably comprises a rotary compressor or a scroll compressor.

The refrigerant R is conveyed in a compression chamber and therein compressed by movement of compressor's mechanism.

An important feature of the compressor is therefore the volume Vd of said compressor chamber. The volume Vd of the compressor chamber is expressed in cubic centimetre (cc).

A rotary compressor preferably utilized in said heat pump system 20 is a rolling-piston, or fixed-vane, rotary compressor. As schematically shown in Figures 3 and 4, a rolling-piston type rotary compressor comprises a cylinder 246 and a roller 247, o roller piston, mounted on a shaft 250 having an eccentric 250a. The shaft 250 rotates about the center of the cylinder 246 and the roller 247 rolls over the inside surface of the cylinder 246, thereby rotating about the eccentric 250a. A compression chamber 260 is defined between the roller piston 247 and the cylinder 246. The refrigerant R is conveyed to the compressor chamber 260 through an inlet port 261 and then discharged, after its compression, through a discharged port 262.

A rolling-piston compressor according to a preferred embodiment of the invention will be better described later with reference to Figure 5.

Another compressor preferably utilized in said heat pump system 20 is a scroll compressor. A scroll compressor uses two interleaving scrolls to compress the refrigerant R. Typically, one of the scrolls is fixed, while the other orbits eccentrically without rotating, thereby trapping and compressing pockets of refrigerant between the scrolls. Another method for producing the compression motion is co-rotating the scrolls, in synchronous motion, but with offset centers of rotation.

Compressors of the invention are further advantageously provided with a quantity of lubricant L. Lubricant L preferably comprises lubricant oil, either synthetic lubricant oil or mineral lubricant oil.

The lubricant L advantageously promotes a safe hydrodynamic lubrication inside the compressor. The lubricant L, in fact, advantageously creates a thin film between the moving parts which constitute the compressor. Said parts may comprise, for example, rotary shafts, rollers, bearings, pistons, or other parts which necessitate lubrication.

Furthermore, a small quantity of lubricant L may be discharged from the compressor 24 into the closed-loop refrigerant circuit 30. This small quantity of lubricant L, therefore, flows in the closed-loop refrigerant circuit 30 together with the refrigerant R. At the working condition, the refrigerant R is typically partially soluble in lubricant L, the extent of solubility typically increasing with refrigerant pressure and decreasing with lubricant temperature. A portion of refrigerant R is hence trapped in the lubricant L.

Figure 5 illustrates a preferred embodiment of a compressor 24 usable in the heat pump system 20 according to the present invention.

The compressor 24 is a rotary compressor, more particularly a rolling-piston compressor.

The compressor 24 comprises sealed container 241, a motor portion 242 in the upper portion of the sealed container 241, and a compression mechanism 244 driven by the motor portion 242. Lubricating oil L to lubricate the compression mechanism 244 is received in the lower portion of the sealed container 241. The motor portion 242 comprises a stator 242a which is press-fitted in the upper portion of the sealed container 241 and which has several refrigerant paths 243 on the outer periphery, and a rotor 242b which is rotated by the stator 242a. The rotor 242b is provided with a rotary shaft 250 integral therewith. The rotary shaft 250 extends downward from the rotor 242b, and is rotatably supported by a main bearing 245 and a sub bearing 248 of the compression mechanism 244. The sub bearing 248 is provided with a valve gear 253 for discharging a refrigerant gas compressed in the compression mechanism 244 into the sealed container 241. The compression mechanism 244 comprises a cylinder 246, and a piston roller 247 is contained in the cylinder 246. The volume between the cylinder 246 and the piston roller 247 defines the compression chamber 260. The piston roller 247 is mounted to a crank portion 250a of the rotary shaft 250, and eccentrically rotated in accordance with the rotation of the rotary shaft 250. The compression mechanism 244 is immovably- supported in the sealed container 241, having the cylinder 246 welded to the inner periphery of the sealed container 241.

The sealed container 241 comprises a cylindrical container 251 sealed at its one end, and a substantially spherical upper lid 252, welded to the cylindrical container 251 over the entire circumference to cover the container. A glass terminal 254 is attached to the vicinity of the centre of the upper lid 252, and a discharge tube 24b (or compressor outlet) is attached to the spherical surface of the upper lid 252.

With the structure explained above, when the compressor is operated, by rotation of the rotary shaft 250 caused by the rotor 242b, the piston roller 247 eccentrically rotates in the cylinder 246, and the refrigerant gas R coming from the compressor inlet 24a is compressed in the compression chamber 260 of the compression mechanism 244 and discharged into the sealed container 241 via the valve gear 253. At this point, lubricating oil L leaks into the compression mechanism 244, therefore, droplets of lubricating oil L are discharged together with the compressed refrigerant R. These droplets of lubricating oil L flow into the upper space of the motor portion 242 via several refrigerant paths 243 provided around the outer periphery of the stator 242a, and are separated from the refrigerant gas R when the droplets collide with and adhere to the inner surface of the upper lid 252. The separated lubricating oil L is carried upward by the flow of the refrigerant gas R along the inner surface of the upper lid 252. Here, as the inner surface of the upper lid 252 is formed to be substantially spherical, the separated lubricating oil L is gradually collected in the centre. The collected lubricating oil L collides with the glass terminal 254 provided around the center of the upper lid 252, and falls onto the lower portion of the sealed container 241 due to its weight. Part of the lubricating oil L flowing along the inner surface of the upper lid 252 may be discharged to the outside of the compressor 24 through the compressor outlet 24b (discharge tube).

It has to be noted that the compressed refrigerant R expelled from the compression mechanism 244 which flows into the upper space of the motor portion 242 via refrigerant paths 243 also cools down the motor portion 242 of the compressor, in particular the stator 242a.

In working condition, said part of the lubricating oil L discharged to the outside of the compressor 24 through the compressor outlet 24b flows along the closed- loop refrigerant circuit 30 together with the refrigerant R and returns to the compressor 24 through the compressor inlet 24a. It is essential that the lubricating oil L discharged to the outside of the compressor 24 returns to the compressor 24 so that a proper level of lubricant oil L, which promotes the lubrication effect, is maintained inside the compressor 24.

The applicant has found that a heat pump system wherein the amount Q of lubricant L is set at a value so that the ratio of the amount Q of lubricant L to the volume Vb of the compressor chamber 260 is comprised between 5 and 15 ml/cc solves the drawbacks of the know laundry dryers.

More preferably the ratio of the amount Q of said lubricant L to the volume Vb of the compressor chamber 260 is comprised between 5 and 10 ml/cc.

The amount Q of lubricant L is here preferably expressed in millilitre (ml).

Advantageously, the applicant has found that with said preferred ratio the quantity of refrigerant R trapped in the lubricant L is reduced.

Furthermore, the applicant has found that the choice of said preferred ratio leads to several advantageous effects.

A first effect is that a proper quantity of lubricating oil L is maintained inside the compressor 24. The lubricating effect is therefore guaranteed prolonging the life of the compressor 24 and increasing reliability of the laundry dryer 1.

Another effect is that a lower quantity of lubricant oil L is deposited on the surfaces of one or both the heat exchangers, the condenser 21 or the evaporator 23. Thermal conductivity (or thermal resistivity) of the condenser 21 and/or the evaporator 23 is therefore not negatively affected. Heat transfer between refrigerant R and drying air A is adequately maintained and also the efficiency of the heat pump system 20 is maintained at a desired value.

In particular, the heat transfer between refrigerant R and drying air A is adequately maintained at the condenser 21 so that the temperature of drying air A which is conveyed to the drum 9 from the condenser 21 is correctly maintained. The drying efficiency is therefore maintained and also the drying cycle duration is maintained at a desired or targeted value.

A further effect is that the risk that lubricant oil L accumulates in particular zones along the refrigerant circuit 30, for example in curves of piping connecting the components of the heat pump system 20, is reduced thus assuring efficiency for the heat pump system 20. Furthermore, reduced values of refrigerant R trapped into the lubricating oil L reduces the portion of refrigerant R which is not used for its purpose (heat transfer), thus assuring efficiency for the heat pump system 20.

Figure 6 shows in details the heat pump system 20 according to a preferred embodiment of the invention. The heat pump system 20 connects via piping 65 the first heat exchanger 23 (condenser), the expansion device 22 such as a choke, a valve or a capillary tube (not visible), the second heat exchanger 23 (evaporator) and the compressor 24. Preferably, said components of the heat pump system 20 are confined in a small area in the basement 44. The components are arranged at substantially the same level with respect to the plane of the ground (X", Y").

Preferably, in correspondence of evaporator 23, the laundry dryer 1 of the invention preferably comprises the removable water container 14 (shown only in fig. 1) which collects the condensed water produced, when the laundry dryer 1 is in operation, inside evaporator 23 by condensation of the surplus moisture in the drying air A arriving from the drum 9. The water container 14 is located at the bottom of the evaporator 23. Preferably, through a connecting pipe and a pump (not shown in the drawings), the collected condensed water is sent in a reservoir located in correspondence of the highest portion of the laundry dryer 1 so as to facilitate manual discharge of the water by the user.

First and/or second heat exchanger 21, 23 will be described hereinafter.

First and/or second heat exchanger 21, 23 include one or more heat exchanger modules 40 located along the drying air A path.

With reference to Figure 6, the basement 44 of a laundry dryer 1 showing a plurality of modules 40 included in the evaporator 23 and in the condenser 21 of the heat pump system 20 according to the invention is depicted. In figure 6, the casing 2 and the drum 9 of the laundry dryer 1 have been removed in order to show the heat exchangers 21, 23 located along the drying air A path. As stated above, although in the appended drawings both evaporator 23 and condenser 21 of the laundry dryer 1 includes heat exchanger modules 40 realized according to the invention, it is to be understood that the evaporator 23 only or the condenser 21 only might include such module(s) 40. In addition, a single module 40 can be included in either evaporator 23 or condenser 21. Moreover, in case both evaporator and condenser include more than one module 40 according to the invention, the evaporator can include a different number of modules from the condenser (as per the appended figure 6 where the evaporator 23 includes two modules 40 and the condenser four modules 40).

Preferably, the condenser 21 includes more modules than the evaporator 23. In case more than one module 40 is included in the laundry dryer 1 of the invention, the modules can be identical or different.

Preferably, modules 40 are located in correspondence of the basement 44 of laundry dryer 1.

The structure of a single module 40 will now be described with reference to two different embodiments depicted in figures 7a-7b and 8a- 8b.

A heat exchanger module 40 includes an inlet header 55 and an outlet header 56. Inlet and outlet headers 55, 56 have preferably the structure of a pipe and more preferably with a circular cross section. The headers have a longitudinal extension along an axis, which corresponds to the main direction of flow of the refrigerant R within the headers. The refrigerant R is flowing into the module 40 via the inlet header 55 and exiting the same via the outlet header 56. A plurality of channels, each indicated with 57, fluidly connect the inlet 55 to the outlet header 56 and vice versa, so that the refrigerant R can enter and exit the module 40. The channels 57, due to their configuration, allow good heat exchange between the refrigerant R and the drying air A.

Channel 57 defines a longitudinal direction X along which it extends. Preferably, the channels 57 are mounted in the module 40 so that their longitudinal extension X is substantially perpendicular to a drying air flow direction Y. Preferably, their longitudinal extension is substantially parallel to the horizontal plane. In other words preferably, when mounted, the longitudinal direction X lies on a plane parallel to the (X" , Y") plane defined by the laundry dryer 1.

Preferably, the refrigerant flow within channels 57 is substantially perpendicular to the drying air flow. However, depending on the direction of the drying air flow, the direction of the drying air stream and the direction of the refrigerant flow can alternatively form an angle therebetween.

According to a preferred embodiment, the channels 57 are grouped in heat exchange layers 58: each heat exchange layer 58 includes a plurality of channels 57 which are preferably adjacent and parallel to each other. More preferably, each module 40 includes a plurality of heat exchange layers 58, more preferably all layers 58 are stacked one above the other(s) in a stacking direction Z and even more preferably parallel to each other, substantially forming a plurality of parallel rows. Preferably the stacking direction Z is the vertical direction, i.e., Z and Z' ' are parallel to each other. Alternatively, the stacking direction Z and the vertical direction Z" can form an angle therebetween.

According to an embodiment of the invention, heat exchange layer 58 includes a single tube, having for example an elongated cross section, including two substantially parallel flat surfaces 59a, 59b. Within the tube, separators 58a are realized in order to longitudinally divide the interior of the tube in the plurality of channels 57. Such a structure is schematically depicted in the cross section of a heat exchange layer 58 of Figure 9. The cross section of the single channel 57 can be arbitrary. Each heat exchange layer 58 has a width W which depends on the number of channels which are located one adjacent to the other (see figure 7b).

Preferably, each couple of adjacent stacked channels layers 58 is connected via a plurality of fins 60. Preferably the upper surface 59a of a heat exchange layer 58 is connected via the plurality of fins 60 to the lower surface 59b of the adjacent heat exchange layer 58.

The width W of the layer 58 defines a direction Y which, together with the longitudinal direction X of channels 57, defines in turn a heat exchange layer plane (X,Y). The heat exchange layer plane (X, Y) might be, when the module 40 is mounted on the laundry dryer 1, either parallel to the horizontal plane (X", Y") defined by the laundry dryer 1 or tilted with respect to the same. Alternatively or in addition, the heat exchange layer plane (X, Y) can be perpendicular to the stacking direction Z or form an angle with the same. Moreover, each heat exchange layer 58 can also be not planar, but for example curved, e.g., having a concavity pointing either up or down along the stacking direction.

As an example, in Figure 10 a section of a header 55, 56 is represented. The header 55, 56 includes a cylindrical envelope 107 in which a plurality of holes 57a are realized, the channels 57 forming a layer 58 being inserted therein. However different configurations are possible.

The cross section of the headers 55, 56 is circular, as shown in the appended drawings, or oblong. The cross section of the header refers to the cross section of the header along a plane perpendicular to the stacking direction Z. Preferably, the oblong cross section is such that its smallest diameter, i.e., the smallest cord passing through the geometrical center of the cross section, is smaller than the width W of the layer 58.

The refrigerant R entering the module 40 via the inlet header 55 can come from the outlet header 56 of another module 40, from the compressor 24 or from the capillary tube/expansion valve 22. Additionally, the refrigerant R exiting the outlet may be directed towards the inlet header 56 of another module 40, towards the capillary tube/expansion valve 22 or towards the compressor 24. The connection between the compressor 24, modules 40 and capillary tube 22 and between modules 40 is made via piping 65, as it can be seen in figure 6. In the following figures, the flow of the refrigerant R will be indicated with a dotted line having a pointing arrow in the direction of the flow.

According to a first embodiment of the module 40 of the laundry dryer 1 of the invention depicted in Figures 7a and 7b, the two headers 55, 56 are mounted vertically (i.e. their axis Z is the vertical axis Z" of the dryer 1) on the basement 44 of the laundry dryer 1, parallel one to the other, and the channels 57 connecting the two headers 55, 56 are substantially straight along the longitudinal direction X. The stacking direction Z is parallel to the vertical direction Z" . Channels 57 are divided in heat exchange layers 58, each of which includes a different tube defining upper and lower surfaces 59a, 59b within which the channels 57 are realized. A plurality of heat exchange layers 58 connects the inlet 55 to the outlet header 56, all heat exchange layers 58 having a first end 58b and a second end 58c longitudinally opposite to each other, the first end 58b being connected to the inlet header 55 and the second end 58c being connected to the outer header 56. Heat exchange layers 58 are stacked one on the other along the vertical direction Z. In addition, each heat exchange layer 58 has a width direction Y perpendicular to the longitudinal extension X of the channels 57. In the present embodiment, this width direction Y is parallel to the horizontal plane (X", Y") and to the air flow direction; i.e. the layer planes (X, Y) are horizontal (parallel to the horizontal plane (X", Y"). In other words, the module 40 is mounted so that the heat exchange layers 58 form parallel horizontal planes between which the process air flows. In each header 55, 56 in correspondence of each heat exchange layer's end 58b, 58c, a plurality of apertures 57a are realized, in each aperture 57a a channel 57 being inserted. The so-formed rows of apertures 57a (visible only in fig. 10) are parallel one to the other and perpendicular to the longitudinal extension Z of the header 55, 56.

The refrigerant R enters the inlet header 55 of module 40 via an inlet aperture 55in along a flow direction parallel to the longitudinal extension Z of header 55 and branches off into the various channels 57 via apertures 57a. The heat exchange layers 58 are "parallel" to each other according to the refrigerant flow direction. In each channel 57, the flow of the refrigerant is substantially parallel to the flow direction of the refrigerant R in the other channels 57 and has the same direction. The refrigerant R then exits the module 40 via an outlet aperture 56out of outlet header 56.

The direction of flow of refrigerant in the headers 55, 56 is perpendicular to the drying air flow. In addition, the flow of the refrigerant in the inlet header 55 is parallel to the flow of the refrigerant in the outlet header 56, but with opposite direction.

According to an additional embodiment of the module 40 of the laundry dryer 1 of the invention, depicted in Figures 8a and 8b, the module 40 includes only two headers 55, 56, the inlet and the outlet header. In this case, the headers are lying on the horizontal plane (X, Y) and more preferably are disposed along the air flow direction Y. In addition, not all layers are connected to both inlet and outlet headers 55, 56, on the contrary only the topmost and the lowermost layers are connected to the inlet and the outlet layer, respectively. All other layers 58 have their ends 58b, 58c connected to their adjacent layers, e.g. one end to their lower and one end to their upper layer. Thus, the various layers 58 are substantially formed by a single channels' tube bending on itself several times in order to form the stacked layers. Being the inlet and the outlet headers 55, 56 disposed within the basement 44 substantially parallel to the drying air flow direction Y, also the resulting refrigerant flow within the headers is parallel to horizontal plane (X", Y"). However, the inlet and outlet headers 55, 56 are located within the basement 44 at different height along the vertical direction Z", so the plurality of layers 58 all formed by the single tube are stacked one above the other in a stacking direction Z which still corresponds to the vertical direction Z". Channels layers 58 are parallel to each other and their longitudinal extension X is perpendicular to the process air flow direction Y. The single tube within which the various channels 57 are realized has a first rectilinear portion 58e defining the first channels layer connected to the inlet header 55 via one of its ends 58b, it then includes a U-shaped bend 58f and it extends for a second rectilinear portion 58g parallel to the first rectilinear portion 58e defining the second channels layer, and so on, till the last rectilinear portion 58z forming the last layer, which is connected by one of its ends 58c to the outlet header 56. In this way, a single row of apertures 57a is formed in each header 55, 56 and the flow of refrigerant in the various layers 58 can be considered in series with respect to the refrigerant flow. The flows of refrigerant within the various channels 57 forming the channels layers are parallel to each other. Additionally, the channels layer planes (X, Y) are parallel to the horizontal plane (X", Y").

The flows of the refrigerant R in the inlet and outlet headers 55, 56 are preferably parallel to each other. The two flows can have the same direction, or opposite directions.

Preferably, the channels 57 above described of both embodiments are cylindrical tubes, i.e. have a circular cross section. Advantageously, said channels 57 have a hydraulic diameter DH smaller or equal than 5 mm, i.e. DH < 5.

Nevertheless, the channels 57 may have different shape with different cross section shape. Accordingly, the hydraulic diameter DH of each of the channel, where the hydraulic diameter DH is defined as

DH=4*A/P

where A is the cross sectional area of the channel and P is the wetted perimeter of the cross-section of the channel 57, is smaller or equal than 5 mm, i.e. DH < 5 mm, more preferably DH < 3 mm, even more preferably DH < 1 mm.

The present invention is particular advantageous when heat exchangers of the type above described with reference to figures from 6 to 10 are used. In particular, the choice of lubricant L according to the resent invention, reduces or completely avoids that lubricant oil L is deposited at inlet and/or outlet headers 55, 56 of said module 40, which will at least partially impede the flow of refrigerant R through channels 57.

The heat transfer efficiency between refrigerant R and drying air A at evaporator 23 and condenser 21 is therefore substantially maintained.

In further preferred embodiments, first and/or second heat exchanger generally includes a plurality of channels to enable the refrigerant R to flow therethrough. Preferably, said channels have a hydraulic diameter smaller than 5 mm.

In heat pump system of laundry dryer having one or both the heat exchangers of reduced size and/or of the type above described, i.e. with channels having a hydraulic diameter smaller than 5 mm, a small amount of refrigerant R is needed for the proper functioning.

Preferably, the amount of refrigerant R (refrigerant charge) used in such heat pump laundry dryer is preferably smaller or equal than 300gr.

Advantageously, use of hydrocarbons as refrigerants, which are flammable, can be therefore also considered, due to the low amount required.

In different embodiments, the amount of refrigerant R (refrigerant charge) may be bigger than 300gr.

According to a characteristic of the invention, the amount Q of lubricant L is set at a value so that the ratio of the amount Q of lubricant L to the amount of refrigerant R is preferably comprised between 0,2 and 0,5 ml/gr, in particular when the refrigerant charge is smaller or equal than 300gr.

In different embodiments and according to another characteristic of the invention, the amount Q of lubricant L is set at a value so that the ratio of the amount Q of lubricant L to the amount of refrigerant R is preferably smaller than 0,25 ml/gr, in particular when the refrigerant charge is bigger than 300gr.

Applicant has found that the choice of the amount Q of lubricant L according to said criteria further enhances the above mentioned advantageous effects.

Preferably, the refrigerant R used in the refrigerant circuit 30 of the heat pump system 20 according to the present invention may be preferably one of the refrigerants of the group comprising: HydroFluoroCarbons (HFC), such as R134a and R407C; HydroFluoroHolefins (HFOs) or hydrocarbons (HC), such as R290 or R441a. Hydrocarbons (HC) are particularly preferred in a heat pump system using at least one heat exchanger with channels having a hydraulic diameter smaller than 5 mm.

It has thus been shown that the present invention allows the set objects to be achieved. In particular, it makes it possible to obtain a laundry dryer having an increased reliability and/or energy efficiency.

Although illustrative embodiments of the present invention have been described herein with reference to the accompanying drawings, it is to be understood that the present invention is not limited to those precise embodiments, and that various other changes and modifications may be affected therein by one skilled in the art without departing from the scope or spirit of the invention. All such changes and modifications are intended to be included within the scope of the invention as defined by the appended claims.

Claims

CLAIMS 1. Laundry dryer (1) of the type comprising a heat pump system (20) having a refrigerant circuit (30) where a refrigerant (R) is adapted to flow and comprising a drying air circuit (10), where drying air is adapted to flow, in communication with a laundry container (9) suited for receiving laundry to be dried, said refrigerant circuit (30) comprising:

a first heat exchanger (21) for heating said drying air (A) and cooling said refrigerant (R);

a second heat exchanger (23) for cooling said drying air (A) and heating said refrigerant (R);

a refrigerant expansion device (22) arranged in said refrigerant circuit (30) between said first heat exchanger (21) and said second heat exchanger (23), and a rotary or a scroll compressor (24) arranged in said refrigerant circuit (30) between said second heat exchanger (23) and said first heat exchanger (21), said compressor (24) comprising a compressor chamber (260) for said refrigerant (R) and a lubricant (L);

wherein the ratio of the amount (Q) of said lubricant (L) to the volume (Vd) of said compressor chamber (260) is comprised between 5 and 15 ml/cc.

2. The laundry dryer (1) of claim 1, wherein said ratio is comprised between 5 and 10 ml/cc.

3. The laundry dryer (1) of any one of the preceding claims, wherein said first and/or said second heat exchanger (21 ; 23) further comprises a heat exchanger module (40), said module (40) including:

- an inlet header (55) to direct a flow of said refrigerant (R) into said module (40);

- an outlet header (56) to discharge said refrigerant (R) from said module (40); and

- a plurality of heat exchange layers (58) fluidly connecting said inlet (55) to said outlet header (56) to enable said refrigerant (R) to flow from said inlet to said outlet header and/or vice versa; said layers (58) being stacked one above the others in a predetermined stacking direction (Z; Z') and each layer (58) including a plurality of channels (57).

4. The laundry dryer (1) of claim 3, wherein said heat exchange layers (58) are substantially parallel one to the others.

5. The laundry dryer (1) of claim 3 or 4, wherein said plurality of channels (57) are substantially parallel one to the others.

6. The laundry dryer (1) of any one of the claims 3 to 5, wherein said heat exchange layers (58) are formed by a single tube including said plurality of channels (57) and the tube comprises U-shaped bends (58f) in order to form the stacked layers (58).

7. The laundry dryer (1) of any one of the claims 3 to 6, wherein said channels (57) have a hydraulic diameter smaller or equal than 5 mm, preferably smaller or equal than 3 mm, more preferably smaller or equal than 1 mm.

8. The laundry dryer (1) of claim 1 or 2, wherein said first and/or said second heat exchanger (21 ; 23) includes a plurality of channels to enable said refrigerant (R) to flow, wherein said channels have a hydraulic diameter smaller than 5 mm.

9. The laundry dryer (1) of any one of the preceding claims, wherein the amount of said refrigerant (R) in said refrigerant circuit (30) is smaller or equal than 300gr.

10. The laundry dryer (1) of any one of the preceding claims, wherein the ratio of said amount (Q) of lubricant (L) to the amount of said refrigerant (R) in said refrigerant circuit loop (30) is comprised between 0,2 and 0,5 ml/gr.

11. The laundry dryer (1) of claim 1 or 2, wherein the amount of said refrigerant (R) in said refrigerant circuit (30) is bigger than 300gr.

12. The laundry dryer (1) of claim 1 or 2, wherein the ratio of said amount (Q) of lubricant (L) to the amount of said refrigerant (R) in said refrigerant circuit loop (30) is smaller than 0,25 ml/gr.

13. The laundry dryer (1) of any one of the preceding claims, wherein said rotary compressor is a rolling-piston compressor.

14. The laundry dryer (1) of any one of the preceding claims, wherein said refrigerant is one of the refrigerants of the group comprising: HydroFluoroCarbons (HFC), HydroFluoroHolefins (HFOs) or Hydrocarbons (HC).

15. The laundry dryer (1) of any one of the preceding claims, wherein said refrigerant is one of the refrigerants of the group comprising: R134a; R407C; R290; R441a.

16. The laundry dryer (1) of any one of the preceding claims, wherein said drying air circuit (10) is a closed-loop drying air circuit (10).

17. The laundry dryer (1) of any one of the preceding claims, wherein said compressor (24) is driven at a variable rotational speed, preferably by means of an inverter motor.

18. The laundry dryer (1) of any one of the preceding claims, wherein said heat pump system (20) further comprises a cooling fan unit (70) for said compressor (24).

19. The laundry dryer (1) of any one of the preceding claims, wherein said refrigerant (R) expelled from said compressor chamber (260) is apt to cool down said compressor (24), preferably is apt to cool down an electric motor (242) of said compressor (24).