FIELD OF THE INVENTION The present invention relates to a dehumidifier and to dehumidifying an enclosure.

BACKGROUND OF THE INVENTION Cabinets are widely used for protecting electronic, electrical and

electromechnical devices and the like. Such cabinets can be used to protect devices that are stored within the cabinet and can also be used to protect users from the devices (for example, to protect an operator from electric shocks).

Figure 1 is a highly schematic block diagram of a system for generating electrical power. The system, indicated generally by the reference numeral 1, comprises an array of solar cells 2, a cabinet 4, a solar inverter 6 and an electricity grid 8. As is well known in the art, the solar inverter 6 can be used to convert DC electrical power generated by the array of solar cells 2 into AC power provided to the electricity grid 8. The solar inverter 6 is often located in a potentially hostile environment (being exposed, for example, to high temperatures, low temperatures, rain, dust etc.). The cabinet 4 is intended to provide the solar inverter 6 with at least some protection from the environment.

In the use of the system 1, when the temperature of the environment falls at night, the temperature inside the cabinet 4 falls. As the

temperature inside the cabinet falls, water vapour within the cabinet 4 condenses and can cause short-circuits and other damage to the electrical circuits of the solar inverter 6. The cabinet 4 is typically constructed in such a way that the passage of air into and out of the cabinet is highly restricted in order to protect the contents of the cabinet (the solar inverter 6 in this example) from, for example, dust. Such a construction hinders the dispersal of humid air, thereby making the problem of condensation within the cabinet worse.

The problem of humid air condensing is common to many cabinet applications and the solutions provided by the present invention can be used in many such applications. The problems associated with humidity are, however, particularly prevalent in the solar industry. This is because solar inverters are not used at night (when there is no sun). Thus, the solar inverter 6 within the cabinet 4 does not, in normal use, generate heat during the night. Other types of electrical equipment are in use during the night and therefore generate heat, which reduces problems with condensation. In use, water typically condenses on the solar inverter 6, which can cause electrical problems when the solar inverter is activated in the morning and can also cause corrosion. The present invention seeks to address at least some of the problems outlined above.

SUMMARY OF THE INVENTION The present invention provides a dehumidifier comprising : a desiccant holder for holding a desiccant (such as silica gel); a bias mechanism (such as a spring biasing mechanism) configured to bias the dehumidifier into a first configuration, wherein, in use, desiccant held by the desiccant holder is exposed to an interior of an enclosure when the dehumidifier is in the first configuration; and a translation means (such as a solenoid or some other actuator, such as a micro electrical mechanical system (MEMS) or a geared motor) configured to overcome the bias mechanism such that, when activated, the translation means moves the dehumidifier into a second configuration, wherein, in use, the desiccant is exposed to an atmosphere outside the enclosure when the dehumidifier is in the second configuration.

The present invention also provides a system comprising : an enclosure and a dehumidifier, wherein the enclosure includes an opening and the dehumidifier is mounted in the opening, the dehumidifier further comprising : a desiccant holder for holding a desiccant (such as silica gel); a bias mechanism (such as one or more biasing springs) configured to bias the dehumidifier into a first configuration in which desiccant held by the desiccant holder is exposed to an interior of the enclosure; and a translation means (such as a solenoid) configured to overcome the bias mechanism such that, when activated, the translation means moves the dehumidifier into a second configuration in which the desiccant is exposed to an atmosphere outside the enclosure. The enclosure may include a plurality of openings and the system may comprise a plurality of

dehumidifiers as set out herein, wherein a dehumidifier is provided for each of the said openings.

In the first configuration, the desiccant is exposed to the interior of the enclosure but is not exposed to the atmosphere outside the enclosure and the desiccant can therefore be used to dehumidify the interior of the enclosure. In the second configuration, the desiccant is exposed to the atmosphere outside the enclosure and is not exposed to the interior of the enclosure. Thus, in the second configuration, moisture previously absorbed by the desiccant can be released to the atmosphere outside the enclosure such that the desiccant can be regenerated. The present invention provides a simple, flexible arrangement for dehumidifying an enclosure and for regenerating the desiccant used to dehumidify the enclosure. Regenerating the desiccant ensures that the desiccant can be re-used multiple times. The solution can be provided with many different enclosures, is scalable and can be retrofitted into existing enclosures. In both the first and second configurations described above, the enclosure with which the dehumidifier is being used can be made airtight. The first configuration is typically a first position : the second configuration is typically a second position. Thus, the translation means and the bias mechanism can be configured to cooperate to set the position of the desiccant holder such that the desiccant is exposed to either the interior of the enclosure (in the first position) or the exterior of the enclosure (in the second position) .

The desiccant holder may take the form of a basket having openings that are sufficiently small to ensure that desiccant is retained within the basket, but sufficiently large to allow air to readily circulate through the desiccant.

In many forms of the invention, the desiccant is silica gel ; however, the skilled person will be aware of many alternative regeneratable desiccants that could be used in accordance with the principles of the present invention.

The dehumidifier may include a heater adapted to heat the desiccant when the dehumidifier is in the second configuration. The heater may, for example, be a heating pad. Of course, many alternative forms of heater, such as a heating coil, could be provided. Alternatively, or in addition, an airflow heater may be provided wherein, in the second configuration an airflow from the atmosphere outside the enclosure is heated by the airflow heater before being directed through the desiccant. In this way, the desiccant may be heated by passing warm air through the desiccant such that the desiccant is heated (for regeneration of the desiccant) and the air removes the water vapour from the vicinity of the desiccant. The airflow may be encouraged by using a fan.

The present invention further provides a method comprising : biasing a dehumidifier into a first configuration, wherein a desiccant holder of the dehumidifier is exposed to an interior of an enclosure when the

dehumidifier is in the first configuration; and activating a translation means (such as a solenoid) to overcome the biasing in order to move the dehumidifier into a second configuration, wherein the desiccant holder is exposed to an atmosphere outside the enclosure when the dehumidifier is in the second configuration.

The dehumidifier may be biased into the first configuration using a spring mechanism of the dehumidifier. The dehumidifier may be moved into the second configuration under the control of a solenoid.

The dehumidifier may include a heater adapted to heat the desiccant when the dehumidifier is in the second configuration. The heater may, for example, be a heating pad or a heating coil. Alternatively, or in addition, an airflow heater may be provided wherein, in the second configuration an airflow from the atmosphere outside the enclosure is heated by the airflow heater before being directed through the desiccant.

The configuration of the dehumidifier may be set under the control of a timer mechanism, e.g. the system may operate in the first configuration for a first period of time before operating in the second configuration for a second period of time. The timer may then be reset and the operation repeated. The first period and/or the second period may be set by a user (e.g. by an installation engineer).

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in further detail with reference to the following schematic drawings, in which:

Figure 1 is a block diagram of a solar power generation system; Figure 2 is an exploded view of a dehumidifier in accordance with an aspect of the present invention;

Figure 3 is a partially cut-away view of the dehumidifier of Figure 2; Figure 4 is a cross-section of an enclosure including the

dehumidifier of Figures 2 and 3 used in a first mode of operation;

Figure 5 is a cross-section of an enclosure including the

dehumidifier of Figures 2 and 3 used in a second mode of operation;

Figure 6 is a flow chart showing an algorithm in accordance with an aspect of the present invention;

Figure 7 is a flow chart showing an algorithm in accordance with an aspect of the present invention; and

Figure 8 is a block diagram of a dehumidifier in accordance with an aspect of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Figure 2 is an exploded view of a dehumidifier, indicated generally by the reference numeral 10, in accordance with an aspect of the present invention. Figure 3 shows a partially cut-away view of the dehumidifier 10. The dehumidifier 10 comprises a top cover 12, a top cover gasket 14, a set of top cover springs 16, a mounting holder 18, a mounting holder gasket 20, a desiccant holder 22, top cover connectors 25, a bottom cover/casing 26 and a solenoid 38.

Figure 4 is a cross-section of an enclosure 32 including the dehumidifier 10 described above when used in a first mode of operation of the present invention . Figure 5 is a cross-section of the enclosure 32 including the dehumidifier 10 used in a second mode of operation .

As shown in Figures 4 and 5, the dehumidifier 10 is mounted, using the mounting holder 18, in an opening in a cabinet 32 such that desicca nt 34 in the desiccant holder 22 is outside the cabinet and the top cover 12 is inside the cabinet.

As shown in Figure 4, when the solenoid 38 is not activated, the springs 16 of the dehumidifier 10 push the cover 12 away from the opening in the cabinet 32. The dehumidifier is pushed vertically upwards (in the arrangement shown in Figure 4). The dehumidifier is thus positioned such that the desiccant 34 is exposed to the atmosphere inside the cabinet 34 but is not exposed to the atmosphere outside the cabinet. In this configuration, the desiccant 34 acts to remove moisture from the atmosphere within the cabinet 32. With the dehumidifier in the

configuration shown in Figure 4, the cabinet 32 is airtight.

In Figure 5, the solenoid 38 has been activated and overcomes the bias mechanism provided by the springs 16. As a result, the solenoid moves the top cover 12, desiccant holder 22 and the bottom cover 26 vertically downwards (in the arrangement shown in Figure 5) until the top cover 12 comes into contact with the mounting holder 18. The top cover gasket 14 forms a seal with the mounting holder 18 such that the desiccant 34 is no longer exposed to the air within the cabinet 34, but is exposed to the air outside the cabinet. With the dehumidifier in the configuration shown in Figure 5, the cabinet 32 remains airtight. The dehumidifier 10 also includes a heating pad 36. In the configuration shown in Figure 5, the heating pad 36 is heated, such that the desiccant 34 is heated. As is well known in the art, heating a desiccant, such as silica gel, causes moisture stored by the desiccant to be released. This process is called regeneration and results in the desiccant being reusable.

The springs 16 provide a biasing mechanism that biases the dehumidifier into the configuration shown in Figure 4. Thus, in the event of a failure, such as a power failure or a failure of the solenoid 38, the dehumidifier will be retained such that the desiccant is exposed to the interior of the enclosure.

Note that the use of the springs 16 shown in Figures 2 and 3 is not essential to all forms of the invention. Any mechanism that biases the dehumidifier into the first configuration shown in Figure 4, but which biasing can be overcome could be used. Similarly, the use of the solenoid 38 is not essential. Any mechanism that can selectively overcome the biasing mechanism (whether provided by one or more springs or otherwise) could be used. Figure 6 is a flow chart showing an algorithm, indicated generally by the reference numeral 50, in accordance with an aspect of the present invention.

The algorithm 50 is called when a "regenerate" procedure is initiated. The regenerate procedure may be called by another controlling program, such that the algorithm 50 forms a sub-routine. Before the algorithm 50 is initiated, the dehumidifier 10 is in the position shown in Figure 4. Thus, moisture in the enclosure is absorbed by the desiccant 34. The regenerate command indicates that the desiccant stored in the desiccant holder 22 should be regenerated.

The algorithm 50 starts at step 52 where the solenoid 38 is activated. Activating the solenoid overcomes the force provided by the biasing springs 16 so that the dehumidifier moves to the position shown in Figure 5. In this position, the desiccant 34 is exposed to the air outside the enclosure 32.

With the desiccant exposed, the algorithm 50 moves to step 54 where the heating pad 36 is turned on. This causes the desiccant to be heated, which, as described above, causes moisture stored by the desiccant to be released into the atmosphere outside the enclosure 32 in order to regenerate the desiccant.

Next, at step 56, it is determined whether or not the regeneration period has expired. Once the regeneration period has expired (so that it is expected that the desiccant 34 has been fully regenerated and is ready for use), the heating pad 36 is turned off (step 58 of the algorithm 50) and the solenoid is released (step 60 of the algorithm 50). The algorithm 50 then terminates.

When the solenoid is released in step 60 of the algorithm 50, the biasing springs 16 pull the dehumidifier back into the position shown in Figure 4. Thus, the desiccant 34 is once again able to remove moisture from the enclosure 32. Thus, in use, the dehumidifier 10 spends a first period of time in the position shown in Figure 4, where the desiccant 34 is used to remove moisture from inside the cabinet 34. Further, the dehumidifier spends a second period of time in the position shown in Figure 5, where the desiccant 34 is regenerated. When the second period has elapsed, the dehumidifier is returned to the position shown in Figure 4 and the process repeats.

In one form of the invention, the dehumidifying period (i.e. when the dehumidifier is in the position shown in Figure 4) is 2 weeks and the regeneration period (i.e. when the dehumidifier is in the position shown in Figure 5) is 70 minutes. Of course, these periods could be varied in different embodiments of the invention. Variables such as the size of the enclosure being dehumidified and the amount of desiccant being used to dehumidify that enclosure will have an impact on the optimum

dehumidifying and regenerating periods.

In some forms of the invention, the algorithm of Figure 6 is only used when the overall apparatus is generating electricity. Thus, in the case of the solar power generation system described above with reference to Figure 1, the algorithm 50 would only be initiated when the solar inverter 6 was generated electricity. In this way, the power required to operate the dehumidifier is only consumed when power is being generated. Figure 7 is a flow chart showing an algorithm, indicated generally by the reference numeral 70, in accordance with an aspect of the present invention. The algorithm 70 may be an initialisation procedure and may be performed only once in some embodiments of the invention.

The algorithm 70 starts at step 72 where the dehumidifying time period set. The dehumidifying time period is the time that the dehumidifier spends in the position shown in Figure 4. Next, the algorithm moves to step 74, where the regeneration time period is set. The regeneration time period is the time that the dehumidifier spends in the position shown in Figure 5. Finally, the algorithm 70 moves to step 76 where other parameters may be set. The algorithm 70 then terminates.

There are many parameters that could be set in the step 76. For example, a delay may be desired between the heating pad 36 being turned off and the desiccant being cool enough to be exposed to the interior of the cabinet 34. Thus, a delay may be introduced between steps 58 and 60 of the algorithm 50 and this delay period may be set in the step 76. Other parameters that might be set include whether the solenoid should only be operated when power is being generated (e.g . during the day in the case of a solar inverter) . The skilled person will be aware of other parameters that could be set in this way.

The present invention is applicable to systems of many different

dimensions. By way of example only, the present invention could use 50g of silica gel to dehumidify a 50 litre enclosure.

The exemplary embodiments of the invention described above show a single dehumidifier. This is not essential to all forms of the invention . Multiple dehumidifiers may be provided for a single enclosure. In such an arrangement, the dehumidifiers may be controlled so that there is always at least one dehumidifier having desiccant that is exposed to the interior of the enclosure.

The embodiments of the invention described above all include a heating pad as part of the dehumidifier. This is not essential to all forms of the invention . For example, instead of directly heating the desiccant (for regeneration purposes), air that flows through the desiccant may be heated . Figure 8 is a highly schematic block diagram of a system of a dehumidifier, indicated generally by the reference numeral 80, comprising a fan 82, a heater element 84 and a desiccant 86. In a regeneration mode, the fan 82 and the heater 84 are both turned on such that warm air is forced to flow through the desiccant 86. In this way, the desiccant is regenerated, without requiring a heater to directly heat the desiccant.

The embodiments of the invention described above are provided by way of example only. The skilled person will be aware of many modifications, changes and substitutions that could be made without departing from the scope of the present invention . For example, although the present invention has generally been described in relation to solar inverters, this is not essential . The principles of the present invention could be applied to a dehumidifier that is used in any cabinet, enclosure or other closed cavity. The claims of the present invention are intended to cover all such modifications, cha nges and substitutions as fall within the spirit and scope of the invention .