EP2586907B1

EP2586907B1 - A laundry dryer with a heat pump system and air recirculation

Info

Publication number: EP2586907B1
Application number: EP11187243.8A
Authority: EP
Inventors: Francesco Cavarretta
Original assignee: Electrolux Home Products Corp NV
Current assignee: Electrolux Home Products Corp NV
Priority date: 2011-10-31
Filing date: 2011-10-31
Publication date: 2019-06-26
Anticipated expiration: 2031-10-31
Also published as: AU2012331506B2; CN103946443B; WO2013064236A1; AU2012331506A1; EP2586907A1; CN103946443A

Description

The present invention relates to a laundry dryer with a heat pump system according to the preamble of claim 1.
In a laundry dryer the heat pump technology is at present the most efficient way to dry laundry by reduced energy consumption. In a conventional heat pump laundry dryer an air stream flows in a closed air stream circuit. The air stream is moved by an air stream fan and passes through a laundry drum removing water from wet clothes. Then, the air stream is cooled down and dehumidified in an evaporator or gas heater and heated up in a condenser or gas cooler. At last, the air stream is re-inserted into the laundry drum again.
A refrigerant flows in a closed refrigerant circuit. The refrigerant is compressed by a compressor. Then, the refrigerant is condensed in the condenser or cooled down in the gas cooler. Next, the refrigerant is laminated in an expansion device. At last, the refrigerant is vaporized in the evaporator or heated up in the gas heater. If the refrigerant operates at a pressure equal or higher than the critical pressure, then it is cooled down in the gas cooler and heated up in the gas heater, respectively. The temperatures of the air stream and the refrigerant are strictly connected to each other.
The cycle of the laundry dryer with the heat pump system comprise two phases, i.e. a transitory phase and a steady state phase. At the beginning of the cycle, the temperatures of the air stream and the refrigerant are usually at ambient temperature. During the transitory phase the temperatures of the air stream and the refrigerant increase up to a desired level. During the steady state phase the temperatures of the air stream and the refrigerant are kept constant until the laundry is dried.
During the transitory phase the drying rate is very low, since the temperature at the inlet of the laundry drum is still low. In order to remove water from the wet laundry a high temperature at the inlet of the laundry drum is required. Further, the high temperature allows then, that the air stream is dehumidified in the evaporator. Moreover, the temperature of the air stream at the outlet of the evaporator decreases in the beginning of the cycle below the initial value, i.e. the ambient temperature, since the temperature of the refrigerant decreases in the evaporator, after the compressor has started to work.
FIG 2 illustrates the time development of the temperatures of the air stream at several points of the air stream channel. The temperature T-LD-OUT of the air stream at the outlet of the laundry drum corresponds with the temperature T-EV-IN of the air stream at the inlet of the evaporator. The temperature T-EV-OUT of the air stream at the outlet of the evaporator corresponds with the temperature T-CO-IN of the air stream at the inlet of the condenser. The temperature T-CO-OUT of the air stream at the outlet of the condenser corresponds with the temperature T-LD-IN of the air stream at the inlet of the laundry drum.
At the beginning of the drying cycle the above temperatures T-LD-OUT, T-EV-OUT and T-CO-OUT of the air stream are at the ambient temperature T-AM. The temperature T-CO-OUT of the air stream at the outlet of the condenser increases during the transitory phase. The temperature T-LD-OUT of the air stream at the outlet of the laundry drum can decrease marginally, but increases during the substantial part of the transitory phase. The temperature T-CO-OUT of the air stream at the outlet of the condenser decreases at first, but increases during the substantial part of the transitory phase. However, during the first half of the transitory phase the temperature T-EV-OUT of the air stream at the outlet of the evaporator is below the ambient temperature T-AM. The ambient temperature T-AM remains constant the whole time. In this example, after about 50 minutes, the drying cycle enters the steady state phase. During the steady state phase the temperatures T-LD-OUT, T-EV-OUT and T-CO-OUT of the air stream are substantially at constant values.
The condensation temperature of the refrigerant is close to the temperature T-CO-OUT of the air stream at the outlet of the condenser, while the evaporation temperature is marginally lower than the temperature T-EV-OUT of the air stream at the outlet of the evaporator. The flow rate of the refrigerant depends on the evaporation temperature. The higher the evaporation temperature, the higher is the flow rate of the refrigerant and the heating and cooling power of the heat pump system. In fact, the higher evaporation temperature causes a higher evaporation pressure and a higher density at the inlet of the compressor. At the same time, the temperature of the air stream depends on the condensation temperature of the refrigerant. Thus, it would be advantageous, if the transitory time is relative short and the temperatures of the air stream increase fast.
EP 1 664 647 B1 discloses a drying apparatus for drying a subject, wherein the refrigerant is circulated through the compressor, a radiator, an expansion mechanism and the evaporator. The drying air is heated by the radiator, flown to the subject to be dried and dehumidified by the evaporator. A part of the drying air heated by the radiator flows through a bypass circuit directly to the evaporator without coming into contact with the subject to be dried.
DE 43 06 217 A1 discloses a program controlled laundry drier having an process air circuit, wherein the process air passes by evaporator and passes through a condenser.
EP 1 493 860 A2 discloses a drier with an air circulation path for circulating, by air blowing means, air from the radiator into the evaporator through a storage room.
US 3,739, 487 A discloses a drying apparatus having air displacing means for drawing air in from a chamber and passing same over an evaporator of a refrigerating plant and then over a condenser of said refrigerating plant.
DE 40 23 000 A1 discloses a laundry drier having a process air channel for the process air to be driven by a fan, wherein between a condenser and an evaporator an air inlet is arranged.
It is an object of the present invention to provide a laundry dryer with a heat pump system, which allows a shortened transitory phase by low complexity.
The object of the present invention is achieved by the laundry dryer according to claim 1.
According to the present invention the air stream circuit includes a recirculation channel, wherein an inlet of said recirculation channel is arranged between an air stream outlet of the first heat exchanger and an inlet of the laundry drum and an outlet of said recirculation channel is arranged between an air stream outlet of the second heat exchanger and an air stream inlet of the first heat exchanger.
The main idea of the present invention is the recirculation of the air stream from the connection between the air stream outlet of the first heat exchanger and inlet of the laundry drum to the connection between the air stream outlet of the second heat exchanger and the air stream inlet of said first heat exchanger. In particular, the recirculation of the air stream is activated during the transitory phase or warm-up phase of the drying cycle. In this case, only a part of the air stream is transferred into the laundry drum. The recirculation channel effects that the increasing of the temperature of the air stream during the transitory mode is speeded up. Thus, the drying cycle is shortened.
For example, the air stream fan is arranged downstream of the first heat exchanger, wherein the inlet of the recirculation channel is preferably arranged downstream of said air stream fan.
Alternatively, the air stream fan is arranged upstream of the first heat exchanger, wherein the inlet of the recirculation channel is preferably arranged downstream of said first heat exchanger.
Preferably, the recirculation channel comprises at least one airflow adjusting device or corresponds with at least one airflow adjusting device, wherein said airflow adjusting device is provided for opening and closing the recirculation channel. Thus, the recirculation channel is controllable.
For example, the airflow adjusting device is provided for opening and closing the recirculation channel by an on-off mode.
Alternatively, the airflow adjusting device may be provided for a continuous opening and closing of the recirculation channel, so that the amount of the recirculated air stream is controlled or controllable by the airflow adjusting device.
Further, the airflow adjusting device is controlled or controllable in dependence of the temperature of the air stream. In particular, the airflow adjusting device is controlled or controllable in dependence of the temperature of the air stream at an inlet of the laundry drum. Moreover, the airflow adjusting device may be controlled or controllable in dependence of the temperature of the air stream at an air stream inlet of the first heat exchanger.
Additionally or alternatively, the airflow adjusting device is controlled or controllable in dependence of the temperature of the refrigerant. For example, the airflow adjusting device is controlled or controllable in dependence of the temperature of the refrigerant at a refrigerant inlet of the first heat exchanger. In a similar way, the airflow adjusting device may be controlled or controllable in dependence of the temperature of the refrigerant at a refrigerant outlet of the first heat exchanger.
According to another example, the airflow adjusting device is controlled or controllable according to a predetermined time scheme.
For example, the airflow adjusting device comprises at least one flap. Further, the airflow adjusting device may comprise at least one valve.
The first heat exchanger acts as a gas cooler, if the refrigerant remains in a gaseous state. In another situation the first heat exchanger may act as a condenser, if the refrigerant at least partially transfers from the gaseous state to a liquid state.
The second heat exchanger acts as a gas heater, if the refrigerant remains in the gaseous state. In contrast, the second heat exchanger acts as an evaporator, if the refrigerant at least partially transfers from the liquid state to the gaseous state.
The invention will be described in further detail with reference to the drawings, in which

FIG 1: shows a schematic diagram of a heat pump system for a laundry dryer according to a first embodiment of the present invention,
FIG 2: shows a schematic diagram of the heat pump system for the laundry dryer according to a second embodiment of the present invention, and
FIG 3: shows a schematic diagram of temperatures of an air stream at several point of an air stream channel as a function of the time.

FIG 1 illustrates a schematic diagram of a heat pump system for a laundry dryer according to a first embodiment of the present invention. The heat pump system includes a closed refrigerant circuit 10 and a closed air stream circuit 12.
The refrigerant circuit 10 includes a compressor 14, a condenser 16, an expansion device 18 and an evaporator 20. The compressor 14, the condenser 16, the expansion device 18 and the evaporator 20 are switched in series and form a closed loop. The air stream circuit 12 includes the evaporator 20, the condenser 16, an air stream fan 24, a laundry drum 26 and a recirculation channel 22. The evaporator 20, the condenser 16, the air stream fan 24 and the laundry drum 26 are switched in series and form a closed loop. The recirculation channel 22 is arranged anti-parallel to the condenser 16 and air stream fan 24. In other words, the recirculation channel 22 is arranged parallel to the laundry drum 26 and evaporator 20.
The condenser 16 comprises an air stream inlet and an air stream outlet as well as a refrigerant inlet and a refrigerant outlet. In a similar way, the evaporator 20 comprises an air stream inlet and an air stream outlet as well as a refrigerant inlet and a refrigerant outlet.
The refrigerant is compressed by the compressor 14 and condensed by the condenser 16. The refrigerant is laminated in the expansion device 18 and vaporized in the evaporator 20. The air stream is driven by the air stream fan 24 and passes through the laundry drum 26 removing water from wet laundry. Then, the air stream is cooled down and dehumidified by the evaporator 20, heated up in the condenser 16 and re-inserted into the laundry drum 26 again.
By the recirculation channel 22 a part of the air stream flows from the outlet of the condenser 16 directly to the inlet of said condenser 16 via the air stream fan 24 during a transitory phase of the drying cycle. This part of the air stream passes by the laundry drum 26 and the evaporator 20 through the recirculation channel 22. Then, this part of the air stream is mixed with that part of the air stream, which comes from the evaporator. In this way, the temperature of the air stream at the inlet of the condenser 16 increases, so that the temperatures of the air stream at the outlet of the condenser 16 and at the inlet of the evaporator 20 increase as well. Thus, the partially recirculation of the air stream from the outlet to the inlet of the condenser 16 allows an increasing of the temperatures of the air stream and a shortening of the transitory phase of the drying cycle.
An airflow adjusting device, for example a pivoting flap, a valve, a valve assembly or another similar device, is provided in order to open and close said recirculation channel 22. Thus, the recirculation channel 22 can be activated and deactivated by the airflow adjusting device. Preferably, the airflow adjusting device is arranged within the recirculation channel 22. The airflow adjusting device is not explicitly shown in FIG 1.
Preferably, the recirculation channel 22 is interconnected between the outlet of the air stream fan 24 and the inlet of the condenser 16 as shown in FIG 1. In other words, an inlet of the recirculation channel 22 is arranged downstream of the air stream fan 24.
Since the recirculation channel 22 can be activated and deactivated by the airflow adjusting device, the heat pump system can work in two different operation modes, namely in a partial recirculation mode and in a traditional mode. In the partial recirculation mode the airflow adjusting device is opened or partially opened, so that a part of the air stream is recirculated from the outlet to the inlet of the condenser 16. In the traditional mode the airflow adjusting device is closed, so that the complete air stream from the outlet of the condenser 16 is transferred to the inlet of the laundry drum 26. The traditional mode corresponds with a heat pump system without the recirculation channel 22. The recirculation channel 22 effects that the increasing of the temperature of the air stream is speeded up during the transitory mode. Thus, the increasing of the condensation and evaporation temperatures of the refrigerant is also speeded up and the transitory phase is shortened. Only a part of the air stream passes through the recirculation channel 22. The main part of the air stream passes through the laundry drum 26 and evaporator 20 in the same way as in a conventional heat pump system.
The partial recirculation mode is switched off by closing the airflow adjusting device. Preferably, the partial recirculation mode is switched off, if the temperature of the air stream at the air stream inlet and/or the air stream outlet of the condenser 16 reach a predetermined value. Further, the partial recirculation mode may be switched off, if the temperature of the refrigerant at the refrigerant inlet and/or the refrigerant outlet of the condenser 16 reaches a predetermined value. Moreover, the partial recirculation mode may be switched off after a predetermined time. For example, said predetermined time starts, when the compressor 14 begins to work. When the recirculation channel 22 is closed by the airflow adjusting device, then the complete air stream passes through the laundry drum 26, the evaporator 20 and the condenser 16.
Further, the airflow adjusting device can be continuously opened and closed, so that the amount of the air stream through recirculating channel 22 is variable. Thus, the amount of the recirculated air stream can be adapted to the thermodynamic conditions of the heat pump system. Additionally, the changeover from the partial recirculation mode and to the traditional mode can be smoothed.
The above heat pump system with the recirculation channel 22 is also suitable, if the refrigerant, e.g. carbon dioxide, operates at least at the critical pressure in a high pressure portion and eventually in a low pressure portion of the refrigerant circuit 10, so that the refrigerant is always in the gaseous state and no condensation and eventually no evaporation occur.
FIG 2 illustrates a schematic diagram of the heat pump system for the laundry dryer according to a second embodiment of the present invention. The heat pump system includes the closed refrigerant circuit 10 and the closed air stream circuit 12.
The refrigerant circuit 10 includes the compressor 14, the condenser 16, the expansion device 18 and the evaporator 20 switched in series and forming a closed loop. The air stream circuit 12 includes the evaporator 20, the air stream fan 24, the condenser 16, the laundry drum 26 and the recirculation channel 22. The evaporator 20, the air stream fan 24, the condenser 16 and the laundry drum 26 are switched in series and form a closed loop. The recirculation channel 22 is arranged anti-parallel to the air stream fan 24 and the condenser 16. In other words, the recirculation channel 22 is arranged parallel to the laundry drum 26 and evaporator 20.
In the second embodiment the air stream fan 24 is arranged upstream of the condenser 16, while the air stream fan 24 is arranged downstream of the condenser 16 in the first embodiment.
FIG 3 illustrates a time development of the temperatures of the air stream at several points of the air stream channel. The temperature T-LD-OUT of the air stream at the outlet of the laundry drum 26 corresponds with the temperature T-EV-IN of the air stream at the inlet of the evaporator 20. The temperature T-EV-OUT of the air stream at the outlet of the evaporator 20 corresponds with the temperature T-CO-IN of the air stream at the inlet of the condenser 16. The temperature T-CO-OUT of the air stream at the outlet of the condenser 16 corresponds with the temperature T-LD-IN of the air stream at the inlet of the laundry drum 26.
At the beginning of the drying cycle the above temperatures T-LD-OUT, T-EV-OUT and T-CO-OUT of the air stream are at the ambient temperature T-AM. The temperature T-CO-OUT of the air stream at the outlet of the condenser 16 increases during the transitory phase. The temperature T-LD-OUT of the air stream at the outlet of the laundry drum 26 can decrease marginally, but increases during the substantial part of the transitory phase. The temperature T-EV-OUT of the air stream at the outlet of the evaporator 20 decreases at first, but increases during the substantial part of the transitory phase. However, during the first half of the transitory phase the temperature T-CO-OUT of the air stream at the outlet of the condenser 16 is below the ambient temperature T-AM. The ambient temperature T-AM remains constant the whole time. During the steady state phase the temperatures T-LD-OUT, T-EV-OUT and T-CO-OUT of the air stream are substantially at constant values.
The heat pump system with the recirculation channel 22 allows a shorter transitory phase of the drying cycle. Thus, the time for the drying cycle is reduced. That part of the cycle, in which the temperature T-EV-OUT becomes lower than the ambient temperature T-AM is reduced or eliminated.

List of reference numerals

10: refrigerant circuit
12: air stream circuit
14: compressor
16: first heat exchanger, condenser, gas cooler
18: expansion device
20: second heat exchanger, evaporator, gas heater
22: recirculation channel
24: air stream fan
26: laundry drum

T-LD-OUT: temperature at the outlet of the laundry drum
T-EV-OUT: temperature at the outlet of the evaporator
T-CO-OUT: temperature at the outlet of the condenser
T-LD-IN: temperature at the inlet of the laundry drum
T-EV-IN: temperature at the inlet of the evaporator
T-CO-IN: temperature at the inlet of the condenser
T-AM: ambient temperature

Claims

A laundry dryer with a heat pump system comprising a refrigerant circuit (10) for a refrigerant and an air stream circuit (12) for an air stream, wherein
- the refrigerant circuit (10) includes a compressor (14), a first heat exchanger (16), an expansion device (18) and a second heat exchanger (20) connected in series and forming a closed loop,

- the air stream circuit (12) includes at least one air stream fan (24), a laundry drum (26), the second heat exchanger (20) and the first heat exchanger (16) forming a closed loop,

- the refrigerant circuit (10) and the air stream circuit (12) are thermally coupled by the first heat exchanger (16) and the second heat exchanger (20),

- the first heat exchanger (16) is provided for heating up the air stream and cooling down the refrigerant, and

- the second heat exchanger (20) is provided for cooling down the air stream and heating up the refrigerant, wherein
the air stream circuit (12) includes a recirculation channel (22), wherein an inlet of said recirculation channel (22) is arranged between an air stream outlet of the first heat exchanger (16) and an inlet of the laundry drum (26)
characterized in, that
an outlet of said recirculation channel (22) is arranged between an air stream outlet of the second heat exchanger (24) and an air stream inlet of the first heat exchanger (16), such that a part of said air stream leaving the outlet of the first heat exchanger (16) flows from said outlet of the first heat exchanger (16) through said recirculation channel (22) to the inlet of the first heat exchanger (16), when the air stream is driven by the air stream fan (24).
The laundry dryer according to claim 1,
characterized in, that
the air stream fan (24) is arranged downstream of the first heat exchanger (16), wherein the inlet of the recirculation channel (22) is arranged downstream of said air stream fan (24).
The laundry dryer according to claim 1,
characterized in, that
the air stream fan (24) is arranged upstream of the first heat exchanger (16), wherein the inlet of the recirculation channel (22) is arranged downstream of said first heat exchanger (16).
The laundry dryer according to any one of the preceding claims,
characterized in, that
the recirculation channel (22) comprises at least one airflow adjusting device or corresponds with at least one airflow adjusting device, wherein said airflow adjusting device is provided for opening and closing the recirculation channel (22).
The laundry dryer according to claim 4,
characterized in, that
the airflow adjusting device is provided for opening and closing the recirculation channel (22) by an on-off mode.
The laundry dryer according to claim 4 or 5,
characterized in, that
the airflow adjusting device is provided for a continuous opening and closing of the recirculation channel (22), so that the amount of the recirculated air stream is controlled or controllable by the airflow adjusting device.
The laundry dryer according to any one of the claims 4 to 6,
characterized in, that
the airflow adjusting device is controlled or controllable in dependence of the temperature of the air stream.
The laundry dryer according to claim 7,
characterized in, that
the airflow adjusting device is controlled or controllable in dependence of the temperature of the air stream at an inlet of the laundry drum (26) and/or at an air stream outlet of the first heat exchanger (16).
The laundry dryer according to any one of the claims 4 to 8,
characterized in, that
the airflow adjusting device is controlled or controllable in dependence of the temperature of the refrigerant.
The laundry dryer according to claim 9,
characterized in, that
the airflow adjusting device is controlled or controllable in dependence of the temperature of the refrigerant at a refrigerant inlet of the first heat exchanger (16) and/or at a refrigerant outlet of the first heat exchanger (16).
The laundry dryer according to any one of the claims 4 to 10,
characterized in, that
the airflow adjusting device is controlled or controllable according to a predetermined time scheme.
The laundry dryer according to any one of the claims 4 to 11,
characterized in, that
the airflow adjusting device comprises at least one flap.
The laundry dryer according to any one of the claims 4 to 12,
characterized in, that
the airflow adjusting device comprises at least one valve.
The laundry dryer according to any one of the preceding claims,
characterized in, that
the first heat exchanger (16) acts as a gas cooler and the second heat exchanger (20) acts as a gas heater, if the refrigerant remains in the gaseous state.
The laundry dryer according to any one of the preceding claims,
characterized in, that
the first heat exchanger (16) acts as a condenser and the second heat exchanger (20) acts as an evaporator, if the refrigerant at least partially transfers from the liquid state to the gaseous state.