Air cooling unit: design and installation 

Air cooling unit: design and installation - from drawing to launch

High qualityair cooling unit: design and installationdetermine 80% of the success of the entire thermoregulation system at an industrial facility. In our practice, we have repeatedly encountered a situation where customers saved money at the design stage, choosing equipment “by eye,” and then paid triple the price for reworking pipelines and replacing failed compressors due to water hammer. This article was written by engineers who personally installed hundreds of such systems in the harsh climate of Siberia and the hot summers of the southern regions. We will analyze not theoretical calculations from textbooks, but real nuances: how to calculate the pitch of trusses under the weight of the harness, why vibration loads cannot be ignored, and what errors in the PID control circuit lead to fluctuations in the process temperature.

If you are planning on introducing a new line or upgrading an existing one, understanding the principles of operation of the BAVO (air cooled unit) is critically important. Incorrect selection of a fan or incorrect calculation of hydraulic resistance can reduce the efficiency of heat transfer by 30-40%, which will directly affect production profitability. Below we will describe in detail the process from receiving the technical specifications to signing the commissioning certificate, based on GOST standards and international ISO standards.

Design stages: thermal load calculation and configuration selection

Design begins not with the choice of a fan model, but with an in-depth analysis of the technological process. The engineer must obtain clear data from the customer: flow rate of the cooled medium (m³/h), inlet temperature and required outlet temperature, as well as permissible fluctuation limits. There was a case in our company when a client indicated the average air temperature of +25°C, without taking into account the peak values ​​in July, when the thermometer rises to +38°C. As a result, in the summer the air-cooling unit simply could not cope with the load, and production had to be stopped. Therefore, the first step of the project is the collection of weather data for the last 10 years for a specific installation location.

Calculation of thermal power requires taking into account the safety factor. Standard practice is to add 10-15% to the design capacity to compensate for contamination of the finned tubes during operation. However, blindly following this rule without considering the type of product may lead to oversizing of equipment. For example, when cooling viscous petroleum products, contamination occurs more slowly than when working with gases containing impurities. We use specialized software to simulate aerodynamic flows, which allows us to visualize hot air recirculation zones. If the hot air emitted by the fan is sucked back into the suction zone, the efficiency drops catastrophically.

The choice of unit configuration depends on available space and service requirements. Vertical sections take up less horizontal space, but require higher racks and make access to the tube bundles more difficult for cleaning. Horizontal blocks are easier to install and maintain, but are sensitive to wind loads and require a larger area. When designing, we always take into account the possibility of dismantling tube bundles without disassembling the entire frame. This requirement is often ignored by newcomers, which turns scheduled cleaning into a week-long downtime for the entire workshop.

The most important element of the project is the wiring diagram. Here it is necessary to provide bypass lines to regulate the temperature in winter. The use of shutters or frequency converters on fan motors allows for flexible performance control. However, the installation of frequency converters requires protection from harmonics and proper cable shielding, otherwise they will interfere with instrumentation sensors. The design must reflect the points of drainage, air removal and installation of pressure gauges. The absence of even one air vent can make it impossible to fill the system with coolant.

The project documentation must comply with the requirements of the ESKD and include a specification of materials indicating steel grades. For aggressive environments, ordinary carbon steel is not acceptable - stainless steel or bimetallic pipes with aluminum fins are required. This is where the partner’s production base plays a key role. For example, specialistsWuxi Kaisheng Electric Power and Petrochemical Equipment Co., Ltd.specialize in the development and production of complex heat exchange equipment capable of operating in extreme conditions. Their expertise in creating tube bundles from C46400 marine brass, copper-nickel alloys and high-strength N06625 nickel alloys allows them to solve problems where standard materials fail quickly. Certified to stringent international ASME and PED standards, the company's products are widely used in petroleum refining, chemical processing and seawater desalination, providing high corrosion resistance and thermal efficiency even at high pressures and temperatures.

We recommend that at the design stage an analysis of the corrosiveness of the atmosphere at the installation site be carried out. If the facility is located in an offshore area or near a chemical production facility, the protective coating of the frame must be reinforced, and the materials of the tube bundles must be selected taking into account the specifics of the environment, as Wuxi Kaisheng engineers do, offering customized solutions from titanium, 316 stainless steel or special alloys. Ignoring this factor leads to the fact that after 3-4 years the supporting structures lose their strength.

Recommendation:Before approving the design, request aerodynamic drag calculations from the contractor and check for service access points for each row of pipes. Ensure that the specification specifies motors with an energy efficiency rating of at least IE3, as this will reduce operating energy costs by 15-20%.

Site preparation and foundation work for the apparatus unit

Installation of a block of air cooling units is impossible without a well-prepared base. Errors at this stage cannot be corrected by cosmetic repairs - they lead to distortion of the frame, destruction of welds and vibration, which destroys the pipes. The foundation must be designed not only for the static load from the weight of the equipment (which can reach tens of tons), but also for the dynamic loads from operating fans. Vibration is transmitted to the ground, and if the foundation is not rigid enough, resonance occurs. We have seen cases where bolted connections weakened after just a month of work due to micro-shifts in the supports.

Geodetic survey of the site is required before the start of excavation work. A height difference of more than 5 mm along the length of the foundation is unacceptable for large blocks. Concreting should be done using vibrators to remove air voids, especially in areas where anchor bolts are installed. Anchors must be installed strictly vertically with a tolerance of no more than 2 mm. Misalignment of anchors by even an inch will create huge problems when installing frame columns, forcing installers to heat the metal or drill holes, which reduces the load-bearing capacity of the structure.

For regions with low temperatures, it is important to consider insulating the foundation or using frost-resistant grades of concrete. Freezing of the soil under one of the supports can cause uneven settlement. It is also necessary to organize drainage around the foundation so that melt water does not erode the foundation. Customers often forget about embedded parts for fastening stairs, service platforms and cable routes. Adding them after the fact requires diamond drilling and compromises the integrity of the concrete.

The installation height of the unit above the ground is dictated by safety requirements and the need to place the piping below. Typically the clearance is from 3 to 6 meters. This space must be accessible for the passage of repair equipment. We recommend immediately at the concreting stage to lay sleeves for the passage of cables and pipes through the foundation to avoid subsequent chiselling. Waterproofing the upper surface of the foundation is also required to prevent capillary rise of moisture in the metal structure.

Before delivering equipment to the site, it is necessary to check the readiness of access roads. The cranes required for the installation of BAVO sections are heavy and require a hard covering. A dirt road washed out after rain can stop installation for several days. The logistics of delivering long sections (sometimes up to 12 meters) also requires careful route planning and the availability of manipulators with the appropriate carrying capacity.

Recommendation:After the concrete has hardened, carry out a repeated geodetic check of the coordinates of the anchors and draw up an as-built diagram. Only with this document in hand can you give a command to ship metal structures from the factory. Any discrepancies must be resolved prior to installation.

Technology for assembling metal structures and installing sections

Assembling the frame of an air cooling unit is a high-precision job that requires qualified welders and installers. Metal structures are usually supplied in transportable blocks that are joined on site. The joining of columns and beams is done using high-strength bolts or welding, depending on the project. We prefer bolted connections for the main load-bearing elements, as they allow control of the tightening force and are easier to inspect in the future. Welds made in the field are more difficult to inspect for defects without expensive ultrasonic testing.

When lifting sections, it is important to follow the slinging diagrams specified in the product data sheet. Improper slinging can deform thin-walled fin elements or damage the commutators. Sections are installed sequentially, starting from a fixed support. Temperature gaps between sections must be observed strictly according to the design, otherwise, during thermal expansion of the pipes, colossal stresses will arise that can tear the pipes out of the tube sheets. We use special calibrated gaskets to ensure uniform gaps.

Installation of pipe bundles is the most critical stage. Tube sheets must be installed strictly horizontally. A misalignment of even a fraction of a degree will result in some of the pipes working inefficiently and others experiencing overloads. The flange connections of the pipes are assembled using new proparonite or spiral wound gaskets. Reusing old gaskets is strictly prohibited - this is a guaranteed leak under pressure. The bolts are tightened crosswise using a torque wrench with force control.

Particular attention is paid to the installation of diffusers and fan guards. The gap between the fan blades and the diffuser wall should be uniform around the entire perimeter (usually 10-15 mm). Increasing the gap reduces the efficiency of the fan, while decreasing it leads to noise and the risk of blade breakage due to vibration. Modern fan blades are made of fiberglass or aluminum and require careful handling. Scratches on fiberglass can become sources of destruction under the influence of centrifugal forces.

After assembling the frame and installing the sections, installation of service platforms, stairs and fences is carried out. All these elements must comply with labor safety standards. The railing must withstand a load of at least 400 N at any point. The flooring of the platforms is made of corrugated steel or expanded metal to prevent slipping. We always check the reliability of fastening of each element, since falling a tool from a height can lead to tragedy.

Recommendation:Use laser-type level gauges to control the horizontal level of each installed section. Don't rely on visual assessment. After installing each section, temporarily secure it with spacers until the entire unit is finally secured.

Electrical installation and connection of fan drives

The electrical part of the air cooling unit is its “nervous system”. Errors here lead not only to equipment shutdown, but also to fire hazards. Cable routes are laid in trays or pipes protected from mechanical damage and ultraviolet radiation. Cables are inserted into electric motors and control cabinets through sealed leads that provide a degree of protection of at least IP54 (for moderate climates) or IP65 (for dusty and humid areas). We often see installers being lazy about installing seals, and moisture gets inside the boxes, causing a short circuit.

Connecting fan motors requires correct phasing. Incorrect connection of a three-phase motor will cause it to rotate in the opposite direction, which will dramatically reduce performance and may damage the impeller. Before the first start-up, the insulation resistance of the windings must be checked with a megohmmeter. The value must be at least 0.5 MOhm. If the engine has been stored in storage for a long time, it may need to be dried before starting.

Control cabinets (CCC) are installed in a protected location, often in a separate area or in the operator’s room. Inside the control room there are circuit breakers, contactors, thermal protection relays and, if necessary, frequency converters. Thermal relays are configured strictly according to the rated motor current indicated on the nameplate. Overestimating the settings will result in the engine burning out before the protection operates. Underestimation leads to false shutdowns.

The automation system includes temperature, pressure and vibration sensors. Temperature sensors are installed in special sleeves on the inlet and outlet manifolds. It is important to ensure good thermal contact of the sensor with the environment. Vibration sensors are mounted on bearing units of motors or gearboxes. Their signals are used for emergency stop when permissible values ​​are exceeded. Cables from sensors must be shielded and laid separately from power cables to avoid interference.

Grounding all equipment is a mandatory safety requirement. The housings of motors, cabinets, metal structures and cable trays must be connected to a grounding loop. Grounding resistance should not exceed 4 ohms. We use copper busbars to organize the main grounding line. The lack of reliable grounding makes operation of the unit illegal and dangerous for personnel.

Recommendation:Carry out a test run of each motor in the “jog” mode (short-term switching on) to check the direction of rotation. Only after making sure that all fans are rotating correctly can you proceed to long-term tests.

Hydraulic testing and commissioning

The final step before the commissioning of the facility is hydraulic testing. They are carried out with water (or other working fluid) under pressure exceeding the working pressure by 1.25–1.5 times, according to the rules of Rostechnadzor. The purpose of the tests is to identify hidden welding defects, leaks in flange joints and cracks in pipes. The pressure rises in stages, with a pause at each stage for inspection. We require the presence of a customer representative and a technical supervision inspector during this work.

During testing, all vents must be open to completely remove air from the system. Air pockets distort pressure gauge readings and create the danger of water hammer. After filling the system and reaching the test pressure, the holding time is usually from 10 minutes to several hours, depending on the volume and standards. The pressure drop is unacceptable. Detected leaks are eliminated only after the pressure is released. Tightening bolts under pressure is prohibited.

Commissioning (commissioning) includes comprehensive testing of equipment under load. The operation of the automatic temperature control system is checked. The algorithm must smoothly change the angle of rotation of the blades (for axial fans with variable pitch) or the rotation speed (for VFDs), maintaining a given outlet temperature. We tune PID controllers through trial and error, achieving the minimum transient time without overshoot. Sudden temperature changes are harmful to the technological process.

Vibration and noise measurements are carried out at operating conditions. The vibration level should not exceed the values ​​specified in GOST or the equipment passport. Increased vibration indicates fan imbalance, shaft misalignment or structural resonance. The noise level of the unit is also normalized, especially if the object is located in a residential area. If necessary, noise silencers are installed at the fan exhaust.

Training of customer personnel is an important part of commissioning. Operators must know the algorithms for starting, stopping, actions in emergency situations and the procedure for carrying out routine maintenance. We provide the customer with a complete set of as-built documentation, including equipment passports, materials certificates, hidden work reports and test logs. Without this package of documents, commissioning of the facility is impossible.

Recommendation:Keep a detailed log of commissioning work, recording all parameters every 30 minutes on the first day of operation. This will help identify hidden defects that only appear when the equipment warms up.

Typical installation errors and methods for eliminating them

Despite the apparent simplicity of the design,air cooling unit: design and installationwhich is carried out with violations, becomes a source of constant problems. One of the most common mistakes is ignoring temperature compensators on piping pipelines. Rigid attachment of pipes to the block when the temperature changes leads to separation of the pipes. The solution is to install bellows expansion joints or U-shaped loops.

The second common problem is improper air flow organization. Installing the unit in an enclosed yard or too close to a building wall causes hot air to recirculate. Efficiency drops and equipment wears out. Correcting the situation requires installing guide screens or moving the unit to a more open location, which is expensive and difficult.

The third mistake is saving on the quality of fasteners. The use of ordinary bolts instead of high-strength ones in critical components leads to their shearing under the influence of vibration. We insist on using fasteners of strength class 8.8 and higher with the mandatory installation of spring washers or the use of anaerobic thread lockers.

The fourth point is the lack of protection against icing in winter. When gases with a high moisture content are cooled, ice forms on the fins, which can block air flow and destroy the pipes. It is necessary to provide an anti-icing system (hot air recirculation or electric heating) and a “reverse” fan operating mode to discharge ice.

The fifth mistake is careless attitude to the paintwork during installation. Scratches and chips of paint received during transportation and assembly must be repaired immediately. Otherwise, corrosion will start from these places and quickly spread. We require installers to have kits of repair paint and apply it immediately after completing work on the site.

Recommendation:Conduct regular audits of the condition of fasteners and paintwork during the first year of operation. Make a map of defects and eliminate them before the next season.

Service maintenance and service life extension

The durability of the air cooling unit directly depends on the quality of service. The maintenance schedule should include monthly inspection, quarterly lubrication of bearings and an annual full inspection. Fan and gear bearings require the use of only lubricants recommended by the manufacturer. Mixing different types of lubricants is unacceptable and leads to coking and jamming.

Keeping tube bundles free of dust, lint and dirt is a critical procedure. Dirty fins act as a heat insulator, dramatically reducing heat transfer efficiency. Cleaning should be done with compressed air or low pressure water to avoid bending the slats. For complex contaminants (oil, bitumen), chemical washing with special solutions is used.

Belt tension (if a belt drive is used) is checked regularly. Loose belts slip, heat up and wear out. Overtightened belts create excessive load on the motor and fan bearings. The optimal belt deflection is checked using a torque measuring device.

Analysis of oil in gearboxes makes it possible to predict wear of gears and bearings. The appearance of metal shavings in the oil signals the beginning of the destruction of the mechanisms. Timely replacement of oil and filters extends the life of the gearbox significantly.

We recommend concluding a long-term service agreement with a qualified organization. The presence of spare parts (belts, bearings, gaskets) in the customer’s warehouse will reduce downtime in the event of an accident. Self-repair without experience often leads to worsening damage.

Recommendation:Implement a system for monitoring the condition of equipment (vibration diagnostics, thermography) to move from scheduled preventive maintenance to repairs based on actual condition. This saves up to 30% of the maintenance budget.

Conclusion and selection of a reliable partner

Well implementedair cooling unit: design and installationwhich are made in accordance with modern standards, becomes a reliable asset of the enterprise for decades. It ensures process stability, reduces energy consumption and minimizes the risk of emergency stops. However, achieving this result is only possible in collaboration with professionals who have experience working with similar systems in various climatic zones.

Our company has full competence to perform the entire cycle of work: from engineering calculations and development of design documentation to equipment supply, installation supervision and commissioning. We work closely with leading component manufacturers such asWuxi Kaisheng Electric Power and Petrochemical Equipment Co., Ltd., whose specialization in the development and production of world-class heat exchange equipment allows us to offer customers optimal solutions. Whether titanium shell-and-tube heat exchangers, ASME high-pressure units or complex corrugated tube bundles made from N06625 and C70600 alloys, Wuxi Kaisheng products guarantee high corrosion resistance and efficiency in the most severe conditions of the oil refining, chemical industry and shipbuilding.

Do not risk your production by entrusting installation to unverified contractors. Errors in the cooling system are too expensive. Contact us today to discuss the details of your project and receive a quote. We guarantee transparency of calculations, compliance with deadlines and high quality of work, using only proven equipment from partners such as Wuxi Kaisheng.

For more information about our services and examples of completed projects, visit the sectioncompleted projects of industrial cooling systemson our website. There you will find photo reports, technical specifications and customer reviews confirming our expertise.