Keeping Things Cool
Equipment cooling is essential to keep industrial process applications running smoothly.
Numerous studies have tested and shown that modern industrial electrical and electronic components — from switches and timers to PLCs and AC drives/inverters — operate most reliably and have the longest service life when the temperatures they are subjected to are kept at or below the manufacturer-specified rating. In any industrial facility, many electrical panels and cabinets are used to house the necessary electrical devices to operate and control the machinery and processes. In situations when a process shuts down or a machine malfunctions, the problem often is thermal in nature. The excessively high or low temperatures of the electrical and sensitive electronic equipment within the control panels and electrical cabinets trigger the shutdown or malfunction.
When a machine or process shuts down due to an overheated electrical component, the cost impacts can be massive. Imagine the effects of one hour of downtime to industries such as an automotive manufacturing site or a steel production facility. In the time it takes to locate the failed component and replace it — if the plant engineers are lucky enough to have a spare on the shelf — a sizable loss of productivity will occur. The lost productivity can be many times as costly as the component that failed. In smaller operations, the cost of failed components such as a large frequency drive can wipe out a week’s worth of profits. Keeping the enclosure and the components inside electrical cabinets at or below the manufacturer-recommended temperature is the goal of an effective enclosure cooling system.
The benefits of an effective method of cabinet cooling are threefold:
- Eliminating downtime and malfunctions caused by the overheating of the electrical components.
- Lowering the costs of the manufacturing process (through less expensive maintenance cycles and installation costs).
- Lengthening the service life of the electronic components.
The temperature rise within an electrical cabinet is the result of internal and external factors. Understanding the sources of all of the heat loads impacting an enclosure is important.
Internally, the electrical components are not 100 percent efficient. As such, some of the energy is wasted in the form of heat. The sum of the electronics and the heat given off is cumulative and quickly can add up to a sizeable amount.
For external heat loads, if the enclosure is located in an environment that is warmer than the desired internal temperature, there will be some heat transferred to the cabinet from the outside. For cabinets that are in close proximity to boilers, ovens, furnaces and other hot environments, the external heat loads can be greater than that of the internal electrical components.
The combination of the heat generated within the cabinet and the heat-load effects of the environment is the total amount of heat that must be managed in order to keep the cabinet at the desired internal temperature. Removal of the heat is the primary function of a cabinet cooler system.
Enclosure Cabinet Design Influences Cooling Demand
Proper design of the control panel can go a long way to minimizing the thermal effects on the cabinet. At the design and installation phase, utilizing proper sizing of the enclosure, material selection and insulation level will have an important impact on the thermal effects. The layout and location of the components within the cabinet also can help in the management of the generated heat. It is a good practice to not locate the highest heat-generating components immediately next to the most temperature-sensitive devices. The location of the cabinet installation also will have an impact. Utilizing natural airflows and shielding the cabinet from external heat sources will ensure the least external heat loads.
A cabinet cooler keeps equipment up and running at a water treatment plant.
Once the cabinet is built and installed, the final aspect of the temperature management is the cabinet cooling. To decide on what temperature to which to cool the enclosure, start with a breakdown of the internal components and the recommended operating temperature for each. For instance, fuse and contactors may be rated for 113°F (45°C) and PLCs and VFDs at 95°F (35°C). The sizing of the cooling system then will need to be designed according to the component that has the lowest required temperature.
Several technologies are available for cooling electrical cabinets. These include:
- Ventilation fans.
- Compressor-based refrigerant air conditioners.
- Vortex coolers.
- Air-to-air heat exchangers.
In addition, in many industrial enclosure cooling applications, an added requirement is to provide the cooling without allowing hot, humid and dirty air from the plant environment into the enclosure.
In applications such as these, fans are not useful because they bring in large amounts of dirty humid air and cycle it right through the enclosure. It does not take long for the electronics to get a buildup of dirt, dust, oil and grime. Early failures of the components can occur due to this condition and certainly should be avoided. Filtering the air works for a while, but the filters must be changed. If they are not changed regularly, this will lead to reduced airflow and potential for overheating. Air-to-air heat exchangers and refrigerant systems also have filters for blocking the ingress of the dirt and debris.
Using a vortex-tube-type cabinet cooler provides a good solution for preventing dirty air from entering the cabinet. Vortex-tube cabinet cooler solutions require that the enclosure be airtight, with all openings, vents and other possible entry paths for dirty air covered up. The airtight enclosure must not allow any outside dirt, debris or humid air to enter. The design of the vortex-tube coolers is such that the only air that enters the cabinet is the filtered and clean compressed air. The cabinet cooler provides air typically 50 to 54°F (28 to 30°C) cooler than the compressed air supply temperature. A point-of-use filter separator installed prior to the cooler system will ensure that the air is clean and free of condensate. An oil-removal filter further removes oil from the compressed air if the air has oil in it from the compressor system or has been lubricated for tools and other equipment.
Once the cool, clean air enters the enclosure, it can be routed throughout the cabinet using a cold air distribution kit. More cold air can be directed to warmer areas as needed, providing the utmost flexibility in a system.
With the cabinet cooler mounted toward the top of the cabinet, the warm air will exit the cabinet back through the cooler unit. In this way, the cooling cycle is completed without any outside air entering the enclosure.
Generally, a maximum internal relative humidity of 60 percent is recommended to avoid condensation. Typically, the internal relative humidity will settle in at a measure of 45 percent. As a result, moisture is not deposited within the enclosure, keeping the electronics clean and dry.
Using a vortex-tube-type cabinet cooler provides a good solution for preventing dirty air from entering the cabinet. Vortex-tube cabinet cooler solutions require that the enclosure be airtight, with all openings, vents and other possible entry paths for dirty air covered up.
To maintain the enclosure temperature while keeping operational costs to a minimum, the use of a thermostat is recommended. A few types of thermostats used include the bimetallic electrical contact type and the thermocouple style. The thermocouple type has the advantage of being able to be set up with a controller and the internal enclosure temperature monitored on a display. This provides ease of adjusting the temperature setpoint. The thermostat is set to the target enclosure temperature and is used to control a solenoid valve that opens and closes the compressed air supply, which in turn controls the cooling cycle. The thermostat ensures that cooling does not occur during situations such as periods of shutdown and startup where the heat levels have not built up yet. It also can be useful during seasonal times where ambient conditions are such that the cabinet cools naturally. Thermostats are typically adjustable, providing flexibility. For instance, if the most sensitive electrical component is replaced with a more robust type, the temperature setpoint could be raised by 5°F (3°C), reducing the operational costs to cool the enclosure.
The location of the thermostat within the cabinet is an important consideration. Options include locating it at the top of the cabinet (possibly the hottest area) or next to the most sensitive electrical component.
It is important to match the NEMA or IEC rating of the cabinet cooler system to the enclosure. Some common ratings are NEMA 12 (IP55), NEMA 4 (IP66) and NEMA 4X (IP66). The ratings are from the National Electrical Manufacturers Association (NEMA).
- NEMA 12 generally is considered oil- and dust-tight for use in general areas where liquids and corrosives are not present.
- NEMA 4 is generally watertight, dust-tight and splash-resistant for indoor/outdoor service.
- NEMA 4X is the same as NEMA 4 but adds corrosion resistance.
Be sure that the cabinet cooler system NEMA rating meets or exceeds the enclosure design requirement for the environment in which it is located.
In summary, an important part of the industrial process is the prevention of electrical shutdowns and failures leading to lost operational time, expensive repairs and component replacement caused by heat-related issues. Utilizing a vortex-tube-based cabinet cooler will eliminate downtime and malfunctions caused by overheating and lengthen the life of electrical components within an electrical enclosure. A vortex-tube cabinet cooler provides a reliable, low maintenance and fast cooling solution for optimal operation.