Modern multi-function electronic controls, variable-frequency drives and switchgear are highly sensitive to thermal issues, a challenge exacerbated by confined electrical cabinets. Excessive heat causes electrical components to bake, with numerous unwanted outcomes: digital displays can start to misread, drives could start running at de-rated performance, while starters and breakers can trip below rated loads. There is also the potential loss of warranty on cabinet equipment and even, in some cases, catastrophic production line failures.
So what is the solution? Well, small fans akin to those found in PCs are probably the most common way of cooling electrical panels. Many panel builders fit fans of this ilk as a matter of course, and they prove adequate in many applications. However, some suggest they only serve to circulate warm air around the enclosure. Fans also pull in dusty air from the surrounding environment, creating another potential source of failure as dust can conduct electrical charge and cause circuitry to short. Sometimes it is not always obvious to engineers how much dust is present within local air.
IN THE LOOP
Choosing the optimal electrical enclosure cooling solution hinges on a number of factors, reports James Swanson, global product training manager at electrical enclosure provider nVent Hoffman in the US (formerly known as Eldon in the UK). He says: “It’s important to look at the different types of cooling – open-loop, closed-loop and conductive – because, based on the equipment inside the electrical cabinet and the temperature at which it can properly function, we have to make our choice.”
Ambient temperature plays a large part in selecting a cooling system. For instance, open-loop cooling will always result in temperature above ambient, making it a factor that demands attention.
“Any time you bring outside air into the enclosure, it is open-loop cooling, whether it’s via louvres, fans or filtered fans,” says Swanson. “There are different definitions of UL [NEMA] type rating that can be open-loop cooling. Type 1 is louvres and unprotected fans, but you can have a filtered fan that’s able to meet the UL Type 12 [IP52] test and maintain the integrity of your Type 12 enclosure, keeping it dust-tight.”
However, the introduction of outside air means bringing in all contaminant types present. The filter will take out dust, but not moisture or corrosive chemical agents, for example.
“With closed-loop cooling, you are recycling the air inside the enclosure, which means you’re not introducing moist outside air, protecting your electrical equipment,” says Swanson. “Closed-loop cooling doesn’t have to be an air conditioner; it can be an air-to-water heat exchanger.”
The other type of cooling is conductive, which entails taking the enclosure and oversizing it to make the skin of the cabinet become the heat exchanger. However, this approach only works in situations where it is permissible for the temperature inside the panel to be warmer than the outside temperature.
nVent Hoffman offers advice including its online cooling selection tool for new-build enclosures. In addition, for retrofit applications, it provides thermal audits, as well as remote access control for continuous monitoring.
EASY MISTAKES
Closed-loop cooling via air conditioning units is an increasingly popular option, but taking advice is essential because there are numerous potential pitfalls, such as mistakenly oversizing the unit. This error might cause temperatures to fall too quickly so the duty cycle becomes too low for effective humidity control. Also, the air conditioner must conform to NEMA/IP ratings or it will invalidate the enclosure’s rating.
Another common mistake is upgrading electrical equipment without reviewing the heat load. In short, the heat load and the air conditioner’s cooling capacity must match. Introducing new electrical equipment often upsets this balance, particularly if the changes involve the addition of inverter drives or controllers that generate high heat levels. As a point of note, heat load comprises two main components: the internal heat load (which is the heat generated by the electric components inside the enclosure) and the external heat load, namely the amount of heat gained or lost through the walls of the enclosure.
Although air conditioning units offer a perfectly adequate solution to cooling electrical enclosures in numerous applications, sometimes there is a requirement for a lower-cost, lower-maintenance alternative that delivers cool air without the use of Freon or other refrigerants. One such option is ITW Vortec’s Vortex cooler for electrical enclosures (pictured below), which runs using compressed air and features no moving parts or refrigerant.
“We call it a ‘little generator’ and it looks similar to a stepped fan blade,” explains Steve Hand, sales and project engineer at SolvAir, the UK distributor for ITW Vortec. “The bigger the step height, the more air volume you get inside the panel. As the compressed air hits the stepped blade, it creates a toroidal shape which gives the movement of the vortex passing up and down the length of the tube to generate cold air.”
The vortex tube splits the stream in two: sub-zero temperature air exits one outlet into the panel, where it displaces existing warm air that exits another outlet into atmosphere. A ducting kit allows users to dissipate cold air throughout the entire enclosure, or direct it towards a particular ‘problem’ component showing excessive heat load. The system sits on top of the enclosure, taking up no space inside and making for easy installation. It can run constantly or switch and on and off between pre-defined temperature limits using thermostatic control.
“The system also combats the issue of dust entering from the surrounding environment, as it creates a small amount of positive pressure within the panel,” reveals Hand. “By constantly delivering cold air into the enclosure, it creates a pressurised vessel that dust cannot penetrate.”
He adds: “Air conditioning units can sometimes clog in dusty environments, leading to ongoing filter changes. Also, air conditioners use refrigerant, which you may have to recharge, while also monitoring leaks to avoid performance dropping off.”
Most applications seen by SolvAir involve existing panels demonstrating thermal issues. In these instances, the company will size the enclosure cooler appropriately, taking into account existing temperatures inside and outside the panel, and the desired target temperature.
“Electrical components have a rated operating temperature range, and while most panel designers will be aware that components such as inverters require attention, some types of common switchgear get overlooked,” says Hand.
While specifying enclosure cooling adds cost, the long-term TCO (total cost of ownership) is likely to be significantly lower because the electrical equipment housed within the panel will function within its specifications. The upshot is greater reliability and fewer premature failures.