Improve Airflow at Fan Inlets & Outlets

Flow patterns have a substantial impact on fan out- put and system resistance. Fans and system components are sensitive to the profile of an entering airstream. Non-uniform air patterns cause fans and system components to display flow/pres- sure-drop characteristics that are different from the manufacturer-supplied data.

Many fan performance problems can be avoided by designing the system so that the inlet and outlet ducts to and from the fan are as straight as possible within the physical constraints of the available space. If a fan's inlet is too close to an elbow in the air duct, the swirls caused by this elbow will decrease the efficiency of the fan. One general guideline is to provide a straight duct length of at least 3 times the duct diameter just prior to the fan inlet.

Similar to the inflow, swirls and vortices on the outflow side also reduce fan efficiency. In order to avoid these, tees and other fittings should be placed far enough downstream of a fan for the airflow to become more uniform. Similarly, where possible, fans should be oriented so that the airflow profile out of a fan matches the airflow behavior created by fittings such as an elbow.

If locating the fan away from the elbows or tees at the in- or out-let ends is not feasible, use of of turning vanes, air splitters, and flow straighteners should be considered to correct the air flow.

Development Status Products

Improve Airflow at Fan Inlets & OutletsCosts & Benefits

Parent Process: Fan Systems
Energy Savings Potential

This measure is estimated to offer following improvement potentials (UNIDO, 2010):
• 10% for low efficiency base cases;
• 5% for medium efficiency bas cases;
• 1%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 1833 20122
Canada 336 4190
EU 1293 12146
Thailand 226 2273
Vietnam 104 1477
brazil 413 4611
CO2 Emission Reduction Potential

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

US 1105
Canada 167
EU 564
Thailand 118
Vietnam 51
brazil 60


Estimated typical capital costs of this measure for different system sizes (S) are:
• US $1000  for S < 37 kW;
• US $2000 for 37 kW < S < 75 kW;
• US $3000 for 75 kW < S < 150 kW;
• US $5000 for 150 kW < S < 375 kW;
• US $10000 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 16.7
Canada 16.2
EU 18.5
Thailand 5.4
Vietnam 5.4
brazil 5.9

Improve Airflow at Fan Inlets & Outlets Publications

Page Number: 

24, 64-76