The Effect of Low Temperature Heating Systems on Convective Heat Transfer Coefficient in Real Size Rooms

Because of their importance in industry and living places, natural convection and temperature and velocity distribution problems in enclosures are widely studied not only numerically, but also experimentally in appropriate real size building geometries. Convective heat transfer coefficient (CHTC) is one of the most common term for the measure of thermal comfort in living places. In the era in which we encounter many energy crisis, it also has great importance since it remarkably affects energy consumption in buildings. Heating and cooling systems with vertical walls, floor and ceiling (radiant panels) have not been extensively utilized for many years. Nevertheless, especially heating technologies with low water temperature began to be reassessed due to the austere energy policies pursued by goverments throughout the world. As well as the progression of renewable energy techniques and low temperature heating systems, improving computational methods and reducing solution periods for calculation of natural convection problems in real size building rooms provide us to use CFD (computational fluid dynamics) programs in order to obtain CHTC's with proper numerical solution preferences. In this study, a room has been numerically heated from wall and cooled from the opposite wall in order to create a real room simulation. Effects of cooled wall temperature and characteristic length (distance between heated and cooled wall) on average CHTC in the enclosure (the room) wall have been researched numerically for two (2-D) and three (3-D) dimensional modeling states. Since, the difference between two modeling choices has been found approximately 10% and overwhelming part of heat transfer occur two dimensionally; 2-D model which has shorter solution periods was preferred. Dimensions of model have been determined as 4.00 by 2.85 by 4.00 m while 2.85 m is the height of the room which is suitable for a real size room. The cold wall temperature has been chosen as 10°C constant and the hot wall temperature were varied from 20°C to 35°C, that is asserted as the maximum wall temperature for this heating system by the manufacturer company. CHTC's and Nusselt numbers for the room have been calculated. According to the Nusselt numbers and CHTC's acquired through the numerical solution, (Rayleigh - Nusselt) and (CHTC - temperature difference between hot and cold walls) graphics were drawn and two correlations have been derived for this enclosure geometry. Also, temperature and velocity magnitude contours for each temperature difference between hot and cold walls were drawn. As result, effect of temperature difference over CHTC's and Nusselt numbers for similar size room geometries were determined and in order to validate results, these were compared with correlations explored by other researchers within close Rayleigh ranges through substituting the calculated temperature difference and Rayleigh / Grashof numbers in their correlations. Comparisons has shown significant coherence.