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A dusty workshop is a good reason to keep outside air out of a control cabinet. It is not enough reason to choose an air-to-air heat exchanger. The first question is how much cooler the air entering the exchanger will be than the permitted cabinet temperature during production.
If the cabinet must stay at 40 °C and the exchanger draws in 40 °C air, a larger exchanger will not solve the problem. There is no temperature difference available to carry the heat away at that target. SUWI starts with this check before comparing models.
Filter fans provide an economical cooling solution by exchanging internal cabinet air with surrounding air. However, they require external air exchange, which may introduce dust, moisture, or other contaminants into the enclosure.
Enclosure air conditioners use refrigeration to remove heat and can cool below ambient temperature within their specified operating range. Compare their electrical consumption and maintenance requirements at the actual load and temperatures, rather than assuming one technology is always more efficient.
See the TopTherm air-to-air heat exchanger for the product configuration. The selection below explains how to read its W/K output against the application.
An air-to-air heat exchanger transfers heat from warmer cabinet air to cooler external air through a heat-transfer core. It has no refrigeration circuit and cannot maintain cabinet air below the external inlet air temperature while removing heat.
The heat transfer is driven by the temperature difference. Fans normally move air through the internal and external circuits, so the unit still requires electrical power. The absence of a compressor does not mean the device operates without fans or maintenance.
The two circuits remain separate. That keeps external cooling air out of the cabinet, but it does not remove moisture already inside.
Check the mounting seal, cut-out dimensions, cable entries and intended installation orientation against the selected model’s instructions.
An air-to-air heat exchanger operates using two independent airflow circuits.
For a given model, less temperature difference means less heat can be removed. Read the output in W/K together with the manufacturer’s reference temperatures and rating conditions. It is not a fixed cooling capacity in watts.
Use the permitted cabinet temperature and the highest credible external inlet temperature at the exchanger. A room thermostat reading can miss hot air trapped behind the cabinet or recirculated from nearby equipment.
The internal airflow circuit continuously circulates air inside the electrical cabinet. Heat generated by components such as PLCs, servo drives, variable frequency drives, and power supplies is absorbed by the internal air.
This heated internal air passes through the heat exchanger core, where thermal energy is transferred to the external airflow circuit.
The external airflow circuit draws ambient air across the opposite side of the heat exchanger core and removes the transferred heat to the surrounding environment.
Although heat is transferred between the two air streams, the air itself does not mix.
The important difference is whether the cooling method can meet the temperature target and whether outside air may enter the cabinet.
| Cooling Method | Filter Fan | Air-to-Air Heat Exchanger | Enclosure Air Conditioner |
|---|---|---|---|
| Cooling principle | Air exchange | Heat transfer | Refrigeration |
| External air enters cabinet | Yes | No | No |
| Cooling below ambient temperature | No | No | Yes, within specified operating limits |
| Protection against dust and moisture | Depends on the fan/filter assembly and installation | Depends on the unit rating, seals and installation | Depends on the unit rating, seals and installation |
| Energy consumption | Fan power; check required airflow | Fan power; check available temperature difference | Depends on load, temperatures and control method |
| Maintenance requirement | Inspect and replace filters as required | Inspect fans, seals and external heat-transfer surfaces | Inspect air paths, condensate handling and model-specific service items |
| Main selection condition | Where clean external air and sufficient temperature difference are available | Where air separation is needed and W/K output meets the load at the available temperature difference | Where refrigeration is needed and capacity is adequate at the design point |
For a detailed comparison of filter fans and enclosure air conditioners, refer to:
Filter Fan vs Enclosure Air Conditioner
Maintaining High Enclosure Protection
The exchanger separates the cooling air circuits. Whether the finished cabinet meets its required IP rating still depends on the selected unit and installation. Check this once against the exact model and mounting instructions; do not infer it from the enclosure shell.
The outside core is still in the workshop air. Leave room to inspect and clean it. If cleaning requires moving the cabinet or removing adjacent machinery, that is an installation problem to resolve before ordering.
Suitable for Dusty and Contaminated Environments
Industrial environments often contain conditions that can negatively affect electrical components, including:
Using a filter fan in these environments may require frequent filter replacement and maintenance.
What You Save by Avoiding a Compressor
Unlike enclosure air conditioners, air-to-air heat exchangers do not require compressors or refrigerant circuits.
Their cooling performance relies on:
An air-to-air unit has no compressor load, but it still uses fan power. Compare the candidate units at the temperatures and heat load they will actually see. A low electrical input is of little use if the exchanger cannot hold the required cabinet temperature.
Check the temperature difference and required output first. Then check air separation, installation space and environmental suitability.
Applications Requiring High Protection Levels
When electrical cabinets must maintain protection against dust, water, or industrial contamination, maintaining a sealed enclosure is often a priority.
Specify the protection required for the completed assembly, then verify the heat exchanger’s rating, gasket and mounting details. Air separation alone does not establish water-jet, outdoor or corrosion suitability.
When an Air-to-Air Heat Exchanger May Not Be Suitable
Does the Output Cover Your Load?
Do not treat an air-to-air heat exchanger as the next capacity step above a filter fan. Both depend on cooler external air. The heat exchanger is considered when air separation is needed and its output is sufficient at the available temperature difference.
Compare the required W/K output, electrical supply, mounting space and protection requirements against the selected model. Use our filter fan and air-to-air heat exchanger category to review the relevant product options.
Before selecting a heat exchanger, engineers should calculate the cabinet heat load to confirm whether the cooling capacity meets the application requirements.
Reference:
Cabinet Heat Load Calculation Guide
Environments Where External Air Quality Is Poor
An exchanger that only just covers the calculated load in its clean rated condition leaves no allowance for performance loss from contamination. Oil mist can bind dust to the outside surfaces. Confirm the cleaning method and access, and use the manufacturer’s sizing guidance to assess the allowance needed. Do not assume the data-sheet W/K output will remain available regardless of fouling. If oil deposits are expected to build up quickly and the external surfaces cannot be cleaned in place, resolve that restriction before choosing this arrangement—even if the clean-unit calculation passes.
If you do not know the heat load, start with the component list.
Send the full article numbers and quantities of the drives, power supplies and other installed devices, together with the cabinet dimensions and layout. State which devices run together, their typical and demanding operating states, and whether any heat-producing parts are mounted outside the enclosure. Include manufacturer loss data if available. Motor rated power alone is not the heat released by its drive inside the cabinet.
You do not need to invent a wattage before asking SUWI for a selection review. We can review the supplied component and application data and identify which loss figures still need confirmation. A preliminary assessment based on incomplete data should remain provisional.
The next step is to put numbers against the temperature difference. “Moderate heat load” is too vague to select a model.
Cabinet Heat Load
The cooling requirement depends on:
Determine the net heat removal required from the exchanger at the design condition. Include component losses and relevant solar or surface heat gains, and account for heat dissipated through the enclosure walls without counting it twice. Follow the manufacturer’s calculation method for internal fan losses and other model-specific allowances.
Use the cabinet heat-load calculation guide to prepare the inputs, then compare the required output with a heat exchanger model at the relevant temperatures.
Reading a W/K rating: a 300 W example
For an initial estimate: required specific thermal output G = Q / ΔT. Here G is in W/K, Q is the net heat removal required from the exchanger in watts, and ΔT is the positive difference between the internal design temperature and the external inlet temperature, using the manufacturer’s reference conditions. A temperature difference of 1 °C equals 1 K.
Assume the exchanger must remove a net 300 W and the permitted cabinet temperature is 40 °C. These are illustrative inputs, not a customer case or model recommendation.
| External inlet | Available difference | Initial required output |
|---|---|---|
| 30 °C | 10 K | 300 / 10 = 30 W/K |
| 35 °C | 5 K | 300 / 5 = 60 W/K |
| 40 °C | 0 K | Cannot remove the positive load at a 40 °C cabinet target. |
Does a 30 W/K result mean you should order a 30 W/K unit?
Not yet. At a 10 K temperature difference, 30 W/K gives an estimated 300 W under the simplified assumptions. That only matches the example load; it does not establish an allowance for uncertain losses, contamination or installation effects. First confirm that the manufacturer’s rating conditions match the calculation and that the 300 W is the exchanger’s net duty. Then check mounting, airflow and the expected condition between cleaning intervals. Use the manufacturer’s sizing method to decide whether the candidate is adequate. Do not apply an unexplained percentage margin or assume the next size up resolves every issue.
At 5 K, the same 30 W/K unit gives an estimated 150 W. It would not meet the example’s 300 W duty. More favourable workshop temperatures cannot compensate for an inadequate output during the required production condition.
The same load requires twice the W/K output when the available temperature difference falls from 10 K to 5 K. If the external air reaches the cabinet limit, selecting a larger exchanger does not restore that missing temperature difference.
Rittal lists SK 3126.100 at 17.5 W/K. Under the same simplified assumptions, that gives about 175 W at 10 K and 87.5 W at 5 K. Both are below the example’s required 300 W, so this model does not pass that initial screen. This is not a final model selection: confirm the rating conditions, complete enclosure heat balance and installation allowances with the manufacturer’s method.
Check the data sheet before comparing products: “Specific thermal output” is the W/K figure used for the thermal calculation. “Rated operating voltage” determines the supply variant. “Dimensions” and the installation drawing determine physical fit and cut-out requirements. Air throughput is a separate parameter; a free-air m³/h value is not a W/K rating. Confirm the complete article number so data from different electrical variants are not mixed.
Rittal SK 3126.100 manufacturer data · Rittal air/air heat exchanger technical guide
Ambient Temperature Conditions
Send the temperature information separately. One figure labelled “cabinet temperature” is not enough to tell us whether it is a limit, a measurement or a setting.
| Input | What to send | How it is used |
|---|---|---|
| Device limit | Device article number, permitted ambient or inlet temperature, source manual and relevant derating conditions | This identifies the equipment constraint. It is not automatically the exchanger’s design reference temperature. |
| Measured internal air | Temperature, exact location, machine load, door status and time of measurement | Distinguish air at a device inlet from air near the cabinet roof or exchanger return. |
| External inlet air | Highest relevant temperature where air enters the exchanger, with machine and nearby equipment operating | A room thermostat can miss local hot-air recirculation. |
| Controller setting | Existing setpoint, sensor location if known, and any alarm settings | The setting is a control instruction, not proof of the actual temperature at a device. |
The exchanger can satisfy the overall heat balance while a badly supplied device inlet still runs too hot. Check local airflow as well as the temperature reference used for sizing. Do not raise the design temperature simply to obtain a smaller exchanger unless the installed equipment and layout permit it.
If the required cabinet temperature is at or below the external inlet temperature, assess refrigeration or a suitable colder liquid source instead. Even a small below-ambient requirement cannot be met by a conventional air-to-air exchanger alone.
Installation Environment
Engineers should consider:
Inspect the external intake location for hot-air recirculation. Check access to the outside core, fan clearances, exposure to oil mist and the unit’s suitability for the actual outdoor or corrosive conditions.
Enclosure Protection Requirements
Check the exact model’s stated protection details, gasket, cut-out and mounting orientation. Indoor suitability, water-jet resistance and corrosion resistance are separate checks; two separated air circuits do not establish all three.
Selecting a Heat Exchanger for Excessive Heat Loads
Compare the net required heat removal with the output available at the smallest credible temperature difference. A model that meets the load in a cool workshop may not meet it at the final installation.
Ignoring Temperature Difference Requirements
Check the hottest external inlet condition that can coincide with the load. Do not use a daily average if the cabinet must remain within limits during the afternoon peak.
Overlooking Airflow Design
Check both circuits. On the cabinet side, cooled air must reach the heat-producing components before returning. Outside, discharge air must not feed straight back into the exchanger inlet.
The checks differ with the installation. These are the points to settle before treating an application as suitable.
CNC Machine Control Cabinets
For CNC cabinets, check sustained drive losses and oil-mist loading on the external core. Confirm that cleaning access remains available after the cabinet is installed beside the machine.
Robot Control Cabinets
For robot control cabinets, use the intended production duty rather than idle losses. Check drive inlet temperatures and keep cabinet-side supply and return paths clear of cable bundles.
Outdoor Electrical Cabinets
For outdoor cabinets, combine solar heat gain with the hottest relevant inlet temperature. Verify the selected unit’s outdoor suitability. A sealed air path does not compensate for insufficient temperature difference.
Process Automation Systems
For process installations, check cleaning practices, corrosive exposure and maintenance access against the selected model. Specify the environment before assuming a standard indoor exchanger is suitable.
If there is not enough temperature difference, stop comparing larger air-to-air models and review the cooling method. If there is enough, compare the required W/K output with the candidate model, then check mounting, air paths and cleaning access.
Send SUWI the cabinet layout, component losses, temperature limits with their reference locations, maximum external inlet temperature, supply voltage and site conditions. Include solar exposure where relevant. We use these to check whether an air-to-air exchanger is a viable route, compare the required output with a candidate model, and identify missing information that prevents a selection. Mark unknowns as unknown; cabinet dimensions alone cannot establish the required output.
Send your heat-load and temperature inputs to SUWI for a heat exchanger selection review. If below-ambient cooling is required, see Blue e+ cooling technology for a refrigeration-based alternative to assess.