Solar air collectors have various applications: on the one hand, they can be used for air heating in cold seasons; on the other hand they can be used in summer to evacuate the warm and polluted air from residential, offices, industrial, and commercial buildings. The paper presents experimental results of a solar collector air, under the climatic conditions of the Southeastern Europe. The relationships between the direct solar irradiation, the resulting heat flow, the air velocity at the outlet, the air flow rate, the nominal regime of the collector and the efficiency of conversion of solar energy into thermal energy are all highlighted. Thus, it was shown that after a maximum 50 min, solar air collectors, with baffles and double air passage can reach over 50% efficiency for solar irradiation of 900–1000 W/m². The article also presents a mathematical model and the results of a computational program that allows sizing solar collectors for the transfer of air, with the purpose of improving the natural ventilation of buildings. The article is completed with case studies, sizing the area to be covered with solar collectors, to ensure ventilation of a house with two floors or for an office building. In addition, the ACH (air change per hour) coefficient was calculated and compared.

A closed-loop system based on a detailed flat-plate collector model and a water storage tank operating in a fully mixed regime has been considered. The system operates in Timisoara, Romania, under a southeastern European temperate continental climate. Four empirical strategies for flow-rate control have been compared with an optimal control strategy, used as an ideal reference. Days for all seasons and all cloudiness classes have been considered. Also, days with more-stable or less-stable radiative regimes have been used. Under the specific climatic conditions, the most appropriate empirical control strategy uses the momentary values of solar irradiance as input data. It provides good results during all seasons, independent of the class of relative sunshine and the stability of the radiative regime. An empirical strategy based on the constant-mass flow rate has been also identified as a good alternative. This strategy might be easier to implement since it involves a single-speed pump. The recommen...

A small Savonius wind turbine of helical type was tested in an open jet wind facility for identifying the optimum position of the rotor blades aiming the maximization of static torque. The two blades of the wind turbine of U shape were twisted up to 180⁰ from bottom to top and three values for blade overlap were considered i.e. 0.35, 0.2 and 0.0. The turbine torque was measured for no load conditions and wind velocities between 2-8 m/s. In the same time the air flow through Savonius rotor was observed by using a visualization setup aiming to identify the correlation between the torque and the flow pattern inside the returning blade at rotating angles where the torque has highest values. Best results for the torque coefficient of 0.72 and power coefficient of 0.265 were obtained at a wind velocity of 5.8 m/s and low overlap ratio of 0.2. By measuring the overall torque of the rotor for each case study, the positive effect of pressure recovery was explained as a result of air flow through the blade overlap from the concave side of the advancing blade to concave side of the returning blade for a certain interval of the rotating angle a = 50-60°.

Solar air collectors have various applications: on one side, they can be used for air heating in cold seasons; on the other side they can be used in summer to evacuate the warm and polluted air from residential, offices, industrial and commercial buildings. The paper presents experimental results of a solar collector air, in climatic conditions from South Eastern Europe. The relationships between the direct solar irradiation, the heat flow resulted, the air velocity at the outlet, the air flow rate, the time of input in nominal regime of the collector and efficiency of conversion of solar energy into thermal energy are highlighted. Thus, it was shown that after maximum 50 minutes, solar air collectors, with baffles and double pass of air can reach 50 % efficiency for solar irradiation of 900-1000 W/m. 2The article also presents a mathematical model and the results of a computational program that allows sizing solar collectors for the transfer of the air, for their purpose to improve the natural ventilation of buildings. The article is completed with a case study, sizing the area to be covered with solar collectors to ensure ventilation of a house with two floors or for an office building. Also, the ACH coefficient was calculated and compared.