Thermal simulation and test in closed-shading turtle greenhouse

Abstract: It is very important to maintain an optimum inside environment during the different stages of aquatic animals growth for modeling thermal behavior of aquaculture greenhouse. A mechanistic model was developed to describe the thermal behavior of a shading turtle greenhouse system with polystyrene foamed plastic envelope. Energy balance equations have been written considering the effects of conduction, convection, radiation, evaporation and ventilation. Numerical computations have been performed for special days in the month of January 2012, under the climatic conditions of Hangzhou in Eastern China. The governing equations are numerically solved using Matlab 7.0 software to predict the inside and outside surface temperature of the envelope, room temperature, relative humidity, and water temperature. At the same time, on-site measurements were taken at a turtle-breeding facility in Hangzhou for comparisons with predictions. Results showed that the average absolute errors of air temperature, water temperature, and relative humidity were 1.3, 0.32℃ and 3%, respectively. The results also showed that the internal air temperature and water temperature could maintain a relatively stable state by using two sets of 2.7 kW ground-source heat pumps for the turtle greenhouse heating (about 540 m2), a suitable thermal environment for the turtles growth. Model simulations were used to investigate the effects of the greenhouse on the air and water temperature and to examine the heat ?uxes. The results suggest that the daily mean temperature is 5.8℃, the solar radiation is 132 W/m2, the room temperature maintains 35℃, and the water temperature maintains 30℃ when the heat pump provides 40 W/m2 in January near Eastern China-Hangzhou. An examination of the heat ?uxes suggests that thermal radiation and underground heat conduction are major mechanisms of heat loss for the greenhouse covers and water. About 44.5% of heat loss was caused by underground heat exchange, about 43% by built envelopment heat exchange, and about 12.5% was by air leakage. Reducing these heat ?uxes will help conserve and utilize energy. Moreover, the model was deemed to be a useful tool for exploring the performance of heating greenhouse systems under different scenarios, such as different cover materials, sizes and climates.