There is much confusion on how best to grow crop in a semi - closed glasshouse . Godfrey Dol , an expert on growing in semi - shut glasshouse , shares his experience .
To explain the difference of opinion between a conventional and a semi - unsympathetic nursery , let ’s have a smell at how a conventional greenhouse exchanges air . In chassis 1 , a dewy-eyed diagram explicate the airflows .
bod 1 , Airflows in a semi - closed nursery
The gullible coloured orbit act a to the full - grown vine crop . The rows of vine create a roadblock preventing air to penetrate down low into the glasshouse . Most of the melodic line substitution takes property above the crop at the top of the glasshouse . The many windows in the roof replace enough air to keep the glasshouse cool on a ardent summertime mean solar day .
After the nerveless outside air enters the glasshouse it is warm up by the sun and it leave the glasshouse as warm gentle wind through the same vent . The temperature in this greenhouse is largely determine by the outside temperature , the rate of air exchange ( vent opening night and wind hurrying ) , chill capacity of the crop and the saturation of the radiation . Glasshouses with hanging sewer accomplish a good penetration as aura can move through the space underneath the gutters .
Figure 2 , The Semi - shut Glasshouse front view
Roof vents or recirculationThe growth of a commercial-grade semi - closed nursery is considered by many to be the most profound change in nursery design of the last 40 years . In Figure 2 the airflow in a semi - closed glasshouse is schematically express . The departure between the two type of glasshouse becomes clear like a shot .
In a semi - closed glasshouse , all the air enrol the nursery from the bottom . To leave the nursery all the air must move upwards past the plants . This has meaning consequences for transpiration and CO2 uptake . The outside melody is sucked into the mood chamber through a cooling pad rampart . The temperature of the air enter the glasshouse can be as low as 10 ° speed of light below the temperature of the glasshouse air . This is reach by placing a cooling pad at the point where the external air enters the climate chamber . The fans blow the cooled air into the hosepipe and the small holes in the hose lot the air evenly throughout the glasshouse .
There are only two way that this gentle wind can get off from the greenhouse . Either through the roof outlet , or through recirculation . Venting through the roof means that the air is pushed outside . In recirculation musical mode , the greenhouse line re - enters the mood chamber through the recirculation window and is blown back into the glasshouse . The outside conditions largely determine the way of cognitive process .
Figure 3 , The Semi - Closed Glasshouse side view non - closed in organisation
A grower can also employ both alternative at the same sentence . When the air is pushed outside it is considered air through the roof . In recirculation style , the air is re - used , and the greenhouse operate in a “ shut ” mode . Hence the name “ semi - shut ” . The side view in figure 3 shows the flow of air .
Non - circulation modeAs the air come up above the industrial plant canopy it gets exposed to sunlight and warms up . The semi - closed greenhouse has layer of melodic line with different temperature . Cold air enter the glasshouse from the bottom and spicy airwave model at the top of the greenhouse . At the cap of the glasshouse , it can be as hot as 40 - 50 ° C . If the fan speed is too high and turbulence occur , the hot line can be draw down onto the crop . If despite screening and evaporative cooling the temperature still rise , the fan speed need to be increased . In sunny weather condition , the hot breeze may be warming up faster than what the fans can push the aviation out . If the fan speed is fast enough , the cool line fight the warm layer up faster than the sun can warm up it up .
In non - recirculation mode , the outside air is cooled by evaporative cooling in the mood bedchamber . The air pushed into the glasshouse in a semi - closed in nursery is thus cooler compare to outside air entering through the roof volcano in a conventional nursery . To keep the same temperature , the semi - closed in nursery will , therefore , require less air telephone exchange . The reduced air substitution results in higher CO2 level , which is one of the reasons in which a semi - closed nursery can be financially justified .
PressurisationAside from superscript air trend , the forced air movement and cooling , the semi - closed nursery provide some significant other advantage . The sports fan supercharge the glasshouse . This stand for that the volcano in the roof work opposite to vents in a conventional glasshouse . or else of scooping air in , the vents countenance the melodic phrase out . In this process the roof vent become pressure level moderation valves and accordingly less vents are used .
A typical glasshouse has about 400 vents per hectare , versus 80 in a semi - unsympathetic glasshouse . The positivistic pressure and reduced number of vents make it potential to put insect sack up on the vents . The air inlet is also screened which tolerate for a significant lower insect pressure in the greenhouse . All craw - damaging insects , except for russet mites ( and little thripid ) will be screened out . The mesh size of it of the screen can not be reduce to a smaller size because they would become clogged with dust particles . The positive insistency inside the nursery will create an air flow to the outside so that when a door opens , it is harder for belittled dirt ball to fly into the glasshouse . The reduced instauration of industrial plant attacking insects by no agency completely prevents an irruption . However , it makes it far more likely that an Integrated Pest Management ( IPM ) introducing good insects will be successful . Screened air in and outlets changes the betting odds to the husbandman ’s advantage .
The fans are never change state off , cater sizeable air effort at dark , reducing the relative incidence of fungous diseases without have to heat .
Growers are opt semi - closed glasshouse types to reduce pesticide and fungicide economic consumption . The success charge per unit of IPM will be higher and paves the way for reducing chemicals . This is especially straight in warmer climate where the semi - closed greenhouse can cool down a nursery down from 40 + degrees Celsius to below 30 Celsius . Besides shading , the semi - closed glasshouse does that with the awesome power of evaporative cooling which will be talk over in the next variation .
This clause is part of a series about growing in a semi - shut greenhouse . Read here - go’sfor semi - closed glasshouses andcooling .
For more data : Glasshouse Consultancywww.glasshouse-consultancy.com
Godfrey DolLinkedIn[email protected]+81 80 700 94 006
