1.
J Jensen; B Schiebler; S Kabelac; F Giovannetti
Modeling of solar thermal heat pipe collectors with overheating prevention in system simulations Artikel
In: Solar Energy, Bd. 282, S. 112861, 2024, ISSN: 0038-092X.
@article{Jensen2024,
title = {Modeling of solar thermal heat pipe collectors with overheating prevention in system simulations},
author = {J Jensen and B Schiebler and S Kabelac and F Giovannetti},
doi = {10.1016/j.solener.2024.112861},
issn = {0038-092X},
year = {2024},
date = {2024-11-01},
urldate = {2024-01-01},
journal = {Solar Energy},
volume = {282},
pages = {112861},
abstract = {Solar thermal collectors can provide renewable heat in an efficient way. They face however issues of overheating under certain circumstances, which can lead to thermal stress and steam formation. One solution to this issue consists in using solar thermal collectors with overheating prevention based on heat pipes. This paper presents the new TRNSYS type 839 that accurately reproduces the heat pipe overheating prevention effect. The model is validated using data from high accuracy solar tracker measurements as well as real solar thermal systems. A mean absolute deviation in the validation of less than 2% shows the functionality and accuracy of type 839. The results were compared with simulations using the existing Type 832 (without heat pipe limitation) and the simpler 2-part efficiency curve approach adapted from practice-oriented planning tools. By comparison, type 832 shows a mean absolute deviation of 44.8% using the same data. The use of the 2-part efficiency curve approach results in a mean absolute deviation of 49 %. With type 839 it is possible to design and evaluate solar thermal collectors with heat pipe limitation in TRNSYS and assess their use in a wide variety of systems. The new model is particularly recommended for applications with a relatively high and constant temperature level (e.g. process or district heating), for gross heat yield simulations or for the design of systems in order to correctly analyze the influence of the heat pipe limitation.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Solar thermal collectors can provide renewable heat in an efficient way. They face however issues of overheating under certain circumstances, which can lead to thermal stress and steam formation. One solution to this issue consists in using solar thermal collectors with overheating prevention based on heat pipes. This paper presents the new TRNSYS type 839 that accurately reproduces the heat pipe overheating prevention effect. The model is validated using data from high accuracy solar tracker measurements as well as real solar thermal systems. A mean absolute deviation in the validation of less than 2% shows the functionality and accuracy of type 839. The results were compared with simulations using the existing Type 832 (without heat pipe limitation) and the simpler 2-part efficiency curve approach adapted from practice-oriented planning tools. By comparison, type 832 shows a mean absolute deviation of 44.8% using the same data. The use of the 2-part efficiency curve approach results in a mean absolute deviation of 49 %. With type 839 it is possible to design and evaluate solar thermal collectors with heat pipe limitation in TRNSYS and assess their use in a wide variety of systems. The new model is particularly recommended for applications with a relatively high and constant temperature level (e.g. process or district heating), for gross heat yield simulations or for the design of systems in order to correctly analyze the influence of the heat pipe limitation.
2.
B Schiebler; J Köhler; L Wagner; J Jensen; F Giovannetti
In: Solar Energy Advances, Bd. 3, S. 100040, 2023.
@article{Schiebler2023c,
title = {Heat pipe collectors with overheating prevention in a cost-optimized system concept: Monitoring of system performance and stagnation loads under real conditions},
author = {B Schiebler and J Köhler and L Wagner and J Jensen and F Giovannetti},
doi = {10.1016/j.seja.2023.100040},
year = {2023},
date = {2023-05-26},
urldate = {2023-01-01},
journal = {Solar Energy Advances},
volume = {3},
pages = {100040},
abstract = {Heat pipe collectors can significantly reduce stagnation loads in solar thermal systems due to their thermophysical properties. The paper experimentally investigates a novel system concept based on both evacuated tube collectors and flat-plate collectors with overheating prevention. Due to the resulting temperature limitation in the collector, the use of polymeric pipes as well as a significantly downsized expansion volume is possible. We implemented this concept in five demonstration plants and monitored their behavior over more than one year of operation. Both domestic hot water systems and combi-systems with space heating support in residential and office buildings are under consideration. The measured collector performance in all the systems matches the theoretical collector efficiency curve with a maximum deviation of five percentage points. Depending on the individual system configurations, the specific annual yield ranges between 174 kWh/m² and 445 kWh/m². During stagnation, we report a maximum temperature between 105 °C and 127 °C. In comparison to state-of-the-art systems, the maximum temperature in the solar circuit is 80–100 K lower and evaporation does not occur. The approach leads to reductions in investment costs of up to 16% and can significantly decrease the annual maintenance effort. Assuming a system lifetime of 25 years, we estimate a cost reduction of up to 22% in Levelized Cost of Heat (LCoH) compared to common system configurations.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Heat pipe collectors can significantly reduce stagnation loads in solar thermal systems due to their thermophysical properties. The paper experimentally investigates a novel system concept based on both evacuated tube collectors and flat-plate collectors with overheating prevention. Due to the resulting temperature limitation in the collector, the use of polymeric pipes as well as a significantly downsized expansion volume is possible. We implemented this concept in five demonstration plants and monitored their behavior over more than one year of operation. Both domestic hot water systems and combi-systems with space heating support in residential and office buildings are under consideration. The measured collector performance in all the systems matches the theoretical collector efficiency curve with a maximum deviation of five percentage points. Depending on the individual system configurations, the specific annual yield ranges between 174 kWh/m² and 445 kWh/m². During stagnation, we report a maximum temperature between 105 °C and 127 °C. In comparison to state-of-the-art systems, the maximum temperature in the solar circuit is 80–100 K lower and evaporation does not occur. The approach leads to reductions in investment costs of up to 16% and can significantly decrease the annual maintenance effort. Assuming a system lifetime of 25 years, we estimate a cost reduction of up to 22% in Levelized Cost of Heat (LCoH) compared to common system configurations.
3.
B Schiebler; F Weiland; F Giovannetti; O Kastner; S Jack
Improved flat plate collector with heat pipesfor overheating prevention in solar thermal systems Proceedings Article
In: Proceedings ISES Solar World Congress 2019 / IEA SHC International Conference on Solar Heating and Cooling for Buildings and Industry 2019, S. 61-72, 2020.
@inproceedings{Schiebler2020,
title = {Improved flat plate collector with heat pipesfor overheating prevention in solar thermal systems},
author = {B Schiebler and F Weiland and F Giovannetti and O Kastner and S Jack},
doi = {10.18086/swc.2019.01.08},
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 = {61-72},
abstract = {Heat pipes in solar thermal collectors can reduce thermal loads in the solar circuit by using the physical effect of dry-out limitation. By avoiding high temperatures and vapor formation, simplified, more reliable and cost effective solar thermal systems can be designed. This paper presents a theoretical study ondifferentheat pipe andmanifoldconfigurationsfor flat plate collectors. The focus is ona highthermal efficiency in the operating rangeand a significant temperature limitation in stagnation mode. Several prototype collectorsaremanufactured and experimentallyinvestigated by means of indoor performance measurements. Thereby,a conversion factor of 73%isreported, whichrepresents an increase of 4percentage pointscompared to a previous prototype. Duringstagnationeventswe localizea maximum fluid temperature about130°C within the manifold, whichdecreases to values below 100°C towardsthe collector connections.Finally, we evaluate the system performance of the prototypewithanexemplary solar DHW-systemby means of dynamic TRNSYS-simulations. The results show that the calculated annual yield ispredictedonly 5% lower than the one of a comparabledirect flow collectorand critical stagnation eventscan be fully avoided.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
Heat pipes in solar thermal collectors can reduce thermal loads in the solar circuit by using the physical effect of dry-out limitation. By avoiding high temperatures and vapor formation, simplified, more reliable and cost effective solar thermal systems can be designed. This paper presents a theoretical study ondifferentheat pipe andmanifoldconfigurationsfor flat plate collectors. The focus is ona highthermal efficiency in the operating rangeand a significant temperature limitation in stagnation mode. Several prototype collectorsaremanufactured and experimentallyinvestigated by means of indoor performance measurements. Thereby,a conversion factor of 73%isreported, whichrepresents an increase of 4percentage pointscompared to a previous prototype. Duringstagnationeventswe localizea maximum fluid temperature about130°C within the manifold, whichdecreases to values below 100°C towardsthe collector connections.Finally, we evaluate the system performance of the prototypewithanexemplary solar DHW-systemby means of dynamic TRNSYS-simulations. The results show that the calculated annual yield ispredictedonly 5% lower than the one of a comparabledirect flow collectorand critical stagnation eventscan be fully avoided.