Multiscale modeling and performance analysis of evacuated tube collectors for solar water heaters using diffuse flat reflector

• Published in: Renewable energy 2016-02, Vol.86, p.360-374
• Main Authors: Milani, Dia, Abbas, Ali
• Format: Article
• Language: English
• Subjects: Azimuth angle; Beam radiation; Diffuse radiation; Heat transfer; Solar thermal collector; Tilt angle
• ISSN: 0960-1481; 1879-0682
• DOI: 10.1016/j.renene.2015.08.013

Using evacuated tube collectors (ETCs) in solar water heaters (SWHs) may endure deficiencies (i.e. in winter season) in collecting the necessary thermal energy for water heating. This is because of the cylindrical shape of evacuated tubes which makes the upper circumference of the cylinder is directly exposed to sunrays, while the lower circumference usually misses the beam and also most of the diffuse irradiance. In this paper, the role of using a diffuse flat reflector (DFR) at the back of ETC array to improve heat capture rate is examined. A comprehensive model to estimate the annual energy savings and small-scale technology certificates (STCs) is developed. This model is applied on four major Australian cities representing four Australian solar zones. The tilt and azimuth angles for these four zones are optimized. This optimal setting along with DFR presence could improve the STC entitlements by 14.6% for zone 1; 20.2% for zone 2; 25.9% for zone 3; and 27.9% for zone 4, respectively. This specific-tailored model may increase the annual energy saving up to 95.8% for zone 1; 91.3% for zone 2; 81% for zone 3; and 74% for zone 4 correspondingly. •A genetic algorithm to optimize the physical parameters for a diffuse flat reflector is developed.•A sensitivity analysis to identify the optimum location-specific collector orientation is carried out.•Two dynamic sub-models for solar irradiance profile and load-dependent hot water profile are integrated.•The objective to maximize the annual energy saving and small-scale technology certificates entitlement is fulfilled.