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

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

(semi)closed greenhouses with cooling

ducts under the gutters are: high CO 2

concentrations, vertical temperature gradients,

high humidities, combined conditions

of high light intensity and high

CO 2 concentration, and increased rates

of air movement. Investigations showed

that air circulation did not change the

photosynthesis light-response curves. Yield

increase was therefore attributable only to

the instantaneous effects of elevated CO 2

concentration. It was also shown that at

high irradiance, the optimum temperature

for crop photosynthesis increased with

CO 2 concentration.

The higher humidities cause a reduction

in transpiration, and thereby increased

temperatures of the top of the canopy. In

systems where cooling ducts are below the

gutters, temperature differences of 5°C between

roots and top of the plant can occur.

This affects the time necessary for fruits to

mature. At lower temperatures, fruits need

more time to ripen. Tomato fruits were

found to be more sensitive to temperature

in their later stages of maturation at which

they are at lower temperatures in (semi)

closed greenhouses.

Development of new greenhouse concepts

is ongoing. Current examples are

greenhouse systems which even create

a surplus of energy to be delivered to

neighbor greenhouses, other industries or

houses. Concepts like Sunergy Greenhouse,

Sun Wind Greenhouse or Flow-

Deck Greenhouse are examples for that.

With different technological concepts an

energy surplus has to be generated. Currently

these three concepts are shown at

the Innovation and Demonstration Centre

in Bleiswijk. The innovations are intended

to inspire commercial operations to take

advantage of sustainable solutions for climate

neutral production. The performance

of the systems is currently investigated by

Wageningen UR Greenhouse Horticulture.

Sunergy Greenhouse

The sunlight that enters the greenhouse is

absorbed by plants and heats the greenhouse

air. During the summer, this energy

can be collected from the greenhouse air

by means of heat exchangers. The heated

water is then stored in an aquifer until it

can be used during the winter to provide

energy to a heat pump of the greenhouse

and those of third parties. The objective

of the Sunergy Greenhouse 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 equipped

with anti-reflective glass (GroGlass).

The greenhouse is seven metres in height

and has an ultra-lightweight substructure

(Twinlight). There are no roof vents. The

climate is controlled by means of pipe rail

heating, an air-treatment unit with slurves

under the gullies, and overhead cooling

units (1/100 m 2 ). Heat loss is limited by

a double screening system consisting of a

transparent screen (XLS 10 ultra plus) and

an aluminized screening material (XLS

18). A new sliding system prevents leaking

gaps. The transparent screen is closed at

night and during cold days. The aluminized

screen is closed during the night and

when the outside temperature drops below

12 0C. Dehumidification is accomplished

by drawing in outside air. This greenhouse

concept is based on storing heat collected

during the summer in an aquifer.

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. A shade cloth can prevent

solar energy from entering the greenhouse,

and light not transmitted into the greenhouse

can be collected with a screen that

acts as a solar collector. 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 greenhouse. The warm

water is then stored in a special buffer

under the greenhouse for re-use during

the winter.

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 one-sided continuous

roof ventilation. The post height is three

meters, ridge height nine meters and trellis

girder 11.80 meters. Climate control

is conventional. When heat is required,

the greenhouse is heated with water from

the buffer delivered by means of a standard

heating system. For a commercial

operation, a wind turbine will generate

the electricity for the pumps. The excess

electricity will be delivered to the power

grid. During calm periods, electricity will

be drawn from the power grid.

This concept is developed by Thermotech

and Gakon greenhouse builders.

FlowDeck Greenhouse

During cold periods, the greatest loss of

heat occurs through the greenhouse roof

and sides. During the summer, the reverse

occurs and the greenhouse collects a great

deal of solar energy. A roof consisting of a

double layer ‘Flowdeck’, is better insulated

than a standard glass greenhouse. During

very sunny periods, pre-treated water can

flow between these layers to improve

light transmittance to benefit the crop.

The greenhouse roof also collects heat;

this keeps the greenhouse climate cooler

and promotes the dehumidification of the

greenhouse. The heated water is stored in

an aquifer for re-use during the winter.

The greenhouse roof consists of hollow-core

polycarbonate sheeting through

which water flows from the gutter to the

ridge and back. The supply and drainage

system is integrated into the gutter. Light

transmittance through a Flowdeck is equal

to that of conventional acrylic sheeting but

when filled with water is equal to normal

single horticultural glass. The greenhouse

has a traditional Venlo structure with a gutter

height of seven metres and an extended

span of 6.40 metres. The greenhouse has

ENERGY IN FOCUS 37

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