Electrical and electronic equipment as well as components typically are housed in electrical enclosures designed to provide protection from the external environment. These components and equipment are sensitive to temperature changes, and at high temperatures, a number of issues can arise. They include drive performance derating and IC-based devices adversely affected by erratic output or voltage migration. Additionally, the properties of silicone materials change with temperature extremes. In wiring insulations, elasticity and strength are reduced along with experiencing a temporary increase in ductility and atomic mobility.
In short, exposing electronics to high temperatures can have a significantly harmful impact on equipment performance and useful life. Given this risk, there is a strong need for finding a way keep an electrical enclosure cooled to prevent overheating electronics.
Simply adding cooling can help solve the issue with temperature. Yet, if not done properly — with thought about the environment around the enclosure — other issues could be created. Improperly managed cooling of the enclosure can lead to temperatures falling below the dewpoint, resulting in condensation which then promotes corrosion, battery failure and IC-based devices not operating correctly. Therefore, the focus should be on keeping the enclosure space at an optimal temperature setpoint for ideal performance and maximized life expectancy of all electronic components housed within.
Advantages of an Optimal Temperature Setpoint
Sources of Heat Load in Industrial Enclosures
There are several types of devices housed in the enclosure of an automation control system – a variable-frequency drive (VFD), servo drive, programmable logic controller (PLC), starter kit, power supply, inverter, relays, terminal blocks, indicator lights and, in many cases, transformers. These electronic components generate heat that has to be removed from the enclosure for maximum component life. As information processing becomes more powerful, the heat generated from electronics continues to increase. All inefficiencies of the devices contribute to heat generation. This heat can only be removed by using some form of active or passive heat transfer equipment. When there is active temperature control associated with a cooling unit, choosing the right enclosure cooling setpoint is very important.
As we understand how temperature extremes can prove dangerous for the equipment, we can begin to find solutions that help maintain the optimal temperature to run devices and extend service life. The setpoint for electronics can be higher as compared to the average air temperature setpoint inside a house. We should consider choosing a setpoint that is ideal for cooling electronic products instead of what we typically think of as comfortable for the human body.
Preventing Condensation in Industrial Enclosures
By itself, moisture in the air is not a problem for electronic equipment or components — until the moisture condenses due to cold surfaces. If the enclosure is being cooled by an air conditioner, most of the moisture is condensed by the evaporator coil and removed through a drain system or active condensate management. However, to avoid the condensation in unwanted locations inside the cabinet, it is necessary to understand the possible sources of moisture and to mitigate those beforehand to reduce the extent of the problem.
Effects of Condensation. Corrosion and short circuiting are two potential problems associated with condensed water inside an electronic cabinet. Corrosion causes increased electrical resistance, which, in turn, generates additional heat and contributes to decreased and inconsistent component performance. In addition, corrosion can lead to rusting of critical electrical components, increasing the risk of circuits shorting out as well as dangerous occurrences of arcing and sparking. Needless to say, any failure will have financial impact as well. In order to ensure optimal life expectancy of components, users should take several precautions to help prevent these harmful conditions.
Moisture Sources and Control. Moisture can enter an enclosure from numerous sources in many environments and applications. For example, in indoor washdown applications, it is possible for high pressure spray with soap lubricants to penetrate the cabinet. In cases where conduit or pipe fittings are not sealed properly, condensation may form on electrical components and equipment inside the enclosure and result in corrosion and damage to those components and equipment.
In wet or humid applications and environments, moisture enters an enclosure when the enclosure’s door is opened for service or maintenance purposes. When the enclosure surfaces cool to the dewpoint as a result of a shutdown, lower evening temperatures or lower outside air temperatures caused by a cool rain and other circumstances, condensation forms. Large temperature variations between the inside and outside of the enclosure also can result in pressure differences that may create a vacuum and draw water through the fittings and the component and gasket seals.
If it is evident that all sources of moisture are external, and moisture is prevented from seeping inside the cabinet, the internal components will be in dry air. A properly sealed, maintained cabinet that includes gaskets can help stop the leakage of outside moist air. Also, making sure the enclosure door shuts fully and properly after every use, and less frequent opening and closing of enclosure door, will prove favorable in preventing any resulting condensation issues. If there is a continuous drain of water from the cabinet, it clearly signifies that there is a leak of outside moist air into the enclosure space, which is being constantly condensed by the air conditioner inside the enclosure.
Preventing Condensation with Optimal Temperature Setpoint
To ensure the optimal life expectancy of components, users should take several precautions. It is necessary to choose the correct setpoint to avoid condensation issues. Condensation occurs when moist air is cooled or comes into contact with a cool surface that is at or below its saturation point, also known as its dewpoint. At this temperature, air can no longer hold all the moisture, and water vapor condenses into droplets, which can contact critical surfaces. The higher the moisture content in the air, the higher the dewpoint. A high depoint can result in condensation if the surrounding surface is colder than the dewpoint. To help prevent condensation from occurring, it is important to establish the optimal temperature setting of the cabinet. If the temperature is below the dewpoint of the external or internal air temperature, the condensation can occur on internal components inside the enclosure.
Most enclosure test standards are rated at 95°F (35°C) for the inside enclosure temperature, which makes it safe to assume that the electronic components would work fine at or below this maintained temperature. However, a thermostat or controller will have a hysteresis, which means that if set to a particular setpoint, the unit will control temperatures inside the cabinet at the setpoint, plus or minus the hysteresis. The temperature within the cabinet might also vary at the corners, which do not get as much airflow. Hence, to take care of the variation of the temperature inside the cabinet and the hysteresis of the thermostat and controller — and still keep the temperature below the permissible limits for optimal performance — the setpoint of 80°F (26°C) is recommended. As an example, if the hysteresis of the controller is 10°F and the setpoint is 80°F, the cabinet temperature can rise to 90°F (10°F above the setpoint), which is still close to optimal operating temperature for electronics and should cover any temperature variations across the cabinet to keep it below 95°F.
Properly managing and setting electrical enclosure temperature setpoints is a critical element to protecting and getting the best performance out of your electrical equipment. It also will lead to better returns on your overall investment by minimizing downtime due to equipment failures and enabling you to focus on what’s really important: servicing your customers.