Efficient Fan Filter Units

Fan filter units are increasingly used in contamination control environments such as cleanrooms. They consist of a small fan, controller, and a HEPA/ULPA filter enclosed in a box. They maintain specific airflow, and are commonly installed into ceiling grids, typically 2x4 ft or 4x4 ft.

LBNL developed a standard method of evaluating fan-filter-unit (FFU) performance, providing a set of useful metrics. This test standard yields baseline information on energy use and air movement performance that can be applied to utility incentive programs and was intended for industry use, including fan-filter unit manufacturers, end users, utility companies, and designers.

Among the 17 units tested to-date we have seen power consumption ranging from 100 to 400 watts per FFU, and huge variations in efficiencies (in excess of ten-fold) depending operating conditions, defined in terms of air flow rates (or velocity) and pressure loss elsewhere in recirculation system. Also, for a given typical operating condition we have observed a factor of three or more variation in energy efficiency.

Standard Method of Evaluating FFU

  • Principles: Laboratory testing to obtain multiple accurate measurements under various operating conditions.
  • Device Layout: The FFU to be tested will be mounted horizontally or vertically on the exit of the air chamber.
  • Control and Methods: Use an ancillary fan and a damper to control the airflow rate across the FFU tested.
  • Instrumentation: Unit airflow rate, total power usage, and static (and total) pressure across the FFU.

Metrics

  • Unit Airflow Rate (Speed): Airflow rate through the FFU tested with a specific static pressure, in cfm or m3/min (fpm, or m/s for airflow speed).
  • Total Power Usage: Total electrical power input to operate the FFU at certain airflow conditions, including the fan motor, controller, etc. in W.
  • Airflow Velocity Power: Portion of the total power that is moving air through the FFU at certain airflow conditions, in W.
  • Total Pressure (Power) Efficiency: Ratio of airflow velocity power to total power input to an FFU, %. A higher value indicates higher operating efficiency.
  • Energy Performance Index (EPI): Unit's total power usage normalized by the airflow rate through the FFU under certain conditions, in W/cfm. Lower values correspond to higher operating efficiency.