Variable Speed Drives for Compressed Air Systems

Variable speed drives are accepted as an efficient means of regulating rotary compressor capacity. With the use of VSDs, the motor speed is adjusted to meet the variable demand requirements.  VSDs allow adjusting compressor discharge pressure with high precision (at +/- psi levels) over a wide range of output. This allows additional system energy savings. Efficiency with VSD is generally improved at reduced capacities. The best energy savings are realized in applications where the running hours are long, with a high proportion in the mid- to low-capacity range. At system loads over 75%, it will be more cost-efective to use on-load/off-load control system.  

Development Status Products

Variable Speed Drives for Compressed Air SystemsCosts & Benefits

Parent Process: Compressed Air Systems
Energy Savings Potential

This measure is estimated to offer following improvement potentials:
• 20% for low efficiency base cases;
• 15% for medium efficiency base cases;
• 5% for high efficiency base cases.

Electrical and primary energy savings potential of this technology for different countries is estimated as following (UNIDO, 2010):

  Final (GWh/y) Primary (TJ/y)
US 2268 24908
Canada 599 7460
EU 1985 18654
Thailand 253 2553
Vietnam 114 1629
brazil 392 4370
CO2 Emission Reduction Potential

Total emisson reduction potential, as kt CO2/y for different countries are estimated as (UNIDO, 2010): 

US 1367
Canada 297
EU 866
Thailand 131
Vietnam 56
brazil 57


Estimated typical capital costs of this measure for different system sizes (S) are:
• US $12000  for S < 37 kW;
• US $20000 for 37 kW < S < 75 kW;
• US $40000 for 75 kW < S < 150 kW;
• US $70000 for 150 kW < S < 375 kW;
• US $100000 for 375 kW < S < 745 kW; (UNIDO, 2010)

Cost of conserved energy, expressed as US $/MWh-saved, in different countries are estimated as following (UNIDO, 2010):

US 164.1
Canada 166.9
EU 184.7
Thailand 123.9
Vietnam 122.3
brazil 121.9

Parent Process:
Energy Savings Potential
CO2 Emission Reduction Potential



Variable Speed Drives for Compressed Air Systems Publications

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