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

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

greenhouse

If screens are used almost permanently,

they can reduce the energy use by more

than 35%. Due to restrictions for closing

in commercial practice, reduction in

energy use by thermal screens is restricted

to 20%. Efficient screening strategies can

save energy while maintaining crop production

level.

Semi-closed greenhouse concepts

The last years several greenhouse concepts

were developed. It started with using the

greenhouse itself as solar collector (solar

greenhouse “Zonnekas”), followed by fully

closed greenhouses, towards energy producing

greenhouses (“Kas als energiebron”)

and latest developments toward electricity

producing greenhouses (“Elkas”). In closed

greenhouses, the excess of solar energy

in summer is collected and stored e.g. in

aquifers to be reused in winter to heat the

greenhouse. These concepts result in a

reduction in primary energy use of 33%.

But to reduce investment costs, growers

tend to choose a semi closed system.

Cooling capacity of this system is lower

and insufficient to keep the temperature

below the maximum, so ventilation windows

will be opened. CO2 emission in

(semi)closed greenhouses is considerably

lower than in open greenhouses. In a

recent experiment, in which tomatoes

were grown at a maximum concentration

of 1000 ppm, the open greenhouse used

54.7 kg CO2 m-2 in contrast 14.4 kg CO2

m-2 in the closed greenhouse.

Sustainable greenhousees

Specific characteristics of climate in (semi)

closed greenhouses are: high CO2 concentrations,

vertical temperature gradients,

high humidities, combined conditions of

high light intensity and high CO2 concentration

and increased rates of air movement.

Yield increase is due to the effects

of elevated CO2 concentration at high

irradiance, and the optimum temperature

for crop photosynthesis increased with

CO2 concentration.

The following concepts are shown at

the Innovation and Demonstration Centre

in Bleiswijk and investigated by Wageningen

UR Greenhouse Horticulture. These

and future concepts might even create a

surplus of energy to be used in the surroundings.

Sunergy Greenhouse

The objective is to obtain the greatest possible

light transmittance. A double screen

traps heat to reduce the greenhouse’s own

heat consumption. This greenhouse combines

the best of the existing technologies

now being applied in horticulture. The

roof of the greenhouse is anti-reflective

glass (GroGlass). The greenhouse is seven

metres with an ultra-lightweight substructure

(Twinlight) but no roof vents. Heat loss

is limited by a double screening system

with a new sliding system preventing

leaking gaps. The concept is developed

by Wageningen UR and P.L.J. Bom greenhouse

builders.

Sun Wind Greenhouse

Many pot plants are shade plants that

require a high degree of screening during

the summer. An innovative paneled screen

installed in the Sun-Wind Greenhouse collects

energy in the form of warm water and

prevents direct sunlight from entering. The

warm water is then stored in a special buffer

under the greenhouse but with a conventional

climate control. The greenhouse

roof faces south and consists of adjustable

solar collector panels sandwiched between

double glazing at a 35° slope. The

north side of the greenhouse consists of

acrylic sheets with a slope of 60° and onesided

continuous roof ventilation. The post

height is three meters, ridge height nine

meters and trellis girder 11.80 meters. This

concept is developed by Thermotech and

Gakon greenhouse builders.

FlowDeck Greenhouse

The greenhouse roof consists of hollowcore

polycarbonate sheeting through

which water flows from the gutter to

the ridge and back. Light transmittance

through Flowdeck is equal to conventional

acrylic sheeting but when filled with

water is equal to normal single horticultural

glass. The greenhouse has a Venlo

structure with a gutter height of 7 metres

and an extended span of 6.40 metres. The

greenhouse has roof vents on the sheltered

side. An air-handling unit is connected to

an air distribution system with perforated

flexible pipes installed under the cultivating

systems. Forced-air heating/cooling

units are installed. The greenhouse is also

equipped with a single shade cloth. This

concept is developed by Climeco Engineering

and Maurice greenhouse builders.

Energy efficient

climate control

Within semi-closed greenhouse concepts,

an energy efficient climate control leads to

further reduction in energy consumption

and/or increase of production. New growing

strategies are currently developed for

several crops. The aim of such concepts is

to reduce energy consumption dramatically

without production losses. In the new

growing strategy for tomato e.g. the energy

consumption has to drop from 40 m 3 to

26 m 3 gas per m 2 greenhouse area. Other

concepts are developed for other crops.

There are several possibilities to decrease

energy consumption in greenhouse

horticulture in the future. The challenge is

to reach it with low-cost solutions.

Semi-closed greenhouse concepts are

permanently in development in order to

optimize the systems concerning costs and

performance. In order to apply new greenhouse

concepts and growing strategies

into horticultural practice cooperation, an

active exchange of knowledge between

growers, horticultural industry, extension

service and research is necessary.


ENERGY IN FOCUS 7

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