Experimental And Simulation Research Of The Thermal And Moisture Environment In A Passive Greenhouse

Passive greenhouse with compacted soil wall as the enclosure structure is a characteristic greenhouse type which is widely used in China. With simple construction and low cost, this type of greenhouse could take full advantage of the light and thermal resource and gain great social and economic benefits.Took the typical soil-walled passive greenhouse in Jinan of Shandong province as example, experimental test and numerical simulation as a combination of methods was adopted to carry on the study of the thermal and moisture environment of it.Proper test was taken to the thermal and moisture environment, parameters including outdoor solar radiation, temperature and relative humidity of air, soil temperature and water content, heat flow of soil and wall were tested. The test result shows that the indoor thermal and moisture environment is enough to maintain the growing of plants on a full day; As an efficient regulation and control measure, upper vents plays a certain role in cooling and dehumidifying in passive greenhouse.Took the test greenhouse as an physical model, established an unsteady tri-dimensional thermal and moisture environment model with natural ventilation, adopted the low Reynolds number k-εTurbulence model and rational solution strategy, study of the distribution of thermal and moisture environment under complicated conditions was carried on. The simulation result and test data matched well with the temperature and relative humidity fitting degree of 99.81% and 99.72%,respectively. Both of these two parameters got high reliability and verified the feasibility and veracity of the model, presented a foundation on the deep study of the effect of natural ventilation on thermal and moisture environment in greenhouse.Based on the established numerical model, an unstable numerical simulation for thermal and moisture environment inside greenhouse under different conditions of wind velocity and wind direction was carried on. The results showed that, without ventilation, it is not obvious that the distribution of temperature field, relative humidity field and air velocity field change with different wind velocity and direction outside; under ventilation, the distribution of temperature, relative humidity and air velocity inside changed markedly with the changes of wind outside.Under ventilation, when wind velocity outside changes from 2.5m/s to 4.5m/s, the change law of temperature field, relative humidity field and air velocity field are as follows: The air velocity and relative humidity increase, and the ascendant extent decreases with the increasing of wind velocity outside. The temperature decreases, and the decrease extent decreases with the increasing of wind velocity outside. Temperature is influenced more than relative humidity by wind outside. With south wind, air velocity and relative humidity inside reach the minimum value, the temperature inside reaches its highest value; with south-west wind, the conditions of air velocity, temperature and relative humidity are opposite to those of south wind. Differences in the distribution of temperature and relative humidity are associated with the heat transfer cased by air flowing inside greenhouse.