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

agrotech.dk

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

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