Compressed air systems have several different types of control methods. Identifying the right technology for each individual site can result in significant gains in efficiency and reduction in operating costs for the plant.
Common control methods include: Start/Stop; Load/Unload; Modulation; Variable Speed Drive (VSD); and, Variable Displacement.
A thorough and detailed usage profile needs to be established to determine the control method that will maximise efficiency and minimise operating costs at a particular site. A usage profile consists of reading and analysing the plant’s demand for air over time. This is usually collected using an auditing device that can be configured to the compressed air system to measure the air demand in the plant over an extended period. The detailed usage profile can then be analysed and the control method that will deliver the greatest efficiency identified.
There are generally four distinct types of profiles identified in most plants:
Constant demand occurs when a plant typically requires a consistent amount of air delivery to the plant during all shifts. A plant with a constant demand benefits most from a fixed speed, load/unload controlled air compressor with a correctly sized air receiver to minimise cycles and extend off-load time.
Widely Varying Demand
Widely varying demand occurs when a plant’s air demand fluctuates significantly during and between processes and shifts. VSD compressors offer the most efficient control method as it can alter air production to meet the plant’s requirements at all times ensuring there is no wastage.
Changing demand profiles occur where there are different air demands between processes and/or shifts. For example, a day shift may require a higher volume of compressed air whereas a night shift may require only half the amount of the day shift. The best control method for changing demand levels is multiple sequenced compressors. Sequencing multiple compressors enables the system to automatically determine the most efficient operating mode to produce the amount of compressed air required in the plant at any stage during production.
Short Term High Demand
Short term high demand occurs when a plant has specific times of peak demand in an otherwise constant demand profile. There are certain processes that only occur a few times during a shift but require a high level of compressed air. The best control method for short term high demand is generally a fixed speed, load/unload compressor with an engineered air receiver that has enough storage to handle the short peak demands.
Only an air audit conducted on the plant can help determine a usage profile and the best control method for the application. Implementing the best control method for the plant will reduce energy and maintenance costs leading to significant savings.
Southern Cross Compressors Australia Pty Ltd can assist with further advice on control methods for compressed air systems.