The potential of covered profiled steel cladding as a building-integrated solar collector for the UK climate
Profiled steel cladding can be modified to act as an air heating solar collector by the addition of a transparent cover system. A mathematical model of the thermal performance of such an arrangement has been derived for the situation of a building-integrated solar collector facade, allowing for the condition of differing temperatures at front and rear faces of the collector. By introducing an equivalent ambient temperature, it is possible to quantify the performance of such a collector arrangement in terms of existing parameters as derived in the standard Hottel-Whillier-Bliss analysis. Using a purpose-built solar simulator, a set of standard performance characteristics for the proposed collector geometry is derived; these characteristics are used to confirm the validity of the derived model for use in this application area, i.e. as a building-integ rated system with the standard thickness of back insulation. Those conditions of front/rear temperature difference and rear insulation level for which the standard Hoftel-Whillier-Bliss analysis is no longer valid, are identified. The model has been encoded as a new subroutine within the thermal simulation program TRNSYS in order to investigate the energy performance of a typical profiled metal-clad building in the UK climate with and without the assistance of such a collector system. The effects of orientation of the solarcollector facade, together with collection area, steel-to-cover spacing and fan power requirements were determined. Assessment of capital maintenance, operating costs and energy savings permitted the cost-effectiveness of such a system to be evaluated. Guidance for future designers of such buildingintegrated systems is presented for UK conditions. It is concluded that the use of such a collector system can approach cost-effectiveness in electrically fuelled buildings, and that this is likely to be especially so if the building has a significant requirement for pre-heated fresh air. The system is shown to be not cost-effective at present for gas-fuelled installation in the UK, such as in the case of a retrofit to a typically profiled-clad sports centre, though factors other than that of payback alone may well influence such investment decisions in the future.