Energy & economic assessment of façade-integrated solar thermal systems combined with ultra-low temperature district-heating

Authors: Roberto Garay, project coordinator of RELaTED and Mikel Lumbreras, researcher at TECNALIA, Basque Research and Technology Alliance (BRTA). This paper, published in the journal Renewable Energy (Volume 159, October 2020, Pages 1000-1014), conducts an energy and economic assessment of District Heating (DH) integrated Solar Thermal (ST) systems. An implementation with building-integrated ST collectors coupled to a Low Temperature District Heating (LTDH) system is studied, with special focus on unglazed collectors. ST heat is exploited in the building through direct use, while excess heat is delivered to the network. A novel control strategy for heat flows in the system is proposed. A meta-analysis of several DH configurations, interconnection schemes and installed ST capacity is performed in three different climates: Sevilla (Spain), Bordeaux (France) & Copenhagen (Denmark). Heat loads corresponding to buildings with various insulation levels and domestic hot water loads are assessed in hourly simulations. The proposed interconnection concept provides a variety of connection modes to the DH network, allowing up to a 50% increase in the provision of solar heat compared to an isolated ST system. Positive Return of Investment (ROI) for such a setup is achieved in 22% of the studied cases. The DH network is found to be a suitable heat sink in up to 25% of the buildings with ST systems installed