Veröffentlichungen
2020 |
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F. Giovannetti, C. Lampe, M. Kirchner, M. Littwin, S. Asenbeck, and S. Fische Experimental Investigations on Photovoltaic-Thermal Arrays Designed for the Use as Heat Pump Source Inproceedings Proceedings ISES Solar World Congress 2019 / IEA SHC International Conference on Solar Heating and Cooling for Buildings and Industry 2019, 177-188, (2020). Abstract | Links | BibTeX | Schlagwörter: field test, heat exchanger, heat pump, heat transfer coefficient, Photovoltaic-thermal collector @inproceedings{Giovannetti2020,
title = {Experimental Investigations on Photovoltaic-Thermal Arrays Designed for the Use as Heat Pump Source}, author = {F Giovannetti and C Lampe and M Kirchner and M Littwin and S Asenbeck and S Fische}, doi = {10.18086/swc.2019.05.03}, year = {2020}, date = {2020-06-10}, booktitle = {Proceedings ISES Solar World Congress 2019 / IEA SHC International Conference on Solar Heating and Cooling for Buildings and Industry 2019}, pages = {177-188}, abstract = {Uncovered, liquid-basedphotovoltaic-thermal (PV-T) collectors can becombined withground-coupled heat pump systems for different purposes: toincrease the evaporator temperature,to regenerate geothermal resourcesor for pre-heatingdomestic hot water. Thispaperexperimentally investigates the behavior of a novel PV-T panelwith enhancedambient heat transfer propertiesandprimarily conceived for the operation as the sole heat source for brine-to-water compression heat pumps. After presenting the results of the thermal efficiency measurement of the panel, which attest itsunusual parameters (c1= 23W/m²K, c3= 7.6J/m³K, c6= 0.1s/m),we report onthe long-term performance tests carried out on large roof-mounted PV-T fields at two different locationsin Germany. The investigation focuseson the impact of real environmentalandinstallation conditions on the performanceof the field as ambient heat exchanger,operating at fluid temperatures below ambient air temperature. The results confirmthehigh overall heat transfer coefficient Uof the field,up to 40 W/m²K,which isreduced by about20%in comparison to the U-value determined for thesingle panel, however. The reduction can be attributed to a largeextent to the high sensitivity of the collector design to convective heat transfer mechanismsand to the different wind exposure during the tests.For the same reasons we report a 30% decrease in the U-value compared to the basic configuration by usingjoint plates to cover the gaps of the field with the aim of improvingthe reliability and aestheticsof the installation.}, keywords = {field test, heat exchanger, heat pump, heat transfer coefficient, Photovoltaic-thermal collector}, pubstate = {published}, tppubtype = {inproceedings} } Uncovered, liquid-basedphotovoltaic-thermal (PV-T) collectors can becombined withground-coupled heat pump systems for different purposes: toincrease the evaporator temperature,to regenerate geothermal resourcesor for pre-heatingdomestic hot water. Thispaperexperimentally investigates the behavior of a novel PV-T panelwith enhancedambient heat transfer propertiesandprimarily conceived for the operation as the sole heat source for brine-to-water compression heat pumps. After presenting the results of the thermal efficiency measurement of the panel, which attest itsunusual parameters (c1= 23W/m²K, c3= 7.6J/m³K, c6= 0.1s/m),we report onthe long-term performance tests carried out on large roof-mounted PV-T fields at two different locationsin Germany. The investigation focuseson the impact of real environmentalandinstallation conditions on the performanceof the field as ambient heat exchanger,operating at fluid temperatures below ambient air temperature. The results confirmthehigh overall heat transfer coefficient Uof the field,up to 40 W/m²K,which isreduced by about20%in comparison to the U-value determined for thesingle panel, however. The reduction can be attributed to a largeextent to the high sensitivity of the collector design to convective heat transfer mechanismsand to the different wind exposure during the tests.For the same reasons we report a 30% decrease in the U-value compared to the basic configuration by usingjoint plates to cover the gaps of the field with the aim of improvingthe reliability and aestheticsof the installation.
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2018 |
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S. Brötje, M. Kirchner, and F. Giovannetti Solar Energy 170 , 406-418, (2018), ISSN: 0038-092X. Abstract | Links | BibTeX | Schlagwörter: Detachable compound, Heat transfer modelling, Photovoltaic-thermal collector, Uncovered collector @article{Brötje2018c,
title = {Performance and heat transfer analysis of uncovered photovoltaic-thermal collectors with detachable compound}, author = {S Brötje and M Kirchner and F Giovannetti}, doi = {10.1016/j.solener.2018.05.030}, issn = {0038-092X}, year = {2018}, date = {2018-08-01}, journal = {Solar Energy}, volume = {170}, pages = {406-418}, abstract = {Concerning the manufacturing of uncovered, liquid-based photovoltaic-thermal (PVT) collectors, design requirements or low expenses have higher priority than the all-out optimization of the thermal efficiency. The specific impact of inevitable thermal resistances caused by wavy surfaces and imperfect contacts between PV modules and heat exchangers has not been comprehensively investigated yet. This paper focuses on the performances of uncovered PVT collectors with detachable mounting of PV modules on heat exchangers and the effect of macroscopic air gaps. Two prototypes with thin film modules were built without using silicon glue, other adhesives or heat conductive paste. Measured in sun simulator in electrical open-circuit mode, the thermal zero-loss efficiencies for the adhesive-free collectors are η0,M = 66.8% (copper pipe meander laser-welded on aluminium sheet) and η0,M = 69.2 % (aluminium roll-bond) based on gross areas. These results are similar or better than the efficiencies of commercially available collectors. Due to the thermal resistance of air gaps, we calculated temperature differences of 12 K and higher between absorbing sheets and heat carrier, which have to be considered while estimating the electrical yield by means of system simulations. For comparison, we built a prototype with a roll-bond heat exchanger and a very thin adhesive layer and thereby an optimized heat transport (η0,M = 76.8 %). Using numerical, two-dimensional models, we can verify the efficiency measurements and determine the influence of design and boundary conditions on heat transfer mechanisms in the collectors. Simulations show good agreement with experimental results and prove to be an effective tool for design optimization.}, keywords = {Detachable compound, Heat transfer modelling, Photovoltaic-thermal collector, Uncovered collector}, pubstate = {published}, tppubtype = {article} } Concerning the manufacturing of uncovered, liquid-based photovoltaic-thermal (PVT) collectors, design requirements or low expenses have higher priority than the all-out optimization of the thermal efficiency. The specific impact of inevitable thermal resistances caused by wavy surfaces and imperfect contacts between PV modules and heat exchangers has not been comprehensively investigated yet. This paper focuses on the performances of uncovered PVT collectors with detachable mounting of PV modules on heat exchangers and the effect of macroscopic air gaps. Two prototypes with thin film modules were built without using silicon glue, other adhesives or heat conductive paste. Measured in sun simulator in electrical open-circuit mode, the thermal zero-loss efficiencies for the adhesive-free collectors are η0,M = 66.8% (copper pipe meander laser-welded on aluminium sheet) and η0,M = 69.2 % (aluminium roll-bond) based on gross areas. These results are similar or better than the efficiencies of commercially available collectors. Due to the thermal resistance of air gaps, we calculated temperature differences of 12 K and higher between absorbing sheets and heat carrier, which have to be considered while estimating the electrical yield by means of system simulations. For comparison, we built a prototype with a roll-bond heat exchanger and a very thin adhesive layer and thereby an optimized heat transport (η0,M = 76.8 %). Using numerical, two-dimensional models, we can verify the efficiency measurements and determine the influence of design and boundary conditions on heat transfer mechanisms in the collectors. Simulations show good agreement with experimental results and prove to be an effective tool for design optimization.
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