ABSTRACT
The ‘Harmony P and PD’ surface mounted extract fans from Greenwood Airvac each contain a double inlet impeller designed to be self balancing for most application. An air fl ow of 85 m3/W is attained against a static head of 30 N/mm2 when only one intake is used the air fl ow will be reduced to approximately 75 per cent. The installed resistance will be dependent on the ductwork: Data for calculation of static pressure are given in the IHVE Guide for Pipes and Bends in a variety of materials.
