All electrical equipment produces heat. Protective devices, power breakers, busbars, contactors, relays, power supplies, PLCs, and drives all produce heat as they work. In many electrical systems, these devices are densely packed in metal cabinets with very little room for air to circulate. If this heat is not properly dissipated, the internal temperatures of these cabinets can quickly exceed the ratings of the devices, shortening their useful life, potentially causing early failure of the electronics, increasing humidity and condensation problems, and creating safety risks, including the possibility of fire. The general rule of thumb used in electrical design is that for many electronic devices, every 10°C increase above their optimal operating temperature can reduce their useful life by half. This means that cooling is not a nicety, but a necessity of thermal engineering. The heat load of a switchboard is a very important consideration that is often overlooked. It is imperative to consider an assessed cooling system that can handle the internal heat produced by the components as well as the environmental conditions.

The Challenge of Tropical and Hot Climates

In Australia, there are many areas that have high ambient temperatures, for example, north Queensland, the Northern Territory, and inland Western and South Australia during summer. This sets a higher standard for thermal management because, in some cases, passive cooling alone may not be adequate, and environmental factors such as humidity and corrosive conditions, for example, salt spray from the sea, also come into play, while indoor plant rooms can be prone to heating if air-conditioning is inadequate.

How Heat Builds Up in Switchboards

The sources of heat in a switchboard are two: internal heat and external heat. Internal heat is produced whenever there is current flow. The larger the load, the larger the current, and the more power electronics, the greater the internal heat. Power breakers and contactors are major heat producers, while variable speed drives and inverters produce heat from semiconductors. Power supplies and transformers also produce heat. Even if the internal heat is low, a high ambient temperature will make it difficult for the system to remove heat. When the ambient temperature is 40-45°C, as it is in Australian summer conditions, it becomes difficult to remove heat from an enclosure without cooling.

Cooling Strategies: From Passive to Active

There are four types of solutions that are commonly employed for cooling switchboards or cabinets. These solutions have their own set of advantages and disadvantages, along with a specified IP rating. The first solution is passive ventilation. This is the most basic form of cooling. In cases where the heat load is low and the cabinet is not subjected to extreme temperatures, fixed ventilation holes can be provided on the sides or doors of the cabinet. In natural convection cooling, the hot air rises and escapes through the ventilation holes, and if the cabinet size is increased, it helps in efficient heat dissipation. This solution is very cheap and does not have any moving parts, but the heat load capacity is low. The maximum IP rating that can be achieved in passive ventilation cooling is IP56 when a protective hood is placed over the ventilation holes. Otherwise, the maximum rating is IP54.

Forced ventilation is the subsequent step in cooling. Fans are employed to blow air through the cabinet and remove hot air. Fans can be designed to run all the time, only during hot seasons, or controlled through a thermal cut-out. Since hot air tends to collect at the top of the cabinet, fans are usually mounted there for greater efficiency. Forced ventilation can be highly effective during moderate heat loads. The highest IP protection for fans with exterior grills is IP56 when a protective hood is used; otherwise, the highest IP protection is IP54.

Heat exchangers are a slightly more advanced method of cooling that involves removing heat from the source using air or liquid. Heat exchangers have fewer moving parts, allowing for higher IP protection. They are highly effective in dusty or rough environments since they can maintain internal temperatures while preventing external materials from entering. Heat exchangers that are properly sealed can provide a maximum IP protection of IP55.

Air conditioning is the most effective cooling solution and is recommended for situations with high heat loads and high ambient temperatures. In panel-mounted air conditioning units, heat is removed from the cabinet through refrigerant, just like in split air conditioning systems. Although air conditioning is much more expensive than other cooling solutions, it can effectively deal with high heat loads. Waterproof versions of air conditioning units are also available for outdoor installation, and their IP protection level can go up to IP55.

Condensation Management and Anti-Condensation Heaters

Even in a controlled setting, condensation can occur inside switchboards during cold nights, humid conditions, or when there are sudden changes in temperature. When moisture is present inside an enclosure, it can lead to corrosion of busbars and terminals, insulation tracking, damage to sensitive electronics, or false alarms and protective trips. Anti-condensation heaters are a simple and effective remedy for this issue. Anti-condensation heaters are thermostatically controlled and are usually set to activate when the temperature inside the enclosure falls below 10°C. By maintaining a slightly higher temperature inside the enclosure, anti-condensation heaters can effectively prevent the condensation of moisture. They are usually used in conjunction with other cooling solutions to protect equipment in outdoor cabinets, near the coast, or in cold indoor plant rooms. Anti-condensation heaters work well because they are thermostatically controlled, which means they only activate when needed, thus minimizing energy costs without compromising the lifespan of the equipment.

Key Design Considerations for Cooling Systems

It is critical to estimate the heat produced by all the internal components accurately before choosing a cooling solution. It is necessary to compare the heat load to the cooling solution’s capability to ensure it performs well in the worst-case scenario. The operating environment, including the climate of the region, whether it is indoors or outdoors, and the presence of environmental contaminants like dust, salt, or moisture, must also be taken into account. Ingress protection ratings are influenced by the addition of vents, fans, or air-conditioning units. It is necessary to use weatherproof fan assemblies, louvres, or fan mounts to maintain the protection rating while allowing airflow. Thermostatic control of fans, air-conditioning units, or anti-condensation heaters is advisable to enhance efficiency and safeguard components. In humid or cold environments, condensation control by heaters or hygrostats is necessary to avoid moisture-related component failures.

Practical Applications and Examples

For a small indoor distribution board with moderate load, passive ventilation with thermostatic fans may be adequate, and a small anti-condensation heater will be sufficient to protect against moisture. For a large industrial control panel with multiple PLCs, drives, and transformers, heat exchangers with thermostatic control will be effective to maintain the internal temperature and IP rating, and anti-condensation heaters will protect against humidity. For outdoor switchboards in a coastal area, panel-mounted air-conditioning units with waterproof casing will be necessary, and thermostatically controlled anti-condensation heaters will be required to create a controlled internal environment, protect against corrosion, and control condensation.

Regular maintenance is essential to ensure the effective functioning of cooling systems. Filters in ventilation and heat exchanger systems need to be checked and replaced periodically, and fans need to be checked for functionality. Thermostats and anti-condensation heaters need to be checked annually to ensure that they are working properly. IP seals need to be checked after maintenance or any changes in the enclosure. Possible symptoms of cooling or condensation control system failure include high internal temperatures, fan failure, condensation inside the enclosure, or false alarms due to moisture.