- Greenhouse designers and manufacturers seek technological solutions for more sustainable agricultural production, both economically and environmentally.
- J. Huete Greenhouses, a Spanish company, exports its new model of semi-closed hydroponic plastic greenhouses
The fundamental objective of the evolution of the agricultural sector is to increase the quality and quantity of production, transforming, thanks to technology, into what is known as precision agriculture. Highly technical agriculture not only improves efficiency and productivity, but also contributes to sustainability by optimizing the use of resources and reducing environmental impact.
Protected agriculture, in particular, increasingly incorporates technology, resulting in high-quality products that have also been produced in a more efficient and environmentally friendly way. One of these advances are greenhouses with semi-closed plastic covers that allow, compared to conventional greenhouses, to achieve better climate control, maintaining optimal growing conditions throughout the year, thus allowing greater yields and shorter crop cycles.
Semi-closed greenhouses: what they are and why they represent progress
Semi-closed greenhouses have an air distribution system using sleeves through which air is pushed thanks to powerful electronically regulated fans.These sleeves are located below the crop lines and have strategically designed perforations along their length to ensure that air is distributed evenly throughout the growing surface. This driven air is previously adapted in an area specially dedicated for this. In this area, also called the climatic corridor, you can adjust the air temperature (cooling or heating it), adjust the humidity (increasing or decreasing it) and increase the CO2 content to carry out carbon fertilization of the crop. To cool the air, everything from evaporative refrigerant systems to chillers can be incorporated, and in the same way to heat the air, it is possible to use hot air or hot water systems. Once we have distributed the adequate air within the growing area, it can be recirculated and returned to the adaptation area or released through the overhead windows.
All this technology is complemented by the rest of the systems that we find in conventional greenhouses such as screens (shading, energy saving, photoperiod), localized irrigation and fertilization system, climate control or assimilation lighting. Thanks to all this technology, semi-closed plastic greenhouses have a series of advantages:
Semi-closed greenhouses of greater length and more uniform climate
Distribution sleeves allow air to be carried to distances from crop lines of more than 100 m long. This is a great advantage, especially if we compare it with traditional pad&fan type evaporative systems that must be adjusted to no more than 40-50 m distance between the extractors and the cellulose evaporative panels. This represents a limitation when designing the installation as, even without exceeding these distances, this system generates significant temperature gradients between opposite areas of the greenhouse that can reach more than 6 degrees with the consequent consequences for the crop. This temperature difference within the greenhouse not only complicates climate management, but also influences the fertigation strategy since plants subjected to higher temperatures need a greater supply of water. This can give rise to inequalities in terms of the level of development and phenological state of the plants within the same productive area. In semi-closed systems, high thermal uniformity is achieved, ensuring that these temperature differences do not exceed 1.5ºC.
Saving energy and water
The air recirculation system of the semi-closed greenhouses allows the number of renewals per hour to be reduced and together with the electronically regulated fans, reductions in energy consumption of around 30% are achieved. Savings in water consumption are also achieved. Again, if we compare it with a conventional greenhouse with a pan&fan system, it requires a greater number of renewals/hour, between 30 and 60 times, while in semi-closed systems it can be reduced to 10-12 renewals. This leads to a reduction in the consumption of water that passes through the evaporative panels.
An analogous way happens when we want to heat the semi-closed greenhouse. Recirculation and sleeves allow a more uniform temperature increase and maintenance strategy that results in lower consumption of the heating systems used.
Positive pressure in semi-closed greenhouses
Semi-closed plastic greenhouses allow you to work under positive pressure, that is, they allow you to maintain an air pressure slightly higher than that outside. Generating positive pressure within the crop growth zone prevents the entry of insect vectors and pests.
In this way we avoid phytopathologies that can potentially reduce the yield and/or quality of production. Consequently, by minimizing the entry of pests, the need to apply pesticides and other chemicals is reduced. This results in a cleaner product at a lower cost.
Hydroponic growing systems
Soilless or hydroponic growing methods are used in this type of high-tech facility. Crops without soil or in substrate such as coconut fiber or rock wool allow precise fertilization with localized irrigation systems that optimize the use of resources to the maximum. This type of cultivation technique makes it possible to collect and reuse irrigation drains that are disinfected and re-incorporated into the irrigation system, taking advantage of both the water and the nutrients it contains.
Climate control and sensors
Controlling all climatic parameters within the greenhouse is a complex process that requires automation, intelligent software and measurement sensors.
The climate outside greatly influences the climate inside the greenhouse and the growing strategy. Therefore, a weather station is essential for the climate management of greenhouses, as it is an essential component to take timely measurements based on external weather conditions. The weather stations have a temperature sensor, pyranometer, anemometer, wind direction sensor, rain sensor and outdoor relative humidity sensor.
Once inside the greenhouse, it is also necessary to monitor the conditions by taking measurements in order to obtain data that tells us what the situation is in the crop growth zone. Different and varied types of sensors can be incorporated, such as humidity and temperature sensors, pressure sensors, PAR radiation sensors, CO2 sensors, etc., which will provide data to the climate control software.
With all the data collected by the weather station, the sensors inside the greenhouse, the configuration and programmed climate strategy, the climate control equipment will automatically carry out the necessary actions.
For example, the software is configured so that if the interior temperature is higher than 35ºC, the roof windows must open 100% automatically. Thus, when this temperature is reached or exceeded, the software will give the order for the window motors to open as much as possible without human intervention. However, the influence of the wind can also be incorporated into this configuration so that if there is a wind outside of more than 30 km/hour, the windows are closed to safeguard the integrity of the structure, whatever the temperature inside.
Current climate control software allows a wide configuration of different parameters and the influences between them so that the management of climatic conditions within the greenhouse is optimal at the crop level, but also in terms of energy consumption and the proper functioning of the devices. installed equipment.
Without forgetting that these systems allow remote control and management of the installation, without needing to be physically in the greenhouse. Intelligent algorithms are even incorporated to analyze data and provide personalized recommendations on crop management, input use and irrigation strategies. Algorithms that predict the temperature throughout the day, allowing field technicians to make very precise climate adjustments every few minutes in an easy and intuitive way.
Particularly, at J. Huete Greenhouses we have been working with agricultural projects that incorporate high-tech greenhouses around the world for many years, so we know how important it is to have climate control equipment. Our experience makes us convinced that the future is highly technical precision agriculture in which decision-making is carried out based on big data and in which innovations such as the semi-closed plastic model come into play to develop a profitable and increasingly efficient agricultural practice.
Authors:
Juan Francisco Moreno and María Giménez. Technical department. J. Huete Greenhouses
