A METHOD FOR PRE~EATING VENTILATION AIR IN A BUILDING
This invention relates generally to a method of controlling the entry of ventilation air to a building, and preheating the air with a combination of solar heat and the natural building heat loss.
BACKGROUND OF THIS JNVENTION
Commercial and industrial buildings require ventilation, and it is common for the natural leakage around doors, wall-ceiling joints, etc. found in standard building construction to allow sufficient ventilation air to enter the building. A pressure drop from the exterior to the interior of the building can arise from many factors, such as high winds, exhaust fans and combustion air for fuel-burning furnaces. This tends to draw outside air into the building through any crack or opening.
The problem with the conventional approach is that the amount of ventilation air is not controlled, and additional heat must be provided to heat the outside air 20 to room temperature during the fall, winter and spring months.
This problem has typically been solved by installing air make-up fans with gas or electric heaters to heat the incoming air. When solar panels are used to 25 heat a building, air is re-circulated from the building through the panels and then back again to the building.
The efficiency of a solar collector is maximized when the temperature of the air entering the collector is the same as the ambient temperature. Under normal winter 30 conditions, the ambient temperature is lower than the room temperature, and therefore a recirculating ~olar collector operates at a much reduced efficienc~ level in wintertime.
GENER~L DESCRIPTION OF THIS INVENTION
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In accordance with this invention, instead of using consumable energy sources like gas or electricity to heat incoming air, and instead of simply recirculating interior air from the building through a solar collector and back to the building, fresh make-up air for ,,~,,~, ~ v 2 ventilation purposes is in-troduced into the interior of -the building after first passing through a solar collector located on a south-facing wall of the building. The solar collector can be either a commercially built solar collector, or a site-built collector consisting of glazing over a darkened wall. The air thus travels through the air space defined in ~he collector and enters the building through a duct system within the interior.
More specifically, this invention provides a method of preheating ventilation air for a building, com-prising the steps:
a) providing a vertical, air-heating solar collector surface on a south facing wall of the building, in such a way that heat being lost from the interior through the south-facing wall is available at said surface and can contribu-te heat to air passing through the solar collector panel means, b) providing glazing spaced outward from said surface, c) passing outside air through the solar collector panel means in a generally vertical direction from a lower inlet, the air passing between said surface and said glazing, and heating the air with a combination of solar heat and the heat being lost from the interior through the south-facing wall, and d) withdrawing the heated air from the solar collector panel means at a location near the top thereof and using air-moving means to expel the heated air into the interior of the building.
~dditionally, this invention provides apparatus for preheating ventilation air for a buildin~, comprising:
air-heat.ing solar collector means provided on a south-facing wall of the building, the solar collector means including a blackened surface in heat-transfer contact with said wall, and glazing means spaced from said blackened surface, an air inlet along the lower edge of said solar collector means, and an air exit adjacent the top thereof, air-moving means and duct means arranged to allow heated air to be withdrawn from the collector means and expelled into the 2a interior of the building, the air exit communicating with said air-movlng means.
GENERAL DESCRIPTION OF THE DRAWING
In the drawings:
Figure 1 is a perspective view of a make-up or ventilation air system for a building, constructed in accordance with this invention' and Figure 2 is a graph of a typical collector efficiency - curve.
DETAILED DESCRIPTION OF THE DRAWING
Attention is now directed to Figure 1, which shows a partly broken-away perspective view of a system for performing the present invention. A building wall is shown in part at 10 in the figure, this being typically a block construction, or a block-and-brick composite structure. As with all building walls, even those well-insulated, a steady heat loss is experienced through the wall when the outside temperature is below the inside 10 temperature.
The numeral 12 designa-tes a portion of the wall 10 which has been blackened by the application of paint or other suitable solar-collective coating, rendering the portion 12 of the wall 10 highly absorptive in the visible and infra-red region of the spectrum. A
plurality of glazing panels 14, which may be of glass, plastic or other suitable transparent material, is located in spaced relation outwardly from the blackened portion 12 to define a plurality of air passageways 16 between each g]azing panel 14 and the wall 10, the passageways 16 being separated by partitions 18 (one being visible in the Figure) which act to support the glazing panels 14 along their ver-tical edges. The specific support structure between the partitions 18 and the glazing panels 14 does not form a part o~ this invention, and need not be described in detail. The important point is that the passageways 16 have an access at the bottom to allow entry of outside air. If desired, a screen 19 may be provided at the bottom of passageways 16, to prevent entry by birds, insects and the like.
At the top, the passageways 16 defined between the panels 14 and the wall 10 communicate with the interior of a hood unit 20 which is triangular in section and includes a sloping upper wall 22 and a substantially horizontal bottom wall 23. The bottom wall 23 extends from the outer edge 25 of the upper wall 22 to the upper edges o~ the panels 14. Inwardly, the hood unit is secured in air-tight manner against the wall 10 above the blackened portion 12 thereof, and has flanges 27 for this i8~S
purpose. Alternatively, the hood unit 20 could include a vertical inner wall to be placed directly against the wall 10 of the building. End walls 28, of which one is seen in the figure, complete the hood unit 20 and allow it to define a substantially air-tight chamber into which air from the passageways 16 empties.
Communicating with the internal chamber in the hood unit 20 is a fan housing 30 which contains a conventional fan or air-impeller (not visible) and includes motorized dampers 32 which allow air from the interior of the building to be mixed with heated air coming from the hood unit 20.
Communicating with the housing 30 is a fabric air duct 34 which is preferably flame retardant and made Of polyfabric, the duct 34 being suspended by a plurality of duct hangers 36 from a suitably strung support wire or rod 38. The air duct 34 has a plurality of openings 40 through which the heated outside air can pass from the duct 34 into the interior of the building. By appropriately sizing the openings 40, the air can enter the interior of the building as a high-velocity air jet, thus promoting good mixing within the interior of the building, and minimizing stratification.
It will be understood that, by placing blackening material on the portion 12 of the wall lO, i.e. directly in contact with the wall 10, the outside air moving upwardly along the passageways 16 will derive heat not only from the sun's energy, but also from the heat being lost from the interior of the building through the wall 10. This, however, would be the case with any design of solar collector, so long as the wall lO were in heat communication with the collector portion of the solar collector.
It is preferred that the duct 34 be located at ceiling le~rel within the building, for the sake of convenience, however other levels could also be utilized.
The fan within the housing 30 would typically be sized to meet the ventilation requirements and eliminate the negative pressure problem if such exists. ~ positive ~ 3 pressure can be achieved with outside air entering the building through the fan in the housing 30, the air being heated by the solar heat, the building heat loss, and stratified heat found near the ceiling. Air can then leave the building through the cracks and openings where previously air had entered.
It will be noted that the hood unit 20 overhangs the panels 14, and thus a shadow is cast upon the panels 1~ during late spring and early summer, when the sun at mid-day is quite high in the sky. This automatically avoids solar heating of the air during the hotter portion of the year. In any event, with the sun being located high in the sky, and the panels 14 vertical, only a small portion of the sun's radiation would enter the solar collector, even if it could fall upon the panels 14.
Referring to Figure 2, it can be seen that a typical solar collector operates near or at maximum efficiency when the fluid (air) inlet temperature equals the ambient temperature. In a typical solar heating installation, internal air is recirculated, and assuming that the space temperature is 20C while the outside temperature is -10C, there is a difference of 30C. The maximum solar insolation in round numbers is approximately 1000 watts per square meter. The situation just deEined would give .03 on the X scale which, in the case of this collector curve , would yeild an efficiency of 32~. In the present invention, on the contrary, in which the inlet temperature and the ambient temperature are the same, the X scale position is 0, resulting in the maximum efficiency oE 55~.
While one embodiment of this invention has been illustratecl in the accompanying drawing and described hereinabove, those skilled in the art will appreciate that changes and modifications may be made therein without departing from the essence of the invention as set forth in the appended claims.