Chapter-10.qxd
11/1/2007
2:03 PM
Page 395
GREEN TECHNOLOGIES, PERFORMANCE AND INTEGRATION
Examples of integration Roof and attics Conceptual: the roofs of houses in warm and hot climates are principally defensive elements against heat and rain intrusion; however, their functions have been adapted to include not only protection, but also collection of water and heat. For the roof to act as a primary element for harvesting the natural available solar radiation and water supply, its configuration and form must be adapted to better accommodate these new functions. Current thinking on the roofβs technical integration is that it provides an opportunity to use PV, solar hot water and rainwater collection systems. PV cells are very easy to install on a range of roof types and protect the roof area that they cover. The PV array can be mounted above and parallel to the roof surface with a standoff of several inches for cooling purposes. Sometimes, in the case of a flat roof, a separate structure can be mounted to give optimum tilt; but very often these systems look unsightly. Four main design criteria apply: 1 2 3
4
The orientation, shading and angle of the roof for optimal yield: this depends upon the latitude, but is typically at 35Β°, facing the equator. Ventilation is needed for PV cells since overheating can reduce performance. The roof needs to be adequate structurally to take the additional load of the systems; with PV systems that are integrated with the roof, it is critical that strong materials such as steel are used to avoid shifting of the systems. Self-cleansing of the surface is needed to maintain the yield of the systems; an angle of inclination of at least 5ΒΊ is needed so that runoff will remove dirt from the face of the systems.
Technical integration has given way to elemental integration with the development of PV shingles. These are made from complementary roof tile materials such as concrete or steel. These are less visually intrusive and conform to conventional roofing materials, but impose a trade-off in output efficiency. The use of spatial integration in the roof can facilitate the storage of rainwater. The attic space created by the roof is a large void that is often underutilized. Atria PV atrium designs are a progressive architectural concept, opening possibilities for harnessing translucent PV/glass technologies that are integrated within the roof and wall elements of atrium spaces so that a balanced passive and active solar outcome is achieved. Careful design of these spaces is needed to avoid excessive heat gain.
395