A solar chimney often referred to as a thermal chimney is a way of improving the natural

ventilation Ventilation may refer to: * Ventilation (physiology), the movement of air between the environment and the lungs via inhalation and exhalation ** Mechanical ventilation, in medicine, using artificial methods to assist breathing *** Respirator, a ma ...

building A building or edifice is an enclosed Structure#Load-bearing, structure with a roof, walls and window, windows, usually standing permanently in one place, such as a house or factory. Buildings come in a variety of sizes, shapes, and functions, a ...

s by using

convection Convection is single or Multiphase flow, multiphase fluid flow that occurs Spontaneous process, spontaneously through the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoy ...

of air heated by passive solar energy. A simple description of a solar chimney is that of a vertical shaft utilizing solar energy to enhance the natural

stack ventilation Stack may refer to: Places * Stack Island, an island game reserve in Bass Strait, south-eastern Australia, in Tasmania’s Hunter Island Group * Blue Stack Mountains, in Co. Donegal, Ireland People * Stack (surname) (including a list of people ...

through a building. The solar chimney has been in use for centuries, particularly in the

Middle East The Middle East (term originally coined in English language) is a geopolitical region encompassing the Arabian Peninsula, the Levant, Turkey, Egypt, Iran, and Iraq. The term came into widespread usage by the United Kingdom and western Eur ...

and

Near East The Near East () is a transcontinental region around the Eastern Mediterranean encompassing the historical Fertile Crescent, the Levant, Anatolia, Egypt, Mesopotamia, and coastal areas of the Arabian Peninsula. The term was invented in the 20th ...

by the

Persians Persians ( ), or the Persian people (), are an Iranian ethnic group from West Asia that came from an earlier group called the Proto-Iranians, which likely split from the Indo-Iranians in 1800 BCE from either Afghanistan or Central Asia. They ...

, as well as in

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

by the Romans.

Description

In its simplest form, the solar chimney consists of a black-painted

chimney A chimney is an architectural ventilation structure made of masonry, clay or metal that isolates hot toxic exhaust gases or smoke produced by a boiler, stove, furnace, incinerator, or fireplace from human living areas. Chimneys are typical ...

. During the day solar energy heats the chimney and the air within it, creating an

updraft In meteorology, an updraft (British English: ''up-draught'') is a small-scale air current, current of rising air, often within a cloud. Overview Vertical drafts, known as updrafts or downdrafts, are localized regions of warm or cool air that mov ...

of air in the chimney. The

suction Suction is the day-to-day term for the movement of gases or liquids along a pressure gradient with the implication that the movement occurs because the lower pressure pulls the gas or liquid. However, the forces acting in this case do not orig ...

created at the chimney's base can be used to ventilate and cool the building below. In most parts of the world it is easier to harness

wind power Wind power is the use of wind energy to generate useful work. Historically, wind power was used by sails, windmills and windpumps, but today it is mostly used to generate electricity. This article deals only with wind power for electricity ge ...

for such ventilation as with a windcatcher, but on hot windless days a solar chimney can provide ventilation where otherwise there would be none. There are however a number of solar chimney variations. The basic design elements of a solar chimney are: * The solar collector area: This can be located in the top part of the chimney or can include the entire shaft. The orientation, type of glazing, insulation and thermal properties of this element are crucial for harnessing, retaining and utilizing solar gains. * The main ventilation shaft: The location, height, cross section and the thermal properties of this structure are also very important. * The inlet and outlet air apertures: The sizes, location as well as aerodynamic aspects of these elements are also significant. A

principle A principle may relate to a fundamental truth or proposition that serves as the foundation for a system of beliefs or behavior or a chain of reasoning. They provide a guide for behavior or evaluation. A principle can make values explicit, so t ...

has been proposed for

solar power Solar power, also known as solar electricity, is the conversion of energy from sunlight into electricity, either directly using photovoltaics (PV) or indirectly using concentrated solar power. Solar panels use the photovoltaic effect to c ...

generation, using a large

greenhouse A greenhouse is a structure that is designed to regulate the temperature and humidity of the environment inside. There are different types of greenhouses, but they all have large areas covered with transparent materials that let sunlight pass an ...

at the base rather than relying solely on heating the chimney itself. (For further information on this issue, see Solar updraft tower.) Solar chimneys are painted black so that they absorb the sun's heat more effectively. When the air inside the chimney is heated, it rises and pulls cold air out from under the ground via the heat exchange tubes.

Solar chimney and sustainable architecture

Solar chimneys, also called heat chimneys or heat stacks, can also be used in architectural settings to decrease the energy used by mechanical systems (systems that heat and cool the building through mechanical means). For decades, air conditioning and mechanical ventilation have been the standard method of environmental control in many building types, especially offices, in developed countries. Pollution and reallocating energy supplies have led to a new environmental approach in building design. Innovative technologies along with bioclimatic principles and traditional design strategies are often combined to create new and potentially successful design solutions. The solar chimney is one of these concepts currently explored by scientists as well as designers, mostly through research and experimentation. A solar chimney can serve many purposes. Direct sunlight warms air inside the chimney causing it to rise out the top and drawing air in from the bottom. This drawing of air can be used to ventilate a home or office, to draw air through a geothermal heat exchange, or to ventilate only a specific area such as a composting toilet. Natural ventilation can be created by providing vents in the upper level of a building to allow warm air to rise by

and escape to the outside. At the same time cooler air can be drawn in through vents at the lower level. Trees may be planted on that side of the building to provide shade for cooler outside air. This natural ventilation process can be augmented by a solar chimney. The chimney has to be higher than the roof level, and has to be constructed on the wall facing the direction of the Sun. Absorption of heat from the Sun can be increased by using a glazed surface on the side facing the Sun. Heat absorbing material can be used on the opposing side. The size of the heat-absorbing surface is more important than the diameter of the chimney. A large surface area allows for more effective heat exchange with the air necessary for heating by solar radiation. Heating of the air within the chimney will enhance convection, and hence airflow through the chimney. Openings of the vents in the chimney should face away from the direction of the prevailing wind. To further maximize the cooling effect, the incoming air may be led through underground ducts before it is allowed to enter the building. The solar chimney can be improved by integrating it with a trombe wall. The added advantage of this design is that the system may be reversed during the cold season, providing solar heating instead. A variation of the solar chimney concept is the solar

attic An attic (sometimes referred to as a '' loft'') is a space found directly below the pitched roof of a house or other building. It is also known as a ''sky parlor'' or a garret. Because they fill the space between the ceiling of a building's t ...

. In a hot sunny climate the attic space is often blazingly hot in the summer. In a conventional building this presents a problem as it leads to the need for increased

air conditioning Air conditioning, often abbreviated as A/C (US) or air con (UK), is the process of removing heat from an enclosed space to achieve a more comfortable interior temperature, and in some cases, also controlling the humidity of internal air. Air c ...

. By integrating the attic space with a solar chimney, the hot air in the attic can be put to work. It can help the convection in the chimney, improving ventilation. The use of a solar chimney may benefit natural ventilation and passive cooling strategies of buildings thus help reduce energy use, CO₂ emissions and pollution in general. Potential benefits regarding natural ventilation and use of solar chimneys are: * improved ventilation rates on still, hot days * reduced reliance on wind and wind driven ventilation * improved control of air flow through a building * greater choice of air intake (i.e. leeward side of building) * improved air quality and reduced noise levels in urban areas * increased night time ventilation rates * ventilation of narrow, small spaces with minimal exposure to external elements Potential benefits regarding passive cooling may include: * improved passive cooling during warm season (mostly on still, hot days) * improved night cooling rates * enhanced performance of thermal mass (cooling, cool storage) * improved thermal comfort (improved air flow control, reduced draughts)

Precedent Study: The Environmental Building

The Building Research Establishment (BRE) office building in Garston, Watford, United Kingdom, incorporates solar-assisted passive ventilation stacks as part of its ventilation strategy. Designed by architects Feilden Clegg Bradley, the BRE offices aim to reduce energy consumption and CO₂ emissions by 30% from current best practice guidelines and sustain comfortable environmental conditions without the use of air conditioning. The passive ventilation stacks, solar shading, and hollow concrete slabs with embedded under floor cooling are key features of this building. Ventilation and heating systems are controlled by the building management system (BMS) while a degree of user override is provided to adjust conditions to occupants' needs. The building utilizes five vertical shafts as an integral part of the ventilation and cooling strategy. The main components of these stacks are a south facing glass-block wall, thermal mass walls and stainless steel round exhausts rising a few meters above roof level. The chimneys are connected to the curved hollow concrete floor slabs which are cooled via night ventilation. Pipes embedded in the floor can provide additional cooling utilizing groundwater. On warm windy days air is drawn in through passages in the curved hollow concrete floor slabs. Stack ventilation naturally rising out through the stainless steel chimneys enhances the air flow through the building. The movement of air across the chimney tops enhances the stack effect. During warm, still days, the building relies mostly on the stack effect while air is taken from the shady north side of the building. Low-energy fans in the tops of the stacks can also be used to improve airflow. Overnight, control systems enable ventilation paths through the hollow concrete slab removing the heat stored during the day, which then remains cold for the following day. The exposed curved ceiling gives more surface area than a flat ceiling would, acting as a

heat sink A heat sink (also commonly spelled heatsink) is a passive heat exchanger that transfers the heat generated by an electronic or a mechanical device to a fluid medium, often air or a liquid coolant, where it is thermal management (electronics), ...

, again providing summer cooling. Research based on actual performance measurements of the passive stacks found that they enhanced the cooling ventilation of the space during warm and still days and may also have the potential to assist night-time cooling due to their thermally massive structure.

Passive down-draft cool tower

A technology closely related to the solar chimney is the evaporative down-draft cooltower. In areas with a hot, arid climate this approach may contribute to a sustainable way to provide

for buildings. The principle is to allow water to evaporate at the top of a tower, either by using evaporative cooling pads or by spraying water.

Evaporation Evaporation is a type of vaporization that occurs on the Interface (chemistry), surface of a liquid as it changes into the gas phase. A high concentration of the evaporating substance in the surrounding gas significantly slows down evapora ...

cools the incoming air, causing a downdraft of cool air that will bring down the temperature inside the building. Airflow can be increased by using a solar chimney on the opposite side of the building to help in venting hot air to the outside. This concept has been used for the Visitor Center of Zion National Park. The Visitor Center was designed by the High Performance Buildings Research of the

National Renewable Energy Laboratory The National Renewable Energy Laboratory (NREL) in the US specializes in the research and development of renewable energy, energy efficiency, energy systems integration, and sustainable transportation. NREL is a federally funded research and ...

(NREL). The principle of the downdraft cooltower has been proposed for solar power generation as well. (See Energy tower for more information.) Evaporation of moisture from the pads on top of the Toguna buildings built by the Dogon people of Mali, Africa, contribute to the coolness felt by the men who rest underneath. The women's buildings on the outskirts of town are functional as more conventional solar chimneys.

References

Sources

* * * * *

External links

* Solar Chimney – * Solar Innovation Ideas – Victorian Solar Innovation Initiative * Architectural Environmental Analysis – A guide to environmental design * Passive Solar Heating & Cooling Manual {{DEFAULTSORT:Solar Chimney Appropriate technology Architectural elements Building engineering Chimneys Convection Heating, ventilation, and air conditioning Low-energy building Solar architecture Solar-powered devices Sustainable building Sustainable technologies