|Author: ||H. Tantau|
In winter-time light is a limiting factor for plant production in greenhouses.
Therefore the insertion of artificial light has increased in practice.
As the costs of installation and the running costs are very high, the economic results of supplementary light are not always positive.
In order to improve the economy of artificial lighting it is necessary to consider not only the physiological but also the technical and energetic aspects: For the operation of artificial light a high input of electrical energy of about 50 [W/m2] is necessary.
More than 90 % of the supplied electrical energy is converted to heat.
If a cogeneration unit is used, an additional 100 [W/m2] of heat will be produced the generation of electricity.
To use up the reject heat of artificial light, better control strategies have to be developed.
One of these strategies is called "heating with light" (Meyer, 1989). The main idea of this strategy is to use the total amount of reject heat of the lamps for heating.
That means, that the artificial light will only be switched on, when a heat demand of more than 50 [W/m2] is exceeded.
So this strategy must not reduce the total amount of light supplied to the plants, it only changes the temporary distribution: at low outside temperatures the amount of artificial light will be increased, while it decreases at higher outside temperatures.
With our strategy the overall heat consumption of a greenhouse can be reduced and the economy of artificial light can be improved.
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