## 3 Thermal Aspects for Improving Energy Performance
### Maintenance of the Greenhouse Environment
#### 3.1.4 Active Heating and Cooling Systems
Evaporative cooling uses water to absorb heat, a process in which water, when evaporating, removes heat from the air, thus reducing the temperature of the environment, while exhaust fans and fans ensure air circulation, promoting constant air renewal and efficiency in removing hot air [122; 160]. In addition to the techniques, there are additional approaches such as shading and reflection that use special materials that reflect solar radiation to prevent overheating [161]. These materials, by reflecting sunlight, reduce the amount of heat that enters the greenhouse, thus maintaining the internal temperature at lower levels. Composite systems are also used, taking advantage of the constant temperature of the subsoil or groundwater to cool the air in the greenhouse [161]. These systems route air through underground pipes where, due to the lower temperature of the soil or groundwater, the air is cooled before being reintroduced into the greenhouse. Geothermal energy and passive radiative cooling are other techniques used, the first uses underground heat to heat or cool the greenhouse [162]. For cooling, the geothermal system can be used to extract heat from inside the greenhouse and dissipate it underground, taking advantage of the lower ground temperature to cool the internal environment. This is particularly useful in hot climate regions where excess heat can be detrimental to plant growth. Radiative cooling uses materials that emit infrared radiation into space, cooling themselves in the process and reducing the temperature of the greenhouse [163]. Finally, solar cooling uses solar energy to operate absorption or adsorption cooling systems, offering a sustainable cooling alternative with low energy consumption [164]. These innovative techniques provide efficient and sustainable methods for maintaining the ideal environment within greenhouses, reducing the need for conventional energy and promoting more sustainable agricultural practices. And they can be used in combination to increase energy efficiency and reduce costs. It is important to choose the appropriate technology for each greenhouse, considering factors such as the local climate, greenhouse size, investment capacity and energy efficiency. The right choice can significantly reduce operating costs and improve crop production. The selection of climate control technology for greenhouses is a balancing act that considers local variables, accessibility to energy sources, the allocated budget and the specific requirements of the plant species grown. Active heating and cooling systems face several limitations, such as high energy consumption, which significantly increases consumption rates in buildings, and integration challenges with the built environment, including complicated control, acoustic issues, and higher initial costs. Additionally, efficiency and thermal constraints limit the applicability of these systems, requiring active cooling solutions to provide a significant thermal advantage over passive options to be considered viable. These factors combined highlight the need for continued research to overcome these obstacles and develop more efficient systems that are well integrated into the built environment [165; 166; 167]. Efficient climate management in greenhouses is essential for reducing energy consumption and greenhouse gas emissions, as demonstrated in a series of recent studies. In a comprehensive overview of studies on energy efficiency in greenhouses. [PERSON] et al. [169] carried out a detailed analysis of the greenhouse agricultural sector in the European Union (EU), emphasizing the dependence on fossil energy sources and the variation between high-energy systems in the north (predominantly for heating and cooling) and low-energy systems in the south (involving heating, cooling, irrigation, lighting, fertilizers and pesticides). They proposed the adoption of renewable energy sources and energy efficiency measures. [PERSON] et al.