Electrical Enclosure Cooling: Heat Load, Cooling Methods and Fanless Computers for Sealed Cabinets

Electrical enclosure cooling is the removal of heat produced inside a closed cabinet or enclosure, by drives, power supplies, PLCs, switches and computers, so the air inside stays within the temperature ratings of the equipment. Heat can leave through the enclosure walls on their own, or with help from filtered fans, heat exchangers, air conditioners, vortex coolers or thermoelectric coolers, and each method trades cost, sealing and maintenance differently.

The question has become more pressing as computing has moved into the cabinet. Machine vision, edge AI, protocol gateways and local data logging now run on industrial edge computers that sit beside the drives and PLCs, often in sealed or waterproof boxes chosen to keep out dust, water and contaminants. A sealed box keeps the dirt out, but it also keeps the heat in.

This guide sets out the cooling methods and how they compare, how to calculate the heat load of an enclosure with a worked example, which temperature to design for, how NEMA and IP ratings limit the choice, and how to choose a computer that adds as little as possible to the problem, including flat-top systems that use the enclosure wall as their heatsink.

There are seven common ways to cool an electrical enclosure. The first two exchange air or heat with the room and can only bring the inside down towards the outside temperature; the rest can hold the inside at or below it. The capacities are typical ranges across catalogue products, not limits.

Two questions settle most choices. Is the air outside the enclosure always cooler than you need the inside to be? If it is, natural convection, fans or a heat exchanger can do the job. Does the enclosure have to stay sealed against dust, oil mist or water? If it does, filtered fans are out and the choice is between the closed-loop methods. Everything after that is a matter of capacity, running cost and what utilities the site can provide.

Heaters belong in the same plan. An enclosure that sits in an unheated building or outdoors can fall below the lower rating of its contents or below the dew point overnight, and a small thermostatic heater keeps it above both. Our FAQ on preventing condensation on electronics covers the dew point side of that.

Natural convection and filtered fans

With no cooling equipment at all, heat leaves an enclosure by conduction through its walls and by convection and radiation from the outer surface. The amount depends on the wall area, the material and the difference between inside and outside temperature, which is why a closed cabinet that is fine in winter can overheat in July.

Filtered fans push room air through the enclosure and out of an exhaust grille. They move a lot of heat for little cost, but the inside can never be cooler than the room, the filters clog in dusty air and the openings reduce the ingress rating to around IP54 at best. Mount the fan low and the exhaust high so it works with the natural rise of warm air.

Heat exchangers

An air-to-air heat exchanger keeps two separate air loops: internal air circulates across one side of a heat exchange core and ambient air across the other, so heat passes through without the outside air entering. It keeps the enclosure sealed, but like a fan it needs the outside air to be cooler than the inside. An air-to-water heat exchanger replaces the outside air loop with a water circuit, which lets it cool below a hot room if cool water is available.

Air conditioners, vortex coolers and thermoelectric coolers

An enclosure air conditioner uses a refrigeration circuit to hold the inside below the outside temperature, with a closed internal loop that preserves the seal. It handles the biggest loads in the hottest places, but it needs a condensate drain or evaporator, coil cleaning and, like any refrigeration plant, power of its own.

A vortex cooler turns filtered compressed air into a cold stream inside the enclosure, with no moving parts or electrics in the cabinet, which suits washdown and hazardous areas that already have plant air. A thermoelectric cooler uses Peltier modules to pump heat through the wall electrically. It is compact, solid state and works in any orientation, but its efficiency is lower than a compressor, so it suits small loads.

Every watt that a device draws and does not send out of the enclosure as useful work ends up as heat inside it. Power supplies and drives lose a few per cent of what they handle, while computers, PLCs and switches turn almost all of their input into heat. The figures below are typical ranges to start an estimate; use the manufacturer’s stated losses wherever you have them.

The computer is often the easiest line in the list to shrink. A low-power gateway on an embedded processor adds a fraction of the heat of a build on a 65 W desktop processor, and a computer that conducts its heat straight into the enclosure wall stops warming the air around the other equipment. Our guide to processor TDP explains how the processor power figure relates to the heat a system really produces.

The calculation balances three quantities: the heat produced inside, the heat the walls can pass to the outside at the temperature difference you allow, and the gap between them, which the cooling equipment must cover.

Here k is the heat transfer coefficient of the wall material and A is the effective surface area, the sides that can actually shed heat. A wall-mounted cabinet loses little through its back, and a cabinet in a row loses little through the sides it shares, so sizing guides weight each surface by its position. The method in IEC TR 60890, which IEC 61439-1 allows panel builders to use within limits to verify temperature rise by calculation, works the same way.

These are typical values used in sizing guides; enclosure makers publish their own figures, and they should be used where you have them. Altitude matters too: thinner air carries less heat, so the fan factor rises above sea level and air-cooled equipment may need derating.

Take a wall-mounted painted steel cabinet 800 mm high, 600 mm wide and 300 mm deep in a factory that reaches 35 °C in summer. It holds a small drive, a PLC, a 24 V supply, a managed switch and a 35 W fanless box PC running vision software.

The walls alone remove about a third of the heat, so the cabinet needs help. In a clean room a filtered fan rated comfortably above 36 m³/h with its filter fitted would do; on a dusty floor, a heat exchanger of about 12 W/K keeps the seal. If the same cabinet sat beside a furnace where the air reaches 45 °C, neither would work and an air conditioner of roughly 250–300 W would be needed.

Now change one line. Replace the 50 W box PC with a 15 W-class gateway on an Intel Atom or Processor N part and the internal load falls to about 145 W, cutting the shortfall by roughly a third. Replace it instead with a flat-top computer bolted to the cabinet wall and its heat goes straight into the steel rather than into the air around the drive. The heat still has to leave through the wall, but the PLC and drive see cooler air. This is why the computer is part of the cooling design, not an afterthought.

Design to the lowest maximum rating of anything inside. Many PLCs and drives are rated for an ambient of 40 to 55 °C inside the enclosure, often with derating above 40 °C, and many panel builders aim to hold the inside at about 35 °C to leave margin. Fanless industrial computers usually reach 50 to 70 °C, so they are rarely the limiting item, but SSDs, batteries and touch displays may be.

Lower is not always better. Cooling the inside far below the room air invites condensation whenever the door opens or the cooler cycles, so set air conditioners no lower than the equipment needs. Electronics also age faster as they get hotter; as a rule of thumb, the life of electrolytic capacitors roughly halves for every 10 °C rise, which is one reason reliability predictions depend on temperature, as our guide to MTBF explains.

An enclosure rating describes what the box keeps out. Any cooling device mounted through the wall has to match it, or it becomes the weak point. NEMA 250 types and IEC 60529 IP codes are tested differently, so they are not exact equivalents; the comparisons below are the ones commonly quoted, and a NEMA type can be said to meet an IP code but not the other way round. Our FAQ on NEMA vs IP ratings covers the differences.

In food and beverage plants the cooling device also has to survive the cleaning regime. A NEMA 4X stainless enclosure with a vortex or thermoelectric cooler is a common answer, and our IP rating chart sets out what each IP level is tested against. Cable entries matter as much as the cooler, since every gland or connector is another possible leak path.

The best computer for a sealed enclosure is one that runs at the enclosure’s internal temperature without needing air moved across it, and that adds as little heat as the workload allows. In practice that means a fanless design, a processor sized for the sustained load rather than the peak, and a temperature rating that covers the inside of the box rather than the room.

Why there is more computing in the cabinet

Four trends have pushed more processing into closed enclosures. AI accelerators, from GPUs to NPUs built into the processor, let an edge AI computer run inspection, anomaly detection and predictive maintenance beside the machine instead of in a data centre. Compact designs put that compute into spaces that once held only terminals and relays. 5G and low-latency networks make it practical to link many small edge nodes rather than one central server. And low-power processors with dynamic power management let a computer run from a solar or battery supply at a remote site.

Each trend adds a computer, and its heat, to an enclosure that was sized for something else. Choosing an industrial PC with the enclosure in mind avoids most of the trouble.

Finned convection or flat-top conduction

A finned fanless industrial computer sheds heat into the air around it, which in a sealed box is the enclosure air. That works when there is space around the fins and the internal air stays well below the computer’s rating. Our guide to how a fanless PC works covers fin orientation and clearances.

A flat-top computer replaces the fins with a broad, flat heat spreader that bolts to the enclosure wall or a cold plate, turning the cabinet itself into an extended cooling surface. Reserved screw holes in the heat spreader hold it firmly against the wall, and a thermal pad fills the gaps. Mounting to bare metal, ideally aluminium, gives the best result, and the surface area and the air outside the wall decide how much heat it can pass on. A flat-top design is also lower than a finned one, which saves depth in shallow cabinets and machine housings. Our FAQ on conduction cooling explains the principle.

Manufacturers rate flat-top systems on a defined plate, so read the condition behind the number. Neousys rates its NRU-154-JON8 from −25 to 60 °C in its 20 W mode when it is mounted on a 50 × 50 cm metal plate or cabinet, but only to 45 °C without that conduction path. The wall is part of the cooling, and an undersized or painted mounting face changes the result.

Size the processor for the box

Fanless systems are rated for a maximum processor power at a maximum ambient, and the two trade off. Several of our flat-top builds run 65 W desktop processors configured to 35 W for the in-cabinet envelope, and many embedded processors let the power limit be set in the BIOS. A processor that runs steadily within its limit avoids thermal throttling when the cabinet is at its hottest, and our comparison of active vs passive cooling covers when a fan-cooled build is the better fit.

Wide-temperature components finish the job. A system rated to 70 °C often reaches that figure only with industrial temperature SSDs and memory, so specify them with the computer; our wide temperature computers list the rating for each build.

These systems show the approaches above. We configure the BIOS power limits to suit the enclosure, fit wide-temperature memory and storage where the site needs them, image the operating system and test every computer before it ships.

Where the computer has to sit outside a cabinet altogether, our guide to designing outdoor computer enclosures covers solar gain, sealing and mounting for roadside and pole-top boxes, and ways to mount an industrial computer compares wall, DIN rail and panel mounting. In practice, an outdoor PC for weather monitoring and a waterproof AI computer on autonomous tractors show sealed systems at work.