Most industrial air compressors comprise of multiple air compressor and supplying air to the same header/receiver system. One or more of these multiple compressors are VFD driven which the users invest to save on energy consumption during reduced loads.

However these VFD compressors have to take the fluctuating load and not the base load and similarly the fixed speed compressors have to take the base load and as far as possible should run on full load (where they operate at its peak efficiency) to realise the best of the resources available

Sometimes one may have multiple compressors each operating with its individual panel with its independent logic. The above situations can cause huge energy losses if multiple compressor installations operate with no integrated system management.

To elaborate with an example, say there are 4 compressors in a system each of 100 cfm/8 bar, each of 20 kW power capacity. The system demand at a given time is between 200-400 cfm.

Case 1

When the demand is 400 cfm, all compressors will run on full load.

All 4 compressors on full load = 400 @ 8 bar

Power consumed = 20 x 4 = 80 kW

System efficiency =400/80 = 5 cfm/kW

Case 2

When the system has a demand of 200 cfm the 4 compressors will run at 50% load and consume about 15 kW power each (since unload power is not zero and considering 75% power consumption @ 50% load).

Then system efficiency = 200/(15 x 4) = 3.3 cfm/kW

The desired situation, which quite obviously is for 2 compressors to run on full load and other 2 remain in off mode. The system efficiency in that case will be 200/40 =5 cfm/kW

Case 3

When the system has a demand of 325 cfm, then 3 compressors will run at 100% load and 1 compressor will run at 25% load. The power consumption of the compressor running at 25% load will be 12 kW (since unload power is not zero and considering 60% power consumption @ 25% load).

Then system efficiency = 325/[(20 x 3) + (12 x 1)] = 4.5 cfm/kW

The desired situation here will be 3 compressors running on load and one compressor with VFD taking the demand of 25%. Then the power consumption of compressor with VSD running at 25% load will be 5 kW.

The system efficiency in that case will be = 325/[(20 x 3) + (5 x 1)] = 5 cfm/kW

Above desired situations can be brought about by Elgi's Automated Supply Side Controller (ASSC).

The ASSC has multiple programmable logic and helps to manage a system in the following ways:

• Complete system manager of multiple compressor user
• Maintains system pressure by using optimum number and type of compressors
• Identifies an VSD compressor and uses it for taking the system's fluctuating demand, and
• Multiple programmable and sequencing controls for pressure, timing, energy equal hours, etc.

(Mr Rajshekar Mahendrakar, AGM Business Development, Elgi Equipments Limited, Coimbatore. Mobile: 097900-26201. Email: Rajshekhar@elgi.com)