Additional cooling of air coolers 

Why standard airflow is often not enough for stable operation

In our practice of servicing industrial heat exchangers, we have repeatedly encountered a situation where a device designed according to all standards ceases to cope with the load at the height of the summer season. The key problem is not equipment defects, but the fact that calculated ambient temperatures are often underestimated relative to actual peak values ​​in specific operating regions. Additional cooling of air coolers becomes a critical solution precisely when the difference between the process temperature and the fan inlet temperature is reduced to a critical minimum. We've seen cases where a line down due to overheating coolant has cost a plant tens of thousands of dollars per hour, even though installing a water pre-injection or recirculation system would have cost a fraction of that.

Engineers often make the mistake of relying solely on the rated fan power indicated in the product data sheet. The reality is this: as the outside air temperature rises above +35°C, air density drops, mass flow decreases, and heat transfer efficiency can drop by 40-50%. This is not a theoretical calculation, but a physical law that has to be dealt with at facilities from oil refineries to cold storage warehouses. If your process requires maintaining the liquid temperature at +45°C, and the air outside has warmed up to +40°C, a standard device simply will not be able to remove the heat without modernization.

There is a common misconception that adding more fans will solve the problem. In fact, this often only leads to an increase in energy consumption without a significant increase in heat transfer, since the heat transfer coefficient depends on the temperature difference. The correct approach requires analysis of the thermodynamic cycle and selection of an intensification method that suits the specific site conditions. In this guide, we'll look at proven methods that allow you to return your device's performance to its design values, even in extreme heat.

Technical methods for intensifying heat transfer: from atomization to recirculation

The choice of retrofit strategy depends on the available resources on site and the cleanliness requirements of the process. We classify the main methods of additional cooling of air coolers into three groups: evaporative cooling of incoming air, hot air recirculation and hydraulic optimization. Each method has its own limits of applicability and technical limitations that must be taken into account at the design stage.

Water pre-injection systems (Adiabatic Cooling)

The most effective way to reduce the incoming air temperature is to use fine water spray systems in front of the heat exchange sections. The operating principle is based on an adiabatic process: water evaporates, taking the latent heat of vaporization from the air flow, which allows the air temperature to be reduced by 10-15°C below the dry bulb temperature. In our projects we use high pressure nozzles that create mist with a droplet size of less than 50 microns, which guarantees complete evaporation before contact with the finned tubes.

The critical parameter here is water quality. The use of untreated tap water will lead to the rapid formation of scale on the fin lamellas, which after two seasons of operation will completely neutralize the cooling effect and create additional aerodynamic drag. We strongly recommend installing reverse osmosis systems or using demineralized water. One of our clients in Kazakhstan saved 30% of energy on fan drives by implementing such a system, but only after replacing the nozzles with ultrasonic ones and installing fine filtration.

The automatic control of such a system must respond not only to the temperature of the process, but also to the humidity of the surrounding air. At high relative humidity, evaporation efficiency decreases and the system must automatically shut down to avoid dropwise entrainment of moisture. Modern controllers make it possible to integrate humidity and temperature sensors into a single control circuit, ensuring that the installation operates only in an economically feasible mode.

Hot air recirculation and flow control

In conditions where the use of water is impossible due to resource shortages or environmental restrictions, the method of recirculating part of the hot air is used. It sounds paradoxical: why return hot air? However, this method makes it possible to stabilize the suction temperature in winter and prevent freezing of the coolant, and during transition periods it is possible to regulate performance without a frequency converter. For summer mode, this method is modified: deflectors are installed that change the flow path to prevent hot air from flowing back into the suction.

A common mistake when installing air coolers is ignoring the direction of the prevailing winds. If the outlet of the hot jet is oriented against the wind or is located in the aerodynamic shadow zone of neighboring structures, natural recirculation occurs, reducing the efficiency of the device by 20-25%. Correcting trim geometry and installing windbreaks often has a greater effect than replacing engines. We carried out measurements at a refinery where a simple reorientation of the louver grilles reduced the product exit temperature by 4°C without capital investment.

Airflow is also controlled through adjustable louvres. Unlike frequency control of motors, which effectively reduces energy consumption, louvers allow precise dosing of the volume of passing air, maintaining a flow rate sufficient to wash the pipes. This is especially important at partial loads, when reducing the fan speed can lead to laminarization of the flow and deterioration of heat transfer.

Hydraulic optimization and surface cleanliness

We cannot talk about additional cooling while ignoring the state of the heat transfer surfaces themselves. Contamination of the fins with dust, fluff or industrial emissions creates an insulating layer that acts as a thermal insulator. Regular high pressure washing using specialized chemicals is a mandatory maintenance procedure. In our practice, there was a case when, after three years of operation without cleaning, the performance of the device dropped by 60%, although there were no mechanical breakdowns.

Retrofitting tube fins is also an efficiency improvement technique. Replacing smooth lamellas with perforated or wavy ones increases the turbulence of the air boundary layer, increasing the heat transfer coefficient. However, such a solution requires careful calculation of aerodynamic resistance, since the load on the fan motor increases. Before making a decision to replace sections, it is necessary to conduct an audit of the current condition of the pipes and evaluate the residual life of the metal.

Optimizing the distribution of coolant inside the device plays an equally important role. Uneven filling of sections leads to the fact that some of the pipes work at maximum load, while the other part is idle. Installing balancing valves and redistribution manifolds allows you to equalize the hydraulic resistance and use the entire heat exchange surface evenly. This simple step can often extract an additional 10-15% of productivity from existing equipment.

Calculation of economic efficiency and payback periods for modernization

The decision to implement additional cooling systems should be based on a clear economic justification, and not on intuitive feelings. The main indicator here is the cost of production downtime compared to the capital costs of modernization. If stopping a line due to overheating costs a business $5,000 per hour, then any system that prevents this downtime for even 100 hours a year pays for itself instantly. We recommend conducting an audit of potential losses before starting a project.

Energy efficiency is the second key factor. Adiabatic cooling systems consume electricity to operate high-pressure pumps, but can significantly reduce the load on the main fans or increase their efficiency. The calculation shows that when the temperature of the incoming air decreases by 10°C, the power required to remove the same amount of heat decreases in proportion to the increase in temperature pressure. In numbers, it looks like this: an investment in a spray system pays off in 1.5–2 years due to energy savings and avoidance of fines for exceeding technological parameters.

Operating costs must also be taken into account. Water systems require constant monitoring of water quality, replacement of filters and nozzles. Water consumption is approximately 1-2 liters for every kilowatt of heat removed, depending on air humidity. In regions with high water costs, this can be a limiting factor. Dry methods, such as airflow optimization or fin replacement, have virtually zero operating costs after installation, but require a higher initial investment in equipment and installation.

The service life of additional equipment also affects the calculation. High-quality nozzles made of stainless steel or ceramics last up to 5-7 years, while cheap plastic analogues can fail in one season due to abrasive wear or corrosion. We advise you to budget for the purchase of premium components, since replacing them during operation requires stopping the device, which again leads to production losses. Component reliability directly impacts the total cost of system ownership.

Typical mistakes when designing and installing cooling systems

Even properly selected equipment may not work if errors are made at the integration stage. The most common problem is incorrect placement of nozzles in adiabatic cooling systems. If the sprayers are installed too close to the heat exchanger, the water does not have time to evaporate and ends up on the hot pipes. This causes a thermal shock to the metal, the formation of local stresses and, as a result, microcracks in the welds. In the long term, this leads to depressurization of the circuit and mixing of media, which is unacceptable in chemical production.

The second critical mistake is ignoring the corrosive activity of the environment. Introducing moisture into the air stream changes the chemical composition of the atmosphere around the device. If the frame and structural elements are made of ordinary carbon steel without high-quality anti-corrosion protection, they will begin to rust at an accelerated pace. We require the use of galvanized structures or stainless steel AISI 304/316 for all elements exposed to humidified air. Saving on case material here results in replacing the entire device in 3-4 years.

Errors in automatic control lead to the system working in vain. Temperature sensors must be installed at the correct locations: air inlet, air outlet, and process piping. Often installers place sensors in stagnant areas or in direct sunlight, which distorts the data for the controller. The result is that the system turns on when not needed, or turns off during peak load. Calibration of measuring instruments and the correct logic of operation of PID controller algorithms are the key to stable operation.

Another nuance that is often forgotten is the impact on the surrounding infrastructure. Moist air ejected from fans can create fog over plant areas, reducing visibility or causing icing on structures in winter. In some cases, this requires installing drift eliminators or changing the direction of discharge. It is also necessary to take into account the noise factor: additional pumps and changes in the operating mode of fans may exceed the permissible noise standards at the border of the sanitary protection zone.

Compliance with GOST, EAC and international requirements

Any modernization of industrial equipment must be carried out in strict accordance with current regulatory documents. In the EAEU countries, the main regulatory document is GOST 31228-2018 “Air cooling devices. General technical conditions". This standard regulates not only the parameters of the device itself, but also the safety requirements for auxiliary systems. When installing water pre-injection systems, it is necessary to ensure that they do not violate fire safety requirements, especially if the device is located in an explosive area.

Certification according to the technical regulations TR CU 010/2011 “On the safety of machinery and equipment” is mandatory for all newly introduced units. This applies to pumping stations, control systems and electrical equipment. The presence of an EAC certificate confirms that the equipment has passed the necessary tests and is safe for use. Ignoring this requirement may lead to fines from supervisory authorities and refusal to insure production risks.

For export deliveries or work on international projects, compliance with API 661 (Petroleum, Petrochemical and Natural Gas Industries—Air-cooled Heat Exchangers) standards is often required. This standard places stringent requirements on materials, welding and testing. For example, API 661 requires leak testing at 1.5 times operating pressure and strictly regulates manufacturing tolerances for finned tubes. Our engineers take these requirements into account when selecting upgrade components to ensure compatibility with global quality standards.

Environmental regulations also play an important role. Discharge of water from cooling systems or use of water treatment chemicals must comply with local environmental regulations. In a number of regions, a closed water cycle is required, eliminating the discharge of wastewater into sewers without preliminary treatment. The design of the system should include a section on environmental safety with the calculation of water and chemical balances.

Practical cases of implementing solutions at industrial facilities

Let's consider a real example of modernization at a gas processing plant in Siberia. The main problem was the impossibility of hydrocarbon condensation in the summer, when the air temperature reached +38°C. The design condensation temperature was +42°C, which left a margin of only 4 degrees. Any deviation led to the release of the product to the flare. The solution was to install a pulsed water spray system in front of the four fan sections. After implementation, the incoming air temperature was consistently maintained at +26°C even at noon. This allowed not only to restore the design capacity, but also to increase the processing depth by 12%. The payback period for the project was 8 months.

Another case is related to the refrigeration center of a logistics complex in the southern region. Here water was in short supply and the use of wet systems was excluded. The problem was that the old fans did not provide the required pressure due to wear on the blades and increased aerodynamic drag from dirty heat exchangers. Instead of an expensive replacement of the entire device, we carried out a comprehensive cleaning using alkaline reagents, replaced the fan blades with a new generation profile with improved aerodynamics, and installed frequency converters. This made it possible to increase air volume flow by 18% while reducing electricity consumption by 10%. The temperature in the storage chamber has stabilized without the need to build new facilities.

The third example demonstrates the importance of proper design. The oil depot installed an additional cooling system, but did not take into account the wind direction. As a result, the hot emissions from one row of devices were sucked into the adjacent row. The process temperature began to rise instead of falling. After conducting a thermal imaging survey and installing vertical partition screens between the rows, the problem was solved. This case highlights that additional cooling of air coolers requires a systematic approach and consideration of all environmental factors, rather than simply purchasing equipment.

Integrated solutions from Wuxi Kaisheng LLC: reliability of materials and engineering approach

Successful modernization of cooling systems is impossible without a reliable component base that can withstand aggressive environments and extreme loads. This is where the company's experience plays a key role.Wuxi Kaisheng Electric Power and Petrochemical Equipment Co.,Ltd" Specializing in the design and manufacture of advanced heat transfer equipment, the company offers solutions that perfectly complement the intensification methods described above.

When it comes to implementing adiabatic cooling systems or operating in conditions of high humidity and corrosive activity, the material used becomes a critical factor. Wuxi Kaisheng products, including titanium shell-and-tube heat exchangers, 316 stainless steel corrugated tube bundles and nickel-based alloys (N06625), offer exceptional corrosion resistance. This is especially important for air coolers (air coolers) being retrofitted to operate in marine climates or petrochemical plants, where conventional steel quickly fails.

The company produces a wide range of components needed for deep retrofits, from C46400 brass and C70600 copper-nickel alloy tube sheets to ASME and PED certified high-pressure heat exchangers. The use of materials such as marine brass and special alloys not only extends the life of the equipment, but also increases its thermal efficiency due to optimal thermal conductivity. Whether it is replacing old sections with new ones with improved fin geometry or completely replacing the heat exchanger unit in a waste heat boiler, Wuxi Kaisheng engineering solutions ensure process stability in the oil refining, chemical industries, shipbuilding and energy industries around the world.

Frequently Asked Questions

Can regular tap water be used for pre-injection systems?

Strongly not recommended. Ordinary water contains hardness salts (calcium, magnesium), which, when evaporated, remain on the surface of the fins in the form of a solid deposit. This layer acts as a heat insulator and quickly clogs the space between the lamellas, stopping the passage of air. After one season of such operation, the efficiency of the device will drop below the original, and cleaning will require expensive chemical rinsing or mechanical cleaning, risking damage to thin lamellas. Use only prepared water: demineralized, after reverse osmosis or specially softened.

How often should the after-cooling system be serviced?

The frequency of maintenance depends on the quality of the water and dust levels in the air. Spray nozzles must be checked and cleaned every 2-3 months during active use. Fine water filters must be replaced quarterly or according to the readings of the differential pressure gauge. Heat transfer surfaces should be inspected for contamination and corrosion at least twice a year: before and after the summer season. Full automation diagnostics and sensor calibration are required annually. Neglecting the maintenance schedule will lead to system failure at the most critical moment.

Does the installation of additional equipment affect the warranty of the main device?

This depends on the terms of the contract with the original equipment manufacturer. Generally, design changes that affect thermal or aerodynamic performance may void the warranty unless approved by the manufacturer. However, most manufacturers support the upgrade if it is performed by certified specialists and does not exceed the maximum pressure and temperature parameters. We recommend that before starting work, you request an official letter of approval from the vendor or involve authorized service centers for installation, which take responsibility for the compatibility of solutions.

Which cooling method is the cheapest to operate?

In terms of direct monetary costs for resources, the cheapest are methods that do not require consumables: optimization of flow geometry, cleaning, replacement of fins. They only require electricity costs (which may even decrease) and infrequent service. Systems with water always have variable costs for water consumption and chemical treatment. However, if we compare the cost per unit of heat removed during the peak period, adiabatic cooling is often more profitable than purchasing and installing a new additional air cooler, since the CAPEX for modernization is several times lower than the cost of a new machine.

Conclusion and next steps

Additional cooling of air coolers is not just a technical option, but a strategic necessity to ensure the continuity of modern production in a changing climate and increasing loads. Ignoring this possibility leads to direct financial losses and the risk of emergency stops. A properly selected modernization method, supported by the use of high-quality materials from partners such as Wuxi Kaisheng LLC, can extend the life of equipment, reduce energy consumption and guarantee compliance with technological regulations even on the hottest days of the year.

We have experience in implementing similar projects at facilities of varying complexity and scale. Our engineers are ready to audit your current equipment, perform thermal calculations and offer an optimal solution that will pay for itself in the shortest possible time. Don't wait until summer's peak temperatures arrive to discover a power shortage. Preventative modernization is always cheaper than emergency repairs.

Contact us today for a consultation and cost estimate for upgrading your air cooler fleet.Request a technical auditor explore our catalogheat transfer intensification systemsto select a suitable solution.