Rittal SK 3273.500 TopTherm Blue e Roof-Mounted Cooling Unit

A roof-mounted cooling unit for enclosures up to about one kilowatt

The Rittal SK 3273.500 is a TopTherm Blue e roof-mounted cooling unit for control cabinets. It has a total cooling output of 1.1 kW at 50 Hz and 1.2 kW at 60 Hz under the L35/L35 test condition, an integral e-Comfort controller and electric condensate evaporation as standard, so no drain pipe is required. The condenser carries a hydrophobic RiNano coating and the unit arrives fully wired, with a plug-in terminal strip, a drilling template and assembly parts.

Technical specifications

Refrigerant status and the Blue e+ alternative

The datasheet carries a product modification note: the unit will be available with R134a refrigerant until 31 December 2026, and from 1 January 2025 it no longer meets the GWP requirements for the US market. Rittal recommends a Blue e+ cooling unit as the alternative, and a wall-mounted Blue e+ range is covered on the Rittal Blue e+ cooling units page. Check availability and refrigerant before ordering.

Sizing and installation

The e-Comfort controller can be linked to an IoT interface through the Blue e IoT adaptor for units from 500 W output. Rittal also notes that the low noise level suits office applications. Roof units mount through a cut-out in the enclosure roof using the drilling template. Size the unit from the internal heat loss, the maximum internal temperature and the ambient temperature at the site: at an ambient of 50 C the output falls to 0.85 kW. Keep internal and external air circuits unobstructed and avoid air short-circuits.

Key features of the SK 3273.500

• Roof mounting: the unit sits on top of the enclosure, leaving the side walls and door free for components, operator devices and cable entries.
• Separated air circuits: the internal circuit recirculates cabinet air through the evaporator while the external circuit carries heat away through the condenser, so dusty ambient air does not enter the enclosure.
• e-Comfort controller: the set point is adjustable within the published range and the controller is prepared for connection to the Blue e IoT adaptor.
• Electric condensate evaporation: moisture removed from the cabinet air is evaporated by the unit itself, which avoids a drain hose running down the outside of the cabinet.
• RiNano coated condenser: the hydrophobic coating reduces the tendency of dust and oily deposits to cling to the condenser fins.
• Delivered ready to install: fully wired, with plug-in terminal strip, drilling template and assembly parts in the box.

How to check whether 1.1 kW is enough

The cooling output of an enclosure cooling unit has to cover two heat sources: the losses of the installed equipment (drives, power supplies, PLCs, contactors) and the heat that enters through the enclosure walls when the ambient air is hotter than the desired internal temperature. In a cool climate the second term is small or even negative; on a sunny site in Oman it is often the larger of the two. A sound selection therefore adds the published power loss of every device to a calculated wall heat gain based on enclosure surface, mounting position and the temperature difference between outside and inside.

Rittal publishes two cooling output values for this unit. The L35/L35 figure is the standard comparison point; the L35/L50 figure is lower and reflects a smaller temperature lift. Compare the calculated load against the output at the condition closest to your real site rather than the headline number, and leave a margin for dust on the condenser and ageing of the equipment. Where the calculated load is clearly above the rating, the answer is a larger unit or a Blue e+ unit, not a lower set point.

Operating limits worth noting

The datasheet gives an operating ambient range up to 55 °C at 50 Hz, reduced to 50 °C at 60 Hz. Outdoor enclosures in direct summer sun in the GCC can exceed the air temperature around them, so shading, a canopy or a sun-protected location for the cabinet helps keep the unit inside its envelope.

Installation and maintenance practice

Cut the roof opening using the supplied drilling template and make sure the enclosure roof is flat and stiff enough to carry the unit without flexing, because a distorted seal lets unconditioned air bypass the cooling circuit. Keep the internal air path clear: tall components or cable ducts directly under the cold-air outlet can short-circuit the air flow and leave hot spots lower in the cabinet. Cold air should never be blown directly onto active electronics.

The enclosure itself should be well sealed. Open cable entries, missing gland plates or a door that is often left ajar draw in humid air, which the unit must then dehumidify; this increases condensate and reduces the useful cooling. A door limit switch connected to the controller, as Rittal recommends for its cooling units, switches the fans off while the door is open.

On the external side, the condenser is the part that suffers most in desert and coastal conditions. Inspect it at regular intervals, clean it with compressed air or a soft brush, and check that nothing obstructs the external air inlet and outlet. A clogged condenser raises the condensing pressure, reduces the cooling output and can trigger high-pressure alarms on the controller.

Typical applications in Oman and the GCC

Roof-mounted units of this size are used on control panels for pumping stations, packaged water treatment skids, HVAC plant rooms, conveyor and packaging lines and small motor control centres where floor space beside the cabinet is limited. In oil and gas support facilities and utilities, they are often specified on local control panels that house a PLC, a few drives and power supplies with a modest total loss. Because the unit is closed-loop, it also suits sites with sand-laden or salty air where filter fans would quickly clog or let contamination in.

What to include in an RFQ

• Model number SK 3273.500 and the quantity required.
• Supply voltage and frequency at site (the unit is rated 230 V, 1~, 50/60 Hz).
• Enclosure dimensions, installation type (free-standing, wall, row) and whether it stands indoors or outdoors.
• Total equipment heat loss and the maximum ambient temperature you expect.
• Whether an R134a unit is acceptable for your project or a Blue e+ alternative must be offered.
• Any accessories such as the Blue e IoT adaptor or a door limit switch.

Documents and quotation

The Rittal datasheet for SK 3273.500 is available on this page, and further climate products are listed under Cooling. For a quotation send the enclosure heat load, ambient temperature, supply voltage and frequency, and quantity.