INTRODUCTIONPhase change materials (PCM) are substances with specific heat that varies in response to the temperature changes and increases rapidly in temperature of phase transition. It means that heat capacity of PCM tank compared to heat capacity of water tank at the same volume is several times higher. This gives the possibility for long-term heat and cold storage. Number of deep charge and discharge cycles -number of phase changes from solid to liquid -is one of the limitation of phase change materials. Therefore, the best solution is to charge and consume energy stored in PCM tank as PCM is in transition phase. This requires developing an adaptive control system enabling evaluation of charge and discharge rate of PCM storage tank. In order to achieve that, it is necessary to perform simulation tests using PCM mathematical model. There was a need to modify this model due to the fact that PCM characteristics in operating conditions are different from classical model. Phase change materials (PCM) are substances that are characterised by significant increase of specific heat in transition phase as they change their physical state, for instance from solid to liquid. Therefore, heat capacity of PCM tank compared to heat capacity of water tank at the same volume is much higher. This enables PCM, which is put in airtight container, to act as energy storage with the possibility for long-term heat and cold storage. Despite the fact that phase change materials have been used since the late 19th century, the technology of producing, storing and also controlling charge and discharge system of PCM tank is still being improved and developed. Phase change materials are used in different sectors of the economy due to their physico-chemical characteristics. There are research projects studying the potential of using PCM in hybrid supply system combining solar thermal installation and compressor, ground source heat pump that would cover demand of residential building for cold and heat. Thermal Energy Storage System for Energy Efficient Buildings. Application in domestic solar thermal systems and heat pumps (TESSe2b) is one of these projects and is financially supported by the Horizon 2020 Research Innovation Action (RIA) of the European Commission.The main operational problems are the control of PCM tank system and real-time calculation of the energy stored in the tank. These problems are the result of differences between PCM characteristics in operating conditions and those specified in catalogues [1]. The solution is to develop an adaptive control system, which requires simulation tests. In order to perform them, it is necessary to modify classical model of phase change material so that its adaptation to PCM characteristics in operating conditions would be possible. CLASSICAL PCM MODELIf the value of P max is 0.5, the curve representing the changes in PCM specific heat as a function of temperature is symmetric with respect to the point whose coordinates are (x 3 , y 3 ). If the value of P max is below 0.5, the slope of the ...
This paper analyses the thermal states of the flat solar collector using the state variable method. The knowledge of the transient states describing the state of the solar heating installation under operating conditions enables the analysis of the heat exchange process and the development of control strategies. The analysis of variable states under operating conditions requires the development of a mathematical model describing the dynamic properties of the whole solar heating installation and the definition of the variables describing the state of the system from the energy balance perspective. The paper presents a method enabling the analysis of variables in the condition of a solar heating installation and a single solar collector based on the comparison of two models: an analogue model developed by the Equivalent Thermal Network method and a digital model, developed on the basis of performance data by the Parametric Identification method. Corresponding author: pawel_obstawski@sggw.pl
In solar heating systems with an absorber area of more than 20 m 2 , a plate heat exchanger is used as a separator between the primary glycol-based refrigerant and secondary water. The use of a plate heat exchanger enables an increase in the heat exchange area compared to the standard coil heat exchangers located inside the domestic hot water tank. An important problem is to determine the volume flow rate on both the primary and secondary side of the exchanger. The paper presents an analysis of the influence of the circulation pump efficiency on the primary and secondary side of the heat exchanger installed in a solar heating installation on the intensity of the heat exchange process. Corresponding author: pawel_obstawski@sggw.pl
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