Air cooled Heat Exchanger

Air-cooled heat exchangers (ACHE or “air coolers”) are robust heat-rejection units that transfer process heat to the atmosphere using ambient air. In these closed-loop units, the hot fluid (oil, gas, water, etc.) flows inside finned tubes while powered fans blow ambient air across the tube bundle. This convective cooling rejects heat efficiently without using any cooling water or towers. ACHEs come in forced-draft and induced-draft types: forced-draft units have fans mounted below that push air upward through the fins, while induced-draft units have fans on top that pull air across the tubes. Figure 1 (below) shows a typical forced-draft air cooler, and Figure 2 shows an induced-draft cooler. Both designs usually use multiple axial fans to provide redundancy and ensure >40% fan coverage of the finned surface.


Figure 1: A forced-draft air-cooled heat exchanger (fans below the tube bank push ambient air through the fins).

In operation, the process fluid circulates through the finned-tube bundle while fans continuously move outside air across the fins. Heat is conducted from the hot fluid to the tube walls and fins, then convected into the air stream. Because fans keep air moving, ACHEs can reject large heat loads even in warm climates – though they generally work best when the design air temperature is met or exceeded only a few percent of the time.


Figure 2: An induced-draft air-cooled heat exchanger (fans above the bundle pull air across the finned tubes).

The induced-draft arrangement provides a more uniform air distribution and higher exhaust air velocity, reducing hot-air recirculation. In practice, forced- and induced-draft coolers perform similarly, and the choice depends on site layout and noise considerations (induced-draft can be slightly quieter and avoid hot-air recirculation). Both types can be built in horizontal single- or multi-row tube banks and arranged in bays for larger capacities.

Key Features & Benefits of United’s Air-Cooled Models

United Heat Exchangers’ ACHE units offer a range of customer-focused features, blending high heat-transfer efficiency with low operating costs and rugged durability. Key highlights include:

• Efficient Fin-Tube Design: Each tube block uses high-performance fins on the exterior of the tubes (typically aluminum fins on steel tubes, with options for higher-alloy or galvanized fins). This maximizes surface area and heat transfer. United’s finned tubes support high heat-transfer coefficients across a range of temperatures. Because the fins and tubes are mechanically bonded or brazed, thermal contact is excellent. “Highly efficient fin-to-tube heat transfer” is specifically noted as a product feature.
  
  
• No Water Required: United’s air coolers operate in a closed loop with no external cooling water. This means zero water consumption and no need for cooling towers or treatment systems. In fact, United’s literature highlights “zero water wastage due to closed loop operation” and the elimination of makeup water or evaporative losses. This design avoids all the fouling, scale and corrosion issues common to water systems, drastically simplifying maintenance. Customers save on water costs and avoid environmental discharge permits – making ACHEs an inherently “green” technology.
  
  
• Closed-Loop Isolation: The process fluid (oil, water, chemicals, etc.) is completely contained inside the tubes and headers. This means the fluid never contacts outside air, eliminating contamination or evaporation. If a tube leak ever occurred, outside air would simply pass through (rather than dilute the process stream). As one specialist notes, leaks in an ACHE “do not cause contamination with the process liquid, unlike other heat exchangers”. This closed-loop design also keeps the fluid clean, so the cooler itself stays free of biofilms or microorganisms.
  
  
• Durable Materials & Coatings: United’s units are built from quality steels and aluminum, with options to suit any environment. Tubes and headers can be carbon steel, stainless (300/316/317/321 series), duplex or high-alloy depending on the fluid and service. Fins are usually aluminum (excellent corrosion resistance and thermal conductivity), though galvanized steel fins are available for extreme outdoor durability. For example, galvanized fins provide up to 30-year service life in harsh conditions. United also offers special coatings (e.g. epoxy/polyurethane) that further protect fins and metal surfaces against salt, sand, or chemicals. These coatings maintain thermal performance while extending service life.
  
  
• Versatile Fan & Drive Options: Depending on customer needs, fans can be arranged for forced or induced draft. Fans are high-quality axial units, either direct-drive or belt-driven, and can be two-speed or variable-pitch for control. Motors are selected to match the power requirements (generally moderate kilowatt ratings per fan). United’s designs follow best practices (e.g. API 661 recommendations for fan sizing). Multiple fans (typically ≥2 per bank) are used so that the unit still provides cooling if one fan is offline. All fan and motor assemblies are readily accessible for service.
  
  
• Low Noise Design: When noise is a concern (e.g. near public areas), United offers low-noise fans with extra blades or slower tip speeds. The typical fan tip speed can be adjusted to reduce dB levels without sacrificing airflow. Some units include inlet louvres or sound attenuating shrouds. Overall, because ACHEs rely on multiple moderate-speed fans, noise can be managed by proper design and control (unlike single high-speed fans, multi-fan units can be run at lower RPM for the same duty).
  
  
• Long Service Life: When properly maintained, air coolers are built to last. Industry experience suggests 20–30 years of service is common under normal conditions. United’s robust construction (rigorous fabrication, ASME/API standards, etc.) ensures longevity. Unlike open wet coolers, there’s no corrosion from standing water or chlorine, and regular cleaning of fins or tubes is infrequent. United even notes in product literature that ACHE maintenance is negligible compared to wet systems.
  
  
• Compact Footprint for Dry Cooling: Although ACHEs are larger than compact shell-and-tube exchangers (due to the large airside area), United’s designs strive for compactness in their category. They use high face velocities (typically ~3 m/s air across fins) to minimize fin length. When plotting an installation, units can be banked in parallel to save space. In any event, United’s air cooler avoids the need for separate ponds or towers – freeing up plant real estate.
  
  
• Operational Flexibility: United ACHEs handle a wide range of fluids and temperatures. Standard units cool from near-ambient up to ~230–250 °C fluid temperatures (above that, special alloys or low-fin options are used). They can operate at pressures from vacuum up to dozens of bar (even custom high-pressure headers up to 500 bar are possible). Units are also offered in split-pass tube arrangements or multiple banks to accommodate large temperature drops or multi-fluid duties. The modular design (stacked bundles) makes scaling and installation flexible.
  
  
• Energy Savings: In many cases, ACHEs cost less to operate than water-cooled systems. Fans do draw electric power, but power costs are often offset by eliminating pumps, water-treatment chemicals, and tower drift. Because ambient air is free and non-corrosive, ACHEs avoid many operational expenses. Studies show that even if fans run continuously, the absence of condensate or evaporation losses yields net savings. United highlights that the closed-loop ACHE minimizes operating costs – there’s no water makeup, no tendering to fouling, and simple on/off fan control is usually sufficient.
  
  
• Green Technology: By rejecting heat directly to air, these coolers are inherently environmentally friendly. There is no cooling-water effluent or chemical discharge. In fact, United advertises ACHEs as a “consistent-quality, efficient, and green technology solution” for cooling needs. The lack of water usage means negligible environmental impact (no thermal pollution of rivers, no humidity plumes). This makes air coolers especially attractive in arid regions or where water is expensive or scarce.

Combined, these features make United Heat Exchangers’ air-cooled models technically robust and cost-effective. They offer high heat-duty capacity in industries where reliability and low maintenance are priorities. Below is a summary of typical technical data for United’s standard ACHE series.

Technical Specifications

Specification	Typical Values / Options	Notes / References
Tube Material	Carbon Steel, Stainless Steel (304/316/317/321), Duplex, High-Alloy (600/800 series)	Customer can specify based on fluid corrosion, pressure and temperature requirements.
Fin Material/Type	Aluminum fins (standard); Galvanized steel fins; L-fin or G-fin profile.	Aluminum fins are lightweight and easy to clean; steel fins offer extra durability (30+ year life in extreme climates).
Fans & Drives	Axial flow fans (forced or induced draft); Direct-drive or Belt-drive motors; TEFC electric motors.	2+ fans per bay (for redundancy) with built-in oversizing margin; drives selected per duty.
Cooling Capacity	~200 kW up to several MW per cooler (scalable by banks and rows).	Dependent on design conditions; United often provides turnkey multi-bank assemblies.
Fluid Temperature Range	30 °C to 240 °C (standard); special units up to 270 °C.	Minimum approach ~4–5 °C above ambient air; higher ranges use special alloys.
Pressure Rating	Up to ~6000 psi (400 bar) (design per application).	Standard ASME headers up to ~200–300 bar; custom forgings available for very high pressure.
Fan Coverage	≥40% of finned face area.	Ensures unit can run on reduced fans without overheating.
Number of Tube Rows	4 – 8 rows (in airflow direction).	More rows increase duty (especially when ambient is high); typically up to 6 rows unless site restrictions.
Face Velocity (Airside)	~3 m/s (typical); up to ~5 m/s (high-performance).	Balances heat transfer vs. fan power/noise.
Unit Size (max)	Width up to ~8 m (26 ft); Length up to ~21 m (70 ft); Weight up to ~68 metric tons.	Very large fans (>3 m diameter) and headers may increase size; units often installed atop pipe racks to save ground space.
Fin Density	200–300 fins per meter (standard); custom as needed.	Determines airside resistance and heat transfer.
Orientation	Horizontal (standard); inclined “roof” type (for condensers).	Roof-type design for large steam condensers, A-frame banks for extreme duties.
Certifications	ASME U, S, R, NB; API 661 compliance; ISO 9001; etc.	United meets global standards and can provide specified quality tests.

Table: Representative technical specifications for United’s Air Cooled Heat Exchangers (fin fan coolers). Actual values depend on model and customer design conditions. See sources.

Applications Across Industries

United’s air-cooled heat exchangers serve virtually any industry that requires reliable fluid cooling without large water systems. Typical applications include:

• Oil & Gas (Upstream, Midstream, Downstream): Refineries and petrochemical plants use ACHEs on process streams, reflux coolers, and fractionator condensers. As noted in industry literature, “a large proportion of the process cooling in refineries and chemical plants takes place in air cooled heat exchangers”. In pipelines and compressor stations, fin-fan coolers reject heat from natural gas, crude oil, lube oil, and other fluids. The robust finned-tube design resists corrosion from sulfur and chlorides common in oilfield environments. United’s coolers often meet API 661 standards for oil & gas service.
  
  
• Power Generation: Thermal power plants and gas turbine installations use ACHEs for condenser cooling, turbine inlet cooling, and generator or transformer cooling. Electrical utilities have long relied on FOA (forced oil air) coolers – a type of air-cooled exchanger – to cool transformer oil at substations. Diesel engine power plants also use compact ACHE units (often called “radiators” or “dry coolers”) to cool lube oil and charge air. United supplies large multi-fan coolers for both steam turbines and reciprocating engines, delivering the high capacities needed for megawatt-scale heat loads.
  
  
• HVAC and Commercial Cooling: In large commercial buildings, data centers or industrial facilities, ACHE-like units appear as dry coolers and condenser units. Instead of water-cooled chillers, these systems use finned coils with fans to condense refrigerant or cool glycol. United’s ACHEs in this sector help eliminate the need for cooling towers, reducing maintenance and humidity issues. (For example, its product pages list “Commercial & Real Estate” and “Power” under typical industries.) Air-cooled condensers from United are also used in chillers and industrial refrigerators.
  
  
• Chemical Processing: Plants handling chemicals, polymers, and pharmaceuticals use ACHEs for cooling process streams (acids, solvents, etc.). The closed design is advantageous for sensitive chemicals since there’s no open evaporation or contamination. Fin materials can be chosen for chemical compatibility. Industry surveys note ACHEs are widely used where ultra-pure water is not available and where any fluid loss must be avoided.
  
  
• Other Industries: Cement plants, steel mills, power distribution, mining, and even refrigeration industries use air coolers. For example, cement kiln cooling oils and steel mill coolant oils are often routed through fin-fan coolers. Any application requiring medium-to-high-temperature fluid cooling without easy access to water is a candidate for United’s ACHE units.

In short, from offshore platforms and LNG trains to power plants, malls and manufacturing facilities, air-cooled exchangers are a universal solution wherever dry cooling is needed. United’s global projects have included oil refineries, natural gas compressors, petrochemical crackers, HVAC plants, and more – showcasing the technology’s versatility.

Maintenance Tips & Best Practices

Air-cooled heat exchangers are generally low-maintenance, but proper care ensures reliable long life:

• Regular Visual Inspection: Periodically check the fins and tubes for debris (dust, leaves, insect nests, etc.). Ensure the air inlet is clear and the fan areas are unobstructed. Clean or blow off fins if heavy fouling occurs (high-pressure air or water can be used carefully). Unlike water-based coolers, chemical cleaning is rarely needed since there is no risk of biological growth or scale from the air side.
  
  
• Fan & Drive Maintenance: Inspect fan blades and hub for damage, and ensure the blades are clean. Check that belt-driven units have proper belt tension and alignment (adjust belts per manufacturer specs). Lubricate fan bearings and motor bearings on schedule. Because United’s fans are axial flow with accessible casings, routine checks are straightforward. (Refer to the owner’s manual for oiling intervals.) Fans should turn freely; any vibration or unusual noise can indicate imbalance or bearing wear – address these immediately.
  
  
• Motor and Electrical Checks: Verify motor connections, insulation resistance, and that motors run smoothly at the correct voltage and current. If variable-frequency drives are used for fans, ensure their filters and cooling are maintained.
  
  
• Tube Bundle Inspection: Though ACHEs are closed-loop, it’s wise to inspect the internals during major outages. Header boxes usually have plugs on each tube (standard design), allowing visual tube inspection. Check for any signs of corrosion on tubes or header plates. Over time, plugging a few tubes (if slight leaks occur) is easier than with shell-and-tube exchangers. Replace any finned-tube sections if needed – United’s modular design allows bundling spare sections.
  
  
• Ensure Proper Operation: Verify that all fans operate as intended. On multi-fan coolers, ensure at least one fan is running at all times for baseline cooling, with additional fans staged based on temperature or load. United’s units can be shipped with built-in switches or thermostats to automate fan staging. Confirm the control sequence annually.
  
  
• Protective Coatings: If the cooler is in a corrosive environment (salt air, chemical fumes, etc.), consider periodic recoating of exposed metal. While aluminum fins are corrosion-resistant, applying protective coatings can further extend life.
  
  
• Winter Care (if applicable): In freezing climates, angle fans downward or use heated louvres to prevent ice build-up on the bundle. Warm the fluid if freezing risk exists, or circulate anti-freeze fluid.

By following these steps, United’s customers typically find that maintenance is simple – often just a quick inspection and cleaning a couple of times a year. In general, “air-cooled heat exchangers require relatively little maintenance” because the lack of water prevents corrosion or fouling.

Why Choose Us?

At United Heat Exchangers, we don’t just manufacture equipment—we deliver performance, reliability, and long-term value. Our Air Cooled Heat Exchangers are trusted by industries worldwide for their efficiency, durability, and customized engineering. Here’s why businesses choose us:

• Proven Engineering Expertise – With decades of experience in heat exchanger technology, we design solutions that maximize thermal performance and energy efficiency.
  
  
• High-Quality Manufacturing – Built using premium materials and strict quality control standards to withstand harsh operating conditions.
  
  
• Customized Designs – Every unit is tailored to match your process requirements, whether for oil & gas, power plants, chemical processing, or HVAC applications.
  
  
• Energy & Cost Savings – Our air-cooled systems reduce water consumption, cut operating costs, and lower maintenance requirements compared to traditional cooling methods.
  
  
• Durability & Reliability – Designed for continuous operation in demanding environments, ensuring consistent performance and minimal downtime.
  
  
• Global Reach with Local Support – Serving clients across industries and geographies, backed by responsive customer service and after-sales support.
  
  
• Sustainability Focus – By eliminating water usage and enhancing heat transfer efficiency, our systems support eco-friendly and sustainable operations.

“Looking for a reliable, low-maintenance cooling solution? Contact Us today for custom-designed Air-Cooled Heat Exchangers built to your specifications.”

Frequently Asked Questions

1. How does a forced-draft ACHE differ from an induced-draft ACHE?
   
   
Ans: The difference is fan placement. In a forced-draft unit, fans are located below the finned tube bundle and push air up through the bundle. In an induced-draft unit, fans are above the bundle, pulling air up across the tubes. Both achieve the same goal of moving ambient air over the fins. Forced-draft designs generally have slightly higher fan power for the same cooling (since fans are blowing into a static pressure), while induced-draft designs may have better airflow distribution and marginally lower power use. The choice depends on installation: forced-draft is often easier to service (fans accessible below), whereas induced-draft is often chosen when minimizing hot air recirculation is critical.


2. Can an air cooler completely replace a water-cooled heat exchanger?
   
   
Ans: Possibly, depending on conditions. ACHEs have no cooling-water loop, which is a major advantage. However, they generally require more heat transfer area (more fans and fins) to achieve the same duty as a water-cooled exchanger. If a facility lacks reliable cooling water or wants to avoid water use, an ACHE is often the best solution. In some cases, plants use a hybrid approach: for example, using a shell-and-tube exchanger ahead of an air cooler, so the air cooler only handles the residual heat. Ultimately, United’s engineers can model both options. For large temperature approaches (>5 °C above ambient), ACHEs are very effective; for very close approaches (<5 °C), additional measures (like fans or even refrigeration) might be needed.


3. Are United’s air coolers noisy? How is noise controlled?
   
   
Ans: Fans do generate sound, but ACHEs are designed with this in mind. By using multiple fans at moderate speeds, the sound frequency is distributed and can be kept below common limits. United offers low-noise fans (more blades, optimized pitch) and variable-speed drives if needed. In general, noise correlates with fan tip speed and airflow: running fans slightly slower or using larger diameter blades can greatly reduce decibels. According to engineering references, lowering face velocity and increasing surface area (i.e. oversizing the cooler) allows very low-noise operation. For most industrial sites, the noise from an ACHE is comparable to other large machinery, and it rarely poses a problem with proper layout and controls.


4. What maintenance does an air-cooled exchanger need compared to a water-cooled one?
   
   
Ans: ACHEs require much less routine care. Without water, there is no scale, corrosion from chlorine, or biological growth to remove. Typical maintenance involves periodic cleaning of the fins (such as using compressed air or gentle water spray) to remove any dust or debris. Fans and motors should be checked and oiled per schedule. Valves and controls should be tested, but generally no chemical cleaning of internals is needed. In fact, United notes that their ACHE units have “negligible maintenance cost as water treatment, makeup water, and replacement of fills are not required”. In contrast, water-cooled systems need regular tube cleaning, water treatment, and larger pump servicing.


5. What fluids can be cooled in a United ACHE?
   
   
Ans: Almost any fluid that a conventional heat exchanger can handle. United’s units cool oil, water/glycol mixtures, lube oil, process water, hydrocarbons, ammonia, refrigerants, chemical solvents, etc. By selecting appropriate tube material and fin coating, ACHEs can handle corrosive or high-purity fluids. Standard tube alloys cover most applications, and custom materials are available for extreme chemistry. The closed-loop design means the fluid is never exposed to open air, preserving its purity.


6. How efficient are air-cooled exchangers compared to other coolers?
   
   
Ans: Efficiency depends on conditions. For high ambient temperatures or very tight approach requirements, water-cooled systems can sometimes cool better because of water's higher heat capacity and evaporation. But air coolers shine in many scenarios: they can achieve high effectiveness when the ambient air is cool or when the heat load is intermittent. Modern ACHE design (optimized fins, multiple fans, variable speed drives) yields excellent performance. According to United and industry sources, ACHEs can often achieve cooling very close to design duty with about 4 °C approach above ambient. When considering overall plant efficiency and lifecycle cost, eliminating pumps and towers often makes ACHEs the winner.


7. What is the typical lifetime of a United air-cooled heat exchanger?
   
   
Ans: With proper maintenance, 20–30 years or more. The main components (steel structures, aluminum fins, steel tubes) have a very long life, especially since ACHEs avoid many sources of damage. United and other manufacturers design these units for decades of service; it’s common to see ACHEs in oil refineries that are 30–40 years old and still operating reliably.