Abstract:In order to explore an energy-efficient thermal environment control model in greenhouse, the application of thermal environment phase change control system was studied in solar greenhouse. A solar greenhouse root zone thermal environment control system was designed and built, including the phase change thermal unit, latent heat storage and exchange unit, root temperature control unit, circulation pump group and circulation pipeline. The latent functionally thermal fluid was used as liquid heat transferring medium in the heat collection, delivery and release of solar radiation. The system included three different work modes, and the thermal performance testing project was formulated. In winter of 2014, the operation performance of the designed system and application effect on lettuce seedlings were tested through controlled experiment of three different operation conditions, using two greenhouse models with the same construction and root zone thermal environment control system. The results indicated that the designed system significantly reduced the indoor air and shallow substrate temperature fluctuations in experimental greenhouse model, and significantly lowered the everyday highest indoor temperature and obviously increased root zone temperature of root zone substrates in winter, thus improving balance of temperature distribution among substrate layers with different depths. During the whole winner test process, the everyday highest indoor air temperature and the average fluctuation range of air temperature were averagely decreased by 7.2% and 5.1%, respectively, and the average 20cm depth root zone temperature and the average fluctuation range were increased by 15.1% and 39.0%, respectively. Among the three operation stages, system performances of the stage with flow rate of 3~4L/min was the optimum one, with the most obvious increases of average temperature and average fluctuation range of 20cm deep substrate, as well as the most significant rise in reduction percentages of temperature differences between 5cm deep and 20cm deep substrates. In addition, the plant height, stem diameter, leaf area per plant and width of maximum leaf of lettuce seedlings in the model were increased by 13.4%, 11.9%, 79.1% and 35.3%, respectively. Overall, the effect of the system was remarkable in sunny days. In conclusion, the phase change heat collecting system can effectively control the air the root zone thermal environment in greenhouse and promote seedling growth of vegetables.
