Imminent climatic ramifications can be averted by adoption of renewable energy resources so as to limit global temperature rise by 1.5°C. Amongst the proposed approaches and energy efficient systems, the zero or plus energy office buildings have shown promising results. Nonetheless, research has shown that such plus energy office buildings ought to attain very high building standards in addition to calling for highly efficient energy supply systems due to space limitations for renewable installations. Conventional solar cooling systems use photovoltaic electricity or thermal energy to run either a compression-cooling machine or an absorption-cooling machine in order to produce cooling energy during daytime, while they use electricity from the grid for the nightly cooling energy demand. With a hybrid photovoltaic-thermal collector, electricity as well as thermal energy can be produced at the same time. These collectors can produce also cooling energy at nighttime by longwave radiation exchange with the night sky and convection losses to the ambient air. Such a renewable trigeneration system offers new fields of applications. Unfortunately, the technical, ecological and economical aspects of such systems are still largely unexplored.
To address this, German researchers from the University of Applied Sciences Stuttgart: Maximilian Haag, Jonas Stave, Nermeen Abdelnour and led by Professor Ursula Eicker (currently Canada Excellence Research Chair in Next Generation Cities at Concordia University) in collaboration with Reiner Braun at the Reutlingen University investigated the potential of a PVT system to heat and cool office buildings in three different climate zones. Their objective was to assess the use of hybrid collectors (PVT) for trigeneration of electricity, heat and cold. Their work is currently published in the research journal Solar Energy.
For this purpose, the research team undertook a parametric simulation study so as to evaluate the system design with different PVT surface areas and storage tank volumes to optimize the system for three different climate zones and for two different building standards. The team investigated the PVT collectors act as a heat source and heat sink for a reversible heat pump.
The authors reported that due to the reduced electricity consumption (from the grid) for heat rejection, the overall efficiency and economics improved compared to a conventional solar cooling system using a reversible air-to-water heat pump as heat and cold source. In addition, the annual costs for such a system were seen to be comparable to conventional solar thermal and solar electrical cooling systems.
In summary, the study demonstrated the applicability of PVT collectors as a heat source and heat sink for a reversible heat pump (rev. HP) in three different climates. In order to analyze the potential of PVT systems to achieve net zero energy, passive building standards were compared to more conventional construction standards. Overall, their work showed that through their new approach, a specific system dimensioning could be found at each of the investigated locations worldwide for a valuable economic and ecological operation of an office building with PVT technologies in different system designs.
Reiner Braun, Maximilian Haag, Jonas Stave, Nermeen Abdelnour, Ursula Eicker. System design and feasibility of trigeneration systems with hybrid photovoltaic-thermal (PVT) collectors for zero energy office buildings in different climates. Solar Energy, volume 196 (2020) page 39–48.