Do not rely on a visual inspection of the HVAC filters alone, since medium and high-efficiency filters that appear “dirty” often have not reached their optimum efficiency levels due to depth loading. In fact, filters should appear dirty. This is a good indication they are doing their job. As a filter loads up with particles, it becomes more efficient at particle removal, but increases pressure drop through the system, thus reducing air flow while consuming more energy.
This is where differential pressure switch comes handy. It recognises the right clogging levels of the HVAC filters and alerts the maintenance personnel to change the filters at the right time. The result is that the filters are used to the optimum level, do not allow bypass of unfiltered air and at the same time, do not lead to use of inefficient use of electricity in the HVAC systems.
All filters – if loaded to excess – will become deformed, unload dust, and even “blow out” of their filter rack. When filters blow out, bypass of unfiltered air can quickly lead to problems such as clogged coils and dirty air ducts. Flow capabilities of the system fan may also be affected.