Analysis of a gas-driven absorption heat pumping system used for heating and domestic hot water preparation

Part of: Thermally driven heat pumps for heating and cooling. – Ed.: Annett Kühn – Berlin: Universitätsverlag der TU Berlin, 2013 ISBN 978-3-7983-2686-6 (print) ISBN 978-3-7983-2596-8 (online) urn:nbn:de:kobv:83-opus4-39458 [http://nbn-resolving.de/urn:nbn:de:kobv:83-opus4-39458]In the building sector the use of thermally driven heat pumps can contribute substantially to energy conservation and the reduction of end-use energy. Within the IEA HPP Annex 34 a medium size absorption heat pump application installed in a storehouse in Graz has been monitored over a period of one year. The system consists of two directly natural gas-driven ground source ammonia/water absorption heat pumps (each with ca. 40 kW heating capacity). Via a buffer storage space heating of an office building and a storage depot as well as domestic hot water preparation is provided. During the monitoring period the system showed reliable operation and high energy performance. Based on the lower heating value of the natural gas the seasonal performance of the year 2010 was 1.54 which is approx. 60% higher compared to a condensing gas boiler with a seasonal performance of 96%. However, also room for improvements has been detected, especially at start/stop operation for domestic hot water preparation in summer

The formation of non-condensable gases in ammonia/ water absorption heat pumps made of stainless steel - literature review and experimental investigation

Part of: Thermally driven heat pumps for heating and cooling. – Ed.: Annett Kühn – Berlin: Universitätsverlag der TU Berlin, 2013 ISBN 978-3-7983-2686-6 (print) ISBN 978-3-7983-2596-8 (online) urn:nbn:de:kobv:83-opus4-39458 [http://nbn-resolving.de/urn:nbn:de:kobv:83-opus4-39458]Highly efficient ammonia/water absorption heat pumping (AHP) processes (e.g. the GAX-process) require a high desorption temperature level of e.g. 200°C and above. At these conditions the formation of non-condensable gases can take place, which can be dedicated to two chemical processes: corrosion of steel and thermal decomposition of ammonia. Within a research project the possible use of stainless steel components at high temperature level has been investigated. Tests with an absorption/desorption test rig operating at temperatures up to 290°C as well as corrosion tests using autoclaves at temperatures up to 220°C have been performed. The produced non-condensable gas has been analysed using gas-phase chromatography in order to identify the responsible chemical process. The results show a large initial corrosion rate which decreases with time. This may be explained by a passivation process of the steel surface. At all tests the carbon steel (ST37) autoclaves has shown significant lower corrosion rates compared to the stainless steel components. Regarding the thermal decomposition no dissociation products has been detected up to a temperature level of 290°C

Control-oriented modeling of a LiBr/H2O absorption heat pumping device and experimental validation

Absorption heat pumping devices (AHPDs, comprising absorption heat pumps and chillers) are devices that use thermal energy instead of electricity to generate heating and cooling, thereby facilitating the use of waste heat and renewable energy sources such as solar or geothermal energy. Despite this benefit, widespread use of AHPDs is still limited. One reason for this is partly unsatisfactory control performance under varying operating conditions, which can result in poor modulation and part load capability. A promising approach to tackle this issue is using dynamic, model-based control strategies, whose effectiveness, however, strongly depend on the model being used. This paper therefore focuses on the derivation of a viable dynamic model to be used for such model-based control strategies for AHPDs such as state feedback or model-predictive control. The derived model is experimentally validated, showing good modeling accuracy. Its modeling accuracy is also compared to alternative model versions, that contain other heat transfer correlations, as a benchmark. Although the derived model is mathematically simple, it does have the structure of a nonlinear differential-algebraic system of equations. To obtain an even simpler model structure, linearization at an operating point is discussed to derive a model in linear state space representation. The experimental validation shows that the linear model does have slightly worse steady-state accuracy, but that the dynamic accuracy seems to be almost unaffected by the linearization. The presented new modeling approach is considered suitable to be used as a basis for the design of advanced, model-based control strategies, ultimately aiming to improve the modulation and part load capability of AHPDs

Ionic liquids as new absorbents for absorption chillers and heat pumps

Part of: Thermally driven heat pumps for heating and cooling. – Ed.: Annett Kühn – Berlin: Universitätsverlag der TU Berlin, 2013 ISBN 978-3-7983-2686-6 (print) ISBN 978-3-7983-2596-8 (online) urn:nbn:de:kobv:83-opus4-39458 [http://nbn-resolving.de/urn:nbn:de:kobv:83-opus4-39458]In this paper, ionic liquids are proposed as new absorbents for absorption chillers and heat pumps. The theoretical and experimental based research of Technische Universität Berlin, Bavarian Center for Applied Energy Research (ZAE Bayern) and Graz University of Technology is presented and test and simulation results are discussed. The results show the suitability and promising potential of ionic liquids as absorbents but the research organizations agree in the need of further effort in R&D

Evaluation of different heat pump systems for sanitary hot water production using natural refrigerants

[EN] Heat pumps that work with a high degree of subcooling in subcritical systems have shown a significant margin of improvement when working with sanitary hot water applications. Recently, two different approaches to overcome the high degree of subcooling have been presented in the literature: with a subcooler (separate from the condenser) and by making all the subcooling in the condenser. In this paper, a comparative evaluation between both alternatives is presented, and the obtained results are compared with a representative solution already available on the market using natural refrigerants for this application. The results of this analysis have shown that in a system with subcooling in the condenser, it is possible to obtain a COP comparable to that of transcritical CO2 heat pump water heaters. Furthermore, the system with subcooling has been demonstrated experimentally as being capable of producing water up to 90ºC and has shown a COP up to 20% higher than some CO2 commercial products (catalogue data reference).This work has been developed in the Seventh Framework Program of the European Union by the project, Next Generation of Heat Pump Technologies (NEXTGHP), grant agreement 307169. The authors thank the support given. Part of the work presented was carried by Miquel Pitarch-Mocholí with the financial support of a PhD scholarship from the Universitat Politècnica de València. The authors would like also to acknowledge the Spanish ‘MINISTERIO DE ECONOMIA Y COMPETITIVIDAD’, through the project ref-ENE2014-53311-C2-1-P-AR ‘‘Aprovechamiento del calor residual a baja temperatura mediante bombas de calor para la produccion de agua caliente” for the given supportPitarch, M.; Navarro-Peris, E.; Gonzálvez-Maciá, J.; Corberán, JM. (2017). Evaluation of different heat pump systems for sanitary hot water production using natural refrigerants. Applied Energy. 190:911-919. https://doi.org/10.1016/j.apenergy.2016.12.166S91191919

A propane water-to-water heat pump booster for sanitary hot water production: Seasonal performance analysis of a new solution optimizing COP

[EN] Electrical heat pumps for sanitary hot water production achieve a high performance with a good matching of water and refrigerant temperature profiles during the heat rejection stage, as it happens in CO2 systems. This work considers the thermodynamic possibility to adapt the condenser pressure of a propane heat pump to maximize the COP, while producing sanitary hot water up to 60 C from a heat sink equal to 15 or 25 C. The performance of the heat pump is calculated through specific models which, in combination with a TRNSYS model of the whole system, allowed to assess its seasonal performance for a hotel in Strasbourg, also varying the control logic and the size of the storage tank. Results obtained led to the conclusion that, for achieving a high seasonal performance, the control logic of the tank has the largest influence.Part of the results of this study were developed in the mainframe of the FP7 European project ‘Next Generation of Heat Pumps working with Natural fluids’ (NxtHPG). Part of the work presented was carried by M. Tammaro during his visit at the Instituto de Ingenierı´a Energetica, Universitat Politecnica de Val encia and by C. Montagud during her visit at the Department of Industrial Engineering, Federico II University of Naples, with the financial support of the POLIGRID project.Tammaro, M.; Montagud Montalvá, CI.; Corberán Salvador, JM.; Mauro, AW.; Mastrullo, R. (2015). A propane water-to-water heat pump booster for sanitary hot water production: Seasonal performance analysis of a new solution optimizing COP. International Journal of Refrigeration. 51:59-69. https://doi.org/10.1016/j.ijrefrig.2014.12.008S59695

Transgenerationale Schuld? : die transgenerationale Übertragung des NS-Erbes an die Enkelgeneration von Nazi-Tätern und -Mitläufern unter besonderer Berücksichtigung der Verarbeitungsniveaus

Wiltrud Barbara Rieberer-MurerKlagenfurt, Alpen-Adria-Univ., Dipl.-Arb., 2012(VLID)241603

The ionic conductivity of a Nafion® 1100 series of proton-exchange membranes re-cast from butan-1-ol and propan-2-ol

The ionic conductivity of Nafion® 1100 extruded membranes re-cast from solutions of butan-1-ol and propan-2-ol is measured in 0.5 mol dm-3 H2SO4 at 295 K, using an immersed, four-electrode d.c. technique. The general trend is an increasing conductivity for the thicker membranes. Materials which were solution-cast from butan-1-ol yielded the highest conductivity while a series of membranes with lower conductivities (similar to those of an extruded Nafion® 1100 series of membranes) was found using propan-2-ol. The conductivity results indicate that membranes manufactured by extrusion and casting from various solvents might have different structures. Differences in the water content and conductivity of the membranes are considered to arise from the impact of processing conditions on the surface and bulk structure of the membranes