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Sure fresh air is always required. How you manage to introduce can be changed but it is needed. Most common type is introducing FAHU on roof.
10% of Fresh air for each FCU is required.
As per the design requirement or client requirement, the fresh air needed for these FCU varies. FAHU is provided in case where the rooms are located in the middle of the building, where there is no other alternative to introduce fresh air. If the room is located such that, fresh air can be introduced with just wall opening with louvers, it is very cost effective.
The fresh air is a compulsory requirement to achieve the desired indoor air quality, you may introduce the fresh air through controlled window openings, fresh air fans only, or FAHUs depend on the fresh air quality required by your local authority and project specifications.
Air-handling units (AHU, sometimes referred to as ‘air handlers’) form part of the heating,
ventilating and air conditioning system (HVAC) that supplies, circulates and extracts air from buildings.
Air handling units can be supplied in a range of sizes, and with a variety of capabilities, but typically they comprise an insulated box that forms the housing for; filter racks or chambers, a fan (or blower), and sometimes heating elements, cooling elements, sound attenuators and dampers (that can be operated manually or automatically to regulate or prevent specific air flows). In some situations, such as in swimming pools, air handling units might include dehumidification.
Heating and / or cooling can be generated within the unit itself, or can be provided by connection to the building’s boilers or chillers.
Generally, air handling units will be connected to the ductwork within the building that supplies air to and extracts air from the interior, but they can be used to supply and extract air direct to a space, or they may be located on a roof (rooftop units or RTU).
Air handling units that consist of only a fan and a heating or cooling element, located within the space they are serving, may be referred to as fan coil units (FCU).
Air handling units can be used to re-circulate a proportion of ‘stale’ air within a building, mixing this with fresh air to reduce the amount of air conditioning that is required. They can also include heat recovery, recovering heat from return air and using it to warm the supply air.
Fans may be single speed, may have a range of set speeds, or may be variable frequency drive. Flow rates may also be controlled by inlet vanes or outlet dampers.
Air handling units generate noise (and vibration) which can be disruptive, and this can be compounded where ductwork passes between acoustically separate spaces. In this case, acoustic attenuators might be used. In addition, vibration can be generated. This vibration can be isolated by inserting flexible sections between the unit and ductwork and by isolating the unit from the building structure.
Where air handling units are located outside buildings, they can be the source of complaints by neighbours because of the noise and vibration they generate and sometimes because of odours they expel (typically where they are serving kitchens). It is important that these units are properly designed, installed and maintained to minimise this disturbance.
‘Wet’ systems, that include water evaporative cooling, can present a hazard to health. Businesses using such systems are required to carry out a risk assessment and put in place procedures to ensure there is no risk to public health.
The fresh air is a compulsory required
always the space need to ratio of fresh air substitut exhust air . we use FAHU to provid fresh air over ceiling
Fresh air for villas can be introduced into the villa by providing undercut below the doors and increasing the exhaust air fans flow ,this way infiltration will occur which can be covered by increasing the cooling load of the units .
so its not necessary in villas but it is necessary in buildings and shopping malls and hospitals.
Fresh air is required as adding fresh air to a heating or cooling system accomplishes two primary indoor air quality goals: It pressurizes a building, and increases indoor air quality by diluting polluted or stale indoor air. Adding a fresh air inlet to most systems is typically a simple and relatively inexpensive proposition
for human ocupancy always need fresh air, FAHU on top, the most comman practice for air quality.
