## 3 Thermal Aspects for Improving Energy Performance
### Maintenance of the Greenhouse Environment
#### 3.1.2 Humidity Maintenance  
Humidity regulation in greenhouse environments is a topic of academic and practical relevance in agronomy and plant science, acting as a determining factor in optimizing the microclimate for plant development. According to scientific literature, relative air humidity directly influences the transpiration rate of plants and the ability of leaves to absorb \(CO_{2}\) during the photosynthesis process, two fundamental mechanisms for biomass production and photosynthetic efficiency [118; 119]. Transpiration, as an essential physiological process, helps in the plant's thermal regulation, nutrient absorption and maintenance of cell turgor. However, excessively high relative humidity can decrease the vapor pressure gradient between the leaf and the environment, reducing the rate of transpiration and, consequently, limiting the absorption of \(CO_{2}\) and the translocation of nutrients. This can result in stunted vegetative growth and increased susceptibility to pathogens, due to air stagnation and increased leaf moisture, which favor the proliferation of fungi and bacteria [116; 120; 121]. On the other hand, low relative humidity can accelerate water loss through transpiration, exceeding the water absorption capacity of the roots, leading to a water deficit that results in water stress, stomatal closure and ultimately, a reduction in photosynthesis. Prolonged water stress can cause irreversible damage to cellular structure, severely limiting plant growth and productivity [117]. Thus, humidity management in greenhouses emerges as a critical component in agricultural management, requiring a multidisciplinary approach that integrates knowledge of plant physiology, meteorology and engineering. The use of remote sensing technologies for continuous monitoring of relative humidity, together with automated climate control systems, represents a significant advance in the precision of environmental management in greenhouses, enabling real-time adjustments to maintain humidity within optimal ranges for each species. To effectively manage humidity in greenhouses, various equipment and strategies are used to balance the relative humidity of the air. Ventilation systems, for example, are essential for renewing air and eliminating excess humidity, while misting or sprinkler systems can increase air humidity through the evaporation of finely sprayed water [122]. Irrigation control is another crucial aspect, adjusting the amount of water supplied to plants according to specific water needs and avoiding excess moisture in the soil. Ground covers and absorbent materials are used to keep soil moisture regulated, reducing unnecessary evaporation and conserving water. Environmental maintenance technologies in greenhouses are essential for creating ideal growing conditions for plants, involving precise control of temperature, humidity, \(CO_{2}\) concentration, and light levels. Technological advances allow the implementation of both manual and automated systems that monitor and adjust these environmental factors in real-time, using sensors and actuators to maintain conditions within optimal ranges. Heating and cooling systems, forced ventilation, \(CO_{2}\) injection, and supplementary artificial lighting are examples of technologies used to optimize the microclimate inside greenhouses. These technologies not only ensure the healthy growth and productivity of plants but also contribute to the sustainability of agricultural production, minimizing the use of natural resources and dependence on external climatic conditions. The technologies used to regulate the temperature of greenhouses can be categorized into passive and active systems. Passive systems include elements such as heat storage walls [9]--which capture heat during the day and disperse it at night (Figure 7b)--and openings that promote natural ventilation (Figure 7a). On the other hand, active systems are made up of devices such as fans, heaters, underfloor heating systems and air conditioning units.