Experimental And Theoretical Study On The Greenhouse-type Solar Hot Water System

Energy and environment are two main topics about sustainable development. As a new and renewable energy, solar energy is clean to the environment without pollution. Developing and using solar energy has much significance to both release the traditional energy scarcity and protect the environment. In this paper, solar greenhouse and hot water technologies were combined to establish green house-type solar hot water system. Measurements were taken on temperatures of greenhouse air, collector surfaces and storage water. Based on these, system performances represented by average daily efficiency and non-steady state efficiency were investigated. The measured result shows system circulation is well and storage water temperature is very high up to 73℃. But average daily efficiency is a little lower and its average value in measured period is 30.2%. In order to improve system performance, greenhouse-type solar hot water system mathematic model was developed. Under several different weather conditions, comparisons were made between predicted results and measured data, which show that the model has preferable accuracy and wide applicability. Then, the effects of height difference between storage tank and collector, mass of storage water and cycle pipe diameter on system performance were analyzed. The predictions show the height difference has a little effect on system performance. The mass of storage water is a main factor on influencing system performance. System average daily efficiency becomes higher obviously with increasing mass of storage water, while storage water temperature decreases on verse. The effect of cycle pipe diameter on system performance is not very obvious. Additionally, it is not always an advantage to enlarge cycle pipe diameter to improve system performance, so a specific system should have an optimized cycle diameter. Finally, average daily efficiency being chosen as the objective function under the condition of storage water temperature at 16:00 higher than 45℃, system geometry parameter was optimized and the optimized results at various mass area ratios were presented. Based on these optimized results, some advices were proposed to further optimize the system configuration.