WO2015087035A1

WO2015087035A1 - Passive cooling system for wind tower

Info

Publication number: WO2015087035A1
Application number: PCT/GB2014/052263
Authority: WO
Inventors: Ben Hughes; John CALAUTIT; Hassam CHAUDHRY
Original assignee: University Of Leeds
Priority date: 2013-12-09
Filing date: 2014-07-24
Publication date: 2015-06-18
Also published as: GB201321709D0; GB201610893D0; GB2536164A; GB2536164B

Abstract

A passive cooling system for installation in a wind tower for a building, a wind tower for a building, a building comprising one or more wind towers and a method of retrofitting a wind tower with a passive cooling system are described. The passive cooling system includes a roof section configured to be placed over the top of the wind tower, the roof section having an upper surface and a lower surface. The system also includes a plurality of elongate heat pipes extending downwardly from the lower surface of the roof section for insertion into a duct of the wind tower.

Description

PASSIVE COOLING SYSTEM FOR WIND TOWER

FIELD OF THE INVENTION This invention relates to a wind tower for a building.

BACKGROUND OF THE INVENTION

Wind towers are structures that have long been used for providing natural ventilation and cooling for buildings, especially in regions having hot climates.

Typically, a wind tower is provided on the roof of a building, and includes an inlet for receiving a flow of air which is then directed to the interior of the building by a duct located within the tower itself. Typical heights of known commercial wind towers are in the range 1- 2 m, with the inlet being provided at the top of the tower. Placing the inlet at this elevated position can allow the tower to receive a relatively clean flow of air and also allow the tower to receive a flow of air that is not inhibited by surrounding structures such as neighboring buildings. Wind towers commonly include multiple inlets which face in separate directions, so that the tower is able to operate effectively even if the direction of the prevailing winds changes. Each inlet can be connected to its own respective duct within the tower. In these types of wind tower, a leeward and side facing inlet can act as an outlet, forming a return path for stale air to exit the building. In an example of a wind tower having multiple inlets, a four sided tower can be provided that is square in cross section, with an inlet provided on each side. In some cases (commercial wind towers), the inlets are provided with louvers, which can serve to inhibit the entrance of dust, sand or other materials into the building. The louvers can also be used to direct the air entering the tower, thereby to optimize the direction of airflow within the duct itself.

Some wind tower systems are provided with passive cooling. This can involve directing the flow of air received by the tower through underground cooling tunnels or over moist surfaces before entering living spaces in the building interior. However, passive cooling in this way can inhibit the circulation of air, reducing ventilation. Oftentimes, wind tower systems are not provided with passive cooling of this kind and act primarily to ventilate the building interior. The most common traditional wind towers are the Malkaf and the Badgir wind tower

(for a description of these, see a journal article by Hughes BR, Calautit JK and Ghani SA entitled "The development of commercial wind towers for natural ventilation: a review", published in Applied Energy 2012; 92:606-27). In hot and dry regions such as the Middle East, there is a large dependence on electricity to run mechanical systems for providing ventilation and thermal comfort. Increasing focus on reducing energy consumption has raised public awareness of renewable energy resources, particularly the integration of natural ventilation devices in buildings such as wind towers.

A known type of passive cooling device is the heat pipe. Heat pipes operate on the evaporation-condensation phenomena, and do not have moving parts. A heat pipe can be gravity-assisted or can include a wick material. Typically, a heat pipe can comprise a hollow elongate body containing a phase change material such as water. Water evaporating within the heat pipe spreads toward a cold end of the pipe, where it condenses. As it condenses, the water vapour gives up the heat it acquired during evaporation. The condensed water then returns to the opposite end of the pipe to complete the cycle.

The possibility of including heat pipes in a wind tower to provide passive cooling is described in a journal article by Calautit JK, Chaudhry HN, Hughes BR and Ghani SA entitled "Comparison between evaporative cooling and a heat pipe assisted thermal loop for a commercial wind tower in hot and dry climatic conditions", published in Applied Energy, vol. 101, pp.740-755, 2013. See also a journal article by Hughes BR, Chaudhry HN and Calautit JK entitled "Passive energy recovery from natural ventilation air streams", published in Applied Energy, vol. 113, pp.127-140, 2014.

EP 1,785,675 Al describes a ventilation arrangement for ventilating a building interior which comprises first and air duct arrangements which extend in use from roof level to an interior on a building to be ventilated to convey air between the exterior and the interior of the building. The ventilation arrangement further includes ventilation openings which are arranged to direct moving air caused by wind movement through the first air duct arrangement into the building interior and a fan which is operable to convey air between the exterior and interior of the building through the second air duct arrangement. The ventilation arrangement includes a photovoltaic arrangement, desirably in the form of a photovoltaic panel, for providing electrical energy to the fan to operate the fan.

WO 2012/080736 Al describes a natural ventilator for a building having a plurality of vent blades that define a stack of louvers. The vent blades are capable of movement in a vertical direction between an extended configuration in which the blades are spaced apart from one another and a collapsed configuration in which the blades are brought together to reduce the space between them in the vertical direction to prevent rain and noise ingress when the ventilator is not in use.

WO 2009/138768 Al describes a natural ventilator for a building configured to supply optimum rates of fresh air into a building interior. The ventilator is optimised with regard to spacing between vent blades of the louver and the angle of inclination of each blade relative to a horizontal plane.

US2007224929A describes a solar roof-ventilating device for compulsorily generating the flow of indoor and outdoor air that includes a hollow ventilating casing provided on the roof to communicate the inside and outside of the roof with each other. The interior of the ventilating casing is provided with a heat dissipator constituted of a plurality of heat-dissipating pieces. A plurality of heat-conducting pipes penetrates through the heat dissipator. The other end of the heat-conducting pipe is connected to a heat absorbing plate made of heat-absorbing materials. The front of the heat-absorbing plate is coated with a layer of black coating to facilitate the heat-absorbing speed of the heat-absorbing plate. Therefore, after the heat-absorbing plate has absorbed the solar energy, the heat can be conducted to the heat dissipator via the heat-conducting pipe. In this way, the temperature of the heat dissipator increases to generate a rising hot air, thereby to compulsorily cause the flow of the indoor air and achieve the ventilating effect. US2013196587A describes a louver arrangement for a ventilation arrangement.

US2013273828A describes a ventilation arrangement housing which has an upper curved guide member and a cruciform arrangement of divider plates to define the housing into quadrants. Air may enter and exit the housing via a louver arrangement.

WO12010823A1 describes a housing for a ventilation arrangement.

EP2292985A2 describes a ventilation arrangement for ventilating the interior of a building. The arrangement includes a duct extending to above the roof of the building. The duct is square in cross section and is divided into four quadrants by internal vertical divider plates. A louver arrangement is provided on each side of the upper part of the duct to receive air into the building on a windward side of the duct, and to expel air from a leeward side of the duct.

SUMMARY OF THE INVENTION

Aspects of the invention are set out in the accompanying independent and dependent claims. Combinations of features from the dependent claims may be combined with features of the independent claims as appropriate and not merely as explicitly set out in the claims.

According to an aspect of the invention, there is provided a passive cooling system for installation in a wind tower for a building. The system includes a roof section configured to be placed over the top of the wind tower. The roof section has an upper surface and a lower surface. The system also includes a plurality of elongate heat pipes extending downwardly from the lower surface of the roof section for insertion into a duct of the wind tower.

A passive cooling system according to the claimed invention can allow a wind tower to be retrofitted so that it can provide enhanced cooling of a flow of air entering a building. The provision of a cooling system having plurality of elongate heat pipes that extend downwardly from a lower surface of a roof section can allow the system conveniently to be installed in an existing wind tower by lowering it over the tower so that the heat pipes are inserted into a duct of the wind tower. According to another aspect of the invention, there is provided a wind tower for a building. The wind tower includes an inlet. The wind tower also includes a duct for delivering a flow of air received at the inlet to an interior space of the building. The wind tower further includes a roof section located at the top of the wind tower. The roof section has an upper surface and a lower surface. The wind tower also includes a plurality of elongate heat pipes located in the duct of the wind tower and extending downwardly from the lower surface of the roof section.

A wind tower according to the claimed invention may be constructed by retrofitting an existing wind tower with a passive cooling system, or may alternatively be provided as a new wind tower incorporating roof section with downwardly extending heat pipes for installation in a building. The downwardly extending orientation of the heat pipes can allow a phase change material in the heat pipes to fall to a lower end of the pipes under gravity. A wind tower according to the claimed invention can allow the heat pipes conveniently to be accessed for maintenance, for example through an opening in the roof section or by lifting out the roof section to expose the pipes. To this end, in some embodiments, the roof section can be detachable from the top of the wind tower.

In some embodiments, the roof section can include a cold sink. Provision of the cold sink in the roof section allows for ease of access to working components of the cold sink for maintenance, since the roof section is located at the top of the wind tower and is thus not obscured by other feature of the tower or building on which the tower may be located.

An upper end of each heat pipe can be in thermal contact with the cold sink. By keeping the upper ends of the heat pipes at a reduced temperature, the cooling power of the heat pipes in the duct can be enhanced. The cold sink itself can include a tank containing a coolant, for example, water. The upper end of each heat pipe can be located within the tank to make thermal contact with the coolant. The cold sink can operate a cooling cycle to maintain the temperature of the coolant. The cooling cycle can be powered by a solar panel, which itself can be located on the upper surface of the roof section.

The heat pipes can be arranged in a plurality of rows. The heat pipes in each row can be regularly spaced, and can be coextending so that they are substantially parallel with each other and with the heat pipes in a neighbouring row.

The heat pipes in each row can be offset with respect to the heat pipes a neighbouring row. This configuration can allow a flow of air to pass effectively over each heat pipe in the system without the heat pipes in a given row being obscured by heat pipes in a neighbouring row. In one example, the amount of the offset can be approximately equal to 0.5d_pi_pe, where dpipe is a spacing between adjacent heat pipes within each row.

A spacing d_row between each row, measured from the centres of the heat pipes, can be given by 0.8D < d_row≤ 1 -2D, where D is a diameter of the heat pipes. A spacing d_pi_pe between adjacent heat pipes within each row, measured from the centres of the heat pipes, can be given by 2.3 < d_pi_pe < 2.7. In some embodiments, a spacing d_row between each row, measured from the centres of the heat pipes, is approximately equal to D, and a spacing d_Pj_pe between adjacent heat pipes within each row, measured from the centres of the heat pipes, is approximately equal to 2.5D. The heat pipes can be arranged into a plurality of groups. In one embodiment, a wind tower having a plurality of inlets for receiving a flow of air from a plurality of respective directions and a plurality of ducts for delivering the flow of air received at each respective inlet to the interior space of the building can be provided with heat pipes grouped within each respective duct. In this way, the tower can provide cooling of a flow of air entering the building irrespective of the direction of the prevailing winds. For a given kind of existing wind tower, a passive cooling system can be provided having groups of heat pipes arranged to be compatible with the configuration (e.g. size and layout) of the ducts of the tower. This allows retrofitting of a wind tower having multiple ducts, allowing the retrofitted wind tower to provide cooling of a flow of air entering the building irrespective of the direction of the prevailing winds.

Louvers can be provided at the inlet or inlets of the wind tower for adjusting a direction of the flow of air received at the inlet. For example, the louvers can direct air flow over the heat pipes.

In some embodiments, adjustable dampers can be located at a lower end of the duct or ducts of the wind tower for adjusting a volume and/or direction of airflow into the interior space of the building. According to a further aspect of the invention there can be provided an array of heat pipes for a passive cooling system for a wind tower. The array includes a first row of regularly spaced, coextending heat pipes. The array also includes a second row of regularly spaced, coextending heat pipes. The heat pipes in the first row are substantially parallel to the heat pipes in the second row. The heat pipes in the first row are laterally offset with respect to the heat pipes in the second row.

As noted above, offsetting the heat pipes can allow a flow of air to pass effectively over each heat pipe in the system without the heat pipes in a given row being obscured by heat pipes in a neighbouring row. As noted above, the amount of the offset can be approximately equal to 0.5dpj_pe.

In one embodiment, the array can have exactly two rows of heat pipes. Adding a third row of heat pipes to the array can overly restrict a flow of air across the pipes.

The spacings d_row and d_Pi_pe can take the values noted above (0.8D < d_r0w≤ 1-2D; 2.3 < dpipe < 2.7). In one embodiment, as noted above, the spacing d_row can be approximately equal to D and the spacing d_pi_pe can be approximately equal to 2.5D.

According to another aspect of the invention, there can be provided a passive cooling system comprising an array of heat pipes of the kind described above.

According to a further aspect of the invention there can be provided a wind tower comprising an array of heat pipes of the kind described above.

According to another aspect of the invention, there is provided a building comprising one or more wind towers of the kind described above. According to a further aspect of the invention, there is provided a method of retrofitting a wind tower with a passive cooling system. The method includes lowering a passive cooling system of the kind described above over the wind tower to insert the elongate heat pipes into a duct of the wind tower and to place the roof section over the top of the wind tower.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will be described hereinafter, by way of example only, with reference to the accompanying drawings in which like reference signs relate to like elements and in which:

Figures 1A and IB show external views of a wind tower in accordance with an embodiment of the invention;

Figure 2 shows a building having a wind tower in accordance with an embodiment of the invention;

Figure 3 shows a passive cooling system for a wind tower, and a wind tower in accordance with an embodiment of the invention;

Figure 4 shows a cut away view of a wind tower in accordance with an embodiment of the invention;

Figure 5 shows a cut away view of a wind tower in accordance with an embodiment of the invention;

Figure 6 shows a cut away view of a heat pipe that can be used in a wind tower in accordance with an embodiment of the invention;

Figure 7 schematically illustrates a wind tower in accordance with an embodiment of the invention;

Figure 8 shows the layout of an array of heat pipes that can be used in a passive cooling system for a wind tower in accordance with an embodiment of the invention, and

Figures 9A and 9B illustrate the cooling effect of a wind tower in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

Embodiments of the present invention are described in the following with reference to the accompanying drawings.

Embodiments of this invention can provide wind towers for buildings that, in addition to providing conventional ventilation, can also provide enhanced cooling of air entering an interior space of the building. In some examples, the wind tower may be provided as a complete unit including an inlet and one or more ducts for delivering a flow of air to the interior space, as well as a roof section that is located at the top of the wind tower from which a plurality of heat pipes extend into the duct(s). However, it is also envisaged that a passive cooling system can be provided that includes a roof section and a plurality of elongate heat pipes that extend from a lower surface of the roof section. This passive cooling system can be used to retrofit existing wind towers to provide them with passive cooling. A method of performing this retrofitting of existing wind towers is also envisaged.

Figures 1A and IB show external views of a wind tower 10 in accordance with an embodiment of the invention. The wind tower 10 in this example is square in cross-section and has four sides. It is envisaged that wind towers according to this invention may have a different number of sides (for example, the wind tower may be triangular, hexagonal, octagonal, etc.). The wind tower 10 has a base 6. The base 6 can be provided with features for attaching the wind tower 10 to the roof or other surface of a building. The base 6 can be dimensioned to increase the overall height of the wind tower 10 in accordance with design requirements.

The wind tower also includes one or more inlets 4. An inlet 4 can be provided on each side of the wind tower 10. Accordingly, in the present example the wind tower 10 has four separate inlets 4. In other examples, a wind tower may be provided with fewer inlets that the number of sides of the tower, so that only some of the sides of the tower have inlets.

The inlets 4 are provided to receive a flow of air that is then directed by the wind tower 10 to the interior of a building. By providing a plurality of inlets 4, each inlet 4 facing in a respective direction, the wind tower 10 can operate to deliver the flow of air to the building interior irrespective of the prevailing wind direction. As will be described in more detail below, the inlets 4 can also act as outlets to form a return path for stale and/or warm air exiting the building. Also as described below, the inlets 4 can be provided with features such as louvers 8.

The wind tower 10 also includes a roof section 2. The roof section 2 is located at the top of the wind tower 10. The roof section 2 can be detachable from the wind tower 10 to allow access to the interior of the wind tower 10 or to allow access to the heat pipes described below. Accordingly, detachment of the roof section 2 can allow for maintenance or replacement of the features of the wind tower 10 and the cooling system incorporated within it.

The roof section 2 can be provided with a flange 16 that can rest against the upper end of ducts that are provided within the wind tower 10, thereby to seal the open ends of the ducts against a flow of air (other than through the inlets 4) and to ensure secure positioning of the roof section 2.

The roof section 2 has an upper surface 12 and a lower surface 14. The upper surface 12 can provide space for receiving features such as a solar panel. The upper surface 12 can, in some examples, be sloped to prevent the accumulation of rain or other materials.

Figure 2 schematically illustrates the configuration of the wind tower 10 when it is installed in a building 40. The building 40 includes an interior space 42. The building 40 also includes a surface 44, which would typically be the roof of the building 40, upon which the base 6 of the wind tower 10 can be mounted.

As can be seen from Figure 2, the inlets 4 of the wind tower 10 lead to a number of respective ducts 30. In the example of Figure 2, two ducts are visible, namely the duct 30A and the duct 30B. Each duct 30 allows a flow of air received at a respective inlet 4 to be delivered down through the wind tower into the interior space 42 of the building 40. A partition section 32 can be provided within the wind tower 10 to define the interior volume of the ducts 30. In normal operation, a windward facing inlet 4 receives a flow of air which enters the corresponding duct 30 within the wind tower 10 and is directed into the interior space 42 of the building 40. Correspondingly, a leeward duct 30 (facing away from the incoming wind), would typically act as a return path for stale or warm air to exit the building 40. For more detail in this regard, see Figures 9A and 9B and the related description below.

Figure 2 also shows that the wind tower 10 includes heat pipes 20. These heat pipes extend downwardly from the lower surface 14 of the roof section 2. For example, the heat pipes 20 can have a substantially vertical orientation within the wind tower 10. The lateral location of the heat pipes 20 can, in some embodiments, be adjacent the inlets 4, thereby to receive and cool the flow of air received by the inlets 4 before it is delivered to the interior space 42. The heat pipes 20 can, in some examples, correspond in vertical dimension to the vertical dimension of the inlet 4, thereby to ensure that the majority of the air entering the inlet 4 is incident upon some part of the heat pipes 20.

As mentioned above, in some examples, the roof section 2 may be detachable. Also, in accordance with some embodiments of this invention, a passive cooling system 50 of which the roof section 2 is a part can be provided separately for installation in an existing wind tower. Figure 3 illustrates a passive cooling system 50 incorporating a roof section 2 and a number of heat pipes 20. The passive cooling system 50 is shown to be positioned over an existing wind tower (from which the original roof has been removed) to illustrate how this installation can be achieved. In particular, to install the passive cooling system 50 it can first be manoeuvred over a top of the wind tower 10 so that the heat pipes 20 that extend downwardly from the lower surface 14 of the roof section 2 are correctly aligned with the one or more ducts 30 of the tower 10. Then, the passive cooling system 50 can be lowered over the wind tower 10 so that the heat pipes 20 are inserted into the corresponding ducts 30. The lowering of the passive cooling system 50 in this way can continue until the roof section 2 is placed over the wind tower 10 to seal the open end of the ducts 30. Figure 4 is a bottom view revealing the interior of the wind tower 10, to illustrate the configuration of the ducts 30 and the layout of the heat pipes 20 that extend from the lower surface 14. In this example, the wind tower 10 has four ducts 30A, 30B, 30C and 30D. Each duct 30 is substantially triangular in cross-section. The ducts 30A, 30B, 30C and 30D are defined by the inner walls of the outer frame of the wind tower 10 and by a partition section 32 located within the wind tower 10. Although the example described herein illustrates the provision of substantially triangular ducts, it is envisaged that other shapes may be used. From Figure 4, it can be seen that the heat pipes 20 can be arranged into rows. In the present example, the heat pipes 20 are arranged into two adjacent rows. In other examples, only a single row of pipes 20 could be used. The use of more than two rows of pipes 20 is also envisaged, but may not be preferred as this can inhibit air flow across the array. The configuration of these rows will be described in more detail below in relation to Figures 7 and 8.

Figure 4 also illustrates that the heat pipes 20 can be arranged into a number of groups. In the present example, four groups of heat pipes 20 are provided. Each group of heat pipes 20 is located in a respective one of the ducts 30 of the wind tower 10. Accordingly, each group of heat pipes 20 is located to receive and cool air entering the wind tower 10 through a respective one of the inlets 4.

Figure 5 shows a cut-away view of the wind tower 10 which illustrates the flow of air as it enters the inlet 4 of the duct 3 OA. The local direction of air flow is indicated by the arrows labelled A, B and C in Figure 5. Initially, the flow of air A is incident upon the inlet 4 of the wind tower 10 and enters the duct 30A. In the present example, the inlet 4 is provided with louvers 8. These louvers 8 can be provided to redirect the air as it enters the inlet 4. For example, as shown in Figure 5, the louvers 8 in this embodiment direct the incident air upwards toward the lower surface 14 of the roof section 2. The air is incident upon the lower surface 14 in the general location indicated by the arrow labelled B in Figure 5 and is deflected from the lower surface 14 and partition section 32 downwards as shown by the arrow labelled C in Figure 5. The effect of this is to produce a steady flow of air that is forced downwards through the duct 3 OA and into the interior space 42 of the building 40. In some embodiments, adjustable dampers 36 can be provided at a lower end of the duct 30. These dampers 36 can be rotated to adjust the volume and/or direction of the flow of air as it enters the interior space 42. The dampers 36 may also be used to seal off the duct 30 completely (e.g. by rotating them through 90°). Figure 5 also illustrates the flow of air over the heat pipes 20. As air flows over the heat pipes 20 it is cooled and consequently the air entering the interior space 42 is somewhat cooler than the external air entering the inlets 4 of the wind tower 10.

Figure 6 illustrates an example of a heat pipe 20. Heat pipes 20 are a well-known device and the heat pipes used in accordance with embodiments of this invention can indeed be conventional. A heat pipe typically operates by absorbing heat at a first end and then emitting the absorbed heat at an opposite end. In accordance with the present invention, one or more heat pipes extend downwardly from the roof section 2. The lower ends 24 of the heat pipes 20 are therefore positioned to absorb heat from a flow of air within the duct 30, as the air enters the inlet 4.

Inside the heat pipe 20 there can be provided a phase change material such as water. The heat absorbed at the lower end 24 of the heat pipe 20 causes evaporation of the phase change material. The vapour within the heat pipe 20 then rises toward an upper end 22 of the heat pipe 20 where it recondenses back into the liquid state. The recondensed phase change material then falls down under the force of gravity to the lower end 24 of the heat pipe 20 to complete the cycle.

Referring now to Figure 7, it is illustrated that the heat pipes 20 can be arranged so that their upper ends 22 are in thermal contact with a cold sink 60. In this way, heat emitted by the upper ends 22 of the heat pipes 20 can be carried away from the heat pipes 20. The cooling power of the heat pipes 20 in accordance with embodiments of this invention is at least in part governed by the operating temperature at which the upper ends 22 of the heat pipes 20 is maintained.

In some examples, and as shown in Figure 7, the upper ends 22 of the heat pipes 20 are located within the cold sink 60 itself, to provide a good area of overlap for heat exchange.

In the present example, the cold sink 60 comprises a tank containing a coolant. The coolant can be, for example, water. The coolant can be maintained at a low temperature for carrying heat away from the upper ends 22 of the heat pipes 20 to maintain the upper ends 22 at a correspondingly low temperature thereby to enhance the cooling power of the heat pipes 20. Conventional refrigeration means can be provided to maintain the coolant within the tank at the low temperature noted above, and the cooling cycle can be powered by, for example, connection to mains electricity or alternatively by a renewable energy source such as a solar panel provided on the upper surface 12 of the roof section 2.

Figure 8 illustrates an example of the layout of the heat pipes 20 extending downwardly from the lower surface 14 of the roof section 2. As noted above, the heat pipes 20 can be arranged into an array having one or more rows. The heat pipes 20 in each row can be regularly spaced. In the example of Figure 8, two rows of regularly spaced heat pipes 26A and 26B are provided. It is envisaged that in some examples no more than two rows of heat pipes may be provided, since the addition of further rows can inhibit effective air flow across the heat pipes 20. The heat pipes 20 in each row can coextend with each other and can also coextend with the heat pipes 20 in the other row(s) in the array. In some examples, each of the heat pipes 20 in the array is parallel to each of the other heat pipes 20 in the array.

In some embodiments, the heat pipes 20 in each row can be offset with respect to the heat pipes in a neighbouring row. An example of this is illustrated in Figure 8 in which the heat pipes in the row 26A are offset with respect to the heat pipes 20 in the row 26B by an amount approximately equal to 0.5d_Pj_pe, where d_Pj_pe is the spacing between adjacent heat pipes within each row. In this way, the tendency for the heat pipes 20 in one of the rows to be obscured from the path of the incoming air by the heat pipes 20 in a neighbouring row can be minimised.

The spacing between the rows of heat pipes 20 (denoted by d_row)₅ as measured from the centres of the heat pipes 20, can be selected to enhance cooling in a flow of air passing across the array of heat pipes 20. In particular, it has been found that an inter-row spacing drow is optimally around 0.8-1.2 times the diameter D of the heat pipes themselves. Also, it has been found that the spacing d_pj_pe between adjacent heat pipes 20 within each row of heat pipes 20 is optimally around 2.3-2.7 times the diameter D of the heat pipes 20. An ideal layout for the heat pipes 20 in terms of cooling power has been found to be an array having two rows as shown in Figure 8, where d_pi_pe is approximately equal to 2.5D and the inter-row spacing d_row is approximately equal to diameter D of the heat pipes 20. It is noted that an array of heat pipes of this kind (having the above referenced offset and spacing parameters) can be employed in a wind tower having heat pipes that do not necessarily extend downwardly from the lower surface of a roof section. For example, the heat pipes could be located at a base of the wind tower 10, and may extend laterally across the ducts 30. The heat pipes in this kind of wind tower 10 can thus have a substantially horizontal orientation.

Figures 9A and 9B illustrates the cooling effect of a wind tower 10 of the kind described herein on air entering an interior space 42 of a building 40. In particular, Figures 9A and 9B show the results of CFD (computational fluid dynamics) simulations that show the temperature of air inside and outside a building 40, and within the wind tower 10 itself. The approximate calculated temperature as a function of position is represented using isobars (the temperatures associated with these isobars, which are generally in the region of 309K-318K, are also shown). Figure 9B is a close up view of the dashed area indicated in Figure 9A.

In this example, air (wind) enters the wind tower 10 from a direction indicated by the arrow labelled W from the surrounding environment 70. Initially, the air enters the wind tower 10 and passes over heat pipes 20 located in a first duct 30B. Having been cooled by the heat pipes 20, the air passes down through the duct 30B and enters the interior space 42 of the building 40 as shown by the arrow labelled B. The inlet 4 of the wind tower 10 facing in a leeward direction with respect to the prevailing wind (W) acts as an outlet for the return path of warm and/or stale air. Thus, as indicated by the arrow labelled A, stale and warm air can rise up through the duct 30 A and exit the wind tower 10 as shown at the position labelled 76.

The temperature of the air in the surrounding environment 70 is relatively high, it being assumed that the wind tower 10 may be used in a hot country. From Figure 9B it can be seen that the air entering the inlet 4 of the wind tower 10 is substantially cooled by the heat pipes 20 before passing through the duct 30B into the interior space 42. The air within the interior space 42 typically has a temperature which is somewhat lower than the temperature of the air in the surrounding environment 70. Warmer air within the interior space 42 tends to rise up through the leeward facing duct 30A (and/or a sideward facing duct) of the wind tower 10. As shown in Figure 9B, this air is still cooler than the air in the surrounding environment 70, but is somewhat warmer than the air entering the interior space 42 through the duct 30B. As the air rising up through the leeward facing duct 30 A passes over the heat pipes 20 in the duct 30 A it is substantially cooled. The cooling of this air is incidental however, since it then leaves the wind tower 10 through the leeward facing inlet 4.

The temperature difference between the air in the surrounding environment 70 and the air in the interior space 42 of the building 40 that can be achieved using an arrangement of the kind shown in Figure 9 has been calculated using the above-mentioned CFD models. The results of these simulations, which assume an external temperature of 318K, are summarised in Table 1 below.

Table 1 : Simulation results with the four-sided wind tower with heat pipe arrangement.

Typically, the temperature difference that is achievable depends on a number of external factors such as the external wind speed (see the velocity inlet speed column in Table 1). Typically, a greater cooling effect is achievable at lower wind speeds, since the contact time of air entering the wind tower against the heat pipes 20 is greater if the velocity of the flow of air is lower. Note that in table 1 , the diffuser supply velocity refers to the velocity of the flow of air passing down through the dampers 36 that can be provided in the wind tower 10.

Accordingly, there has been described a passive cooling system for installation in a wind tower for a building, a wind tower for a building, a building comprising one or more wind towers and a method of retrofitting a wind tower with a passive cooling system. The passive cooling system includes a roof section configured to be placed over the top of the wind tower, the roof section having an upper surface and a lower surface. The system also includes a plurality of elongate heat pipes extending downwardly from the lower surface of the roof section for insertion into a duct of the wind tower.

Although particular embodiments of the invention have been described, it will be appreciated that many modifications/additions and/or substitutions may be made within the scope of the claimed invention.

Claims

1. A passive cooling system for installation in a wind tower for a building, the system comprising:

a roof section configured to be placed over the top of the wind tower, the roof section having an upper surface and a lower surface; and

a plurality of elongate heat pipes extending downwardly from the lower surface of the roof section for insertion into a duct of the wind tower.

2. The passive cooling system of claim 1, wherein the roof section comprises a cold sink, and wherein an upper end of each heat pipe is in thermal contact with the cold sink.

3. The passive cooling system of claim 2, wherein the cold sink comprises a tank containing a coolant, and wherein the upper end of each heat pipe is located within the tank to make thermal contact with the coolant.

4. The passive cooling system of claim 2 or claim 3 comprising a solar panel located on the upper surface of the roof section for powering a cooling cycle of the cold sink.

5. The passive cooling system of any preceding claim, wherein the heat pipes are arranged in a plurality of rows, wherein the heat pipes in each row are offset with respect to the heat pipes a neighbouring row.

6. The passive cooling system of claim 5, wherein a spacing d_row between each row, measured from the centres of the heat pipes, is given by 0.8D < d_row≤ 1.2D, where D is a diameter of the heat pipes.

7. The passive cooling system of claim 5 or claim 6, wherein a spacing d_Pi_pe between adjacent heat pipes within each row, measured from the centres of the heat pipes, is given by 2.3 < d_Pi_pe < 2.7, where D is a diameter of the heat pipes.

8. The passive cooling system of claim 5, wherein a spacing d_row between each row, measured from the centres of the heat pipes, is approximately equal to D, and wherein a spacing d_pi_pe between adjacent heat pipes within each row, measured from the centres of the heat pipes, is approximately equal to 2.5D, where D is a diameter of the heat pipes.

9. The passive cooling system of any preceding claim, wherein the heat pipes are arranged into a plurality of groups, each group for insertion into a respective duct of a multidirectional wind tower.

10. A wind tower for a building, the wind tower comprising:

an inlet;

a duct for delivering a flow of air received at the inlet to an interior space of the building;

a roof section located at the top of the wind tower and having an upper surface and a lower surface; and

a plurality of elongate heat pipes located in the duct of the wind tower and extending downwardly from the lower surface of the roof section.

11. The wind tower of claim 10, wherein the roof section is detachable from the top of the wind tower to allow the roof section and heat pipes to be removed from the wind tower for maintenance.

12. The wind tower of claim 10 or claim 11, wherein the roof section comprises a cold sink, and wherein an upper end of each heat pipe is in thermal contact with the cold sink.

13. The wind tower of claim 12, wherein the cold sink comprises a tank containing a coolant, and wherein the upper end of each heat pipe is located within the tank to make thermal contact with the coolant.

14. The wind tower of claim 12 or claim 13 comprising a solar panel located on the upper surface of the roof section for powering a cooling cycle of the cold sink.

15. The wind tower of any of claims 10 to 14, wherein the heat pipes are arranged in a plurality of rows, wherein the heat pipes in each row are offset with respect to the heat pipes a neighbouring row.

16. The wind tower of claim 15, wherein a spacing d_row between each row, measured from the centres of the heat pipes, is given by 0.8D < d_row≤ 1.2D, where D is a diameter of the heat pipes.

17. The wind tower of claim 15 or claim 16, wherein a spacing d_Pj_pe between adjacent heat pipes within each row, measured from the centres of the heat pipes, is given by 2.3 < dpipe < 2.7, where D is a diameter of the heat pipes.

18. The wind tower of claim 15, wherein a spacing d_r0w between each row, measured from the centres of the heat pipes, is approximately equal to D, and wherein a spacing dpipe between adjacent heat pipes within each row, measured from the centres of the heat pipes, is approximately equal to 2.5D, where D is a diameter of the heat pipes.

19. The wind tower of any of claims 10 to 18 comprising a plurality of louvers at the inlet for adjusting a direction of the flow of air received at the inlet.

20. The wind tower of any of claims 10 to 19 comprising adjustable dampers at a lower end of the duct for adjusting a volume and/or direction of airflow into the interior space of the building.

21. The wind tower of any of claims 10 to 20 comprising:

a plurality of inlets for receiving a flow of air from a plurality of respective directions; and

a plurality of ducts for delivering the flow of air received at each respective inlet to the interior space of the building,

wherein the heat pipes are arranged into a plurality of groups, and wherein each group of heat pipes is located within a respective duct.

An array of heat pipes for a passive cooling system for a wind tower, the array comprising:

a first row of regularly spaced, coextending heat pipes; and

a second row of regularly spaced, coextending heat pipes; and wherein the heat pipes in the first row are substantially parallel to the heat pipes in the second row, and wherein the heat pipes in the first row are laterally offset with respect to the heat pipes in the second row.

The array of claim 22, wherein a spacing d_row between each row, measured from the centres of the heat pipes, is given by 0.8D < d_row≤ 1.2D, where D is a diameter of the heat pipes.

The array of claim 22 or claim 23, wherein a spacing d_Pj_pe between adjacent heat pipes within each row, measured from the centres of the heat pipes, is given by 2.3 < d_Pi_pe < 2.7, where D is a diameter of the heat pipes.

25. The array of claim 22, wherein a spacing d_row between each row, measured from the centres of the heat pipes, is approximately equal to D, and wherein a spacing d_Pi_pe between adjacent heat pipes within each row, measured from the centres of the heat pipes, is approximately equal to 2.5D, where D is a diameter of the heat pipes.

26. A passive cooling system comprising the array of heat pipes of any of claims 22 to 26.

27. A wind tower comprising the array of heat pipes of any of claims 22 to 26.

28. A building comprising one or more wind towers according to any of claims 10 to 21 or claim 27.

29. A method of retrofitting a wind tower with a passive cooling system, the method comprising lowering a passive cooling system according to any of claims 1 to 9 or claim 26 over the wind tower to insert the elongate heat pipes into a duct of the wind tower and to place the roof section over the top of the wind tower.

30. A passive cooling system substantially as hereinbefore described, with reference to the accompanying drawings.

31. A wind tower substantially as hereinbefore described, with reference to the accompanying drawings.

32. A building substantially as hereinbefore described, with reference to the accompanying drawings.

33. A method of retrofitting a wind tower, wherein the method is substantially as hereinbefore described, with reference to the accompanying drawings.

34. An array of heat pipes substantially as hereinbefore described, with reference to the accompanying drawings.