IMPROVED SUPPLY OF DISTRICT HEAT TO HYDRONIC SPACE HEATING SYSTEMS Patrick Lauenburg Doctoral thesis Division of Efficient Energy Systems Department of Energy Sciences Faculty of Engineering Lund University, Sweden 2009 Akademisk avhandling för avläggande av teknologie doktorsexamen vid tekniska fakulteten vid Lunds universitet. Avhandlingen kommer att försvaras vid en offentlig disputation onsdagen den 16 december 2009, kl 10.15 i hörsal B, M-huset, Ole Römers väg 1, Lund. Academic thesis which, by due permission of the Faculty of Engineering, will be publicly defended on Wednesday December 16th, 2009, at 10.15 a.m. in lecture hall B, at M-huset, Ole Römers väg 1, Lund, for the degree of Doctor of Philosophy in Engineering. Fakultetsopponent är / The faculty opponent is: Dr. Otto Paulsen, Teknologisk Institut, Taastrup, Denmark. IMPROVED SUPPLY OF DISTRICT HEAT TO HYDRONIC SPACE HEATING SYSTEMS Patrick Lauenburg IMPROVED SUPPLY OF DISTRICT HEAT TO HYDRONIC SPACE HEATING SYSTEMS © 2009 Patrick Lauenburg Printed in Sweden by E-husets Tryckeri, Lund, 2009 ISRN LUTMDN/TMHP--09/1069--SE ISSN 0282-1990 ISBN 978-91-628-7976-1 ii ABSTRACT The studies presented in this thesis concern hydronic space heating systems connected via heat exchangers to a district heating network: referred to as an indirect connection. The objective has been to improve the reliability of district heat supplies and to lower the return temperature from consumer substations. Two of the disadvantages of an indirect connection have been addressed: the thermodynamic loss and the local dependency on electricity involved during the use of a heat exchanger. The results show that the influence of these disadvantages can be reduced by employing several variants of so-called low-flow processes in hydronic heating systems. Concerning the reliability of district heat supplies, the present work has led to new knowledge regarding the dependence of the district heating technology on electricity. A substantial heat supply can be maintained in numerous buildings in case of an electric power failure since natural circulation can be expected to take place in the heating systems. A turbine-driven circulation pump has the potential to further reduce the dependence on electricity. Concerning a low return temperature from consumer substations, which is a key performance measure for district heating substations, a new method for the control of the heating system has demonstrated a potential of reducing the district heating return temperature. The method involves the control of both the supply temperature and the flow rate in the heating system. The possibility of achieving a low return temperature from different connection schemes of the substation has also been studied. Keywords: District heating, hydronic space heating, natural circulation, low return temperature iii ACKNOWLEDGEMENTS Many have participated in and helped out during this work, and I am very grateful to everyone. Thanks to: My supervisor, Professor Svend Frederiksen, for giving me the opportunity to conduct my PhD studies at the division, for sharing your impressive knowledge on district heating with me, and for guiding me through the work. My co-supervisor, Dr Janusz Wollerstrand, for our (almost) daily discussions, your patience with an often confused PhD student, and for sharing your great technical skills with me. Per-Olof Johansson, for all the hours spent on performing measurements in dirty basements, in front of the computer writing papers and building computer models and, last but not least, drinking coffee. The project leader for the project concerning district heating in case of power failure, Mr Lennart Lindsjö, and the consultative group, Messrs Lennart Andersson, Jan Berglund, Conny Håkansson, Kurt Ericsson, Egon Lange and Jan-Peter Stål, for your valuable support, and Mrs Anna Envall Lundberg, communicator for the project. Mr Harald Andersson at E.ON, who came up with the idea to study natural circulation and initiated the project. Chairman and members of the Scientific Committe of the Nordic Energy Research Programme “Primary Energy Efficiency”, Messrs Rolf Ulseth, and the project group, Carl-Johan Fogelholm, Olafur Petur Palsson, Andres Siirde, and Lars Gullev, together with my Nordic fellow PhD students Monica Berner, Thomas Kohl, Marta Ros Karlsdottir and Eduard Latosov, all for guidance and interesting seminars. v The consultative group in the adaptive control project, Messrs Kjell Andersson, Holger Feurstein, Gunnar Nilsson, Östen Tordenmalm, Robert Duimovich, Lars Hansson and Hampus Ekvall, for valuable support. Mr Hans Magnusson at Karlshamnsbostäder, for helping out in the adaptive control project by always making our visits to Karlshamn a pleasure. Messrs Christian Johansson and Fredrik Wernstedt at BTH/Noda IS AB, for all the help in Karlshamn and for letting us use your equipment. Karlshamn Energi AB and Alfa Laval AB for help with the adaptive control project. Göteborg Energi AB and Grundfos A/S for help with the project on the turbine-driven pump. All caretakers and other personnel, rendering possible the field experiments. All colleagues at my division, Lennart Thörnqvist, Professor Emeritus, Jurek Pyrko, Professor, Fahrad Derakhshan and Tommy Persson (who guided me during my first year before he left), as well as everybody at the department, especially Magnus Fast and Klas Jonshagen, for your appreciated company. Svensk Fjärrvärme AB, Energimyndigheten, Nordic Energy Research, E.ON Värme Sverige AB, Malmö Stad, Stadsfastigheter, MKB Fastighet AB and Göteborg Energi Research Foundation for financial support. My family: mother, father and brother, and the most important person to me: my wife Sofi, for your support! vi List of publications This thesis is based on the following papers, referred to in the text by their Roman numerals. The papers are appended at the end of the thesis. Please note that I changed my name in 2008, from Ljunggren to Lauenburg. Paper I Optimised space heating system operation with the aim of lowering the primary return temperature Ljunggren, P., Johansson, P.-O., Wollerstrand, J. Conference proceeding from the 11th International Symposium on District Heating and Cooling, 2008, Reykjavik, Iceland. Paper II Obstacles for natural circulation in heating systems, connected to district heating via heat exchangers, during a power failure Johansson, P.-O., Ljunggren, P., Wollerstrand, J. Conference proceeding from the 11th International Symposium on District Heating and Cooling, 2008, Reykjavik, Iceland. Paper III Modelling space heating systems connected to district heating in case of electric power failure Lauenburg, P., Johansson, P.-O., Wollerstrand, J. Conference proceedings from Building Simulation 2009 (11th International Building Performance Simulation Association Conference and Exhibition), Glasgow, UK. Paper IV A turbine-driven circulation pump in a district heating substation Wollerstrand, J., Lauenburg, P., Frederiksen, S. Conference proceedings from ECOS 2009 (22nd International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems), Foz do Iguaçu, Brazil. Paper V Improved cooling of district heating water in substations by using alternative connection schemes Johansson, P.-O., Lauenburg, P., Wollerstrand, J. Conference proceedings from ECOS 2009 (22nd International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems), Foz do Iguaçu, Brazil. vii Paper VI District heating in case of power failure Lauenburg, P., Johansson, P.-O., Wollerstrand, J. Article in press, accepted manuscript, Applied Energy (2009). Paper VII Adaptive control of radiator systems for a lowest possible district heating return temperature Lauenburg, P., Wollerstrand, J. Submitted for publication (2009). viii