Optimization of tank-volume-to-collector-area ratio for balcony wall-mounted flat-plate solar water heater in hot summer and warm winter region of China

Abstract: The thermal performance and economical efficiency of the flat-plate type solar water heater has been studied by researchers at home and abroad. In order to ensure the efficient operation of the solar water heater and user's demand to the terminal temperature of tank, the countries all over the world with different climates have given different recommended value for tank-volume-to-collector-area ratio (the ratio was abbreviated as Vt/Ac) of the flat-plate solar water heater. However, the value range of recommended value from literatures was too big for the practical application due to the complex climates. In addition, the main residential buildings in large and medium-sized cities in China were mostly high-rise buildings. The solar water heater installed on roof could only meet hot water use for the top six to eight floors. The application of the balcony wall-mounted solar water heater was the one of the effective ways to solve hot water needs for the rest of users in high-rise buildings. Based on the typical meteorological data of 13 cities in hot summer and warm winter region of China, the values of Vt/Ac, azimuth factor and solar reliability fraction of the balcony wall-mounted flat-plate solar water heater have been calculated by using the established mathematical model. The water tank terminal temperature of 60 ℃, the collector angle of 60?-90? and the azimuth angle of 0-90? were used in theoretical calculation. The results showed that, for south-facing balcony wall-mounted solar water heater in hot summer and warm winter region, the ranges of (Vt/Ac)n in spring, summer, autumn, winter and the whole year were 21.1-50.3, 22.9-55.7, 33.8-57.9, 25.0-54.6 and 28.3-49.3 kg/m2, respectively. For convenience of the practical application, the linear regression relations between the annual average (Vt/Ac)n and the tilt angle, daily total solar radiation on the horizontal and the ratio of temperature to daily total solar radiation were given for south-facing balcony wall-mounted solar water heater. For the non-south-facing balcony wall-mounted solar water heater, the seasonal and annual average azimuth factors decreased with the increase of the azimuth angle. The seasonal and annual average azimuth factors ranged from 0.67 to 0.99 and 0.74 to 0.99 when the tilt angle and azimuth angle were respectively at 60?-90? and 10?-90?. The azimuth angle had about 3%, 7%, 10% and 15% effect on Vt/Ac for winter and spring, summer, autumn and the whole year when the azimuth angles were less than or equal to 20?, 30?, 40? and 50?. The azimuth angle had about 20%-33% effect on the above-mentioned Vt/Ac when the azimuth angle increased form 60? to 90?. Further discussion found that the annual average solar fraction ranged from 0.41 to 0.56 for the south-facing balcony wall-mounted flat-plate solar water heater used in hot summer and warm winter region of China.