Abstract
The production cost of greenhouse cultivation depends mainly upon significant amounts of energy consumption in order to keep the optimum environmental condition for plant growth. Τhe expenditure on energy, either for heating or cooling, ranges between 30% to 60% of the total production costs, and any attempt to save energy will result in a positive effect on the potentiality of production accordingly, affecting the greenhouse product prices. Research has shown that CO2 enrichment in greenhouses significantly increases the yield of most indoor cultivation of plants of the C3 category. For these plants, when the CO2 concentration increases by three times above that of the atmosphere (380 ppm), the optimum plant growth temperature shifts higher by 5 °C to 10 °C reaching up to 30 °C to 32 °C. Therefore, huge amounts of solar energy can be captured inside the greenhouses, as the ventilation can be decreased. Alongside this, the use of a simple passive solar system consisting of plastic sleeves filled with water is considered to be an improved way to increase the energy inside greenhouses. In this work, three experimental trials were conducted to examine the benefit of the solar energy captured inside a greenhouse during CO2 enrichment at high temperatures. Finally, a modeling approach based on the heat loss equation was developed in order to establish the energy saving inside the greenhouses under the circumstances mentioned.
Highlights
The cost of heating and cooling are the major sources of production expenditure in order for the optimum indoor climatic conditions to prevail for both better quality and higher yield
The recording of temperatures started at the beginning of April and terminated in the middle of May, when the air temperature inside the greenhouse rose above 16 ◦ C during the night for three successive nights
At the beginning of this period, artificial heating is applied to the commercial greenhouses in order to maintain the air temperature to at least above 12 ◦ C; this study gave the opportunity to ascertain the effects of the artificial heating that was reduced during the spring cultivation period
Summary
The cost of heating and cooling are the major sources of production expenditure in order for the optimum indoor climatic conditions to prevail for both better quality and higher yield. During the main cultivation periods of spring and autumn, the day and night temperatures inside a greenhouse are frequently not kept at the optimum levels and are characterized by a wide variation; this indicates the necessity of daytime cooling and overnight heating. The cost of energy consumed ranges from around 50% of the total production costs, and this percentage may rise to 80% during cold periods of the year; this fact is shown in the prices of the product, which in many cases are a great deal higher in winter than in summer. Any actively growing crop, in a greenhouse with no ventilation, can reduce the CO2 concentration in the air during the day to as low Energies 2020, 13, 1242; doi:10.3390/en13051242 www.mdpi.com/journal/energies
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