Patent Description:
Such a tumble dryer is shown for instance in <CIT>, one problem with such tumble dryers is how to improve their energy efficiency further.

Other examples of tumble dryers are:
<CIT>, which relates to a laundry dryer comprising a blower situated to blow dry air such that the dry air sequentially circulates from the drum, heat absorber, radiator, to the drum again.

<CIT> relates to a clothes dryer including a drum, a heat pump cycle having a first evaporator, a compressor and a condenser, wherein the heat pump cycle includes second to nth evaporators disposed in series with the first evaporator within an air duct.

<CIT> relates to a heat pump laundry dryer including a closed refrigerant circuit and a drying air circuit. The refrigerant circuit includes a compressor, a condenser, an expansion device and a main evaporator. The drying air circuit includes the main evaporator, the condenser, a laundry drum and at least one fan.

<CIT> relates to a laundry treating apparatus including a cabinet for receiving laundry, a machinery compartment with an air supply unit for dehumidifying or heating air in the receiving space and supplying the dehumidified air into the receiving space.

<CIT> relates to a washing machine with an evaporator and a condenser housed upstream and downstream in a heat exchange duct. When a compressor and a fan device are operated, dehumidification is performed based on cooling of air in a water tank by the evaporator, and air is warmed based on heating of dehumidified air by the condenser.

<CIT> relates to a heat pump laundry dryer comprising a laundry drum, a process air fan, a heat pump system with a variable speed compressor, and a cooling fan unit arranged for cooling the compressor and for cooling an inverter board of the compressor.

One object of the present disclosure is therefore to provide a tumble dryer with improved efficiency. This object is achieved by means of a tumble dryer as defined in claim <NUM>. More specifically, the rotatable drum comprises a circular rear wall with air inlet openings and a radial cylindrical wall with air outlet openings, and the compressor is adapted to be run by an inverter, allowing the compressor output to be varied. The expansion valve is also controllable. With such a configuration, a high process air flow can be maintained through the drum, even if a front door of the dryer is opened. At the same time, the compressor and the expansion valve can be controlled to provide a heat pump effect that varies depending on the circumstances to provide improved efficiency.

The evaporator may comprise a flow divider, dividing a refrigerant fluid flow into a plurality of sub-flows for different portions of the evaporator. The controllable expansion valve may be attached to the flow divider. A close connection between the expansion valve and the flow divider provides a more laminar flow achieving an equal division of the refrigerant into the different sub-flows. This in turn provides a more efficient evaporator.

The conduit between the expansion valve and the flow divider may be straight, and may preferably have a length less than <NUM>.

The expansion valve and the compressor may be controlled by means of a controller based on sensor data from a first and a second pressure sensor and a first and a second temperature sensor. The first pressure sensor and the first temperature sensor may be located in the refrigerant fluid flow from the expansion valve to the compressor, while the second pressure sensor and the second temperature sensor may be located in the refrigerant fluid flow from the compressor to the expansion valve. With such a sensor configuration, the controller has knowledge of both the high and low temperatures and pressures of the heat pump circuit, and can therefore control the heat pump to a desired heat pump cycle envelope. This enables a heat pump operation with improved efficiency.

There may be provided a threaded connection adapted to receive a replacement sensor in each of the heat pump circuit path from the expansion valve to the compressor, and/or from the compressor to the expansion valve. This allows a malfunctioning pressure or temperature sensor to be replaced without physically removing the faulty sensor and possibly without removing most of the refrigerant in the heat pump circuit. Instead, a replacement sensor is simply fitted at the threaded connection to record temperature or pressure data.

The inverter comprises a heatsink cooled by heat pump flow which provides efficient cooling of the inverter electronics and reuses some of the dissipated energy in the heat pump drying process.

In an example not forming part of the claimed invention, the heat pump flow may be a refrigerant flow, where the heat sink is cooled by a suction line between the evaporator and the compressor. Then, a loop of the suction line may be embedded in the heat sink. The heat pump circuit may be enclosed in an insulating shell, and the suction line may reach out of the insulating shell to reach the heat sink.

According to the claimed invention, the heat pump flow is a process air flow, the heat sink being cooled by the process air flow leaving the evaporator. The heat pump circuit may be enclosed in an insulating shell and the heat sink may reach to the inside of the shell. The inverter electronics may be located in the comparatively dryer environment outside the shell.

The drum in the tumble dryer is accessible through a door, and control of the compressor may be adapted to keep the refrigerant flow on, i.e. the compressor switched on when the door is opened, while only reducing the refrigerant flow. This implies fewer start/stop cycles of the compressor if the door e.g. is opened frequently to add or remove laundry. The refrigerant flow may however be reduced to <NUM>-<NUM>% of the flow before the door was opened. When the door has been open a predetermined period of time, e.g. one minute, the compressor may subsequently be switched off.

The heat pump may be enclosed in an insulating shell and there may be provided an opening in the shell between the condenser and the inlet of the drum. This serves to avoid overpressure in the drum that could cause hot and humid air to be pressed into spaces containing electronics and the like, which should be avoided. There may be provided a corresponding opening in the outer housing.

The space outside the drum's cylindrical periphery may be configured as a duct leading to a filter. This may provide a considerable flow area with a comparatively small restriction of the air flow, which may allow for a high capacity.

A filter for removing lint from the air flow may be located below the drum. This allows the use of a large filter, substantially as wide as the cylindrical diameter of the drum, and as deep as the depth of the drum. This provides a relatively small flow restriction.

The present disclosure relates generally to a tumble dryer which is provided with a heat pump in order to achieve energy-efficient drying of laundry. An example of a tumble dryer <NUM> is illustrated in <FIG>. The tumble dryer <NUM> has a housing <NUM> with a front side <NUM> which is provided with a door <NUM> or hatch, attached to the front side <NUM> with hinges <NUM>, which provides access to a tumble dryer drum where wet laundry can be loaded.

<FIG> illustrates a cross section through a tumble dryer with a heat pump arrangement. In a heat pump tumble dryer, process air drying the laundry can circulate mostly within the outer enclosure of the tumble dryer, although some exchange of air with the outside may be allowed as will be shown. <FIG> illustrates in a cross section, components of such a tumble dryer as well as a process air flow path <NUM>. As mentioned, the tumble dryer comprises a drum <NUM> in which wet laundry is placed. While the drum <NUM> rotates, a flow <NUM> of relatively dry process air is fed therethrough. The flow is provided by a fan <NUM> or blower, which in the illustrated case is located in a space below the drum <NUM>.

The tumble dryer includes a heat pump arrangement with an evaporator <NUM>, a compressor <NUM>, a condenser <NUM>, and an expansion valve <NUM> (cf. A refrigerant medium is forced through the heat pump arrangement by the compressor <NUM>, and gathers energy in the evaporator <NUM> which is released in the condenser <NUM>, as is well known per se.

As illustrated in <FIG>, an air flow <NUM> is achieved where hot, humid air is extracted from the perforated drum <NUM> by means of the fan <NUM>. The air flow passes a filter <NUM> before reaching the fan <NUM> and arrives at the evaporator <NUM>, which cools the air flow such that moisture therein condenses into liquid water. This water is collected in the bottom section of the tumble dryer and may be drained therefrom through a tube (not shown). A compressor <NUM> is provided to obtain the heat pump refrigerant flow.

The process air flow <NUM>, which is now cooler and contains less water, is passed to the rear section of the tumble dryer and subsequently passes the condenser <NUM>, which heats the air again. Then, the heated, dry air is reintroduced into the drum <NUM> where it is again capable of absorbing water from the laundry therein. The heat pump may be enclosed in an insulating shell <NUM>, for instance made of expanded propylene, EPP. This improves the energy efficiency of the tumble dryer, as less heat may leak to the ambient space.

The present tumble dryer involves a number of improvements, for instance providing increased energy-efficiency and/or capacity. In the illustrated examples, a high-capacity tumble dryer mainly intended for professional use or for use in shared laundry facilities is shown. Such tumble dryers may comprise a drum <NUM> with air inlet openings in its circular rear wall and air outlet openings in its radial cylindrical wall, particularly in the front part thereof, to provide a process air flow through the drum. This may be combined with a lint removing filter <NUM> located below the drum, rather than with a filter provided outlet located in connection with the front wall door <NUM>. To a great extent however, the improvements described herein may also be used in connection with typical domestic tumble dryers intended for use a couple of times per week.

<FIG> shows a perspective view of the heat pump arrangement of the tumble dryer in <FIG>, and <FIG> illustrates schematically the heat pump circuit <NUM> of the heat pump in <FIG>. In this example, the compressor <NUM> is adapted to be run by an inverter-controlled motor <NUM>. An inverter <NUM> is provided allowing the compressor <NUM> output to be varied. This is in contrast to systems where compressors are merely switched on and off to control their operation. Further, the expansion valve <NUM> is controllable, typically being an electronic expansion valve, EEV.

The compressor <NUM> and the expansion valve <NUM> are controlled by a controller <NUM>, based on a number of inputs. A control signal C for the compressor <NUM>, and a control signal V for the expansion valve <NUM> are thus provided.

The heat pump circuit <NUM> may comprise a first <NUM> and a second <NUM> pressure sensor and a first <NUM> and a second <NUM> temperature sensor. The first pressure sensor <NUM> and the first temperature sensor <NUM> are located in the refrigerant fluid flow from the expansion valve <NUM> to the compressor <NUM>, i.e. in the cold side of the circuit. The second pressure sensor <NUM> and the second temperature sensor <NUM> are located in the refrigerant fluid flow from the compressor <NUM> to the expansion valve <NUM>, i.e. in the hot side of the circuit <NUM>.

This allows the heat pump arrangement to be controlled e.g. for optimal energy efficiency. <FIG> schematically illustrates an operation cycle where the refrigerant fluid is affected by the compressor, a, condenser, b, the expansion valve, c, and the evaporator, d, while energy W is taken away from and moved back to the process air flow <NUM>, cf. With knowledge of the high and low temperatures as well as the high and low pressures of the cycle optimal control of the operation cycle envelope indicated in <FIG> depending on circumstances may be achieved. This may imply providing a maximum output as well as reducing the same. Typically, the expansion valve is controlled to match the compressor output. For example, when during a drying process the air flow begins to become dryer, less energy is retrieved from the flow when leaving the drum. This can be sensed by the controller that reduces the compressor rpm correspondingly. As a result, the compressor uses less power and losses need to be cooled to a lesser extent. A significant amount of energy can be saved this way.

Further, if the door <NUM> is opened, which may be sensed by a door sensor/switch <NUM> (cf. <FIG>), the compressor <NUM> output may be reduced, although it may be advantageous to run the compressor <NUM> rather than switching it off completely. For example, the compressor output may be reduced to <NUM>-<NUM>% of the output before the door was opened, in terms of compressor rpm. Typically, the compressor <NUM> may go from <NUM> to <NUM> when the door is opened. This may for instance improve the durability of the compressor as the number of start/stop cycles during normal use can be reduced.

When the door is opened, the rotation of the drum however may stop completely. The process air flow can nevertheless be maintained.

When the door has been open for a predetermined period of time, the compressor <NUM> is switched off as is the fan arrangement <NUM>.

It is also possible to control the heat pump circuit <NUM> based on e.g. a sensed humidity from a humidity sensor <NUM> in the process air stream <NUM> when leaving the drum <NUM>. This allows for instance leaving a residual humidity in the laundry that may be preferred in some types of fabric. It is also possible to achieve a process cycle with a predefined maximum process air temperature, which may be preferred for other fabrics.

<FIG> shows enlarged a portion A of <FIG> where a part of the heat pump circuit is shown, namely leading from the condenser <NUM> to the expansion valve <NUM> and via a filter <NUM>. As shown in <FIG>, there is provided a connection <NUM> that branches away from the heat pump circuit <NUM>. This connection <NUM> has a threaded end, which in the illustrated state is plugged. However, in case of malfunction of the temperature <NUM> or pressure <NUM> sensor (cf. <FIG>) in this part of the circuit, the threaded connection can be used to fit a replacement sensor, which allows for simplified maintenance. The temperature and pressure sensors that the heat pump circuit is originally provided with may be built into the circuit and the malfunctioning sensor may remain at its location while its leads are instead connected to the replacement sensor. Such a threaded connection can be useful also in tumble dryers with other drum configurations, such as tumble dryers with a drum outlet arranged at the tumble dryer door.

Switching circuits of the inverter <NUM> that controls the compressor motor <NUM> (cf. <FIG>) produce heat that need be dissipated to ensure proper function. This also applies to other electronics of the tumble dryer, such as for instance electronics of the control unit <NUM>. Normally, this would be done simply by connecting the electronics to a heat sink, dissipating the heat to the ambient space. The present disclosure suggests using a heat pump flow to improve this cooling. This provides very efficient cooling of inverter and optionally other electronics and may additionally improve the energy efficiency of the tumble dryer as a whole. The heat pump flow may be the flow of the heat pump's refrigerant, or the flow of air dried by the heat pump.

<FIG> show a first example of a heat pump flow cooled inverter. In this case, which is not part of the claimed invention, a suction line <NUM> for leading refrigerant in the heat pump circuit from the evaporator <NUM> to the compressor <NUM> is used to cool the electronics, as shown in <FIG> illustrating the heat pump arrangement as seen from the rear of the tumble dryer. This suction line <NUM> is led out of the insulating shell <NUM> to provide an external loop. The electronics may be attached to a heat sink block <NUM> through which the suction line <NUM> passes. Electronics to be cooled may be located on both sides of the heat sink block <NUM> as best seen in the side view of <FIG>.

<FIG> shows the same view as in <FIG> with the suction line <NUM> exposed, and <FIG> illustrates enlarged the portion C of <FIG>. With reference to <FIG>, the heat sink block <NUM> may comprise two halves that are fitted to enclose the suction line loop <NUM>. A groove suitable to enclose a part of the suction line may be machined into the heat sink block <NUM> halves, which may be a solid metal blocks, for instance made of aluminum. It is possible to provide a heat transferring paste in the grooves to increase heat conduction from the heat sink although this is not necessary. In this way, very effective transfer of heat from the heat sink block <NUM> to the suction line <NUM> takes place, and the electronics becomes very efficiently cooled. Additionally, the cool refrigerant flow in the suction line becomes heated before reaching the compressor, which improves the heat pump efficiency further.

<FIG> shows an alternative for cooling an inverter with a heat pump flow. In <FIG>, the rear wall of the insulating shell has been taken away to expose the interior of the heat pump arrangement. In this example, the inverter <NUM> electronics is attached to a heat sink block <NUM> which reaches through a wall of the insulating shell <NUM>. This allows the other end of the heat sink <NUM> to reach into the process air stream <NUM> inside the shell. Typically, the heat sink projects into the air stream between the evaporator and the compressor, i.e. in the cooler portion of the stream path. This as well provides efficient cooling of the inverter electronics and recycling of heat that would otherwise be lost in the tumble dryer. The inverter <NUM> electronics may be placed outside the shell <NUM> where humidity is lower.

It should be noted that the cooling arrangements illustrated in <FIG> may be useful also in tumble dryers with other drum configurations, such as tumble dryers with a drum outlet arranged at the tumble dryer door.

Returning to <FIG>, there is shown an opening <NUM> in the outer shell <NUM>. This opening <NUM> is located above the condenser <NUM> and connects the process air path <NUM> to the ambient space outside the shell <NUM> at this location. This means that any overpressure in the air flow reaching the drum <NUM> can be reduced, which is useful, since such overpressure could otherwise force humid air into devices, e.g. ball bearings or electronics, that should preferably be kept dry. As illustrated in <FIG>, a corresponding opening <NUM> may be provided in the outer housing <NUM> to let the hot air out of the tumble dryer.

<FIG> shows a tumble dryer drum <NUM>. The drum has a circular rear wall <NUM> with air inlet openings and a radial cylindrical wall <NUM> with air outlet openings in the indicated area <NUM>. This area may comprise a large number of openings/holes, together providing a significant outlet. It may be advantageous to locate the openings of the cylindrical part in the front part of the drum such that the air flow passes most of the drum's <NUM> space. However, as no outlet connected to the tumble dryer door <NUM> (cf. <FIG>) is needed, it is possible to run the air flow <NUM> through the drum <NUM> even if the door is temporarily opened. If for instance the user adds additional wet laundry to the drum <NUM> or withdraws laundry therefrom, the processes can be kept running, although suitably at a lower level. This reduces the number of starts/stops of the compressor and may improve its durability. When the door has been opened a predetermined period of time, the heat pump is switched off.

With a tumble dryer drum <NUM> flow that passes from rear inlet to outlets located in the outer cylindrical periphery of the drum, a filter <NUM> (cf. <FIG>) may be placed under the drum, and may take up a large part of the area between the drum and the filter arrangement. This allows the use of a large, high-capacity filter, and high process air flows. Further, as air is let out of the drum <NUM> through a considerable flow area comprised by the openings in the outlet area <NUM>, flow restriction can be reduced, as compared to where openings are arranged at the door. Additionally, the space outside the drum's cylindrical periphery almost as a whole can be used as a duct leading down to the lint filter under the drum <NUM>. In this way, the flow through the drum can be increased which is particularly useful in a high-capacity heat pump tumble dryer.

It may be preferred to locate <NUM>% or more of the outlet openings to the front half of the cylindrical portion of the drum.

<FIG> shows an enlarged portion B of <FIG>. There is shown a flow divider <NUM> that splits the refrigerant flow from the expansion valve <NUM> into a number of sub-flows <NUM> that are passed to different portions of the evaporator. As shown, the controllable expansion valve <NUM>, controlled electronically by means of a solenoid <NUM>, is connected to the flow divider <NUM> by means of a straight conduit <NUM>. This means that a less disturbed, more laminar flow will reach the divider <NUM>. As a result, the flow is more evenly divided between the sub-flows <NUM> that reach different parts of the evaporator <NUM>. It may be preferred that the conduit <NUM> is short, e.g. shorter than <NUM> to improve this effect further.

Claim 1:
Tumble dryer (<NUM>) comprising a housing (<NUM>), a drum (<NUM>) in the housing being accessible from a front side (<NUM>) of the housing and being rotatable about its center axis, a fan arrangement (<NUM>) for producing a flow of process air passing through the drum, and a heat pump for drying the process air before entering the drum, the heat pump comprising a compressor (<NUM>), a condenser (<NUM>), an expansion valve (<NUM>), and an evaporator (<NUM>) forming a refrigerant fluid loop, wherein the rotatable drum (<NUM>) comprises a circular rear wall (<NUM>), and wherein the compressor (<NUM>) is adapted to be run by an inverter (<NUM>), allowing the compressor output to be varied, characterised by said fan arrangement (<NUM>) being placed in the flow of process air between the drum (<NUM>) and the evaporator (<NUM>), wherein the flow of process air passes a filter (<NUM>) before reaching said fan arrangement (<NUM>),
the rotatable drum (<NUM>) comprising a radial cylindrical wall (<NUM>) with air outlet openings, wherein the inverter comprises a heatsink (<NUM>;<NUM>) cooled by heat pump flow, and wherein the heat sink (<NUM>) is cooled by the flow of process air leaving the evaporator (<NUM>), and
the expansion (<NUM>) valve being controllable.