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

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

Janni Bjerregaard Lund, Ole Skov and Bent S. Bennedsen, AgroTech A/S

The intelligent greenhouse concept

The vision behind our concept is a 60%

reduction in energy from fossil fuel

when producing potted plants in a one

layer greenhouse and without any negative

effect on the quantity or quality of the

produce.

This objective will be achieved through a

combination of;

• Improved strategies for climate

control

• Extraction of surplus heat and

storing it in ground water reservoirs

• Improved curtain systems

• Introduction of a novel wireless

sensor system

• Further improvements of the

climate control software, in order

to utilize the potentials in the

new sensor technology, heat

extraction, LED lighting, and curtains.

The concept is being implemented and

tested on the greenhouse production

plant “Hjortebjerg” located 23 kilometres

north-west of Odense at Funen Island

(Latitude 55° N). The main production is

potted Euphorba milii Des. Moul.

The first step was carried out in 2007

and consisted of a climate check. This

involves construction of a mathematical

model, which simulates the greenhouses,

and computes the energy consumption

at different climate control strategies. The

result was that by introducing dynamic

climate control, an energy reduction of

at least 21% could be obtained. During

2008, the actual reduction was 35%, from

375 kWh/m 2 in 2007 to 241 kWh/m 2 in

2008.

Calculations have shown, that the irradiance,

received by a greenhouse over

the year, is twice the energy requirement

during the same period. However, there is

a surplus during the summer, which is lost

through ventilation and a deficiency in the

winter, which is supplemented by heating.

In our concept, we extract heat from hot

air, collected below the roof ridge of the

greenhouses, and store it in groundwater

reservoirs. During the summer, ground

water of 10 o C is passed through an air to

liquid heat exchanger, which raises the

water temperature to an average of 30 o C

with a maximum of 35°C.

The water is then pumped back into

the ground water reservoir, at a depth of

40 m, where it will maintain its temperature,

albeit with a slight loss, until winter.

The process is reversed during winter by

pumping the water up and cooling it by

means of heat pumps. This generates 70

– 80 o C water for heating the greenhouses.

The system is not able to fully extract heat

on hot summer days and will be comparable

to what is known as the semi-closed

greenhouse.

The combined effect of optimized climate

control and heat storage will be a

50% energy reduction.

Further reductions will be achieved by

introducing new curtains and improved

sensor technologies for more accurate

climatic information and further improved

climate control.

A system of two layers of curtain will be

introduced to improve the insulation and

thereby reduce heat radiation. The “NIR

curtain” and a LS16 curtain (AB Ludvig

Svensson) will be installed in the demonstrations

house at Hjortebjerg.

The new sensor system, which is being

developed by Danfoss IXA Sensor Technologies,

will comprise a relatively large

number of small, wireless sensors, which

will measure temperature, relative humidity,

CO 2 level, radiation and leaf temperature.

The sensors will be located in the

foliage of the plants, and hence give more

accurate and detailed information about

the actual conditions, which the plants are

experiencing. This will permit the grower

to fine tune his climate control, and thus

reduce the energy input.

The projects will continue until 2012,

by which time, we are confident that the

objective of a 60% energy reduction will

be achieved for the Hjortebjerg plant.

Further, based on the knowledge acquired

during the projects, other greenhouse production

plants will be able to achieve the

same amount of reduction of energy and

CO 2 emission.


ENERGY IN FOCUS 39

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