VSD Screw Air Compressor

KB-KD INV Series

KE-KG INV Series

Energy can represent over 70% of a compressor’s lifecycle costs. Generating compressed air can account for more than 40% of a plant’s total electricity bill. Most production environments have a fluctuating air demand depending on the time of day, week, or even months per year. With Adekom’s VSD technology monitoring compressed air requirements, fluctuating demand no longer equals high energy costs. Assuming 70% workload running for 5800 hours per year, paid back period for Adekom VSD compressor itself could be 2 – 3 years!

Working principle of inverter controlled screw compressor:

VSD compressor monitors the system air demand and forming a closed control circuit with frequency inverter, pressure transducer and inverter duty motor. The target working pressure could be set in PLC controller and the system pressure being sourced by pressure transducer, the signal is then converted to 4-20 mA current signal and revert back to the controller. This signal is compared with the pre-set value by PID calculation instantaneously which provides accurate data for the frequency inverter to output corresponding frequency to change the motor speed and in return to deliver the adequate air capacity to match preciously with the system air demand and at last achieving the aims of constant pressure air delivery and energy saving.

Principle of Vector Control VSD Technology:

The integrated flux vector control of the inverter system makes it possible to achieve high torques, even at low motor speeds. The sensor-less vector control system of the INV series enables fast, high-precision speed and torque regulation. Fast response/high accuracy speed control (zero speed control, servo lock), torque control and position control can be performed. Vector control frequency inverter offers excellent control characteristics when compared to traditional V/F control and other control techniques, achieving the control characteristics equal to those of DC machines.

How does it actually be energy-saving?

First Saving: Air delivered according to system demands; on/off control losses are eliminated. VSD compressor precisely follows the varying air demand by adjusting motor rotation speed, this prevents unnecessary full load high current operation and energy consumed during unload operation (approx.45% of full load amount).

Second Saving: Precise pressure control, avoiding wastage due to start/stop pressure band. VSD compressor delivers air at stable net pressure (e.g. 6bar.g), this not only maintains accurate target working pressure but also avoids losses due to high current operation within cut-in/cut-out pressure band.

Standard compressor starts up under high current, it operates at full load condition until cut-out pressure (e.g. 8 bar.g) is reached, and starts up again when pressure drops to cut-in pressure (e.g. 6 bar.g). This start/stop control creates two wastages: (i) losses incurred during unload operation; (ii) losses due to 8-6=2 bar.g cut-in/cut-out differential pressure.

Standard compressor operates between the range of 6 and 8 bar.g, it means 6 bar.g delivered pressure can meet with production requirement, the additional 2 bar.g pressure is an inherent wastage of standard compressor.

Sample calculation of energy saving:

For example a standard 55kW screw compressor delivers air at 70% loading and operates 5800 hours per years. Taking electricity cost of USD 0.15/kWH, the additional energy consumed as comparing with VSD compressor will be:

A. Energy consumed during unload operation assuming unload shaft power absorbed is 45% of full load amount: 30% unload times x loss during unload time = (45% x 55kW) x 5800 hour/year x USD 0.15 = USD 6,460/year.

B. Energy consumed due to cut-in/cut-out pressure band of 2 bar.g assuming this counts for 14% of full load amount: 70% loading time x additional 2 bar.g of differential pressure loss = (14% x 55kW) x 5800 hour/year x USD 0.15 = USD 4,689/year.

Total energy saved by using VSD compressor will be = USD 6,460/year + USD 4,689/year = USD 11,149/year.

In a conclusion, a VSD compressor can save annually the electricity cost of USD 11,149, 3 years can then save USD 11,149 x 3 = USD 33,447 which could be more than capital investment for purchasing another VSD compressor.

Direct energy saving with 70% loading and operating 5,800 hours per year:












Saved electricity cost(USD/ per year)