WO2012152275A2

WO2012152275A2 - An electronics cabinet

Info

Publication number: WO2012152275A2
Application number: PCT/DK2012/000057
Authority: WO
Inventors: Kirsten Stentoft HANSEN; Jørgen Jessen MØLLER
Original assignee: Danfoss Solar Inverters A/S
Priority date: 2011-05-09
Filing date: 2012-05-08
Publication date: 2012-11-15
Also published as: WO2012152275A3; DK177319B1; DK201100356A

Abstract

An electronics cabinet accommodating an electronic circuit and at a heating element, the heating element being spaced apart from the electronic circuit, such that the electronic circuit is not in direct contact with a heating element. The effect is that thermal convection is possible in the space between the electronic circuit and the heating element.

Description

AN ELECTRONICS CABINET FIELD OF THE INVENTION

The present invention relates to an electronics cabinet accommodating a first electronic circuit and a first heating element. The heating element and the electronic circuit are spaced apart such that they are no in direct contact with each other.

BACKGROUND OF THE INVENTION

Nowadays, electric, electromagnetic and electronic components are used for many different purposes in almost every technological field. For protecting those electric, electromagnetic and electronic components (and also for protecting operating personnel, the environment or the like from an electric shock), such components are usually arranged in essentially closed cavities, for example in cabinets. Those cabinets generally offer protection against unintended contact with the components therein or even protection from wilful destruction by criminal subjects. Such cabinets are used, for example, in connection with solar inverters, which is a piece of equipment which takes DC power from one or more solar panels, and converts it into AC power suitable for connecting to the electrical grid. In a typical field system a number of solar panels will feed into a single box mounted outside. This box would contain a solar inverter and the output AC to an electrical grid.

When a box containing electronic equipment is placed outside it is influenced by both the temperature of the environment and the humidity of the air. One problem that occurs is that when temperatures fall during the night, water contained in the humid air inside the box condenses within the box on the electrical components thus causing short-circuits. Furthermore, boxes suitable for outdoor use are often constructed in a way in which passage of air in and out of the box is constrained in order to protect the contents from, for example, dust. Such a construction also hinders the dispersal of accumulated humidity within the box that might occur of there was free passage of air. Whilst this is a problem for any box containing electronic equipment, it is particularly noticeable for boxes containing solar inverters, since the solar inverter is not used during the night - because there is no sun - and therefore generates no heat during that period. Other types of equipment may well continue to generate heat and therefore not suffer so much with this problem. If condensation occurs regularly then is may also lead to longer term problems such as corrosion which may reduce the lifetime and/or reliability of the electronic equipment. It will be appreciated that an electrical cabinet may "breathe" due to the temperature variation throughout a period of time. Air may be expelled from the cabinet as the environment warms up, and new air is sucked into the cabinet as the environment cools down. Such cycle may take place daily for a cabinet installed outside, and subject to heating due to the sun. Moreover, it will be appreciated that the water content of atmospheric air can vary e.g. due to weather conditions. During some periods the water content in the atmospheric air is high, while it in others is low.

Accordingly the outside air, and water vapour contained in it, is regularly being introduced into the cabinet and this could damage the electrical components. It is an object of one or more embodiments of the present invention to provide an inexpensive and reliable solution to the problem of condensation in electric cabinets.

Moreover, it is the object of one or more embodiments of the present invention to provide a dehumidifying device, in particular a dehumidifying device for an essentially closed cavity device that is improved over dehumidifying devices according to the state of the art. DESCRIPTION OF THE INVENTION

In a first aspect, the present invention relates to an electronics cabinet accommodating a first electronic circuit and at a first heating element, the first heating element being spaced apart from the first electronic circuit, such that thermal convection is possible in the space between the first electronic circuit and the first heating element.

By providing heating elements, the relative humidity of the air may be maintained below a critical level, whereby failure in the electrical components may be prevented. By spacing the electronic circuit and the heating element apart such that they are not in direct contact, thermal energy from the heating element is not transferred to the electronic circuit by means of thermal conduction. Rather, the thermal energy is transferred from the heating element to the electronic circuit exclusively radiation and convection. One advantage of this is arrangement is that the convection helps to develop air circulation in the electronics cabinet such that the warmth from the heating element is distributed in the electronics cabinet. Another advantage of this arrangement is that by radiating the thermal energy to the electrical components (rather than attaching the heating element to the printed circuit board carrying the electronic components and thus conducting the thermal energy through the printed circuit board), the thermal energy is used to heat the electrical components instead of the printed circuit board.

In the context of the present invention, the term 'in direct contact', when applied to two components, shall be understood such that the two components abut and/or touch each other.

In the context of the present invention the term 'Absolute Humidity' is a measure of the quantity of water in a particular volume of air, and can be quoted in grams per cubic metre, for example. In the context of the present invention the term 'Relative Humidity' (RH) of an air mass is defined as the ratio of the partial pressure of water vapour (in air) to the saturated vapour pressure water at a given temperature. This can also be expressed as the amount of water vapour in the air mass compared to the maximum water vapour that the air mass is able to hold without the water vapour condensing. RH is quoted as a percentage, where 100% RH at a particular temperature means that the water vapour will condense to liquid water.

The space defined between the electronic circuit and the heating element may be wider than twice the height of any electrical component of the electronic circuit board, such as three times the height, such as four times the height, such as five times the height, such as ten times the height, such as twenty times the height, such as fifty times the height. In this context, the height of the electronic components shall be understood as the distance from a surface of the circuit board accommodating the electrical component to that part of the electrical component which is furthest away from this surface, when measured in a direction parallel to a normal of the surface. Accordingly, when the circuit board is arranged such that the surface onto which the electrical component is mounted faces in an upwards direction, the height is the distance from the surface to the uppermost point of the electrical component.

In one embodiment, the space between the heating element and the electrical circuit or circuit board is at least 1 centimeter, such as at least 5 centimeters, such as at least 10 centimeters, such as at least 15 centimeters, such as at least 20 centimeters, such as at least 25 centimeters. In one embodiment, the first electronic circuit is accommodated on a first carrier element. The carrier element shall be understood as an element such as a plate which mechanically supports and electrically connects electronic components using conductive pathways, tracks or signal traces formed on a non-conductive substrate. One example is a printed circuit board. In one embodiment, the first carrier element and the first heating element are arranged in a generally vertical direction so as to facilitate thermal convection in the space between the first carrier element and the first heating element. It will be appreciated that by arranging the carrier element(s) and the heating element(s) vertically, a chimney-like passage is defined by the vertically extending space. By a chimney-like passage shall be understood a passage which guides ascending air along a predetermined path and in a predetermined direction. Thus heat from the heating elements, will move in an upwards direction in the space. More than one carrier element may be provided. Thus in one embodiment, the electronics cabinet comprises a second carrier element accommodating a second electronic circuit. In this embodiment, the first heating element may be spaced apart from and arranged between the first and the second carrier elements such that thermal convection is possible in the space between the first heating element and each of the first and second carrier elements. In the latter embodiment, the first heating element is sandwiched between the first and the second carrier elements, whereby a chimney-like passage is defined by the spaces defined between the first heating element and each of the two carrier elements. During use, the heat from the heating element will cause air to flow upwards in these chimney-like passages due to thermal convection. Moreover the thermal energy will be radiated from the first heating element towards those of the electrical components of the first and second carrier elements which faces the first heating element, thereby further contributing to elevating the temperature of the electronic circuits. Alternatively, or as a supplement, the electronic cabinet may further comprise a second heating element, and the first carrier element may be spaced apart from and arranged between the first and the second heating elements such that thermal convection is possible in the space defined between the first carrier element and each of the first and the second heating elements. In the latter embodiment, the first carrier element may be sandwiched between the first and the second heating element, whereby chimney-like passages are defined in the spaces defined between the two heating elements and the first carrier elements. As both sides of the carrier elements faces a heating element, electrical components provided in either side of the carrier element will be subjected to thermal radiation from the first and second heating elements. It will be appreciated that the electrical cabinet may comprise any number of carrier elements and/or any number of heating elements. Thus in one

embodiment, the electrical cabinet comprises a plurality of carrier elements each of which accommodating an electronic circuit, and a plurality of heating elements. In the latter embodiment, the plurality of carrier elements may comprise the first and the second carrier elements and the plurality of heating elements may comprise the first and the second heating elements.

In order to achieve the chimney-like passage, one or more of the carrier elements (such as any) of carrier element may be spaced apart from and arranged between two heating elements. Alternatively, or as a supplement, any heating element is spaced apart from and arranged between two carrier elements.

The heating element may comprise one or more means which when an electrical current flows therethrougth generates thermal energy. One example of such an element may be a resistive element. In one embodiment, the same amount of thermal energy is generated for any position of the heating element, when the heating element is operated. As an example the resistive element may be evenly distributed along the surface of the heating element.

Alternatively, the heating element may be designed to have a first zone in which a first amount of thermal energy per unit area is generated during use and a second zone in which a second amount of thermal energy per unit area is generated during use, the second amount of thermal energy per unit area being larger than the first amount of thermal energy per area unit (e.g. per square centimeter). The latter may be achieved by providing a first amount of the resistive material in the first zone and a second amount of resistive material in the second zone. The second amount being larger than the first amount.

As an example, the second zones (which generate a larger amount of thermal energy) may be located in positions corresponding to vital electrical

components on the opposing carrier board. This way vital components may be subjected to an even larger amount of thermal radiation.

In one embodiment, one or more— such as each— of the heating elements comprises no electrical components except for one or more resistive elements. In one embodiment, one or more— such as each— of the heating elements comprises no electrical components except for one or more electrical wires or conductive paths and one or more resistive elements. In yet another

embodiment, the heating elements, comprise no active electrical components and only one kind of passive electrical component. This single kind of passive electrical components may be a resistive element. In order to ensure that the electrical components are subjected to thermal radiation, the electrical components on each carrier elements may be arranged relative to the respective carrier element and any neighbouring heating element such that the electrical components face one of the neighbouring heating elements whereby these electrical components are at least partly heated by radiation from said heating element when the heating elements are operated.

The electrical cabinet may be used for housing an electric inverter for transforming a DC current into an AC current. One example is an inverter for a solar panel.

It will be appreciated that the heating elements need only be used in certain situations e.g. typically when the temperature drops and/or when the humidity increases. Thus in one embodiment, the electrical cabinet further comprises a controller which is adapted to activate one or more of the heating elements when a predetermined condition is met. The predetermined condition may be one or more of: predetermined point in time, a predetermined temperature outside the electronics cabinet, a predetermined temperature inside the electronics cabinet, a predetermined humidity inside the electronics cabinet, a predetermined humidity outside the electronics cabinet, a predetermined temperature difference.

In one embodiment, the predetermined point in time (at which the one or more heating elements are activated) is a predetermined period of time prior to sunset such as 120 minutes prior to sunset, such as 90 minutes, such as 60 minutes, such as 30 minutes. Similarly, the controller may be adapted to deactivate the heating element(s) a predetermined point in time, such as a predetermined period of time after sunrise, such as 120 minutes after sunrise, such as 90 minutes, such as 60 minutes, such as 30 minutes.

In one embodiment, the controller is adapted to activate the heating elements in response to the weather conditions such as when the weather changes from sunny to cloudy.

In one embodiment, the predetermined temperature outside the electronics cabinet (below which the one or more heating elements are activated) is 20 degrees Celsius, such as 15 degrees Celsius, such as 10 degrees Celsius, such as 5 degrees Celsius. In one embodiment, the predetermined temperature inside the electronics cabinet (below which the one or more heating elements are activated) is 20 degrees Celsius, such as 15 degrees Celsius, such as 10 degrees Celsius, such as 5 degrees Celsius.

Whilst condensation normally - under clean conditions - will happen when the RH is very close to 100%, in other conditions it may happen at much lower values of RH. For example, if the electrical cabinet is placed in a coastal area then there will normally be salt in the air. If surfaces are contaminated by this salt, then water can condense at lower values of RH, perhaps 77% RH. To ensure that under almost all circumstances condensation is minimised, then the relative humidity inside the cabinet should be lowered to about 65% RH.

In one embodiment, the predetermined relative humidity inside the electronics cabinet (above which the one or more heating elements are activated) is 50% RH, such as 60% RH, such as 65% RH, such as 70% RH, such as 75% RH, such as 80% RH, such as 85% RH, such as 90% RH, such as 95% RH.

In one embodiment, the predetermined relative humidity outside the electronics cabinet (above which the one or more heating elements are activated) is 50% RH, such as 60% RH, such as 65% RH, such as 70% RH, such as 75% RH, such as 80% RH, such as 85% RH, such as 90% RH, such as 95% RH.

The predetermined temperature difference Td (at which the one or more heating elements are activated) may be the temperature difference between the temperature inside and outside the cabinet. That is to say, if the temperature outside the cabinet is Tout and the temperature inside the cabinet is T_m , then the temperature difference, Ta , may be defined as:

T d = T in - T out

In one embodiment, the predetermined temperature difference is at least two degrees Celsius, such as at least four degrees Celsius, such as at least six degrees Celsius, such as at least eight degrees Celsius, such as at least ten degrees Celsius. In one embodiment, the predetermined temperature difference is 7 degrees Celsius.

As is explained in further detail in relation to the figures, increasing the temperature of the air entering the cabinet by a predetermined amount may ensure that the relative humidity of the air is maintained at an acceptable level. This is due to the relative humidity of a body of air decreasing with an

increasing temperature. As an example, raising the temperature of air with a humidity of 100% RH from 10 degrees Celsius to 17 degrees Celsius, causes the relative humidity to decrease to 65% RH.

Accordingly, it is an advantage to keep the temperature inside the cabinet warmer than the temperature outside the cabinet e.g. 7 degrees warmer. This may be done by using at least two temperature sensors; one measuring the outside temperature, and one measuring the temperature within the cabinet. When the temperature inside the cabinet is found to be less than 7°C above the outside temperature, then the heating elements are turned on in order to raise the inside temperature. It should also be noted that although a system controlled by direct

measurement of the humidity, or relative humidity, is the most obvious, in practice there are advantages to be gained by avoiding the use of humidity sensors. This is because reliable humidity sensors are costly, and cheaper forms of sensor suffer from the need to be recalibrated, and often yield less reliable results.

In a second aspect, the present invention relates to a system comprising one or more solar panels which are electrically connected to one or more solar inverters, the solar inverters being accommodated in an electronics cabinet.

The electronics cabinet may comprise any combination of features and elements of the invention according to the first aspect.

In a third aspect, the present invention relates to an electronics cabinet comprising at least one electronic circuit and at least one heating element, and wherein a controller is adapted to activate one or more of the heating elements when one or more predetermined conditions is/are met. The predetermined condition may be: predetermined point in time, a

predetermined temperature outside the electronics cabinet, a predetermined temperature inside the electronics cabinet, a predetermined humidity inside the electronics cabinet, a predetermined humidity outside the electronics cabinet, a predetermined temperature difference.

The invention according to the third aspect may comprise any combination of features and elements of the invention according to the first aspect. In a fourth aspect, the present invention relates to a system comprising one or more solar panels which are electrically connected to one or more solar inverters, the solar inverters being accommodated in an electronics cabinet according the third aspect of the invention.

The invention according to the fourth aspect may comprise any combination of features and elements of the invention according to the first and the third aspect.

In a fifth aspect, the present invention relates to a method for reducing condensation within an electronics cabinet, comprising the step of increasing the amount of heat generated within the cabinet when a predetermined condition is met. In one embodiment, the heating elements of the first aspect may be utilised.

The predetermined condition may be one or more of: predetermined point in time, a predetermined temperature outside the electronics cabinet, a

predetermined temperature inside the electronics cabinet, a predetermined humidity inside the electronics cabinet, a predetermined humidity outside the electronics cabinet, a predetermined temperature difference.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1 discloses an electrical diagram of a system comprising a solar panel and a solar inverter which is accommodated in an electronics cabinet, Fig. 2 discloses a system comprising a solar panel and a solar inverter which is accommodated in an electronics cabinet,

Fig. 3 discloses a side elevational cross-sectional view of a first embodiment of an electronics cabinet according to a first embodiment of the invention, Fig. 4 discloses a side elevational cross-sectional view of a second embodiment of an electronics cabinet according to a second embodiment of the invention,

Fig. 5 discloses a side elevational cross-sectional view of a third embodiment of an electronics cabinet according to a third embodiment of the invention,

Fig. 6 discloses a top cross-sectional view of the third embodiment of the invention, and

Fig. 7 discloses the effect of raising the temperature of an air body by 7 degrees Celsius.

DETAILED DESCRIPTION OF THE INVENTION

Figs. 1 and 2 disclose a solar power system 100 comprising a solar panel 102 and a solar inverter 104 which is accommodated in an electronics cabinet 106. The solar inverter 104 is electrically connected to the solar panel 102 by means of electrical cables 108. The solar panel 102 is supported on a structure - in the case of the figure a pole 112 - and angled relative the rays of the sun in order to increase the electrical energy generated by means of the solar panel 102. It will be appreciated that in other embodiments, the electronics cabinet 06 may be secured to another element such as a wall, the solar panel etc.

Fig. 3 discloses a first embodiment of the electronics cabinet 106. The electronics cabinet 106 defines a cabinet housing 110 which is supported relative to the ground by means of a pole 112. Inside the cabinet housing 110 is provided a first electronic circuit 114 and a second electronic circuit 116. The electronic circuits 1 4, 116 form part of a solar inverter 104 which is electrically coupled the solar panel 102 via the electrical cables 108, see Figs. 1 and 2. As the cabinet housing 110 is provided outside, dew may be formed inside the cabinet housing 110. In order to avoid this, a first heating element 118, a second heating element 120 and a third heating element 122 are provided. These heating elements may be operated to maintain the temperature at a level above the dew point. The electrical circuits 114, 116 are arranged between the heating elements 118, 120, 122, such that a space 124 is defined between the heating elements 118, 120, 122 and the electrical circuits 114, 116. Due to this space 124, the heat generated by the heating elements 118, 120, 122 may radiate towards the electrical circuits 114, 116 and thus cause the temperature of the electrical components of the electrical circuits 114, 116 (not visible in the figures) to be elevated.

Accordingly in the embodiment of Fig. 3, electrical components arranged on either side of the electronic circuits 114, 116 will be subjected heat radiating from the heating elements 118, 120, 122.

Moreover, the provision of the space 124 results in a chimney-like passage being defined between the heating elements 118, 120, 122 and the electrical circuits 114, 116. The result is that when the heating elements 118, 120, 122 are operated air will be caused to flow as indicated by arrows 126 due to thermal convection.

In the embodiment of Fig. 4, three electronic circuits are provided, namely a first electronic circuit 114, a second electronic circuit 116 and a third electronic circuit 128. Between the electronic circuits two heating elements are arranged namely a first heating element 118 and a second heating element 120.

Again, a space 124 is defined between the electronic circuits 114, 116, 128 and the heating elements 118, 120, whereby a chimney-like passage is defined in which air will flow due to thermal convection generated by the heat of the heating elements 118, 120 when these are operated. Moreover, the heat from the heating elements 118, 120 will be radiated towards the electronic circuits 114, 116, 128 such that the temperature of any electrical components (not shown) of the electronic circuits 114, 116, 128 will be elevated, thus further adding to the prevention of the formation of dew. It will be appreciated that in order to achieve this effect, the electrical components must be provided on a side of the electronic circuits 114, 116, 128 which faces one of the heating elements 118, 120. Accordingly this effect is achieved on either side of the second electronic circuit 116, while it is only achieved on the right side of the first electronic circuit 114 and on the left side of the third electronic circuit 128.

Figs. 5 and 6 disclose a third embodiment of the invention. Again the electronic circuits 114, 116 are provided in a cabinet housing 110 which is secured to the ground by means of a pole 112. In order to prevent formation of dew, a heating structure 130 is provided which defines a first chimney 132 and a second chimney 134. The chimneys 132, 134 are defined by a first, second and third heating element 118, 120, 122 which are interconnected by means of a fourth and a fifth heating element 136, 138.

Fig. 6 illustrates a section A-A' of Fig. 5 and thus illustrates the chimneys 132, 134 in which the first and the second electronic circuits 114, 116 are provided. It can be seen from Fig. 7 that (for example) if air entering the cabinet when the outside temperature is 10°C has a 100% RH, then increasing the temperature of that air by 7°C will reduce the RH to 65% which is sufficient, under many circumstances, to prevent condensation. Thus it is an advantage to keep the temperature inside the cabinet 7°C warmer than the temperature outside the cabinet. This may be done by using at least two temperature sensors; one measuring the outside temperature, and one measuring the temperature within the cabinet. When the temperature inside the cabinet is found to be less than 7°C above the outside temperature, then a heating device is turned on in order to raise the inside temperature. Such a heating device can, with advantage, comprise the heating elements described in this document. The RH within a cabinet by can thus be controlled by control of the internal temperature. This also makes it possible to control the internal RH in response to the nature of contamination in the air. In a preferred embodiment, a temperature of around 7 deg C higher inside the cabinet than outside is found to be appropriate. In environments with heavy (or a risk of heavy) contamination , then a higher temperature difference may be appropriate.

Claims

CLAIMS . An electronics cabinet accommodating a first electronic circuit and at a first heating element, the first heating element being spaced apart from the first electronic circuit, such that thermal convection is possible in the space between the first electronic circuit and the first heating element.

2. An electronics cabinet according to claim 1 , wherein the first electronic circuit is accommodated on a first carrier element, and wherein the first carrier element and the first heating element are arranged in a generally vertical direction so as to facilitate thermal convection in the space between the first carrier element and the first heating element.

3. An electronics cabinet according to any of the preceding claims, further comprising a second carrier element accommodating a second electronic circuit, and wherein the first heating element is spaced apart from and arranged between the first and the second carrier elements such that thermal convection is possible in the space between the first heating element and each of the first and second carrier elements.

4. An electronics cabinet according to any of the preceding claims, further comprising a second heating element, and wherein the first carrier element is spaced apart from and arranged between the first and the second heating elements such that thermal convection is possible in the space between the first carrier element and each of the first and the second heating elements.

5. An electronics cabinet according to any of the preceding claims, comprising a plurality of carrier elements each of which accommodates an electronic circuit, and a plurality of heating elements, wherein the plurality of carrier elements comprises the first and the second carrier elements and wherein the plurality of heating elements comprises the first and the second heating elements.

6. An electronics cabinet according to claim 5, wherein any carrier element is spaced apart from and arranged between two heating elements

7. An electronics cabinet according claim 6, wherein any heating element is spaced apart from and arranged between two carrier elements.

8. An electronics cabinet according to any of the preceding claims, wherein each of heating element comprises no electrical components except for one or more resistive elements.

9. An electronics cabinet according to any of the preceding claims, wherein none of the heating elements is in direct contact with one or more of the carrier elements.

10. An electronics cabinet according to any of the preceding claims, wherein the electrical components on each carrier elements are arranged relative to the respective carrier element and any neighbouring heating element such that the electrical components face one of the neighbouring heating elements whereby these electrical components are at least partly heated by radiation from said heating element when the heating elements are operated.

11. An electronics cabinet according to any of the preceding claims, wherein the electronics cabinet is a cabinet for an inverter.

12. An electronics cabinet according to any of the preceding claims, further comprising a controller which is adapted to activate one or more of the heating elements when a predetermined condition is met.

13. An electronics cabinet according to claim 12, wherein the predetermined condition is one or more of: predetermined point in time, a predetermined temperature outside the electronics cabinet, a predetermined temperature inside the electronics cabinet, a predetermined humidity inside the electronics cabinet, a predetermined humidity outside the electronics cabinet, a predetermined temperature difference.

14. A system comprising one or more solar panels which are electrically connected to one or more solar inverters, the solar inverters being accommodated in an electronics cabinet according to any of the preceding claims.