Solar chimney to improve natural cooling

Solar chimney article in wikipedia:
illustrations are missing, it shows an earthtube to cool incoming air, and an exhaust via a pipe with southfacing glass enclosure



This solar chimney draws air through a geothermal heat exchange to provide passive home cooling.[2]
Air conditioning and mechanical ventilation have been for decades 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 gain 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 convection 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. 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. 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.[3]
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:


CAD(TAS) Solar Chimney model
Improved ventilation rates on still, hot days
Reduced reliance on wind and wind driven ventilation
Improved control of air flow though 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
Allow 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)
[edit]Precedent Study: The Environmental Building

The Building Research Establishment (BRE) office building in Garston, 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 theses 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 and storing coolth for the following day. The exposed curved ceiling gives more surface area than a flat ceiling would, acting as a cool ‘radiator’, 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.[4]
[edit]Passive down-draft cooltower



Cool tower at Zion National Park's Visitor Center provides cool air.
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 air conditioning for buildings.
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.
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 cools the incoming air, causing a downdraft of cool air that will bring down the temperature inside the building.[5] 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.[6] 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 (NREL).
The principle of the downdraft cooltower has been proposed for solar power generation as well. (See Energy tower for more information.)
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