An improved compressed air system utilizes one or more base compressors, such as fixed speed drive compressors, to meet the compressed air demands and one or more trim compressors, such as variable speed drive compressors, to meet the variations in the demand. The operation of both the base and trim compressors may be controlled to provide improved overall efficiency while meeting the transient load demands. The control may spread the demands over the various base compressors to improve the overall loading on each base compressor. Efficiency metrics may be utilized to control the switching between base and trim compressors. Unloading of a base compressor may be controlled to avoid undesirable changes in system performance.

An improved compressed air system utilizes one or more base compressors, such as fixed speed drive compressors, to meet the compressed air demands and one or more trim compressors, such as variable speed drive compressors, to meet the variations in the demand. The operation of both the base and trim compressors may be controlled to provide improved overall efficiency while meeting the transient load demands. The control may spread the demands over the various base compressors to improve the overall loading on each base compressor. Efficiency metrics may be utilized to control the switching between base and trim compressors. Unloading of a base compressor may be controlled to avoid undesirable changes in system performance.

There are provided an operation number control device and a method for controlling the same that can level the operation times of the fluid machines, which are connected to the operation number control device. A fluid machine system comprises a plurality of fluid machines, and an operation number control device capable of individually controlling start and stop of the fluid machines. The operation number control device sets a continuous operation time for each of the fluid machines based on total operation times of the fluid machine and other fluid machines. When among fluid machines in operation, there is a fluid machine for which the continuous operation time set for the fluid machine has elapsed and there is a fluid machine at stop, the operation number control device causes the fluid machine at stop to start and causes the fluid machine to stop.

A positive displacement pump includes at least two pumping chambers and associated plungers. Each plunger is driven by an associated variable speed motor, such as a stepper motor, in a reciprocating motion. The stepper motor varies speed during each stroke of the plunger. A controller controls speed and direction of each stepper motor. Each stepper motor is coupled to a leadscrew having an associated guide rod mounted on the leadscrew to move along the leadscrew as the leadscrew rotates and actuate an associated plunger. The controller varies the speed, displacement and duration of the stepper motors' steps to maintain a constant outflow without pulses.

A control device controls a plurality of inverter-driven pumps disposed between a heat source device and an air-conditioner. The control device includes a perceiving unit that perceives a cumulative operation time and a rotation speed distribution during operation of each of the pumps, a degradation degree derivation unit that derives a degradation degree of each of the pumps based on the cumulative operation time and the rotation speed distribution during operation of each of the pumps, and a determining unit that determines the pump to be next operated/stopped based on the degradation degree of each of the pumps. The degradation degree derivation unit further derives an increased amount of the degradation degree of each of the pumps in a predetermined period. The determining unit determines the pump to be next operated/stopped based on the increased amount of the degradation degree of each of the pumps in the predetermined period.