Ventilation in greenhouses is achieved either naturally (driven by wind or buoyancy or both) or mechanically (using fans). Using this result together with published data, it was shown that the ratio of the ventilation rate with a screen to the value obtained with the same ventilator without a screen could be represented by the quantity e (2-e) where e is the screen porosity. Measurements showed that an insect screen with a porosity of 0Á39 under the rolling ventilator in the roof, gave a 35% reduction in the ventilation rate. A deficiency in the method of estimating the stack effect was identified that results in its failure for ventilators in horizontal roofs. Theory showed that the stack effect made a significant contribution to sidewall and roof with sidewall ventilation. However, agreement was less good for sidewall and roof with sidewall ventilation. Theoretical predictions of natural ventilation agreed well with the measured values for roof ventilation with root mean square and mean deviations of less than 1Á2 m 3 /s and AE2%, respectively. The global wind pressure coefficient was found to be ventilation system dependent. With the flap ventilators there was a non-linear increase in ventilation with increasing ventilator angle. The ventilation rates per unit area of rolling ventilator were highest for sidewall ventilation (42%), followed by roof and sidewall ventilation (37%). The lowest rates of roof ventilation were obtained with the rolling ventilators (28%) in this case the ventilation rate was independent of wind direction. With roof ventilators, the highest ventilation rates per unit ventilator area were obtained when flap ventilators faced the wind (100%), followed by flap ventilators facing away from the wind (67%). Ventilation rates for different configurations of the ventilators were measured using the dynamic tracer-gas method (decay rate method), with nitrous oxide (N 2 O) as the tracer gas. An 882 m 2, five span, polyethylene film covered parral greenhouse was fitted with either a rolling or a flap ventilator attached to one side of each ridge and rolling ventilators in two 38 m sidewalls. Saving Earth Britannica Presents Earth’s To-Do List for the 21st Century.A study was carried out at the Experimental Station Las Palmerillas of Cajamar to characterise the natural ventilation of the parral greenhouse.Britannica Beyond We’ve created a new place where questions are at the center of learning.100 Women Britannica celebrates the centennial of the Nineteenth Amendment, highlighting suffragists and history-making politicians.COVID-19 Portal While this global health crisis continues to evolve, it can be useful to look to past pandemics to better understand how to respond today.Student Portal Britannica is the ultimate student resource for key school subjects like history, government, literature, and more.Demystified Videos In Demystified, Britannica has all the answers to your burning questions.This Time in History In these videos, find out what happened this month (or any month!) in history.#WTFact Videos In #WTFact Britannica shares some of the most bizarre facts we can find.Britannica Classics Check out these retro videos from Encyclopedia Britannica’s archives.Britannica Explains In these videos, Britannica explains a variety of topics and answers frequently asked questions.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |