PhD Projects

Optimization of solar heating systems with advanced numerical algorithms

Kassel University - Oleg Kusyy

The research project is aimed in development of new numerical algorithms and application of the existing ones to optimizing solar heating systems. Multi-objective real-time optimization should be carried out for achieving the best performance of systems dependent on various configuration parameters as well as changing outer conditions.

The algorithms being developed should allow one to couple between different target functions like costs of the system, its energy consumption, etc, by using the coupling coefficients. They should also be sufficiently fast in order to provide the real-time optimization with changing outer conditions. Sensitivity of the optimizing system to concrete parameters should be taken into account for reducing the computational efforts. The algorithms should be general enough and applicable to various systems.

The project result should be a user-friendly optimization tool integrated with the TRNSYS simulator, which will help user to make practical recommendation to system set-up.

Building integrated solar thermal collectors optimised for solar heating and cooling applications

Czech Technical University - Juliane Metzger

The research project is concentrated on building integration of solar collectors for heating and cooling and associated aspects. Aim of the project is theoretical and experimental investigation and parametric description of general solar collector behaviour in the interaction with building, influence of building integration on heat transfer in collector and building envelope, energy balance of integrated solar system, influence of collector thermal behaviour on microclimatic parameters in the building indoor environment (summer overheating, winter heat gains), characterization of extreme states in the integrated collector and envelope (stagnation conditions, heat transfer fluid boiling conditions), heat and humidity transfer at dynamic conditions in envelope (larger temperature oscillations in collector).

Investigations are planned with computer simulations as well as experimental investigations on the real house “Cercany”. These simulations carried out with the program TRNSYS will be very detailed including pipes, insulation, air heating unit, etc. There will be evaluation and comparison with long-term experimental monitoring with special view on solar system and energy balance. Talking about the real-system “Cercany” it should be mentioned that this single-family house is a low energy building which is made of a timber frame construction with a calculated heat loss of 4.7 kW. As it is shown in the figures below four flat plate solar collectors are integrated into the building façade; on the right field with an air gap and on the left field two collectors directly integrated into the building insulation. Each of the solar collectors has a size of 2.3 m² (total collector area Ac = 9.2 m²), they are connected in parallel. The system will be operated in high-flow and low-flow mode (Experiments are planned to run the system in high-flow mode the first year, and then the second year low-flow operation is planned).

A solar combisystem for domestic hot water and space heating is built in this single-family house. Experimental investigations of façade integrated collector heat gains, associated indoor comfort and user profiles as well as measurement of system electricity demand are planned. The test station is equipped with a pyranometer, flow meters, temperature sensors and humidity sensors. Monitoring is planned for the next two or three years; the first evaluation will follow after one year of measurements.

Furthermore, efficient flat-plate solar collectors for higher temperature levels (above 70 °C, solar heating and cooling applications) - aerogel or vacuum flat-plate collector for direct envelope integration will be developed with respect for collector-envelope thermal bridges elimination (slim compact construction). Thermal behaviour analysis of high temperature collector and impact on building indoor environment will be investigated.

Development and optimization of a novel desiccant and evaporative system for solar air conditioning

Politecnico di Milano - Alexandra Lozano

The summer air-conditioning of buildings is nowadays primarily carried out with conventional electrically driven technology. Thus the recent trend of air-conditioning demand increase causes a raise in electricity consumption and high load peaks, which imply high costs and higher difficulties in managing the supply network's bottlenecks. An alternative to these systems typology are thermally driven air-conditioning processes - where the air-conditioner is supplied instead of electricity with heat. The heat used to operate this machines, depending on the technology and as consequence from the temperature levels, can be supplied by solar thermal collectors. At present the most common thermally driven technology for direct air-conditioning (cooling, dehumidification) are based on a combined evaporative cooling process. In the commercial applications of this plants the process potential is enhanced through the use of a dehumidifier, therefore they are called desiccant and evaporative cooling (DEC) systems. This sort of systems have the following disadvantages:

  • the air through the dehumidifier rotor is not only dehumidified but heated up too;
  • the heat freed during the water vapour sorption process in the dehumidifier leads to an increase in temperature of the sorbent material and thereby limits the dehumidification;
  • leakages between the supply and the exhaust streams, over the rotor's seal, sets limits to the use of this technology for small capacity systems.

A new process, which overcomes these disadvantages has been developed: ECOS - indirect Evaporative counter-flow COoling with Sorption. Implementing the latter a considerable air dehumidification can be achieved with simultaneous significant temperature sinking.
 Their commercial applications use solid sorbent materials.

Photovoltaic-thermal generator optimised for solar heating and cooling applications

Universitat de Lleida - Bahy Abdel-Mesh

This thesis focuses on the characteristics of the Fresnel concentrating prototype BiFres 22. BiFres 22 is a system that uses mirrors to concentrate the incoming sun rays 22 times on photovoltaic modules. Water runs beneath the cells to cool them down thus producing hot water simultaneously with the electricity. The objective is to study the optical, thermal, and electrical aspects of the prototype. The study includes experimental work, theoretical modeling, and simulations. The long term objective is to show a system capable of producing electricity and heat at a competitive feasible cost for future market dissemination.

Errors in the surface of mirrors of the concentrator affect the quality of the reflected rays and their distribution on the modules which affect the electrical efficiency of the solar cells. Therefore, a novel experimental method that involves photography and a geometrical algorithm, based on the principles of perspective, is formulated to analyze the produced images thus assessing the surface slope errors of the mirrors. The experimental work includes measurements of the real prototype concentration ratio, spectrometer tests on the reflectivity of the mirrors, illumination profile on the PV modules, and the thermal and electrical performance of the prototype BiFres 22. The quasi-dynamic test of the European standard EN 12975 is used for the modeling of the thermal output data of the prototype. The TRNSYS simulation environment is used to model the thermal and electrical experimental data. The TRNSYS analytical non-standard model 262 is tested and validated in order to simulate the performance of the BiFres 22 prototype. A parametric study is carried using this model to show the performance of the concentrator under various operating conditions and to compare it to flat plate collectors.

The potential of using the heat generated from concentrated photovoltaicthermal systems, which is a by-product, for solar cooling is an interesting application to extend the functions and usability of the generator. The aim is to assess the effect of the operation of a solar driven absorption cooling machine on the performance of linear concentrators at medium concentration ratios. The outlet temperature of the photovoltaic thermal concentrator should be kept between 75 ºC and 95 ºC in order to operate the chiller and this affects the cells performance as their efficiencies degrade with the increase in temperature. Different configuration setups are investigated to connect both the concentrator and the chiller as well as different cold and hot storage tank sizes are studied for better understanding of the interaction between the various components of the system.

Advanced solar combi system

Technical University of Denmark - Eshagh Yazdanshenas

Investigations have shown that the energy consumption during summer periods for space heating and domestic hot water supply is unexpectedly high in many Danish residential buildings. Therefore solar combi systems for combined space heating and domestic hot water supply can be attractive solutions in the future.

 In Denmark the auxiliary energy supply system for most solar heating systems is natural gas boilers or oil burners. Both the thermal efficiency and cost-efficiency of a solar combi system are strongly influenced by the efficiency of the auxiliary energy supply system and by the interplay between the solar collectors and the auxiliary energy supply system. In this connection it is very important that the auxiliary energy supply system is controlled and that the heat storage is designed in such a way that the heat transfer to the heat storage from the auxiliary energy supply system can be reduced to a minimum by fitting the auxiliary energy supply to the heating demand and that thermal stratification in the heat storage is built up in the best possible way. This has been elucidated for solar domestic hot water systems, while research in this field is needed for solar combi systems for combined space heating and domestic hot water supply.

The aim of the study is to carry out the basic research needed to establish the basis for development of an advanced smart heat storage and control system for solar combi systems with an oil fired boiler or a natural gas burner used as the auxiliary energy supply system.

The study will focus on research of the thermal behaviour of differently designed solar combi systems for one family houses. The systems will be based on smart heat storages, which by an oil fired boiler or a natural gas burner can be heated from the top in such a way that both the water volume and water temperature at the top of the heat storage heated by the boiler/burner can vary.

Combined solar and pellet heating systems - Improvement of energy efficiency by advanced heat storage techniques, hydraulics and control

Graz University of Technology - Michel Haller

The objective of this project was the improvement of energy efficiency of combined solar and pellet heating systems for space heating and domestic hot water preparation by advanced heat storage techniques, hydraulics, and control.

 For these studies a boiler model has been developed based on measurements performed on a pellet boiler, a wood chip boiler and a solar storage integrated pellet burner. Additionally, the work has been based on the analysis of data measured by cooperation partners on two pellet boilers, two oil boilers and two gas-boilers. A collector model has been adapted for the simulation of small time steps. Based on measurements performed on the storage tank with the integrated pellet burner, a storage model has been parameterized and used for subsequent system simulations. Methods for the determination of the stratification efficiency of themal energy storage processes have been reviewed and tested, and a new method has been developed. This new method has been evaluated both theoretically and practically with own measurements performed on a thermal energy storage with direct charging and discharging and with measurements performed by a cooperation partner on a tank-in-tank storage unit. Data from field measurements performed on five solar and biomass micro heating nets has been evaluated and analyzed.

 Simulations have been performed for three principally different solutions for solar and pellet heating systems for a single family house. The first system was based on the solar storage tank with the integrated pellet burner that has also been tested in the laboratory, the second system was based on an external pellet boiler connected to a solar storage tank with an immersed heat exchanger spiral for domestic hot water preparation, and the third system was an external boiler connected to a solar storage of the tank-in-tank type. Starting with simulations parameterized based on the results of the laboratory measurements on existing components, a large potential for improvements has been detected for all these systems that may lead to an additional 10% - 20% of pellet fuel savings.

It has further been found that the currently implemented control strategies for charging a thermal energy storage with a pellet boiler were not able to effectively use the possibility of combustion power modulation to match the heat demand. Different control strategies have been tested with simulation studies and a control strategy has been found that reduces the number of burner starts by a factor of three and at the same time increases the energy efficiency significantly.

Simulation and control of solar adsorption cooling plants for air-conditioning in buildings

University of Applied Sciences Stuttgart - Antoine Dalibard

The topic of this PhD is about solar cooling plants that use adsorption chillers. The main goal of this work is to optimize the operating conditions of solar adsorption cooling plants by implementing novel control strategies in order to elaborate some general guidelines for planners and designers. This work will be done by using simulation tool. Therefore, an important part of this work is the modeling of the different components of the installation especially the adsorption chiller and the solar collectors.

The application project of this PhD is the new headquarters of the company Festo in Esslingen (Stuttgart), where cooling is provided by earth heat exchangers and 1 MW adsorption chillers powered by cogeneration heat. In future a solar thermal plant is planned to supplement the cogeneration heat.

Some experimental investigations of data analysis of the adsorption chillers (Festo) and of the solar collectors (installed in the University of Applied Sciences in Stuttgart) will permit to validate the models.

Long term monitoring of large-scale solar thermal systems

Kassel University - Corry de Keizer

The aim of the project is to develop and validate a simulation based method for monitoring, failure detection and failure identification for large-scale solar thermal systems. It will be useful to develop such a failure detection system, since failures and defects are likely to occur during the life time of a solar thermal system, resulting in energy and economic losses. To minimize these losses a monitoring and failure detection approach will be developed, that functions for the entire life time of the system, which should detect the malfunctions automatically, accurately, quickly and cost-efficiently. The method should also identify the failures, so that it will be easier to find and repair the problem. Current approaches do not succeed in a fast and accurate detection and identification of failures.

The development of the method will not start will build further on the work which was done by Wiese in his PhD-thesis  (see figure 1). The focus will be on a further development of the simulation based failure detection and identification step. TRNSYS Studio will be used to develop and validate decks for typical large scale systems. The developed method and its accuracy will be extensively tested by for at least 10 large-scale solar thermal systems.

Combined Solar and Pellet Heating Systems – Boiler Interaction with the Solar Heating System

Solar Energy Research Center SERC - Janne Paavilainen


The main aim of the project is to find out under what conditions a combination of solar and pellet heating is advantageous compared to pellet heating only. The project consists of component measurements, component modelling, (sub)system measurements, (sub)system modelling, model validation, combisystem simulations on yearly basis. The project focuses on water based heating systems only. Short term transient behaviour of the boiler+burner combination is taken into account in a more detailed level than has been done earlier as this might have impact on conclusion drawn about e.g. emission levels based on simulated boiler cycling. TRNSYS will be used as a simulation tool

Development of Solar Thermal System with Radiation Balanced Solar Collectors for High Solar fraction for Electrically Heated Houses

Lund University - Luís Ricardo Bernardo

There exist around half a million single family houses in Sweden which are electrically heated. There is a big demand for suppressing the use of electric energy in them. Development of cost effective solar thermal system for these houses are therefore very important. The solar thermal system can be introduced when the old heating system is replaced or solar collectors can be added on the old system.
In our laboratory facilities, three solar hot water systems were built and are continuously tested at the moment. Two of these systems are standard and used as reference. The third system, being continuously developed, is made of an existing hot water boiler where solar collectors were connected. All the three systems are shown below. Regarding future patentability, no details are shown on the sketches of the system under development.
 Our experimental work shows that it is possible to make use of existing standard hot water boilers for solar heating throughout a solar collector connection box. Furthermore, preliminary simulation results show that the solar fraction of the developed system is in the same range as the standard solar collector systems. Hence, potential investment savings can be achieved by retrofitting existing