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

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

Timo Kaukoranta and Juha Näkkilä, MTT Agrifood Research Finland, Horticulture

Toivonlinnantie 518, 21500 Piikkiö, Finland, e-mail: timo.kaukoranta@mtt.fi, juha.nakkila@mtt.fi

Using Novarbo cooling with cucumber,

tomato and sweet pepper

in summer 2009

key component of an energy efficient

A greenhouse is a system that removes

humidity and heat from the greenhouse

to allow it to operate without ventilation

when deemed economically meaningful.

Novarbo system by Biolan Company, Finland,

performs that task by creating a

curtain of falling, cool water droplets that

extract from greenhouse air sensitive heat

by convection and humidity by condensation.

In the configuration installed at our

greenhouse at MTT Agrifood Research Finland,

at Piikkiö, the droplets are led to an

outside basin to be re-cooled by a Waterix

evaporative water cooler. The basin serves

also as a buffer in the system that allows

the droplet curtain and water cooler to

operate separately. Electrical energy is

consumed by the system for pumping cool

water from the basin into the greenhouse

and for operating the Waterix cooler.

In an experiment in 2009 we aimed to

fully closed greenhouse, constantly high

carbon dioxide concentration (CO 2 ), and

high radiation, supplemented by moderate

inter-row (169, 175, 125 W/m 2 ) and

over-top lighting (169, 175, 125 W/m 2 ) by

HPS lights whenever total solar radiation

outside falls below 200 W/m 2 except for

a break in the night. In the table below

is summarized total cooling (sensitive +

latent), electricity consumption of the

Novarbo droplet curtain, and electricity

consumption of the Waterix cooler in three

different weather periods and three crops,

each grown in a compartment of 130 m 2 .

The goal of fully closed greenhouse

lead to rather high electricity consumption,

which however could be economically

justified. High maximum temperature (28-

30°C) and humidity (85%) settings led

to clearly lower energy consumption in

Cucumber Tomato Sweet pepper

Weather 2009 Ctot Drops Wix Ctot Drops Wix Ctot Drops Wix

Cool dry, May 12-18 - - - 2.0 0.03 0.15 2.1 0.04 0.16

Cool rainy, Jun 7-13 3.4 0.06 0.10 5.3 0.13 0.13 5.1 0.06 0.13

Warm humid, Jul 21-27 4.8 0.13 0.12 5.6 0.17 0.14 6.5 0.14 0.16

cucumber production than lower settings

in tomato (27°C, 75-80%), and sweet pepper

(28°C, 80-90%) production. Aiming at

fully closed greenhouse with cucumber

and pepper may not be economically the

most optimal goal. In fact, it is often not

even practical. Temperature can be quite

easily controlled by cooling but humidity

control is less straightforward. In a sunny

morning, ventilation with some heating

is needed for moving air to prevent condensation

of humidity on fruits. During

daytime, lowering humidity and temperature

to ensure pollination of tomato

flowers can lead to a control spiral where

absolute humidity and temperature fall

simultaneously with no decrease in relative

humidity. To cut the spiral, ventilation

is needed.


Table 1. Daily mean of sum of sensitive and latent heat extracted from a greenhouse compartment by Novarbo

(Ctot), electricity consumption by droplet curtain (Drops) and by Waterix water cooler a (Wix) allocated to each

crop. All units kWh/day/m 2 of greenhouse. During cool weather daily maximum temperature was 12 to 15°C, during

warm weather 20 to 25°C.

ENERGY IN FOCUS 41

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