ABSTRACT: The building sector is responsible for 36% of global final energy consumption. The energy used in buildings is largely required for creating a thermally and visually comfortable environment for building occupants. Glazed façades play an important role in determining a building's energy performance and are called upon to perform a range of, sometimes conflicting, functions. They are required to i) regulate heat transfer to and from the external environment by solar and long wave radiation, conduction and convection ii) allow transmittance natural daylight to provide interior illumination, reducing the need for supplementary electric lighting and to provide an aesthetic function, both in terms of their influence on building appearance and providing occupants a visual link to the external environment. Improving fenestration energy performance can make a significant contribution to reducing building energy loads. It is reported that optimal glazing design could reduce residential building energy consumption by 10-50% in most climates, while for commercial, institutional and industrial buildings, a properly specified fenestration system could reduce lighting and air-conditioning costs by 10-40%. This project has designed and developed a novel PV integrated smart window (as shown in Fig). The window automatically responds to climatic conditions by varying the balance of solar energy between PV electricity generation and transmission into a building to provide of light and heat. Therefore, renewable electricity can be generated onsite while providing comfortable daylight and passive heat for buildings. The developed window has the potential to significantly reduce building energy loads and meet the building’s electricity requirement.

A comprehensive model has been developed to accurately predict the thermal, optical properties and electrical output of the smart window systems, and a workflow developed to yield detailed daylight and energy performance (heating, cooling, lighting and power output) predictions of these systems when applied in buildings. Through this approach, the thermal characteristics of complex fenestration systems are obtained from a validated Computational Fluid Dynamics model, and a ray-tracing technique is used to obtain Bidirectional Scattering Distribution Function (BSDF) data to represent their optical characteristics. In addition, the electrical power output is realised through Sandia tests. These characterises may be used in building simulation software (in this case EnergyPlus) to obtain building heating, cooling, lighting energy and PV power output estimates for a room incorporating smart glazing systems. Detailed visual comfort predictions including useful daylight illuminance, daylight uniformity and glare may also be made, using a complementary optical model run using RADIANCE simulations. Finally, the occupants' visual perception for these smart windows in office environment were investigated through Virtual Reality conditions developed using physically based image techniques.
 

Advanced façade, thermal characterisation, optical characterisation