FAQ: the 7 most common mistakes when choosing a dry cooler (and how to avoid them)
In industrial cooling, the dry cooler is often seen as a simple plant utility. In reality, it is one of the components that most affect the system’s overall energy efficiency.
The return temperature of the process fluid determines the load level of the refrigeration compressors, the thermal stability of the loads and the energy consumption of the whole plant.
Despite this critical role, selection is still often made from standard catalogue sheets, based on nominal conditions that rarely reflect real operating conditions.
Complex industrial layouts, tight technical spaces, variable thermal loads and extreme climate conditions instead require a more thorough engineering approach.
The most common mistakes in selecting a dry cooler arise precisely from this oversimplification.
Mistake 1: underestimating a dry cooler’s thermal approach in summer conditions
The first mistake concerns assessing the thermal differential between ambient temperature and fluid temperature.
A dry cooler works by exploiting heat transfer between the fluid and the ambient air. However, when the outdoor air temperature approaches the fluid’s set-point, the exchange capacity drops drastically.
This limit is linked to the dry-bulb temperature, which represents the minimum physical limit an air-cooling system can reach.
In summer, when ambient temperatures exceed 35 °C, many dry coolers designed with insufficient margins can no longer maintain the set-point required by the process. In real conditions, a dry cooler often works with thermal approaches of 5–8 °C relative to the dry-bulb temperature. When this margin drops below 3–4 °C, the delivered capacity falls significantly and the system loses operational stability.
A frequent mistake is trying to solve the problem by oversizing the exchange surface, increasing costs and bulk.
A more efficient solution is to integrate adiabatic systems, such as PAD systems or spray systems, which temporarily lower the temperature of the air entering the coil during summer peaks.
This makes it possible to stabilise the system’s operation without excessively increasing the unit’s size.
Mistake 2: ignoring the actual airflow in tight industrial layouts
A second common mistake concerns assessing the fans’ actual airflow.
Many selections assume an airflow in ideal conditions, with no aerodynamic obstacles.
In industrial reality, dry coolers are often installed in:
- technical courtyards
- rooftops with parapets
- confined spaces between buildings
In these conditions the airflow meets significant resistance, altering the quality of the real flow through the coil, both in terms of rate and temperature. Even seemingly modest obstacles (parapets, perimeter walls or nearby machines) can generate aerodynamic losses or recirculation that cause the unit’s performance to deviate from the manufacturer’s figures.
If the airflow through the coil is compromised by obstacles, the system works under hot-air recirculation, with a higher inlet temperature and a drastic reduction in cooling capacity.
Design must therefore consider not only the nominal flow rate, but also the correct installation of the unit and the aerodynamic pressure losses generated by the plant layout.
Mistake 3: choosing materials unsuited to the operating environment
Another frequent mistake concerns the selection of the exchange coil’s materials.
The most common configuration in dry coolers uses copper tubes and aluminium fins. In moderately aggressive environments this solution is generally adequate.
However, in harsher environmental conditions such as coastal areas, industrial atmospheres or waste-treatment plants, this combination can be vulnerable to accelerated corrosion.
The presence of salts or chemical compounds can trigger galvanic corrosion or pitting, progressively reducing the coil’s service life.
In these contexts, more resistant construction solutions may be necessary, such as:
- stainless steel tubes
- aluminium-magnesium (AlMg) alloy fins
- protective cataphoresis coatings
The choice of material should therefore be driven not only by the initial cost, but by the environmental conditions and the required operating life.
Mistake 4: choosing a dry cooler on initial price alone
One of the most widespread mistakes is assessing the dry cooler solely on the initial purchase cost (CAPEX).
In reality, the fans’ energy cost is a significant component of the unit’s Life Cycle Cost.
Fans fitted with traditional AC motors generally run at constant speed, regardless of the real thermal load.
Using modulating EC motors instead allows the rotation speed to be adapted to operating conditions.
Given the relationship between speed and absorbed power, a 20% reduction in fan speed can significantly cut electricity consumption. In continuously running plants, this difference can translate into thousands of kWh saved each year per unit.
Over an operating horizon of 8–10 years, the energy cost can far exceed the unit’s initial cost.
For this reason, the assessment should always be carried out in terms of Life Cycle Cost (LCC).
Mistake 5: neglecting acoustic constraints
In urban or industrial contexts near residential areas, noise is often one of the main design constraints.
A frequent mistake is assessing the sound level solely in terms of overall decibels, without considering the spectral distribution of the acoustic emissions.
Low-frequency (<250 Hz) emissions, typical of industrial fans, can travel long distances and be particularly critical at night.
Corrective measures installed after the fact, such as sound-absorbing barriers, only partly reduce the problem and can compromise the unit’s airflow.
Correct design, on the other hand, should provide optimised aerodynamic management of the fan from the outset. High-efficiency diffusers and speed-control systems can improve fan efficiency by as much as 10–15%, simultaneously reducing acoustic emissions and energy consumption.
Mistake 6: ignoring structural vibrations
Besides aerodynamic noise, dry coolers can generate structural vibrations that propagate through the building’s structure.
When the unit is installed on metal roofs or lightweight structures, these vibrations can turn the whole building into a resonance chamber.
Over the long term, vibrations can also cause:
- loosening of mechanical connections
- micro-fractures in the headers
- deterioration of structural supports
For this reason it is essential to provide properly sized anti-vibration isolation systems. Even small-amplitude vibrations, in the order of 0.5–1 mm/s RMS, can propagate through the building’s structure and be amplified on the metal surfaces of the roof. Using elastomeric mounts and anti-vibration frames reduces structural transmission, while “floating coil” configurations help preserve the unit’s mechanical integrity over time.
Mistake 7: underestimating maintenance accessibility
A final mistake concerns designing the unit from a maintenance standpoint.
Dry coolers designed to minimise bulk can be difficult to inspect or clean once installed.
The presence of dust, pollen or atmospheric contaminants can progressively reduce the coil’s exchange capacity.
If access for cleaning is limited, the system tends to work with increasingly high operating ΔT, with a consequent rise in energy consumption.
Maintenance-oriented design solutions, on the other hand, reduce the MTTR (Mean Time To Repair) and preserve performance over time.
Choosing a dry cooler should not be seen as a simple purchasing decision.
When designed correctly, this component can become a key element in improving the energy efficiency, thermal stability and durability of the whole plant.
At Refteco we approach the design of cooling systems starting from real process data: thermal loads, climate conditions, layout constraints and acoustic requirements.
This approach makes it possible to turn a component often perceived as a simple utility into a strategic asset of the plant.
If you are designing a new cooling system or considering upgrading an existing dry cooler, share your operating data and plant layout with us: correct design can make the difference between a standard solution and a system that is truly efficient over the long term.
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