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THECOMMERCIAL GREENHOUSEGROWER • MARCH 2017
• SCREENS
breathablematerials are using screens for longer, and adopting
theNGG technique of venting above a closed screen at night
rather than screen gapping or increasing pipe temperature.”
In general UK growers seemmore cautious of NGG
techniques than their Dutch counterparts. “We know there are
growers in the north-east who are experimentingwithNGG
which includes venting above the open screen as the first
step in controlling humidity, although I don’t have any details
on numbers at themoment,” commentsDebbie. “Dutch
uptake has been driven through user groupswhich share their
progress and experience; at present UK growers are at the
early stages of adoption.”
She points out that screen opening and closing is linked to
different environmental influences anddesigned tomanage
energy, light levels and summer stress, for example. “TheNGG
approach of introducing a control system in the space above
the screen has been introduced as a concept, through the
AHDB fundedGrowSave project,” she adds.
“Some of themore recent environmental computer systems
have introducedmore sophisticated softwarewhich enables
further integration of various control systemswhile also
incorporating the latest thinking on some aspects of screen
management,” agreesMaxManning of Hortisystems. “Using
multiple horizontal screens gives growers the ability to get a
higher level of control and greater energy savings, perhaps by
mixing an energy screenwith a lighter shade screen. However,
multiple screens can increase shading from the screen
structure, evenwhen open, and increase capital costs.”
Consequently the use of additional screens needs careful cost
benefit analysis, but there are reports that someDutch growers
are nowmoving to triple screen systems.
“Multiple horizontal screens provide the opportunity to benefit
from greater energy saving by further reducing air leakage,
and their insulating effects,” explains Jon. “They also allow
improved tailoring of the environment beneath the screens
without compromising the evenness of that effect. Next
generation growing techniques requiremore screen operations
and keeping them closed for longer. In turn this requires
changes in venting considerations, such asmore aggressive
venting above a closed screen to enable humidity and
temperature control.”
“Double screen systems, such as a top shading system
and an energy system on the bottom, is amajor trend at the
moment according toAlweco, the screen supplier and partner
for BridgeGreenhouses. “There is no doubt about using
screens for energy saving, or cooling and shading, both can
nowbe done using a double screen system.”
Bridge’sDavidSummerfield adds, “Using double screens
gives a vast improvement in the control of the growing
environment, and energy saving, as there is no need to
compromise between ventilation, shading and energy saving
for example.”
The other main development is in the use of newmaterials
which allow screens to have different properties, such as
being fire retardant, transmitting different levels of humidity
andpreventing condensation. “Themain changewe have
seen over the last few years is the introduction of translucent
white plastic screen fabric replacing the aluminium based
shading,” commentsMax. “This has been led by Svensson’s
NewHarmonymaterial, which givesmuchmore diffuse
light penetration into the crop but at the expense of a slight
reduction in energy saving properties. It is interesting to note
that the flame retardant versions of thismaterial are significantly
more cost effective than aluminium based flame retardant
mercial GreenhouseGrower_92x131 (24-2) -drukklaar.indd 1
13-02-17 15:52
Alweco’snewUltraGroovecabledrum includes
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