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Tomato cultivation without artificial illumination in a modern glass greenhouse inThe United Arab Emirates
No shading screens are used
The temperature setpoints are equal across scenarios (a consequence of RTR-based temperature control), as light conditions are equal across scenarios
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The cold production is expressed below as net sensible cooling power provided to the greenhouse by each cooling system. The pad and fan system also produces latent cooling power via evaporative cooling. The combined sensible and latent cooling power of pad and fan (3.2) was comparable with the sensible cooling power of mechanical cooling (3.3-3.4).   |
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The water use of the natural ventilation Scenario (3.1) provides an indicator for comparison. The pad and fan system (3.2) requires tremendous amounts of water, which are lost to the exterior air. The closed greenhouse allows the mechanical cooling system to regain a significant share of transpiration (3.3-3.4). As a result, the pad and fan system requires ~5 times more water than the mechanical cooling system.   |
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Performance
The overall performance is , expressed in terms of environmental and economical feasibility and sustainability and some key numbers and sustainability, is compared in the Table table below.
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Crop production is greatly influenced by cooling systems.
Crop production varies greatly between the cooling systems. The temperature transgressions and extremes resulted in a compromised production for natural ventilation (3.1) and to a lesser extent for pad and fan (3.2). When adequately supplemented with CO2, mechanical cooling realizes the best climate for crop production (3.4)Cooling increases energy and electricity demand.
The greenhouse without active cooling (3.1) naturally has the lowest energy costs, but has also a substantial lower production. The lower production will have a detrimental impact on the financial feasibility and was therefore excluded from further consideration.Pad and fan systems have the lowest energy and electricity demand.
Pad and fan (3.2) has a significantly lower electricity use than mechanical cooling (3.3-3.4). Electricity is only required to establish air flow for evaporative cooling in pad and fan systems. The chillers with pumps and fans used for mechanical cooling dramatically increase electricity use.CO2 emissions will be directly related to the local energy mix.
The CO2 footprint is the direct result of the CO2 footprint of the local energy mix, as no fossil fuels were used for the operation of these greenhouses.
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Conclusions
Scenario with lowest energy use:
Natural ventilation (4.1) logically requires the lowest energy use. Using cooling can increase energy use, variable costs and crop production significantly. When cooling is applied, pad and fan systems (3.2) require the lowest energy use.Scenario with lowest CO2 emissions in future energy net:
The CO2 footprint is the direct result of the CO2 footprint of the local energy mix, as no fossil fuels were used for the operation of these greenhouses. In a fully renewable energy network, the CO2 footprint would remain zero across Scenarios. Water use is at the moment not included in the CO2 footprint of the greenhouse.Scenario with lowest CO2 emissions in current energy net:
The CO2 footprint is the direct result of the CO2 footprint of the local energy mix, as no fossil fuels were used for the operation of these greenhouses. In a mixed energy network, the CO2 footprint is proportional to the energy use. Water use is at the moment not included in the CO2 footprint of the greenhouse.
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Scenario 2
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