Sustainable Architecture: Natural Ventilation Strategies
Sustainable building is characterized by the conscious use of existing resources, an environmentally and user-friendly design and forward-looking planning, which enables the minimization of energy costs.
The sustainability concept can be illustrated using the three-pillar model, consisting of economy, ecology and the social-cultural aspect. Economy refers to the fact that the building is viewed over its entire life cycle and that intelligent planning results in lower construction and maintenance costs of the building. Ecology stands for the resource and environmentally friendly construction of buildings which, considering the climate change and limited resources of our earth, is of great relevance for future generations. The social focus is on the user of the building and how the architecture affects his health and activity. A sustainable building reconciles these three dimensions.
The sustainability concept is applied in all phases of the project, in design, execution and demolition. Materials, their transport, construction, use, maintenance and disposal are taken into consideration.
Sustainable design intervenes in everyone’s consciousness by sharpening the perception of indoor and outdoor spaces in relation to our environment. It teaches how to use natural resources and how intelligent planning saves costs and thus also reduces housing costs.
Several Design strategies and elements for sustainable architecture will be considered in PikArk. For example Natural Ventilation, Natural Heating and Cooling, Facades, Urban Recycling, etc..
Clean air is a natural resource that has a critical impact on our health, concentration and well-being. The increasing consciousness about this and the demand for reduction in energy consumption leads to a changing building design. Instead of technical ventilation systems, architects and engineers apply passive systems or hybrid systems. The latter combines the passive and active system. It might be necessary to ensures thermal comfort also in big scale projects and projects located in extreme climate zones, as well as the compliance with code requirements to smoke and fire.
Natural Ventilation is an overly complex subject. In the following paragraphs some specific ventilation concept will be presented, exemplified by architecture projects, including realized modern architecture, projects designed in an existing building and projects in process.
The buoyance or stack effect arises from temperature differences of air masses within a building. Warm air rises because it has a lower density than cold air. The rising air masses create a slight vacuum in the lower area of the building, which means that fresh air is drawn inside through openings near ground level. The warm air exits through air outlets, such as sheds and clerestory, in the ceiling of the building. When increasing the height of a building the stack effect becomes stronger. Thus, air outlets should be placed significantly higher than air inlets. A fully passive buoyance driven ventilation requires that the indoor temperature at the air outlet point is warmer than the outdoor temperature (approx. Five degrees Celsius). Fan assisted natural ventilation systems might be reasonable, in order to support ventilation in warmer seasons and necessary to fulfill fire protection measures.
In 2015, the Office KeranTimberlake chose an old factory as its new home in Philadelphia. Already the original design of the factory was intended to use passive ventilation. Large clerestory windows, fans at the roof level to boost airflow when required, and windows on the occupant level let the buoyance ventilation become operative. The building has a hybrid control system that allows to have an optimal working climate and allows to maximize time spent in natural ventilation.
A chimney allows a stronger buoyance effect, regardless of the building’s height and without changing the Indoor temperature. In the chimney the air is heated by solar energie, rising faster and resulting in a higher air exchange rate.
The Arbour is a new, not yet realized institutional building of the George Brown College designed by Moriyama & Teshima Architects and Acton Ostry Architects. The Design is very much based on the concept of natural ventilation. Fresh air enters the classrooms and is then directed through the corridors to the breathing rooms at the two ends of the building. These high rooms reaching across all floors, have an outer partition wall with outlets that allow the warm air to exit into the solar chimney, finally exhausting out of the building. When the Arbor was designed, further possible functions of the chimney were taken into account. It will not only be used for ventilation, but also for passive heating during winter and passive cooling during summertime. The respective mode is regulated with openings in the chimney.
Atrium Driven Ventilation
This strategy is based on cross ventilation, where used air from the building exits into an atrium and following rises to the building’s exhausts because of the stack effect. The ventilation shows a great effect in high rise buildings and is effective for many building types. During the design process it is crucial to define the temperature in the atrium and the quantity and quality of air. Moreover, the natural-ventilation system must complete a circuit through the space by open plans, transom windows, or louvres.
The project of the Portland State University School of Business Administration, realized by Behnisch Architekten and SRG Partnership, includes a total renovation of the existing school and a new building (Karl Miller Center). Between these two buildings, an atrium drives natural ventilation for all perimeter spaces throughout the building. Acoustically isolating transfer vents were necessary in order to achieve a circuit of air through all rooms. Based on a scientific approach an acceptable upper thermal comfort limit was fixed which defined the building’s design. A key advantage was the orientation: the atrium and new building are located at the north side of the existing building. That way protected, the new part was designed with glass facades and big windows generating light spaces.
Wind direction determines which windows let air in and which windows exhaust air from the building. For a well-functioning wind-induced ventilation the ground floor windows on the sheltered side are opened more than the windows on the wind-exposed side, whereas only the windows in the sheltered side of the roof are opened. Optimally, a building is orientated with its ridge perpendicular to the summer winds to maximize the ventilation effect. The consideration of local wind conditions during the Building design, can make buoyancy and cross ventilation much more effective.
Natural Cross Ventilation
Cross ventilation is achieved with the arrangement of openings on the opposite or adjacent walls. If the windows on both sides of the room are opened the overpressure on the side of the building facing into the wind, and/or low pressure on the opposite, sheltered side, will create a current of air across the room. Indicated for buildings in climatic zones with higher temperatures, the system allows a constant exchange of air in the building, renewing it and still, considerably reducing the internal temperature.
In the early 20th century Le Corbusier dealt with the subject of healthy living. The narrow flats of the Unité d’Habitation Marseille are mostly arranged as two-story duplexes, which interlock in pairs around a central access corridor. This means that the apartments stretch the full 21-metre depth of the block on each end with panoramic windows, enabling natural cross ventilation.
Source: transsolar.com | windowmaster.com