Bertram - Heat Pump Systems with Vertical Ground Heat Exchanger and Uncovered Solar Thermal Collectors Solar Ground Regeneration - Dynamic Simulation, Measurement and Dimensioning

Erik Bertram

Heat Pump Systems with Vertical Ground Heat Exchangers and Uncovered Solar Thermal Collectors

Solar Ground Regeneration - Dynamic Simulation, Measurement and Dimensioning

Erik Bertram, Heat Pump Systems with Vertical Ground Heat Exchangers and Uncovered Solar

Thermal Collectors

2015 der vorliegenden Ausgabe:

Verlagshaus Monsenstein und Vannerdat OHG Mnster

www.mv-wissenschaft.com

2015 Erik Bertram

Alle Rechte vorbehalten

Satz: E. Bertram

Umschlag: MV-Verlag

Umschlagabbildung: Erik Bertram, Institut fr Solarenergieforschung GmbH Hameln/Emmerthal

Illustrationen: E. Bertram

ISBN 978-3-95645-481-3

eBook-Herstellung und Auslieferung:
readbox publishing, Dortmund
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Acknowledgements

I am grateful to Dirk Bohne, professor for building technology at Leibniz University of Hannover, for mentoring this thesis and his trust in me that he showed by accepting me as an external doctoral candidate. Also, my sincere gratitude goes to Stephan Kabelac, professor at the Institute of thermodynamics at Leibniz University of Hannover, who gave valuable comments on many aspects of this thesis.

This thesis was mainly conducted at the Institute for Solar Energy Research Hameln (ISFH). I like to express my gratitude to Professor Rolf Brendel and especially Gunter Rockendorf at the ISFH who always supported my intention to write this dissertation and never doubted its successful outcome. Representative for the whole department my sincerest thanks goes to the working group Thermal Energy systems: Jan Steinweg, Jens Glembin, Peter Prisch, Rainer Tepe, Jonas Warmuth, Christoph Bttner, Oliver Mercker, Martin Stegmann, and Oliver Arnold. The mutual support in TRNSYS, and especially the component measurements of Peter Prisch, have been a privileged starting point for the system simulations. I could always rely on the technical support from Wolfgang Wetzel, Henri Diekmann, and Maik Kirchner. Sebastian Fste and Federico Giovannetti gave important support and valuable survival tips in the wilderness of my doctorate process. For me, the persons and the working atmosphere at ISFH are exceptional. I am honestly grateful and want to thank all colleagues at ISFH for the very cooperative, productive and fruitful time we shared.

This dissertation was part of the research project GeoSolar-WP (EFRE, W2-8011 4860). The project was funded by the European Union and the Federal State of Lower Saxony, which I gratefully acknowledge.

In the course of this project my work was continuously stimulated through the exchange with other researchers and practitioners. Holger Jensen, Martin Duddek and Wolfgang Wirth (State Authority for Mining, Energy and Geology, LBEG) always encouraged me and confirmed the practical relevance of my work. Johannes Brugmann (Stiebel Eltron), and Markus Sommer (Lohr Consult) gave valuable insight from the perspective of real applications in systems and their planning. Phillip Oberdorfer and Ekkehard Holzbecher (University of Gttingen) contributed with hard data and general discussion on modelling around their detailed multiphysics FEM model of a ground heat exchanger.

The work in the IEA SHC Task 44 / HPP ANNEX 38, led by Jean-Christoph Hadorn, must be highlighted because the international meetings had a remarkabley cooperative and open atmosphere. The Task also coined my understanding of good scientific practice and mutual beneficial exchange.

I deeply appreciate the opportunity to take part in the subtask working group Modeling and Simulation. The vivid scientific dialogue and cooperative work on system simulations and component modelling gave this thesis the right context. I worked and learned a lot about modelling of collectors, heat pumps, and complex systems from discussions with Michel Haller, Daniel Carbonell (SPF, Switzerland), Bengt Perers (DTU Denmark), Fabian Ochs (University of Innsbruck, Austria), Sarah Eicher, Mircea Bunea, Jaques Bony (Lesbat, Switzerland) Tomas Afjei and Ralph Dott (FHNW Switzerland), Werner Lerch and Andreas Heinz (TU Graz, Austria).

I also appreciate very much that Anja Loose (ITW Stuttgart, Germany), Jrn Ruschenburg, and Sebastian Herkel (Fraunhofer ISE, Germany) exchanged their valuable experience on solar assisted heat pump systems monitored. Bernard Thissen, (Energie Solaire, Switzerland) also provided great insights into uncovered solar thermal collectors and systems aspects from the manufacturers perspective. Likewise, my sincere thanks goes to Roberto Fedrizzi, Matteo DAntoni and the whole solar thermal systems group at EURAC, Italy. Their invitation and strong support allowed me to include solar assisted air heat pumps to this thesis. This task and the people in it were a stroke of luck for my thesis and a real pleasure for me to work with.

Finally, science is just a small world within a much more complex universe. My family, my friends, Ruaidhri OBolguidhir, who had the questionable pleasure of proofreading large parts of this thesis, the Trillke, and of course Janika have been absolutely crucial for this thesis.

I would never have made it without you all.

Abstract

Vertical ground heat exchanger and uncovered collectors are studied as a hybrid heat source in heat pump systems.

The effects are separated into over-seasonal effects and effects with an impact shorter than one year. Within one year the improvement due to solar thermal assistance is small. A defined temperature potential revealed a 5 K increase only due to the uncovered solar collector. Dynamic system simulations confirm that there is little improvement in efficiency as shown in numerical experiments. The system simulations adopt a reproducible simulation framework from SHC Task 44 / HPP Annex 38 of the International Energy Agency and modified and validated models for the vertical ground heat exchanger as well as the heat pump. Nevertheless, the small changes in temperature due to solar regeneration allow for 10-20% ground heat exchanger shortening.

This possible shortening increases significantly in the case of over-seasonal effects where an interference between multiple borehole heat exchangers occurs. It is correspondingly highly relevant in larger or adjacent systems. It is demonstrated in theoretical analysis and in case studies that solar regeneration eliminates the interference and correspondingly allows free scaling of systems with vertical ground heat exchangers.

Simple dimensioning rules have been derived that allow for collector dimensioning on a monthly data basis. Moreover, a method for vertical ground heat exchanger dimensioning is presented in the case of an even heat balance. The methods are successfully validated against data from measured systems and the dynamic system model. As a rule of thumb, around 1.1 m2 uncovered collector per MWh of heat used suffices for solar regeneration of the vertical ground heat exchanger.

Key words:

Temperature potential, solar ground regeneration, dimensioning method for uncovered collector

Kurzfassung

Vertikale Erdwrmesonden und unabgedeckte Kollektoren wurden als hybride Wrmequelle in Wrmepumpensystemen untersucht.

Die Einflsse werden in bersaisonale und einjhrige Einflsse aufgeteilt. Die Verbesserung innerhalb eines Jahres ist klein. Das definierte Temperaturpotential zeigte nur eine Temperaturverbesserung um 5 K durch den unabgedeckten Kollektor auf. Dynamische Systemsimulationen besttigen den geringen Einfluss auf die Systemeffizienz in numerischen Experimenten. Die Systemsimulationen verwenden modifizierte und validierte Modelle fr die vertikalen Erdwrmesonden und die Wrmepumpe und eine reproduzierbare Simulationsumgebung aus dem SHC Task 44 / HPP Annex 38 der Internationalen Energie Agentur. Dennoch erlaubt die solare Regeneration eine Krzung der Erdwrmesonde um 10 -20%.