Climate and screen management
For tomato growers in Northern & Eastern Europe
Version 4, January 2011
Content
Although the information in
this manual is composed with
care, no claims can be based
on this information. Ludvig
Svensson BV does not
warrant the accuracy or
completeness of this
information and does not
accept any liability for
damages as a consequence
of the use of this information.
More detailed information
about the products can
be obtained from Ludvig
Svensson BV or its
distributors. The products
of Ludvig Svensson BV and
affiliated companies are
only delivered under
appropriateness of the terms
of sales and delivery of Ludvig
Svensson BV, in which the
restrictions of liability are
taken regarding eventual
defects of the products. The
terms of sales and delivery
of Ludvig Svensson BV are
available on request.
For tomato growers
in Northern &
Eastern Europe 3
Climate control basics
4
Screen types
5
Controlling
an energy saving screen
in winter
6
2
Typical set points
13
The energy screen
in summer
14
Svensson helpdesk
15
For tomato growers
in Northern & Eastern Europe
This document offers guidance on how to make the most of your greenhouse
climate. Only a rational application of our climate screens will bring you the expected
benefits, such as greater yields, higher quality and lower energy costs. The main
function of our screens, when growing tomatoes in Northern and Eastern Europe,
is energy saving. Beyond this, the screen is a valuable instrument for controlling
the greenhouse growing climate. As these functions are interlinked, knowledge of
greenhouse climate control is key, which is why we begin with some of the basics.
Furthermore, all guidance is based on growing tomatoes in greenhouses without
artificial lighting.
We hope this document will provide valuable insights to help make your
greenhouse ­operation even more successful. Additionally, our consultants will
be happy to provide you with further information and grower specific advice.
Climate and screen management 3
Climate control basics
Essentially, the climate inside a greenhouse consists of temperature, humidity,
light intensity and CO2 concentration. These elements are influenced by:
1. Outside conditions: radiation, temperature, humidity, rain and wind speed
2. Greenhouse conditions: ventilation, heating, screening, lightning
3. Plant conditions: transpiration
Outside conditions are unchangeable, and plant transpiration is the result of
countless influences. However, greenhouse conditions can be managed and
controlled more easily. As many of the variables influence one another, this
requires a climate computer.
1.
4
1. The main factors
influencing a greenhouse
climate.
Screen types
The Svensson climate screens most commonly used in tomato greenhouses
in Northern and Eastern Europe are:
SLS 10 Ultra Plus
XLS 10 Revolux
XLS 10 Ultra Revolux
These are chosen for their individual properties as follows:
light transmission
direct
diffuse
energy
saving
flame
retardant?
diffuse
Energy saving and shading screens:
SLS 10 Ultra Plus
88%
81%
43%
no
yes
XLS 10 Revolux
85%
78%
47%
yes
no
XLS 10 Ultra Revolux
85%
76%
47%
yes
yes
Climate and screen management 5
Controlling
an energy saving screen in winter
Basic principles
You should aim for as many screen hours as possible – especially during the night
when screen usage has no affect on light loss at all. Having said this, Svensson
energy saving screens have very high levels of light transmission, and can therefore
be used during the day when outside radiation levels are low. In this way the value
of the energy saved can exceed the production losses due to the minor light loss
of screening. In practice this means the screen remains closed after sunrise until
a predefined radiation level is reached and is closed again before sunset when
­r adiation drops below a predefined level. And on very cold days with low radiation
levels the screen may stay closed for the whole day.
Excessive use of energy screens should be avoided. For example, using the screens
at relatively high outside temperatures – approximately 10–15 °C – will slow down
plant development and increase the risk of fungal diseases. Furthermore, using the
screen under these conditions reduces the heating pipe temperature to insufficient
levels. Remember that a minimum pipe temperature is required to
activate the crop and remove water vapor from around it.
6
A good criteria for energy saving is Delta T
This is the difference between the temperatures inside and outside. The Delta T
should be larger than a predefined value before closing the screen, securing a
­m inimum heat supply through the heating pipes. This is not only important for
keeping the crop active, but also prevents excessive humidity and fungal diseases.
We recommend the following Delta T values:
Weeks after planting
Delta T Inside
– outside at which point the screen will close
1–4
5
5–8
10
>9
12
Well developed crops require a larger Delta T before the screen closes. The reason
for this is that mature crops produce more humidity and therefore require a higher
pipe temperature to remove their water vapor. What’s more, a somewhat higher
pipe temperature is beneficial for the ripening process.
In practice this means the screen will always be closed at night during the first
month after planting. This will be the case during most nights during the second
month, except when outside temperatures are higher than 7 ºC. From the third
month on, the screen should be open when the outside temperature is higher than
ca. 5 ºC.
Climate and screen management 7
Controlling
an energy saving screen in winter
In this typical night time example, the screen closes when the outside temperature
drops below 5°C. When the temperature reaches or exceeds 8°C, the screen
opens again. This prevents the screen from opening and closing due to small
fluctuations in temperature.
Measured
outside
temperature
open
Outside
temperature
open
8º C
Deviation outside
temperature open
3º C
Outside
temperature
close
5º C
close
2.
Daytime use
For a mature tomato crop, the screen will be in the open position throughout most
of the daytime. This is also the case when outside temperatures are low. This is
due to the considerable evaporation of the mature crop. In practice this means
that the screen opens approximately 1–2 hours after sunrise, and closes 1–2 hours
before sunset. The exact moment of opening and closing varies with the solar
radiation level.
8
2. An example of night
time outside temperature
control of the energy saving
screen.
Example: Radiation setting screen open = 80 W/m2, Radiation setting
screen close = 50 W/m2
This means that in the morning, after sunrise, the screen will open when the
radiation reaches a level of 80 W/m 2; in the late afternoon the screen will close
when the radiation drops below 50 W/m 2. These settings normally change
according to the age of the crop. In general, higher radiation settings are used
just after planting, while lower radiation settings apply as the crop matures.
It’s generally accepted that the outside temperature level is the parameter that
controls the closing of the energy screen during night time, while the solar radiation
determines the moment of opening the screen in the morning and closing it in the
late afternoon.
Opening the screen
After sunrise, when radiation levels exceed the setting for Radiation Screen
Open (see above), the energy screen should be opened to take advantage of the
available sun light. At this point it can still be relatively cold outside. To prevent a
sudden temperature drop in the greenhouse, open the screen gradually – in stages.
Failure to do so may result in condensation on the plants, which has a negative
­e ffect on growth and can lead to botrytis.
Climate and screen management 9
Controlling
an energy saving screen in winter
In this example the screen is opened in 4 stages: 1%–2%–4%–93% over 45 minutes.
During these 45 minutes the heating system will increase the water temperature in
the pipes and adjust to the situation with the screen open. Together with a small
screen gap of 1–7%, this results in a more controlled air exchange above and below
the screen, minimizing the drop in greenhouse temperature. The 15–minute delay can
be shortened if the outside temperature is closer to the ­t emperature in the greenhouse.
100%
99%
97%
position screen
93%
0%
sunrise
time
10
3.
sunrise
+45 min
3. Opening the screen in
stages. Note: 100% screen
position means the screen
is closed. It is saving
energy. 0% screen position
means it is completely
open. It is on the package.
Closing the screen
At the end of the day the energy saving screen can be closed completely without
delay (the screen can be closed from 0–100% in one go). However, we recommend
that you decrease the water temperature in the heating pipes 10–20 minutes before
closing. This will prevent a temperature peak directly after closing the screen.
Humidity control
A key feature of a Svensson climate screen is that water vapor can easily pass
through it. This helps prevent extreme humidity levels and the formation of
condensation on the screen. Although, as the crop matures it can produce such
high levels of transpiration that you might still need to open the screen a ­fraction
to release excess humidity. We call this a screen gap, and it helps to prevent
­e xcessively high Relative Humidity (RH) levels below the screen.
100%
98%
RH
85%
position screen
4. Example of screen gap
control based on RH.
0%
time
4.
Climate and screen management 11
Controlling
an energy saving screen in winter
Under a completely closed screen, when Relative Humidity rises above 85% the
screen will be opened with an adjustable gap of 1–5%. This will result in a screen
position of 95–99%, while keeping the RH at 85%. When the RH falls below 85%,
the gap is closed again – closing the screen 100%. The position of the vents, the
outside temperature and the outside RH determine the size of the gap needed in
relation to RH inside. In this example a 2% gap is sufficient. A varying screen gap
is shown below.
This example shows how a small gap of 1% is applied when the RH value exceeds
85%. At an RH of 90% the screen gap is at its maximum of 5%.
screen gap
5%
0%
85%
RH
12
5.
90%
5. Example of a varying
screen gap based on an
excessively high RH.
Typical set points
for energy screen control with tomatoes
Energy saving in tomatoes
SLS 10
Ultra Plus
XLS 10
Revolux
XLS 10
Ultra Revolux
Delta T inside-outside for screen closure [ºC]
5–12
5–12
5–12
Outside temperature open [ºC] (deviation open)*
3
3
3
Radiation open [W/m2]
50–100
50–100
50–100
Radiation close [W/m2]
40–80
40–80
40–80
Screen gap [%] for humidity [%]
3 for 90
3 for 90
3 for 90
*How many °C the temperature should rise above the closing temperature before the screen should open
Climate and screen management 13
The energy screen
in summer
Under normal circumstances, a tomato crop in northwestern Europe requires
no shading. However, there can be special reasons to apply some shading – if
you’re dealing with a weak crop, for example. Or, if there’s a sudden change in the
weather: Going from cool and rainy to warm and sunny, for example, your crop may
very well benefit from reduced solar radiation.
Also, the combination of sunshine and windy weather from inland can result in low
humidity levels in the greenhouse. In which case a Svensson energy saving screen
can help by reducing solar radiation (approximately 15%) and diffusing the light.
Both effects will help to reduce crop and fruit temperature. And low greenhouse
humidity levels (approximately 50%) won’t be further reduced by the use of the
screen. To prevent lack of ventilation, close the screen no more than 80%.
14
Svensson helpdesk
We made this document
to provide some general
insight into the use of our
climate screens for tomato
production in Northern and
Eastern Europe. For further
information or grower
specific advice, please
don’t hesitate to get in
touch with us!
Ludvig Svensson BV
Marconiweg 2
3225 LV Hellevoetsluis
The Netherlands
+ 31 181 392 666
[email protected]
Climate and screen management 15