Nowadays, industrial control panels are being installed closer to the processes they are monitoring. Many of these panels are designed for installation outdoors and exposed to the elements. The controls, which can include PLCs, VFDs, remote I/O and HMI panels, are complex and susceptible to environmental changes. The control panels must be designed to ensure that the internal temperature of an enclosure does not exceed the operating temperature of the controls.

With this in mind, imagine that a control panel must be mounted in an area that is hazardous, potentially flammable or explosive. What should you consider in this instance? The following nine tips can help sort out considerations.

 

1. Know the Hazardous Location Requirements

Keep in mind that many sites have multiple classifications or zones. Moving the control panel by just a few feet can change the area classification, which may reduce and simplify the installation requirements.

Once you have established the area classification, you must follow the rules that apply to the requirements and environmental concerns of that particular classification. Most applications in the United States are designated as Class/Division/Group locations (figure 1). In Canada, existing sites typically use a similar scheme; however, new build sites are required to follow the zone classification scheme.

Understanding the area location will help determine the protection methods that can be used. Every protection method has advantages and limitations when it comes to industrial process heating or cooling. The requirements associated with gas and dust locations also may be different. As an example, consideration of a dust layer would add to the thermal insulation properties of the protected enclosure and would need to be addressed in the design. The appropriateness of the equipment in the dust-hazard environment also would need to be addressed. The T code and the dust layer must be a combined consideration.

graph graph

FIGURE 1. Marking details for equipment mounted in hazardous locations are shown.

2. Consider the Heat Dissipation of the Controls and Related Environmental Factors

Items to consider when evaluating the control panel for heating and cooling requirements include:

  • Ambient temperature for the control panel.
  • Heat dissipation of the controls.
  • Solar loading.

Depending on the type of enclosure and protection method, there will be multiple ways to add the required heating or cooling.

The enclosure material, whether metal, plastic or fiberglass, can affect its thermal characteristics. Likewise, the layout, configuration and mounting orientation can change the enclosure’s ability to dissipate or contain heat. In ordinary (non-hazardous) locations, cooling and exhaust fans can be used to provide simple, effective heat mitigation. In hazardous areas, this approach is not typically permissible because including such an element introduces a potential ignition source.

purged panel vortex cooler

Purged panel and vortex coolers can be used on enclosures and systems mounted in hazardous environments.

3. Explosionproof and Flameproof Control Panels

Explosionproof enclosures use the enclosure as the protection method. Thick-walled metal enclosures are designed and built to contain the pressure of an internal explosion and quench the flame before it can propagate out of the enclosure.

Because of the nature of this type of enclosure protection, cooling the enclosure is difficult. Heating is simpler because standard, general-purpose heaters can be used. A fan-forced heater can be used if adequate space is available. To verify compliance with T code on the outside of the enclosure, a thermal fuse or other means will be required to protect against thermal runaway.

When considering the addition of a heater and the spacing requirements necessary for maintaining the system, you will likely compare a single, large enclosure against the cost of multiple, smaller enclosures. Each application will be different, so there is not a one-size-fits-all approach for the control equipment.

Heating and cooling elements

Heating and cooling elements used for industrial control panels are much different in hazardous environments. Compliance, cost and expertise are critical to a well-designed system.

4. Purge and Pressurized Panels: Types X, Y and Z

Purged and pressurized panels use air or inert gas for protection against explosion. They rely on separate controllers mounted on the enclosure or cabinet. Compressed air is available throughout many plants. This can make purge and pressurization a good choice because it can be applied to cabinets as large as 450 ft3 (12.1 m3), and the enclosure size is flexible. The process for adding heating and cooling to purged and pressurized enclosures is similar to the process in ordinary locations. The external surface of the enclosures, however, must not reach the temperature code maximum for the hazardous location.

If the enclosure must be heated before the safety-related purge cycle is initiated, the heaters must be rated as explosionproof. This is because they will not be protected by the purge system. If heating is not required until after the enclosure has been purged, a fan-forced heater can be used. In all cases, the enclosure surface must remain below the temperature code restrictions assigned to the hazardous area classification. Regular testing or continuous monitoring of the temperature may be required to maintain a safe condition.

These enclosures can be cooled using multiple techniques. If only a small amount of cooling is required, the instrument air can be used to cool the enclosure. Some purge systems are advanced enough to provide this function and can be programmed for customized operation for the application.

Vortex coolers are another viable option for reducing internal heat and are available from 900 to 5,000 BTU of cooling capacity. High capacity vortex coolers require more air, which can affect the intended operation of the safety-related purge/pressurization system. The system must be designed to avoid nuisance tripping if too much air is being consumed during peak demand. As a result, an adequate air supply must be available during maximum loading of the system.

explosionproof enclosures

Due to their thick walls and tightly enclosed structure, explosionproof enclosures require different schemes when considering heating and cooling features.

5. Non-Incendive or Division 2 Panels

If all elements of a control panel are suitably rated for the area location, any heating or cooling also must be rated for use in that area classification. Heaters and thermostats that employ explosionproof technology can be used for these types of applications. Larger panels may be needed to accommodate the space necessary for a heater, however.

For cooling, properly rated air-conditioning and thermoelectric coolers for use in Division 2 locations are available. This equipment may be the same style as, or similar to, those used for purged enclosure panels. You must verify that the controls used on the air-conditioning systems do not require air for protection.

 

6. Insulation and Static Protection

The extreme effects of solar loading and low temperatures can be addressed by adding insulation and sunshields. In the United States, insulation requirements typically are addressed in the Standard for Industrial Control Panels, UL508A, section 26. Insulation must be kept at a safe distance from all live parts and mechanically fastened to the enclosure. Solar shields can be added to the enclosure to provide shade and eliminate or reduce the need for additional cooling. Standoffs on the outside of the enclosure can be used to provide the means for mounting the solar shield. Users should ensure that any fasteners maintain the type (NEMA) or IP rating of the enclosure.

explosionproof enclosures

Due to their thick walls and tightly enclosed structure, explosionproof enclosures require different schemes when considering heating and cooling features.

7. Compliance

To ensure compliance or certification according to standards for safety, nationally recognized testing laboratories (NRTLs) are available. Suitably trained and authorized panel shops also can provide system certificates. Panel shops that offer these types of solutions are certified and accredited. They are familiar with the code requirements, including how to heat and cool panels effectively in hazardous areas. Not all panel shops can provide this complete service for panels going into hazardous areas. Properly accredited shops will have the appropriate certificates, which can be verified online. These will identify the types of solutions they are authorized to build. Experienced shops can help with the design and assembly of your solution.

 

8. Evaluate Cost vs. Performance

There are several acceptable ways to heat or cool an enclosure in a hazardous location. Long-term cost and characteristics should be considered when evaluating alternative designs. Some components and solutions might seem like a bargain at first, but the long-term maintenance or energy usage can make them less desirable compared to a solution with a higher initial cost. For example, a vortex cooler mounted to an enclosure may have a cost-effective, simple design with virtually no long-term maintenance costs. However, if the coolers will be running continuously, energy costs could be high. This calculation must be considered during the evaluation of the overall cost of the installation.

 

9. Consult with Experts When Needed

If there is a temperature requirement that cannot be solved or is difficult to solve, it is best to learn about and understand the requirements early on before you are committed and constrained by cost or other limiting factors. Many panel shops and suppliers have in-house application assistance for quick answers and design recommendations. Often, sales engineers can provide insight into standard design techniques used in similar applications. They also can be used to gain access to company experts for solid answers and best practices.  Partnering with these experts will save you hours of research by providing expert advice on products that may be implemented in your application. For the do-it-yourself engineers, white papers, calculation tools, engineering guides and videos from various suppliers can be referenced. PC