What is the Right Temperature Set Point for My Electrical Enclosure?

Electrical enclosures serve to protect electrical devices from adverse environmental influences, such as dirt, other particulates, moisture, or chemicals that could damage components.

Plus, by housing electrical devices inside a secure enclosure or box, personnel are protected from electrical hazards such as electric shock, arc flash, and burns. However, electrical devices generate heat as a byproduct of their operation. When the heat load of the electrical devices within an enclosure exceeds the heat dissipation achieved through natural convection, the temperature inside the enclosure will rise. Since the performance and life span of electrical devices will degrade as temperature increases, this excessive heat must be removed in order to keep the temperature within acceptable operating limits. The rule of thumb warns that for every 10°C more than their rated temperature limit, the life expectancy for electrical components gets cut in half.

When convection cooling would fail to successfully regulate the temperature in an enclosed environment, cooling units can preserve the life span and performance of enclosed electrical components. Cooling units provide closed-loop cooling, using a refrigeration cycle to move heat to the outside of a sealed enclosure while maintaining the enclosure’s mechanical isolation from the ambient environment. Excessive moisture condenses on the evaporator, located on the enclosure side of the closed loop, where it can be effectively removed to keep the humidity level down and electrical components dry. These functions usually provide great value; however, too much of a good thing can diminish the efficacy of these units—and actually damage components. To avoid risking the safety and efficiency an enclosure is designed to ensure, operators must optimally set the temperature set point for any enclosure cooling unit.

When to Use a Cooling Unit for an Electrical Enclosure

any components commonly housed within electrical enclosures generate heat: variable frequency drives (VFDs), servo drives, programmable logic controllers (PLCs), starter kits, power supplies, inverters, relays, terminal blocks, indicator lights, transformers, and more. Many of these devices are rated for operation to 60°C (140°F); however, heat-producing semiconductor devices, such as diode rectifiers and transistor inverters, produce significant amounts of heat, which radiates to adjacent circuitry. In order to keep this temperature in check, heat sinks are used for dissipation, and a lower operating environment temperature rating is needed for the heat sink’s convection to be effective. As a result, a common rating for VFDs is significantly lower at 40°C (104°F).

When unfavorable, high-temperature ambient conditions exist, convection alone—whether passive through venting of the enclosure and surface area dissipation, or forced, by using fans to exhaust the heat—cannot adequately maintain an acceptable operational temperature. In other words, if the temperature outside the box exceeds the target temperature intended inside the box, convection cooling is not going to work. In these cases, active cooling must be utilized. The enclosure air conditioner or “cooling unit” is often used to serve this purpose.

Factors for Determining Optimal Set Point

The enclosure cooling unit is intended to keep electrical equipment in an acceptable working environment, but this environment is not the same as the 72°F (22.2°C) comfort space that people would like to experience. Rather, a higher working environment temperature is acceptable—and in most instances desired for electrical equipment. As previously stated, the acceptable working environment temperature for most electrical devices exceeds 40°C (104°F) and excessive cooling can lead to several pitfalls.

Condensation—always a concern for electrical equipment since moisture will cause corrosion, compromise resistivity, and increase the risk of short circuiting, equipment failure, sparking, and fire—forms on surfaces whose temperature falls below the dew point. It is common for the evaporator to be colder than the dew point, and cooling units facilitate the management of condensation that forms on the evaporator through collection and drainage or burn-off. Problems occur when the air temperature within the enclosure falls below the dew point, leading to the formation of condensation on the electrical components themselves. The risk of condensation problems increases as the temperature set point of the cooling unit is lowered, or the dew point temperature is raised by an increase in relative humidity. Energy consumption and efficiency are ongoing concerns for operation managers and enclosure cooling units should not be exempt from scrutiny in these areas since compressor-based refrigeration technology consumes a fair amount of electricity. Excessive cooling leads to wasted energy, increased costs, and unnecessary wear and tear on the cooling units themselves. Additionally, the needless run time circulates more air through the cooling unit—resulting in increased maintenance needs for changing filters, rinsing condensers, and cleaning components. This is particularly true in environments with dusty, dirty airborne contaminants. Heat energy is also a necessary component for the optimal performance of the refrigeration cycle of the cooling unit. The evaporator is the heat exchanger responsible for transferring the heat energy of the enclosure air to the refrigeration circuit where it can be exhausted to the ambient environment at the condenser. This heat energy transfer increases as the temperature difference between the surface temperature of the evaporator and the air temperature within the enclosure increases. In other words, the refrigeration circuit operates in a less efficient manner when the enclosure air temperature is lower.

Another performance risk involves both the formation of condensation on the evaporator and, due to the set point being too low, the lack of adequate heat energy transfer to the refrigeration cycle. Since the evaporator itself can become quite cold, a lack of heat energy transfer can cause condensation which forms on the evaporator to turn to ice. Since ice will compromise the ability of the evaporator to exchange heat, the problem will cascade and more ice will form—ultimately causing a breakdown of the refrigeration cycle altogether. Should this occur, heat is not removed from the enclosure and the high temperature sensed by the cooling unit’s controller signals demand for additional work by the refrigerant compressor. That, in turn, support the continued formation of ice and leads to a compounded negative situation. Eventually, this leads to compromise or failure of the electrical equipment inside the enclosure due to excessive heat.

Cooling Units Provide Effective, Efficient Temperature Regulation

In conclusion, cooling units—when properly set up—provide an excellent method for active cooling of an electrical enclosure in order to keep electrical devices from exposure to temperatures that are beyond their acceptable operating limits.