| Solar energy is a kind of renewable energy,which is endless and wide-ranging,has unique advantages in realizing the sustainable development of resources and environment. In the usage of solar energy,solar water heater can provide customers with hot water for production and daily life because of its sophisticated techniques and reasonable cost.In this paper,the day to day total solar radiation of inclined plate in different azimuth angles and inclined angles was calculated by adopting the brief and practical model "Hay", and all calculations are based on the typical weather-year horizontal day to day solar total radiation in KunMing region.According to detailed analysis,we concluded that:The optimum azimuth angle for fiat-plate collector is the south·direction;The optimum inclined angles is depended on when and how long to use the solar water heater system.For a year round solar system,when the azimuth angie|γ|≤15°,the ideal inclined angle ranges from 25 to 30 degree;and When 15°＜|γ|≤45°,the ideal inclined angle ranges from 15°≤β≤20°.For a summer half-year system,the ideal inclined angle ranges from 0 to 10 degree.For a winter half-year system,when the azimuth angle |γ|≤15°,the ideal inclined angle ranges from 40 to 45 degree;and when 15°＜|γ|≤45°,the ideal inclined angle ranges from 25 to 30 degree.Based on the typical weather-year horizontal day to day weather data,some processes such as hot water producing,using and reserving are simulated.In addition,a mathematics model of solar fraction of solar water heater system(SWHS)was established.By using it, the solar fraction of domestic SWHS in Kunming region and the natatorium for the 7th National Games for the Handicapped was worked out and analyzed.We found that the solar fraction of domestic SWHS increases with the collector area increasing,and when the collector area amounts to 5 square meters,slope of the area-fraction curve obviously decreases.It is nearly invalid to continue enlarging the area for enhancing the solar fraction.Further more,when the volume of the tank is increasing, solar fraction increases at first and then drops off.It is because that when the volume is increasing,the hot water is abundant and the system works at lower temperature,so solar fraction is enhanced since the efficiency and heat accumulation property of water tank are quite high,and vice versa.For a solar system of the natatorium,the solar fraction increases nonlinearly with the increase of the collector area.For instance,when collector area is less than 2100 square meters,solar fraction of the SWHS in the natatorium mentioned above increases with collector area increasing.When it is beyond 2100 square meters,the trend of increment of solar fraction comes down.Especially as the collector area rises to 3000 square meters, solar fraction increases very slowly.On the base of energy price in Kunming and for the object of most life cycle savings,we obtain the most economical system form and best solar fraction of SWHS under the certain heat load.For a domestic SWHS with heat load of 200 liter hot water at 50℃,the most economical collector area is 5 square meters and tank volume is 0.25 cubic meters, accordingly the optimal solar fraction is about 81.4%.For the SWHS in the natatorium,the most economical collector area is 2500 square meters and optimal solar fraction is about 87.4%.Via this research,a method of calculating the solar fraction based on daily meteorological data and parameters of solar system was obtained.That will make calculation of solar fraction more practical and more rational,and lay a reliable foundation for optimum design for SWHS. |
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