Effect Of Partial Displacement Ventilation On Environmental Factors Of Multi-Span Greenhouses In Northern China

Controlling air temperature is one of the annoyance questions to most of cultivator in summer. Over-heated air in between up covering film and thermal net can reach 60#. In order to solving this matter, an approach, named Partial displacement ventilation system, was introduced. The system was made up of up fan, thermal net and wet-pad. In the system, intake air entered the ventilation space through wet-pad beneath the thermal net, to replace the warm air through the thermal net, finally the exhaust air above thermal net was drove out by fan. A model for ventilation in Huabei type of greenhouse in summer was established.Model of thermal radiation mechanism was built for studying thermal radiation of surface on the basis of concept 'effective radiation'. The system for a Huabei type three-span experimental greenhouse was evaluated using a computational fluid dynamics (CFD) model. Principles of optimal design were recommended. Related experiments were designed and carried outIn the experiment, temperature, humidity, air velocity, net radiation were measured. Data processing indicated that the system was an effective method of controlling greenhouse air temperature and relative parameter. Partial displacement ventilation had direct effect on surface temperature of control zone covering material. When the outdoor air temperature is 29.8#, the system could reduce indoor temperature of the greenhouse in summer, up to 3.4#, compared with mechanical ventilation method, its energy saving ratio can achieve 9.6%. Average U valve of the whole experiment greenhouse involving thermal net gap was 4.21 (W/m2. #) in winter. Air speed and indoor air temperature were simulated, compared the results between measured and simulated air speed (position of thermal net gap), their pertinence was 0.96.