10/16/2009

1

Crop production in low�energy

greenhouses

Leo Marcelis

Increased awareness: save fossil energy

Aims for energy saving (Reduction of CO2 emission;

from 1990 to 2020)

Glasshouses: 48%

Netherlands: 30%

EU: 20%

Need for energy saving in greenhouse horticulture

� Energy costs: 15�30% of a grower

� Greenhouses: 10% of national gas consumption

� Energy for

� heating, reducing air humidity, lighting, CO2

€ -

€ 0.05

€ 0.10

€ 0.15

€ 0.20

€ 0.25

€ 0.30

€ 0.35

€ 0.40

€ 0.45

2-1-2003 2-1-2004 1-1-2005 1-1-2006 1-1-2007 1-1-2008 31-12-2008

Gas

pric

e (€

)

Energiebalance tomato (reference)

Bron: T. Dueck

Solar radiation

Floor 177 MJ m�2` yr�1

Heat 2

Heat 1

roof

wall

How to reduce energy use?

� screens

� Lower temperature

� Temperature integration (within 24 h, several days)

� Postponing starting date

� Control of air humidity

� Cultivar choice

� Less lighting

10/16/2009

2

Recent years many new developments

� Co�generation heat and power

� Geothermal heat

� Electricity producing greenhouse (ELKAS)

� LED lighting

� (semi�)closed greenhouse

Co�generation of heat and power

� Very efficient use of heat, electricity and CO2

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!

10/16/2009

3

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

Energy harvest in summer

Aquifers (porous sand between 2 clay layers)5�8oC 16�18oC

Use energy from aquifer in winter

v Heat Pump

Aquifers (porous sand between 2 clay layers)5�8oC 16�18oC

Features of a closed greenhouse

� Active cooling and dehumidification

� Heat storage in summer in aquifers

� Use of stored heat in winter

Advantages of a closed greenhouse

� Reduced energy consumption & CO2 emission(about 30% less fossil fuel needed)

� Reduction in biocide use

� Reduction in water use

� Higher yields, because of* High CO2 in summer* Air movement (boundary layer �)* Higher light transmissivity

(no ventilators in roof)

Closed or semi�closed greenhouse

Disadvantage of closed greenhouse

� High costs

� Semi�closed greenhouse is more realistic

� Less cooling capacity; allow some window opening

10/16/2009

4

CO2 concentrations in closed and conventional greenhouse

High values in summer !

0

300

600

900

1200

1500

1800

0 10 20 30 40 50 60

Week number after planting

CO

2 co

ncen

tratio

n (p

pm)

(closed symbols = closed greenhouse)

Simulated (lines) and measured tomato yield

0

10

20

30

40

50

60

0 30 60 90 120 150 180 210 240 270

Day number of the year

Yie

ld (

kg/m

2)

Closed symbol is closed greenhouse, open symbol is control

Both in measurements and simulation 16% higher yield in closed greenhouse

Cooling from underneath

sunny weather: 5˚C cooler under crop than above

Above

Below

Bron: Dieleman et al

Time (hour)

Air t

em

pera

ture

(˚C

)

Cooling from below: bigger tomato fruits

80

90

100

110

120

130

140

15 20 25 30 35 40

Week number

Fru

it si

ze (

g) boven

onder

open

Bron: Dieleman et al

Above

Below

Open

Higher air humidity in semi closed greenhouse

(summer)

0

2

4

6

1:00 5:00 9:00 13:00 17:00 21:00

Time (hour)

Vap

our

defic

it (g

/m3 )

Open houseSemi-closed house

Bron: Dieleman et al

Temperature on a sunny day

Open house: plant temperature lower than air

Closed house: plant temperature higher than air

15

20

25

30

35

0:00 6:00 12:00 18:00 0:00

Time of day

Tem

pera

ture

(oC

)

Open: air

Open: crop

Closed: airclosed: crop

Bron: Dieleman et al

10/16/2009

5

Semi�closed greenhouse

� Semi�closed rather than closed greenhouse.

� Energy saving of up to 30%

� Increase in crop yield: 20% desired

� Economics: investment is high

How to reduce energy use?

� screens

� Lower temperature

� Temperature integration (within 24 h, several days)

� Postponing starting date

� Control of air humidity

� Cultivar choice

� Less lighting

How to save energy at a nursery with high intensity lighting and co-generation?

� Most instances surplus of heat

� Hardly any saving through temperaure or humidity control

� If heat buffer is empty, let temperature drop at night!

Temperature

� Most important factor for energy use (75�90% when no lights)

� Energy use depends on :

� Heating set point

� Temperature integration

� Isolation greenhouse (isolation value, window opening, screen)

� Outside temperature, wind, radiation loss

Energiebalance tomato (temp. setpoint 2oC lower)

Bron: T. Dueck

Solar radiation

Floor �31 MJ m�2

Yield: �3%Gas use: �15.5%

Heat 2

Heat 1

roof

wall

Temperature integration

� Crop often responds to long term average temperature, rather than instantaneous values

� Make use of flexibility of the plant

� Automatic by program of climate computer

� By hand

10/16/2009

6

Temperature integration

� Within 24 h

� 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

� Several day

� Day with much wind and less sun: accept lower greenhouse temperature: to be compensated later (not needed always!) ; Independent of outside temperature

�

�

Temperature integration (TI) within 24h

Sun setSun rise

setpoint

referenceTI�sunny day

Temperature greenhouse air

Energy saving: lower temperature at night (heating) higher temperature during day (windows closed)

Additional advantage of closing windowus: higher CO2 concentration �

Temperature integration within 24h in sweet pepper

0

100

200

300

5 10 15 20 25 30

Time (weeks)

Dry

mas

s fr

uits

(g/

plan

t)

optimaal

standaard

`

Optimal: � same average temp.; fluctuation 16�30oC� during daytime less ventilation, at night less heating

2.5 m3 gas saved; same fruit set and production Bron: A. Dieleman.

Conclusions

� By a combination of factors: energy saving of 50% is possible with the same yield

Thank you for your attention

© Wageningen UR