Solar cooling with absorption chillers [Elektronische Ressource] : control strategies and transient chiller perfomance / vorgelegt von Paul Kohlenbach
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English

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Solar cooling with absorption chillers [Elektronische Ressource] : control strategies and transient chiller perfomance / vorgelegt von Paul Kohlenbach

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Solar cooling with absorption chillers: Control strategies and transient chiller performance vorgelegt von Diplom-Ingenieur Paul Kohlenbach Von der Fakultät III – Prozesswissenschaften der Technischen Universität Berlin zur Erlangung des akademischen Grades Doktor der Ingenieurwissenschaften - Dr.-Ing. - genehmigte Dissertation. Promotionsausschuss: Vorsitzender: Prof. Dr.-Ing. G. Tsatsaronis Berichter: Prof. Dr.-Ing. F. Ziegler Prof. Dr.-Ing. A. Luzzi Tag der wissenschaftlichen Aussprache: 13.01.2006 Berlin 2006 D83 Acknowledgements II Acknowledgements This thesis has been conducted on the solar cooling system and its components at Phönix SonnenWärme AG in Berlin, Germany, during the author’s employment as director of the research and development department. Part of the work on this thesis has been co-financed by the European Union and the federal state of Berlin within the UEP-programme (contract. No. 10530 UEP OÜ2). First and foremost I would like to thank my supervisor, Prof. Dr.-Ing. Felix Ziegler, for his constant support and help throughout this work. His competence combined with the skill to always ask the right questions has fuelled my scientific curiosity and inspired me a lot of times. It was extremely enjoyable and beneficial to work with him, especially during the last months of this thesis work. I also would like to thank Prof.

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Publié par
Publié le 01 janvier 2006
Nombre de lectures 12
Langue English
Poids de l'ouvrage 13 Mo

Extrait





Solar cooling with absorption chillers:
Control strategies and transient chiller performance

vorgelegt von

Diplom-Ingenieur
Paul Kohlenbach

Von der Fakultät III – Prozesswissenschaften
der Technischen Universität Berlin
zur Erlangung des akademischen Grades

Doktor der Ingenieurwissenschaften
- Dr.-Ing. -

genehmigte Dissertation.



Promotionsausschuss:

Vorsitzender: Prof. Dr.-Ing. G. Tsatsaronis
Berichter: Prof. Dr.-Ing. F. Ziegler Prof. Dr.-Ing. A. Luzzi

Tag der wissenschaftlichen Aussprache: 13.01.2006


Berlin 2006
D83
Acknowledgements II






Acknowledgements


This thesis has been conducted on the solar cooling system and its components at Phönix
SonnenWärme AG in Berlin, Germany, during the author’s employment as director of the research
and development department. Part of the work on this thesis has been co-financed by the
European Union and the federal state of Berlin within the UEP-programme (contract. No. 10530
UEP OÜ2).

First and foremost I would like to thank my supervisor, Prof. Dr.-Ing. Felix Ziegler, for his constant
support and help throughout this work. His competence combined with the skill to always ask the
right questions has fuelled my scientific curiosity and inspired me a lot of times. It was extremely
enjoyable and beneficial to work with him, especially during the last months of this thesis work. I
also would like to thank Prof. Ziegler for providing me with an office room for part of the thesis
work.

A special thanks goes to Raoul von der Heydt from Phönix SonnenWärme AG for his generous
support during my employment there. His interest and open attitude towards this thesis has been a
base of my work.

I would like to thank Volker Clauss, Oliver Tamm and Enno Wiegand for contributing to this thesis.

Niels Braunschweig is gratefully acknowledged for his intensive proof-reading and comments.





Abstract III




Abstract

This thesis reports on improvements of the state of the art in controlling solar cooling systems with
absorption chillers. In this context, two main approaches are being presented.
In the first approach, control strategies for the system circuits are being presented and
discussed. Various possibilities of temperature and mass flow control for the external circuits of
hot, cooling and chilled water are being described in this thesis in a state of the art overview.
Guidelines for the incorporation of the storage tank in the system control are being given with
regard to reference layer and hysteresis temperature. The solar circuit as the most complex circuit
is being investigated deeper. A differential, a temperature-based and an insolation-based mass
flow control strategy for the heat carrier fluid in this circuit are being tested in TRNSYS simulations
and experiments with regard to the overall system performance. There, the focus of attention are
the key figures of cooling capacity and power consumption which are being integrated and
combined in a daily yield factor. The yield factor is being used for the comparison of the individual
strategies in simulation and experiment. The ambition is to find the strategy with the lowest power
consumption and simultaneously biggest cooling effect. In the comparison of simulation and
experiment, good agreement has been found for both the dynamic course of the variables as well
as the integrated energy balance expressed in the yield factor. From the simulations, the
insolation-based strategy (INSOL) has been found to perform best at cloudless conditions
regarding the yield factor. An improvement of 6% in the yield factor for the insolation-based
strategy compared to the other strategies has been found in simulations. From the experimental
comparison of the dynamic behaviour, the temperature-difference based control strategy (TDIFF)
has been found to yield the best performance. However, from the experimental comparison of the
integrated energy balances for all three control strategies a clear tendency towards one strategy
cannot be seen. Several improvements on the experimental methodology have been derived from
this result.
The second approach describes investigations on the main system component, the
absorption chiller. Two different methods of determining the thermal transfer behaviour are being
presented, an experimental identification and a theoretical simulation method. For both methods,
the transfer function between hot water input and chilled water output is being determined as
necessary for a chilled water temperature control. Using the experimental method, transfer
functions for the three-way valve in the hot water circuit and the absorption chiller have been
determined using the system identification method of Ljung. With the combined transfer functions
of valve and chiller a chilled water temperature controller has been designed and successfully
tested on a solar cooling system. The theoretical simulation method includes the development of a
mathematical model of the transient internal heat and mass transfer of the chiller. A dynamic
simulation model with transient behaviour implemented via thermal and mass storage terms as well
as delay times is being presented in this thesis. General functionality and internal consistency of
Abstract IV


the model have been demonstrated and the thermodynamic calculations of the model have been
found to reproduce the real chiller with sufficient accuracy. The focus of attention has been laid on
the dynamic model performance. Using experimental data for verification, it has been proven that
dynamic effects are being accounted for in a very satisfying way. Maximum dynamic deviations
between vessel temperatures in simulation and reality are in the magnitude of approximately 2%.
The model developed in this thesis has been designed for the Phönix 10 kW absorption chiller but
can easily be adapted to other LiBr/water absorption chillers. It can be used for the development
of a temperature control strategy or as a useful tool in the overall design process of absorption
chillers.

This thesis work extends the knowledge-base on control strategies of solar cooling systems using
absorption chillers. A foundation for energy-saving operation of such systems has been laid by the
research on solar circuit control and further research paths towards this goal have been paved. A
helpful tool for controller design and general performance analysis of absorption chillers has been
made available with the dynamic model presented. The model is a significant improvement of
present steady-state simulations of absorption chillers.

Kurzzusammenfassung V






Kurzzusammenfassung

In der vorliegenden Dissertation werden neueste Erkenntnisse und Methoden zur Regelung solarer
Kühlsysteme mit Absorptionskälteanlagen vorgestellt. Schwerpunkte werden dabei auf die
Untersuchung von Regelungsvarianten für den solarthermischen Teil eines solchen Systems sowie
die Ermittlung des transienten Übertragungsverhaltens der Absorptionskälteanlage mit dem Ziel
der Entwicklung einer Kaltwasserregelung gelegt. Die Arbeit kann in zwei hauptsächliche Teile
aufgeteilt werden.
Im ersten Teil wird zunächst ein allgemeiner Stand der Technik zu Regelstrategien für die
Systemkreise von Heiss-, Kühl- und Kaltwasser vorgestellt. Die Einbindung eines
Heisswasserspeichers wird diskutiert hinsichtlich der Wahl der Speicherreferenzschicht für eine
Temperaturdifferenzregelung. Weiterhin werden vertiefende Untersuchungen zu Regelstrategien
des Solarkreises präsentiert. Ziel dabei ist, eine möglichst stromsparende und gleichzeitig
thermisch ergiebige Regelstrategie zu finden. Zu diesem Zwecke werden drei verschiedene
Varianten einer Massenstromregelung des Wärmeträgers im Solarkreis verglichen. Diese
beinhalten eine Konstantmassenstromregelung sowie zwei variable Massenstromregelungen,
abhängig von Temperaturdifferenz bzw. solarer Einstrahlung. Alle drei Regelvarianten werden
sowohl experimentell als auch mittels TRNSYS-Simulationen getestet und verglichen. Als
Vergleichsgröße wird der Quotient aus gelieferter Kälteenergie und Stromverbrauch, die
sogenannte Arbeitszahl, verwendet. Im simulierten Vergleich liefert die einstrahlungsgeführte
Massenstromregelung eine um 6 % größere Arbeitszahl als die beiden anderen Strategien. Aus
den experimentellen Ergebnissen läßt sich eine solch klare Tendenz jedoch nicht ablesen.
Aufgrund eines relativ hohen Meßfehlers sowie verschiedener anderer Einflüsse liegen die sich
experimentell ergebenden Unterschiede zwischen den Strategien im Bereich des Fehlerbalkens.
Als Konsequenz werden in dieser Arbeit Verbesserungen der experimentellen Methodik abgeleitet
und diskutiert.
Im zweiten Teil der Arbeit wird die Absorptionskälteanlage als Hauptkomponente eines
solaren Kühlsystems hinsichtlich ihres thermischen Übertragungsverh

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