TECHNICAL FIELD

This invention relates to the utilisation of solar energy to induce ventilation. In particular, though not exclusively, this invention relates to a solar chimney for ventilating a building and a building having the solar chimney installed thereon.

BACKGROUND

Ventilation is the process of intentionally displacing the air inside a building (or structure) with outdoor air. It is necessary in buildings to avoid the build-up of pollutants, which can adversely affect human health and productivity. Furthermore, ventilation can provide other benefits such as the control of temperature, humidity and air motion within a building.

Broadly speaking, ventilation can be classified as mechanical (forced) or natural (passive). Mechanical ventilation is typically driven by fans. Natural ventilation is driven by pressure differences in different parts of a building arising from natural forces, for example due to wind or differences in temperature and/or humidity. Whilst mechanical ventilation can provide greater control over air quality, flow rate and temperature, natural ventilation is usually preferred since it is quieter, requires less maintenance and does not consume energy.

Solar chimneys (also known as thermal chimneys) are a type of natural ventilation system that utilise the sun’s energy to provide ventilation. Solar chimneys are generally vertical channels having a dark coloured, matt external surface designed to absorb solar energy. The absorbed solar energy warms air within the chimney causing it to rise. The rising air is vented out of the top of the chimney and in doing so draws more air into the chimney at the bottom. This creates a suction force at the chimney’s base, which is used to draw air through and ventilate the building below. There remains a need for improved solar chimneys that can provide enhancement of ventilation. It is an object of the invention to address at least one of the above problems, or another problem associated with the prior art.

SUMMARY OF THE INVENTION

A first aspect of the invention provides a solar chimney comprising: an inner channel bounded by an outer channel, the inner and outer channels being separated by an interior wall, wherein the outer channel comprises an exterior wall comprising a thermal panel to absorb solar heat to create a temperature differential between the interior wall and the exterior wall, the temperature differential facilitating airflow in the outer channel.

It has been found that in a solar chimney according to a first aspect of the invention, solar heat absorbed by the thermal panel can increase the temperature of the exterior wall relative to the interior wall. Within the outer channel, this can increase the temperature of air adjacent to the external wall relative to air adjacent to the interior wall, thereby reducing the density of air adjacent to the external wall (i.e. making it more buoyant). This can result in the air adjacent to the external wall rising above the cooler (and therefore more dense, i.e. less buoyant) air adjacent to the interior wall. This may advantageously drive air through the outer channel, thereby enhancing the rate of flow of air through the chimney.

In some embodiments, the outer channel comprises a constriction to draw air out of the outer channel through an outer opening. The presence of a constriction can increase air velocity due to the Venturi effect. The Venturi effect is the observed reduction in fluid pressure, and associated increase in fluid velocity, that results when a fluid flows through a constricted section of a channel. Hence, the presence of a constriction may further facilitate airflow in the outer channel.

Suitably, the thermal panel of the outer channel may taper towards the inner channel to define the constriction. Such an arrangement may simplify construction of the solar chimney. Suitably, the inner channel may be generally vertical and the outer channel may taper towards an upper end of the inner channel to define the constriction. In this way, the outer channel may become increasingly constricted towards an upper end of the outer channel. Thus, air flowing through the outer channel may be accelerated towards the upper end of the outer channel as a result of the Venturi effect. This can help draw air through the outer channel in a generally upwards direction, thereby helping to draw air into the outer channel from a space below the chimney, for example such as a building space.

In an embodiment, the outer opening may comprise a vent cover. The vent cover may advantageously allow airflow to be maintained through the outer opening, whilst protecting the outer channel from wind and rain ingress. The vent cover may, for example, may comprise one or more louvres (i.e. slats). Alternatively, or additionally, the vent cover may comprise a diffuser, ventilation grille or gravity flap.

In an embodiment, the thermal panel may comprise a phase change material (PCM). The PCM may be of any suitable type. A wide range of PCMs are known in the art. Such materials can be used to store solar heat by causing a change in the "state" or "phase" of the materials, for example from a solid to a liquid. In this way, the thermal panel can absorb solar heat during the day, and radiate it back out after sunset. This can allow the solar chimney to continue to provide ventilation through the evening and night-time.

By way of illustration, in a solid/liquid PCM, the heat applied to the PCM in a solid state is absorbed by the PCM resulting in an increase in the temperature of the PCM. As the temperature of the PCM reaches its phase change temperature, that is the temperature at which the PCM changes from a solid state to a liquid, the PCM stops increasing in temperature and "consumes" the heat being applied thereto and stores it as latent heat, until all the PCM has changed into a liquid. In reverse, as the PCM drops in temperature, the sensible heat which was consumed by the change to a liquid phase and stored as latent heat is released at the phase change temperature of the PCM as the PCM changes back into its solid state. Latent heat is the heat gained by a substance without any accompanying rise in temperature during a change of state. In essence, it is the amount of heat necessary to change a substance from one physical phase to another (more disordered), for example, the solid state to the liquid state. Once the PCM has completely changed to the more dis-ordered phase, for example a liquid state, the temperature of the PCM begins to rise again as the applied heat is now absorbed as sensible heat.

In various embodiments of the invention, the PCM may comprise an organic material. For example, the PCM may comprise paraffin or a paraffin-derived hydrocarbon, a carbohydrate, a lipid, or a mixture thereof. Non-limiting examples of suitable organic materials include n-tetradecane (C-14), n-hexadecane (C-16), and n-octadecane (C-18) and olefin.

Alternatively or additionally, the PCM may comprise an inorganic material such as an inorganic salt hydrate or eutectic material. Non-limiting examples of suitable inorganic materials include calcium chloride hexahydrate, glauber salt, Na ₂ SO ₄ .10H ₂ O, CaCI ₂ .6H ₂ O, NaHPO ₄ .12H ₂ O, Na ₂ S ₂ O ₃ .5H ₂ O and NaCO ₃ .10H ₂ O. Heat and Cold Storage with PCM, Mehling, H; Cabeza, L.F, (ISBN: 978-3-540- 68556-2) provides information on various PCMs and phase change temperatures.

In some embodiments of the invention, the thermal panel may comprise a high thermal mass material. High thermal mass materials are those having a capacity to absorb, store and release solar heat. Thus, like PCMs, high thermal mass materials may absorb solar heat during the day, and radiate it back out after sunset. Examples of high thermal mass materials include concrete, stone, plaster and ceramic. In a particular embodiment, the thermal panel may comprise a concrete block filled with a PCM.

In an embodiment, the inner channel comprises a turbine ventilator (i.e. turbine blower) exposed to the atmosphere for drawing air out of the inner channel. This may advantageously help to drive air through the inner channel, thereby increasing the rate of flow of air through the chimney. Suitably, the turbine ventilator may be arranged at an upper end of the inner channel.

The turbine ventilator may optionally comprise a rain shelter, to protect the turbine ventilator from wind and rain ingress, whilst at the same time allowing airflow to be maintained through the turbine ventilator. The rain shelter may, for example, comprise a canopy or cover.

In an embodiment, the interior wall may comprise a gap to allow air to flow between the inner and outer channels. In the event that too much heat builds up in the inner channel (resulting in a build up of pressure), the presence of a gap can allow air to escape from the inner channel into the outer channel so that it may exit the chimney, for example, through the outer opening.

Suitably, the gap may be located above a constriction in the outer channel.

In some embodiments, the gap may be controlled by a non-return damper or valve. This can permit the flow of air through the gap from the inner channel into the outer channel, but prevent backflow of air from the outer channel to the inner channel. Suitably, the gap may be controlled by a flipper.

In some embodiments, an upper end of the inner channel may comprise a light well. This can allow sunlight to enter the inner channel and travel through the solar chimney to provide natural lighting for a room or building space underlying the inner channel, thereby advantageously reducing the need for electric lighting.

The light well may suitably comprise glass. The glass may be double glazed and/or comprise low-emissivity (low-e) glass, to minimise any heat loss from the solar chimney through the light well. In some embodiments, the glass may be tempered or toughed to increase it’s strength. Suitably, an inner side of the interior wall may comprise a reflective surface to aid light transmission through the inner channel to a room or building space underlying the inner channel.

In various embodiments, a lower end of the inner channel may comprise a light diffuser for diffusing light into a room or building space underlying the inner channel. The presence of a light diffuser can further help to disperse the natural light entering the inner channel through the light well into the room or building space.

In some embodiments, the inner channel may be surrounded by the outer channel.

Suitably, the inner channel and the outer channel may be concentric. For example, the inner channel may sit (i.e. nest) within at least a portion of the length of the outer channel.

The inner channel and the outer channel may be of any suitable shape. For example, the inner channel and/or the outer channel may be generally cylindrical, rectangular, or square-shaped.

In some embodiments, a lower end of the inner channel may be sealed such that the inner channel provides a reservoir for receiving the exhaust (i.e. waste heat) from a mechanical ventilation system. In such embodiments, an upper end of the inner channel may advantageously comprise a turbine generator arranged to be driven by the exhaust air exiting the inner channel and generate electricity.

In embodiments where a lower end of the inner channel comprises a light diffuser, the light diffuser itself may suitably seal the lower end of the inner channel.

In some embodiments, the solar chimney may comprise a heat exchanger for cooling air in the outer channel, and the interior wall may comprise an inlet arranged to transfer at least a portion of the cooled air from the outer channel to the inner channel.

In this way, warm air drawn into the outer channel from a space below the solar chimney may be cooled by the heat exchanger, and at least a portion of the resulting cooled air may be directed through the inner channel back into the space below the solar chimney to provide cooling for the space. Thus, the solar chimney may advantageously provide enhancement of thermal comfort.

The term “warm air,” as defined herein, refers to air having an initial temperature (Ti) prior to being cooled by the heat exchanger. The term “cooled air”, as defined herein, refers to air cooled by the heat exchanger that has a second temperature (T ₂ ) lower in temperature than the initial temperature Ti.

In a particular embodiment, the heat exchanger may comprise a heat pipe. Heat pipes are passive heat transfer devices known in the art. Heat pipe based systems - Advances and applications, Jouhara, H; Chauhan, A; Nannou, T; Almahmoud, S; Delpech, B; Wrobel, L.C, (http://dx.doi.Org/10.1016/j.energy.2017.04.028) provides a comprehensive overview of heat pipe technology.

The heat pipe may suitably comprise a first end (i.e. an evaporator) and a second end (i.e. a condenser) connected by a capillary structure or wick. The heat pipe may suitably comprise a working fluid. The working fluid may, for example, comprise one or more of 1 ,1 ,1 ,2-tetrafluoroethane (Freon ^(RTM) R134a), paraffin and/or a paraffin-derived hydrocarbon, ammonia, and/or water. Additionally or alternatively, the working fluid may comprise a PCM, for example such as any PCM mentioned above as being suitable for the thermal panel.

When the first end of the heat pipe (i.e. the evaporator) is exposed to warm air, liquid-phase working fluid in the first end may turn to vapour by absorbing heat energy from the warm air, thereby cooling the warm air. The resulting vapourphase working fluid may then travel along the heat pipe to the second end (i.e. the condenser), which may be at a lower temperature than the first end, and condense back into a liquid, thereby releasing the absorbed (i.e. latent) heat from the second end of the heat pipe. Liquid-phase working fluid may then return to the first end of the heat pipe through the wick by capillary action.

In this way, when warm air is drawn into the outer channel from a space below the chimney, the first end of the heat pipe may absorb heat energy from the warm air, thereby cooling it. At least a portion of the resulting cooled air may then be transferred from the outer channel to the inner channel via the inlet in the interior wall and circulated back into the space below the solar chimney to provide a cooling air supply for the space.

Suitably, the first end (i.e. the evaporator) of the heat pipe may be located generally at or towards a lower end of the outer channel. In this way, the first end of the heat pipe may be conveniently positioned for cooling warm air entering the outer channel. In various embodiments, the first end of the heat pipe may be located in the outer channel in a position generally below (i.e. lower than) the thermal panel. This may help to reduce any interference of the cooled air with the temperature differential in the outer channel.

Suitably, the second end (i.e. the condenser) of the heat pipe may be located generally at or towards an upper end of the outer channel. In this way, the second end of the heat pipe may be conveniently positioned to release the absorbed (i.e. latent) heat near to where air exits the outer channel, allowing for more effective removal of the absorbed (i.e. latent) heat from the solar chimney.

In an embodiment, at least a portion of the heat pipe between the first and second ends may be generally located in the inner channel. This may advantageously save space in the outer channel and reduce any interference of the heat pipe with the temperature differential and/or with airflow in the outer channel. In various embodiments, the inlet may comprise and/or be controlled by one or more fans. The use of a fan (or fans) to control the inlet may help to maintain airflow in one direction from the outer channel to the inner channel. Suitably, the one or more fans may be solar powered. For example, the solar chimney may comprise one or more photovoltaic (PV) cells or panels for powering the one or more fans. In some embodiments, the one or more photovoltaic (PV) cells or panels may be mounted on the thermal panel.

In an embodiment, the outer channel may comprise one or more baffles or plates for directing at least a portion of the cooled air in the outer channel towards the inlet. This may advantageously increase the amount of cooled air transferred from the outer channel to the inner channel by the inlet.

In some embodiments, the inner channel may comprise one or more baffles or plates for directing airflow in the inner channel towards a lower end of the inner channel. Specifically, the inner channel may comprise one or more baffles or plates for directing the cooled air transferred to the inner channel from the outer channel via the inlet to a lower end of the inner channel. Thus, the one or more baffles or plates may help to direct the cooled air generally downwards into a space below the solar chimney.

The one or more baffles or plates in the inner channel may suitably comprise a transparent material to allow sunlight to travel through the inner channel. For example, the one or more baffles or plates in the inner channel may comprise glass, such as double glazed and/or low-emissivity (low-e) glass. The one or more baffles or plates in the inner channel may be generally cone-shaped.

A second aspect of the invention provides a building having installed thereon a solar chimney according to the first aspect of the invention or an array of solar chimneys according to the first aspect of the invention.

The solar chimney(s) may suitably be installed on the roof of a building. Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of the words, for example “comprising” and “comprises”, mean “including but not limited to”, and do not exclude other components, integers or steps. Moreover the singular encompasses the plural unless the context otherwise requires: in particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Preferred features of each aspect of the invention may be as described in connection with any of the other aspects. Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in 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/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a sectional view of a solar chimney in accordance with a first embodiment of the invention; and

Figure 2 is a sectional view of a solar chimney in accordance with a second embodiment of the invention.

DETAILED DESCRIPTION

Figure 1 shows a sectional view of a solar chimney 100 according to a first embodiment of the invention. The solar chimney 100 is installed on a building 101 , from which it extends generally vertically upwards.

The solar chimney 100 has a generally cylindrical inner channel 102, which is surrounded by a generally cylindrical outer channel 104. The inner and outer channels 102, 104 are separated by a generally cylindrical interior wall 120. The interior wall 120 is formed from stainless steel (for example, type 304 stainless steel). The inside face of the interior wall 120 (facing toward the inner channel 102) is covered with a reflective material 124.

The outer channel 104 is bounded by an exterior wall 140, which defines the outermost wall of the solar chimney 100. The lower portion of the exterior wall 140 is formed from a generally cone-shaped thermal panel 142, which is attached to and extends generally upwards from the building 101. The thermal panel 142 comprises a phase change material (PCM). The thermal panel 142 tapers towards an upper end of the interior wall 120 to define a constricted region 130 in the outer channel 104.

The upper portion of the exterior wall 140 is formed from a cylindrical tube 144, which extends upwards from the upper end of the thermal panel 142. The upper end of the cylindrical tube 144 supports and is attached to a double-glazed low-e tempered glass cover 150, which extends over both the inner and outer channels 102, 104 to define the roof of the solar chimney 100. The cylindrical tube 144 has two openings 146 on opposite sides of the cylindrical tube 144. A series of three horizontal louvres 148 is held within each of the openings 146 to protect the outer channel 104 from wind and rain ingress. The tempered glass cover 150 extends over the openings 146 to provide additional protection.

Located in the centre of the tempered glass cover 150 is a ventilation hole 152. The ventilation hole 152 is positioned above the inner channel 102. A ventilator turbine 154 is attached to the tempered glass cover 150 and sits over the ventilation hole 152.

A cylindrical tube 160 extends upwards from the upper end of the interior wall 120 and adjoins the tempered glass cover 150. The cylindrical tube 160 has two openings 162 on opposite sides of the cylindrical tube 160. The openings 162 in the cylindrical tube 160 are aligned with the openings 146 in the cylindrical tube 144 of the exterior wall 140. Each of the openings 162 is covered by a flipper 164. Each flipper 164 is held in a pair of brackets 166 attached to the tempered glass cover 150.

The lowermost end of the interior wall 120 is capped by a light diffuser 170. Incident sunlight 172 enters the inner channel 102 through the tempered glass cover 150. The incident sunlight 172 is reflected downwards through the inner channel 102 by the reflective material 124 until it reaches the light diffuser 170. The incident sunlight 172 passes through the light diffuser 170 and forms scattered light 174, which is dispersed into the building 101 below to provide natural lighting.

Incident sunlight also strikes the thermal panel 142, resulting in the thermal panel 142 absorbing heat energy in the form of solar heat. This causes the temperature of the thermal panel 142 to rise, thereby creating a temperature differential in the outer channel 104 between the thermal panel 142 and the interior wall 120. Within the outer channel 104, this increases the temperature of the air directly adjacent to the thermal panel 142 relative to the air adjacent to the interior wall 102, thereby reducing the density of the air adjacent to the thermal panel 142 (i.e. making it more buoyant). As a result the air adjacent to the thermal panel 142 rises above the cooler (and therefore more dense, i.e. less buoyant) air adjacent to the interior wall 102. This generates rising air 180 in the outer channel 104.

The lower end of the outer channel 104 has an opening 182, which connects the outer channel 104 to the space within the building 101 below the solar chimney 100. The rising air 180 creates a suction force at the opening 182, which draws air from the space within the building 101 up through the opening 182 and into the outer channel 104. In this way, the solar chimney 100 provides ventilation for the building 101 .

As the rising air 180 rises upwards through the outer channel 104, it moves into the constricted region 130 of the outer channel 104. The rising air 180 thus becomes constricted air 184. Due to the Venturi effect, the velocity of the constricted air 184 increases relative to the rising air 180 below. This accelerates airflow through the outer channel 104, thereby creating a larger suction force at the opening 182 and further facilitating the drawing of air from the space within the building 101 up through the opening 182 and into the outer channel 104.

The constricted air 184 flows out of the outer channel 104 through the horizontal louvres 148 held within the openings 146 on opposite sides of the cylindrical tube 144. The exhaust air 186 exits the openings 146 and rejoins the atmosphere outside the solar chimney 100.

Wind outside the solar chimney 100 strikes the ventilator turbine 154 causing it to rotate. The rotation of the ventilator turbine 154 generates a suction force at the ventilation hole 152 located in the centre of the tempered glass cover 150. The suction force draws air within the inner channel 102 upwards through the inner channel 102. This creates rising air 190 which rises up through the inner channel 102.

The light diffuser 170 has two inlets 192, which connect the inner channel 102 to the space within the building 101 below the solar chimney 100. The rising air 190 creates a suction force at the inlets 192, which draws air from the space within the building 101 up through the inlets 192 and into the inner channel 102.

The rising air 190 flows out of the inner channel 102 through the ventilation hole 152 and the ventilator turbine 154. The exhaust air 194 exits the ventilator turbine 154 and rejoins the atmosphere outside the solar chimney 100.

Optionally, instead of having two inlets 192, the inner channel 102 may be hermetically sealed by the light diffuser 170, and the interior wall 120 may have one or more mechanical exhaust inlets 196 arranged to transmit the exhaust (i.e. waste heat) from a mechanical ventilation system (not shown in Figure 1 ) to the inner channel 102. In this case, the ventilator turbine 154 may be replaced with a turbine generator (not shown in Figure 1 ) arranged to be driven by the exhaust air 194 exiting the inner channel 102 and generate electricity.

Figure 2 shows a sectional view of a solar chimney 200 according to a second embodiment of the invention. The solar chimney 200 is installed on a building 101 , from which it extends generally vertically upwards.

The solar chimney 200 has a generally cylindrical inner channel 202, which is surrounded by a generally cylindrical outer channel 204. The inner and outer channels 202, 204 are separated by a generally cylindrical interior wall 220. The interior wall 220 is formed from stainless steel (for example, type 304 stainless steel). The inside face of the interior wall 220 (facing toward the inner channel 202) is covered with a reflective material 224.

The outer channel 204 is bounded by an exterior wall 240, which defines the outermost wall of the solar chimney 200. The lower portion of the exterior wall 240 is formed from generally cone-shaped thermal panel 242, which is attached to and extends generally upwards from the building 101. The thermal panel 242 comprises a phase change material (PCM). The thermal panel 242 tapers towards an upper end of the interior wall 220 to define a constricted region 230 in the outer channel 204. A photovoltaic (PV) panel 243 is mounted on the thermal panel 242.

The upper portion of the exterior wall 240 is formed from a cylindrical tube 244, which extends upwards from the upper end of the thermal panel 242. The upper end of the cylindrical tube 244 supports and is attached to a double-glazed low-e tempered glass cover 250, which extends over both the inner and outer channels 202, 204 to define the roof of the solar chimney 200. The cylindrical tube 244 has two openings 246 on opposite sides of the cylindrical tube 244. A series of three horizontal louvres 248 is held within each of the openings 246 to protect the outer channel 204 from wind and rain ingress. The tempered glass cover 250 extends over the openings 246 to provide additional protection. Located in the centre of the tempered glass cover 250 is a ventilation hole 252. The ventilation hole 252 is positioned above the inner channel 202. A ventilator turbine 254 is attached to the tempered glass cover 250 and sits over the ventilation hole 252. A cover 255 is arranged over the ventilator turbine 254 to protect it from wind and rain ingress.

A gap 262 provided between the upper end of the interior wall 220 and the tempered glass cover 250 allows air to flow between the upper end of the outer channel 204 and the upper end of the inner channel 202.

The solar chimney 200 comprises a pair of heat pipes 222, both of which appear in cross-section in Figure 2. Each of the heat pipes 222 is assembled from an evacuated copper tube 223 surrounded by a porous capillary wick 224. Each of the copper tubes 223 is partially filled with water, which is the working fluid used in this example.

Each of the heat pipes 222 has a first end (i.e. an evaporator) 225 located towards the lowermost end of the outer channel 204 below the thermal panel 242, and a second end (i.e. a condenser) 226 located towards the uppermost end of the outer channel 204 above the constricted region 230. Each of the heat pipes 222 passes through the interior wall 220 into the inner channel 202 at two separate points so that the middle portion of each of the heat pipes 222 (i.e. between the first and second ends 225, 226) is located in the inner channel 202.

The interior wall 220 has two pairs of inlets 267 on opposite sides of the inner channel 202. A solar powered fan 268 is mounted within each of the of the inlets 267. A baffle 269 is positioned above each inlet 267 in the outer channel 204 for directing air in the outer channel 204 towards each inlet 267.

A cone shaped baffle 298 is located in the inner channel 202 towards an upper end of the inner channel 202, which serves to help maintain airflow in a generally downwards direction through the inner channel 202. Incident sunlight (omitted from Figure 2 for clarity) enters the inner channel 202 through the tempered glass cover 250, in the same way as shown for the solar chimney 100 in Figure 1. The incident sunlight is reflected downwards through the inner channel 202 by the reflective material 224 until it reaches the lowermost end of the inner channel 202, after which it enters into the building 101 below to provide natural lighting.

Incident sunlight also strikes the thermal panel 242, which results in the thermal panel 242 absorbing heat energy in the form of solar heat. This causes the temperature of the thermal panel 242 to rise, thereby creating a temperature differential in the outer channel 204 between the thermal panel 242 and the interior wall 220. Within the outer channel 204, this increases the temperature of the air directly adjacent to the thermal panel 242 relative to the air adjacent to the interior wall 202, thereby reducing the density of the air adjacent to the thermal panel 242 (i.e. making it more buoyant). As a result the air adjacent to the thermal panel 242 rises above the cooler (and therefore more dense, i.e. less buoyant) air adjacent to the interior wall 202. This generates rising air 280 in the outer channel 204.

Furthermore, incident sunlight strikes the PV panel 243 to generate electricity, which is used to provide power to the solar powered fans 268 mounted within the inlets 267. Excess electricity may be stored in a battery (not shown in Figure 2), which can provide electricity to the solar powered fans 268 when there is little or no incident sunlight striking the PV panel 243, for example during the night-time or when it is cloudy.

The lower end of the outer channel 204 has an opening 282, which connects the outer channel 204 to the space within the building 101 below the solar chimney 200. The rising air 280 creates a suction force at the opening 282, which draws air from the space within the building 101 up through the opening 282 and into the outer channel 204. In this way, the solar chimney 200 provides ventilation for the building 101 . As the rising air 280 rises upwards through the outer channel 204, it moves into the constricted region 230 of the outer channel 204. The rising air 280 thus becomes constricted air 284. Due to the Venturi effect, the velocity of the constricted air 284 increases relative to the rising air 280 below. This accelerates airflow through the outer channel 204, thereby creating a larger suction force at the opening 282 and further facilitating the drawing of air from the space within the building 101 up through the opening 282 and into the outer channel 204.

The constricted air 284 flows out of the outer channel 204 through the horizontal louvres 248 held within the openings 246 on opposite sides of the cylindrical tube 244. The exhaust air 286 exits the openings 246 and rejoins the atmosphere outside the solar chimney 200. Excess constricted air 284 may flow into the upper end of the inner channel 202 through the gap 262 above the upper end of the interior wall 220.

Wind outside the solar chimney 200 strikes the ventilator turbine 254 causing it to rotate. The rotation of the ventilator turbine 254 generates a suction force at the ventilation hole 252 located in the centre of the tempered glass cover 250. The suction force draws air out of the upper end of the inner channel 202 through the ventilation hole 252 and the ventilator turbine 254. The exhaust air 294 exits the ventilator turbine 254 and rejoins the atmosphere outside the solar chimney 200. The cone shaped baffle 298 in the inner channel 202 shields the lower part of the inner channel 202 from the suction force created by the ventilator turbine 254.

On each side of the solar chimney 200, a portion of the rising air 280 entering the outer channel 204 through the opening 282 passes the first end (i.e. the evaporator) 225 of the heat pipe 222. Liquid-phase working fluid, i.e. water in this example, in the first end 255 of the heat pipe 222 turns to vapour by absorbing heat energy from the rising air 280 (as indicated by the arrows 291 in Figure 2, which represent heat energy being absorbed by the first end 225), thereby cooling the rising air 280. The resulting vapour-phase water then travels upwards along the evacuated copper tube 223 of the heat pipe 222 until it reaches the second end (i.e. the condenser) 226. The second end 226 of the heat pipe 222 is at a lower temperature than the first end 225, and so the water condenses back to the liquid- phase, thereby releasing the absorbed (i.e. latent) heat from the second end 226 (as indicated by the arrows 293 in Figure 2, which represent latent heat energy exiting the second end 226). The liquid-phase water then returns to the first end 225 of the heat pipe 222 by capillary action through the porous capillary wick 224. Some of the cooled rising air 280 is caught by the baffles 269 and directed towards the inlets 267. The solar powered fans 268 in each inlet 267 drive the cooled air through the inlets 267, transferring the cooled air to the inner channel 202. The cooled air collects in the inner channel 202 and flows downwards to provide a cool air supply 190 which exits the inner channel 202 through an opening 192 at the base of the inner channel 202. The cool air supply 190 flows into the building 101 below the solar chimney 200, thereby cooling the building 101.