UC Santa Cruz

Integrated building elements, which combine their structural, control and architectural functions with that of energy generation, are expected to become increasingly important in the future scenario of energy efficient buildings, and they could significantly contribute to the thermal behavior of the building envelope in order to provide energy savings. A prototype of a building-integrated photovoltaic thermal (BIPV/T) solar air collector was built, consisting of a double-glazed airflow window wall with photovoltaic (PV) louvers embedded in it. The collector is intended to either be used as a modular window wall unit that would form a ventilated double-skin façade, or as an independent airflow window, and it provides combined heat and power generation, while still allowing light transmission, shading control and thermal insulation as a conventional window.

In this work, the prototype's thermal and electrical performance have been tested, and the experimental data served to develop and validate a thermo-fluid dynamic model in COMSOL Multiphysics. This served as a first reference model and starting point to build more expanded 2D models, as well as to develop 3D models of some portions of the window, which were used for optimization and design by editing the prototype’s features, such as geometrical layout, material properties and operational parameters. CFD simulations were used to enhance PV cooling and thermal insulation, in order to optimize both the thermal and electrical efficiency. The optimization of the glazing system, frame heat losses minimization and several strategies for PV-to-air heat transfer enhancement are discussed. These included parametric analysis of the effects of airflow rate and glass spacing on PV temperature and thermal generation, the use of extended surfaces and a new layer structure of the PV absorbers. The field measurements on existing prototype determined a maximum temperature rise of 31 °C and average thermal and electrical efficiency of 31% and 7%, respectively. The optimization showed that significant increases in air temperature rise and thermal efficiency by up to 70% and 60%, respectively, as well as up to 25% decrease in PV temperature can be achieved. Lastly, the design of new prototypes in SolidWorks, which were developed based on the simulation results, are presented.