Single-walled or
double-walled?

What do single-walled and double-walled mean?

For outdoor enclosures, the term describes the wall construction: a single-walled enclosure has a single outer wall. A double-walled enclosure additionally has an inner wall shell with an air gap or insulation. This second shell acts as a thermal buffer zone — against the sun in summer and the cold in winter.

For equipment that operates permanently outdoors (5G base stations, inverters, battery storage, traffic technology), temperature stability is decisive for service life and reliability. This is exactly where the double wall plays to its strengths.

In terms of design, the double wall consists of the load-bearing outer shell and an inner shell, separated by a defined air gap. The gap is designed so that air can circulate from bottom to top — the heated air leaves the cavity at the edge of the roof without touching the enclosure interior. In the ZPAS SZD series, both shells are made of aluminium: corrosion-free, light and a good heat conductor, which additionally promotes dissipation via the outer shell.

Single-walled vs. double-walled compared

When single-walled is enough

A single-walled outdoor enclosure is the economical choice when the ambient conditions are moderate and the installed equipment generates little heat of its own — for example passive distribution units, shaded or roofed installation sites. It is lighter and cheaper and can be supplemented with ventilation or a sun shield roof if required.

When the double wall pays off

If the enclosure is in direct sunlight or contains active, heat-generating equipment (5G baseband, inverters, battery storage, edge computing), the double wall noticeably reduces the external heat load. This lowers the cooling demand — and with it the energy consumption across thousands of sites. How much cooling is ultimately needed can be estimated in advance: → calculate cooling capacity.

Double wall + active climate control = the best result

Double wall and active cooling are not an either-or: the double wall reduces the load, the climate control maintains the target temperature. This combination is the most efficient at high heat loads, because the cooling unit can be sized smaller and uses less energy.

Solar load in figures: a worked example

A simple rough calculation shows how large the effect of the sun is. On a clear summer day in Central Europe, up to 1,000 W of radiant power per square metre strikes a sunlit surface. An outdoor enclosure with an 800 × 600 mm footprint and a height of 2,000 mm offers the sun — depending on its position — around 2 m² of exposed surface (long side plus roof). With a light-coloured powder coating, roughly half of the incident radiation is absorbed: this creates several hundred watts of additional heat load, 700 W and more at the midday peak. That corresponds to the power loss of another large inverter — except that this load cannot be switched off and occurs precisely when the ambient temperature is already at its highest.

With a double-walled enclosure, the radiation first strikes the outer shell. The air in the wall cavity heats up, rises and carries a large part of the heat away by convection before it reaches the inner shell — on the same principle as a rear-ventilated façade. Only a fraction of the solar load reaches the enclosure interior, and the cooling unit can be sized correspondingly smaller. You can calculate the actual design with the cooling capacity calculator.

Condensation: the underestimated problem

Besides heat, condensation is the second great enemy of outdoor installation. At night the enclosure wall cools down; when warmer, humid air inside then meets the cold wall surface, the temperature falls below the dew point — water condenses on the ceiling and walls. The consequences: corrosion, leakage currents and, in the worst case, electronics failures.

Single-walled enclosures are more susceptible to this, because the inside of the outer wall almost reaches the outside temperature at night. The double wall acts like a vacuum flask: the inner shell stays closer to the internal temperature, and the temperature falls below the dew point far less often. Condensation cannot be prevented completely by design, however — for critical equipment, a thermostat-controlled enclosure heater is therefore part of the package, reliably keeping the internal temperature above the dew point. More on humidity and material selection: → corrosion protection outdoors.

The energy balance over the service life

The second wall shell is paid for once — cooling costs money every operating day. Where the double wall significantly reduces the solar load, both the required cooling capacity and the operating hours of the cooling unit go down. Over a typical service life of 10 to 15 years this adds up: lower consumption, less wear on the cooling unit, longer maintenance intervals. For operators with many identical sites — mobile communications, charging infrastructure, rail technology — the effect multiplies across the entire fleet.

The greatest leverage comes from combining the double wall with the AHP heat pump, which cools and heats with a single unit (COP up to 5) and uses less energy than a conventional air conditioner combined with a separate electric heater: reduced load times efficient technology.

When does the double wall pay off?

As a rule of thumb, the double wall pays off whenever at least one of these points applies:

• Directly south-facing without shading — full solar load for hours
• Active equipment with high power loss (baseband, inverters, battery storage, edge servers)
• Critical availability — every temperature-related failure costs more than the extra wall shell
• Many identical sites — the energy-saving effect multiplies across the fleet
• Extreme sites with severe frost or large day-night fluctuations (condensation risk)

Conversely: at a shaded or roofed site with passive equipment, the single-walled enclosure remains the economical choice — the money saved is often better invested in well-designed ventilation.

More on this topic: outdoor enclosure guide · aluminium, steel or stainless steel? · IP54 or IP55?