Abstract

Thermal performance of the solar thermal systems are estimated using numerical methods and software since the solar processes are transitient in nature been driven by time dependent forcing functions and loads. The system components are defined with mathematical relationships that describe how components function. They are based on first principles (energy balances, mass balances, rate equations and equilibrium relationships) at one extreme or empirical curve fits to operating data from specific machines such as absorption chillers. The component models are programed i.e. they represent written subroutines which are simultaneously solved with the executive program. In this thesis for executive program is chosen TRNSYS containing library with solar thermal system component models. Validation of the TRNSYS components models is performed i.e. the simulation results are compared with experimental measurements. With the simulations are determined the long-term system performance i.e. data are obtained for the energy consumption, solar fraction, collector efficiency also it is performed parametric analysis to determine the influence of specific parameters like collector area, tilt and orientation, mass flow rate etc. to the system performance. In this thesis are considered only the residential buildings.

Abstract

Because human population is growing at such a high rate, as well as the energy consumption per person, new ways of preserving and efficiently using available energy must be explored. Until new and abundant energy sources are found and means of their exploitation developed, research attention should be focused on finding ways of proper and safe use of what is nowadays available. In that sense, storage of thermal energy plays an important role both in heating and/or cooling applications, such as in residential or commercial buildings, and in industrial processes. Some of the technical solutions are based on phase change materials (PCM) which can help to preserve and to increase the efficiency of energy use when used at right temperature levels at which PCMs change their phase. Thus in just a few degrees of temperature difference, a large quantity of energy can be stored. PCMs might find their application in fixing the energy storage problems in different fields, for they represent a kind of thermal battery. PCM may allow keeping the temperature of the room stable because of their high density of energy storage. PCMs can help keeping the temperature level of a water tank at a certain point. The successful usage of PCMs is not only a question of energy storage density, but on the other hand it is a question of proper charge and discharge of the energy stored with power suitable for the desired application [1]. The aim of this work is to design and analyze up to three different systems for thermal energy storage based on application of PCMs and, where applicable, examine their performance in comparison with water used as a storage fluid. In order to do this simulation program TRNSYS is used. TRNSYS model TYPE 840 is used for representation of water storage tank with PCM material included. Model TYPE 840 is validated in the work of other authors [3]. Different experiments are simulated in order to investigate feasibility of the use of PCM modules in these systems. The following applications of thermal storage are considered in this work: • a tank with an electric heater, • a tank in a solar thermal application, and• a simple heat exchanger with a PCM module inside, that might be used as a portable thermal accumulator (battery). For the first and second system, simulation in TRNSYS is done to evaluate the features of PCM incorporation in a water tank and for the third system, a simulation is also done to show the characteristics of the heat exchanger designed.