1. 10/16/2009
Increased awareness: save fossil energy
Crop production in low energy
greenhouses
Leo Marcelis
Aims for energy saving (Reduction of CO2 emission; Need for energy saving in greenhouse horticulture
from 1990 to 2020)
Energy costs: 15 30% of a grower
Glasshouses: 48% Greenhouses: 10% of national gas consumption
Energy for
heating, reducing air humidity, lighting, CO2
Netherlands: 30%
€ 0.45
€ 0.40
EU: 20% € 0.35
€ 0.30
Gas price (€)
€ 0.25
€ 0.20
€ 0.15
€ 0.10
€ 0.05
€-
2-1-2003 2-1-2004 1-1-2005 1-1-2006 1-1-2007 1-1-2008 31-12-
2008
Energiebalance tomato (reference)
How to reduce energy use?
Solar radiation roof
screens
Lower temperature
wall
Temperature integration (within 24 h, several days)
Heat 2
Postponing starting date
Heat 1
Control of air humidity
Cultivar choice
Floor 177 MJ m 2` yr 1
Less lighting
Bron: T. Dueck
1

2. 10/16/2009
Recent years many new developments Co generation of heat and power
Co generation heat and power
Geothermal heat Very efficient use of heat, electricity and CO2
Electricity producing greenhouse (ELKAS)
LED lighting
(semi )closed greenhouse
Geothermal heat ELKAS: Electricity producing greenhouse
Energy saving with LED lights? Greenhouse energy use
Solar radiation provides much more energy than
needed on annual basis, however ….
Provided in summer; needed in winter
Problem of timing
Solution: closed greenhouse!
2

3. 10/16/2009
Energy harvest in summer
Energy storage in aquifers
Harvest solar energy in summer; use it in winter
Proven technology, but new in horticulture
More than 160 applications in the Netherlands
(office buildings, hospitals, apartment blocks)
Aquifer = layer of porous sand
holding water between 2 clay layers Aquifers
5 8oC 16 18oC (porous sand between 2 clay layers)
Use energy from aquifer in winter
Features of a closed greenhouse
Active cooling and dehumidification
v Heat Pump
Heat storage in summer in aquifers
Use of stored heat in winter
Aquifers
5 8oC 16 18oC (porous sand between 2 clay layers)
Advantages of a closed greenhouse Closed or semi closed greenhouse
Reduced energy consumption & CO2 emission
(about 30% less fossil fuel needed)
Reduction in biocide use Disadvantage of closed greenhouse
High costs
Reduction in water use
Higher yields, because of Semi closed greenhouse is more realistic
* High CO2 in summer Less cooling capacity; allow some window opening
* Air movement (boundary layer )
* Higher light transmissivity
(no ventilators in roof)
3

4. 10/16/2009
CO2 concentrations in closed and conventional greenhouse Simulated (lines) and measured tomato yield
(closed symbols = closed greenhouse) Closed symbol is closed greenhouse, open symbol is control
60
1800
CO2 concentration (ppm)
50
1500
Yield (kg/m2)
40
1200
30
900
20
600
10
300
0
0 0 30 60 90 120 150 180 210 240 270
0 10 20 30 40 50 60 Day number of the year
Week number after planting
Both in measurements and simulation 16% higher yield in
High values in summer ! closed greenhouse
Cooling from underneath Cooling from below: bigger tomato fruits
sunny weather: 5˚C cooler under crop than above
140
130
Above
Fruit size (g)
120
Air temperature (˚C)
Above
boven
110 Below
onder
100 open
Open
90
Below
80
15 20 25 30 35 40
Week number
Time (hour)
Bron: Dieleman et al Bron: Dieleman et al
Higher air humidity in semi closed greenhouse Temperature on a sunny day
(summer) Open house: plant temperature lower than air
Closed house: plant temperature higher than air
Open house
6
Vapour deficit (g/m3)
Semi-closed house
35
4
30
Temperature (oC)
Open: air
Open: crop
2 25
Closed: air
closed: crop
20
0
1:00 5:00 9:00 13:00 17:00 21:00 15
0:00 6:00 12:00 18:00 0:00
Time (hour)
Time of day
Bron: Dieleman et al Bron: Dieleman et al
4

5. 10/16/2009
Semi closed greenhouse How to reduce energy use?
screens
Lower temperature
Semi closed rather than closed greenhouse. Temperature integration (within 24 h, several days)
Energy saving of up to 30%
Postponing starting date
Increase in crop yield: 20% desired
Control of air humidity
Economics: investment is high
Cultivar choice
Less lighting
How to save energy at a nursery with high Temperature
intensity lighting and co-generation?
Most important factor for energy use (75 90% when no lights)
Energy use depends on :
Most instances surplus of heat
Heating set point
Hardly any saving through temperaure or humidity control
Temperature integration
If heat buffer is empty, let temperature drop at night! Isolation greenhouse (isolation value, window opening, screen)
Outside temperature, wind, radiation loss
Energiebalance tomato (temp. setpoint 2oC lower)
Temperature integration
Solar radiation
roof
Crop often responds to long term average
wall
temperature, rather than instantaneous values
Heat 2
Heat 1 Make use of flexibility of the plant
Automatic by program of climate computer
By hand
Floor 31 MJ m 2
Yield: 3%
Gas use: 15.5%
Bron: T. Dueck
5

6. 10/16/2009
Temperature integration Temperature integration (TI) within 24h
Temperature greenhouse air
Within 24 h TI sunny day
reference
Two situations:
Let the sun heat greenhouse during the day (for free). Less heating at
night
Day time: less heating while heating at night when closed screen setpoint
Several day
Sun rise Sun set
Day with much wind and less sun: accept lower greenhouse
Energy saving: lower temperature at night (heating)
temperature: to be compensated later (not needed always!) ;
Independent of outside temperature higher temperature during day (windows closed)
Additional advantage of closing windowus: higher CO2 concentration
Temperature integration within 24h in sweet pepper Conclusions
Optimal: same average temp.; fluctuation 16 30oC
during daytime less ventilation, at night less heating
300
Dry mass fruits (g/plant)
200
optimaal
By a combination of factors: energy saving of 50%
standaard is possible with the same yield
100 `
0
5 10 15 20 25 30
Time (weeks)
2.5 m3 gas saved; same
fruit set and production Bron: A. Dieleman.
Thank you for your attention
© Wageningen UR
6