It’s summertime, and like it or not, the weather is HOT! We all beat the heat by staying inside a nice air-conditioned room, but what about your electrical components? Not only are they subject to the same ambient heat that we have to endure, but they also generate heat as they run in a control enclosure. This heat needs to be dissipated from the enclosure to protect your components from excessive temperatures. But at what temperature should you be concerned, and how do you mitigate the heat in your enclosure? Let’s cool down and dive in:
How hot is too hot?
Electrical components are usually designed to operate under a maximum temperature of 50°C, or 122°F. This might trick some into thinking they don’t need to worry about climate control, but think again. Your components can withstand
these temperatures, but are they benefitting from these high temperatures? The short answer is—NO. Ultimately, these temperatures decrease service life, raise the risk of component failure, and can affect manufacturer warranties. In fact, if you maintain an internal cabinet temperature 10°C
(or 50°F) lower
than your components’ recommended maximum temperature you will double
their service life and significantly decrease the risk of failure. That’s why it’s a best practice to keep your control cabinet’s internal temperature at or below 35°C (or 95°F)
to ensure the maximum service life for your components.
How do I mitigate the heat?
In principle, there are two ways to dissipate heat from an enclosure: active cooling and passive heat dissipation.
With this method, a medium (typically air or cooling water) conveys the heat away from the enclosure. This requires additional equipment such as fan-and-filter units, cooling units, or air/water heat exchangers. The downside of active cooling is just that—you’ll need to purchase extra equipment. But, if your cabinet isn’t equipped to handle passive heat distribution (which we’ll explain next), active cooling might be your best option for cooling down your components.
There are many systems available for active cooling. The simplest and most cost-effective solution is to use filtered fans
. Filtered fans (and also blowers, impellers, and direct air cooling systems) provide low to moderate heat removal when used in environments where the ambient air is moderately cool and clean. If your environment is cool but also hazardous, or has dirty or corrosive air, using an air-to-air heat exchanger
provides cooling capacity similar to filtered fans, only they use a closed-loop system to keep contamination out of the cabinet. For locations with high ambient air temperatures, enclosure air conditioners
can bring the internal temperature down below the ambient air temperature and can also be used in harsh locations. But for extreme conditions where air conditioners would be subject to failure, air-to-water heat exchangers
are a great solution as no moving parts are exposed to the environment.
Other active cooling methods include chillers, vortex coolers, and thermoelectric coolers, to name a few. If you’re considering applying an active cooling method to your cabinet, do some research to find the best method for your environment and application.
Passive Heat Dissipation
With passive heat dissipation, no extra equipment is necessary because the panels of the control cabinet are engineered to adequately dissipate the heat. The main benefit of this method is that no extra equipment is required, resulting in no extra energy and maintenance costs. This method also allows for a completely closed-loop enclosure to facilitate electromagnetic compatibility (EMC) protection, protection from dust and debris, and prevent the condensation that active cooling sometimes creates. Also, passive heat distribution creates uniform heat loss, which in turn, creates a constant temperature within the enclosure. So components are less susceptible to stresses due to changes in temperature that potentially can occur with active climate control.
To utilize passive heat dissipation, the control cabinet needs to be carefully
specified to meet the demands of the equipment inside. The material of the enclosure panels, the total surface area of the control cabinet, the ambient air temperature, and the amount of heat the electrical equipment emits ALL need to be taken into consideration. Let’s take a deeper dive into each of these topics:
Enclosure Surface Area
The surface area of the enclosure is important since we’re relying on the cabinet walls to dissipate the interior heat. When measuring the surface area, keep in mind that only panels exposed to open air
are available for heat transfer (so enclosure baying, wall mounting, or covering a panel of an enclosure reduces the surface area). In general, the larger the surface area of the enclosure, the more it can dissipate heat, so it’s very common to use free-standing enclosures when executing passive heat distribution. To determine an enclosure's surface area in square feet, measure all
of the cabinet’s walls and follow the calculation example in Fig. 1 below. If any surface is not available for transferring heat (for example, the surface is mounted against a wall), the surface area of that panel should be subtracted
from the total enclosure surface area.
Electrical Component Heat Loss
The heat loss of a component is the wattage it generates while in use (basically, it’s how hot it gets while running). This information is usually available in your component’s datasheet, but if you can’t find it, a quick call to the component’s manufacturer may be necessary.
The material of your enclosure exterior has an important influence on passive heat dissipation. For example, spray-finished sheet steel or stainless steel enclosures are a common choice for industrial applications and have a heat transfer coefficient of approx. k=5.5 W/(m2
x K). But the coefficient may change according to the design (for example, with double-walled or insulated enclosures for outdoor applications). Pay careful attention to the materials used in your enclosure and know their proper heat transfer coefficient to calculate the heat dissipation properly.
Ambient Air Temperature
The air surrounding the control cabinet must also be taken into account when applying passive heat dissipation. A cool and climate-controlled room will allow for easier heat dissipation, while a hot environment will negatively impact your cabinet’s climate control. Therefore it is especially important to check on your cabinet’s temperature during the hot summer months, especially if the environment isn’t climate controlled.
Once you have correctly determined the above four factors with a little bit of math, you can calculate the internal temperature of your electrical cabinet in °C. See the calculation example below:
Fig. 1. Calculation example to determine internal enclosure temperature using passive heat dissipation. Source: Rittal GmbH & Co. KG
If the enclosure components’ heat loss and enclosure surface area are defined, you can also use the chart below (Fig. 2) to estimate the maximum temperature of the enclosure’s interior in °C. (Remember, you ideally want the temperature to be at or under 35°C).
Fig. 2. Maximum enclosure temperatures at an ambient temperature of 25°C based on the effective enclosure surface area for various heat loads with purely passive dissipation. Source: Rittal GmbH & Co. KG
If your actual calculations are above 35°C, fear not. With a few tweaks, you may still be able to utilize passive dissipation. First, you can try increasing your cabinet’s surface area by using a slightly larger enclosure. With small enclosures especially, a slight increase in surface area can significantly reduce the maximum internal enclosure temperature. Installing components with particularly high heat losses (such as braking resistors) outside
of the enclosure is yet another option to consider. By increasing the size of your enclosure and repositioning the components with highest heat loss, you just might be able to utilize passive heat dissipation after all. And if all else fails, you can always implement an active cooling method to supplement your climate control.
Electrical components produce heat – there’s no way around it. Luckily, there are plenty of ways to keep it under control. With careful planning and a few calculations, you can utilize passive heat dissipation to beat the heat with no extra equipment or energy costs. However, if passive cooling doesn’t keep the internal temperature of your cabinet low enough, there’s always the option to utilize active cooling methods, such as fans, heat exchangers, and air conditioners. Either way, it’s essential to recognize the importance of keeping your cabinet’s temperature under control, especially during the summer when temperatures are at their highest. Keep cool!