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FAHU is the abbreviation used for FRESH AIR HANDLING UNIT. These are usually centralized units employed to induce fresh air quantities to the confines spaces. They come into picture wherever there are limitations to fresh air intake either directly or through AHUs. FAHUs are either of normal construction having100% fresh air through a blower fan or Treated FAHU that employs an additional cooling coil to induce treated air into the confined space without deteriorating the indoor conditions. It all depends upon the selection of the designer to provide an optimum HVAC solution.
For instance, there is a department having private & semi-private rooms. Here the best solution would be using FCU dedicated for each room with individual control. In addition, treated fresh air can be induced in each room; the main duct of which runs in the common corridor. Here the cavity above false ceiling is less congested than in a case where AHU with VAVs for each rooms are used. In this case, the AHU shall have damper for fresh air intake in the return line & an appropriate amount can be exhausted as compensation.
The amount of fresh air depends upon the occupancy & application of the room.
