Patent Application
20100186308
The present application generally relates to a device and a method suited for sterilizing and/or heating air by means of free energy, such as solar energy. For instance, the device can be used for heating and sterilizing the air of a building.
Ultraviolet rays (UV rays) are known to have a purifying effect on water as well as on air.
In closed systems, the re-circulated building air accumulates pathogeneous organisms that may generate diseases. Among the various types of UV rays, the UV-C rays are known to inhibit the growth and the reproducing of germs, viruses, allergies and bacteria's that circulate in warm or cold air ducts systems.
Over the years various UV rays generators have been developed in an attempt to process and purify air in a given environment. While it is known that solar radiation contains UV rays that have a sterilizing effect, there is, according to applicant's knowledge, no device currently on the market which makes active use of the benefits or solar energy to sterilize the air. There is a need to take advantage of solar radiation in the duct systems to further increase the effectiveness of existing UV ray systems.
Design of traditional glazed solar air heaters generally comprises a glass or transparent cover placed in front of a dark solar absorber. The front transparent cover is provided for minimizing heat losses from the top of the collector. Fresh outside air is traditionally admitted at one end of the collector between the solar absorber and the insulated bottom of the collector. The air passes through the collector along tins and absorbs heat from under the solar absorber as it travels therealong. Warm or hot air is discharged at the opposite extremity of the collector. As air progresses inside the collector, its temperature rises above ambient. The higher the temperature in the collector is, the higher the heat loss towards the ambient becomes. Heat loss happens through the bottom, the edges and the top (where the glazing is) of the collector. Typically the edges and the bottom are insulated, so that heat loss mostly occurs through the top, that is by convection between the absorber and the glazing and then by conduction through the glazing. When the glazing becomes very warm, the collectors become less efficient.
Various unglazed solar air heaters have also been designed over the years. Current transpired collector designs are such that the solar absorbing surface is located outside facing the sun, unprotected by means of a glazing. The perforated absorber is coupled to a fan which creates a negative pressure between the building (or the bottom of the collector) and the absorber. When the fan is in operation, the air is drawn through the absorber. The air passing through the perforations in the outer opaque absorber breaks the naturally occurring warm film of air on the outside facing side (the boundary layer) of the absorber. This method provides acceptable performances when the flow of air per unit area exceeds 6 cfm per square foot of collector. However, for unitary flow rates below 5 cfm per square foot, the amount of cool air leaching the perforated plate is insufficient to prevent the collector plate from heating up, thereby negatively affecting the overall thermal efficiency of the system. Efficiencies at the rate of 2 cfm per square foot drop to 30% or even less.
The air circulating under or behind the absorbers never “sees” sunlight and therefore the sterilizing properties of the sun are not being put to advantage. Furthermore, traditional glass used as top glazing is not transparent to the sun's UV rays, therefore the heated air never gets the sterilizing benefits of the sun's UV rays.
In view of the foregoing, there is a need for a relatively low maintenance and simple solar energy based device that can be used to sterilize and/or heat air.
It is therefore an aim to address the above mentioned issues.
According to one general aspect of the present application, there is provided a solar heat collector which also provides for air sterilization by allowing the incoming UV rays to irradiate the air passing behind or under a UV transmissive surface.
In accordance with another general aspect of the present application, there is provided a heat collector and air sterilization device comprising a UV transmissive glazing exposed to the ambient, the UV transmissive glazing allowing at least a portion of the UV rays of the sunlight to pass therethrough, the UV transmissive glazing being spaced from a back surface to define a plenum therewith, a plurality of perforations defined through the UV transmissive glazing for allowing outside air to flow through the transparent glazing into the plenum, the perforations being distributed over a surface area of the UV transmissive glazing, the plenum having at least one outlet through which air contained in the plenum can be removed after having been warmed up and at least partly sterilized by the UV rays of the sunlight. The back surface can be provided in the form of a solar radiation absorbing panel or the like.
In accordance with another general aspect, there is provided a device for heating and sterilizing air comprising a perforated UV transmissive surface allowing at least part of the solar radiations, including UV rays, to pass therethrough, a solar radiation absorption surface located behind said perforated UV transmissive surface for absorbing the solar radiations, and a plenum defined between said perforated UV transmissive surface and said radiation absorption surface, the air flowing in the plenum absorbing heat from the radiation absorption surface while being exposed to UV rays, thereby providing for the combined heating and sterilization of the air in the plenum by solar energy. The perforations in the UV transmissive surface provides for a reduced temperature delta through the UV transmissive surface, thereby ensuring a better heat transfer efficiency.
In accordance with still another general aspect, there is provided an outdoor transparent and perforated surface exposed to the ambient. The perforated transparent surface is permeable to UV rays and spaced from a back surface so as to define an air gap or plenum therebetween. Fresh outside air is drawn into the plenum through the perforated transparent surface. The back surface can, for instance, be provided in the form of a bottom of a solar collector, a building wall or roof, an outer surface of a greenhouse, a photovoltaic panel, a ground surface or any non-porous surface. Between the perforated transparent surface and the back surface, the gap of air is maintained under negative pressure due to mechanical or natural means. An outlet is provided for allowing air flowing through the plenum to be drawn into a duct or a channel, for use as make-up, ventilation, process or combustion air to a device which consumes or needs thermal energy. As the air travels along the plenum it is being purified under the action of the UV rays passing through the perforated transparent surface.
The air in the plenum can be heated either by incident solar radiation on the surface of the back panel, which acts as a solar absorber, and/or by heat escaping from the back surface. The device can therefore act as a solar air heater and/or as a heat recovery unit and/or as a sterilization unit. When used as a solar air heater, the back surface can be of a dark color, so that incident solar radiation passing through the perforated transparent surface is absorbed by the back surface in the form of heat and not reflected back to outer space. However, if the back surface, for any aesthetic reason or other, must be of light color, the solar thermal efficiency remains higher than other conventional unglazed collector design. This is particularly true when the device is used as a heat recovery device, since the back surface can be of any color with substantially no influence on efficiency (it can even be transparent like in the case of a greenhouse), but the lower the thermal resistance (insulation) of the back surface, the greater the heat recovery rate. The device can be simultaneously used for all three functions of solar heating, heat recovery and UV sterilization.
It is understood that in warmer climates, the back panel or surface may event be of white color, of reflective surface or even transparent if no solar heat gain is necessary.
If necessary, the preheated air leaving the device can have an auxiliary heating device located downstream (e.g. a gas-fired system) to bring its temperature to a given set point.
If necessary, the at least partially sterilized air leaving the device can be further processed by an auxiliary air sterilizing device (e.g. a UV-C generator system or chemical based purifying system) located downstream of the outlet of the outdoor plenum to further purify the air to a given set point.
In accordance with a still further general aspect, there is provided an outdoor system for sterilizing the air of a building, the outdoor system comprising:
The system for sterilizing the air of a building may further comprise: at least one auxiliary sterilization device that can be disposed downstream of the air sterilization device in order to further sterilize the air before the same be returned back into the building. The auxiliary sterilization device could for instance take the form of a UV ray generator, a chemical sterilization device or a photocatalyst device.
A controller could be provided for selectively actuating the auxiliary sterilizing device. For instance, the controller could be programmed or otherwise configured to actuate the auxiliary sterilization device for producing additional UV rays during the night or by covered weather. Suitable sensors could be connected t o the controller to provide feedback on the quality of the air and the intensity of the sun rays.
According to an embodiment, the system for sterilizing the air of a building can comprise at least two auxiliary sterilization devices mounted in parallel or in series.
In accordance with a still general aspect, the system can also be used to pre-heat the air before returning the same into the building. This can be accomplished by providing a solar radiation panel behind the UV transmissive cover of the plenum. Also, if an income of fresh outside air is desired, the UV transmissive cover can be perforated to allow fresh outside air to flow into the plenum and mix with the recirculation air of the building.
The air sterilization device of the system can take the form of an outdoor conduit connected to the ventilation system of the building. In this example, at least a portion of the conduit would be transparent to UV rays to allow the air flowing through the conduit to be exposed to the UV rays of the sun while flowing through the conduit.
The roof mounted conduit may comprise a plurality of duct sections adapted to be connected end to end in fluid flow communication to form a fluid passage for allowing air to flow therethrough. At least some of the plurality of duct sections could be provided with a ballast receiving portion, and a ballast material could be placed on said ballast receiving portion for anchoring the duct sections to a flat roof under the weight of the ballast material. The duct sections and the ballast material would have a combined weight selected to render the duct sections substantially immovable to side winds on the flat roof of the building.
According to a still further general aspect of the application, there is provided a method for heating and sterilizing air, the method comprises directing air to be processed into a plenum having a UV transparent surface, exposing air through said UV transparent surface to UV rays of the sun, absorbing at least a portion of the sun rays passing through said UV transparent surface onto a solar radiation absorbing surface located behind said UV transparent surface, and heating the air in the plenum with the solar radiation absorbed by said solar radiation absorbing surface.
According to a still further general aspect, there is provided a process for building a heat and sterilization device according to anyone of claims 1 to 16 comprising the step of assembling the different constituting elements of the device. The assembly can be done through the used of any suitable methods including welding, fitting, bolting and/or screwing.
According to a still further general aspect, the system for sterilizing the air of a building can be used for disinfecting buildings such as hospital, school, grocery stores, office towers, medical practices, waiting rooms etc. This can contribute to substantially reduce the amount of disinfecting compounds such as biocides, fungicides, bactericides and antibiotics injected in the air circulating in such buildings.
According to a still further general aspect, there is provided a process for heating and at least partially disinfecting a contaminated air source, which process comprises circulating the contaminated air at least one time through at least one sterilization device as generally defined hereinabove.
The term “glazing” is herein intended to broadly refer to any transparent surface allowing the light to pass therethrough.
The terms “UV transparent” and “UV transmissive” are herein intended to refer to a surface which allows sunlight to pass through without substantially blocking the UV rays.
The perforated glazing 12 and the solar radiation absorber plate 14 define a plenum 16 therebetween. A fan or other suitable air moving means 17 can operatively connected to an outlet 18 provided at one end of the back panel to draw fresh outside air through the perforated glazing 12 into the plenum 16 before being directed to a ventilation system, such as a building ventilation system. The solar radiations passing through the perforated transparent glazing 12 are absorbed by the absorber plate 14. The air in the plenum 16 picks up the heat absorbed by the absorber plate 14 before being drawn out of the plenum 16. As air travels longitudinally along the plenum 16 between the absorber plate 14 and the perforated glazing 12, additional fresh outside air is drawn through the perforated glazing 12. In this way, the glazing 12 remains at a temperature substantially equal to the ambient temperature. Accordingly, the temperature differential between the incoming air and the ambient is equal to zero or close to zero, so that thermal efficiency remains at the highest possible value. Heat losses through the glazing cover are thus kept to a minimum.
As shown in
As shown in
As mentioned hereinbefore, the sun facing glazing 12 of the various embodiments of the heat collector illustrated in
The UV transmissive glazing is preferably made of a material selected from the group consisting of: polycarbonates and fused silicae. The UV transmissive glazing could, for instance, be made of fused silicate offered by the company ESco Products.
Particularly recommended for use as the sun facing glazing 12 of the above described embodiments of the solar air heater are S1-UV Ultraviolet Grade Fused Silica, Grades A and B of the ESco Products company. As shown in
Such pure fused silica materials offer good transmittance down into the deep UV. They provide great homogeneity making them ideal for applications demanding superior wavefront performance. As fused silica materials, they show no fluorescence or discoloration when exposed to radiation shorter than 290 nm. S1-UVA has slightly better homogeneity and fewer and smaller bubbles than S1-UVB.
Other materials that are permeable to UV rays of the C-type, and having a UV transmittance rate that is higher than 80%, and preferably higher than 85%, more preferably higher than 90% are contemplated as well.
The residence time of the air in the plenum behind the UV transmissive glazing 12 can be lower or equal to about 5 minutes and preferably no longer than about 1 minute. However, the air must be exposed to the sun UV rays for a sufficient period of time in order for the sterilization process to occur. The residence or UV exposed time will vary depending on the intensity of the sun rays and the mass flow of air in the plenum 16′.
According to one example, the auxiliary UV generator 33 is:
It is understood that the auxiliary UV generator could take the form of any other suitable air purifying system. For instance, a chemical sterilization device or a photocatalyst device could be used in place of the UV ray generator 33. Also more than one auxiliary air sterilizing devices could be disposed between the UV exposed plenum 16′ and the conduit 35.
The integration of such a passive UV air sterilization device in the ventilation system of a building:
Furthermore, as can be appreciated from the above embodiments, the device can be used in several applications including:
Also various apparatus can be provided downstream of the device for further processing the air. For instance, the device could be coupled to the following units:
The above described UV transmissive perforated glazing offers numerous benefits. The incoming air is admitted throughout the glazing surface, either on a large proportion of its surface or over the entire surface. Accordingly, the glazing surface remains cold so that collector top heat loss is substantially prevented. Furthermore, the air temperature inside the collector remains relatively cold, lowering heat losses through the bottom and the edges, or, if in a specific design with high residence time of the solar-heated air within the collector, the edges and bottom may be appropriately insulated. The proposed perforated transparent glazing design provides solar efficiencies at least as good as that provided by the perforated plate design at high flow rates. For lower flow rates, however, the solar efficiency remains high and by far exceeds that of opaque perforated collectors, and even exceeds that of glazed collectors, for less than half the cost. This high efficiency at low flow rates is a major advantage for air sterilizing applications where relatively long residence times are or may be needed. High efficiencies at low flow rates can be readily appreciated from
It will be apparent to one skilled in the art that modifications may be made to the illustrated embodiments without departing from the spirit and scope of the invention as hereinafter defined in the Claims.
| Number | Date | Country | |
|---|---|---|---|
| 61146813 | Jan 2009 | US |
