Article. Energy in fokus - from Kyoto to Copenhagen. - AgroTech

Anker Kuehn, AgroTech, ank@agrotech.dk • Eva Rosenqvist, KU-Life, ero@life.ku.dk •
Hans Andersson, LS, haa@ludvigsvensson.com and Jørn Rosager, jr@dgssupply.dk
What can we
use NIR curtains for?
NIR curtains are the newest type of curtain from Ludvig Svensson.
Near infrared reflecting curtains that reflect some of the heat radiation
and allow almost all photosynthesis-active light to pass through.
Can plants tolerate more light when the heat radiation is reduced?
When we shade plants from
high influxes of radiation from
the sun, it is usually not to reduce the
amount of light, but rather to avoid scorching
the plants. When the influx of
visible light is high, the level of invisible
NIR is also high. NIR radiation is
heat radiation that plants cannot utilise in
their photosynthesis and because, in most
cases, greenhouses are warm enough as it
is, the heat is a waste product.
In principle most plants can withstand
high exposures to light, as many of the
species grown in Danish greenhouse
nurseries love the sun, however they
must be kept cool during exposure. If the
leaf temperature becomes too high, the
plant cannot keep up with the vapour
pressure, meaning that the water that
evaporates from the leaves is not replaced
quickly enough. The plant protects
itself from dehydrating by closing its pores,
leading to the arrest of photosynthesis. If
the plant is exposed to increased vapour
pressure, the outer layer of cells on its leaves
will be damaged; what we call leaf
scorch. When the pores are closed, temperature
increases can lead to scorching
of the middle part of the leaf.
We can prevent this damage to leaves
if we provide shade for the plants,
and regular curtains, e.g. XLS16, block
64% of the radiation influx and reflect it
out from the greenhouse. Unfortunately
this type of curtain also blocks 64% of
the visible (and photosynthesis-active)
light out, thereby preventing photosynthesis.
NIR curtains
The new NIR curtain differentiates between
the visible part of the spectrum
(380-750nm, where plants use 400-700nm
in the photosynthesis) and the near infrared
(NIR) area (800-1200nm). The NIR
area also makes up a large part of what we
call heat radiation.
So, these curtains can block out up to
80% of heat radiation while at the same
time only blocking out 20 % of the visible
and photosynthesis-active light.
This means that we block out less photosynthesis-active
light while at the same
time preventing overheating of the greenhouse.
In this way CO2 can be administered
over a longer period, and we can
achieve more photosynthesis and growth.
The curtains look like regular lightshading
curtains because the shade rate
is for the part of the spectrum that we
cannot see.
We expect NIR curtains will allow for
increased growth without risk of scorching.
Hopefully we will also see lower
leaf temperatures under NIR curtains.
Testing NIR curtains
Together with a diffuse curtain, NIR
curtains are currently being tested at
KU-Life in cooperation with Ludvig Svensson.
The tests will be looking at room and
leaf temperatures under the different curtains.
First chrysanthemums, potted roses,
begonias and kalanchoë are being used
as test plants, as they have different types
of leaves and therefore their water balance
and control of leaf temperature with regard
to radiation also differs.
NIR curtains have also been installed
in the demonstration facility at Hjorte-
bjerg greenhouse nursery, where they are
on public display. See the article about
the Hjortebjerg plant – a demonstration
facility for new energy technologies.
ENERGY IN FOCUS 17