Pic. 33 - Secondary School “Giovanni Pascoli”, Bolzano, Project: arch. Ranzani
Closer bibliographical and web site analysis
Marco Sala, Integrazione Architettonica del Fotovoltaico, Casi studio di Edifici Pubblici in Toscana, Firenze, Alinea, 2003.
Gaetano Melzi, Dizionario di opere anonime e pseudonime di scrittori italiani o come che sia aventi relazione all’Italia, Milano: L. di G. Pirola, 1848-1859, 3 volumi
http://www.bbri.be/activefacades/new/content/1_home/en.html
Closer Analysis
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There are some advantages in the use of a similar façade:
- reduction of the risk of cracking and detachment, because the elements are assembled ‘dry-stone’ without using glues;
- an easy installation;
- maintenance and the possibility to work on every single layer; - protection of the building from atmospheric agents;
- elimination of heat bridges;
- increase of the internal heat during winter; - reduction of energetic transmissions;
- possibility of ventilation during the night in order to reduce the temperature of the rooms and refresh the internal still structures;
- possibility of perfect integration with solar shields; - maximum exploitation of natural light;
- better acoustic services, through a protection system from external noises, but also noises coming from different floors of the building.
Some disadvantages can occur using this kind of façade:
- the initial investment for a double skin façade is 20-80% expensive than for a single façade
- higher cleaning costs;
- the need of more energy for production, for building and demolition, so a bigger environmental impact than a standard building;
- less volume at disposal, caused by the bigger façade;
- the necessity of a mechanical supporting unit to ventilate and refresh the rooms during summer;
- little protection from fire because smoke and fire easily spread within the hollow space dedicated to ventilation.
We can choose the correct kind of façade and its working process only on the basis of specific conditions of the project, such as climatic conditions, the predominant winds and the pressure on the skin of the building, the acoustic pollution, the dimensions of the rooms and the mechanical systems of aspiration.
The services of a double skin façade will depend on several factors, the most important of all the difference in pressure caused by chimney effect. External air enters in the in-between space of the façade only through the air vents, usually smaller than the depth of the corridor, so that a peak of speed and a following decrease of the pressure within the hollow space are generated; in order to improve the effect of upward air flows is necessary that the dimension of the upper opening of the ‘chimney’ is double than the lower one.
The presence of air vents permits to have a system of changing facade which changes according to the season, closing both air vents in winter so as to use the greenhouse effect, and opening them in summer letting the excessive heat in the hollow space flow out.
The design of the hollow space can be carried out with no particular dimensional commitments; to its increase corresponds a small and unremarkable decrease of air temperature, whereas a continuous hollow space causes difficulties connected to the correct ventilation of internal rooms, because there is the risk of mixing between the air expulsed from the lower rooms and that which enters from above; we can avoid this problem sectioning the hollow space on the basis of the different floors and of the single functional units.
Environmental quality degree of improvement
1
2
3
4
5
Materials and construction technologies
02
02.12
Glasshouses and Buffer Spaces
Pic. 34 - Kingsdale School London.
Description of the strategy
Glasshouses are solar systems integrated in the building and are able to contribute to the heating of the rooms, within which is possible to reach good environmental comfort without using mechanical air conditioning systems, reducing in this way energetic costs.
The ‘Buffer space system’ constructive strategy is based on the creation of small rooms with a controlled micro-climate located in the spaces among the different blocks of the building; these buffer spaces, characterised by transparent surfaces on the cover help to reduce heat loss and keep internal rooms warmer during winter.
These characteristics make glasshouses and ‘Buffer spaces’ good building systems for schools, where ‘cushion spaces’ are very important because those spaces can be used for recreational activities and during the whole year.
Note
Within glasshouses sun radiation turns into heat because of the greenhouse effect: when a percentage of short waves sun radiation which passes through the glass reaches the objects in the room turns into long wave radiation, which can only partly flow outside and partly is absorbed as thermal radiation.
Target - Mediterranean area
In the design of this kind of glasshouses is very important to choose a south orientation, so as to exploit the sun light during winter; yet, in order to limit overheating during summer, in the areas with a Mediterranean climate is better to adopt a south- east orientation, with a maximum angular variation of 30°. During the design of these systems is also important to project external moving shading systems and doors and windows which can be easily opened in order to help ventilation and they should cover at least 50% of the glass surface. Another important and effective shading system is the use of deciduous trees, which, if placed on the west side of the glasshouse, guarantee a good shadowing during summer.
Estimate of achievable saving
30 %
Pay back period
Long