Almost everyone involved in the maintenance of electrical enclosures has, at one time or another, faced problems with overheated electrical enclosures. In most instances, the obvious solution was to install or upgrade the cabinet cooling fan only to find that it didn’t work too well.
Here are some reasons why the obvious solution may not have worked.
1. Assuming Ambient Temperature Doesn’t Matter
Although everyone understands these problems occur in hot weather, most maintenance personnel instinctively assume that blowing more air through the enclosure will help. While it is true that this will reduce the enclosure temperature slightly, it may not be the right solution.
The first step is to establish the maximum allowed enclosure temperature based on the thermal rating of the equipment inside. If this is lower than the ambient temperature, increased air flow won’t help because fans only remove heat, they don’t cool, and consequently the enclosure temperature will always be higher than the ambient temperature. An enclosure air conditioner is needed.
2. Ignoring the Heat Load
The enclosure’s temperature is directly related to three factors: the ambient temperature measured in degrees Fahrenheit, the heat load of the enclosure in watts and the cooling fan airflow in CFM.
In very simple terms, the temperature inside the enclosure is calculated as follows:
Enclosure Temperature = (3.16 x Heat Load)/Air Flow + Ambient temperature
Although this formula ignores factors such as cabinet surface area and solar heat load, it clearly shows the linear relationship between heat load and cooling capacity. When faced with enclosure overheating problems, it’s a good idea to establish the current enclosure heat load, and using an online Enclosure Temperature Management Calculator, calculate the enclosure’s cooling requirements to see how much cooling is needed.
3. Using Fans That Are Inadequate
It’s not uncommon to find that cabinet cooling fans were installed without much thought given to the application; invariably they are too small. This may have been because of an earlier overheating problem or because of a belief that the enclosure needed cooling without consideration being given to the heat load. If the fans are too small, the enclosure will overheat.
4. Incorrectly Positioned Fans
Fans should always be positioned so that they support the natural tendency of hot air to rise. The air inlet must be at the bottom and the outlet at the top. Generally, it’s better to pressurize the enclosure by fitting fans at the bottom inlet, but it’s also feasible to use exhaust fans fitted at the top outlet.
5. Not Paying Attention to Airflow
Air, like any gas or vapor, will always take the path of least resistance and find the easiest route through the enclosure. Accordingly, it’s essential to provide channels to guide the air to where it’s needed and also to place equipment that generates a lot of heat in the air flow, preferably near the exhaust vents. Make certain that documents, shelves and wiring harnesses don’t interrupt the airflow.
6. Discounting Filtration
Never underestimate the amount of dust and dirt in the air. Fluff drawn into an enclosure blocks inlet vents and restricts air flow. Additionally, hard insulating dust particles damage electrical contacts, leading to open and burnt contacts. Filters should always be installed, even for indoor locations.
Filtration capacity should be matched to the amount and type of dust in the environment. In very dusty locations, clean or replace filters often or give consideration to a closed loop cooling solution.
7. Not Protecting Fans from the Elements
When enclosures are outdoors or in any location where they may be subject to water spray, there will be a natural tendency for cabinet cooling fans to draw in moisture that could damage the fans and harm other equipment. To avoid this, protect the fans by fitting shrouds that keep water out.
8. Using Fans in Corrosive Locations
Similarly, in locations where corrosive vapors are present, these will be drawn into the enclosure and corrode sensitive surfaces. In most instances, filters are of limited use because vapor will pass through them. If corrosion is an issue, a closed loop cooling solution is advisable.
Getting Help with Cooling Fan Problems
Given the right conditions, cabinet cooling fans are a great low-cost cooling solution, but when used incorrectly can lead to expensive downtime and repairs. If you need more information on how enclosure cooling works, download our useful Enclosure Cooling Glossary, or contact our Support Team for help on identifying the cause and finding the right solution.