External heat exchanger

Abstract

There is provided a heat exchanger 30 for use on an exterior of a building, the heat exchanger comprising a tubular element 40 extending between a first end 32 and a second end 34. The tubular element

Description

Technical Field 5 The invention relates to an external heat exchanger for use on an exterior of a building, preferably a heat exchanger using natural forces (such as gravity and capillary forces) and renewable energy sources (such as solar and wind energies) and renewable resources (such as rainwater). The invention also relates to fluid flow systems comprising the heat exchanger, preferably fluid flow systems for cooling and heating. 10 Background Cooled and heated water is not only needed for direct consumption, such as showering or washing, but also is needed for providing space cooling / heating energy to building 15 and homes. Furthermore, it is desirable for cooling and heating systems that are affordable and easily installed, as well as quiet and simple to maintain and repair. Global warming currently presents a serious problem to the environment. Fossil fuel use, for instance for heating and cooling, greatly contributes to global warming because 20 fossil fuels release a large amount of carbon dioxide into the atmosphere. Use of refrigerant gases in cooling and heating systems also contributes to global warming, as these gases deplete the protective ozone layer in the Earth's atmosphere. A renewable and sustainable solution to heating and cooling is therefore needed. 25 Hot and dry regions impose specific requirements on cooling and heating systems. These regions typically experience a high diurnal temperature difference: in summer, daytime temperatures can reach 45°C to 50°C while night-time temperatures are usually in the region of 27°C to 30°C. Mains water flows through long pipes, absorbing heat in daytime due to the pipes being exposed to sunlight. Additional heat is also 30 generated by friction with the inner surface of the pipes due to high speed water flow. Furthermore, water for domestic use is usually stored in on-roof tanks, which get hotter due to daytime sunlight exposure. Thus, in daytime, mains-supplied water can reach temperatures of 40°C or higher, i.e. higher than body temperature, making it too warm for showering. Indoor or underground water tanks do not solve this problem, as these 35 do not benefit from cooler night-time ambient temperatures to lower the temperature of the water. 20 09 24 Conventionally water tank chillers and coolers are used to obtain cold water for showering and daily domestic use. These each come with their own drawbacks. Specifically, water tank chillers consume large amounts of electricity and pose a health hazard due to potential mixing of the refrigerant with the water in the tank. Water 5 tank coolers can be ineffective and can harbour legionella bacteria. Furthermore, they are dangerous due to potential electrical shocks. Even when powered by solar energy, the efficiency of the chillers and coolers is limited by sky conditions, especially on cloudy days. 10 Other renewable resources suffer from several disadvantages that render them unsuitable for hot and dry regions. For example, geothermal and biomass technologies is associated with environmental pollution, earthquake / deforestation problems, high costs and restrictions to locations with suitable geothermal / biomass resources. 15 Summary of the Invention According to a first aspect of the invention, there is provided a heat exchanger for use on an exterior of a building, the heat exchanger comprising a tubular element extending between a first end and a second end, wherein the tubular element is 20 configured to, in use, be inclined relative to a horizontal plane so that its second end is elevated above its first end, the first end configured as a heat source in use, the second end configured as a heat sink in use, wherein the tubular element includes a fluid inlet, a fluid outlet and a capped vent, the fluid inlet for connection to a fluid source, the fluid outlet for connection to a fluid sink, the fluid inlet and fluid outlet 25 arranged at the first end of the tubular element, wherein the fluid inlet is at least partly axially extended inside the tubular element and is elevated above the fluid outlet and the capped vent is arranged at the second end to, in use, enable a first fluid flow to flow from the fluid inlet and within the tubular element from the first end towards the second end and enable a second fluid flow to be formed from the first fluid flow by 30 density variation so as to flow within the tubular element from the second end to the first end and towards the fluid outlet so that the first and second fluid flows move naturally as counterflows in direct contact with each other, wherein the heat exchanger includes a fluid flow controller configured to, in use, control the first fluid flow to flow from the fluid inlet and within the tubular element from the first end towards the second 35 end and control the second fluid flow to be formed from the first fluid flow by density variation so as to flow within the tubular element from the second end to the first end and towards the fluid outlet. 20 09 24 Installation of the heat exchanger on an exterior of a building (e.g. a building roof) enables cooling of the fluid inside the heat exchanger using renewable resources, such as solar and wind energy. The heat exchanger of the invention therefore provides a cost-effective and energy-efficient solution that is capable of harnessing renewable 5 energies suited for use in hot and dry regions. The heat exchanger may be configured so that, in use, the bulk temperature of the first fluid flow is different, preferably higher, than the bulk temperature of the second fluid flow. Preferably the first fluid flow is positioned above the second fluid flow. The 10 movement of the first and second fluid flows as counterflows in direct contact with each other not only enables efficient heat transfer between the two fluid flows via direct heat conduction and natural heat convection, but also facilitates the flow of fluid out of the heat exchanger as a suitably cooled or heated fluid. 15 The angle of incline of the heat exchanger relative to a horizontal plane may vary depending on requirements. In use, the fluid flow controller may be for connection between the fluid inlet and the fluid source. Such a fluid flow controller may include, but is not limited to, a pump. 20 This enables control over the flow of fluid inside the heat exchanger to optimise the exchange of heat between the fluid inside the heat exchanger and the environment outside the heat exchanger and also the exchange of heat between the first and second fluid flows within the heat exchanger. Preferably the first and second fluid flows are controlled to be laminar or substantially laminar. 25 In embodiments of the invention, the heat exchanger may include a fluid retention element arranged on, above, under, beside or around an outer surface of the tubular element, wherein the fluid retention element may be configured to, in use, retain a fluid so as to form a film of fluid on, above, under, beside or around the outer surface 30 of the tubular element. The provision of the fluid retention element enables evaporative cooling to further improve the efficiency of the heat exchanger. In embodiments of the invention, the fluid retention element may include a UV-resistant material and / or a fluid-absorbent material and / or a fabric material. For 35 example, the fluid retention element may include cotton gauze or synthetic cloth, both of which enable fluid to move through the fluid retention element through capillary action in order to replace fluid lost through evaporation. 20 09 24 It is envisaged that different types of fluids may be used by the fluid retention element to achieve the evaporative cooling effect. A preferred choice of fluid is distilled water. Hence, the heat exchanger of the invention may include a distilled water source for providing distilled water to the fluid retention element. Examples of a distilled water 5 source may include, but is not limited to, a still (e.g. a solar still) and a storage tank (e.g. an outdoors storage tank) which may, for example, filter and accumulate rainwater. Also, the water that is produced from mechanical air conditioners and dehumidifiers after filtration may be suitable for evaporation. 10 Different configurations of the tubular element are envisaged. Preferably the tubular element is an elongate tubular element. The tubular element may include a plurality of elongate tubular sub-elements. The 15 fluid inlet and fluid outlet may be arranged at the first end of the tubular element to, in use, enable the first fluid flow to flow within the elongate tubular sub-elements from the first end towards the second end and enable the second fluid flow to flow within the elongate tubular sub-elements from the second end to the first end so that the first and second fluid flows move as counterflows in direct contact with each other. 20 Different arrangements of the plurality of elongate tubular sub-elements are envisaged. The plurality of elongate tubular sub-elements may be spaced apart from each other. The plurality of elongate tubular sub-elements may be arranged to extend parallelly with each other between the first and second ends of the tubular element. 25 The provision of the plurality of elongate tubular sub-elements not only increases the heat exchanger's surface area that is available for heat exchange, but also allows wind to efficiently blow off dust from the outer surfaces of the elongate tubular subelements. 30 Furthermore, the tubular element may include first and second tubular connectors, the first tubular connector fluidly interconnecting the elongate tubular sub-elements at or towards the first end of the tubular element, the second tubular connector fluidly interconnecting the elongate tubular sub-elements at or towards the second end of the 35 tubular element. This not only makes it straightforward to design the flow of fluid into and out of the elongate tubular sub-elements but also makes it easier to handle and install the heat exchanger. 20 09 24 According to a second aspect of the invention, there is provided a heat exchanger for use on an exterior of a building, the heat exchanger comprising a tubular element extending between a first end and a second end, wherein the tubular element is configured to, in use, be inclined relative to a horizontal plane so that its second end 5 is elevated above its first end, wherein the first end is configured to be, in use, inclined relative to a horizontal plane between two corners of the tubular element, wherein the second end is configured to be, in use, inclined relative to a horizontal plane between another two corners of the tubular element, wherein the tubular element includes a fluid inlet, a fluid outlet and a capped vent, the fluid inlet for connection to a fluid 10 source, the fluid outlet for connection to a fluid sink, the fluid inlet and fluid outlet arranged in the tubular element to, in use, enable a fluid flow to flow within the tubular element between the first and second ends, wherein the heat exchanger includes a fluid flow controller configured to, in use, control a first fluid flow to flow from the fluid inlet and within the tubular element from one of the first and second ends towards the 15 other of the first and second ends and control a second fluid flow to be formed from the first fluid flow by density variation so as to flow within the tubular element from the other of the first and second ends to the one of the first and second ends and towards the fluid outlet. 20 The above configuration of the heat exchanger enhances the cooling of the fluid inside the heat exchanger by positioning one corner of the tubular element to be lower than other corners of the tubular element. In particular, in this configuration, the incline of the tubular element is such that the direction of the fluid flow(s) in the tubular element is not perpendicular to the direction of ambient air (such as due to natural convection 25 or intermittent wind energy). This effectively creates a semi-crossflow between the fluid flow(s) and the ambient air that enhances the cooling of the fluid inside the heat exchanger. The fluid inlet and fluid outlet may be arranged at the first end of the tubular element 30 to, in use, enable a fluid flow to flow within the tubular element between the first and second ends. In embodiments of the invention, the fluid inlet and the fluid outlet may be located at or towards a lowest of the corners of the tubular element. 35 In further embodiments of the invention, the capped vent may be located at a highest of the corners of the tubular element. 20 09 24 The heat exchanger may include a single tubular element. The heat exchanger may include a plurality of tubular elements. The provision of a plurality of tubular elements increases the surface area for heat exchange. At least two of the plurality of tubular elements may be configured to share a common fluid inlet and / or a common fluid outlet 5 and / or a common vent. In embodiments of the invention, the first end may be configured to be, in use, inclined relative to a horizontal plane between two corners of the tubular element, wherein the second end may be configured to be, in use, inclined relative to a horizontal plane 10 between another two corners of the tubular element. It will be appreciated that the features of the heat exchanger of any one of the first aspect of the invention and its embodiments may be combined with the features of the heat exchanger of any one of the second aspect of the invention and its embodiments. 15 In embodiments of the invention, the tubular element may include a fluid distribution pipe and a tubular pipe, the fluid distribution pipe connected to the fluid inlet, wherein the fluid distribution pipe may include a transfer pipe for transferring fluid from the fluid distribution pipe into the tubular pipe, wherein the transfer pipe may be axially 20 aligned with the tubular pipe and may be arranged to penetrate the tubular pipe so that, in use, fluid flows directly from the fluid inlet into the tubular pipe. An end of the transfer pipe may be formed to have an inclined fluid diversion wall that extends into the fluid distribution pipe. 25 The tubular element of the invention is shaped preferably as a hexagon, preferably as an elongated hexagon. According to a third aspect of the invention, there is provided a fluid flow system 30 comprising a heat exchanger according to any one of the preceding aspects of the invention and its embodiments, a fluid source and a fluid sink, wherein the fluid inlet of the heat exchanger is connected to the fluid source, and the fluid outlet of the heat exchanger is connected to a fluid sink. 35 The features and advantages of the heat exchanger of the first or second aspect of the invention and its embodiments apply mutatis mutandis to the fluid flow system of the third aspect of the invention and its embodiments. 20 09 24 In embodiments of the invention, the fluid flow system may include a fluid storage tank. The fluid storage tank may be connected to the fluid inlet so that, in use, at least part of the first fluid flow may flow into the heat exchanger from the fluid storage tank via the fluid inlet and / or wherein the fluid storage tank may be connected to the fluid outlet so that, in use, at least part of the second fluid flow may flow into the fluid storage tank from the heat exchanger via the fluid outlet. This enables direct circulation of fluid between the heat exchanger and the fluid storage tank in a loop so that fluid from the fluid storage tank can be cooled inside the heat exchanger before returning to the fluid storage tank. In other embodiments of the invention, the fluid flow system may include a fluid storage tank and a first internal heat exchanger, the first internal heat exchanger extending inside and through the fluid storage tank, the first internal heat exchanger configured so that, in use, a fluid inside the first internal heat exchanger may be physically separated from a fluid inside the fluid storage tank. The first internal heat exchanger may be connected to the fluid inlet so that, in use, at least part of the first fluid flow may flow into the heat exchanger from the first internal heat exchanger via the fluid inlet and / or wherein the first internal heat exchanger may be connected to the fluid outlet so that, in use, at least part of the second fluid flow may flow into the first internal heat exchanger from the heat exchanger via the fluid outlet. This enables direct circulation of fluid between the heat exchanger and the first internal heat exchanger in a loop so that fluid from the first internal heat exchanger can be cooled inside the heat exchanger before returning to the first internal heat exchanger, where heat can be exchanged between the fluids inside the fluid storage tank and the first internal heat exchanger. Accordingly heat exchange is enabled between the heat exchanger and the fluid storage tank via the first internal heat exchanger. Furthermore, the fluid storage tank and the first internal heat exchanger may be configured to use different types of fluids. A fluid distribution device can be connected to the fluid storage tank's outlet for direct consumption, whereby fluid taken from the tank is replaced by fluid entering the tank through its inlet. In still further embodiments of the invention, the fluid flow system may include a fluid circulation conduit connected to the heat exchanger so that, in use, fluid may be circulated through the heat exchanger and the fluid circulation conduit in a loop. The fluid circulation conduit may form part of a building's internal heating and / or cooling system, such as radiant floor pipe or tube loops. 20 09 24 The fluid flow system of the invention may include a second internal heat exchanger, wherein the second internal heat exchanger extends inside and through the tubular element (such as the second tubular connector), the second internal heat exchanger configured so that, in use, a fluid inside the second internal heat exchanger may be 5 physically separated from a fluid inside the tubular element (such as the second tubular connector). The provision of the second internal heat exchanger enables an exchange of heat between the fluids inside the heat exchanger and the second internal heat exchanger. In turn, the cooled fluid inside the second internal heat exchanger may be fed into an external device. For example, the fluid flow system may include a solar 10 collector device, wherein the second internal heat exchanger may be configured to, in use, feed a fluid into an inlet of at least one fluid tube of the solar collector device. This allows the heat exchanger to assist the heating of the fluid inside the solar collector device, thus improving efficiency. 15 It will be appreciated that the use of the terms "first", "second", "third", "fourth" and the like, in this specification is merely intended to help distinguish between similar features, and is not intended to indicate the relative importance of one feature over another feature, unless otherwise specified. 20 Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, and the claims and / or the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and all features of any embodiment can be combined in any way and / or 25 combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. 30 Brief Description of the Drawings Preferred embodiments of the invention will now be described, by way of non-limiting examples, with reference to the accompanying drawings in which: 35 Figure 1 shows a single tubular element of a heat exchanger according to an embodiment of the invention; Figure 2 shows a heat exchanger according to an embodiment of the invention; Figure 3 shows a fluid distribution pipe; 20 09 24 Figure 4 shows a heat exchanger according to another embodiment of the invention; Figures 5 to 7 show a system for wetting the tubular element of Figure 1; Figure 8 illustrates an evaporation cooling process; and 5 Figures 9 to 13 show fluid flow systems according to embodiment of the invention. Detailed Description 10 The figures are not necessarily to scale, and certain features and certain views of the figures may be shown exaggerated in scale or in schematic form in the interests of clarity and conciseness. Figure 1 shows an external heat exchanger according to an embodiment of the 15 invention and is designated generally by the reference numeral 30. The heat exchanger 30 comprises a tubular element capable of carrying a fluid therein. The tubular element extends between first and second ends 32,34, and is installed so as to be inclined relative to a horizontal plane so that its second end 34 is elevated above its first end 32. The tubular element includes a fluid inlet 36 and a fluid outlet 38 that 20 are formed at the first end 32 of the tubular element. In use, the fluid inlet 36 is fluidly connected to a fluid source, while the fluid outlet 38 is fluidly connected to a fluid sink. As shown in Figure 2, the tubular element may comprise a plurality of elongate tubular pipes 40 and first and second tubular connectors 42,44. The elongate tubular pipes 25 40 are spaced apart from each other and are arranged to extend parallelly with each other between the first and second ends 32,34 of the tubular element. The first tubular connector 42 extends perpendicularly to the elongate tubular pipes 40 and fluidly interconnects the elongate tubular pipes 40 at the first end 32 of the tubular element. The second tubular connector 44 extends perpendicularly to the elongate tubular pipes 30 40 and fluidly interconnects the elongate tubular pipes 40 at the second end 34 of the tubular element. As shown schematically in Figure 1, when the heat exchanger 30 is used for water cooling, a first fluid flow 46 comprising hot water flows into the heat exchanger 30 35 through the fluid inlet 36 at the tubular element's first end 32 and through the elongate tubular pipes 40 from the first end 32 to the second end 34 of the tubular element. At the same time the hot water exchanges heat with the outside environment through the wall of the heat exchanger 30, thus reducing the water temperature of the first fluid 20 09 24 flow. A second fluid flow 48 is formed and separated instantly from the first fluid flow 46 at the first end 32 to the second end 34 of the tubular element. The second fluid flow 48 flows out as cooled water through the fluid outlet 38 at the tubular element's first end 32. 5 Thus, the first and second fluid flows 46,48 move as counterflows in direct contact with each other inside the elongate tubular pipes 40, with the first fluid flow 46 above the second fluid flow 48, and with the bulk temperature of the first fluid flow 46 being higher than the bulk temperature of the second fluid flow 48. This is made possible by 10 the tubular element's inclined orientation in combination with the arrangement of the fluid inlet 36 and fluid outlet 38 at the tubular element's first end 32. The configuration of the first and second fluid flows 46,48 as counterflows in direct contact with each other enables efficient heat transfer between the first and second fluid flows 46,68 by way of direct conduction, and so further enhances the efficiency of the water cooling 15 process. Preferably, the flow rates of both fluid flows 46,48 are sufficiently low to maintain laminarity, thus minimising mixing between the two fluid flows 46,48. Since the bulk temperature of the second fluid flow 48 is lower than the bulk temperature of the first 20 fluid flow 46, the cooler second fluid flow 48 has a higher density than the first fluid flow 46. Hence, the flow of the second fluid 48 flow inside the elongate tubular pipes 40 is assisted by natural convection. More specifically, the formation of the first and second fluid flows 46,48 as counterflows 25 inside the heat exchanger 30 is a natural circulation caused by density variation and the tubular element's inclined orientation under the following conditions: a. A temperature difference exists between a heat source and a heat sink; b. The heat source is at a lower elevation than the heat sink; c. Hot and cold fluids must be in contact with each other. 30 These conditions are fulfilled by the external heat exchanger 30 of the invention in which the first end 32 is lower than the second end 34, the first end 32 acts as a heat source in use, the second end 34 acts as a heat sink (which is preferably at ambient temperature) in use, the first fluid flow 46 enters the first end 32 and naturally moves 35 towards the second end 34, and the second fluid flow 48 is naturally formed by density variation caused by temperature differences. As a result, the first and second fluid flows 46,48 are able to move as counterflows in direct contact with each other inside the heat exchanger 30. 20 09 24 As shown in Figure 3, the tubular element includes a fluid distribution pipe 50 at its first end. The fluid distribution pipe 50 is connected to the first tubular connector 42 via a series of transfer pipes 52 so that water in the fluid distribution pipe 50 may 5 branch off into the first tubular connector 42 via the series of transfer pipes 52. Each transfer pipe 52 is axially aligned with a respective one of the elongate tubular pipes 40, and is arranged to penetrate the first tubular connector 42 so that the water flows directly from the transfer pipes 52 into the elongate tubular pipes 40 and so that the first and second fluid flows 46,48 are prevented from completely mixing. Preferably, 10 as shown in Figure 3, an end of each transfer pipe 52 is formed to have an inclined water diversion wall 54 that extends into the fluid distribution pipe 50, where the water diversion walls 54 act as obstacles to the water flowing inside the fluid distribution pipe 50 so as to reroute the water into the individual elongate tubular pipes 40 in equal, or substantially equal, volumetric rates. 15 The fluid inlet 36 is formed on the fluid distribution pipe 50. The fluid outlet 38 is formed on the first tubular connector 42. Therefore, water first enters the fluid distribution pipe 50 via the fluid inlet 36, then flows as the first and second fluid flows 46,48 through the elongate tubular pipes 40 and finally exits the first tubular connector 20 42 via the fluid outlet 38. Preferably the fluid inlet 36 is positioned to be higher than the fluid outlet 38. The tubular element is made of a thermally conductive material, such as aluminium or copper. A length of each pipe 40 may be 200 cm. The elongate tubular pipes 40 in 25 combination may have a width of 100 cm, which includes the spacing between the elongate tubular pipes 40. A diameter of each elongate tubular pipe 40 may be in the range of 5 cm to 6.25 cm. A size of the spacing between neighbouring elongate tubular pipes 40 may be in the range of 6.25 cm to 10 cm. A diameter of each tubular connector 42,44 may be in the range of 6.25 cm to 7.5 cm. Preferably the diameter 30 of each tubular connector 42,44 is larger than the diameter of each elongate tubular pipe 40. As part of a fluid flow system, a heat exchanger coil pipe 56 may be arranged to extend inside and through the second tubular connector 44. The heat exchanger coil pipe 56 35 is configured so that, in use, water inside the heat exchanger coil pipe 56 may be physically separated from water inside the second tubular connector 44. In this way, the heat exchanger coil pipe 56 and the second tubular connector 44 form a shell coil heat exchanger that permits transfer of heat from the water inside the second tubular 20 09 24 connector 44 to the water inside the heat exchanger coil pipe 56. The heated water inside the heat exchanger coil pipe 56 may be fed to an external device 58, such as an evacuated tube solar collector. In other embodiments of the invention, the tubular element may be further inclined so that the first tubular connector 42 is inclined relative to a horizontal plane between two corners of the tubular element and that the second tubular connector 44 is inclined relative to a horizontal plane between another two corners of the tubular element. In this way, one corner of the tubular element is lower than the other corners of the tubular element. As a result, the direction of the fluid flow(s) in the tubular element is not perpendicular to the direction of ambient air (such as due to natural convection or intermittent wind energy). This effectively creates a semi-crossflow between the fluid flow(s) and the ambient air that enhances the cooling of the fluid inside the heat exchanger 30. In an alternative embodiment shown schematically in Figure 4, the heat exchanger 30 comprises two tubular elements that are fluidly interconnected with each other, where the tubular elements are arranged side-by-side. Each tubular element of Figure 4 is structurally and functionally similar to the tubular element of Figure 1, except that the tubular elements share a common fluid inlet 36, a common fluid outlet 38 and a common vent 64. Preferably each tubular element is inclined so that one corner of the tubular element is lower than the other corners of that tubular element. In such an embodiment, the common fluid inlet 36 and the common fluid outlet 38 may be arranged at or towards the lowest corner of each tubular element. The first and second tubular connectors 42,44 and the fluid distribution pipe 50 may be formed to be V-shaped. The fluid outlet 38 is preferably formed at or towards the base 60 of the V-shaped first tubular connector 42. The fluid inlet 36 is preferably formed at or towards the base 62 of the V-shaped fluid distribution pipe 50. Optionally, in various embodiments, a capped vent 64 for venting the heat exchanger 30 may be located in the second tubular connector 44, such as shown in Figures 1 and 2, and such as the apex of the V-shaped second tubular connector 44. The capped vent 64 may include a valve that is operable to allow air bubbles to escape and to prevent dust from entering. The capped vent permits equalisation of the pressure levels of the first and second fluid flows 46,48 by exposing the first and second fluid flows 46,48 to atmospheric pressure. This increases the laminarity and decreases the 20 09 24 turbulency of the fluid flows 46,48, thus encouraging separation between the fluid flows 46,48 to prevent mixing. As shown in Figure 4, support stands 66 may be provided to hold steadily the heat 5 exchanger 30 where the first and second tubular connectors 42,44 are connected. The tubular element is shaped preferably as a hexagon, more preferably as an elongated hexagon. 10 A fluid retention element in the form of cotton gauze 68 is tightly wrapped around the elongate tubular pipe 40 (Figure 5). By stretching the cotton gauze 68, its pores become finer so that the capillarity is increased. The purpose of the cotton gauze 68 is to retain water so as to form a film of water around the outer surface of the elongate tubular pipe 40. 15 Distilled water is supplied to the cotton gauze 68 from a distilled water source. This in turn results in the cotton gauze 68 forming the film of distilled water around the elongate tubular pipe by way of adhesion, gravity and diffusion. Other types of fluidabsorbent fabric materials may be used in place of the cotton gauze 68. 20 The cotton gauze 68 has high capillarity that allows the distilled water to flow from the elongate tubular pipes 40 to the rest of the cotton gauze 68. In addition, the meshed structure of the cotton gauze 68 facilitates the formation of a large film of distilled water on the outer surface of the elongate tubular pipes 40 while providing a reduced 25 surface contact area relative to its surroundings, thus beneficially reducing dust deposits. Even if dust deposits were to form on the cotton gauze 68, the cotton gauze 68 can be easily dried by the sun and cleaned by wind. As a result, the cotton gauze 68 is less prone to dust deposits that can limit the evaporative cooling effect. Moreover, the flexibility of the cotton gauze 68, as well as the cotton gauze 68 being 30 tightly wrapped around the elongate tubular pipes 40, enables the cotton gauze 68 to withstand strong winds. Figure 5 shows a capillary pipe 70 that is located at an upper end of an elongate tubular pipe 40. The capillary pipe 70 supplies distilled water onto an elongate tubular pipe 35 40 at or near the second end 34 of the tubular element. A capillary rope 7lis axially threaded through each capillary pipe 70 at one end and is in contact with the cotton gauze at the other end. An internal diameter of each capillary pipe 70 may be exactly 20 09 24 or about 2mm. Preferably the capillary ropes 71 are made out from cotton or synthesis crave yarn. Figure 6 shows a series of capillary pipes 70, each of which is for supplying distilled 5 water onto respective elongate tubular pipes 40 at or near the second end 34 of the tubular element. The capillary pipes 70 are connected to a common fluid conduit 72 that is located above the second end 34 of the tubular element. The common fluid conduit 72 may be connected to a distilled water source, which may be a small horizontal cylindrical tank 74 (or other storage tank), and the small horizontal 10 cylindrical tank 74 may be supplied with distilled water from a tank 76, where the supply of water is controlled by a pump 78, which in turn is controlled by a controller 150 (as schematically illustrated in Figure 7). The capillary pipes 70 are connected and spaced apart along a length of the common fluid conduit 72 between the first and second ends. By capillary force, relatively equal amounts of distilled water flow out of 15 the capillary pipes 70. Figure 6 shows that the series of capillary pipes 70 are connected to a V-shaped pipe, but other shaped pipes are envisaged. The distilled water flows continuously over and across the capillary pipes 70 because distilled water does not contain salts that could clog the capillary pipes 70. 20 Preferably the capillary pipes 70 and the common fluid conduit 72 are made from coextruded crosslinked polyethylene composite ("pex-al-pex") material. Figure 8 illustrates an evaporative cooling process carried out using the heat exchanger 25 30. Due to the ambient temperature around the heat exchanger 30 being cooler than the temperature of the hot water of the first fluid flow 46 inside the elongate tubular pipes 40, heat from the hot water is transferred through the walls of the elongate tubular pipes 40 to the surrounding environment. The thin film of distilled water on the outer surfaces of the elongate tubular pipes 40 enhances the transfer of heat 30 through evaporative cooling. When the thin film of distilled water absorbs heat energy from the hot water inside the elongate tubular pipes 40 by conduction and from ambient heat by convection, evaporation of water molecules takes place. Consequently, a hot humid layer 80 is 35 formed around the elongate tubular pipes 40, and the humid layer 80 moves upwards by natural convection, thereby leaving a volume of low-pressure air around the elongate tubular pipes. The volume of low-pressure air is then displaced by a volume of high-pressure air 82 from the ambient environment. Heat is thus removed from the 20 09 24 hot water inside the elongate tubular pipes and dispersed into the environment, while cool dry air flows towards the elongate tubular pipes to continue the evaporative cooling process. The evaporation cooling process may also be enhanced by intermittent wind 84, especially during night-time. 5 In an exemplary scenario, for several hours after sunset, the ambient environment in the vicinity of the heat exchanger 30 is heated by the release of solar radiation absorbed by the underlying surface during the day. This may cause the outer surface of the heat exchanger 30 to dry out by convection and radiation, thus increasing 10 distilled water consumption. Delaying the evaporation process by several hours after sunset, for instance by about three hours after a 7 pm sunset, therefore reduces distilled water consumption. Thus, the evaporative cooling process is most efficient at night-time, i.e., from about 10 pm till about 7 am the following morning. The temperature surrounding the heat exchanger 30 reaches a night-time wet bulb 15 temperature, which may be in the range of 14°C to 16°C. Consequently, the temperature of the water inside the heat exchanger 30 is lowered to approximately 6°C to 7°C above the wet bulb temperature, i.e., in the range of 20°C to 23°C. Since the sun rises early in the summer, it is preferable to shield the heat exchanger from direct sunlight from the time of sunrise until the end of the evaporative cooling process 20 at around 7 am in order to enable the evaporative cooling process to gain from the cold and dry morning air. Although evaporative cooling may be slow or may provide a relatively low amount of cooling at any given moment in time, the overnight duration of the evaporative cooling process is sufficient to provide the required overall cooling. 25 As shown in Figure 8, experiments carried out by the inventors show that the heat exchanger 30 cools down the water in the cold water storage tank by as much as 15-16°C in comparison to the water in a control cold water storage tank that is cooled down by only 1.5-1.65°C without the heat exchanger 30. 30 The heat exchanger 30 may be placed on a flat stand on an inclined building roof or may be placed on an inclined stand on a flat building roof. Alternatively, the heat exchanger 30 may be placed on the ground instead of the roof. Insulating materials are located between the stand and the heat exchanger 30. The 35 minimum height of the stands is sufficiently high, preferably 80 cm, in order to not only protect the heat exchanger 30 from radiation due to heat absorbed by the surface underneath the heat exchanger 30 during daytime but also enable easy installation 20 09 24 and removal of the cotton gauze 68 in accordance with cooling and heating requirements. The lengthwise incline ratio (also known as slope ratio) of the elongate tubular pipes 5 40 is selected to enhance the fluid flow inside the heat exchanger 30 by natural convection and also it assists the flow of distilled water onto the elongate tubular pipes 40 by gravity. Preferably the lengthwise incline ratio of the elongate tubular pipes 40 is exactly or approximately 15:100. 10 The widthwise incline ratio of the elongate tubular pipes 40 is selected to allow the hot water to easily flow upwards towards the capped vent to allow air bubbles to escape, assist the movement of the second fluid flow 48 towards the fluid outlet 38, and increase the surface area of the heat exchanger 30 that is exposed to wind to enhance the evaporative cooling process. Preferably the widthwise incline ratio of the elongate 15 tubular pipes 40 is exactly or approximately 4:100. Figures 9 to 13 illustrate fluid flow systems that can be used in water cooling and heating applications. Exemplarily the fluid flow system is used to cool down water in the summer and heat up water in the other seasons. The system is especially suitable 20 for single-family homes in hot and dry regions. in Figures 9, 10 and 11, the fluid flow system comprises the heat exchanger 30 and a fluid circulation conduit 86 that can be used in combination in a closed-loop water cooling application, so that, in use, fluid may be circulated through the heat exchanger 25 30 and the fluid circulation conduit 86 in a loop. The heat exchanger 30 is preferably installed on a roof of a building, due to the wind current not being hampered by walls and trees, but may be installed on the ground in other embodiments. As shown in Figure 10, a fluid flow controller in the form of a pump 88, e.g. a low flow 30 rate pump, is optionally connected between the fluid circulation conduit 86 and the fluid inlet 36 of the heat exchanger 30. In use, the pump 88 is operable to control a flow rate of hot water from the fluid circulation conduit 86 to the heat exchanger 30 so as to enable laminar flow of the first and second fluid flows 46,48 inside the heat exchanger 30. The fluid outlet 38 is connected to the fluid circulation conduit 86 to 35 return cooled water from the heat exchanger 30 to the fluid circulation conduit 86 which may take place by gravity and / or pumping. In this way water circulates between the heat exchanger 30 and the fluid circulation conduit 86. 20 09 24 The fluid circulation conduit comprises radiant floor pipe loops 90 that extend through a floor 92 of the building, which may be a concrete slab. Water is pumped through the radiant floor pipe loops 90. Preferably, a slow flow rate pump is used. The cold water flowing through the radiant floor pipe loops 90 is used for space cooling of the interior 5 of the building by absorbing heat. The warmed up water flowing through the radiant floor pipe loops 90 is then returned to the heat exchanger 30. The temperature of the cold water is typically around 20°C, which is a comfortable temperature for cooling rooms. At the same time, the temperature of the cold water is high enough to prevent condensation on the floor, especially in arid regions where air humidity is low. The 10 radiant floor pipe loops 90 provide a large surface area, thus enhancing the heat exchange and therefore cooling. The cooling effect can be further enhanced by use of a ceiling fan, and the possibility of floor condensation is diminished. As shown in Figure 11, in daytime (e.g. from 7am to 7 pm), the flow of water to and 15 from the heat exchanger 30 may be stopped. As shown in Figure 10, the capped vent 64 in the second tubular connector 44 is optionally connected to a drain back water tank 94, which allows water to be drained from the heat exchanger 30 into the drain back water tank 94 in order to protect the 20 heat exchanger from freezing during severe cold conditions. The drain back water tank 94 is preferably installed inside the building. When the ambient temperature reaches the freezing point, an ambient temperature sensor 96, installed outside the building, sends a signal to a controller 200. The 25 controller 200 in turn sends a signal to switch on a valve 98 placed between the fluid circulation conduit 86 and the drain back water tank 94. When the ambient temperature rises above the freezing point, the drain back water tank 94 is discharged by closing the valve 98 and switching on a pump 100 to refill the heat exchanger 30 through the connecting pipe 102. The connecting pipes 102,104 are substantially 30 parallel, and extend upwards from the drain back water tank 94. The drain back water tank 94 can also be used to empty the heat exchanger 30 during regular maintenance. The drain back water tank 94 also allows repositioning of the heat exchanger 30 towards sunlight when it is used as a solar collector during colder seasons. 35 Alternatively, the fluid flow system may comprise the heat exchanger 30 and a cold water storage tank that can be used in combination in a closed-loop water cooling application. The cold water storage tank is preferably installed inside the building. The cold water storage tank is exemplarily made out of an aluminum plate or sheet lined 20 09 24 with a plastic layer or pex-al-pex material, and is preferably enclosed by insulating material. The aluminium plate or sheet is strong enough to withstand constant and relatively low head pressure. The water inside the cold water storage tank is preferably treated water. 5 Such fluid flow systems may include an internal heat exchanger that extends inside and through the cold water storage tank. Water inside the internal heat exchanger is physically separated from water inside the cold water storage tank. Warm water is brought to the internal heat exchanger via a warm water feed pipe and is cooled while 10 flowing through the internal heat exchanger via heat exchange with the water stored in the cold water storage tank. The cooled water flows out of the internal heat exchanger and can then be used for domestic use or consumption. In an alternative configuration of the fluid flow system shown in Figure 12, the fluid 15 circulation conduit in the form of an internal heat exchanger 86 may extend inside and through the cold water storage tank 106, where a pump 88 is used to control the circulation of water between the heat exchanger 30 and the internal heat exchanger 86. Water inside the internal heat exchanger 86 is physically separated from water inside the cold water storage tank 106. Exchange of heat occurs between the water 20 inside the internal heat exchanger 86 and the water inside the cold water storage tank 106. The pump 88 transfers hot water from the internal heat exchanger 86 to the fluid inlet 36 of the heat exchanger 30, and cooled water is returned from the heat exchanger 30 to the internal heat exchanger 86. In this way water circulates between the heat exchanger 30 and the internal heat exchanger 86. 25 As shown in Figure 13, the pump 88 may be omitted from the alternative configuration of the fluid flow system shown in Figure 12. As previously described, the heated water inside the heat exchanger coil pipe 56 may 30 be fed to an external device. The heated water inside the heat exchanger coil pipe 56 is fed into an inlet of a fluid tube of an evacuated tube solar collector 58. The water inside the fluid tube is then further heated through operation of the evacuated tube solar collector 58. In this way the heat exchanger 30 is able to assist the heating of water by the evacuated tube solar collector 58. In such use, the fluid retention element 35 is removed from the heat exchanger 30 to allow exposure to sunlight because evaporative cooling is not required. 20 09 24 Preferably such heat assistance is carried out during cold periods and / or by tilting the heat exchanger 30 towards the sun. The heat exchanger 30 may be blackened to improve absorption of solar heat energy. A metal plate deck may be added to the underside of the heat exchanger 30 to increase its efficiency in reflecting back 5 unscattered solar radiation. The fluids flowing through the fluid flow system are typically treated water, distilled water, rainwater, and air. Flu id-carrying components, such as conduits and pipes, are preferably made from pex-al-pex material which confer numerous advantages, such 10 as prohibiting algae growth and withstanding bad weather. Pex-al-pex material is non-reactive and therefore suitable for all types of flowing fluids, and also easy to install. The fluid-carrying components of the fluid flow system should be insulated for best efficiency. 15 Algae growth on the heat exchanger 30 is eliminated because the evaporation cooling process takes place at night, and therefore without sunlight. Furthermore, during daytime, the temperature of the heat exchanger 30 rises up to 60°C due to sunlight exposure, whereas at night it sinks to the night-time wet bulb temperature, which is about or in the range of 15°C to 16°C. This wide temperature range prohibits growth 20 of microorganisms on the heat exchanger 30. Further still, intermittent wind interacting with the heat exchanger 30 prevents stable conditions which would be needed for algae growth. It also speeds up drying of the cotton gauze 68, thus further disrupting conditions needed for algae growth. 25 Corrosion of internal walls of pipes in the fluid flow system is prevented because the temperature is relatively low in both the cooling and heating configurations. Specifically, in the parts of the fluid flow system that carry cooled water, the highest temperature of the circulating water does not exceed 50°C. Although the temperature of the water inside the heat exchanger 30 during daytime in the summer may rise up 30 to about 60°C, the water is stagnant because the cooling system is not in operation. In the parts of the fluid flow system that carry hot water, the highest temperature of the circulating water does not exceed 60°C. Furthermore, the flow rate of the circulating treated water is low, for example approximately 2 litres per minute. Further still, because the water has been treated, it does not corrode aluminium, which is a 35 preferred material for the heat exchanger 30, the heat exchanger coil pipe 56 and the internal heat exchangers. 20 09 24 Saved rainwater may be suitable for use as distilled water for evaporation cooling if the amount of annually saved rainwater is enough to provide the required amount of water for evaporation cooling. Filtering may be used to remove leaves, large particles and / or suspended solid particles in the saved rainwater. A cartridge filter may be 5 provided to filter light / small particles in the rainwater prior to the rainwater entering the small horizontal cylindrical tank 74. The entire distilled water assembly may be removed or the supply of distilled water to the elongate tubular pipes 40 may be stopped when the heat exchanger 30 is used as 10 a passive water cooler that benefits from night-time coolness. This is because the thin film of distilled water is no longer required for evaporative cooling. The generated cold water might be suitable for showering because the cooled down water temperature is below human body's temperature. The cooling down process is described as follows: Tap water enters the cold water storage tank 106. When the sun rises, the pump 88 15 between the internal heat exchanger 86 and the fluid inlet 36 of the heat exchanger 30 is turned off. During day time, the water inside the heat exchanger 30 heats up. After a period of time (e.g. 3 hours) from sunset, the cooling process starts when the pump 88 is turned on to circulate water between the heat exchanger 30 and the internal heat exchanger 86. 20 Advantages of the invention include, but are not limited to: efficient water cooling and suitable heating; low cost and simple initial installation; easy to maintain and access; avoids legionella bacteria risk; little to no sound pollution; durable; weather-resistant; minimal or no moving parts; reduces the need for environmentally detrimental fossil 25 fuels and refrigerant gases; and reduces electricity bills. In particular, the heat exchanger 30 of the invention is more cost-efficient than conventional heat exchangers because: a) it saves time. The temperature difference between the heat exchanger 30 and the ambient is larger, thus enabling faster extraction of unwanted heat. Also, 30 the hot water reaches the heat exchanger 30 by crossing less distance and hence less time through the first end 32 rather than through the second end 34, and b) it is more efficient because the evaporation cooling process uses a thin film of water around the tubular pipes 40, which is not applicable to conventional heat 35 exchangers. In particular, the cooled distilled water flows from the second end 34 to the first end 32 in indirect contact counterflow with the first fluid flow 46 flowing from the first end 32 to the second end 34. Heat exchange through counterflow is more effective than heat exchange through parallel flow, which may be used in conventional heat exchangers. The heat exchanger and the fluid flow system according to embodiments of the 5 invention may be scalable to building size and / or building heating or cooling requirements. The listing or discussion of an apparently prior-published document or apparently prior-published information in this specification should not necessarily be taken as an 10 acknowledgement that the document or information is part of the state of the art or is common general knowledge. Preferences and options for a given aspect, feature or parameter of the invention should, unless the context indicates otherwise, be regarded as having been disclosed 15 in combination with any and all preferences and options for all other aspects, features and parameters of the invention. 20 09 24

Claims

20 09 241. A heat exchanger for use on an exterior of a building, the heat exchanger comprising a tubular element extending between a first end and a second end, wherein 5 the tubular element is configured to, in use, be inclined relative to a horizontal plane so that its second end is elevated above its first end, wherein the first end is configured to be, in use, inclined relative to a horizontal plane between two corners of the tubular element, wherein the second end is configured to be, in use, inclined relative to a horizontal plane between another two corners of the tubular element, wherein the io tubular element includes a fluid inlet, a fluid outlet and a capped vent, the fluid inlet for connection to a fluid source, the fluid outlet for connection to a fluid sink, the fluid inlet and fluid outlet arranged in the tubular element to, in use, enable a fluid flow to flow within the tubular element between the first and second ends, wherein the heat exchanger includes a fluid flow controller configured to, in use, control a first fluid flow 15 to flow from the fluid inlet and within the tubular element from one of the first and second ends towards the other of the first and second ends and control a second fluid flow to be formed from the first fluid flow by density variation so as to flow within the tubular element from the other of the first and second ends to the one of the first and second ends and towards the fluid outlet.

202. A heat exchanger according to Claim 1 wherein the fluid inlet and the fluid outlet are located at or towards a lowest of the corners of the tubular element.

3. A heat exchanger according to any one of the preceding claims wherein the 25 capped vent is located at or towards a highest of the corners of the tubular element.

4. A heat exchanger according to any one of the preceding claims wherein the fluid inlet and fluid outlet are arranged at the first end of the tubular element to, in use, enable a fluid flow to flow within the tubular element between the first and second 30 ends.

5. A heat exchanger for use on an exterior of a building, the heat exchanger comprising a tubular element extending between a first end and a second end, wherein the tubular element is configured to, in use, be inclined relative to a horizontal plane 35 so that its second end is elevated above its first end, the first end configured as a heat source in use, the second end configured as a heat sink in use, wherein the tubular element includes a fluid inlet, a fluid outlet and a capped vent, the fluid inlet for connection to a fluid source, the fluid outlet for connection to a fluid sink, the fluid inlet and fluid outlet arranged at the first end of the tubular element, wherein the fluid inlet 40 is at least partly axially extended inside the tubular element and is elevated above the20 09 24fluid outlet and the capped vent is arranged at the second end to, in use, enable a first fluid flow to flow from the fluid inlet and within the tubular element from the first end towards the second end and enable a second fluid flow to be formed from the first fluid flow by density variation so as to flow within the tubular element from the second end5 to the first end and towards the fluid outlet so that the first and second fluid flows move naturally as counterflows in direct contact with each other, wherein the heat exchanger includes a fluid flow controller configured to, in use, control the first fluid flow to flow from the fluid inlet and within the tubular element from the first end towards the second end and control the second fluid flow to be formed from the first 10 fluid flow by density variation so as to flow within the tubular element from the second end to the first end and towards the fluid outlet.

6. A heat exchanger according to any one of the preceding claims, wherein the tubular element includes a fluid distribution pipe and a tubular pipe, the fluid 15 distribution pipe connected to the fluid inlet, wherein the fluid distribution pipe includes a transfer pipe for transferring fluid from the fluid distribution pipe into the tubular pipe, wherein the transfer pipe is axially aligned with the tubular pipe and is arranged to penetrate the tubular pipe so that, in use, fluid flows directly from the fluid inlet into the tubular pipe.

207. A heat exchanger according to Claim 6 wherein an end of the transfer pipe isformed to have an inclined fluid diversion wall that extends into the fluid distribution pipe.25 8. A heat exchanger according to any one of the preceding claims wherein thetubular element is shaped as an elongated hexagon.

9. A heat exchanger according to any one of the preceding claims including a fluid retention element arranged on, above, under, beside or around an outer surface of the 30 tubular element, wherein the fluid retention element is configured to, in use, retain a fluid so as to form a film of fluid on, above, under, beside or around the outer surface of the tubular element.

10. A fluid flow system comprising a heat exchanger according to any one of the 35 preceding claims, a fluid source and a fluid sink, wherein the fluid inlet of the heat exchanger is connected to the fluid source, and the fluid outlet of the heat exchanger is connected to a fluid sink.

11. A fluid flow system according to Claim 10 including:20 09 24a. a fluid storage tank, wherein the fluid storage tank is connected to the fluid inlet so that, in use, at least part of the first fluid flow may flow into the heat exchanger from the fluid storage tank via the fluid inlet and / or wherein the fluid storage tank is connected to the fluid outlet so that, in use, at least5 part of the second fluid flow may flow into the fluid storage tank from theheat exchanger via the fluid outlet; orb. a fluid storage tank and a first internal heat exchanger, the first internal heat exchanger extending inside and through the fluid storage tank, the first internal heat exchanger configured so that, in use, a fluid inside the first10 internal heat exchanger may be physically separated from a fluid inside thefluid storage tank, wherein the first internal heat exchanger is connected to the fluid inlet so that, in use, at least part of the first fluid flow may flow into the heat exchanger from the first internal heat exchanger via the fluid inlet and / or wherein the first internal heat exchanger is connected to the15 fluid outlet so that, in use, at least part of the second fluid flow may flowinto the first internal heat exchanger from the heat exchanger via the fluid outlet.

12. A fluid flow system according to Claim 10 or Claim 11 including a second internal20 heat exchanger, wherein the second internal heat exchanger extends inside and through the tubular element, the second internal heat exchanger configured so that, in use, a fluid inside the second internal heat exchanger may be physically separated from a fluid inside the tubular element.

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