DK2006437T3 - Dryer with heater in the heat pump circuit - Google Patents

Description

The invention relates to a laundry dryer according to the preamble of claim 1.

Laundry dryers of this type, in which the evaporator and the condenser of a heat pump circuit are used for cooling and heating, are characterized by a high efficiency.

In EP 1 884 586 a device of this type is described, which is equipped with an additional heater in the process circuit, which allows to increase the temperature rapidly in particular in the start phase. However, additional heaters of this type are disadvantageous because they create additional flow resistance in the process circuit, are susceptible to pollution and can lead to an ignition of fly-by fluffs.

In EP 1 650 343 a device is described, which has a heater between evaporator and compressor, used to avoid the sucking in of liquid medium by the compressor at the beginning of the process.

An objective of the present invention is therefore to provide a laundry dryer of this type, which has a high efficiency.

This objective is solved by the laundry dryer according to claim 1.

Accordingly, a heater is provided in the heat pump circuit. Thus, energy can be supplied to the system via the heat pump circuit, whereby no additional heater or only an additional heater of lower capacity is required in the process circuit.

The medium in the heat pump circuit can be heated easier than the air in the process circuit because smaller flow cross sections are present in the heat pump circuit. Additionally, the medium of the heat pump circuit is not contaminated by fluffs and the like, such that the problem of a clogging of the heater does not exist.

Additionally, the heater can be designed more compact and cheaper in the heat pump circuit than in the process circuit.

According to the claim, the heater in the heat pump circuit is arranged between the condenser and the evaporator. This is advantageous because there the medium is liquid there, such that a good heat transfer is reached. Even more advantageous is the arrangement of the heater between the throttling member and the evaporator, amongst others because in this case refrigerant directly evaporates due to the supplied heat power and in this way a high power can be supplied to the system.

The additional heater can be used by the controller of the device to increase the temperature in the heat pump circuit by the heater at the beginning of a drying phase. Furthermore, the controller can be adapted to activate the heater only when there is the risk that the compressor sucks in liquid medium in an operation phase after the start phase.

An additional heat exchanger is advantageously arranged in the heat pump circuit additionally to the heater, by means of which heat can be removed from the heat pump circuit.

Further preferred embodiments result from the dependent claims and from the now following description by means of the figures. These show:

Fig. 1 a block diagram of the most important components of a first embodiment of the laundry dryer and

Fig. 2 a block diagram of a second embodiment of the laundry dryer.

The device according to Fig. 1 (the embodiment according to Fig. 1 is not claimed) has a drum 1 for receiving the laundry to be dried. A process circuit is provided (which is shown in Fig. 1 by continuous lines) in which heated process air is conducted through the drum 1, then cooled and then reheated again and conducted back to the drum 1. A fan 10 serves to recirculate the process air.

Furthermore a heat pump circuit is provided (wherein the path of the medium pumped by the heat pump circuit is shown by dotted lines in Fig. 1). The medium is pumped from a compressor 2 to a condenser 3, from there to an additional heat exchanger 4, then via a throttling member 5, e.g. in form of a capillary or of an expansion valve, to an evaporator 6 and then via a heater 9 again back to the compressor 2. The evaporator 6 serves to cool the process air and to extract water from it in this way, while the condenser 3 serves to reheat the process air such that it can absorb new water.

As further shown in Fig. 1, a fan 7 is provided, by means of which ambient air is conducted over the additional heat exchanger 4 for cooling it.

The additional heat exchanger 4 serves to extract heat from the heat pump circuit and therefore from the whole system and to release it to the ambient air. Preferably, the amount of extracted heat is controlled depending on the temperature in the heat pump circuit (and/or depending on the temperature in the process circuit), e.g. by operating the fan 7 with higher power if the temperature increases. The function and the operation of the additional heat exchanger are described in detail in EP 1 884 586.

Preferably, the temperature T1 of the medium circulating in the heat pump circuit after the additional heat exchanger 4 and before the throttling member 5 is used to control the fan 7. However, another temperature of the process circuit or of the heat pump circuit can also be used, for example the one of the medium before the additional heat exchanger 4.

For controlling the fan 7 the device has a correspondingly adapted controller 8 and appropriate temperature sensors 40, 41. Preferably, at least the temperature TI is measured at the entrance of the throttling member 5.

The heater 9 is preferably adapted as an electric heater (i.e. resistance heater), which is arranged e.g. on the outside of the tube of the medium and heats it directly. It is activated by the controller 8 depending on the particular process phase and the process parameters.

The heater 9 has two functions which can be used individually or in combination in a specific embodiment of the device.

On the one hand the heater 9 serves to supply the system with heat energy in the start phase. Thereby the temperatures required for an efficient drying can be reached faster, such that the time required for drying the laundry can be reduced. Therefore, the compressor works in an optimal range practically from the beginning. The heat which is supplied by the heater 9 to the medium, is pumped to a higher temperature level by the compressor. Thereby the process circuit is heated from the beginning with full heating power via the condenser 3.

On the other hand the heater 9 serves to avoid that the compressor 2 sucks in liquid medium in the operation phase, after the start phase. Sucking in liquid medium can lead to a damage of the compressor and is therefore undesired. Thus, an optimal overheating at the suction gas can always be guaranteed (no liquid). However the overheating buffer can be designed small because the heater 9 is able to increase the temperature T2 of the compressor 2 rapidly, if necessary.

For supplying energy in the start phase, the heater 9 is activated by the controller at the beginning of the process, and indeed always if the temperature T2 of the liquid entering the compressor 2 lies below a predefined "sucking temperature range". The "sucking temperature range" is the temperature range in which the temperature T2 lies in the operation phase, i.e. after the end of the start phase. Typically the device is adapted such that the sucking temperature range lies approximately between 20°C to 45°C. In the condenser 3 the temperature is in this case e.g. around 75°C and in the evaporator e.g. about 25°C, such that an efficient water removal is possible in the process circuit.

The start phase can last a fixed preset time, for example about 10 minutes. The start phase may also be ended already beforehand, if a temperature in the process circuit or in the heat pump circuit has reached a threshold value, particularly if the temperature T1 (or another temperature between the condenser 3 and the evaporator 6) has reached such a threshold value. This threshold value lies e.g. between 60 and 70°C for the temperature T1.

After the start phase, the heater 9 is only activated by the controller 8 if the risk exists that the compressor 2 sucks in liquid medium. As described in EP 1 884 586, it is possible to estimate that risk by monitoring the temperatures T1 and T2. Particularly it is shown that the temperature difference

is a measure for that risk. Particularly, the temperature difference ΔΤ can be compared with the temperature T2, as described in EP 1 884 586. Therefore, the controller 8 preferably compares the temperature difference ΔΤ with the temperature T2 in order to decide if the heater 9 shall be activated. Particularly it can activate the heater 9 always and only if the condition T1 - T2 > k-T2 is fulfilled, wherein k lies between 0.1 and 10, preferably k = 1, and wherein T1 and T2 are given in °C.

Thereby, T1 preferably corresponds to the temperature of the medium between the condenser 3 and the evaporator 6, particularly between the condenser 3 and the throttling member.

On the other hand the temperature T2 is the temperature between heater 9 and compressor 2. Generally another temperature value in the heat pump circuit between the evaporator 6 and the compressor 2 can be used as well.

In the embodiment described so far the heater 9 is arranged between the evaporator 6 and the compressor 2. This arrangement is advantageous for various reasons: a) The temperature of the medium is low between the evaporator 6 and the compressor 2, such that the medium can be heated there efficiently. b) If the risk exists that the compressor 2 sucks in liquid medium, the temperature of the sucked medium can be influenced directly and quickly.

But even more advantageous is the arrangement of the heater between the condenser and the evaporator, because the medium is liquid in this area, such that an efficient heat transfer can occur because the thermal transmittance coefficient to the liquid medium is greater than to the suction gas.

The arrangement as shown in Fig. 2 is particularly advantageous, wherein the heater 9 is arranged between throttling member 5 and evaporator 6, because in this area refrigerant directly evaporates with the supplied heat and more power can be supplied to the system in this way.

The suction gas temperature is not increased (at least not above the process air temperature) in this embodiment (in contrast to the embodiment according to Fig. 1) and therefore the mass flow of the refrigerant is not reduced. There is even an increase of the evaporation pressure, whereby the mass flow of refrigerant can be increased. Thereby the laundry dryer can be driven to operation temperature more rapidly.

In contrast to that, the embodiment according to Fig. 1 has the disadvantage that the heating power is supplied to the nearly or even fully gaseous medium, whereby it heats strongly without absorbing very large amounts of energy (no phase change). The supplied power is limited in this case by the rapidly increasing gas temperature (relatively small heat capacity). At the same time the mass flow of refrigerant decreases because the density of the suction gas decreases (the evaporation pressure can hardly be influenced in this variant).

But basically an arrangement of the heater 9 between the compressor 2 and the condenser 3 is also possible (not claimed). This arrangement has the advantage that the danger of overheating of the compressor 2 is smaller. In this case it should be payed attention that the medium fully condenses out in the condenser 3 despite heating operation. For this, one or more temperatures can be monitored between the heater 9 and the additional heat exchanger 4. Preferably, the temperature difference between the condenser 3 and the medium after the condenser 3 and before the additional heat exchanger 4 is monitored: if this temperature difference falls below a preset value of e.g. 3°K, this is an indication that no complete condensation occurs, in which case the power of the heater has to be reduced.

Preferably, as mentioned, the power of the heater 9 is limited in the start phase via the temperature T2 and the length of the start phase via the temperature T1 or the time. However, a limitation of the heater 9 via another temperature in the heat pump circuit is basically possible too. However, the limitation via the temperature T2 has the advantage that it can be responded quickly to a threatening overheating of the compressor by comparing the temperature T2 with an upper limit by the controller 8 and, when reaching the upper limit, an activation of the heater 9 can be suppressed.

The heater 9 can be controlled in a single-stage, multistage or continuous (analogue) manner. It can also be operated in pulse mode. It is dimensioned such that it can supply sufficient heat power to the system. For example it can have a maximal power of 1000 Watt, compared with the compressor power of e.g. 700 - 1000 Watt.

The present invention can be applied independently of the medium used in the heat pump circuit. The exemplary embodiment described here works e.g. with R134a, but the same principle can be applied in case of a C02-circuit when dimensioned accordingly.

Claims (11)

1. Dryer with a control unit (8), a drum (1) for receiving clothes to be dried, a process circuit for passing heated process air through the drum (1), for cooling the process air for extraction of water and for reheating of the process air, a heat pump circuit for passing a medium through a capacitor (3), a throttle member (5), an evaporator (6) and a compressor (2) back to the capacitor (3) where the process air can be heated with the capacitor (3) and the process air can be cooled with the evaporator (6), where a heating element (9), which is an electric heating element, is arranged in the heat pump circuit, characterized in that the heating element (9) is arranged in the heat pump circuit between the capacitor (3) and the evaporator (6). The dryer according to claim 1, wherein the heater (9) is arranged in the heat pump circuit between the throttle member (5) and the evaporator (6). Dryer according to one of the preceding claims, in which an additional heat exchanger (4) is arranged in the heat pump circuit in addition to the heater (9), with which heat can be extracted from the heat pump circuit. A dryer according to claim 3, wherein the auxiliary heat exchanger (4) is arranged between the capacitor (3) and the throttle member (5). Dryer according to one of the preceding claims, wherein the controller (8) is designed to activate the heater (9) when there is a risk of the compressor (2) sucking in liquid medium, the controller (8) being designed to activating the heater (9) depending on a temperature difference ΔΤ, where ΔΤ = T1 - T2, where T1 is a temperature of the medium between the capacitor (3) and the evaporator (6), especially between the capacitor (3) and the throttle member (5), and where T2 is a temperature of the medium between the evaporator (6) and the compressor (2). The dryer according to claims 3 and 5, wherein T1 is a temperature of the medium between the auxiliary heat exchanger (4) and the throttle member (5). Dryer according to one of claims 6 or 7, wherein T2 is a temperature of the medium between the heater (9) and the compressor (2). Dryer according to one of claims 5 to 7, wherein the control unit (8) is designed to compare ΔΤ with the temperature T2 to determine whether the heater (9) is to be activated, and in particular if the control unit (8) is designed thereto, activate the heater (9) when the condition T1 - T2> k-T2 is met, with T1 and T2 in ° C and k = 0.1 to 10 in particular k = 1. Dryer according to one of claims 5 to 8, wherein the control unit (8) is designed to raise, during a start-up phase at the beginning of a drying process, the temperature of the medium in the heat pump circuit with the heater (9) and in an operating phase, after the start-up phase, to activate the heater (9) only when there is a risk of the compressor (2) sucking in liquid medium. The dryer according to claim 9, wherein the device is designed such that the start phase is terminated after a fixed predetermined period of time and / or at the latest when a temperature in the process circuit or the heat pump circuit has reached a threshold, especially when a temperature of the medium between the capacitor (3) and the evaporator is reached. (6) exceeds a threshold of between 60 and 70 ° C. Dryer according to one of the preceding claims, wherein the control unit (8) is designed to compare a temperature (T2) between the heater (9) and the compressor (2) with an upper limit and suppress an activation of the heater (9) when the upper limit is reached.