Energy & economic assessment of façade-integrated solar thermal systems combined with ULT DH

Authors: Roberto Garay, project coordinator of RELaTED and Mikel Lumbreras, a 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 a special focus on unglazed collectors. Solar Thermal 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.