What problems do forced-air systems face?
Forced-air systems face a number of problems. The main problem is due to dust, pollen, bacteria, and other contaminants that enter the system and consequently, get released into the room. This has a negative impact on the air quality and contributes to a higher incidence of breathing disorders, most notably among children.
Foreign particles also affect the efficiency of the system. When these particles enter the system, many of them get stuck to the inner surfaces of the ducts and the air handler. Over time, the increased particle build-up hampers heat transfer by restricting the airflow. This means the components in the system have to work harder, leading to premature wear and tear of the motor. This in turn increases the operating costs of the system.
Why are filters used?
Filters are often attached to the entrances of the ducts where air enters the system. The aim of having a filter is to provide a screen to trap foreign particles and prevent them from entering the forced-air system. Selecting a filter will depend on the type of particles you want to keep out. All filters can trap dust particles since these are large. However, smaller contaminant particles require filters with a very fine mesh size.
Choosing an air filter also depends on its cost. As the mesh size of the filter gets smaller, the filter becomes more expensive. Another factor that impacts filter selection is its maintenance. Fine mesh filters require cleaning at regular intervals. A filter does not function properly if it is dirty.
How do filters affect airflow?
Since filters are placed at the entrances of ducts, they partially obstruct the airflow. This creates a drop in pressure in the system. The air handler needs to compensate for this pressure drop in order to function smoothly. If the handler cannot deal with the pressure drop, it causes damage to the system, increases energy consumption, and leads to air leakage from unsealed ducts.
The problems caused by pressure drop can be minimized by increasing the filter area and regularly cleaning the filters. Pressure drop can also be reduced by installing a more powerful blower in the air handler or making changes to the existing ductwork design.