NOCTURNALLY OPERABLE WATER HARVESTER AND ASSOCIATED METHOD

FIELD OF THE INVENTION The present invention relates to the harvesting of water from the atmosphere and in particular to a water condenser adapted for nocturnal operation. Embodiments of the present invention find application, though not exclusively, in the generation of potable water for consumption or other purposes and find particular application in geographic regions having limited supplies of potable water.

BACKGROUND OF THE INVENTION

Due to a number of factors such as drought, climate change and poor water management, many regions suffer from a lack of fresh potable water. In other regions fresh water may be available; however due to contamination it may require boiling or other treatment before it may be safely consumed. Such circumstances may result in a desperate reliance on variable and unpredictable levels of rainfall, which can be a source of on-going concern and economic hardship for many communities. Additionally, certain activities, such as long distance sailing, for example, and certain localities, such as remote rural communities to which town water cannot be supplied, entail an inherent limitation on the availability of fresh potable water.

It will be appreciated that a stable supply of potable water is essential to sustain life, health and the cultivation of food supplies. Given the seriousness of this issue, the provision of any new water harvesting apparatus is generally highly desirable; particularly if the apparatus is competitive with regard to manufacturing, deployment and operational costs.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome, or substantially ameliorate, one or more of the disadvantages of the prior art, or to provide a useful alternative.

In accordance with a first aspect of the invention there is provided an apparatus

for condensing water from ambient air, said apparatus including: a radiator for emission of radiation to a nocturnal atmosphere so as to cool a heat exchange fluid; a condenser in fluid communication with the radiator for receiving said heat exchange fluid so as to cool a condensation surface to, or below, a dew point such that water condenses from the ambient air onto the condensation surface; and a pump for circulation of the heat exchange fluid between the radiator and the condenser.

The apparatus preferably includes an air flow inducer for inducing an air flow across said condensation surface. In one preferred embodiment, at least some of the air flow flows across the radiator after flowing across said condensation surface.

In a preferred embodiment the radiator includes an emission surface for emission of the radiation to the nocturnal atmosphere. In this embodiment the air flow flows across the emission surface after flowing across the condensation surface. Preferably the emission surface has an external colour, such as black, selected so as to facilitate longwave radiation emission from the surface.

Preferably the radiator includes a thermally insulated reservoir for containment of at least some of said heat exchange fluid. In one preferred embodiment the reservoir includes a first side and a second opposed side and a heat exchange fluid inlet is disposed adjacent the first side and a heat exchange fluid outlet is disposed adjacent the second opposed side. Preferably the reservoir is disposed adjacent the emission surface for heat exchange contact between the emission surface and the heat exchange fluid.

Preferably at least one side skirt is disposed on said emission surface so as to at least partially direct said air flow across the emission surface. The preferred embodiment further includes an air flow chamber having an inlet for receipt of the air flow from the condenser and an outlet for exhausting the air flow adjacent the emission surface. Preferably the air flow chamber includes a plurality of vanes oriented so as to substantially evenly distribute the air flow discharged at the outlet. Preferably the heat exchange fluid has a freezing point equal to, or less than, minus 5 ⁰ C.

A preferred embodiment includes a cover for shielding the radiator from sunlight.

In accordance with a second aspect of the present invention there is provided a method of condensing water from ambient air, said method including the steps of: emitting radiation from a radiator to a nocturnal atmosphere so as to cool a heat exchange fluid; and receiving said heat exchange fluid into a condenser so as to cool a condensation surface to, or below, a dew point such that water condenses from the ambient air onto the condensation surface.

Preferably the method includes the further step of circulating the heat exchange fluid between the radiator and the condenser. A preferred embodiment of the method includes flowing air from the condenser onto the radiator. In such a preferred embodiment of the method the radiator includes an emission surface for emission of the radiation to the nocturnal atmosphere and the air from the condenser flows to the emissions surface.

Any discussion of documents, acts, materials, devices, articles or the like which has been included in this specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed in Australia or elsewhere before the priority date of this application.

The features and advantages of the present invention will become further apparent from the following detailed description of preferred embodiments, provided by way of example only, together with the accompanying drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Figure 1 is a side elevation of a preferred embodiment of the invention; Figure 2 is a plan view of the preferred embodiment;

Figure 3 is a cross sectional view of the preferred embodiment, with the cross section being taken through line A-A of Figure 2; and Figure 4 is a cross sectional view of the preferred embodiment, with the cross section being taken through line B-B of Fig 2.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The preferred apparatus 1 for condensing water from ambient air includes a radiator 2 having an emission surface 8 in the form of a thin metal plate, which emits radiation 9 to the nocturnal atmosphere. In the illustrated preferred embodiment the upper face of the emission surface 8 is oriented horizontally, which generally yields optimum irradiative performance. However, in other embodiments the orientation of the emission surface 8 varies, for example to within 30 degrees from the horizontal. Additionally, the emission surface 8 is ideally positioned such that it is unobstructed from the night sky. In at least some climates the average night sky has been found to simulate a black body absorber having a temperature of minus 7O ⁰ C. The radiation 9 typically has a wavelength longer than that of visible light, such as thermal or infrared radiation. More specifically, the radiation 9 emitted from the radiator 2 is typically longwave radiation having a wavelength of between approximately 5 and 25 microns. In some embodiments, the range of radiated wavelengths typically has a frequency distribution that is centered about a peak of approximately 7 to 9 microns. That is, heat is radiated from the emission surface 8 into the cool night sky.

The radiator 2 has a reservoir 10 for containment of a heat exchange fluid 3 such as brine, glycol or the like. The preferred embodiment utilizes brine having a freezing point equal to, or less than, minus 5 ⁰ C. Thermally insulative panels 11, 12 and 13 form the base and side walls respectively of the reservoir 10. The emission surface 8 encloses the top of the reservoir 10. A reservoir inlet 14 is disposed adjacent a first side 15 of the reservoir 10 and a reservoir outlet 16 is disposed adjacent the second opposed side 17. This allows heat exchange fluid 3 to enter the reservoir 10 adjacent the first side 15 and flow across to the opposite side 17 to exit at the reservoir outlet 16.

Whilst in the reservoir 10, the heat exchange fluid 3 fills the reservoir 10 such that the uppermost fluid 3 physically contacts the underside of the emission surface 8. This allows for heat exchange contact between the emission surface 8 and the heat exchange fluid 3. Hence, the loss of heat from the emission surface 8 due to radiation 9 also draws heat from the heat exchange fluid 3 as the fluid 3 flows across the reservoir 10. Ideally, when exiting the radiator 2, the heat exchange fluid 3 should have a

temperature in the range of minus I ⁰ C to plus 3 ⁰ C.

In alternative embodiments (not illustrated) of the invention the surface area of the underside of the emission surface 8 is increased, for example by the disposition of fins on the underside of the emission surface 8. The fins are immersed in the heat exchange fluid 3 so as to promote higher efficiency of heat exchange between the emission surface 8 and the heat exchange fluid 3. Such higher efficiency is suited to applications requiring a higher flow rate of heat exchange fluid through the radiator 2 as compared to the flow rates suited to embodiments omitting the fins.

The apparatus 1 also includes a condenser 4 in fluid communication with the radiator 2. The cooled heat exchange fluid 3 flows from the radiator 2 to the condenser 4 and is used to cool a condensation surface, in the form of closely spaced metal cooling fins 23. The fins 23 are in heat exchange contact with tubes 22 carrying the heat exchange fluid 3, thereby cooling the fins 23. Each end of the tubes 22 defines a passageway extending from inlet header tube 20 to outlet header tube 21. The fins 23 are cooled to, or below, the dew point of the ambient air, resulting in condensation of water from the ambient air onto the fins 23 of the condenser 4. The condensed water then drips from the fins 23 onto collection funnel 6, which feeds into a storage reservoir (not illustrated) for the harvested water.

A pump 7 circulates the heat exchange fluid 3 between the radiator 2 and the condenser 4. Thermally insulated pump discharge pipe 18 conveys the heat exchange fluid from the pump 7 to the reservoir 10 of the radiator 2. The pipe 18 connects to reservoir inlet 14, which has a plurality of closely spaced holes to evenly disperse the heat exchange fluid 3 into the reservoir 10. The fluid 3 flows across the reservoir 10, is cooled, and then exits from the reservoir 10 via reservoir outlet 16, which has similar closely spaced holes 19 as for reservoir inlet 14. Insulated return line 24 connects reservoir outlet 16 to the top of inlet header tube 20. The fluid 3 flows from header tube 20 through the tubes 22 and in the process cools the fins 23 to cause atmospheric moisture to condense on the fins 23. The fluid 3 flows through the tubes 22 and into outlet header tube 21. Thermally insulated pipe 25 then conveys the fluid 3 from the bottom of the outlet header tube 21 to return to the pump 7.

Ventilated header tank 26 is connected to the top of the outlet header tube 21 via pipe 27. The header tank 26 holds heat exchange fluid 3 so as to maintain a constant

supply of fluid 3 to the pump 7 and to allow for expansion and contraction of the fluid 3 due to temperature variation.

A pump speed control circuit (not illustrated) is responsive to input from a fluid temperature sensor (not illustrated) so as to vary the speed of the pump 7 and therefore the rate of fluid circulation. The fluid temperature sensor is disposed at the reservoir outlet 16 so as to continuously monitor the temperature of the fluid 3 as it exits the reservoir 10. If the temperature of the fluid 3 is higher than the target range of minus I ⁰ C to plus 3 ⁰ C, then the pump speed is reduced so as to slow down fluid 3 circulation, thereby allowing the fluid 3 to remain within the radiator 2 for a longer period for increased cooling. Similarly, if the temperature of the fluid 3 is lower than the target range of minus I ⁰ C to plus 3 ⁰ C, then the pump speed is increased to provide a shorter cooling period.

The apparatus 1 includes an air flow inducer, in the form of a variable speed electric fan 28, for inducing an air flow across the fins 23. In one embodiment the air flow inducer is a barrel fan; whereas in another embodiment it is a centrifugal fan. It will be appreciated, however, that other types of fans may be utilized in yet further embodiments. The fan 28 is disposed intermediate the condenser 4 and the radiator 2 so as to suck air through the condenser 4 and blow air onto the radiator 2.

In some embodiments the speed of the fan 28, and therefore the rate of the air flow across the fins 23, is adjusted to optimise the condensation of water onto the cooling fins 23. The apparatus 1 is typically operated such that the fins 23 are sufficiently cooled without freezing the condensed water. It will be appreciated that for any given prevailing atmospheric conditions, there is a specific humidity value measured in grams of water vapour per kilogram of the air and a corresponding dry bulb temperature. For example, a specific humidity of between 4.5 and 6 grams of moisture per kilogram of air correlates to a dry bulb temperature at saturation of between I ⁰ C and 6.5 ⁰ C. In use, the speed of the fan 28, and hence the rate of the air flow, is adjustable such that the specific humidity of the ambient air discharged from the fins 23 is reduced to a specific humidity correlating with a specific selected dry bulb temperature or temperature range. In general terms, comparatively cool, dehumidified air is discharged from the fins 23 and is subsequently routed to flow across the emission surface 8 via an air flow chamber 29 having an air inlet 30 for receipt of the air flow from the condenser 4 and an

air outlet 31 for discharging the air flow adjacent the emission surface 8. The air flow chamber 29 also has five vanes 32 oriented so as to substantially evenly distribute the air flow discharged at the air outlet 31.

The presence of cool, dehumidified air flowing over the face of the emission surface 8 of the radiator 2 prevents or reduces contact between warm moist ambient air and the emission surface 8 ; thus preventing or reducing the formation of dew on the emission surface 8. Otherwise, the formation of dew on the emission surface 8 has the potential to decrease the efficiency of radiation 9 due to latent heat of condensation causing the radiator temperature to rise. An additional advantage associated with the presence of a thin film of cool air flowing over the face of the emission surface 8 is the reduction of sensible heat flow from warm ambient air to the face of the radiator 2.

Two side skirts 33 and 34 extend along opposite sides of the emission surface 8 so as to at least partially direct the air flow across the full length of the emission surface 8. That is, the side skirts 33 and 34 at least partially constrain the air flow from flowing off the sides of the emission surface 8. This assists to ensure that the beneficial effects of the flow of cool dehumidified air apply along the full length of the emission surface 8.

To avoid or minimize heating of the radiator during the day due to incident sunlight, an embodiment of the invention includes a cover (not illustrated) which automatically covers the emission surface 8 during the day and retracts during the night to allow the apparatus 1 to operate. Yet other embodiments utilize manually removable covers.

In use, the method of operating the apparatus 1 to condense water from ambient air entails circulating the heat exchange fluid 3 between the radiator 2 and the condenser 4, whilst simultaneously: emitting radiation from the emission surface 8 of the radiator 2 to the nocturnal atmosphere so as to cool the heat exchange fluid 3; receiving the heat exchange fluid 3 into the condenser 4 so as to cool the fins 23 to, or below, the dew point of the ambient air such that water condenses from the ambient air onto fins 23; and flowing cool dehymidified air discharged from the condenser 4 onto the emission surface 8 of the radiator 2.

For residential and/or commercial applications, the radiator 2 may take the form of one or more panels (not illustrated) disposed on a roof of a dwelling and the condenser 4 may be disposed remotely of the panels; for example within the roof cavity or elsewhere. Thermally insulated piping may be used to circulate the heat transfer fluid 3 between the condenser 4 and the emission surfaces 8 of the panels. Similarly, thermally insulated piping may be used to convey discharged air from the condenser 4 to the emission surfaces 8.

Advantageously, the main operating costs that are typically associated with the use of the preferred embodiment are the costs to run the pump 7. The use of a radiator 2 dispenses with the need to supply energy to a refrigeration unit. Additionally, with the provision of a battery, or other suitable electrical or mechanical energy source, to power the pump 7, preferred embodiments of the invention can typically be easily deployed in remote areas at which utilities such as electricity and town water are unavailable. Similarly, preferred embodiments of the invention can be utilized in activities such as long distance sailing, and the like, to provide a portable water source.

While a number of preferred embodiments have been described, it will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.