Research On Construction And Microclimate Of Trabeculeless Solar Aquaculture Greenhouse With Hollow Membrane

At present,aquaculture greenhouses in China mostly draw on planting greenhouses.Planting greenhouses are used for providing plants with suitable light and temperature conditions for their growth.Without professional design,there are many problems in aquaculture greenhouses,such as significant difference in diurnal temperature range,difference between air and water temperature,poor labor production environment,low solar energy utilization and high energy consumption.However,in the northern part of China,both of the temperature and sunlight coverage is low in winter,and aquaculture depends on external heating equipment to increase the water temperature in order to maintain the growth and development of aquatic products,which is costly and not environmentally friendly.Drawing on the cultivation of greenhouses for aquaculture workshops can only play a limited role in early spring and late autumn.Therefore,designing and optimizing aquaculture greenhouses and improving their solar energy utilization and production efficiency have become an urgent demand for the development of aquaculture in northern China.In this research,the self-developed trabeculeless solar aquaculture greenhouse with hollow membrane was taken as the research object,and its design and construction,CAD modeling,simulation and verification of microclimate changes,also winter insulation performance and insulation strategy were studied.The results were as follows:1.Using CFD method to simulating trabeculeless solar aquaculture greenhouse with hollow membrane was feasible.The error rate of using CFD method to simulating trabeculeless solar aquaculture greenhouse with hollow membrane was ≤8.9%.The solar radiation model can be loaded by latitude and longitude using the solar ray tracking algorithm.And the discrete coordinate DO radiation model was used to simulate the radiation intensity on the surface of the greenhouse.The turbulence model adopt the standard k-ε equation model.The model was established according to the greenhouse structural parameters and environmental parameters.It can simulate the changes of the environmental factors inside the greenhouse,which has a reference significance for the modeling of aquatic greenhouses in other regions.2.The microclimate inside the aquatic greenhouse was affected by a variety of environmental factors.The light transmittance of the double-layer hollow film was lower than that of the single-layer plastic film.The light intensity of the light transmitted through the double-layer hollow membrane was 75-95% of the single-layer membrane.The aquatic greenhouse formed an airflow field that moved radioactively from the south to the north in the morning.Afterwards,due to the accumulation of solar radiation energy,a clockwise circulation was formed from the top to the south,the north to the low,the bottom to the south,and the south to the high.At night,the airflow flowed from the bottom to the top in the north,the air pressure in the top of the north was high,and then it flowed to the south,forming an opposite circulation to the previous one.The airflow velocity around was higher than the internal,and the top was higher than the bottom.The thermal fields of aquatic greenhouse in the horizontal planes at different heights,in the east-west,north-south vertical planes were unevenly distributed.In the horizontal direction,temperature in the north was higher than in the south.In the east-west thermal field,the temperature in the east rose more rapidly than in the west,but the heat input in the west increased in the afternoon,and the temperature in the west decreased more slowly than in the east.At night,the temperature variation between different locations was within 1 ℃.Vertically,the top heated up fastest and the temperature was highest during the day and the temperature at the bottom was highest at night and the temperature field tended to be even.The envelope structure affected the light intensity.The solar radiation affected the distribution of the temperature field.Accordingly this temperature field affected the distribution of the airflow,and the airflow had a further influence on the temperature field too.Various environmental factors affected each other and restricted each other,which together constituted the microclimate inside the aquatic greenhouse.3.Strategies for efficient thermal energy storage in aquatic greenhouses in winter can be formulated according to its internal microclimate characteristics.The thermal insulation performance of the aquatic greenhouse was as follows: the trabeculeless solar aquaculture greenhouse with hollow membrane> bright aquatic greenhouse> semi-dark greenhouse> sunlight greenhouse.However,in the trabeculeless solar aquaculture greenhouse with hollow membrane,the amount of heat lost from the northern wall was much larger than the amount of incident,which needed to be improved and optimized.The heat retention between the membranes of the wall was large and it was difficult to output.The energy can be stored by the method of air-water heat exchange.It was found in the air-water heat exchange test that the control greenhouse temperature showed a unimodal rise and then decreased.While the air-water heat exchange greenhouse temperature showed a trend of increasing,then decreasing and then increasing again.Its overall temperature was lower than the control greenhouse.The temperature difference between the two greenhouses also showed in a unimodal trend.The temperature difference first increased to its maximum at 24.7 ℃ around 11:30,and then decreased to 2.3 ℃.Carrying out the study of greenhouses with air-water heat exchange found that after air-water heat exchanged,the water temperature increased.The room temperature increased first,then decreased,and then increased.The difference between room and water temperature,as well as the difference between the water outlet and the inlet temperature,appear to increased and decreased alternately.The air-water heat transfer efficiency was affected by the difference between room and water temperature.When the difference between room and water temperature was less,the efficiency was getting low.