The aim of this study was to analyse air exchange and temperature distribution in a greenhouse with combined mechanical and natural ventilation and to design more efficient mechanical ventilation systems.For this purp...The aim of this study was to analyse air exchange and temperature distribution in a greenhouse with combined mechanical and natural ventilation and to design more efficient mechanical ventilation systems.For this purpose,a computational fluid dynamics(CFD)model of the greenhouse was used.Three configurations were considered:Configuration 1(mechanical ventilation and closed roof ventilators),Configurations 2 and 3(mechanical ventilation and roof ventilators open 30%and 100%,respectively).After validation,the CFD model was used to improve the design of the greenhouse mechanical ventilation system in each of the three configurations analyzed.Four greenhouse lengths,28 m,50 m,75 m and 100 m,were used in the simulations.Compared to fan ventilation only,roof ventilation improved the climate of fan-ventilated greenhouses in terms of the air exchange rate(22%)and climate uniformity because the internal air was mixed better than with mechanical ventilation only.As the greenhouse length increased,more advantages were achieved with natural ventilation compared to mechanical ventilation.For most configurations,there was a strong linear correlation between temperature gradient and greenhouse length.The greenhouse whose regression line had the steepest slope was the one with closed roof ventilators.Increasing the fan capacity produced a general reduction in temperature,but the effect was less intense for the greenhouses with open roof ventilators.Compared to box inlet ventilators,an enlarged continuous inlet in the wall opposite the fans increased overall system performance because it eliminated backflow recirculation zones,which are prone to produce high temperatures.展开更多
Increase of indoor temperature compared with outdoor temperature is a major concern in modern house design. Occupants suffer from this uncomfortable condition because of overheating indoor temperature. Poor passive de...Increase of indoor temperature compared with outdoor temperature is a major concern in modern house design. Occupants suffer from this uncomfortable condition because of overheating indoor temperature. Poor passive design causes heat to be trapped, which influences the rise in indoor temperature. The upper part, which covers the area of the roof, is the most critical part of the house that is exposed to heat caused by high solar radiation and high emissivity levels. During daytime, the roof accumulates heat, which increases the indoor temperature and affects the comfort level of the occupants. To maintain the indoor temperature within the comfort level, most house designs usually depend on mechanical means by using fans or air conditioning systems. The dependence on a mechanical ventilation system could lead to additional costs for its installation, operation, and maintenance. Thus, this study concentrates on reviews on passive design and suggests recommendations for future developments. New proposals or strategies are proposed to improve the current passive design through ventilated and cool roof systems. It is possible to achieve the comfort level inside a house throughout the day by reducing the transmitted heat into the indoor environment and eliminating the internal hot air. These recommendations could become attractive strategies in providing a comfortable indoor temperature to the occupants as well as in minimizing energy consumption.展开更多
基金This research work was partially financed by the EUPHOROS project,Efficient Use of inputs in Protected Horticulture,the Seventh EU Framework Programme and INIA project RTA(2008-00109-C03-01).
文摘The aim of this study was to analyse air exchange and temperature distribution in a greenhouse with combined mechanical and natural ventilation and to design more efficient mechanical ventilation systems.For this purpose,a computational fluid dynamics(CFD)model of the greenhouse was used.Three configurations were considered:Configuration 1(mechanical ventilation and closed roof ventilators),Configurations 2 and 3(mechanical ventilation and roof ventilators open 30%and 100%,respectively).After validation,the CFD model was used to improve the design of the greenhouse mechanical ventilation system in each of the three configurations analyzed.Four greenhouse lengths,28 m,50 m,75 m and 100 m,were used in the simulations.Compared to fan ventilation only,roof ventilation improved the climate of fan-ventilated greenhouses in terms of the air exchange rate(22%)and climate uniformity because the internal air was mixed better than with mechanical ventilation only.As the greenhouse length increased,more advantages were achieved with natural ventilation compared to mechanical ventilation.For most configurations,there was a strong linear correlation between temperature gradient and greenhouse length.The greenhouse whose regression line had the steepest slope was the one with closed roof ventilators.Increasing the fan capacity produced a general reduction in temperature,but the effect was less intense for the greenhouses with open roof ventilators.Compared to box inlet ventilators,an enlarged continuous inlet in the wall opposite the fans increased overall system performance because it eliminated backflow recirculation zones,which are prone to produce high temperatures.
文摘Increase of indoor temperature compared with outdoor temperature is a major concern in modern house design. Occupants suffer from this uncomfortable condition because of overheating indoor temperature. Poor passive design causes heat to be trapped, which influences the rise in indoor temperature. The upper part, which covers the area of the roof, is the most critical part of the house that is exposed to heat caused by high solar radiation and high emissivity levels. During daytime, the roof accumulates heat, which increases the indoor temperature and affects the comfort level of the occupants. To maintain the indoor temperature within the comfort level, most house designs usually depend on mechanical means by using fans or air conditioning systems. The dependence on a mechanical ventilation system could lead to additional costs for its installation, operation, and maintenance. Thus, this study concentrates on reviews on passive design and suggests recommendations for future developments. New proposals or strategies are proposed to improve the current passive design through ventilated and cool roof systems. It is possible to achieve the comfort level inside a house throughout the day by reducing the transmitted heat into the indoor environment and eliminating the internal hot air. These recommendations could become attractive strategies in providing a comfortable indoor temperature to the occupants as well as in minimizing energy consumption.
