WP1-3 Flexible hydraulic concepts and stagnation prevention
WP 1-3 Flexible Hydraulic Concepts and Stagnation Prevention
Hosted by: | |
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Student: | Alireza Shantia |
Started: | 01/2014 |
Supervisor(s): | Prof. Wolfgang Streicher |
Short description
The PhD project will be made in three years by Alireza Shantia, a mechanical engineer with experience in HVAC systems and a holder of a master degree in Sustainable Energy Engineering from KTH University in Stockholm with specialization on solar thermal system. The main supervisor of the dissertation is Prof. Wolfgang Streicher, a professor and lecturer at the Unit for Energy Efficient Buildings of the University of Innsbruck; he has a long-term reputation in the field of solar thermal systems and energy efficiency in buildings with numerous publications.
This research aims at developing a modular tool for evaluating complicated thermo-hydraulic networks with focus on pressure drop and heat transfer and consists of both applied research and software development for hydraulic systems. The tool will provide the possibility to evaluate the adaptive control in solar thermal and space heating systems. The optimization and validation of the tool will rely on the fully equipped and state-of-the-art hydraulic test bench at the Unit for Energy Efficient Buildings. Further validation will be performed through collocation with other SHINE PhDs in the district heating work package. The first approach is to simulate the steady-state condition with constant mass flows in large collector fields and space heating systems with different hydraulic schemes and control logics. Later on, the tool will be expanded to also examine the dynamic response caused by thermal inertia and control characteristics in the system.
Hydraulic systems are integral parts of energy systems. The term “hydraulic” is about transferring heat by a medium fluid that implies a non-linear relation between pressure drop and flow rate in a closed circuit of pipes. This bilateral relation results in self-regulation of flow such that pressure correlations hold in the entire system and can give rise to inconsistent behaviour, detectable as deviation from the design flow in reality. Balancing is a practical solution to handle excessive flow rates by altering the local resistance in circuits and has a wealth of applications e.g. in industrial process, HVAC systems and solar thermal systems, etc. In solar collector fields, flow unbalance results in underflows in other segments that may lead to partial stagnation, which affects the entire system operation. The friction force between different layers of fluid, so-called viscosity, plays a key role in pressure drop correlations, hence, the variation of viscosity with temperature is not always negligible for medium liquids other than water, e.g. propylene glycol. In other words, the effect of temperature on viscosity might be considered in pressure drop calculation depending on medium liquid used and temperature range. Although an amazingly short list of simple principles is sufficient for hydraulic analysis, coming up with a systematic and flexible solution is still a painstaking task in complex systems. In energy modelling tools (e.g. TRNSYS and EnergyPlus), the interaction between pressure drop and flow rate is usually ignored by assuming a perfect hydraulic behaviour. Similarly, purely hydraulic tools neglect the dynamic response associated with thermal inertia in distributed systems and control strategies to adjust a parameter, e.g. the outlet temperature in a solar field by varying flow rate. The current research pursues a pragmatic solution to bridge the gap between modelling tools and reality by developing a flexible tool for thermo-hydraulic analysis of energy systems.
The main objective of the project is to develop a flexible tool to evaluate hydronic systems. The work was initially started with studying available modelling environments that possibly can be used as a platform for the tool development with special focus on TRNSYS® and Matlab® Simulink®. In parallel, literature review is performed on hydraulic calculation schemes to develop numerical methods required for both system-oriented and component-oriented approaches. The system-oriented approach, firstly, provides a methodology to derive pressured drop and thermal correlations analysis in hydronic networks, and secondly, develops numerical methods and analysis algorithm for complex systems. The component-oriented approach aims at developing mathematical models for a wide range of hydronic components such as tubes, fittings, valves, pumps, and etc.– each needs due care in terms of operation logic when certain conditions hold in the system. The next step is to implement the calculation scheme in a programming language in two parts. The first part uses the high-level programming language in Matlab in which the physical model, and the algorithm for numerical simulation are optimized and calibrated against experimental data by using the hydraulic test bench at the University of Innsbruck, and cooperating with other SHINE projects. The second part uses a low-level programming language in C++ or Java to improve the code performance as regards to simulation speed and efficiency. The project is followed by designing a graphical user interface (GUI), and setting up a database for different components and medium fluids. Finally, if time allows it, the plug-flow model is implemented to take into account the dynamic response, which results from system thermal inertia and use of sensors and controllers, in large hydronic systems, e.g. district heating networks.
Numerical tools:
- TRNSYS®
- Matlab®
- Simulink®
- CARNOT BlockSet library in Matlab
- Simscape library in Matlab
- C++
- Java
In the first year, the research began with literature review on hydraulic calculation schemes and evaluating programming environments. In the system-oriented approach a simple hydronic system – but still comprehensive in terms of using key elements such as pump, control valves, and balancing valves– is modelled using TRNSYS and CARNOT BlockSet library in Matlab. The model consists of two building blocks with parallel hydronic circuits connected to a central heating plant where the automatic valves control the temperature by altering the circuit resistance in each block. The results prove that none of the tools can alone provide enough flexibility to apply hydronic calculation schemes to compute the correct flow distribution and to cope with internal iterations in each time-step. As a part of the component-oriented approach, the parallel flow distribution in a polymer flat collector is studied, using Simscape library in Matlab® Simulink® in two cases with constant and flow-dependent pressure loss coefficients in junctions.
In the second year, the project will focus on employing the calculation schemes and numerical methods into Matlab. The program will be optimized and calibrated against experimental data for both system and component approaches. Later on, the code performance will be improved in a low-level programming language. In the last year, a graphical user interface will be designed, and a database for system components and medium fluids will be set up together with implementing the plug-flow model for thermal transient response –if time is still left.