Outdoor cabinets across Malaysia, Indonesia, Thailand, the Philippines, Saudi Arabia and the UAE are routinely fitted with a filter fan, a heat exchanger or an air conditioner picked from a catalogue page, and then overheat in the first June. The short version: a fan cannot cool below ambient, an air-to-air heat exchanger obeys the same physics, and a compressor loses a third of its nameplate at 50 °C.
No fan cools below ambient
Most overheating failures we see in Southeast Asia and the Gulf are not enclosure failures. The steel, the gasket and the paint are fine. The cooling strategy failed, because it was sized on a nameplate figure measured at 35 °C and then installed where shade temperature reaches 48 °C for six hours a day.
The mental model to fix first: a filter fan does not cool, it exchanges. It pushes ambient air through the cabinet and the internal temperature settles wherever the heat load and the airflow put it. A 48 °C site gives a 48 °C intake, plus a rise of 8–15 K. No fan produces air colder than the air it draws in.
So the question is not which fan. It is how many kelvin above ambient the equipment can tolerate. Answer that, and half the options eliminate themselves.
Step one: the heat-load and temperature budget
Do this before opening any cooling catalogue. Five numbers are enough, and they belong in the project file, because the enclosure supplier, the integrator and the end user will otherwise assume different values.
- Design ambient. The 1% exceedance temperature in shade, not the annual average. Malaysia, Indonesia, Thailand, the Philippines, Saudi Arabia and the UAE land between 38 °C and 50 °C; inland Gulf and rooftop sites go higher.
- Solar gain. A 2 m cabinet in direct sun absorbs 150–400 W through roof and walls depending on colour, insulation and orientation. Dark grey on a west wall is the top of that range.
- Internal load. Rectifiers, PoE budget, switches, inverters, heaters and battery charging at peak. Use peak, not typical — peaks are when failures happen.
- Allowable internal temperature. Lowest component rating minus 5 K. Electronics are usually rated 55–60 °C; batteries far lower, with a life penalty per degree.
- Altitude. Above 1,000 m, fan curves and exchanger capacity fall about 10% per 1,000 m — a derating nobody applies until the first summer.
Fan cooling then needs roughly 3.1 × Q / ΔT m³/h, Q in watts and ΔT in kelvin, at sea level. A cabinet with 600 W and a permitted 10 K rise needs about 186 m³/h of net airflow after filter and louvre losses. In a 48 °C site that means 58 °C inside — at or past the rating of most outdoor electronics, and far past what a battery will accept. That is the moment to stop sizing fans.
The five options, compared honestly
This is the table we use in quotation reviews. The capacity column is quoted at the ambient the site actually sees, not at the laboratory condition.
| Option | Capacity at 50 °C ambient | Below ambient? | Typical IP | Power draw | Best fit |
|---|---|---|---|---|---|
| Filter fan + louvre | Falls with air density and filter dP | No — internal = ambient + rise | IP54 with filter | 30–120 W | Low load, clean air, site below 40 °C |
| Air-to-air heat exchanger | 30–80 W/K, collapsing as ambient rises | No — needs internal > ambient | IP55, sealed loop | 60–200 W | Dusty or sandy sites, load under 800 W |
| Wall-mount AC | 60–75% of nameplate | Yes, to a 30–35 °C setpoint | IP55 (unit sealed) | 250–600 W | Load above 500 W, any climate |
| Vortex cooler | 200–1,000 W from compressed air | Yes, well below ambient | IP65 maintained | 15–40 scfm of air | Small sealed cabinets, no refrigerant allowed |
| Passive measures only | Cuts the load 20–40% | No | Any | None | Every project, before sizing hardware |
Two rows deserve emphasis. Air-to-air heat exchangers look like air conditioners but obey the same physics as a fan: they only move heat while the inside is hotter than the outside, so capacity collapses exactly when you need it. Vortex coolers do go below ambient and keep IP65, but compressed air is the dominant operating cost, which is why they stay in small sealed cabinets.
Filter fans: sizing rules and the 45 °C wall
Filter fans remain the right answer for a large share of outdoor cabinets, provided the site stays below about 40 °C and the air is not loaded with sand.
- Size on net airflow. Filter and louvre cost 30–50% of free-air delivery once dust builds. Take the catalogue curve, apply the filter loss, then apply altitude.
- Match inlet and outlet. Inlet low, outlet high, never opposite each other on the same wall. An undersized exhaust louvre pressurises the cabinet and recirculates hot air at the top.
- Run positive pressure. Intake fan, filtered exhaust, so dust is pushed out of cable entries and door seals instead of being pulled in.
The wall is thermal, not mechanical. Once ambient plus the permitted rise exceeds the component rating, no fan arrangement fixes it: a second fan shortens the rise, it cannot remove the offset.
Compressor units above 45 °C, and the sealed alternative
Where dust, sand or salt make filtered air risky but the load is small, a sealed cabinet with an air-to-air heat exchanger at IP55 is the better engineering choice. Capacity is quoted in W/K, typically 30–80 W/K, and multiplies straight off the internal-to-ambient difference: 60 W/K against a 10 K difference moves 600 W. It also drops as you improve internal airflow, and it needs a condensate drain on humid tropical nights.
Above roughly 500 W in a hot climate, only a compressor will do. Ask for capacity at the project ambient with the derating curve attached, not a model number and a nameplate kW. Two numbers then decide the outcome.
- Derate the nameplate. Units are declared at 35 °C ambient and 35 °C internal. At 50 °C expect 60–75% of nominal, losing 2–3% per kelvin; standard condensers approach their limit near 55–60 °C, so specify the high-ambient variant.
- Set the setpoint deliberately. 30–35 °C for electronics, 25–30 °C for batteries, never lower than the application needs — every kelvin below ambient costs energy and condensate.
- Treat it as a single point of failure. A sealed cabinet with one unit and no redundancy fails completely when that unit trips. Add N+1 in larger cabinets, or a passive bypass that keeps the load alive until service arrives.
Model the energy at quotation stage. At a COP of 2.5–3.0, removing 600 W costs 200–240 W continuously — a real annual cost in a hot climate, and a reason to spend on passive load reduction first.
Cut the load before buying cooling
A watt removed from the heat budget is five to ten times cheaper than the cooling capacity bought to remove it. These measures are on the enclosure drawing, so they cost little at order stage.
- Shade and orientation. A sun shield or roof extension over a west-facing cabinet removes much of the solar gain. Where layout allows, mount on a north or east wall.
- Colour and insulation. High solar reflectance cuts absorbed radiation; a 10–20 mm insulated panel or double-wall roof flattens the midday peak and reduces internal condensation.
- Split the hot compartment. Cooling a small compartment that holds only the sensitive equipment is far cheaper than cooling the whole envelope.
- Circulate internally and seal properly. A 2 m cabinet without internal fans runs 10–15 K hotter at the top; a few watts of circulation removes the hot spot that actually trips the load. Cable entries, unused knockouts and door gaskets are the usual paths for hot, humid or dusty air.
Dust, sand and salt: the maintenance side
In Gulf and coastal sites the cooling system fails on maintenance more often than on capacity. A G3 filter loaded with fine sand can lose half its airflow within weeks, which raises internal temperature and looks exactly like an undersized fan.
- Filter class and access. G3 for normal dust, G4 where sand is airborne, sized for the higher pressure drop. Specify tool-less access at a reachable height, because filters that need a ladder and a screwdriver will not be changed.
- Condition monitoring. A differential pressure switch or an internal temperature alarm turns a slow failure into a work order.
- Coating. Coastal sites need ISO 12944 C5-M on the enclosure and coated coils; uncoated aluminium fins are the first thing salt destroys.
Frequently asked questions
Can I use a bigger fan instead of an air conditioner?
Only if ambient plus the permitted rise stays below the component rating. In a 48 °C site the inside sits at 55–60 °C whatever the fan size. Above about 45 °C ambient with more than a few hundred watts, mechanical cooling is the only option.
How do I size a filter fan for an outdoor cabinet?
Required flow is about 3.1 × Q / ΔT in m³/h, Q in watts, ΔT in kelvin. For 600 W and 10 K that is 186 m³/h net, so pick a fan whose curve still delivers it after filter, louvre and altitude derating.
Is an air-to-air heat exchanger better than a filter fan?
Where dust, sand or salt make filtered air risky, yes — the internal loop stays sealed at IP55. Thermally it is no better: capacity depends on the internal-to-ambient difference, so it also cannot go below ambient.
Why does my 1 kW air conditioner only deliver 700 W?
Nameplate is declared at 35 °C ambient and 35 °C internal, and capacity falls 2–3% per kelvin above that. At 50 °C, 60–75% of nominal is normal. Ask for the derating curve before accepting a capacity figure.
What internal temperature should a battery cabinet be held at?
25–30 °C in hot climates, because life falls quickly above 35 °C. That is below ambient most of the year in the Gulf and Southeast Asia, so cooling must be mechanical and the load calculation must include battery losses.
How often should filters be changed?
Every one to three months in dusty or sandy sites, and after a sandstorm. Differential pressure is the reliable indicator, not the calendar. A clogged filter is the most common cause of a cabinet that used to run fine.
About Xingyuan Electric (Suzhou) Co., Ltd.
Xingyuan Electric (Suzhou) Co., Ltd. builds sheet metal enclosures and electrical assemblies in Lili Town, Wujiang District, Suzhou, China. A 30+ person team works from a 3,000+ production base with more than 20 laser cutting, CNC bending and welding machines, delivering standard orders in 7–15 days and building to drawing or to sample. We supply telecom and edge cabinets, energy storage cabinets, EV charger enclosures and industrial control panels, including IP55/IP65 outdoor enclosures with insulated roofs, sun shields, filter apertures and pre-cut openings for wall-mount cooling units. Give us the site ambient and the internal load, and we will quote the enclosure with the cooling interface prepared for your chosen system.