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THECOMMERCIAL GREENHOUSEGROWER • MARCH 2017
materials.”
It is not just screen fabric that is developingAlweco’s new
UltraGrove cable drum reduces friction andwear on the pull
cableswhichmove screens, increasing cable operating life.
“This is amajor improvement on the old systemwhere the
wireswould rub against each other and eventually snap,”
explainsDavid. “The new screen cable drum, can be installed
on new and existing screen systems to significantly increase
the life expectancy.”
“Recent developments in screenmaterials are often linked
to humidity control andNGG,” explainsDebbieWilson. “For
example, for the closed screen approach towork thematerial
needs to be conducive towater movement, such as in the
case of Svensson’sH2no product.” Another development
which has been seen in theNetherlands is the integration of
vertical fanswhich pull dry air through the closed screen from
beneath andwhileNivolator vertical fans have gained some
traction in theUK, DrWilson is not aware of any systems
which span the screen.
“Screenmaterials that allowwater tomove through the
material provide the opportunity to reduce screen gapping and
its negative effects on air temperature immediately beneath a
gap,” points out JonSwain. “This does require use of both lee-
andwind-side vents to enable thewetter air to be replaced
effectively above the screen, and as the air above the screen
will be colder than below, opening the screen too earlywill put
increased load on the heating system and consequent energy
increase. By installing ameasuring box above the screen the
conditions above and below can be better matched before
opening to ensure improved climate control.”
Aswell as using screens for energy efficiency, and in some
casesmanipulating plant growth, some peoplewonder if
the increasing use of LED lighting installations could lead to
more blackout screens being used. “Little blackout screening
has been sold since the contraction of AYR chrysanthemum
growing some years ago,” commentsMax. “Using screens for
shading for crop quality and screening for energy saving seem
to be equally important factors in new screen installations.”
While the use of renewable heating systems, such as biomass
boilers, hasmade energy saving less business critical for some
growers, screening is still important as amethod of enhancing
control of the greenhouse environment he points out.
“Almost all our new glasshouse projects are now fittedwith at
least one thermal/shade screen, and often a double screen,”
saysDavidSummerfield. “When artificial lighting is installed
blackout screens often form part of the planning conditions, so
as the use of lighting increases so does the use of blackout
screens.”
Alweco also feels that, “Using a light emission screenwhen
artificial lights are being used in the greenhouse is gettingmore
andmore popular due to the increasing use of artificial light
above the crops.”
SCREENS •
Gapping screenshasbeennecessary for ventilation, but can lead to temperaturechanges [AHDBHorticulture].
