GB2209683A - Atmospheric water condenser - Google Patents

Abstract

A system for inducing atmospheric moisture condensation consisting of a surface 2 cooled by radiative cooling to space and shielded from conduction, convection and radiation of heat from its surroundings, the surface 2 being so arranged as to be accessible to by ambient air so as to condense part of its moisture content as water. The system may use a condensing surface made of optically selective materials, for example, reflecting radiation outside the wavelength range of 8-13 microns but absorbing and emitting within these limits as a black body. Different materials and forms may be used to suit specific site conditions and optimise ambient air movement through the system. For example, air flow enhancement by thermal chimney effect or cooling increased by absorption refrigeration. <IMAGE>

Description

Title; Atmospheric water condenser.

The present invention has in mind a means of extracting water from the atmosphere, in regions of the world where there is a shortage of water; for example deserts, savana, or regions of intermitent rainfall. In such regions there is often quantities of water vapour in the atmosphere, but the conditions for its precipitation rarely occur. Condensation, when it occurs is quickly evaporated.

The invention aims to provide a means of providing the conditions necessary for condensation in quantities useful for growing plants or human consumption.

It is well known that the earth loses heat gained during the day from the sun by radiant cooling to space through day and night. The atmosphere absorbs radiation and acts as a radiator to earth and space in the Far Infra Red (FIR) wavelengths; between approximately 4 and 35 microns, with an 'atmospheric window' between 8-13 microns in which the atmosphere is partially transparent to FIR radiation. The degree of absorption by the atmosphere is greatly affected by the water and gas content. The ground temperature falls on clear nights because the absorption coefficient of oxygen and nitrogen is very low.

On cloudy nights however, the tendency is for the rate of heat loss to decrease very rapidly as the clouds blanket the earth and the radiation exchange takes place mainly between the clouds and the earth rather than earth and space. Long molecules like water vapour and carbon dioxide have a higher absorption coefficient and still have a minor effect even when transparent.

Condensation occurs whenever air meets a surface which is below its dew point.

This happens naturally as dew when the ground temperature falls below air temperature and reaches the dew point,usually during the early morning after a clear night.

The cooling power of a surface depends on its optical characteristics. White paint, for example, keeps surfaces cool because it is a good reflector in the solar wavelengths and a good emitter in the FIR. Materials may be chosen or made for their selective optical characteristics.It may be an advantage, for example to use selective surfaces which reflect all radiation outside the wavelength range 8-13 microns but absorb and emit within these limits as a black body. With shading, such surfaces can maintain cooling throughout the whole day and are claimed to be more effective than a black body radiator.

It is proposed to use such enhanced cooling effects for condensing atmospheric water by lowering the temperature of a cooling surface below the dew point and collecting the condensation which is formed.

The design task for optimum condensate yield may be summarised as: 1. Maximise heat loss, by radiative cooling.

2. Minimise heat gain, from direct or diffuse solar radiation, thermal radiation from the atmosphere or ground, conduction or convection through the air, and the latent heat released by condensation.

3. Provide thermal mass for cold storage to allow condensing to occur at the optimum times.

4. Allow optimum air flow rate to promote condensation on the cooled surface.

5. Provide effective surfaces for the collection and channeling to water storage, for example, by coating with anti misting compounds.

The different design strategies used to regulate or control the factors above result in the variations in form that the condenser may take. Some of these are shown in the accompanying drawings, numbers 1-22.

The simplest form the condenser may take is a shaded tilted surface with a water channel.

To minimise ambient heat gain by conduction or convection, the surface may be insulated against convection, conduction and radiant heat.

The condensing surface may be of low thermal mass and depend on fast temperature response to a lowering of sky temperature. This configuration would require insulation against ground radiation. Using materials of high thermal mass; such as earth, rocks, or water, cold may be stored to allow condensing to continue after cooling has ceased or for when condensation conditions are most favourable; for example when humidity is high or temperature low.

As water vapour condenses latent heat is released to the air. To facilitate continuous condensation it is therefore preferable to vent the dehumidified air. In open configurations this may be by natural airflow over the cool surface by advection currents or wind. It may also be by arranging the condensing surface on a slope to facilitate the heavier, cooled air flowing down through the condenser to the outside air.

Airflow may be induced by attaching a thermal chimney to the condensing space.

The thermal chimney will collect solar radiation during the day and store heat in its construction material of stone, bricks or earth. When conditions are suitable for condensing the thermal chimney is opened to the condenser outlet, drawing air through the condenser. A wind turbine or fan may be used for the same purpose.

The use of solar powered absorption refrigeration in tandem with radiative cooling fits the diurnal cycles of daytime solar radiation and nocturnal cooling. Less cooling is required to reach dew point than freezing for refrigeration. The cold may be stored until favourable ambient air condensing conditions prevail.

Natural conditions for heavy dew formation are the combination of significant night cooling and high input of water vapour during the daytime.These conditions prevail in most locations in the world when clear skies occur, except perhaps the tropics, where the high moisture content prevents night cooling. Meteorological measurements do not usually include dew as it evaporates with the suns arrival and quantity is considered insignificant compared to rain fall. Radiative cooling also depends on geological formation and plant cover, altitude has a major effect on cooling due to the lower density and depth of the atmosphere. Continuous dew formation, or advection dew, requires wind to move large masses of moist warm air over continuously cooled surfaces.

Yields will vary as much as the atmospheric conditions, but in selected desert areas, for example, yields are expected to be in the region of 1-2 Kg/m2/day.

The invention consists of a condensing surface, which may be a wide range of materials, for example, plastic, metal, glass, stone or painted surfaces, which is cooled by radiative cooling to the sky. The surface may be additionally or wholly cooled by refrigeration.

The condensing surface may be shielded from solar radiation during the day by shading the surface with, for example, a wall or removable screen. The screen may be, for example, a highly reflective material such as polished or white painted metal, or aluminised plastic.

Alternatively, a material highly reflective to solar radiation and highly emissive in longwave, Far Infra Red, FIR, radiation between 8 and 13 microns, may be used to reflect solar radiation and sky radiation and effectively radiate to outer space during the day and night. Such optically-selective material may, for example, be aluminised Tedlar, aluminised polythene or aluminised Teflon (HFE). Alternatively, the material may emit throughout the whole FIR spectrum like,for example, titanium dioxide based white paint. Such selective materials may be used as the condensing surface or to shade and allow effective cooling of the condensing surface, or act in both functions.

The forms that the atmospheric condenser may take are many, as may be seen in the accompanying drawings.

In the preferred embodiment, shown in drawing 1, a condensing space 1 is formed by a selective material cover and condensing surface 2, having optical properties most conductive to radiative cooling at the location of the condenser, as described above. The space is further insulated against conduction, convection and radiation by an enclosing wall 3. The condensing cover is supported by pipes 4, which connect the upper condensing surface 2, to the ground condensing surface 5 and across it 6, to draining channels 7, which lead into a main channel 8. Condensate is lead down this sloping channel to a water storage tank 9, connected to above ground surface by a pipe 10.

Ambient air is drawn through the system by a thermal chimney 11, formed by two walls 12, with an air space 13, between. The walls, forming a high thermal mass, absorb solar radiation during the day, and may be used to draw air through the system by day or night. Air enters the system through a vent 14, and condenses water onto the inner surfaces 15. Air also enters down pipes 4, with condensate from the upper condensing surface 2. Dehumidified air is drawn out through a tunnel 16, and is exhausted out through the thermal chimney 17.

A solar powered absorption refrigeration unit 18, further cools the condensing space through a heat exchanger 19. The refrigeration unit is powered by a solar collector 20. The air flow may be controlled by baffles 21, operated by sensor controlled mechanisms connected to programmed electronic circuits powered by a photovoltaic panel 22.

It will be obvious to anyone skilled in the art, that there are many different design configurations in which the basic principles may be applied, some of these are illustrated in drawing 2, numbers 1-22.

FIGURE 2 ATMOSPHERIC WATER CONDENSER: COOLING FORMS I. Dew Pond 2. Selective Surface Pond a. Titanium dioxide based white paint 3. Rock Pile a. Sea wind 4. Vented Underground Cave a. Suction 5. Wall Shade 6. Moveable Shade a. Daytime shade b. Night time cooling 7. Solar Actuator a. Night b. Day c. Solar-inflated bag 8. Shaded Rockpile 9. Convex Condensing Surface IO. Folding Insulated Surface II. Portable Survival Kits I2. Shade Slats I3. Cooling Fins I4. Cooling Wall I5. Thermal PiPe I6. Thermal Wall I7. Thermal Well I8. Insulated Box I9. Solar-refrigerated Box 20. Selective Cover 21. Selective Surface Tensioned a. aluminised 'Tedlar' or polythene 22. Combined System

Claims (26)

1. Claims; 1. A condensing surface cooled by radiative cooling and shielded from the conduction, convection and radiation of heat from its surroundings. The surface being so arranged as to be accessible to by ambient air so as to condense part of its moisture content as water.
2. 2. A system as in claim 1 using a condensing surface formed with selective materials reflecting all radiation outside the wavelength range 8-13 microns but absorbing and emitting within these limits as a black body.
3. 3. A system as in claim 1 using a radiating shallow pond as a collecting surface
4. 4. A system as in claim 1 using a radiating rock pile as a condensing surface.
5. 5. A system as in claim 1 using a sloping radiating surface shaded by a wall.
6. 6. A system as in claim 1 using a sloping surface shaded by a moveable shade.
7. 7. A system as in claim 1 using a sloping surface shaded by a hinged surface opened by a solar inflated bag or solar actuator.
8. 8. A system as in claim 1 where a radiating rock pile is shaded by a solar actuator operated shade.
9. 9. A system as in claim 1 where convex shading surface is insulated from ground radiation.
10. 10 A system as in claim 1 consisting of folding, insulated condensing surfaces.
11. 11. A system as in claim 1 in which a flexible condensing surface is attached to a flexible material reflective to thermal radiation and the space between inflated. With a fixed or removable cover made of a material transparent to longwave, far infra red, radiation.
12. 12. A system as in claim 1 in which slats are used to shade a condensing surface.
13. 13. A system as in claim 1 in which cooling fins are arranged close together so as to shade against solar radiation and induce downward flow of cool air.
14. 14. A system as in claim 1 in which an upright condensing surface is shaded by an insulating wall and induces cool air to flow down between the wall and condensing surface.
15. 15. A system as in claim 1 in which air is drawn down a hole in the ground by a solar absorbing pipe inserted into the hole so that air is drawn down to the bottom of the hole by the thermal chimney effect.
16. 16. A system as in claim 1 in which air is drawn down to the bottom of a hole in the ground by the thermal chimney effect set up by solar radiation absorbed into a wall and a panel transparent to solar radiation.
17. 17. A system as in claim 1 in which air is drawn through underground channels from the ground surface to a hole in the ground by the thermal chimney effect set up by a chimney or pair of walls built around the top of the hole.
18. 18. A system as in claim 1 in which air flows through a pipe which passes through an insulated space sealed with a material transparent to radiative cooling wavelengths.
19. 19 A system as in claim 1 and 18 in which the cooled space is further cooled by a refrigeration system.
20. 20 A system as in claim 1 and 2 in which a sloping surface is shaded by a selective material.
21. 21.A system as in claim 1 and 2 and as described in the preferred embodiment.
22. 22. A system as in claims 1 and 2 and wholly or in part as described in the preferred embodiment.
23. 23. A system as in claims 1 and 22 in which the thermal chimney is replaced by a wind turbine or fan.
24. 24 A system as in claim 1 and 2 - 22, in which an anti-misting surface is used.
25. 25. A system as in claims 1 - 22 in which some or all of the materials used are changed to give a better performance.
26. 26. A system as in claim 1 and any combination of claims 2-23, and as described in the text.