Sustainable energy technologies such as building integrated solar thermal systems may significantly contribute to the reduction of the greenhouse gases emissions by substituting a part of the fossil fuel used in buildings for space heating and domestic hot water preparation. Among these systems, solar thermal facades are good candidates when optimally oriented. Because the building facades are visible, the implementation of commercial solar thermal collector with rectangular shapes and dark colours may raise issues of architectural acceptance. To tackle these issues, non-rectangular (trapeze and triangle) solar thermal collectors with colored absorber plates (green, orange, red etc.) were developed in the Renewable Energy Systems and Recycling Research Centre of the Transilvania University of Brasov, Romania. The novel triangle solar thermal collector has an equilateral triangle shape, a small surface (0.06 m2) and non-dark colours (orange and green) allowing its integration in solar thermal facades with increased architectural acceptance and high coverage factor. Because of the small surface, the water circulates through an internal cavity beneath the entire absorber plate, instead of pipes as in the commercial solar thermal collectors having a significantly higher surface (around 2 m2). In the initial design of this novel solar thermal collector, a thickness of 20 mm resulted for the water layer in the internal cavity from constructive requirements. Indoor testing in standard conditions revealed color dependent efficiencies between 35 and 55%. To further increase the efficiency of the novel triangle solar thermal collector, an optimization process was developed by changing the water layer thickness and the mass flow rate. An absolute gain of 10.78% was obtained for the nominal efficiency and an average absolute gain of 10.35% over the entire range of inlet temperature by decreasing the thickness of the water layer to 5 mm while the mass flow rate was increased to
0.01 kg/s. In this paper, turbulators with various shapes installed in the internal cavity of the triangle solar thermal collector are considered to further improve its efficiency. The turbulators are modelled in SolidWorks and integrated in the 3D model of the triangle solar thermal collector. This 3D model is imported in Ansys Fluent for computational fluid dynamics simulations. The simulation results are comparatively discussed for the selected geometries of the turbulators. The influence of the shapes of the turbulators on the triangle solar thermal collector efficiency is analyzed.

Dr. Macedon Moldovan in 2013-2017 Lecturer at Faculty of Product Design and Environment, Transilvania University of Brasov 1997-2013 Design Engineer – Facilities for buildings, 2017-present Associate Professor at Faculty of Product Design and Environment, Transilvania University of Brasov, 2019-present Coordinator of the Study programme „Engineering of the Renewable Energy Systems”, Faculty of Product Design and Environment, Transilvania University of Brasov, Romania, 2019-present Deputy chairperson of the Technical Committee for Sustainable Energy Systems, International Federation for the Promotion of Mechanism and Machine Science