A commonly overlooked factor behind compressor performance is the influence of on-site conditions and the impact they can have on compressor design, daily operation, and running costs. These factors can directly affect energy consumption, daily operations, and system efficiencies, which are critical metrics for facility operators.
At FS-Elliott, centrifugal compressors are engineered to meet these conditions, delivering customized performance tailored to each customer’s application. This approach helps improve efficiency, stability, and long-term reliability across the entire compressed air or gas system.
How is performance determined?
To understand the impact these conditions can have on a compressor selection it is important to understanding how centrifugal compressors are designed. FS-Elliott uses internally developed engineering tools and advanced aerodynamic design software to evaluate multiple site-specific parameters, including inlet temperature, humidity, elevation, cooling water conditions, process pressure requirements, and expected demand profile.
Most centrifugal air compressors are comprised of multiple stages with cooling in between. A series of calculations are completed to create performance maps or what’s commonly referred to as the compressor selection. Values for specific humidity , volume and flow are established which are then used to determine nonperformance coefficients. Stage performances are expressed as non-dimensional parameters since each site installation will have varying conditions. The coefficients are defined by flow, head, work and efficiency.
Using either test or expected data from design programs, polynomial curves are created for head coefficient and efficiency versus flow coefficient. The work coefficient can then be calculated. In this way, the coefficients can be determined for a known flow, and the flow coefficients can be used to calculate the stage discharge properties, including discharge temperature and pressure.
In general terms, the head coefficient is dependent on the stage’s impeller diameter, the accompanying diffuser, and the pinion speed. The flow through a stage is primarily determined by the impeller and diffuser blade heights, commonly referred to as stage profiles. This process is then repeated as profiles for the second and third stages of compression are calculated, creating a stage family.
Importance of Accurate Operation Conditions
In order to perform an appropriate compressor selection, key inlet conditions such as required flow, discharge pressure, ambient conditions, and driver frequency can have a significant influence on compressor performance and sizing. These conditions can also fluctuate throughout the course of year, leading to several operating points to be considered.
Temperature: Lower ambient temperatures increase mass flow and power consumption, whereas higher temperatures reduce flow capacity. Designs must accommodate both extremes to avoid under sizing the compressor or draw additional power
Humidity: Higher humidity slightly reduces mass flow due to increased specific volume, requiring adjustments during selection.
Coolant Temperature: Warmer coolant reduces intercooler effectiveness, raising stage inlet temperatures and reducing compressor capacity
It is also critical to note the impact of misstated or unrealistic ambient conditions when creating a selection. For example, high temperatures at 100% relative humidity levels would force the compressor to be oversized, resulting in higher power consumption, reduced efficiency, or even increased capital investment due to larger equipment sizing. Utilizing realized conditions can help end users avoid unnecessary expenditures and optimize compressor performance.
Demand profile also plays an important role in aerodynamic design. Some facilities operate with continuous demand, allowing compressor performance to be optimized around a steady operating condition. Other systems experience fluctuations between higher and lower load conditions throughout the day. In addition to load, many facilities consider the discharge temperatures of their machines for downstream process. Hot discharge air can be utilized downstream, such as for Heat of Compression (HOC) drying, or cooled via an aftercooler to meet a desired water return temperature. This process typically goes through multiple iterations with customer feedback ensuring their demands are met.
Tools such as FS-Elliott’s AeroSwap flow comparison calculator help standardize airflow definitions and improve clarity when comparing compressor performance across different flow units.
Efficiency through Control Strategy
While compressor design is critical, effective compressor control does more than simply respond to changing demand. A well-designed control strategy also provides additional operational benefits, helping the aerodynamic design perform as intended for the customer. Manufacturing systems rarely operate at a single fixed condition. Production demand changes, ambient temperatures fluctuate, and system requirements evolve over time.
FS-Elliott’s Regulus control series help facilities adapt to changing operating environments.
For example:
Valve Throttling: Regulating inlet guide vanes and unloading control valves helps manage flow and pressure as either ambient conditions or plant demand fluctuate. Proper control strategies such as base or suction throttle modes help maintain compressor efficiency while delivering the desired performance.
Ambient Compensation Control (ACC) monitors seasonal temperature swings and adjusts the compressor surge line accordingly. This provides greater turndown capability and additional energy savings.
Integrated Compressor Control (ICC) systems allow multiple compressors to communicate as a coordinated system via lead/lag or load sharing scenarios. This allows the system to distribute demand across multiple units to support energy-efficient operation as plant conditions vary.
A Smarter Approach to Compressor Design
Custom aerodynamic design is not about theoretical performance improvements. It is about engineering compressors around the real conditions that facilities operate under every day.
By designing the compressor aerodynamics tailored to the application, manufacturers gain a compression system that supports energy efficiency, stable operation, and long-term equipment reliability.
To learn more about applying custom aerodynamics to your compressed air system, connect with one of our authorized channel partners. You can also hear a deeper discussion on the topic in Episode 4 of our Beyond Compression podcast.
Frequently Asked Questions (FAQs)
What is custom aerodynamic design in a centrifugal compressor?
Custom aerodynamic design means engineering the compressor’s internal flow path components specifically for the operating conditions of a facility, including flow, pressure, gas properties, and inlet conditions.
Why is custom aerodynamic design more efficient than a standard compressor?
Because the compressor operates closer to its optimal aerodynamic point, it requires less excess power to deliver the required flow and pressure.
Does custom aerodynamic design improve reliability?
Yes. Operating closer to the design point reduces mechanical stress on bearings, seals, and rotating components, supporting longer service life and stable operation.
Is custom aerodynamic design only used for new compressors?
It is most common in new compressor designs, but aerodynamic optimization can also be applied during upgrades, rerates, or airend replacements.
How is compressor performance verified?
Performance is validated through testing that confirms flow, pressure, and power at customer-specified inlet conditions using industry-recognized standards.
Which industries benefit most from custom aerodynamics?
Any industry using compressed air or gas systems can benefit from custom aerodynamic design. Because every facility operates under unique conditions, tailoring compressor aerodynamics to the actual application helps improve efficiency, stability, and long-term reliability.