WO2008025377A1

WO2008025377A1 - Humidity control of an electrical device

Info

Publication number: WO2008025377A1
Application number: PCT/EP2006/065920
Authority: WO
Inventors: Mikael Johansson; Torbjörn Nilsson
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2006-09-01
Filing date: 2006-09-01
Publication date: 2008-03-06
Also published as: CN101506590A; EP2057421A1; US20110030388A1; JP2010502020A; CN101506590B; JP4938851B2

Abstract

The invention relates to a device 2 and a method for dehumidifying and control of humidity inside an enclosure 1 comprising electrical equipment. The device 2 comprises a heating element 3 located to be in contact with the ambient air of the exterior of the enclosure 1 and a cooling element 4 located to be in contact with the ambient air of the interior of the enclosure 1. Dew condensed at the cooling element 4 is guided to the heating element 3 so that humidity from the air, condensed at the cooling element 4, may be transported to the heating element 3 to be vaporised wherein the water guiding means comprises a capillary structure 6. In still another aspect of the invention, the functionality of the heating and cooling elements may be switched so as to reverse the flow of water and provide a humidity control arrangement.

Description

HUMIDITY CONTROL OF AN ELECTRICAL DEVICE

TECHNICAL FIELD

The invention relates to a device and a method for dehumidifying and control of humidity inside an enclosure comprising electrical equipment.

BACKGROUND

Electric equipment which is intended to be located where it might be exposed to humid environment or water is often protected by a waterproof enclosure. However, there might be small entrances, e.g. gaps, small holes or diffusive leakages, through which water might enter into the enclosure. To make these cabinets completely waterproof is often a costly procedure and in many cases water, e.g. mist or humid air, may enter into the cabinet already when the product is brand new. Even if the products are made completely waterproof they may be defect due to degradation at normal use, unexpected impacts or violence on the product or exposure to the environment, e.g. sun, wind and rain, which may lead to a degradation of the water proof protecting system so that water or humid air may enter into the cabinet. There is also a risk that moisture or water will come into the cabinet when it is opened for maintenance work. For whatever reason moisture is trapped inside the cabinet, the moisture will cause corrosion problems inside the cabinet if the humidity not is controlled.

The size of the cabinet intended to be dehumidified by the present invention may be in a wide range of varying sizes, e.g. from 2 to 500 litres (0,002 to 0,500 cubic metres). These sizes represent a large number of different low power dissipating equipment for which a long term corrosion protection is desired. For dehumidification of equipment of such sizes as discussed above, it is usually difficult to install dehumidification or ventilation devices generally used in the field of dehumidification. These devices usually comprise some kind of active dehumidification unit, e.g. heating elements, fans and venting conduits, and are in general rather bulky and hard to fit into small spaces. The rather complex construction of such a system also makes them expensive and an advanced construction further contributes to a risk that something in the construction may malfunction and need to be serviced at irregular times in order to work. In many cases, the cabinets for which the dehumidification device is intended to be used are located at inconvenient places or distant from the maintenance personal which makes such maintenance work costly and time consuming.

As of today, one commonly used type of protection for the inside of an enclosure, comprising electric equipment, is to use watertight seals and attach a drying capsule with an absorbent which absorbs the moisture inside the enclosure. This way of making the equipment make the freedom in designing the enclosures of the equipment rather limited since it is important that the sealings are diffusion tight in order to have a low maintenance cost. In such a system, it is often hard to know how to dimension the dehumidification device in order to not become unnecessary space requiring while still having a sufficient load capacity in order to not need to be changed to often. In order to function in a desired manner there is either a need for some kind of indicating system which indicates when the absorbent is full or some kind of regular service when the absorbent shall be checked and may be switched if desired. In either case there is a need to physically open the enclosure and replace the dehumidification capsule. Regardless of how such a dehumidification device is dimensioned there will always be a maintenance need to regularly exchange the drying capsule in order to keep the moisture level in the enclosure below acceptable levels. The long-term cost will therefore be high due to the need of maintenance personnel to check the capsule on site and perform a change when necessary.

There have been suggested some other solutions to the problem with moisture associated with electric equipment which do not involve a drying capsule. One solution is described in US 6,196,003 in which a heating element is used for dehumidifying oil filled electrical apparatuses in order to protect the oil from water. In DE 25 349 09 a dehumidification system for a substation for a mobile network connection is described. According to the idea disclosed therein, a sensor is used as dew point detector which switches on a heater in the substation when dew is detected. However, it is not disclosed how the moisture is removed in these systems but merely how they prevent the moisture from condensing and thus not provides a dehumidified environment for the electrical equipment.

Also EP 368 382 describes a device for dehumidification of an enclosure comprising electrical equipment in which the moisture is removed from the inside of the enclosure. In this device, a cooling element is located to be in contact with the air inside and condense dew from the inside air to be collected in a receptacle wherefrom it is allowed to be guided through a conduit out of the enclosure. However, this device will probably not work very efficient unless there are quite large amounts of water to be condensed. In case there are small amounts of water to be condensed, there will most probably be a problem of transporting the condensed water to the outside. First, in order to make the droplets to fall down into the receptacle, they need to be of a certain size before they will start to travel down by gravity for example. Furthermore, if the outlet conduit is too small, the water may adhere to the inside of the conduit due to capillary forces. On the contrary, if the conduit is too big, moisture in the form of humid air may enter into the enclosure from the outside.

Hence, there is a need for a better dehumidification unit which is still rather small to be fitted into the enclosure without any major modifications. Preferably, the dehumidification shall be able to work continuously without any necessary periodical maintenance work. Even more preferably, the dehumidification unit will allow the enclosure to not necessarily be completely water tight in all sealing so as to allow a greater freedom of design and avoiding a need of over duly precision in the manufacture of the enclosure and its connecting edges. Furthermore, there is a need for an improved dehumidification system which will work satisfactorily in transporting the condensed water from the inside to the outside of the enclosure.

SUMMARY

The present invention provides an improved device and method in order to achieve a satisfactory dehumidification of the inside of an enclosure comprising electrical equipment so as to prevent corrosion due to water or mist present in the enclosure. According to the invention, a dehumidifier comprising a heating element and a cooling element is mounted in connection with the enclosure in such a way that the cooling element is located to be in contact with the ambient air of the interior of the enclosure and the heating element is located to be in contact with the ambient air of the exterior of the enclosure. The dehumidifier is further provided with water guiding means which guides dew condensed at the cooling element to the heating element so that humidity from the air, condensed at the cooling element, may be transported to the heating element to be vaporised there. In order to provide an improved water transport, the water guiding means comprises a capillary structure.

This solution provides a simple arrangement for dehumidifying the air within a cabinet. The invention may be used for all kind of electrical equipment contained in a box or the like. One field of use may for example be base stations in a telecommunicating network.

According to an embodiment of the invention, the capillary structure is in contact with the heating element and adapted to guide water condensed at the cooling element to the heating element. The capillary structure may for example be a mat.

By using a capillary mat which is in contact with the heating element it will be possible to use the suction forces of the capillary mat to suck water to the heating element as water is vaporised at the same. An advantage by using capillary forces for the transport of water is that such a distributing system can work without being obliged to transport water by the use of gravity or any kind of pumping equipment. In this case, the water transport will mainly depend on the vaporisation rate which will free the capillaries at the heating element from water and thereby sucking new, condensed water to the heated capillaries. In this context, it is meant by "capillary mat" any kind of capillary structure which is able to suck a liquid by capillary forces.

In addition to have a first part of a capillary mat which covers at least a part of the surface of the heating element so as to vaporise condensed dew at the hot side, the dehumidifier may be provided with a second part of the capillary mat which covers at least a part of the surface of the cooling element so as to absorb dew condensed at the cold side. The first and second parts of the mat are connected to each other by water guiding means. In a certain embodiment, the water guiding means which connects the first part and the second part of the capillary mat may comprise a third part of the mat.

It shall be noted that the three parts of the mat may be either separate pieces or one entity comprising different regions. Furthermore, it might be advantageous to not provide the whole surface of the cooling element and/or the heating element with the mat. For example, allowing a part of the cooling surface not to be covered with the capillary structure will allow the condensing efficiency to increase since the cooling element will be in direct contact with the ambient air and not being insulated by the mat.

However, it is not necessary that the dehumidifier comprises the second and third capillary mat. In an alternative embodiment it may be possible to collect dew condensed at the cold side in a receptacle to which a part of the first capillary mat is in contact with. Preferably this receptacle is located below the cooling element so that the water will drop into the receptacle by means of gravity. The first capillary mat will then by capillary forces transport the collected water to the heating element whereby the dew is vaporised to the exterior of the enclosure.

In an embodiment of the invention, the heating element and the cooling element are formed as one entity having a first surface and a second surface wherein the heating element is located at the first surface and the cooling element is located at the second surface.

In a certain design, the surfaces are made as ordinary, flat surfaces. In this case, the element is preferably made as a relatively flat plate having the heating element and the cooling element located at opposite sides. In order to prevent heat transfer between the two sides, the plate may be provided with an insulation layer between the two sides.

To be noted, by surface is not necessary meant a flat , continuous structure but may for example on the micro structure scale comprise a porous structure, microfibers or fibers, wave shaped elements or of any desired shape having micro- structural irregularities. Furthermore, on the macro structural scale the elements may be spherical, cylindrical, concave or convex, flat with holes in it or of other geometrical shapes.

When the heating and cooling elements are constructed as one entity, the entity may comprise a peltier element which induces a heating element at one side and a cooling element at the other side. This embodiment provides the advantage of having one element which naturally creates a heating element and a cooling element when it is powered by DC.

In case the heating and cooling elements are constructed as one entity, e.g. a flat peltier element, wherein the first surface and the second surface are located opposite to each other, the third part of the capillary mat may be located at the outer side of the entity so as to guide water between the first part and the second part of the mat. This may be achieved by wrapping a capillary mat or structure around the entity (peltier element) so that the heating element, the cooling element and at least one edge part of the entity is covered by the mat. This provides an easy structure to produce and a relatively small element to be mounted to the enclosure.

In another embodiment, the cooling and heating entity is provided with one or several holes connecting said first, heating surface and said second, cooling surface. In this way, water may be guided from a first part of the mat located at one side through the holes to a second part of the mat located at the second side of the mat. A desired number of holes are preferably provided with a third part of the capillary mat in order to facilitate the transport of water from the cold side to the hot side.

In a similar embodiment as the one described above, i.e. an element comprising one or several holes connecting the first surface and the second surface of the cooling and heating entity, it is not necessary to provide the heating and cooling surfaces with a capillary mat but only the holes are provided with a capillary mat. However, the capillary mat in the holes are located in such a way that the capillary mat is in contact with the heating element and the cooling element within the holes so as to form one or several capillary columns for wicking of condensed water from the cold side to the warm side to be vaporised. It is of course also possible to make an embodiment which is a mixture of this embodiment and the foregoing one, i.e. to provide either the side comprising the heating element or the cooling element with a part of a capillary mat. For example, it might be favourable to provide the cold side with a capillary mat so as to absorb the condensed water in order to avoid water to drip from the cooling element and thus remain in the enclosure.

In the foregoing embodiments, the invention has been described as comprising a single element comprising both the heating element and the cooling element. It shall be noted that the principle of the invention will also work if the heating and cooling elements are separate units which are located at different locations. This might be favourable in view of constructional aspects in certain applications and also have the benefit of better isolating the heat and cold sources. However, in most applications, the combination of the heating and cooling elements as one entity will have the benefit of a compact and simple design with a short distance for transport of water between the elements.

The dehumidifier may be located at different locations in or in connection to the enclosure. In one embodiment the heating element and the cooling element are mounted in or adjacent to an outer wall of the enclosure. In case the heating and cooling elements are constructed as one entity, having its cooling side on the opposite side of the heating side, the element is preferably incorporated as a part of an outer wall of the enclosure, having its cooling element on the inside and its heating side on the outside.

As an alternative, the heating element and the cooling element may be mounted inside the enclosure whereby said heating element is connected to the outside of the enclosure via an air vent duct. In order to prevent re- vaporised water from re-entering the air inside the enclosure, the air vent duct should be tight to not allow the air leaving the enclosure to be in contact with the inside air of the enclosure.

In case the heating element and the cooling element are provided as different entities, it is of course possible to locate them at different locations, e.g. to locate the condensing element in the interior of the enclosure and the heating element adjacent to the wall in such a way that moisture will vaporise directly in the air exterior to the enclosure.

Hence, the present invention provides a dehumidification arrangement which is essentially maintenance free and can be fully automated in respect of humidity control and power consumption. Furthermore, the inventive arrangement will work without any moving parts and will be silent which makes it particularly suitable for all kind of domestic appliances or any kind of devices where a low level of noise is desired. Due to its simplicity, the arrangement will provide a reliable arrangement with little risk of failure or break down. The arrangement can also easily be scaled with respect to the size of to the enclosure and the drying capacity needed. Due to its relatively small size, the arrangement can easily be mounted on and integrated in existing enclosures with no or less efficient dehumidification devices. In the case of a compact, plate shaped heat and cooling device, e.g. a peltier element, it may be mounted in an outer wall or a lid for the enclosure and can easily be fitted to the enclosure by replacing the original wall or lid.

In addition, the dehumidification unit may be provided, if desired, with additional features such as a hygrostat in order to only be active when the humidity is above a certain level.

In order to achieve a more efficient dehumidification, the device may also be provided with a fan. However, such equipment will make the dehumidifier more complex and space requiring and is not required for most applications. If applied, the fan should usually not provide a strong flow of the air but rather a gentle mixing or stirring of the air inside so as to provide transport of humid air to the vicinity of the cooling element.

It shall also be noted that the invention could be useful for the reverse function, i.e. if the heating and cooling elements are switched. In the case of using a peltier element the cooling side and the heating side can easily be switched by changing the poles of the electricity. Hence, for example, a peltier element which is located in or near the wall could condense water from the outside and vaporise it on the inside in order to humidify the air inside the enclosure. By controlling the poles, for example in response to a hygrostat, the invention may be used to control the humidity of the interior air of the enclosure to be within a desired interval.

The invention further relates to a humidity control process for an enclosure comprising electrical equipment, said humidity control process comprising the steps of: - providing a cooling element located to be in contact with the ambient air of the interior of the enclosure so as to condense moisture from the ambient air

- providing a heating element located to be in contact with the ambient air of the exterior of the enclosure

- providing water guiding means which guides dew condensed at the cooling element to the heating element

whereby moisture condensed at the cooling element will be guided to the heating element to be vaporised at the heating element so as to dehumidify the air of the interior of the enclosure.

In a specific embodiment of the humidity control process is the condensed water transported for at least a part of its way from the cooling element to the heating element by means of capillary forces.

The humidity control process, which is mainly intended to be operated in order to dehumidify the air inside an enclosure, may also be used for the reversed function, i.e. to humidify the air inside the enclosure. This may be achieved in an easy way by switching the functionality of the heating element and the cooling element so that the flow of water may be reversed so as to humidify the air of the interior of the enclosure. In this case, the humidity control process preferably comprises a hygrometer which measures the humidity in the air and control the system to dehumidify the air when the moisture content of the air is above a certain level and reverse the function to humidify the air when the moisture content is below a certain value. An easy way of changing the functionality of the heating and cooling element is to use a peltier element, which comprises both elements, and change the poles of the current.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the invention will be described with reference to the following figures which disclose: Fig. 1 An enclosure for electric equipment comprising a dehumidifier

Fig. 2a A schematic view of the positioning of a heating and cooling element according to a first embodiment of the invention

Fig. 2b A schematic view of the positioning of a heating and cooling element according to a second embodiment of the invention

Fig. 2c A schematic view of the positioning of a heating and cooling element according to a third embodiment of the invention

Fig. 2d A schematic view of the positioning of a heating and cooling element according to a fourth embodiment of the invention

Fig. 3 A schematic view of a dehumidifying element

Fig. 4 A schematic view of the water transport in the element in figure 3 when in use

Fig. 5 A schematic view of a variant of the embodiment of the dehumidifying element in figure 3

Fig. 6a A second embodiment of a dehumidifying element

Fig. 6b A first version of the embodiment of the dehumidifying element shown in fig. 6a

Fig. 6c A second version of the embodiment of the dehumidifying element shown in fig. 6a

Fig. 7 A dehumidifying element comprising a peltier element

DETAILED DESCRIPTION

In the following, different embodiments of the invention, i.e. a device for dehumidification of the inside of an enclosure comprising electrical equipment, will be described with reference to the figures. The embodiments (figures) aim to clarify how the different parts of the elements of the dehumidifier , e.g a heating element and a cooling element, may be mounted in connection with the enclosure and how the different constructive details of the dehumidifier.

As a general rule in these figures, solid arrows (when not associated with a number) indicate the flow of water or condensed humidity, i.e. water in liquid state. Dashed arrows indicate the flow of humid air or mist, i.e. the flow of water in a gaseous state.

Figure 1 is a simple schematic overview of the intended use of a dehumidifier 2 and shows an enclosure 1 for an electric equipment (not shown) comprising a dehumidifier 2 which is located in an outer wall 13 of the enclosure.

In figure 2, as figure 1 only shows a very brief general overview, a more detailed description of the dehumidifying arrangement is shown, exemplifying different ways of locating the different parts of the dehumidifier in the casing and how they are connected. Figures 2 a-d discloses four different ways of placing the heating element 3 and the cooling element 4 in an enclosure 1 is shown schematically. In figure 2a, it is shown that the heating element 3 and cooling element 4 are constructed as one entity and located in the outer wall 2 of an enclosure. The cooling element 4 is located on the outside, or forming the outside, of the outer wall. The heating element 3 is located on the inside, or forming the inside, of the outer wall 2. The moisture in the air inside the enclosure 1 will condense at the cooling element 4 and be transported to the heating element on the outside of the outer wall 2 and thereby be vaporised. The mechanism of transporting the condensed water from the cooling element to the heating element in this case will make use of a capillary structure which will be shown and explained in association with other figures.

In figure 2b, another design of the dehumidifier is shown. The heating element 3 and the cooling element 4 are still constructed as one single entity but is located inside the enclosure 1. The heating element 3 is protected from the air inside the enclosure 1 by a casing 14 which is connected to an air ventilation duct 13. The casing 14 of course also protects the interior air of the casing 1 to come in contact with air exterior to the casing so as to prevent humidity in fresh air to enter into the enclosure 1. Except for guiding the air through the air ventilation duct 13 instead of releasing it directly to the fresh air as described in figure 2a, this configuration works according to the same principle as described therein.

In figure 2c, the heating element 3 and the cooling element 4 are separate units. It is therefore necessary to include some kind of water conduit 5 for transporting the condensed water from the cooling element 4 to the heating element 3. As can be seen in the figure, the heating element 3 is located inside the enclosure 1 and is protected from the air inside by a casing 14.

When the condensed water reaches the heating element 3, the water will be vaporised and released into the exterior of the enclosure through ventilation holes in the outer wall 12 at the part of the wall where the casing 14 function as a protective shield for the surrounding air to enter into the enclosure 1. As an alternative, the heating element could also be located at the outside of the outer wall 12 and thereby eliminate the need of having a casing 14 which shields the heating element 3 from the air inside the enclosure 1. If desired, the elements could be located the reverse way also.

In figure 2d, the heating element 3 and the cooling element 4 are separate units as described in figure 2c and a water conduit 5 transports water between the elements. This configuration differs from the one described in figure 2c in that the cooling element is located inside the enclosure 1 (not adjacent to the outer wall 12). It is therefore included an air ventilation duct 13, connected to a casing 14 enclosing the heating element 3, which guides the vaporised water in to the open air.

In the schematic figures 2a - 2d, it is not in detail described how the water is transported between the cooling and heating element. In the cases the elements are located at a distance from each other the connecting may be an ordinary water conduit or a capillary column for example. Examples of how the transportation of water can be arranged when the elements are constructed as one entity will be described below.

Figures 3 -7 shows more in detail different embodiments of how the heating and cooling elements forming part of the dehumidifier may be designed as one entity.

In figures 3 and 4 a first embodiment of such an element is shown where this entity is formed by a compact heating-cooling core surrounded by a water guiding material. The element shown in figure 3 comprises a heating element 3, a cooling element 4 and water guiding means in the form of a capillary mat 6a - 6c so as to form one heating and cooling entity 7 comprising all elements needed for condensing, transporting and vaporising water. As can be seen, the capillary mat 6 is divided into 3 parts whereof the first part 6a is in contact with the surface 8 of the heating element 3, the second part of the capillary mat 6b is in contact with the surface 9 of the cooling element 4 and the third part of the mat 6c is connecting the first part 6a and second part 6b of the mat. As shown in this figure, the third part of the mat 6c is only connecting the other parts of the mat 6a, 6b at one edge part of the heating and cooling entity 7. The capillary mat 6 could of course cover one or several more of the edges so as to increase the connection between the first and second parts 6a, 6b. Furthermore, the mat must not cover the complete surface but may also cover a part, being provided with holes or forming strips so as to reveal a part of the heating or cooling surfaces. In particular it might be advantageous to omit covering the complete cooling surface 9 in order to expose the cold surface 9 to the ambient air so as to improve the condensing effect.

In figure 4, it is shown how the cooling and heating entity 7 will work during use. Moisture from the air within the enclosure will condense on the capillary mat 6 at the part of the mat 6b which is located at the cold surface 9 of the cooling element 4. The mat 6 will absorb the moisture which will be spread in the mat 6 due to capillary forces which strive to reach equilibrium of humidity in the mat 6 and moisture will start to travel towards the dry parts of the mat. Hence, the liquid will start to move from the part of the mat located at the cold side 6b towards the part of the mat located at the hot side 6a via the connecting part 6c. Due to the heating element 3, moisture which has reached the part of the mat 6a located at the hot surface 8 of the heating element 3 will start to vaporise. The vaporisation will make this part of the mat 6a dryer than the other parts of the mat 6a, 6b so that there will be a continuous stream of water or moisture towards the hot side of the element 7. To be accurate, the stream of water will continue as long as the relative humidity is lower at the hot side than on the cold side. Due to the temperature difference between the hot and cold side of the element, the absolute humidity in the air on the hot side may be larger than on the cold side while the relative humidity on the cold side will be higher due to the fact that hot air may be more humid before condensing. Hence, there will be a flow of water from the cold side to the hot side until there is equilibrium of the relative humidity on the outer and inner side near the respective surfaces. However, since the heating and cooling of the elements need to be supplied with some kind of energy in order to function, there is a wish to control the element to switch off when there is no need to dehumidify the air inside the enclosure. The dehumidifying system may be provided with an arrangement which measures the humidity in the enclosure, e.g. a hygrometer, which is connected to a switch which turns on and off the dehumidifier depending on the humidity, i.e. a hygrostat. The switch may also measure the humidity inside and outside the device since there is a risk that humidity may enter into the enclosure through this arrangement when there is a higher relative humidity outside than inside. In order to prevent humidity from entering the enclosure, the device may automatically switch on when the relative humidity is higher outside than inside. This problem could also be adjusted by some other preventive mechanism, e.g. some kind of mechanical arrangement which closes the possibility of water to enter into the enclosure. It is further obvious that the heating and/or cooling elements not must be completely switched on or off but may have a variable effect either changed step less or by predefined steps to achieve a desired effect and thereby a controlled humidity in the enclosure.

As can be relatively easy understood, this arrangement provides an easy way for changing the flow of moisture to work in the opposite direction. The only thing which is needed to be done is to switch the heating element and the cooling element. An easy way of doing such a switch will be discussed more in detail in association with figure 7.

As already mentioned in the general description part, it is not necessary that both the hot side and the cold side are provided with a mat. In fig. 5 an alternative embodiment is shown. In this embodiment, humidity in the air condenses at the cold surface 9 of the cooling element 4 in such a way that droplets 16 will merge on the cold surface. Due to gravity, the droplets 16 will travel downwards to be collected in a receptacle 15. At the other end of the receptacle, it is in contact with a capillary mat 6. This capillary mat consists of a major part 6a which is in contact with the surface 8 of a heating element 3. Hence, the condensed water will travel through the capillary mat 6 to the heating element where it is vaporised and released into the open air.

However, this embodiment will probably work better when there is a relatively large amount of moisture from the air to be condensed. Small droplets tend to stick to the cold wall and will not start to fall down until they have reached a certain size.

As shown in this embodiment, the capillary mat only covers the surface of the heating element and having a part of it reaching into the receptacle so as to be able to suck water from the receptacle to the heating element by capillary forces. By this construction there is no need to cover both sides of the heating and cooling entity 7 with a capillary mat. In addition, the condensing efficiency will be very good since the cooling element will be in direct contact with the air. Another advantage of this construction is that it may work as a moisture trap. If the hygroscopic pressure is larger outside than inside, water will start to travel from the outside to the inside, however, water coming to the inside will accumulate in the receptacle 15 and thus create a high hygroscopic pressure relatively quick resulting in the undesired flow of water from the outside to the inside will stop.

In an alternative of this embodiment the capillary mat could of course continue all the way and cover the lower edge part of the heating and cooling entity 7.

Still another embodiment of the heating and cooling elements of a dehumidifier is shown in figure 6. Figure 6a shows a perspective view of a heating and cooling entity 7 which is shaped as an essentially flat plate having a heating element 3 located at one side and a cooling element 4 located at the opposite side is provided with holes 10.

In fig 6 b, which is an intersectional view of the heating and cooling entity 7 in fig 6 a, the holes 10 are provided with a capillary mat 6 which forms capillary columns 1 1 so as to connect the hot side 3 with the cold side in order to transport water condensed at the cold side 4 to be vaporised at the hot side 3.

Fig 6 c shows an intersectional view of the element described in fig 6 a in which the element 7 has been provided with a capillary mat 6 on the hot side 3 and the cold side 4 as well as in the holes 10. As described earlier, condensed water at the cold side 4 will absorb into the mat 6b at the cold side, be transported by capillary forces through the part of the mat 6c located in the holes so as to form a capillary column 11. The water will be vaporised from the part of the capillary mat 6a located at the hot side 3 of the cooling and heating entity so that water will be dragged from the cold side 4 to the hot side 3. A combination of the embodiments shown in figures 6b and 6c is also possible, i.e. only one of the sides is fully or partly covered by a capillary mat.

In fig 7 is described how the hearting and cooling elements of a compact designed entity as described in figures 3-6 may be made and the heating and cooling entity 7 comprising a heating side 3 and a cooling side 4 is exemplified as a peltier element 17. The element 17 comprises an anode connection 18 and a cathode connection 19. When there is a DC current applied to the connections 18, 19, the element will start to work and the sides 3, 4 of the element 17 will start to get hot respectively cold.

If there is a desire to reverse the process, the poles may be changed. By doing this, the cold side and hot side will switch. This means that the inventive concept of the idea does not only provide an efficient dehumidification device but also an efficient humidity controller. If there is a desire to keep the humidity within a desired range in the enclosure, the system may be provided with a hygrostat and means for alternating the current depending on the value of the hygrostat. When there is a desire to dehumidify, the element in contact with the interior of the enclosure will be the cold side and thereby condensing water which will be guided to the outside. On the other hand, if there is a need to humidify the air inside, the poles may be changed and the element will condense water on the outside and transport it to the inside where it is vaporised. Such an arrangement is in particular suitable for the embodiments where both sides are equally designed, e.g. the embodiments shown in figures 3, 4 and 6. The embodiment shown in fig. 5 will not work equally efficient in both directions and is more suitable to be used only as a dehumidification device.

Claims

1. A dehumidifier (2) for an enclosure (1 ) comprising electrical equipment, said dehumidifier comprising a heating element (3) and a cooling element (4), said cooling element (4) located to be in contact with the ambient air of the interior of the enclosure (1 ) and said heating element (3) located to be in contact with the ambient air of the exterior of the enclosure (1 ), said dehumidifier (2) further provided with water guiding means (5) which guides dew condensed at the cooling element (4) to the heating element (3) so that humidity from the air, condensed at the cooling element (4), may be transported to the heating element (3) to be vaporised wherein the water guiding means comprises a capillary structure (6).

2. A dehumidifier (2) according to claim 1 wherein the capillary structure (6) is in contact with the heating element (3) and adapted to guide water condensed at the cooling element (4) to the heating element (3).

3. A dehumidifier (2) according to claim 2 wherein a first part of said capillary structure (6a) covers at least a part of the surface of said heating element (3) so as to vaporise condensed dew at the hot side and a second part of said capillary structure (6b) covers at least a part of the surface of the cooling element (4) so as to absorb dew condensed at the cold side, said first and second parts (6a, 6b) of the capillary structure (6) are connected to each other by water guiding means(5).

4. A dehumidifier (2) according to claim 3 wherein the water guiding means (5) connecting the first part (6a) and the second part (6b) of the capillary structure (6) comprises a third part (6c) of the capillary structure (6).

5. A dehumidifier (2) according to any one of the previous claims wherein said heating element (3) and said cooling element (4) is formed as one entity (7) having a first surface (8) and a second surface (9), said heating element (3) located at the first surface (8) and said cooling element (4) located at the second surface (9).

6. A dehumidifier (2) according to claim 5 wherein said entity (7) comprises a peltier element (3).

7. A dehumidifier (2) according to claim 4 and 5 wherein said first surface (8) and said second surface (9) of said heating and cooling entity (7) are located opposite to each other and said third part of the capillary structure (6c) is located at the outer side of the entity (7) so as to guide water between the first part (6a) and the second part (6b) of the capillary structure (6).

8. A dehumidifier (2) according to claim 4 and 5 wherein one or several holes (10) are provided in said cooling and heating entity (7) connecting said first surface (8) and said second surface (9) of said cooling and heating entity (7) and said third part (6c) of the capillary structure (6) is located in said at least one hole (10) so as to guide water between the first part (6a) and the second part (6b) of the capillary structure (6).

9. A dehumidifier (2) according to claim 5 wherein one or several holes (10) are provided in said cooling and heating entity (7) connecting said first surface (8) and said second surface (9) of said cooling and heating entity (7), said holes being provided with a capillary structure (6) in such a way the capillary structure (6) is in contact with the heating element (3) and the cooling element (4) so as to form one or several capillary columns (11 ) for wicking of condensed water from the cold side (4) to the warm side (3) to be vaporised

10. A dehumidifier (2) according to any one of the previous claims wherein said heating element (3) and said cooling element (4) are mounted in or adjacent to an outer wall (12) of the enclosure (1 ).

1 1. A dehumidifier (2) according to any one of claims 1 to 9 wherein said heating element (3) and said cooling element (4) are mounted inside the enclosure (1 ) whereby said heating element (3) is connected to the outside of the enclosure (2) via an air vent duct (13).

12. A dehumidifier (2) according to any previous claim wherein the functionality of the heating element (3) and the cooling element (4) are switched so that the dehumidification process is altered to provide a humidification process.

13. A humidity control process for an enclosure (1 ) comprising electrical equipment, said humidity control process comprising the steps of:

- providing a cooling element (4) located to be in contact with the ambient air of the interior of the enclosure (2) so as to condense moisture from the ambient air

- providing a heating element (3) located to be in contact with the ambient air of the exterior of the enclosure (1 )

- providing water guiding means (5) which guides dew condensed at the cooling element (4) to the heating element (3)

whereby moisture condensed at the cooling element (4) will be guided to the heating element (3) to be vaporised at the heating element (3) so as to dehumidify the air of the interior of the enclosure (1 ) wherein the condensed water during at least a part of its transport from the cooling element (4) to the heating element (3) is transported by means of capillary forces.

14. A humidity control process according to claim 13 wherein the functionality of the heating element (3) and the cooling element (4) may be switched so that the flow of water may be reversed so as to humidify the air of the interior of the enclosure (1 ).