4 screw air compressor control methods to optimize efficiency
When it comes to air compressors, the control methods employed can significantly impact the overall operating efficiency. There are several control methods used in the compressor industry. These control methods are designed to optimize performance and energy consumption. Let's explore these methods in detail.
However, this also causes the compressor to draw a vacuum at the inlet, so that it is trying to make high pressure from a lower starting pressure. This causes part-load performance to be very poor. A modulating compressor operating at 0 capacity still uses about 70% of its full load power. A modulating compressor can typically regulate discharge pressure with no or minimal air receiver storage.
Some modulation-controlled machines may be adjusted to fully unload or “blow down” if capacity reduces to a certain level, such as 40%. This saves some energy but requires the use of air storage receivers to meet demand when in the fully unloaded state. It also causes the compressor to draw a vacuum at the inlet, leading to poor part-load performance.
The spiral valve technology optimizes compressor efficiency by adjusting the amount of air being compressed based on demand. At its core is the variable displacement air end, which features specially engineered openings along the air end casting. As the demand for compressed air changes, the spiral valve rotates to progressively open or close bypass ports. When these ports are opened, the effective length of the rotor used for compression is shortened, resulting in less air being compressed. Conversely, when the ports are closed, the entire compression chamber is utilized, allowing for 100% air capacity.
Load/unload, sometimes called load / no-load requires storage receiver volume, and operates the compressor at full capacity until the unload pressure (cut-out) setpoint is reached. At the unload pressure, the compressor switches to unload, producing no compressed air, and venting its internal pressure (blowing down). During this unload period, demand of the plant must be met by the stored air in the receiver(s) and piping. Once a lower load (cut-in) pressure is reached, the compressor returns to full capacity, and the cycle repeats.
During the unload period, the compressor reaches a low unloaded power consumption (approximately 25 to 30% of full load for lubricated screw compressor). On oil flooded screw, however, it may take 30 to 60 seconds of unload time for the compressor to reach this lowest unloaded power consumption. For this reason, the efficiency of these compressors is greatly affected by the amount of receiver volume present in the system, as well. More receiver volume allows longer unloaded periods with lower power consumption. In addition, more receiver volume causes the compressor to cycle less, reducing wear and tear on the machine.
Variable speed drive (variable frequency drive) compressor controls use a frequency drive to control the frequency of the electrical signal to the motor. This, in turn, varies the speed of the motor and airend, controlling capacity. This provides a nearly proportional flow to power ratio at part load. At full load, however, drive losses make the variable speed compressor slightly less efficient than a fixed speed compressor.
Making the choice
When it comes to implementing VSD technology, businesses often face a choice between retrofitting existing systems with VSD components or investing in integrated VSD compressors:
1. Retrofitting existing systems
Retrofitting existing compressor systems with Variable Speed Drive (VSD) components can be a cost-effective way to achieve energy savings by adjusting motor speed to match the actual demand for compressed air. However, this approach comes with several disadvantages. Retrofitting may face integration challenges with existing master control systems and ensuring compatibility with the existing compressor's airend and motor.
Additionally, retrofitted systems might not be as optimized for VSD operation, potentially leading to inefficiencies and reliability issues. The process can also be complex and time-consuming, requiring specialized knowledge and potentially causing disruptions during installation.
2. Integrated VSD compressors
Integrated VSD compressors are designed with VSD components built into the system from the start, offering several advantages. These compressors are optimized for VSD operation, with all components such as the air-end, motor, lubrication, cooling, and speed-range designed to work together efficiently which results in a more reliable system.
Integrated VSD compressors also come with advanced features like inverter duty motors, protection against bearing currents, and electromagnetic compliance, enhancing their performance and durability. Although the initial investment for integrated VSD compressors is typically higher than retrofitting, the long-term benefits in terms of efficiency, reliability, and advanced features often justify the cost.
In conclusion
While the initial investment for integrated VSD compressors is typically higher than retrofitting, the long-term benefits in terms of efficiency, reliability, and advanced features often justify the costs.
