THERMAL LOSS MODELLING AND SUSTAINABILITY-ORIENTED OPTIMISATION OF GLASS TUBE SOLAR COLLECTORS

Abstract

Solar thermal collectors play an important role in low-temperature thermal systems, where reducing heat losses must be balanced against material demand, economic considerations, and environmental impacts. This study investigates the heat-loss and sustainability performance of glass tube solar collectors (GTCs) by jointly analysing heat-transfer mechanisms, structural complexity, and material-related environmental indicators. Four GTC configurations are examined: single-glazed collectors with air and vacuum insulation (SG + Air and SG + Vacuum) and double-glazed collectors with air and vacuum insulation (DG + Air and DG + Vacuum). An analytical equivalent thermal-network model based on iterative thermal-resistance calculations is developed to quantify coupled conductive, convective, and radiative heat losses through cylindrical glass envelopes over absorber temperatures of 40–90 °C and ambient temperatures of 10–30 °C. The thermal analysis is integrated with a unified multi-criteria decision-making framework employing hybrid AHP–Entropy weighting and the SAW and TOPSIS ranking methods. The decision model incorporates heat loss, embodied global warming potential, embodied energy, manufacturing and logistics cost proxies, material mass, and casing surface area. A simplified material-footprint assessment based on a consistent component-level inventory is additionally used to quantify material-related environmental burdens. The results demonstrate that vacuum insulation substantially reduces envelope heat losses compared with air-filled configurations by suppressing natural convection within the intermediate gap. The single-glazed configurations have a total material mass of 2.96 kg, a total embodied energy of 97.04 kWh, and an embodied GWP of 10.84 kg CO2-eq, whereas the corresponding values for the double-glazed configurations are 5.60 kg, 165.15 kWh, and 14.27 kg CO2-eq, respectively. Under the adopted baseline decision assumptions, the SG + Vacuum configuration provides the most favourable compromise between low heat loss, material demand, environmental burden, and economic criteria. The proposed framework provides a transparent basis for the comparative, sustainability-oriented assessment of glass tube solar collector designs by integrating physics-based heat-loss modelling with environmental indicators and multi-criteria decision support.