Investigation of different absorber systems for thermally activated solar chimneys

Modern buildings get more hermetic in order to reduce heat losses, which results in an increase of the energy demand for air conditioning and cooling during the summer. A solar chimney could solve these problems by combining these two issues. Solar radiation heats up an absorber surface inside the chimney causing air flow as a result of a temperature and density difference between the inner part of the chimney and its surrounding. The operation time of this system is limited due to unsettled weather conditions. The solar chimney cannot provide sufficient ventilation if the temperature difference is too low. To increase the effectiveness and to extend the time of operation, a thermal activation of the chimney’s absorber surface could remedy this problem with the use of waste heat. An optimized system would enable a sustainable and permanent operation of the natural ventilation system, saving energy and greenhouse gas emissions at the same time. One of the most important elements of such a system is the absorber. This study analyzes different absorber systems for thermally activated solar chimneys. Different absorber wall structures are investigated using all-season simulations done with TRNSYS. The simulated results show that for a building located in Germany with ventilation from 6 am to 6 pm, the best performance can be achieved with absorber structures, which heat up fast unlike absorber walls with storage mass. The effectiveness can be improved further with additional thermal activation. In addition, different absorber surfaces are investigated experimentally, using an indoor test facility. The investigations were done for three different systems. The highest volume flow of almost 700 m³/h can be achieved using capillary tubes for a 2.5 m high solar chimney. The air volume flow of the copper panels can be increased by 5 % using additional fins.