When making a housing for an electronic device for use in outdoor environments, an important consideration is that the housing should be able to cope with large differences in temperature. That is, the housing should be adapted to both cold and hot environments. Much focus is hence needed on insulation and power consumption, and from a economical and environmental perspective it is desirable to keep power consumption at a low level.
Protective housings for electronic devices for outdoor environments usually have a single sealed shell for the purpose of protecting the electronic devices inside the shell. Heat in the shell generated by the electronic device can easily be conducted through the shell if the external air temperature is low. However, when the external temperature is high or the shell is heated by solar radiation, the internal temperature will rise due to the generated heat from the electronic device and the external heat. A solution to such a problem may be to arrange a sunshade or adding a shell outside the sealed shell.
Conventional double shell housings for electronic devices use air between the shells to prevent the external heat to reach into the inner shell. A ventilation opening is typically provided in the outer shell, and provide a natural convection of the air if the inside of the inner shell is heated by the electronic device to a higher temperature than the external temperature. Another way is to manufacture shells in a heat conducting material so as to facilitate transmission of heat, which is generated by the electronic device, to the outside in order to keep the internal temperature down.
Likewise, in conventional double shell housings, the air between the shells may be useful in cold environments, as the air between the shells is applied as an insulation to maintain a convenient tempered environment inside the inner shell around the electronic device.
In such double shell housings using natural convection and an opening in the outer shell, however, there is a problem with a non-effective heat transportation both from the inside of the inner shell and also between the inner and outer shell.
EP 0746 192 A1 addresses this problem by using a plurality of fans provided between an inner and an outer shell, where the inner shell is hermetically sealed and the outer shell has bimetal valves for support of circulation with the environment outside the outer shell. However, EP 0746 192 A1 has a drawback, in that the fans and any electronics connected to the fans will be exposed to the outside environment. If the outside environment is cold and damp, this will lead to damages to the fans and any connected electronics.
In U.S. Pat. No. 4,984,089 an outdoor surveillance apparatus is disclosed which support movement of a camera assembly. The apparatus is adapted to low and high temperature by use of a heater and multiple fans which are regulated by thermostats.
U.S. Pat. No. 4,419,716 disclose a sealed vapor proof housing with a system for isolating an electrical device from ambient atmosphere. Heat is transferred by use of a fan and that the housing made of metal consists of a multiple number of heat exchange fins.