The replacement of filters for Heating, Ventilating, and Air Conditioning
(HVAC) is often time-consuming and labor-intensive. Organizations having
responsibility for many apartment or dormitory units can spend a
significant fraction of their man-hours replacing such filters. A novel
approach to reducing the labor for this task is to attach one end of
sheet-type filtering material to a dispensing roll, and the other end to a
gathering roll; both rolls being affixed to a frame. The assembly is
installed into an air duct and the filtering material allowed to blouse,
somewhat. The flow of air is intermittent in typical HVAC systems, so when
the air begins to flow, the filtering material is forced, due to its
resistance to flow, in the direction of the flow. This energy--a force
applied through a distance--is utilized by a lever arm bracket to advance
the gathering roll. In this fashion, new material leaves the dispensing
roll and is exposed to the air, while the dirty filter sheet accumulates
on the gathering roll. The process is self-regulating because dirty filter
material will present a greater resistance to flow and will, therefore,
travel through a greater distance, advancing the gathering roll more.
