The main goal of this study was an experimental comparison of six different active magnetic regenerators (AMRs) with gadolinium as the magnetocaloric material. The analysis was carried out for three different parallel-plate AMRs (with different porosities and different orientations of the plates in the magnetic field) and three different packed-bed AMRs (filled with spheres, powders and cylinders). Since the operation of an AMR is strongly affected by the operating conditions, the experiments were performed at different mass-flow rates and at different operating frequencies. These were required in order to define the optimum corresponding operating conditions for the analyzed AMRs. As comparative criteria the maximum temperature span, the cooling capacity and the experimentally predicted COP were taken into consideration. The experimental analysis was performed on a new prototype of magnetic refrigerator designed as an experimental device. Its operation is based on the linear movement of a permanent-magnet assembly over a static AMR. The magnet assembly provides a measured magnetic field of about 1.15 T. The results reveal that the geometry of the AMR (the form of the magnetocaloric material) has a crucial impact on the performance of the magnetic refrigerator. The best overall cooling characteristics (temperature span, cooling capacity and COP) were obtained for the parallel-plate AMR with the smallest porosity (25%) and the orientation of the plates parallel to the magnetic field. This particular AMR generated a temperature span of 20 K, which is also the largest, so-far measured and published temperature span with a parallel-plate AMR for a given magnetic field change generated by permanent magnets. With respect to the comparison of the experimentally predicted COP values, the parallel-plate AMRs show higher efficiencies than the packed-bed AMRs.
COBISS.SI-ID: 12647707
A microclimatic layer of the green façade is proven to have specific temperature and flow conditions on the building envelope. Lower temperatures and wind velocities, and higher relative humidity in the microclimatic layer are the characteristics of vertical greenery systems, which cause lower energy consumption for the cooling and heating of buildings. Despite innovative architectural solutions, there are some drawbacks to applying vertical greenery on building envelopes. In this study, a bionic façade that mimics the positive effects and eliminates the disadvantages of green façades is presented. The bionic façade consists of bionic leaves, which are made of photovoltaic cells and evaporative matrices. A real scale experiment was carried out in the summer to evaluate the potential of the cooling efficiency of the microclimatic layer and a new photovoltaic cooling technique. The results show a good agreement of the thermal performance between the bionic and the green façade and up to 20.8 K lower surface temperatures of photovoltaic cells, which increase the daily electricity yield by 6.6%.
COBISS.SI-ID: 12807707
Thermal energy storage (TES) is regarded as among the most feasible environmentally friendly solutions for saving energy. R&D activities for heating and cooling of buildings lead to the development of various technology types. This paper attempts to give an overview of the energy situation, solar energy potential, TES concepts and technologies used in solar applications around the world with the emphasis on two Mediterranean countries, Turkey and Slovenia. Energy savings and CO2 emission reduction potential when TES is used in various solar applications of buildings are also discussed.
COBISS.SI-ID: 12942619
This paper presents study of mitigation of the heat island effect in the built environment with urban (city) parks. The park cooling island (PCI) effect, considering park grass cover and trees' density and age, is determined for selected extreme summer days at various wind speeds based on an all-day quasi-stationary thermal response. PCI was determined numerically by coupling a CFD model of an urban park and quasi-steady state, two-zone thermal response boundary condition models of each park element. Three-dimensional CFD modelling was used for the determination of temperature, humidity and air velocity fields in an urban park with a size of 140 × 140 m. Based on the comparison of the measured and numerically determined air temperatures in the tree crowns, we proved that the method of linking the models is adequate for temperature and flow condition modelling in the city park environment. It was found out that the cooling effect of the park is up to -4.8 °C at LAIsp, equal to 3.16, which corresponds to a planting density of 45 trees per hectare, with an age of 50 years. It was also found that with the length of the park cooling effect change decreases.
COBISS.SI-ID: 12800539
The plunge test method and the self-heating test method represent two experimental techniques for identifying the dynamic properties of temperature sensors. The dynamic behaviour of a resistance temperature sensor can be described using transfer functions, which differ for the two test methods. It is possible to predict the sensor's dynamic properties for the plunge test with a proper transformation of the identified model for the self-heating test. The main contribution of the presented research work is the software, based on virtual instrumentation, developed to identify and predict the dynamic properties of resistance temperature sensors. The excitation signal and the sensor's response are utilized to identify its transfer function. The number of parameters for the approximation model is determined as a result of an optimization problem. The software was validated and then applied to identify and predict the dynamic properties of a commercial-grade Pt100 sensor. In this case study, the plunge test and the self-heating test were performed with a step change of the surrounding temperature and the supplied electrical power, respectively, under laboratory conditions. The relative difference between the predicted and the identified sensor's time constants for the plunge test equals -7.4%, which is within the acceptance interval of +/-10%. The tested resistance temperature sensor was therefore experimentally validated as being suitable for dynamic testing using the self-heating method.
COBISS.SI-ID: 12775451