Perforated transparent glazing for heat recovery and solar air heating

Abstract

A heat collector comprises a transparent glazing exposed to the ambient. The transparent glazing is spaced from a back surface to define a plenum therewith. A plurality of perforations is defined through the transparent glazing for allowing outside air to flow through the transparent glazing into the plenum and substantially maintain the transparent glazing at the ambient temperature, thereby providing for higher thermal efficiency.

1 . A method of improving the efficiency of a glazed solar collector comprising a glazed cover, a solar absorber disposed behind the glazed cover, and a plenum between the glazed cover and the solar absorber, the glazed cover forming an outer surface of the collector; the method comprising: providing multiple perforations through the glazed cover; and reducing heat looses to the environment through the glazed cover by minimizing a temperature delta across the glazed cover, including cooling the glazed cover by drawing outside air through the multiple perforations at a flow rate between about 2 to about 6 cfm per square foot of glazed surface. 
     
     
         2 . The method of  claim 1 , further comprising cooling the solar absorber by providing a secondary flow of outside air over a front face of the solar absorber, including admitting outside air via at least one outdoor air intake provided at least one of a bottom and a side edge of the collector and, the air drawn through the perforations in the glazed cover and the air admitted through the outdoor air intake mixing together inside the plenum. 
     
     
         3 . The method of  claim 2 , wherein the at least one outdoor air intake comprises a set of lateral air intakes provided in opposed side edges of the collector, and a set of bottom air intakes provided in the bottom edge of the collector, and wherein providing a secondary flow of outside air comprises admitting outside air through the bottom and the side edges of the collector. 
     
     
         4 . The method of  claim 1 , further comprising increasing a linear velocity of the outside air flowing over the solar absorber by providing a secondary flow of outside air in the plane of the solar absorber, the secondary flow entraining the flow of outside air drawn through the perforations of the glazed cover. 
     
     
         5 . The method of  claim 1 , comprising balancing the flow of outside air over the solar absorber by providing additional outdoor air intakes in areas of the solar absorber prone to overheating. 
     
     
         6 . The method of  claim 1 , comprising establishing a temperature distribution profile over the surface of the solar absorber, identifying surface areas prone to overheating, and increasing air flow over said surface areas. 
     
     
         7 . The method of  claim 1 , comprising balancing the flow of outside air over the solar absorber by gradually increasing a width of the plenum towards an outlet thereof. 
     
     
         8 . The method of  claim 1 , comprising ensuring a minimum linear velocity of air over an entire surface area of the solar absorber by varying a distance between the glazed cover and the solar absorber along a length of the plenum, the distance being minimal at locations remote from an outlet of the plenum. 
     
     
         9 . The method of  claim 1 , comprising increasing turbulences over an outwardly facing surface of the glazed cover by providing protuberances around an inlet end of the perforations, the protuberances projecting outwardly from the outwardly facing surface of the glazed cover. 
     
     
         10 . A glazed solar air collector comprising a perforated glazed cover transparent to solar radiation, the perforated glazed cover having opposed front and back faces, the front face of the perforated glazed cover forming an external surface of the collector and being directly exposed to the ambient, a solar radiation absorbing panel disposed behind the perforated glazed cover for absorbing solar radiation passing through the perforated glazed cover; a plenum defined between the back face of the perforated glazed cover and an opposed front face of the solar radiation absorbing panel, the perforated glazed cover having a plurality of perforations distributed over a surface area thereof and collectively forming a main outdoor air intake for admitting fresh outdoor air into the plenum, the distribution of perforations being selected to maintain a temperature delta across the perforated glazed cover close to zero, a secondary outdoor air intake provided at least one of a bottom and a side of the collector and disposed to direct an additional flow of outdoor air over predetermined surface areas of the solar radiation absorbing panel prone to overheating, and air moving means to draw heated air from said plenum via an outlet thereof. 
     
     
         11 . The glazed solar air collector defined in  claim 10 , wherein the perforated glazed cover comprises a plurality of perforated glazed panels assembled in a coplanar relationship. 
     
     
         12 . The glazed solar air collector defined in  claim 11 , wherein each of said perforated glazed panels has top and bottom edges extending between opposed side edges, and wherein a tongue is provided along said top edge for engagement with a corresponding groove extending along the bottom edge of an adjacent panel. 
     
     
         13 . The glazed solar air collector defined in  claim 11 , wherein thermal expansion clips project integrally outwardly from a perimeter of the panels to accommodate thermal expansion in a plane of the perforated glazed cover. 
     
     
         14 . The glazed solar air collector defined in  claim 13 , wherein each of the thermal expansion clips comprises a resilient finger adapted to be deflected in a seat formed in the panel and to spring back to its original outwardly projecting position. 
     
     
         15 . The glazed solar air collector defined in  claim 13 , wherein the thermal expansion clips comprise first and second vertical expansion clips projecting from a top edge of the panel and first and second pairs of horizontal expansion clips projecting from opposed side edges of the panel. 
     
     
         16 . The glazed solar air collector defined in  claim 11 , wherein protuberances are formed around the perforations in the panels, the protuberances projecting outwardly from an outer surface of the panels. 
     
     
         17 . The glazed solar air collector defined in  claim 11 , wherein each panel is provided in the form of an injection molded polycarbonate panel with built-in perforations, expansion clips and top and bottom tongue and groove adjoining edges. 
     
     
         18 . The glazed solar air collector defined in  claim 10 , wherein the plenum is at least partly delimited by a building wall, the plenum being sealed from inside air contained within the building, the plenum being solely fed with outdoor air. 
     
     
         19 . The glazed solar air collector defined in  claim 10 , wherein the perforations and the air moving means provide for a flow rate between about 2 to about 6 cfm per square foot of the collector.