Fans - efficiency measurement

​On January 1 2013, new ecodesign requirements for fans driven by electric motors came into force (Commission Regulation (EU) No 327/2011 of 30 March 2011). The requirements, which are minimum requirements, concerns fans driven by an electric motor with a power input between 125 W and 500 kW and designed at its point of optimum energy efficiency.

The requirements mean that energy efficiency is not to be measured and calculated, as the industry was accustomed to, wherein the efficiency was calculated from the static or dynamic pressure increase, the airflow and the input power of the fan. Energy efficiency is now to be measured and calculated as a total efficiency for the entire ventilation system, i.e. fan, electric motor and control.

According to the Regulation, measurements and calculations must be made using a reliable, accurate and reproducible method, which takes into account the generally recognized state-of-the-art measurement methods, and whose results are deemed to be of low uncertainty.

A measurement and calculation method that lives up to these criteria is the ISO 5801 standard for fans.

1 January 2015, the ecodesign requirements for energy efficiency were tightened up and extended to more types of fans.

The figure below shows energy requirements (target energy efficiencies) for fans applicable since 1 January 2015.

Calculation method

The methodology for calculating the energy efficiency of a specific fan is based on the ratio of gas power to electrical input power to the motor, where fan gas power is the product of gas volume flow rate and pressure difference across the fan. The pressure is either the static pressure or the total pressure, which is the sum of static and dynamic pressure depending upon the measurement and efficiency category.

Measurement category means a test, measurement or usage arrangement that defines the inlet and outlet conditions of the fan under test. The categories, which are described in the ISO 5801 standard for fans, are:

Final assembly

Where the fan is supplied as a ‘final assembly’, the gas power and the electric input power of the fan are measured at its optimum energy efficiency point.

Where the fan does not include a variable speed drive, the overall efficiency is calculated using the following equation:

η_e = P_u(s)/P_e

where:

• h_e is the overall efficiency

• P_u(s) is the fan gas power when it is operating at its optimal energy efficiency point

• P_e is the power measured at the mains input terminals to the motor of the fan when the fan is operating at its optimal energy efficiency point

where the fan includes a variable speed drive, calculate the overall efficiency using the following equation:

η_e = (P_u(s)/P_e) ∙ C_c

where:

• h_e is the overall efficiency

• P_u(s) is the fan gas power when it is operating at its optimal energy efficiency point

• P_e is the power measured at the mains input terminals to the variable speed drive of the fan when the fan is operating at its optimal energy efficiency point

• C_c is a part load compensation factor as follows:

• for a motor with a variable speed drive and P_ed≥ 5 kW, then C_c = 1,04
• for a motor with a variable speed drive and P_ed < 5 kW, then C_c = – 0,03 ln(P_ed) + 1,088

Not final assembly

Where the fan is supplied as ‘not final assembly’, the fan overall efficiency is calculated at the impeller’s optimum energy efficiency point, using the following equation:

h_e = h_r · h_m · h_T · C_m · C_c

where:

• h_e is the overall efficiency

• h_r is the fan impeller efficiency according to P_u(s)/P_a

where:

• P_u(s) is fan gas power determined at the point of optimal energy efficiency for the impeller
• P_a is the fan shaft power at the point of optimal energy efficiency of the impeller

• η_m is the nominal rated motor efficiency in accordance with Regulation (EC) No 640/2009 whenever applicable

• η_T is the efficiency of the driving arrangement

• C_m is the compensation factor to account for matching of components

• C_c is the part load compensation factor

A more detailed description of this method is shown in Commission Regulation (EU) No 327/2011 and Regulation (EC) No 640/2009.

Fan gas power, P_u(s)

The fan gas power, P_u(s) (kW), is calculated according to the measurement category test method chosen by the fan supplier:

1. where the fan has been measured according to measurement category A, fan static gas power P_us is used from the equation P_us = q · p_sf · k_ps

1. where the fan has been measured according to measurement category B, fan gas power

P_u is used from the equation P_u = q · p_f · k_p

1. where the fan has been measured according to measurement category C, fan static gas power P_us is used from the equation P_us = q · p_sf · k_ps

1. where the fan has been measured according to measurement category D, fan gas power

P_u is used from the equation P_u = q · p_f · k_p

Where

• q is the airflow
• p_sf is the fan static pressure which means the fan total pressure p_f minus the fan dynamic pressure corrected by the Mach factor.
• p_f is the fan total pressure which means the difference between the stagnation pressure at the fan outlet and the stagnation pressure at the fan inlet
• The stagnation pressure means the pressure measured at a point in a flowing gas if it were brought to rest via an isentropic process
• The Mach factor means a correction factor applied to dynamic pressure at a point, defined as the stagnation pressure minus the pressure with respect to absolute zero pressure which is exerted at a point at rest relative to the gas around it and divided by the dynamic pressure
• k_ps and k_p are compressibility factors. The value is approximately 1.

At air velocities below 40 m/s the error by calculating the difference between the static or the total pressure at the outlet and the inlet in the traditional way is less than 1 %.

Electric motors

Minimum energy efficiency requirements have been established for electric motors in Commission Regulation (EC) No 640/2009 of 22 July 2009 implementing Directive 2005/32/EC of the European Parliament and of the Council with regard to ecodesign requirements for electric motors, including electric motors equipped with variable speed drives. They also apply to those motors which are part of a motor-fan system. However, many fans covered by this Regulation are used in combination with motors not covered by Regulation (EC) No 640/2009. That is motors like permanent magnet motors (e.g. EC motors) or synchronous reluctance motors. These types of motors are specified to operate exclusively with a VSD (motors that cannot be used directly online) and are excluded from the Regulation.