A parametric study on the thermal performance of unglazed solar water collectors with their colorbond steel absorber plates also used as roofs

In this paper, an innovative unglazed solar water collector with its colorbond steel absorber plate also serving as the roof is proposed. Two most common colorbond steel profiles used as roofs, namely the Lysaght BlueOrb colorbond steel with the cosine profile and the Spandek colorbond steel with a trapezoidal shaped profile, are selected as the absorber plates. A theoretical energy balance model is developed to conduct a detailed parametric study on the thermal performance of this innovative unglazed solar collector with both colorbond steel absorber plate profiles under various configuration and operating conditions. The results show that both types of collectors can achieve high thermal efficiency (˜70%) and can increase the water temperature by about 8 °C, indicating they are suitable for the domestic utilization in at least tropical and similar regions as well; The two types of collectors produce very close thermal performances; improved thermal performance can be achieved through optimizing a number of parameters such as using a selective coating for the absorber plate to enhance its optical properties, using slender collector configurations, and using a compromized mass flow rate to maintain a high efficiency and to attain the higher temperature outputs