A novel methodology assessing the use of Semi-Transparent Photovoltaics integrated onto Double Skin Facades and their impact on the energy consumption of buildings

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

Double Skin Facades Integrating Photovoltaic Panels, Motorized Shades and Controlled Air Flow

A Double Skin Façade (DSF) with photovoltaic panels and automated roller shading devices aims at the reduction of the energy consumption of the building and at the on-site generation of electricity while allowing for the possibility of admitting ventilation air from outside without the direct noise and wind-induced direct inflow from open windows. A detailed transient finite difference model has been developed aiming at analyzing the thermal and electrical performance of an innovative DSF integrating photovoltaics and roller blinds (DSF-P). The model takes into account the effects of wind and the daylight provisions to the adjacent zone of the DSF-P. The energy balance of the system is described by a thermal network and a nodal flow network capable of assessing the wind effects on the cavity along with a daylighting model. In the modeling of the DSF-P the thermal behavior of an adjacent perimeter zone as well as the shading that the photovoltaics and the roller blind provide to the interior skin of the building are also simulated. The model developed was used for the numerical investigation of various flow rates and shading configurations for a south facing three-storey double skin façade considering a typical year in Montreal (Canada). Different flow rates inside the cavity and shading configurations were considered and simulated. It was concluded that the optimal cavity width, in which the electricity consumption of the DSF-P system is minimized is between 0.2m and 0.6m (0.07 and 0.21 L/H); the electricity generated from the photovoltaics integrated on the exterior skin may cover the total electricity consumption of the adjacent zone; and for some cases an energy positive DSF-P can be generated

A detailed dynamic model of multi-story double skin facades with integrated photovoltaic panels

A numerical model is developed for a multi-story Double Skin Façade integrating Photovoltaics (DSF-P). The model has the ability to predict the thermal and electrical performance of the DSF-P system. The air flow inside the cavity may be assisted by a fan to cool down the photovoltaics while providing natural or hybrid ventilation to adjacent zones. Automated roller shades are implemented in the model and along with the shade that photovoltaics on the exterior skin provide, can control solar heat gains and daylight levels in the indoor space. A set of simulations was carried out for January and August in Montreal, for different air velocities inside the cavity, different roller blind positions and different number of floors. The simulations show that a DSF-P system integrating photovoltaics can supply approximately 0.20kWh/m2/day of solar electricity to the adjacent office space covering the daily heating and cooling demand of the office

Double Skin Façades Integrating Photovoltaic Panels: A Comparative Analysis of the Thermal and Electrical Performance

A numerical model is developed for simulating a single or multi–story Double Skin Façade integrating Photovoltaics (DSF-P). The proposed model enables the prediction of the thermal and electrical performance of the DSF-P system. The DSF-P can co-generate solar electricity and heat. The buoyancy-driven air flow inside the cavity may be assisted by a fan to cool down the photovoltaics while providing natural or hybrid ventilation to adjacent zones. Automated roller shades are also implemented in the model, which help regulate heating and cooling loads but also control the daylight levels in the indoor space. A comparative analysis for two different climate zones, Montreal (Canada) and Naples (Italy), is performed with the purpose to apply the proposed methodology for the optimization of the DSF-P system in different climate regions. The simulations show that a DSF-P system integrating photovoltaics can supply approximately 0.20kWh/m2/day of solar electricity to the adjacent office space covering the daily thermal energy demand of the office (cooling and heating). In addition, during the heating period for a threestory DSF-P, the temperature difference between the inlet and the outlet of the cavity can reach up to 18oC giving the opportunity for natural or hybrid ventilation to the building

Experimental comparison on the energy performance of semitransparent PV facades under continental climate

Semi-Transparent Photovoltaic panels (STPV) have become an important element in the building integration of photovoltaic panels (BIPV). STPV panels can be integrated on double skin facades (DSF) and insulating glazing units (IGU) acting as their exterior layer, generating electricity, controlling the solar heat gains and utilizing daylight. In addition, a mechanically ventilated DSF integrating STPV panels (DSF-PV), can cool down the PV panels, increase their efficiency but also use the preheated air to enhance the thermal efficiency of the mechanical system connected to the DSF-PV. Two virtually identical STPV are integrated on a DSF-PV and a IGU-PV respectively and their electrical performance is evaluated experimentally. Under the same exterior and interior conditions, it is found that the DSF-PV has a 3% greater electrical performance than the IGU-PV and if the cavity of the DSF-PV is selectively ventilated, the DSF-PV can generate more than 9% of electric power than the IGU-PV

State-of-the-art and SWOT analysis of building integrated solar envelope systems:deliverables A.1 and A.2

The present document includes a state-of-the-art review of solar envelope systems that are already on the market or that can potentially reach that stage in a short-medium timeframe. The analysis focuses on the technological integration of such solutions in the envelope and building, but non-technical issues such as aesthetic, architectural integration and customer acceptance are also tackled. The solar envelope systems are classified in: Solar harvesting systems: systems that generate electricity or heat; Solar gains control systems, controlling; Hybrid systems: combination of solar harvesting and solar gains control systems