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Olivieri L.,Technical University of Madrid | Olivieri L.,University of Applied Sciences and Arts Southern Switzerland | Frontini F.,University of Applied Sciences and Arts Southern Switzerland | Polo-Lopez C.,University of Applied Sciences and Arts Southern Switzerland | And 3 more authors.
Energy and Buildings | Year: 2015

Abstract Whereas the modern architecture trends to an extensive use of glazing elements, buildings are increasingly required to minimize the external energy demand, cutting down the energy needed and covering the residual demand using local energy generation solutions. In this context, the integration of optimized Semi-Transparent Photovoltaic (STPV) elements seems to present a promising energy saving potential, leading to significant reductions of the heating, cooling and lighting loads while the on-site electricity generation is supplied. In mild climate areas, building glazings are required to perform as solar control systems with a low solar factor in order to avoid overheating. However, g-value is frequently unavailable in the data sheet of the STPV elements, making it difficult to design the optimal building solution. In the present work, an indoor testing facility to analyze the solar factor of STPV elements has been further developed and validated. The operating principles of the calorimetric system as well as the experimental data obtained in the validation stage are presented. Results show that the system accuracy and sensitivity are fully adequate to perform detailed analyses of the solar factor of STPV glazings. Furthermore, g-value variations with the transparency degree have been analyzed over different electrical operating points. © 2015 Elsevier B.V.

Bunea M.,Laboratory of Solar Energetics and Building Physics LESBAT | Perers B.,Technical University of Denmark | Eicher S.,Laboratory of Solar Energetics and Building Physics LESBAT | Hildbrand C.,Laboratory of Solar Energetics and Building Physics LESBAT | And 2 more authors.
Solar Energy | Year: 2015

Combined heat pumps and solar collectors got a renewed interest on the heating system market worldwide. Connected to the heat pump evaporator, unglazed solar collectors can considerably increase their efficiency, but they also raise the coefficient of performance of the heat pump with higher average temperature levels at the evaporator. Simulation of these systems requires a collector model that can take into account operation at very low temperatures (below freezing) and under various weather conditions, particularly operation without solar irradiation.A solar collector mathematical model is developed and evaluated considering, the condensation/frost effect and rain heat gains or losses. Also wind speed and long wave irradiation on both sides of the collector are treated. Results show important heat gains for unglazed solar collectors without solar irradiation. Up to 50% of additional heat gain was found due to the condensation phenomenon and up to 40% due to frost under no solar irradiation. This work also points out the influence of the operating conditions on the collector's characteristics.Based on experiments carried out at a test facility, every heat flux on the absorber was separately evaluated so that this model can represent a valuable tool in optimising the design or the thermal efficiency of the collector. It also enables the prediction of the total energy yield for solar thermal collectors under extreme operating conditions. © 2015 Elsevier Ltd.

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