PhD Oral Exam - Zisis Ioannidis, Building Engineering

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

Building-integrated Photovoltaics (BIPV) can replace building elements in both facades and roofs improving at the same time the thermal, the electrical and the daylighting performance of the building. A novel approach in BIPV is the Double Skin Façade (DSF) that integrates Semi-Transparent Photovoltaics (STPV). In this approach, the air that passes within the cavity created between the layer of the STPV and the building, acts as a buffer zone and depending on the preferred strategy, it can be used for heating, cooling or ventilating the building. In addition, the STPV is the exterior layer of the envelope, controlling the solar gains but also allowing daylight into the interior space.

This thesis identifies the important parameters of a double skin façade integrating semi-transparent photovoltaics (DSF-STPV) as well as the gaps in the existing literature, namely the lack of experimental studies on mechanically-ventilated DSF-STPV buildings and the lack of investigation of heat transfer coefficients within the cavity in the presence of wind effects. In addition, it appears that there are neither tools to simulate such complex systems nor guidelines to assist architects and engineers to optimally design a DSF-STPV system.

A methodology was developed to assess the use of STPV integrated onto DSF and their impact on the energy consumption of buildings. The thermal model employed was verified in an outdoor experimental set-up of a mechanically-ventilated DSF-STPV and an insulating glazing unit (IGU) integrating STPV (IGU-STPV) built at Concordia University (Montreal, Canada). The forced convection within the cavity of the DSF-STPV has been investigated and three Nusselt number correlations were developed and validated. An experimental test-room was also used for a comparison between the DSF-STPV and the IGU-STPV under specific outdoor conditions. From the experimental analysis it has been found that a DSF-STPV can reduce the exterior heat losses due to wind, by more than 20%, whereas the total combined efficiency of the DSF-STPV, can reach the 75% level. The comparison between the DSF-STPV and the IGU-STPV presents increased electrical performance of the DSF-STPV up to 9% and lower average temperature difference that reaches up to 10oC.

The developed Nusselt number correlations were used for the development and validation of a parametric numerical model of a DSF-STPV. The model also allows the user to perform a parametric analysis changing the design parameters of the thermal zone and the DSF-STPV. This model can also simulate battery storage and its effect on peak demand. A parametric analysis was carried out for sixteen (16) different ASHRAE climate zones, two (2) insulation cases for every climate location (baseline and advanced), nine (9) different cavity widths, nine (9) different cavity velocity set-points and twelve (12) different strategies, changing the operation of the DSF-STPV.

An analysis of the optimal operation for all sixteen (16) ASHRAE climate zones was presented, concluding that the climate locations can be separated into three main categories based on their behaviour, i.e. hot and mild, cold, and extreme cold locations, as they present similar patterns and strategies to achieve minimal energy consumption. In addition, the parametric analysis has shown that, for most cases, practical cavity widths under or over 0.50 m - 0.60 m show similar behaviour.

The mismatch between the electricity production by the STPV and the electricity needed for heating and lighting by the adjacent building perimeter zones was investigated, for Montreal, Canada. With the use of a predictive heating strategy, the peak demand of the building can coincide with the peak of the electricity production, resulting in more than 80% reduction in the electricity consumption by the grid during the peak hours.