EP2134897B1 - Dryer with heat recovery and method of operation thereof - Google Patents

Abstract

A dryer is provided having a drying chamber for items to be dried and a process air duct in which are located a heater for heating the process air, a blower for driving the process air from the heater through the drying chamber, and a heat exchanger arrangement. Via the heat exchanger arrangement, heat can be withdrawn from the process air flowing away from the drying chamber, and the process air flowing toward the heater can be fed to the heat exchanger. The process air duct is divided into a main duct and a secondary duct, the secondary duct having an evaporator in which condensate that was separated from the process air in the heat exchanger arrangement can be evaporated into the process air flowing therethrough and is connected to the exhaust opening.

Description

The invention relates to a dryer with a drying chamber for the objects to be dried and a process air duct in which a heater for heating process air and a fan for driving the process air from the heater through the drying chamber and a heat exchanger assembly are through which heat exchanger assembly of the Drying chamber effluent process air heat-extractable and the process air flowing to the heating process can be supplied, wherein the process air duct has a Zuluftöffnung for drawing process air from an environment of the dryer and an exhaust port for expelling process air into the environment of the dryer.

The invention also relates to a method for operating such a dryer.

Such a dryer and such a method are apparent from the EP-A-1541744 as well as from the DE 30 00 865 A1 ,

In general, a tumble dryer is operated as a vented dryer or as a condensation dryer. An exhaust air dryer passes heated air once through the laundry to be dried and carries this moisture-laden air through an exhaust hose from the exhaust air dryer and from the room in which it is placed. A condensation dryer, the operation of which is based on the condensation of moisture evaporated by means of warm process air from the laundry, requires no exhaust hose and allows energy recovery from the heated process air, for example by using a heat pump. However, with such a condensation dryer it is generally necessary to collect the accumulated condensate and either pump it off or dispose of it by manually emptying collection containers.

In the DE 40 23 000 C2 a tumble dryer is described with a heat pump circuit, in which a supply air opening is arranged in the process air channel between the condenser and the evaporator, which is closable with a controllable closure device.

By contrast, in the case of an exhaust air dryer, the air laden with moisture after passing through a laundry drum is generally passed out of the dryer. Compared to a condensation dryer, an exhaust air dryer can be made simpler and thus cheaper. An exhaust air dryer draws air from its environment during operation and uses it directly for drying. Such ambient air is usually relatively dry with a relative humidity of significantly less than 100%, and therefore can absorb a relatively large amount of moisture. By comparison, the circulating process air in a condensation dryer can generally only be dehumidified to 100% relative humidity at the lowest temperature present in the process air cycle, which limits its ability to absorb moisture from the objects to be dried and thus imposes some restrictions on the drying process.

Even in an exhaust air dryer heat recovery is basically possible, however, any such heat recovery implies a cooling of the exhaust air, whereby condensate can fail from the exhaust air and should be disposed of.

The DE 30 00 865 A1 discloses a clothes dryer with heat recovery. The tumble dryer consists of a container receiving and moving the laundry, into which a supply air flow heated by a heating element opens, while the moist warm air is conducted as exhaust air via an outlet. In the supply air flow, a heat exchanger is arranged in front of the heating element, which is flowed through by the moist hot exhaust air from the container. The tumble dryer is designed as a vented dryer.

In an exhaust air dryer with heat recovery, ambient air (of, for example, 20 ° C. and 60% relative humidity, so-called supply air) normally flows into the heat exchanger surfaces of an air-to-air heat exchanger and is heated there by cooling the warm process air coming from the drying chamber. Depending on the cooling capacity or the heat exchange, condensate is produced, which is collected or pumped away in a container. In the first case an emptying is necessary and in the second case a connection to the sewage network. The amount of accumulating condensate is a measure of the heat energy emitted in the heat exchanger and thus a measure of the improvement of energy efficiency.

The object of the present invention is therefore to provide a dryer with high energy efficiency, in which it is unnecessary to pump off condensate formed or to collect in a condensate collecting container for later disposal.

The solution of this object is achieved according to this invention by a dryer with the features of claim 1 and the method of claim 10.

Preferred embodiments of the dryer according to the invention are listed in the subclaims 2 to 9. A preferred embodiment of the method according to the invention is listed in claim 11. In general, preferred embodiments of the dryer according to the invention correspond to embodiments of the method according to the invention, even if reference is not made in detail below.

The invention thus relates to a dryer with a drying chamber for the objects to be dried and a process air duct in which a heater for heating process air and a fan for driving the process air from the heater through the drying chamber and a heat exchanger assembly are through which heat exchanger assembly of The process air duct has a Zuluftöffnung for drawing process air from an environment of the dryer and an exhaust port for expelling process air into the environment of the dryer, characterized in that the process air duct branched between the drying chamber and the heat exchange arrangement in a main channel and a secondary channel, wherein the main channel leads to the heat exchange arrangement and the secondary channel leads past the heat exchange arrangement and a Evaporator contains on which condensate, which was deposited in the heat exchange arrangement of the process air, is evaporable into the process air flowing through, and is connected to the exhaust port.

The condensate separated during drying in this dryer is a measure of the return of heat energy in the drying process. Starting from the

Energy balance of an exhaust air dryer without recirculation of heat, the return of heat in particular be sized and adjusted by appropriate design of the dryer that a predetermined improvement in energy balance is achieved, for example, an improvement by which a classification of the dryer in a desired, compared to the Exhaust air dryer, which is expected to be better energy consumption class according to the usual system in the European Union would be possible. In this context, it may be disregarded to seek a deposition of a maximum of moisture in the heat exchanger assembly. To improve an energy consumption class from C for the simple exhaust air dryer to B for the heat recovery exhaust air dryer, it may be sufficient to strive to deposit no more than 10 grams of condensate per minute. This poses the problem of storing a larger amount of condensate as in the condensation dryer not. Incidentally, it would also be conceivable for a fan of the dryer arranged behind the heat exchanger arrangement to continue after completion of a drying process in order to create an air flow for evaporating any remaining condensate. Also a small separate blower for this application would be conceivable. Finally, depending on the design of the dryer to evaporate any remaining condensate and a draft can be exploited, resulting, for example, by a chimney effect, in the unused dryer. In operation, in particular the drying chamber must be sealed against the environment of the dryer to allow an undisturbed, intended flow of process air. For this purpose, the drying chamber is closed by means of a corresponding door. Apart from such use, this door is usually open and thus also opens the process air duct to the environment of the dryer. A draft of air through the process air duct, including the secondary duct and the open door, can effectively aid in the evaporation of residual condensate in the bypass duct.

In a preferred embodiment of the dryer according to the invention, the main channel is connected to the exhaust air opening behind the heat exchanger arrangement, and the process air channel is connected to the supply air opening before the heat exchange arrangement. Such is the dryer according to the invention, in which in principle an at least partial circulation of the process air is not excluded, perfected as exhaust air dryer.

Preferably, the secondary channel is designed so that it allows the diversion of at most 50 vol .-%, preferably 20 to 40 vol .-%, most preferably 25 to 35 vol .-% of a process air flow in the process air duct after the exit from the drying chamber.

In the evaporation channel is preferably a wettable by the condensate body with a large surface area, such as a non-woven, with which the secondary channel is designed.

The heat exchanger arrangement in the dryer according to the invention preferably has an evaporator and a condenser of a known heat pump circuit, wherein such a heat pump circuit is designed according to the principle of the compressor heat pump. In a dryer equipped with such a heat pump, the cooling of the warm, moisture-laden process air essentially takes place in the evaporator of the heat pump, where the heat transferred is used to evaporate a refrigerant used in the heat pump cycle. The refrigerant of the heat pump evaporated due to the heating is supplied via a compressor to the condenser of the heat pump, where due to the condensation of the gaseous refrigerant heat is released, which is used for heating the process air. The refrigerant circulates in a closed circuit in which it passes from the condenser via a throttle back to the evaporator. In principle, any heat pump can be used. An advantage of the heat pump is that temperature levels for cooling or heating of the process air can be selected with some independence from each other, whereby the energy balance of the dryer under certain circumstances can be further improved; the additional equipment is, however, considerable.

In a preferred embodiment of the dryer according to the invention with a heat pump, the condenser of the heat pump is located in the process air duct between the blower and the heater or between the blower and the supply air opening.

Also preferably, the heat exchange arrangement is a single heat exchanger, in particular an air-to-air heat exchanger, in which the moist, hot process air from the drying chamber (drum) is used for heating supply air, which in turn is then fed to the drying chamber.

Particularly preferred is an embodiment of the dryer, wherein the secondary channel is adapted to store condensate. It is assumed that the absorption capacity of the process air flowing through the auxiliary channel during operation of the dryer for additional moisture is not always the same. At the beginning of the drying process, when the objects to be dried first have to heat up, the process air flow in the drying chamber still absorbs little moisture and can therefore take up and remove condensate that is left over from a previous drying process. In the middle of the drying process, the process air flow removes a relatively large amount of moisture from the objects to be dried and therefore can absorb less condensate; So it is advantageous if condensate, which can not be evaporated immediately, can initially remain stored. Towards the end of a drying process, when the objects to be dried have already given off a relatively large amount of moisture, the process air flow again becomes drier and at the same time warmer, and can therefore again absorb and remove condensate. If not all of the condensate can evaporate, a certain amount may remain stored until a subsequent drying process or be evaporated separately, as described above.

The invention also relates to a method for operating a dryer with a drying chamber for the objects to be dried and a process air duct in which a heater for heating process air and a blower for driving the process air from the heater through the drying chamber and a heat exchanger assembly, through which heat exchanger arrangement the heat withdrawn from the drying chamber process air heat withdrawn and supplied to the heating process air, process air is drawn through an air inlet from an environment of the dryer in the process air duct and ejected through an exhaust vent in the environment of the dryer, according to the invention, the process air branched between the drying chamber and the heat exchange arrangement in a main channel and a secondary channel, wherein the main channel carries a first process air stream to the heat exchange arrangement and the side channel passes a second process air stream past the heat exchange arrangement to a vaporizer at which condensate precipitated in the heat exchange arrangement from the first process air stream is evaporated into the second process air stream and to the exhaust air opening ,

In the method according to the invention, the first process air stream is preferably at most 50% by volume, more preferably from 20 to 40% by volume, and the second partial process air stream at least 50% by volume, more preferably from 60 to 80% by volume, of the process air stream before the decomposition ie after the exit from the drying chamber.

The cooled process air leaving the heat exchange arrangement can be reheated and returned to the drying chamber. Alternatively, the cooled process air can be passed as exhaust air via an exhaust port from the dryer. In this case, the process air fed into the drying chamber consists exclusively of heated supply air. The heating of the supply air takes place here at least partially by heat exchange with the process air from the dryer and / or with the refrigerant in the condenser of a heat pump.

According to the invention, it is preferred if process air, supply air and / or refrigerant in the heat pump are each guided in a cross-flow or countercurrent process through the corresponding heat exchangers.

As the degree of drying of the objects to be dried in the condenser dryer decreases the energy required for drying, it is appropriate to regulate the heating accordingly, that is. with increasing degree of drying to reduce their heat output.

The dryer according to the invention has the advantage that it is in a better energy efficiency than a corresponding dryer without heat recovery and accumulating condensate can be transported without the need for a sump or pump to be emptied only by removal by means of process air to the outside.

• Fig. 1 eine Skizze für ein erstes Ausführungsbeispiel eines Trockners mit Wärmerückgewinnung; und
• Fig. 2 eine Skizze für ein zweites Ausführungsbeispiel eines Trockners mit Wärmerückgewinnung.

Further details of the invention will become apparent from the following description of preferred, non-limiting embodiments for the dryer and for operating this dryer usable method. In detail show:

• Fig. 1 a sketch for a first embodiment of a dryer with heat recovery; and
• Fig. 2 a sketch for a second embodiment of a dryer with heat recovery.

The in Fig. 1 Dryer 1 shown as a sketch has a process air channel 2 and a drying chamber 3, which is a drum 3 rotatable about an axis 4. Process air is guided by means of a blower 5 via a heater 6 through the drum 3 and a lint filter 7. The process air is drawn in through a supply air opening 8 and pushed out through an exhaust air opening 9. In the supply air opening 8 air passes directly from an environment of the dryer 1. At the exhaust port 9 is connected an exhaust hose 10, with which the exhaust air from the dryer 1 away and from a room in which it is placed, is discharged. In addition, a heat exchange arrangement 11, 12 is present; In her or the corresponding inlet channel 12 of the retracted through the supply air 8 process air heat is transferred from the effluent from the drum 3 and the lint filter 7 process air. After passing through the drum 3 so the moist, warm process air is cooled; however, the process air to be supplied to the heating system is preheated. The fully heated by the heater 6 process air is fed into the drum 3, where it comes into contact with the laundry to be dried and then flows to the lint filter 7. Then, the process air stream branches; a main part passes into the main channel 11, which leads through the heat exchanger f11, 12, where it gives off heat to freshly drawn supply air, which flows through the inlet channel 12 of the heat exchange arrangement 11, 12. As I said, the amount of heat transferred must be measured on the basis of a concrete specification with regard to the energy balance of the dryer 1 and does not necessarily correspond to the full amount of heat available in the main duct 11. One of the findings derived from this is that the full stream of process air flowing out of the drum 3 does not have to be used for heat exchange. Therefore, it is possible to use a part of the process air flow to condensate, which during cooling the process air in the main channel 11 is incurred to dispose of. For this purpose, a secondary channel 13 is provided in which a corresponding part of the process air is introduced past the heat exchange arrangement 11, 12. Condensate, which is obtained in the main channel 11, passes through a corresponding channel 14 to the secondary channel 13. For transporting the condensate expediently a natural gradient, which can be formed by appropriate construction of the main channel 11 and an arrangement of the secondary channel 13 under the main channel 11, exploited , The first branch 15 in the process air duct 2, at which the process air stream is divided into a first process air stream to the main channel 11 and a second process air stream to the secondary channel 13, is so dimensioned that the second process air stream comprises about 30% of the total available process air. In the secondary channel 13, the second process air stream absorbs evaporating condensate and reunites at the second branch 16 with the first process air stream. In the secondary channel, a evaporator 17 is designed in the form of a nonwoven 17; the fleece 17 absorbs the condensate and, supported by its relatively large surface area, discharges it to the second stream of process air flowing past it.

In FIG. 2 a second embodiment is shown, but the components of the dryer 1 above the fan 5 and the lint filter 7 are not shown; they correspond to the components according to FIG. 1 ,

The essential difference from the embodiment according to FIG. 1 is that the heat exchange arrangement 11, 12 is not in a simple countercurrent or cross-flow heat exchanger 11, 12, but is formed by an evaporator 11 and a condenser 12 of a heat pump 11, 12, 18, 19, 20, which in addition a compressor 18th , a throttle 19 and a conduit system 20 for a recirculating and cyclically vaporized, to be compressed, to be liquefied and to be expanded refrigerant. The main channel 11 and the sub-channel 13 function as in the dryer 1 of the embodiment according to FIG. 1 However, the heat pump 11, 12, 18, 19, 20 allows a freer adjustment of the temperature level in the main channel 11 and the inlet channel 12, and thus offers further options for optimizing the energy balance of the dryer. 1

Although the embodiments of the invention show exhaust air dryer, it should be noted that the invention is not limited to exhaust air dryer, but in particular also includes those dryers that circulate the process air in any case in part. In any case, a dryer according to the invention allows at least partial recovery of thermal energy that would otherwise be lost to the drying process. This can, but does not have to, use a heat pump. Therefore, the invention is also attractive from an economical point of view, particularly, but not exclusively, in an exhaust air dryer.

Claims (11)

1. Dryer (1) with a drying chamber (3) for the articles to be dried and a process air channel (2), in which a heating means (6) for the heating of process air and a fan (5) for driving the process air from the heating means (6) through the drying chamber (3) as well as a heat exchanger arrangement (11, 12) are disposed, by which heat exchanger arrangement (11, 12) the heat is extractable from process air flowing out of the drying chamber (3) and can be fed to the process air flowing to the heating means (6), wherein the process air channel (2) has an air inflow opening (8) for induction of process air from an environment of the dryer (1) and an air outflow opening (9) for expulsion of process air into the environment of the dryer (1), characterised in that the process air channel (2) is branched between the drying chamber (3) and the heat exchange arrangement (11, 12) into a main channel (11) and a secondary channel (13), wherein the main channel (11) is led to the heat exchange arrangement (11, 12) and the auxiliary channel (13) bypasses the heat exchange arrangement (11, 12) and includes an evaporator (17), at which condensate, which was separated in the heat exchange arrangement (11, 12) from the process air, can be evaporated in the throughflowing process air, and is connected with the air outflow opening (9).
2. Dryer (1) according to claim 1, characterised in that the main channel (11) is connected behind the heat exchange arrangement (11, 12) with the air outflow opening (9) and that the process air channel (2) is connected in front of the heat exchange arrangement (11, 12) with the air inflow opening (8).
3. Dryer (1) according to claim 1 or 2, characterised in that the auxiliary channel (13) is so designed that it causes branching off of at most 50 volume percent of a process air flow in the process air channel (2) after the outlet from the drying chamber (3).
4. Dryer (1) according to claim 3, characterised in that the auxiliary channel (13) is so designed that it causes branching of 20 to 40 volume percent of a process air flow in the process air channel (2) after the outlet from the drying chamber (3).
5. Dryer (1) according to any one of claims 1 to 4, characterised in that the evaporator (17) is a body (17), which is wettable by the condensate, with a large surface.
6. Dryer (1) according to claim 5, characterised in that the body (17) is a nonwoven material.
7. Dryer (1) according to any one of the preceding claims, characterised in that the heat exchange arrangement (11, 12) comprises an evaporator (11) and a condenser (12) of a heat pump circuit (11, 12, 22, 23).
8. Dryer according to any one of the preceding claims, characterised in that the heat exchange arrangement (11, 12) is a single heat exchanger (11, 12).
9. Dryer according to any one of the preceding claims, in which the auxiliary channel (13) is equipped for storage of condensate.
10. Method of operating a dryer (1) with a drying chamber (3) for the articles to be dried and a process air channel (2), in which a heating means (6) for the heating of process air and a fan (5) for driving the process air from the heating means (6) through the drying chamber (3) as well as a heat exchanger arrangement (11, 12) are disposed, by which heat exchanger arrangement (11, 12) the heat is extracted from process air flowing out of the drying chamber (3) and is fed to the process air flowing to the heating means (6), wherein process air is inducted from an environment of the dryer (1) into the process air channel (2) through an air inflow opening (8) and is expelled into the environment of the dryer (1) through an air outflow opening (9), characterised in that the process air is branched between the drying chamber (3) and the heat exchange arrangement (11, 12) into a main channel (11) and a secondary channel (13), wherein the main channel (11) guides a first process air flow to the heat exchange arrangement (11, 12) and the auxiliary channel (13) guides a second process air flow past the heat exchange arrangement (11, 12) to an evaporator (17) at which condensate, which was separated in the heat exchange arrangement (11, 12) from the first process air flow, is evaporated in the second process air flow, and fed to the air outflow opening (9).
11. Method according to claim 10, characterised in that the first process air flow is 20 to 40 volume percent of the process air before the branching.

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