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Papers by Martin Helm
Energy Procedia, 2016
Within IEA-SHC Task 48 "Quality assurance and support measures for Solar Cooling" the most crucia... more Within IEA-SHC Task 48 "Quality assurance and support measures for Solar Cooling" the most crucial components of solar thermal cooling plants have been analyzed in detail aiming at improving their quality. Test procedures for characterizing continuous and discontinuous chillers have been developed; market available heat rejection devices have been investigated, rating their performance through monitoring data and comparing them; pump efficiency has been also investigated and design guidelines for pump selection and hydraulic configuration are now available; a detailed and updated database of medium temperature collectors has been built.
Energy Procedia, 2012
Solar thermal cooling and heating plants with single-effect sorption chillers/ heat pumps promise... more Solar thermal cooling and heating plants with single-effect sorption chillers/ heat pumps promise primary energy savings compared to electric vapor compression chiller systems. Yet, the need of auxiliary electric and fossil energy for the operation and backup of the thermal cooling system possibly worsen the primary energy balance. An auspicious approach to overcome this problem is the application of a more efficient multi-stage sorption chiller with flexible operational modes. A pilot installation of that innovative solar thermal heating and cooling plant comprising a two stage absorption chiller / heat pump is presented. Beginning with the motivation and the system concept, a detailed analysis of the 2011/2012 cooling and heating periods is shown. The influence of the different system componentsespecially the absorption chilleron the overall system performance is analyzed and a comparison to data from a detailed dynamic model is carried out. Recommendations for the improvement with respect to efficiency and economic aspects are given based on the installation process and the operational experience gained in the last 1 ½ years.
Energy Procedia, 2014
A reliable solar thermal cooling and heating system with high solar fraction and seasonal energy ... more A reliable solar thermal cooling and heating system with high solar fraction and seasonal energy efficiency ratio (SEER) is preferable. By now, bulky sensible buffer tanks are used to improve the solar fraction for heating purposes. During summertime when solar heat is converted into useful cold by means of sorption chillers the waste heat dissipation to the ambient is the critical factor. If a dry cooler is installed the performance of the sorption machine suffers from high cooling water temperatures, especially on hot days. In contrast, a wet cooling tower causes expensive water treatment, formation of fog and the risk of legionella and bacterial growth. To overcome these problems a latent heat storage based on a cheap salt hydrate has been developed to support a dry cooler on hot days, whereby a constant low cooling water temperature for the sorption machine is ensured. Therefore the need of a wet cooling tower is avoided and neither make-up water nor maintenance is needed. The same storage serves as additional low temperature heat storage for heating purposes allowing optimal solar yield due to constant low storage temperatures. Four pilot installations between 7 kW and 90 kW nominal cooling capacity were equipped with latent heat storages between 80 kWh and 240 kWh energy content. Annual in situ measurement data shows a positive effect on the seasonal energy efficiency ratio (SEER) for cooling up to 11.4. Furthermore simulation results under different climatic conditions indicate raising efficiency up to 64% compared to a system with solely dry re-cooling. Long-term test bench measuring data concerning performance and durability as well as a new approach for a state of charge detection for latent heat storages are presented as well.
International Journal of Refrigeration, 2009
Chemistry of the Climate System
Chemistry of the Climate System
International Journal of Refrigeration
Proceedings of the EuroSun 2010 Conference, 2010
Proceedings of the EuroSun 2010 Conference, 2010
In solar thermal installations, full annual utilisation is desirable. This can be achieved with s... more In solar thermal installations, full annual utilisation is desirable. This can be achieved with solar space heating during the cold season and solar cooling by means of sorption cooling in the warm season. When low temperature heating and cooling facilities like floor or wall heating systems or activated ceilings are applied for heating and cooling, a low-temperature heat storage using
A Guide to Solar Assisted Cooling and Dehumidification Processes, 2013
Volume 2D: Turbomachinery, 2016
Proceedings of the EuroSun 2010 Conference, 2010
A Guide to Solar Assisted Cooling and Dehumidification Processes, 2013
Energy Procedia, 2016
Within IEA-SHC Task 48 "Quality assurance and support measures for Solar Cooling" the most crucia... more Within IEA-SHC Task 48 "Quality assurance and support measures for Solar Cooling" the most crucial components of solar thermal cooling plants have been analyzed in detail aiming at improving their quality. Test procedures for characterizing continuous and discontinuous chillers have been developed; market available heat rejection devices have been investigated, rating their performance through monitoring data and comparing them; pump efficiency has been also investigated and design guidelines for pump selection and hydraulic configuration are now available; a detailed and updated database of medium temperature collectors has been built.
Energy Procedia, 2012
Solar thermal cooling and heating plants with single-effect sorption chillers/ heat pumps promise... more Solar thermal cooling and heating plants with single-effect sorption chillers/ heat pumps promise primary energy savings compared to electric vapor compression chiller systems. Yet, the need of auxiliary electric and fossil energy for the operation and backup of the thermal cooling system possibly worsen the primary energy balance. An auspicious approach to overcome this problem is the application of a more efficient multi-stage sorption chiller with flexible operational modes. A pilot installation of that innovative solar thermal heating and cooling plant comprising a two stage absorption chiller / heat pump is presented. Beginning with the motivation and the system concept, a detailed analysis of the 2011/2012 cooling and heating periods is shown. The influence of the different system componentsespecially the absorption chilleron the overall system performance is analyzed and a comparison to data from a detailed dynamic model is carried out. Recommendations for the improvement with respect to efficiency and economic aspects are given based on the installation process and the operational experience gained in the last 1 ½ years.
Energy Procedia, 2014
A reliable solar thermal cooling and heating system with high solar fraction and seasonal energy ... more A reliable solar thermal cooling and heating system with high solar fraction and seasonal energy efficiency ratio (SEER) is preferable. By now, bulky sensible buffer tanks are used to improve the solar fraction for heating purposes. During summertime when solar heat is converted into useful cold by means of sorption chillers the waste heat dissipation to the ambient is the critical factor. If a dry cooler is installed the performance of the sorption machine suffers from high cooling water temperatures, especially on hot days. In contrast, a wet cooling tower causes expensive water treatment, formation of fog and the risk of legionella and bacterial growth. To overcome these problems a latent heat storage based on a cheap salt hydrate has been developed to support a dry cooler on hot days, whereby a constant low cooling water temperature for the sorption machine is ensured. Therefore the need of a wet cooling tower is avoided and neither make-up water nor maintenance is needed. The same storage serves as additional low temperature heat storage for heating purposes allowing optimal solar yield due to constant low storage temperatures. Four pilot installations between 7 kW and 90 kW nominal cooling capacity were equipped with latent heat storages between 80 kWh and 240 kWh energy content. Annual in situ measurement data shows a positive effect on the seasonal energy efficiency ratio (SEER) for cooling up to 11.4. Furthermore simulation results under different climatic conditions indicate raising efficiency up to 64% compared to a system with solely dry re-cooling. Long-term test bench measuring data concerning performance and durability as well as a new approach for a state of charge detection for latent heat storages are presented as well.
International Journal of Refrigeration, 2009
Chemistry of the Climate System
Chemistry of the Climate System
International Journal of Refrigeration
Proceedings of the EuroSun 2010 Conference, 2010
Proceedings of the EuroSun 2010 Conference, 2010
In solar thermal installations, full annual utilisation is desirable. This can be achieved with s... more In solar thermal installations, full annual utilisation is desirable. This can be achieved with solar space heating during the cold season and solar cooling by means of sorption cooling in the warm season. When low temperature heating and cooling facilities like floor or wall heating systems or activated ceilings are applied for heating and cooling, a low-temperature heat storage using
A Guide to Solar Assisted Cooling and Dehumidification Processes, 2013
Volume 2D: Turbomachinery, 2016
Proceedings of the EuroSun 2010 Conference, 2010
A Guide to Solar Assisted Cooling and Dehumidification Processes, 2013