## 3 Thermal Aspects for Improving Energy Performance
### Maintenance of the Greenhouse Environment
#### 3.1.3 Passive Heating and Cooling Systems
Further investigations into the pressure distribution function in greenhouses, cross-ventilation models, and ventilation models considering plants are also proposed to increase the accuracy of these models and provide a comprehensive assessment of ventilation performance beyond the ventilation rate. The study by [PERSON] et al. [141], conducted over two years, monitored a compact ventilation concept in a semi-enclosed greenhouse in Belgium. The concept integrates intensive thermal screening with controlled ventilation, aiming for energy-efficient solutions amid rising energy costs and climate change pressures. The first year showed 9.6% higher energy consumption compared to a reference case, attributed to its location in the greenhouse. However, the second year demonstrated a potential energy saving of 12% with improved crop growing conditions, highlighting the importance of greenhouse climate control for optimizing agricultural yield. [PERSON] et al. [146] examine the microclimate in single-slope greenhouses in Weifang, Shandong Province, China, focusing on temperature, humidity, solar radiation, \(CO_{2}\) concentration, wind speed and vapor pressure deficit. It uses a quality conservation method to estimate ventilation volume and humidity growth after ventilation, revealing that changes in the internal environment of greenhouses are influenced by several factors, such as plant density, coverage, growing height and opening times of ventilation, providing insights to optimize ventilation strategies in greenhouses. [PERSON] et al. [140] propose an M-shaped greenhouse with improved wind resistance and ventilation efficiency, designed to offer superior wind resistance and ventilation performance. This study investigates the optimization of the V angle of the M-shaped greenhouse, comparing its performance in terms of wind resistance and ventilation efficiency with traditional large-arch greenhouses. The M-shaped greenhouse is found to have a higher ventilation efficiency and slightly lower temperature compared to traditional arc greenhouses, making it ideal for use in agricultural production, especially in locations prone to strong winds. The study by [PERSON] et al. [73] uses computational fluid dynamics to study the effects of ventilation configuration in greenhouses. This study reveals the importance of the location and type of openings to optimize ventilation, crucial for maintaining ideal temperature and humidity conditions inside the greenhouse, aiming for sustainability and energy efficiency in agriculture. These studies collectively highlight the importance of efficient ventilation for the sustainability and effectiveness of greenhouses. Ventilation is, therefore, one of the main strategies for controlling temperature, humidity and gas concentration inside greenhouses, standing out as a focus of several studies that evaluate different systems and their impact on the growing environment and agricultural production. This technology is essential in the search for more efficient and sustainable cultivation methods, playing a key role in optimizing the environment for plant growth. A passive heating and cooling system is especially effective when combined with the correct orientation of the greenhouse, allowing for maximum use of the prevailing breezes [69; 148]. Additionally, using water through misting systems or water walls can promote evaporative cooling, efficiently reducing air temperature [9]. These strategies, combined with intelligent design and suitable materials, form an integrated system that promotes an ideal growing environment, minimizing the use of external energy and maximizing the sustainability of greenhouse operations. The limitations of natural ventilation in agricultural greenhouses are marked by its direct dependence on external conditions, such as wind speed and direction, as well as the difference in temperature between the interior and exterior, which can result in an inadequate ventilation rate in days with little wind.