Natural ventilation
From Swikipedia
Introduction
Ventilation obtained without the use of mechanical devices and external energy. Natural ventilation is the process of supplying and removing air through an indoor space by natural means, meaning without the use of a fan or other mechanical system. It uses outdoor air flow caused by pressure differences between the building and its surrounding to provide ventilation and space cooling.
Brief Description
Types of Natural Ventilation:
There are two types of ventilation:
• Wind driven ventilation
• Stack driven ventilation
Wind Driven Ventilation:
Wind driven ventilation or roof mounted ventilation design in buildings provides ventilation to occupants using the least amount of resources. Drawbacks include the use of equipment that is high in embodied energy and the consumption of energy during operation. By utilizing the design of the building, Wind Driven Ventilation takes advantage of the natural passage of air without the need for high energy consuming equipment. Wind catchers are able to aid Wind Driven Ventilation by directing air in and out of buildings.
Stack Driven Ventilation:
Buoyancy ventilation can be induced by temperature (known as stack ventilation) or by humidity (known as cool tower). Most commonly used is the stack driven ventilation. For stack ventilation to work properly there must be a temperature difference. However, stack driven ventilation is limited to a lower magnitude than wind driven ventilation. It is also very dependent on the inside and outside temperature differences.
Benefits of Natural Ventilation:
The use of natural ventilation is definitely an advantage with the raising concerns regarding the cost and environmental impact of energy use. Not only does natural ventilation provide ventilation (outdoor air) to ensure safe healthy and comfortable conditions for building occupants without the use of fans, it also provides free cooling without the use of mechanical systems.
When carefully designed, natural ventilation can reduce building construction costs and operation costs and reduce the energy consumption for air-conditioning and circulating fans. Building Design for Natural Ventilation: The design for natural ventilation should incorporate maximizing both the wind and stack driven ventilation design concepts.
General design considerations include:
• Increase air supply intake by ensuring no outside obstruction (such as vegetation or site objects) nor inside obstruction (such as furniture and interior partition) obstruct inlet openings
• All occupied spaces should have an inlet and outlet opening in which at least a minimum of one opening should be an operable window to control flow
• Inlets should supply air at a location low in the room. Outlets should be located across the room and at a higher level
• The long facade of the building and the majority of the openings should be should be directed so that the windward wall is perpendicular to the summer wind
• Use skylights. They are very desirable for night time thermal comfort in houses to vent heated/warm air that rises, and allow heat to be radiated into the cold. It is also a good outlet for wind driven ventilation
• At least 3m allowance for the floor to ceiling
• Window areas should not be excessive and be protected by exterior shading devices
• Design for high thermal capacity and exposed ceilings for night cooling
• Reduce the possibility of wall warming by the sun through use of light-coloured building exteriors, trees/shrubs to provide shading and evaporative cooling, grass and other groundcover to keep ground temperatures low, and ponds and fountains to enhance evaporative cooling
• Internal loading should be kept low
• Consider the use of fan-assisted cooling strategies
Many of the considerations taken above is to either increase the air flow or lower the heat gain so that the natural ventilation can effectively cool the spaces in the building. Mechanical cooling and ventilation systems will be used to supplement the natural ventilation. By lowering the heat gains, the less air flow will be required to remove the heat, thus there will be a lesser need for mechanical cooling systems.
References:
http://www.wbdg.org/resources/naturalventilation.php
http://betterbricksresources.com/book/
