A consulting engineer in Philippines recently asked us to prepare a side-by-side comparison of mixed-flow fan options for a marine & offshore project. The comparison covered performance, installation cost, and ten-year operating cost. This article presents the key findings.
Two Viable Options
A recent marine & offshore project in Philippines gave us the opportunity to compare mixed-flow fan and tube axial fan configurations under identical operating conditions. Both options could meet the specification of 2,000 to 15,000 m3/h at 500 to 3,000 Pa, but the total cost of ownership diverged significantly over the expected equipment life.
The operating environment included temperatures up to -10 to 50 C, requiring careful material selection. The galvanized steel (Q235) construction specified for the mixed-flow fan was also available for the tube axial fan, making the comparison focused on performance rather than materials.
For marine & offshore projects in Philippines, the procurement process for a mixed-flow fan should begin at least 12 to 16 weeks before the required on-site date. This allows time for engineering review, factory testing, and shipping. Custom specifications โ such as non-standard materials (galvanized steel (Q235)), special motor ratings (0.55 kW), or additional certifications โ may extend lead times to 20 weeks. Planning for these timelines early avoids the premium pricing and quality risks associated with rush orders.
Efficiency and Energy
At full design load, the mixed-flow fan achieved 83 percent total efficiency compared to 77 percent for the tube axial fan. This 6-point difference translated to a measurable energy cost difference: the mixed-flow fan with its 0.55 kW IE1 motor consumed about 8 percent less energy per operating hour.
At 50 percent load โ which is where the system operates about 60 percent of the time in this marine & offshore application โ the mixed-flow fan still maintained 78 percent efficiency, while the tube axial fan dropped to 69 percent. This part-load behavior has a larger impact on annual energy cost than the full-load efficiency numbers suggest.
Energy consumption is the single largest operating cost for a mixed-flow fan in a marine & offshore facility. Over a 15-year equipment life, energy costs typically exceed the initial purchase price by a factor of 5 to 8. This means that even small efficiency improvements โ selecting an IE1 motor instead of a lower class, optimizing the duct design to reduce system resistance, or installing a VFD for variable load applications โ compound into significant financial savings over time.
Maintenance and Longevity
Both configurations use similar bearing arrangements and belt drives. The key difference is that the mixed-flow fan impeller, balanced to G6.3 grade, generates lower vibration at the operating point. Over 15 years, lower vibration translates to longer bearing life and fewer unplanned shutdowns.
The ATEX and ABS certifications required for this project were available for both options, with similar documentation and testing requirements.
Our field engineers in Philippines have observed that mixed-flow fan systems in marine & offshore applications often operate at conditions different from what was assumed during design. The most common discrepancy is system resistance: actual duct pressure drop frequently exceeds the calculated value by 10 to 25 percent. This is why we recommend including a 10 percent safety margin on static pressure and verifying the operating point during commissioning against the certified performance curve.
| Parameter | Specification |
| Airflow Range | 2,000 to 15,000 m3/h |
| Static Pressure | 500 to 3,000 Pa |
| Motor Power | 0.55 kW (IE1) |
| Material | galvanized steel (Q235) |
| Temperature Range | -10 to 50 C |
| Impeller Balance | G6.3 (ISO 1940) |
| Noise Level | 45 to 55 dB(A) |
| Certifications | ATEX, ABS |
| Standards | ISO 13348, SOLAS |
Long-Term Performance Expectations
The expected service life of a properly maintained mixed-flow fan in marine & offshore applications is 15 to 20 years, with bearing replacement typically required at 40,000 to 60,000 operating hours. Key factors that determine actual service life include operating temperature (the -10 to 50 C range for this specification), dust loading, vibration levels (maintained below 2.5 mm/s through proper balance at G6.3 grade), and the quality of preventive maintenance.
In Philippines, where ambient conditions can stress equipment, our engineering team provides derating curves for specific motor and drive combinations to ensure reliable operation over the full equipment life.
Integration with Building Systems
For modern marine & offshore facilities in Philippines, a mixed-flow fan system typically integrates with the building management system. Control points include fan start/stop, speed setpoint via VFD, status feedback, alarm feedback, and measured airflow or pressure. The IE1 motor combined with a VFD allows precise control across the full turndown range.
Ensure the control system meets ATEX requirements for emergency operation modes. Fire safety fans must start automatically on alarm signal and reach full speed within 60 seconds. The ISO 13348 standard may define specific response time and performance requirements for emergency ventilation.
Quality Assurance and Testing
Every mixed-flow fan unit leaving our factory undergoes a standardized test procedure that includes a run test at full speed, vibration measurement at all bearing locations (must meet G6.3 grade), and verification of impeller balance. For units above 0.55 kW motor rating, we also perform a witnessed performance test on the AMCA-standard test rig, measuring airflow, pressure, and power consumption at three operating points.
Field testing after installation should replicate key factory measurements to establish the commissioning baseline. The measured airflow and pressure should be within 5 percent of design values. All commissioning data should be documented and retained as part of the project quality records.
Conclusion
Every mixed-flow fan project in marine & offshore applications has its own unique requirements, but the engineering fundamentals remain the same. The parameters and practices discussed here have been validated across hundreds of installations. Contact our team for project-specific guidance.
