Fan Efficiencies

According to research carried out by the Fan Manufacturers Association, fans account for 22% of the industrial motor energy consumption whilst electric motors account for 40% of the UK’s total electricity consumption.

It is relevant that improvements in fan efficiency will lead to the improved efficiency of a building. Fans are present in most buildings from simple axial toilet extract fans to fan systems within large scale Air Handling Units.

If the actual fan efficiency data can be obtained, often a difficult figure to obtain in many existing systems, then this may help to improve the overall energy rating of the building.

The most important measure of fan efficiency for considering energy efficiency in buildings is measured as Specific Fan Power ( SFP) measured as watts per litre second. The SFP is a function of the volume flow of the fan and the electrical power input. There is not a ‘peak’ or ‘best operating point’. Fan manufacturers cannot quote a SFP for a fan without reference to a particular operating point.

The SFP is a function of the volume flow of the fan and the electrical power input and can be calculated as follows:

SFP =  Pe / V

Pe = electrical power input (W) to the fan system or complete air movement installation

V = is volume flow (l/s)

The term SFP is also applied to groups of fans and the complete air movement system. As with fan efficiencies it is important to determine what elements of a fan system have been considered when calculating the SFP and what additional losses need to be added when installed to other elements in the air movement installation.

Legislation and regulations being implemented following European and UK Government commitment to reducing Carbon emissions together with rising energy prices are leading to requirements for greater fan efficiency.