Small scale solar thermal systems are increasingly investigated in the context of decentralized energy supply, due to favorable costs of thermal energy storage (TES) in comparison with battery storage for otherwise economical PV generation. The present study provides the computational framework and results of a one year simulation of a low-cost pilot 3kWel micro-Concentrated Solar Power (micro-CSP) plant with TES. The modeling approach is based on a dynamic representation of the solar thermal loop and a steady state model of the Organic Rankine Cycle (ORC), and is validated to experimental data from a test site (Eckerd College, St. Petersburg, Florida). The simulation results predict an annual net electricity generation of 4.08 MWh/a. Based on the simulation, optimization studies focusing on the Organic Rankine Cycle (ORC) converter of the system are presented, including a control strategy allowing for a variable pinch point in the condenser that offers an annual improvement of 14.0% in comparison to a constant condensation pinch point. Absolute electricity output is increased to 4.65 MWh/a. Improvements are due to better matching to expander performance and lower condenser fan power because of higher pinch points. A method, incorporating this control strategy, is developed to economically optimize the ORC components. The process allows for optimization of the ORC subsystem in an arbitrary environment, e.g. as part of a micro-grid to minimize Levelized electricity costs (LEC). The air-cooled condenser is identified as the driving component for the ORC optimization as its influence on overall costs and performance is of major significance. Application of the optimization process to various locations in Africa illustrates economic benefits of the system in comparison to diesel generation.
The following article illuminates existing challenges and restrictions when implementing available stochastic user behavior models in building performance simulation (BPS). 24 occupancy behavior models from the literature containing a clear mathematical description are attempted to be coupled with a BPS model in a case study. Different methods, amongst others co-simulation approaches benefitting from the Functional Mock-up Interface (FMI) standard, were investigated to realize the implementation. The majority of OB models were coupled successfully with the BPS; however, some were not. The reason for the failed coupling is rather based on the restriction of OB models for BPS use than the coupling methods. Generally, OB models are based on stochastic modeling, while BPS requires a clear decision, a trigger for further interaction. Some OB models do not provide an output in such a binary form. Therefore, it is difficult to use these models in BPS without any assumption from the modeler. Furthermore, the majority of OB models lead to a state change depending on a comparison between its computed probability and a random number, which conflicts with the reproducibility of BPS results. In addition, some OB models result in an improper behavior without a reversal function or hysteresis. Based on the case study, these issues and requirements for OB models for the use in BPS as well as the advantages and disadvantages of various coupling approaches with BPS are discussed
The article presents a calculation method for determining fluid flow temperature field data and convective heat transfer coefficients using a laser optical measurement procedure. Basis for solving the energy transport (heat) equation are velocity fields obtained by stereoscopic Particle Image Velocimetry (PIV) measurements. PIV is a laser optical measurement method for quantitatively capturing velocity fields. Since there is no intrusive sensor necessary it allows for undisturbed flow measurements. Stereoscopic PIV measures generate grid data with pixel-wise information of all three components of velocity vectors within a single two-dimensional image layer of the flow. The temperature distribution at the domain boundaries is determined punctually (by temperature diodes) and surface-wise by extensive infrared imaging. Energy transport from the boundaries through the interior of the measurement area is calculated in terms of the inlet flow characteristics. The energy equation of the Navier-Stokes equations defines the fundamentals for the energy transport within the fluid. Its solution using a numerical model results in the temperature distribution of the measurement area. The method is demonstrated for obtaining convective heat transfer coefficients in the case of the thermal plume of a heated manikin. The procedure is promising since it is possible to get high resolution temperature field data of indoor air flows, as related laser induced fluorescence methods (LIF) are not appropriate indoors as in this case harmful tracers and toxic particles must be used
As current literature states, the transfer of Building Performance Simulation (BPS) tools in terms of holistic assessment capabilities of today's building systems as well as their transfer to the daily design process has stagnated. To antagonize this development, the present work investigates a modular simulation setup based on the recently developed Functional Mock-up Interface (FMI) standard. A procedure for the realization of such an approach is presented and implemented. The main obstacle of the modular simulation is identified to be the collocation of simulation modules, which is addressed using a knowledge-based method enabled through ontology. The procedure allows one to automatically derive a simulation topology based on information about the interfacing variables. A single and a multi-zone BPS serve as examples and illustrate the information requirements as well as the integration of information from building information modeling (BIM) to instantiate a simulation.
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