9
THECOMMERCIAL GREENHOUSEGROWER • MARCH 2017
SCREENS •
SCREENUSE INCREASING
IN THE UK
provide the right impetus to get these fitted from the start.”
“Maintaining even temperatures in the glasshouse, both
horizontally and vertically is one of the fundamentals of Next
GenerationGrowing (NGG), so apex seals and side screens
are now very popular,” explains IanMetcalfe. Apex seals or
screens keep the environment more uniformby preventing
cold air above the energy screen rolling along to low spots
in the glasshouse. GrowSave has produced a factsheet on
itswebsitewhich explains this, and other benefits of modern
screens. They estimate that the installation of apex seals at 30-
40meter intervals along the bay above horizontal screenswill
typically reduce temperature variation by around50per cent.
“Energy cost is the predominant factor in such installations,”
explainsDr DebbieWilson, Head of HorticultureKnowledge
Exchange at AHDB. “This includes the capacity to reach
required night time temperatures in themost severe conditions
without having an excessively large boiler or heating capacity,
which goes hand in handwith energy saving.”
“There is currently a lot of excitement aroundNGGwhich
encompasses awide spectrum of growing and environmental
control strategies andproduct innovations,” commentsDavid
Summerfield of BridgeGreenhouses. Apex screens form part
of thismodel, sowe foresee that their usewill increase as
NGG gainsmomentum in theUK.”
Aswell as apex screens, horizontal screens are also
developing. “So far, very fewUK greenhouses have been fitted
with double screens, mainly because of the extra investment
required. But growerswith existing screenswhich have been
in service for a year or twowill sometimes think about fitting a
new second screen,” says Ian. “However, growerswho have
opted for screenmaterialswith high light transmission and
A thinner versionof theHarmonyflame retardant
material isused for rolling side screens.
The use of screens in greenhouses is increasing amongst
UK growers. The use of newmaterials bymanufacturers,
together with changes in theway inwhich growersmanage
the protected environment, means that there is awider range
of screens, capable of doingmore than ever before. They are
also now commonly specified onmost newbuild heated glass,
while the adoption of new environmental control techniques
means that the use of more than one screen is also becoming
morewidespread.
“The use of thermal and blackout screens is increasing in the
UK,” says IanMetcalfe of CMWHorticulture. “Screens are now
just as important for manipulating the glasshouse environment
as they are for energy saving. These days screens are fitted
as standard for heated crops. Aswell as substantially reducing
energy inputs, screens are also vital for environmental control.
The gradual move towards year round production has a
bearing on the type of screenmaterial installed, as avoiding
light pollution is important to satisfy planning requirements and
keep neighbours happy.”
“We shouldn’t mix up using screensmore and the installation
of screens,” points out JonSwain of FECEnergy, which
delivers theGrowSave initiativewith AHDBHorticulture.
“There is generally a trend to installing additional screens and
upgrading existing screens as they come to the end of their
useful life. Additionally there is interest in the use of apex seals
as a simple delimiter on greenhouse air temperature variations.
Screening side and endwalls is still popularisedby temporary
plastic rather thanmoveable types, largely as a result of the
cost relative to the benefit provided, but newer greenhouses
Harmonyflame retardantmaterial fromSvensson
used inoverhead screens.
