Research On The Thermal Performance Of Large Aquaculture Greenhouse With A Double Layer Of Plastic Film In Winter

The application of large-scale aquaculture greenhouse has become increasingly common. Therefore, the research on the thermal environment of the large-scale aquaculture greenhouse becomes a hot topic due to its broad application prospect. Aimed at the exist problems such as poor heat preservation in winter, the lack of entire designing theory, high cost, this paper studied the thermal environment of aquaculture greenhouse. The outdoor and indoor thermal environment (outdoor solar radiation, outdoor air temperature, outdoor air humidity, wind speed, inter air temperature and water temperature, and film temperature) of large-scale aquaculture greenhouse in Hangzhou was consecutively observed and measured from November 2013 to January 2014. Based on these observed data, the overall thermal performance of aquaculture greenhouse was analyzed. During that time, the main way of heat loss in the large-scale aquaculture greenhouse with double-layer plastic film was radiation, and the heat transfers between outer film and sky radiation, inter film and sky radiation, and water body and sky radiation accounted for 32-53 percent,11.5-22.4 percent, and 9.8-20.3 percent of the total heat loss, respectively.Based on the mass-energy balance principle, the mathematical model of the thermal environment was established after the effects of outer meteorological parameters on greenhouse the environment found out. The accuracy and effectiveness of the model were verified by field test data. Two indicators, the average error and the average relative error of the measured values and simulation values were used to evaluate the accuracy of the model. It was found that the measured values were quite in accord with the simulated values. Results showed that in a typical sunny, cloudy and overcast, the maximum average errors of the water temperature, air temperature, and inter film temperature, outer film temperature, indoor air relative humidity, air temperature of the interlayer, air relative humidity of the interlayer were 0.17℃,0.50℃, and 0.79℃,1.12℃,5.26%,1.87℃ and 2.4% respectively, while the maximum relative errors of 1.76%,3.7%,7.3%,11.9%,5.67%,15.9% and 2.74% respectively.In the final chapter, based on the established thermal environment model, the effects of different water depths on the change of water temperature, the comparison of energy consumption between single-layer film and double-layer films greenhouses, the effects of single-layer film and double-layer film on the change of the heat loss of greenhouse, and the energy demand of different water temperatures in the double-layer film greenhouse were simulated and analyzed, and the main conclusions were follows.1. From December 1st to February 28th in a typical year in Hangzhou, the changes of water temperatures of different water depths were simulated and analyzed based on the model. Results indicated that the average water temperatures were 16.2℃、 16.4℃、16.8℃and 17.1℃ when the water depths were 0.5 m,1 m,2 m and 3.0 m. Thus, it could be seen that the deeper the water in greenhouse pools, the higher the average water temperature.2. From December 1 st to February 28th in a typical year in Hangzhou, the results from the model showed that compared with large-scale aquaculture greenhouse with signal-layer plastic film, the average daily energy consumption of large-scale aquaculture greenhouse with double-layer plastic film was reduced by 3260MJ, 2431MJ,1722MJ and 1074MJ, the equivalent of the heat energy released by 0.111 tons, 0.083 tons,0.059 tons and0.037 tons of standard coal when the water depths were 3m, 2m, 1m and 0.5m.3. From December 1st to February 28th in a typical year in Hangzhou, if indoor water temperatures were maintained at 20 ℃,25℃ and 30℃, the saved total energy by the greenhouse with a shading net were equivalent to the heat energy released by 72.2 tons,78.5 tons, and 85.8 tons of standard coal, respectively.