Facade Integration of Solar Thermal Collectors:A Breakthrough?

One main barrier to the acceptability of façade use of solar thermal collectors is their black appearance and the visibility of piping or absorber irregularities through the glazing. To facilitate façade integration, a project was set up to develop selective filters reflecting only a small part of the solar spectrum in the visible range while letting the rest of the radiation heat the absorber. These filters were successfully produced and, combined with a diffusing glass treatment, have achieved the desired masking effect with minor impact on the collector efficiency (less than 10%). Glasses of various colours combined with several diffusing finishing (acid etching, structured glass etc…) can be produced that are able to hide the absorber. Such glazings will allow the use of the same product both in front of façade areas equipped with solar absorbers (as collector external glass) and in front of the non exposed areas (as façade cladding), opening the way to a broad variety of active façade designs. The active elements can then be positioned at will on the exposed areas, and their quantity determined only by thermal needs. By freeing the dimension of the façade area that can be clad with this glazing from the thermally needed surface for collectors, a major step to help architects use solar thermal on facades has been taken

From Thermal Collectors Integration to Active Façade Systems

One main step to ease facade integration of solar thermal is to conceive new collectors as multifunctional building elements. For flat plate hydraulic collectors (glazed and unglazed) the most natural added function is facade cladding. The new elements should then meet the sets of requirements of both solar and facade systems. Now, for architectural coherence, areas of different solar exposure or too small to host collectors may need the same cladding appearance. This means that the availability, within the system, of elements providing the sole cladding function and of components to interface the system with the other building parts (windows, balconies, eaves…) is fundamental to answer correctly to facade integration issues. Two possible approaches to meet these requirements are presented and evaluated through a practical example: - develop a new façade system around the new collectors - adapt the new collectors to an existing facade system. Both options introduce the new concept of “active facade systems”, which should then logically be developed by façade manufacturers rather than the collector industry alone. This will be globally more economic and effective since it will benefit from the experience, infrastructure and market access of building professionals, for a building product. Finally recent developments in both the fields of glazed and unglazed systems are presented that show the relevance of this novel approach

Towards an improved architectural quality of building integrated solar thermal systems (BIST)

Architectural integration is a major issue in the development and spreading of solar thermal technologies. Yet the architectural quality of most existing building integrated solar thermal systems (BIST) is quite poor, which often discourages potential new users. In this paper, the results of a large web survey on architectural quality, addressed to more than 170 European architects and other building professionals are presented and commented. Integration criteria and design guidelines established and confirmed through the analysis of these results are proposed. Subsequently, a novel methodology to design future solar thermal collectors systems suited to building integration is described, showing a new range of design possibilities. The methodology focuses on the essential teamwork between architects and engineers to ensure both energy efficiency and architectural integrability, while playing with the formal characteristics of the collectors (size, shape, colour, etc.). Finally a practical example of such a design process conducted within the European project SOLABS is given; the resulting collector is described, and integration simulations are presented

Simulation Tool for Architects

The presented work offers an improved planning tool as a response to the demand for active and passive solar architecture. An integral solution is presented for the design of solar assisted heating systems and decentralized electricity production using photovoltaics (PV) on building roof-tops and facades. The tools are applicable in the early stage of architectural planning and the underlying simulation is consistently usable throughout all further steps. In particular, this solution offers a number of sensible approximations at the beginning of the planning process and allows refining the input data at a later stage. The two software programs Lesosai and Polysun form the basis for the project. In a first step, a software interface is created which provides access to the simulation kernel of Polysun through the graphical user interface of Lesosai. Consequently, the architects do not have to install and learn to handle additional software next to Lesosai. Furthermore, no data has to be entered twice and the consistency of all simulation results is guaranteed by the software package. In a second project step, Lesosai’s front-end is optimized with respect to the architects’ needs

Facade Integration of Solar Thermal Collectors: Present and Future

Based on the results of a European survey on architectural integration quality, the paper presents a systematic analysis of the facade integration potential of solar thermal collectors provided by Swiss manufacturers, concentrating on glazed flat plates, unglazed flat plates and evacuated tubes systems. It demonstrates the poor “integrability” of most of them, indicating that novel collectors responding to facade integration issues should be developed. These new collectors should answer to the technical constraints of their specific solar thermal technology, but should also become architectural elements, conceived to be integrated into the building skin. They should provide an adequate level of flexibility in all the system characteristics affecting the building appearance (i.e. collector material and surface texture, absorber colour, shape and size of the modules, type of jointing). To ease the designer integration efforts and reduce overall costs, they should become multifunctional construction elements, facade cladding being the most relevant added function for glazed and unglazed flat plate collectors. Within this application mode, the use of dummy elements (non-active elements with a similar appearance, fulfilling only the construction function) is a key tool manufacturers should provide to make the geometric/architectural dimensioning of the system independent from the sole energetic sizing. A novel system concept responding to these requisites is presented for glazed systems. New glasses have been developed that are able to hide the absorber behind a coloured reflection while letting the solar energy pass through, providing a new freedom level to architects. The same glazing can in fact be used to cover areas of the facade equipped or not with absorbers, finally opening the way to proper multifunctional active facade systems

Nanostructured Coatings on Glazing for Active Solar Facades

Thin films on glazing play an important role in the design of solar energy conversion systems as thermal collectors or photovoltaic panels. Antireflective coatings based on porous silicon dioxide are well established in the field of solar collector glazing. Regarding architectural integration of thermal collectors, colored glass panes based on multilayer interference stacks of dielectric thin films offer a smart alternative to the coloration of the absorber sheets. Materials with tunable refractive index are highly desirable in such coatings in order to give access to optimised designs. Thin films of silicon titanium mixed oxides TixSi1-xO2 have been deposited in a particle free atmosphere by a sol-gel dip-coating process. Optical properties of thin films have been characterized by spectrophotometry and spectral ellipsometry. A nanocomposite structure has been evidenced by Transmission Electron Microscopy (TEM). As low tunable refractive index material, novel nanocomposite thin films based on the elements Mg, F, Si and O have been deposited. Transparent and homogenous thin layers were achieved with variable Mg:Si molar ratios. Surprisingly low refractive index values have been found, reaching desired values for anti- reflective applications. Broad spectral transmittance maxima are observed with values up to 99.8 %. The nanostructure of quaternary Mg-F-Si-O thin films has been investigated by TEM, showing evidence of embedded crystalline nanoparticles. In comparison to existing anti- reflective materials, the novel quaternary thin films might be highly interesting regarding improvement of hardness and improved aging stability with respect to pores filling by hydrocarbons. Intermediate size A4 colored glazing based on TixSi1-xO2 films have been produced exhibiting 14.0 and 12.6 % visible reflectance and only small energy losses (1.4 and 3.4 % with respect to the uncoated substrate) showing the high potential of such materials for colored solar facades. A real-sized prototype of colored thermal solar collector has been realized, providing a convincing demonstration device