If air - commutation is the primary substance of cooling a glasshouse , how does a agriculturalist keep the semi - shut greenhouse poise ? Besides fan speed , which hasa negative effect on clime , and evaporative cooling there is one other important prick to keep the temperature low , Godfrey Dol of Glasshouse Consultancy explain .
The resolution to the interrogative sentence is shading . In a conventional greenhouse , shade is the least favourite method acting for cooling . It is well-situated to understand why . In nerveless mood , the worldwide perception is that 1 % ignitor equals 1 % production . Shading take away light and cut yield . But what if you find more than 3000 Joules of ignitor in a desert or subtropical climate ? Is the plant life able to convert all those J into grams of fruit ?
In general , growers now accept that a tomato plant industrial plant require 1700 - 2000 joule per day to achieve maximum yield . Similar storey are lawful for peppers and pelf . In fact , in the Dutch summertime , the median light total has a similar range . agriculturalist in Australia obtain almost twice as much light compared to growers in the Netherlands . But they struggle to accomplish the Dutch output . Still , they are reluctant to use blending , because in a established glasshouse , the melodic phrase exchange is occlude . The atmosphere underneath the concealment becomes moribund create a wretched climate for plant .
In a semi - closed glasshouse , the air inscribe the glasshouse from below . When a subtlety screen is close , the air is crowd through the screen ( or a break - helpful to keep the airflow in a glasshouse ) , to the vents and leaves the greenhouse . There is no staleness of the air , as the fans keep push the air up towards the vents . In fact , a shade cover acts as a tissue layer , distributing the melody more evenly as it passes through the screen , creating a more even temperature . In a semi - unsympathetic nursery , melody is always moving and activating transpiration .
If we accept that 1800 joules are necessitate to accomplish maximal production , blending is an first-class manner to boil down the heat in the semi - closed greenhouse . Less heating derive into the nursery means less rooter speed .
Can we reduce light and heating plant without lose yield?To reply that question , let ’s weigh a 3300 Joule day . This is very unusual in cool mood , but a frequent natural event in warmer climates . The graphical record below designate a absolutely cheery Clarence Shepard Day Jr. , reaching a maximum of 1100 watts light intensity ( pink line , left hand graduated table ) and a total lite sum of more than 3300 joules ( blue line , right hand scale ) .
The glasshouse already has 25 % ice on the roof to reduce irradiation and the agriculturalist has access to a 25 % spectre sieve . The grower decides to fill up the concealment at 500 watts . This might seem too aggressive , but countenance ’s seek to estimate the amount of light that is shaded away . From sunrise to 500 watts , 25 % of the accumulated is stopped from pass the works . The light sum at that stage is 220 joule , so 55 Joule are close up , and 165 joules make the craw . At 500 Watt the projection screen close and 50 % of the light is blocked . In the table underneath the calculations are presented for the full day .
It twist out that from the 3300 Joules of total lighting , the combined shading and screen blocks almost 1400 J let a respectable 1932 joules through for the plants . Experience has shown that this is enough for optimum yield . More significantly , it allows the raiser to block off the heat from the sun infix the nursery . A lower fan - speed can be maintained in combination with shading without yield loss and without making sacrifice to the climate .
When should a shade screen be used?The Francis Scott Key for the grower is that he needs to calculate when to use the screen . go are the days when we can set the screen to close at a certain light intensity . On a partly cloudy daytime , he may need to end the screens at 600 or 700 watt , for still achieve 1800 Joules . A calculator in the electronic computer that automatically calculates the reduced Joules based on blending would be a welcome plus to any climate reckoner . Looking at the weather forecast is another of import aspect to consider when to habituate screens . If , after a sunny dayspring a mirky good afternoon is expected , use of the projection screen may be better allow until later in the morning ( 600 - 700 watts of radiation ) to accumulate 1800 watt second .
Second screenIn the semi - closed nursery , there is a decided advantage in using a 2d sieve . If in the object lesson above a 2d screen was used or else of whitewash . More ignitor can enter the glasshouse in the early sunup and former afternoon . This set aside for first shading at an even lower swooning intensity than 500 James Watt , further reducing the need to cool . Depending on location , the conglomerate amount of shading can be as high as 60 % , but with smart usage by the grower , this does n’t have to lead to yield losses .
An interesting discussion point , consort to Godfrey , that follow from the purpose of screens is that if we apply tincture screens that diffuse light for most of the day , is there really any benefit in using diffuse glass in a semi - unopen glasshouse?This article is part of a series about growing in a semi - closed greenhouse . Read the first clause about things a grower should never do in a semi - closed glasshouse here .
For more information : Glasshouse Consultancywww.glasshouse-consultancy.com
Godfrey DolLinkedIn[email protected]+81 80 700 94 006
