The problem of condensation collecting on exterior windows is widely recognized and is present in many buildings, particularly in cold weather. The condensation can be unsightly and reduces the natural light available in a building. Also, the condensation may collect at the base of windows, and the resulting dampness problems may cause damage to the building structure and fittings, and encourage the growth of fungi and the like, which can lead to respiratory problems in many individuals.
An early proposal for a ventilator which provides one means for alleviating this problem is disclosed in U.S. Pat. No. 1,308,236 to Glass. The patent discloses a sill which permits air flow from the building exterior through a passage and over the internal surface of a window. The inner end of the passage is provided with a shutter which may be opened or closed as desired, and when open directs the incoming air toward the inner side of the window frame. A conduit is located in the passage and may be used to either heat or cool the air as it passes through the sill.
A further early window ventilator is disclosed in U.S. Pat. No. 1,553,507 to Campbell. Like Glass, Campbell discloses a passage through a sill from the building exterior, which can be opened or closed by means of a suitable shutter. However, in Campbell, a hollow metal frame is provided around the window, the sides of the frame accommodating heating pipes or radiators. Various vents are provided in the frame to allow air to flow from the room, past the heating pipes and back into the room.
In U.S. Pat. No. 2,606,074 to Ackerman, an air distribution nozzle is disclosed which is adapted for use in directing a stream of air over a show window, to keep the window free of condensation. The nozzle is intended for location at the centre of a lower edge of the window and directs air from a single source in a 180.degree. arc through use of radially extending ducts defined by a plurality of internal triangular divisions.
Whereas the earlier patents to Glass and Campbell disclose heating means located in the window frame itself, a number of later patents disclose systems in which heated air is supplied from a remote source, relayed through communicating ducts, and passed through a sill or duct assembly extending along the base of a window. U.S. Pat. No. 2,446,356 to Van Alsburg discloses a system of this type in which an air outlet with an elongate inlet leads into a hollow, sheet metal housing provided with air outlet openings on an upper surface, and an elongate slot in a lower surface. The air passing upwardly through the outlet openings in the upper surface is intended to mingle with the air closest to the window glass, and the air passing through the slot is intended for intermingling with air farther away from the window.
In German Patentschrift No. 883,529, to Jutzi, a hollow sill having apertures in an upper surface is disclosed, warm air being supplied from a blower and burner to the sill, to pass up and over an inner surface of a window.
In U.S. Pat. No. 3,439,601 to Cooper a forced air circulating system is disclosed, in which air is supplied from a fan or pump unit through horizontal ducts. The air passes from the ducts into a larger volume air cavity which reduces the pressure of the air. The air flows upwardly through the cavity to a hollow sill member and exits through slots in the sill member. The dimensions of the slots are considerably smaller than the interior of the sill member to produce an increase in velocity of the air as it passes through the slots such that the air is forced upwards to travel along the inside surface of a window.