Why air duct and AHU cleaning is necessary?

For most of the buildings nowadays, the indoor areas are normally air-conditioned, and hence the indoor air is a closed ecology. The air flows through the air duct pipe to the room areas and then flows back through the return air grill to the air conditioning system before sending back to the air duct again. Therefore, in order to keep the air fresh to the tenants, many things must be done including the air duct cleaning, regular replacement of the air filters, air duct insulation maintenance, and AHU system cleaning.

Also, the air duct is mostly the overlooked area for the cleaning regime, and the fact that the internal duct cannot be seen on daily basis of the tenants, its dirtiness cannot be seen and reported easily unless the situation is quite bad inside. Therefore, as we all accept that cleaning is mandatory in the normal system of building operation for all areas, the air duct cleaning will be thus the area that needs regular monitoring for all buildings.