Samenvatting

This report contains the results of the graduation research of Jurre Kuijper and Martin Volgers. The
research goal is to find an appropriate model to calculate the heat transfer under different sets of system
conditions. The system in this case is a sewer heat system, which consists of a sewage pipe containing
sewage water with residual heat. A heat exchanger extracts some of the residual heat from the sewage
water, and this heat is transferred by a heat pump from the relatively low temperature of the sewage
water to the higher temperature of for example a swimming pool.
Initially it was planned to create an empirical model based on experiments on a scale model. In a
further stage of the research, the scale model was postponed to a later stadium, unfortunately outside
the graduation time frame. Therefore the focus shifted to a more detailed theoretical model with information
about fouling that occurs in sewer heat exchangers.
A literature study was carried out in which an example case, the sewer heat project in Urk, was
further investigated. The literature study also contains all relevant information about the heat extraction
possibilities and the theoretical relations behind these possibilities. Preceding research, so similar research
on the subject, was also investigated in the literature study.
The empirical model, which was originally the main goal of the research, could not be finished due to
a delay in the scale model assembly. However the scale model design and testing plan have been created
still. This gives the possibility for further research on the subject. The scale model design is based
on a dimensional analysis in which complete similarity of the scale model with the full-size system in Urk
has been ensured, with the exception of a few assumptions. The most important being that the influence
of the tube thickness of the heat exchanger on the overall heat transfer coefficient will be negligible.
Based on the theoretical relations and findings of the literature study a theoretical model was created
with which a (sewer) heat system can be designed. It is applicable for every heat system which
consists of a double tube heat exchanger and a heat pump. It can also be used to design solely a heat
exchanger or solely a heat pump. The theoretical model report acts as a user manual to help engineers
understanding the model.
The literature study also contains information about fouling of sewer heat exchangers. During the
research came forth that information was not sufficient in order to be able to determine the right fouling
factor for use in the theoretical model. Therefore another investigation on the subject of fouling was
done in which practical experiences with sewer heat exchanger fouling were investigated.
Sustainability is an important subject nowadays. Information about this specific subject is however as rather scarce. Hence, this research tries to fill this gap and as such contributes to sustainable engineering
as it provides engineers the possibility to thoroughly investigate sewer heat systems.With the
theoretical model it is possible to make a good comparison between sewer heat systems and other
sustainable solutions.
The conclusion gives a comparison between the research questions and the final results. The main
goal of the research was to create a model with which sewer heat systems can be designed and,
most important, design considerations can be visualized. With this model it is possible to make quick,
accurate and well founded designs. These designs will improve the durability of sewer heat systems,
since the model helps to find the most efficient design, which may have been overlooked before.