WO2007041804A1

WO2007041804A1 - A method and apparatus for extracting water from air containing moisture

Info

Publication number: WO2007041804A1
Application number: PCT/AU2006/001518
Authority: WO
Inventors: Peter Terence Clarke; Benjamin Peter Banney; Robert Michael Weymouth; Montag Christian Davis; Brett Robson Manners
Original assignee: Thermoelectric Applications Pty Ltd
Priority date: 2005-10-13
Filing date: 2006-10-13
Publication date: 2007-04-19

Abstract

A method of and apparatus (10) for extrating water from air containing moisture. The method comprises removing thermal energy from the air containing moisture using a thermodynamic pump (12) so as to cool the air containing moisture and thereby extract the water in a liquid or solid phase, directing the cooled air to an air pre-cooler (16) so as to cool the air pre-cooler, and pre-cooling the air containing moisture using the pre-cooler (16) before the air containing moisture reaches the thermodynamic pump (12).

Description

A METHOD AND APPARATUS FOR EXTRACTING WATER FROM AIR

CONTAINING MOISTURE

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for extracting water from air containing moisture.

BACKGROUND OF THE INVENTION

The process of extraction of water from moist air for drinking purposes has been the subject of development over a number of years and several systems are now commercially available. These systems have compressors for extracting thermal energy from the moist air. Cooling associated with the reduction in thermal energy results in condensation or freezing of water vapour contained in the moist air.

The compressors that are used for such water extraction are similar to those used for refrigeration and air conditioning applications. However, such compressors are relatively noisy, heavy and are typically of a relatively large size.

Alternatively, thermoelectric cooling devices may be used. Such thermoelectric devices are relatively light solid state devices and their operation is substantially noise free. However, thermoelectric devices typically require more electrical energy than comparable compressors.

There is a need for technological advancement . SUMMARY OF THE INVENTION

The present invention provides in a first aspect a method of generating water from air containing moisture, the method comprising: removing thermal energy from the air containing moisture using a thermodynamic pump so as to cool the air containing moisture and thereby extract the water in a liquid or solid phase; directing the cooled air to an air pre-cooler so as to cool the air pre-cooler; and pre-cooling the air containing moisture using the pre-cooler before the air containing moisture reaches the thermodynamic pump.

As the air containing moisture is pre-cooled before reaching the thermodynamic pump, energy that is needed by the thermodynamic pump for condensation or freezing of the moisture is reduced. Consequently, size, noise and weight of the thermodynamic pump may also be reduced.

The present invention provides in a second aspect an apparatus for extracting water from air containing moisture, the apparatus comprising: a thermodynamic pump for removing thermal energy from the air containing moisture and thereby cooling the air containing moisture; and a pre-cooler for pre-cooling the air containing moisture before the air containing moisture reaches the thermodynamic pump, wherein the apparatus is arranged for cooling the pre-cooler by the air that has been cooled by the thermodynamic pump.

Throughout this specification, the term "thermodynamic pump" is used for any device that can be used to draw thermal energy from one region to another region. In this specification the terms "thermodynamic pump" and "heat pump" have the same meaning and are used interchangeably.

The thermodynamic pump may comprise a compressor that generates kinetic energy to remove thermal energy. As the air containing moisture is pre-cooled before reaching the thermodynamic pump, energy that is needed for condensation of the water vapour is reduced which typically also reduces noise associated with operation of the compressor.

Alternatively, the thermodynamic pump may comprise a thermoelectric pump having at least one thermoelectric element to remove thermal energy, which has the advantage that noise associated with operation can be reduced significantly.

The thermoelectric pump may comprise at least one thermoelectric module, each thermoelectric module comprising a plurality of thermoelectric elements.

The pre-cooler may comprise a corrugated or finned heat exchanging surface portion. Alternatively or additionally, the pre-cooler may comprise .a curved or spiral-shaped heat exchanging portion.

The pre-cooler may be positioned adjacent a region of the thermodynamic pump and may be directly cooled by the thermodynamic pump. Further, one or more portions of the thermodynamic pump may project into the pre-cooler. Alternatively or additionally, one or more portions of the pre-cooler may project into the thermodynamic pump. With this embodiment, the pre-cooler may comprise a plurality of adjacent channels extending towards the thermodynamic pump, and the apparatus may be arranged such that air flowing towards the thermodynamic pump through a first channel is directed through a second channel adjacent the first channel after passing through the thermodynamic pump and flows away from the thermodynamic pump so that the air flowing in the second channel effects pre-cooling of air in the first channel .

In one arrangement, ends of the channels adjacent the thermodynamic pump are tapered or V-shaped.

BREIF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a plot illustrating the relationship of temperature difference across a heat pump to coefficient of performance (COP) ; Figure 2 is a schematic diagram of an apparatus for extracting water from air in accordance with an embodiment of the present invention;

Figure 3 shows an enthalpy flow diagram of a heat pump configured such that air from a cold side of the heat pump is recycled to the hot side of the heat pump;

Figure 4 shows an enthalpy flow diagram of a heat pump configured such that air from a cold side of the heat pump is used to pre-cool air before reaching the heat pump ;

Figure 5 shows a flow schematic of a prior art apparatus for extracting water from air illustrating variation of air temperature as a function of distance; Figure 6 shows a flow schematic of an apparatus for extracting water from air in accordance with an embodiment of the present invention, the flow schematic illustrating variation of air temperature as a function of distance;

Figure 7 is a diagrammatic representation of a pre- cooling device of an apparatus for extracting water from air in accordance with an embodiment of the present invention;

Figure 8 is a diagrammatic representation of an alternative pre-cooling device of an apparatus for extracting water from air in accordance with an embodiment of the present invention;

Figure 9 is a diagrammatic representation of a further alternative pre-cooling device of an apparatus for extracting water from air in accordance with an embodiment of the present invention;

Figure 10 is a diagrammatic representation of a further alternative pre-cooling device of an apparatus for extracting water from air in accordance with an embodiment of the present invention; Figures HA and HB are diagrammatic perspective and plan representations of a further alternative pre-cooling device of an apparatus for extracting water from air in accordance with an embodiment of the present invention;

Figures 12A and 12B are schematic plan and side views of an apparatus for extracting water from air in accordance with an embodiment of the present invention using thermoelectric type heat pumps;

Figure 13 shows diagrammatic representations of alternative end portions of channels of the apparatus shown in Figure 12; and

Figure 14 is a diagrammatic representation of a thermoelectric module of the apparatus shown in Figure 12.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purposes of this specification, an apparatus for extracting water from air will include, but should not be limited to, apparatus specifically adapted to produce potable water from air at atmospheric pressure; dehumidifiers,- and scientific apparatus which require water for calibration purposes, in particular scientific apparatus used in remote locations .

The apparatus for extracting water from air is of a type which uses a heat pump to draw thermal energy from air and thereby condense or freeze water present in the air. The thermal energy that is drawn by the pump heats a portion of the pump and results in cooling of another portion of the pump .

The coefficient of performance (COP) of a heat pump varies inversely with temperature difference across the heated and cooled portions, as illustrated in Figure 1 which shows the relationship of COP to temperature difference (dT) across the heated and cooled portions. It is clear from Figure 1 that reducing dT has a significant effect on the COP of the heat pump and thereby overall system efficiency of the apparatus.

Referring to Figure 2, there is shown an example apparatus 10 for extracting water from air. The apparatus includes a heat pump 12 having a first passage 14 extending through the heat pump 12, and a pre-cooling device 16 having second 18 and third 20 passages extending through the pre- cooling device 16. _^

The apparatus 10 also includes a first conduit 22 extending from an inlet 24 to the pre-cooling device 16, a second conduit 26 extending between the pre-cooling device 16 and the heat pump 12, a third conduit 28 extending between the heat pump 12 and the pre-cooling device 16, and a fourth conduit 30 extending from the_. pre-cooling device 16 to an outlet 32.

The first, second and third passages 14, 18, 20 are configured and formed of a suitable material such that the passages 14, 18, 20 function as heat exchangers to draw heat from or transfer heat to air passing through the passages.

During operation, air containing moisture is fed into the inlet 24 and passed through the first conduit 22 and the third passage 20 in the pre-cooling device 16. The air then passes through the second conduit 26 into the first passage 14 in the heat pump 12 which draws heat from the first passage 14 and thereby from the air passing through the first passage 14. Cooled air then passes through the third conduit 28 and into the second passage 18 in the pre-cooling device 16. Since the air in the second passage 18 is colder than the air in the third passage 20, the pre-cooling device draws heat from the air in the third passage 20 and transfers the heat to the air. in the second passage 18. The effect of this is to pre-cool the air passing through the third passage 20 before the air reaches the heat pump 12.

In this example, the heat pump 12 is implemented using a compressor (not shown) to draw thermal energy from one 5 portion of the device and heat another portion of the device by evaporating and condensing a refrigerant material, or which may comprise a thermoelectric type device arranged to draw thermal energy from one portion of the device and heat another portion of the device using pn 1.0 semiconductor junctions configured so as to take advantage of the Peltier effect.

It has surprisingly been found that by using the air exiting a cool side of the heat pump of an apparatus for 15 extracting water from air to pre-cool air entering the heat pump, an increase in the efficiency of the apparatus is achieved.

Although the above embodiment is described in relation to 20 an apparatus using cooled air from the heat pump to cool incoming air, it will be understood that other variations are possible. For example, a pre-cooling device which uses a separate cooling arrangement is envisaged. However, using the air exiting the heat pump is 25 particularly advantageous as it does not require further power input .

In some apparatus for extracting water from air, cooled air exiting a condensing section is directed to a hot side ,30 of the heat pump. The thermal energy output from the heat pump includes the thermal energy drawn from the moisture and also thermal energy generated by the heat pump from conversion of electrical energy. As a consequence, the - S - cooled air, while it helps improve efficiency, acts on a heat load that already has been increased by a significant margin. Such an apparatus comprising a heat pump 40 is represented in an enthalpy flow diagram 42 in Figure 3.

In Figure 3, the following variables are identified and referenced:

Qc : amount of cooling energy removed from the ambient air stream

P : input power to heat pump at COP = 1.0, P = Q_c

Q_h: amount of heat delivered to hot side by heat pump

The following analysis assumes perfect heat transfer processes with no losses or inefficiencies. The heat pump 40 is assumed to work at a COP of 1.0 which means that the electrical input power P required to move Q_c from a cold side 44 of the heat pump 40 to a hot side 46 is equal to

Qc.

Ambient air 48 is drawn in through the cold side 44 of the heat pump 40 and is cooled by an amount Q_c. Therefore Q_h = P + Q_c has to be removed from the hot side 46 of the heat pump 40. If the cooled ambient air is recycled then it removes the Q_c and only P is left to be removed by ambient air.

An enthalpy flow diagram 50 for a similar apparatus which uses air from a cold side of a heat pump to pre-cool air entering the heat pump is shown in Figure 4. Like and similar features and variables are indicated with like reference numerals and variables. As with the enthalpy diagram shown in Figure 3, the COP is again assumed to be 1.0.

Ambient air 52 is drawn in through a pre-cooling device 54 which is assumed to operate at 75% efficiency; in other words, 75% of the difference in enthalpy (Q_c) between the an ambient air stream and a cooled air stream is transferred from the ambient air to the cooled air. This means that only 25% of Q₀ is required as active cooling from the heat pump.

Because the COP is 1.0, the electrical energy required to pump heat P' is also 0.25Q_c and the total hot side heat flow is 0.5Q_c.

The simplified analysis illustrated in Figures 3 and 4 shows that up to 75% of electrical input power can be saved by pre-cooling ambient air whilst still extracting the same amount of heat from the ambient air. This is a significant increase in the efficiency of the system.

Referring to Figures 5 and 6, schematic diagrams 60, 70 illustrating temperature changes experienced by air passing thorough a conventional apparatus for extracting water from air and an apparatus for extracting water from air with pre-cooling respectively are shown. Each apparatus is of a type using a heat pump implemented using a compressor.

In the following analysis of the temperature changes shown in Figures 5 and 6, it will be assumed that inlet air temperature is 24 ⁰C, inlet air relative humidity is 50 %, volumetric air flow rate is 100 1/s and moisture production rate is 10 I/day.

Referring to Figure 5, a pathway 62 followed by ambient air is shown diagramtnatically, with the direction of air flow indicated by arrows A and the ambient air shown passing through a heat pump 64.

As shown by temperature diagram 68, the heat pump cools the inlet air from 24 ⁰C and the cooled air leaves the heat pump 64 under saturated conditions at 11.5 ⁰C. Condenser heat ejection then causes the air temperature to increase.

The energy Q₂ required for the cooling process is given by

Q₂=V_aPaΔh where :

^a (100 1/s) is the volume flow rate of air,

P" (1.17 kg/m3) is the density of air, and Δh is the enthalpy change across the heat pump.

The value of ^h is computed from a psychrometric chart by obtaining the absolute humidity ^ωi and ^ω2 required to give a moisture production rate of 10 I/day. This provides a value for Q₂ of 1872W.

Assuming a typical COP of 1.71 for the refrigeration circuit, the compressor power W is computed to be 1872/1.71 = 1095 W and the heat rejection at the condenser Ql is therefore 1872 + 1095 = 2967 W. Referring to Figure 6, a pathway 72 followed by ambient air in an apparatus with pre-cooling is shown diagrammatically, with the direction of air flow indicated by arrows B and the ambient air shown passing through a heat pump 74 and a pre-cooler 76.

As shown by temperature diagram 78, the pre-cooler 16 first cools inlet air from 24 ⁰C to 13.0 ⁰C prior to entering the heat pump 74. The air then experiences a temperature drop in the heat pump to about 11.5 ⁰C. Pre-cooling the ambient air reduces the unproductive sensible component of refrigeration heat load thereby improving the energy utilisation efficiency for moisture production.

With heat recovery, the cooling load of the heat pump is given by

Q^=V_aPaΔh' where : Δh' = (h_!-h'₄)

Thus, the cooling load of the heat pump can be formulated and computed by:

Q₂ = 100x1(T³Xl.17x(49.0-45.0)xl000 = 468 W

Assuming a COP of 1.71 for the refrigeration circuit, the compressor power W is calculated to be 468/1.71 == 274 W and the heat rejection at the condenser Q[ is 468 + 274 = 742 W. It will be appreciated from the above analysis that there is clearly a thermodynamic advantage and an enhanced efficiency obtained by the use of a pre-cooler design.

Pre-cooling devices for use in the present invention can be designed in a variety of configurations.

For example, as shown in Figures 7 and 8 a pre-cooling device having a corrugated sheet of inclined 90 or parallel 94 side configuration may be provided.

A corrugated sheet has the advantage of being space efficient and flexible in its implementation. It also has a high surface area to volume ratio and a low pressure drop due to the short duct length.

During operation, air from a first stream passes along channels on a first side 96 of the corrugated sheet 90, 94, and air from a second stream passes along a second opposite side 98 of the corrugated sheet 90, 94.

Typically the material used for the corrugated sheet 90, 94 is aluminium or copper.

An alternative pre-cooler 100 is shown in Figure 9. The pre-cooling device 100 comprises a first set 102 of connected channels and a second set 104 of connected channels. Ambient air passes through the first set 102 of channels and after passing through the heat pump is directed through the second set 104 of channels in a direction opposite to the direction of ambient air travelling through the first set 102 of channels. In the present example, insulation 106 is provided to prevent heat loss .

In a cooling, dehumidifying application with pre-cooling the inlet air temperature decreases as the air travels through the pre-cooler and the temperature of air used to provide pre-cooling increases. Heat flow occurs through the channel walls perpendicular to the direction of air flow. Because the wall material is very thin (in the range 0.1mm to 1.0mm) it exhibits a very low thermal resistance to heat flow. The efficiency of heat transfer is therefore effectively governed by surface area and the heat transfer coefficient between the channel wall and air flow.

A further alternative pre-cooling device 110 is shown in Figure 10. As with the pre-cooling devices 90, 94 shown in Figures 7 and 8, the pre-cooling device 110 has a corrugated configuration. However, unlike the pre-cooling devices 90, 94 shown in Figures 7 and 8, air is introduced substantially perpendicularly to end folds 112 of the pre- cooling device 110, and flows in paths as illustrated by arrows C in Figure 10.

A further alternative pre-cooling device 120 is shown in Figures 11a and lib. The pre-cooling device 120 is configured so as to form 2 spiral shaped regions separated by a wall 122.

While such a spiral configuration has high efficiency, a higher pressure drop occurs due to the length of the air path. The wall 122 is typically very thin so that it exhibits low thermal resistance.

An alternative embodiment of an apparatus 130 for extracting water from air is shown in Figures 12a and 12b. The apparatus is of a type comprising a thermoelectric type heat pump .

The apparatus 130 comprises an active cooling portion 132 arranged to carry out a heat pump function, and a pre- cooling portion 134 arranged to carry out a pre-cooling function on air passing to the active cooling portion 132. The active cooling portion 132 and the pre-cooling portion form one component, thereby enabling the apparatus 130 to be relatively compact and relatively simple, and for reduced manufacturing costs to be achieved.

Active cooler heat exchangers typically are designed specifically for this dehumidification process since the cooling power is being derived from thermoelectric modules. These thermoelectric modules are small, discrete heat pumps and several are usually required to produce enough cooling power to condense water from air.

Incorporating both pre-cooling and active cooling functions into the same component has several advantages in that the number of ducts, joins and seals can be reduced and problems such as complexity in manufacture associated with changes in cross section can be minimised.

The active cooling portion 132 includes a plurality of first thermoelectric Peltier cooling modules 136 connected to a first thermally conductive spreader bar 138, and a plurality of second thermoelectric Peltier cooling modules 140 connected to a second thermally conductive spreader bar 142. The first and second spreader bars 138, 142 are spaced from each other and substantially parallel. The spreader bars serve to spread the cooling power across the apparatus 130.

Disposed between and extending upwardly of the spreader bars 138, 142 is the pre-cooling portion 134 which in this example is in the form of a corrugated fin heat exchanger 150 defining a plurality of channels 151. The heat exchanger 150 is arranged such that air is able to enter the heat exchanger at a first side 152 of the heat exchanger 150 and exit the heat exchanger from a second opposite side of the heat exchanger 150.

During use, ambient air is drawn into the apparatus 130 at the first side 152 and passes downwardly through alternate channels 151 towards the first and second cooling modules 136, 140. When the air reaches the active cooling portion 132, water present in the air condenses and drips into a collection tray. Air exits the channel 151, turns through 180 degrees and moves upwardly through adjacent alternate channels 151 towards the pre-cooling portion 134. In the pre-cooling portion 134, the cooled dry air absorbs heat from inlet air passing through an adjacent previous channel 151, cooling it down in the process. This process repeats until the dry air exits the apparatus at the second side 154, now nearly at ambient temperature.

It will be appreciated that with this embodiment air passing through each channel 151 towards the active cooling portion 132 is subject to pre-cooling by air passing upwardly through an adjacent successive channel 151.

Fin materials that have been found to be suitable include aluminium and copper. Geometries that have been found to be suitable for combined active cooling and pre-cooling are :

Fin thicknesses : 0. lmm to 1.0mm Fin channel width: lmm to 10mm Fin height: 10mm to 200mm

With relatively narrow channels having a width less than 5mm, surface tension in the water produced in a channel 151 tends to form a bridge across the channel 151. This is particularly evident in the channels carrying air in an upwardly direction because the direction of air flow supports the column of water. The effect of blocked channels is that the pressure drop increases and the air flow rate through the channels will be reduced. If this is allowed to occur with no control over Peltier cooling power, then the resulting lower air flow rate will cause lower fin temperatures which eventually will become subzero. When this happens, any water trapped in the channels 151 will freeze and cause even more blockage. No further water production occurs under this scenario.

In order to avoid blockages in the channels due to surface tension, the channels 151 may be inclined relative to a vertical axis to encourage any water droplets to coalesce and run down the channel 151. An alternative arrangement for avoiding blockages in the channels 151 is shown in Figure 13. In this arrangement, each channel 151 is provided with either a chamfered end 160 or a V-shaped end 162.

A chamfered end 160 or a V-shaped end 162 provides a path for droplets to run down and coalesce at a base of the apparatus 130 rather than collect in the channels. Angles between 10 degrees and 60 degrees have been found to be suitable for inclined sides of the channels 151 defining the chamfered end 160 and the V-shaped end 162.

Because the geometry of the channels 151 serving both the pre-cooling portion 134 and the active cooling portion 132 is fixed, larger channel heights improve pre-cooling efficiency since the surface area is increased. However, larger channel heights will have a detrimental effect on active cooler heat transfer coefficients and therefore efficiency. This is because larger channel heights translate into larger cross sectional air flow areas and for a given volumetric flow this will mean lower air velocities. The relationship between air velocity and heat transfer coefficients is well known and lower air velocities with lower heat transfer efficiencies will lead to lower overall cooling and condensing efficiencies.

In order to overcome such detrimental effects to operation of the active cooling portion 132 by increasing channel size, the air velocity may be increased in the active cooling portion 132 without affecting the air velocity in the pre-cooling portion 134. This may be achieved by disposing an insert in the pre-cooling portion 134 in each channel to form an obstacle to air flow. An example thermoelectric module 170 is shown in Figure 14. The thermoelectric module 170 comprises alternate p and n type semiconductor portions 172, 174 which collectively form a plurality of thermoelectric cooling devices, a heat absorbing surface 176 disposed on a first side of the module 170 and a heat dissipating surface 178 disposed on a second opposite side of the module 170. Conductors 180 are also included.

A further arrangement for reducing dT across a module involves use of a heat pipe. Highly efficient heat pipes have been developed to service computer chip cooling requirements. Heat pipes have an advantage in that they are sealed, self contained and require only a fan to provide ventilation. Noise levels can also be low and they are lightweight and efficient .

Thermoelectric based systems offer some unique advantages over compressor based systems when lower ambient temperatures are encountered. Because a compressor system does not modulate the condensing plate temperature there is a high probability that ice will form on the condensing surface .

In order to remove the ice, the compressor is generally switched off to allow the ice to melt, or gas flows are reversed to actively defrost the ice. Because there is generally only one common condensing heat exchanger, the entire heat exchanger has to be heated and cooled back to temperature, even though only a partial section may be blocked by ice. This process is costly in terms of apparatus down time and in terms of the energy required to heat up the entire surface of the heat exchanger.

Thermoelectric cooling devices offer much more flexibility in the way in which formation of ice can be handled.

Because the cooling power of thermoelectric modules can be controlled simply by varying the current flowing through them, it is relatively simple to prevent ice from forming by sensing the temperature on the heat exchangers and by carrying out appropriate modification of the respective currents passing through the modules. A temperature sensor located on the condensing heat exchanger will provide the input data necessary for this control. When the temperature at one of the sensors approaches zero, a controller reduces the voltage applied to the thermoelectric module which reduces its cooling power, thereby preventing the formation of ice.

Other ways to prevent formation of ice include increasing air flow through the apparatus by providing a fan to direct ambient air across the modules and increasing the speed of the fan. The increase in air flow produced by the increase in fan speed reduces the temperature difference that is achieved by the apparatus and increases the exit air temperature .

In the event that ice does form on the any one of the heat exchangers, the ice can be defrosted simply by reversing the direction of electrical current passing through the or each relevant the thermoelectric module . Collection of water from air for drinking purposes brings with it a requirement to ensure that the water is free from harmful bacteria, viruses and other foreign materials. As a consequence, the surfaces which collect the water must be maintained in a relatively sterile condition.

A suitable method for ensuring that these surfaces are maintained in a clean condition is to carry out a "pasteurization" process at least once daily.

Pasteurization standards, e.g. USDA, call for a exposure at 72°C for at least 15 seconds. This process can be carried out by reversing the polarity of voltage applied to the thermoelectric modules, which has the effect of heating the condensing portion of the apparatus.

Another effective sterilization technique is to spray water having an ozone level greater than 0.1 ppm onto the surfaces requiring sterilization. Ozonated water at this level will effectively kill bacteria, viruses and reduce the biological load to safe levels.

In the foregoing description, where reference is made to components, then known equivalents of such equivalents are incorporated herein as if individually set forth.

Although the invention has been described by way of example with reference to preferred embodiments, modifications and variations may be made to the invention without departing from the scope of the invention.

Claims

Claims :

1. A method of extracting water from air containing moisture, the method comprising: removing thermal energy from the air containing moisture using a thermodynamic pump so as to cool the air containing moisture and thereby extract the water in a • liquid or solid phase,- directing the cooled air to an air pre-cooler so as to cool the air pre-cooler; and pre-cooling the air containing moisture using the pre-cooler before the air containing moisture reaches the thermodynamic pump.

2. A method as claimed in claim 1, wherein thermal energy is removed from the air containing moisture using a compressor.

3. A method as claimed in claim 1, wherein thermal energy is removed from the air containing moisture using at least one thermoelectric heat pump.

4. A method as claimed in claim 3 , wherein the thermoelectric pump comprises at least one thermoelectric module, each thermoelectric module comprising a plurality of thermoelectric elements.

5. A method as claimed in any one of claim 1 to 4, wherein the pre-cooler comprises a corrugated or finned heat exchanging surface portion.

6. A method as claimed in any one of claim 1 to 4, wherein the pre-cooler comprises a curved or spiral-shaped heat exchanging portion.

7. A method as claimed in any one of the preceding claims, further comprising positioning the pre-cooler adjacent a region of the thermodynamic pump so that air is directly pre-cooled by the thermodynamic pump.

8. A method as claimed in claim 7, wherein one or more portions of the thermodynamic pump project into the pre- cooler.

9. A method as claimed in claim 7, wherein one or more portions of the pre-cooler project into the thermodynamic pump.

10. A method as claimed in any one of the preceding claims, wherein the pre-cooler comprises a plurality of adjacent channels extending towards the thermodynamic pump, and the method comprises directing air to flow towards the thermodynamic pump through a first channel, and directing air to flow away from the thermodynamic pump through a second channel adjacent the first channel after passing through the thermodynamic pump so that the air flowing in the second channel effects pre-cooling of air in the first channel.

11. An apparatus for extracting water from air containing moisture, the apparatus comprising: a thermodynamic pump for removing thermal energy from the air containing moisture and thereby cooling the air containing moisture; and a pre-cooler for pre-cooling the air containing moisture before the air containing moisture reaches the thermodynamic pump, wherein the apparatus is arranged for cooling the pre-cooler by the air that has been cooled by the thermodynamic pump .

12. Apparatus as claimed in claim 11, wherein the thermodynamic pump comprises a compressor that generates kinetic energy to remove thermal energy.

13. Apparatus as claimed in claim 11, wherein the thermodynamic pump comprises a thermoelectric pump.

14. Apparatus as claimed in claim 13, wherein the thermoelectric pump comprises at least one thermoelectric module, each thermoelectric module comprising a plurality of thermoelectric elements.

15. Apparatus as claimed in any one of claims 11 to 14, wherein the pre-cooler comprises a corrugated or finned heat exchanging surface portion.

16. Apparatus as claimed in any one of claim 11 to 14, wherein the pre-cooler comprises a curved or spiral-shaped heat exchanging portion.

17. Apparatus as claimed in any one of claim 11 to 16, wherein the pre-cooler is positioned adjacent a region of the thermodynamic pump so that air is directly cooled by the thermodynamic pump.^'

18. Apparatus as claimed in claim 17, wherein one or more portions of the thermodynamic pump project into the pre- cooler.

19. Apparatus as claimed in claim 17 or claim 18, wherein one or more portions of the pre-cooler project into the thermodynamic pump .

20. Apparatus as claimed in any one of claims 17 to 19, wherein the pre-cooler comprises a plurality of adjacent channels extending towards the thermodynamic pump, and the- apparatus is arranged such that air flowing towards the thermodynamic pump through a first channel is directed through a second channel adjacent the first channel after passing through the thermodynamic pump and flows away from the thermodynamic pump so that the air flowing in the second channel effects pre-cooling of air in the first channel.

21. Apparatus as claimed in any one of claims 11 to 20, wherein ends of the channels adjacent the thermodynamic pump are tapered or V-shaped.

22. An apparatus for extracting water from air containing moisture substantially as hereinbefore described with reference to, and as shown in, Figures 1 to 4 and 6 to 15 of the accompanying drawings .

23. A method of extracting water from air containing moisture substantially as hereinbefore described with reference to, and as shown in, Figures 1 to 4 and 6 to 15 of the accompanying drawings .