Greenhouse Ventilation Research Articles

Computational Fluid Dynamics-Based Simulation of Ventilation in a Zigzag Plastic Greenhouse

Zigzag plastic greenhouses are a type of greenhouse with a high natural ventilation capacity, and the number and quantities of their roof vents affect their ventilation and cooling effect. In this study, a CFD model of a greenhouse was constructed based on computational fluid dynamics (CFD) theory to simulate the temperature and airflow distribution of a zigzag plastic greenhouse and to investigate the effects that the number of zigzags and the construction orientation have on the cooling effect of this type of greenhouse. The results show that the average air temperature in a double zigzag plastic greenhouse (DZPG) was 0.58 °C lower than that in a single zigzag plastic greenhouse (SZPG) of the same size during the experiment. When the outdoor temperature is higher than 35 °C, the maximum temperature of the DZPG is significantly lower than that of the SZPG in a 1.5 m horizontal section; when the top vent is on the windward side, there is an obvious advantage of DZPG ventilation and the utilization efficiency of its top vent is higher, and when the top vent is on the leeward side, the distribution of the airflow in the DZPG is more intensive and more uniform. The maximum difference in the average temperature between the eight orientations of the DZPG was 0.17 °C. Therefore, the cooling effect in summer is not influenced by the construction orientation, but the airflow in the greenhouse is slightly worse when the direction of the roof vents is parallel to the prevailing wind direction.

Comparison and optimization of ventilation schemes in multi-span greenhouse under natural ventilation

The temperature and humidity conducive to the thriving growth of crops in the greenhouse are primarily achieved through natural ventilation. Scientifically sound vent opening schemes are crucial for enhancing greenhouse ventilation effect, especially in multi-span greenhouses. This study employs numerical simulations and experiments to investigate different vent opening schemes in an eight-span greenhouse located in Wuhan, quantitatively analyzes the cooling extent and spatial gradient of temperature and humidity for various vent opening schemes, and proposes vent opening optimization strategies aimed at reducing temperature and humidity gradient. The results show that increasing the opening of vent on both sides of the greenhouse and keeping the top vent open bidirectional can improve the cooling effect. When the opening of the top vent is fixed at 0.6 m, the opening of the side vent is 2.3 m and the bidirectional opening of the top vent can minimize the temperature and humidity distribution gradient. The temperature range of the east-west trend and the vertical height is 2.6 °C and 0.4 °C, respectively, and the relative humidity range is 7.4% and 1.2%. After optimizing the opening scheme of vent, it is found that when the opening of the side vent is 2.3 m, the bidirectional opening of the top vent and the opening of the adjacent span vent are 0.1 m different, the effect of reducing the east-west temperature and humidity distribution gradient is the best. This study can provide a valuable reference for the optimization of ventilation strategy and the reduction of greenhouse energy consumption.

Integrated Greenhouse Microclimate Management: A Review

The normal development of plants and an increase in yield depend on the microclimate in a greenhouse being controlled. Key microclimate factors, like carbon dioxide, temperature, sunlight and relative humidity could be altered by a variety of control actions such as humidification and dehumidification, heating, natural or forced ventilation and concentration of carbon dioxide. Factors like effective natural ventilation in greenhouses, considering factors like temperature differences, wind velocity, and appropriate ventilator area, are crucial for regulating internal climate, reducing energy use, and ensuring healthy plant growth. However, these modifications result in higher energy and fuel consumption throughout the manufacturing process. Thus, appropriate management is obligatory to perform the intricate operations related to balancing energy, i.e., lowering the emanations and reducing the cost of production, even though severe climatic conditions could adversely affect the microclimate inside the greenhouse. This review document will provide concise information on the management of greenhouse microclimate, focusing on different factors that affect crop growth and how these factors can be managed.

Exogenous Glycinebetaine Regulates the Contrasting Responses in Leaf Physiochemical Attributes and Growth of Maize under Drought and Flooding Stresses.

Flooding and drought are the two most devastating natural hazards limiting maize production. Exogenous glycinebetaine (GB), an osmotic adjustment agent, has been extensively used but there is limited research on its role in mitigating the negative effects of different abiotic stresses. This study aims to identify the different roles of GB in regulating the diverse defense regulation of maize against drought and flooding. Hybrids of Yindieyu 9 and Heyu 397 grown in pots in a ventilated greenhouse were subjected to flooding (2-3 cm standing layer) and drought (40-45% field capacity) at the three-leaf stage for 8 d. The effects of different concentrations of foliar GB (0, 0.5, 1.0, 5.0, and 10.0 mM) on the physiochemical attributes and growth of maize were tested. Greater drought than flooding tolerance in both varieties to combat oxidative stress was associated with higher antioxidant activities and proline content. While flooding decreased superoxide dismutase and guaiacol peroxidase (POD) activities and proline content compared to normal water, they all declined with stress duration, leading to a larger reactive oxygen species compared to drought. It was POD under drought stress and ascorbate peroxidase under flooding stress that played crucial roles in tolerating water stress. Foliar GB further enhanced antioxidant ability and contributed more effects to POD to eliminate more hydrogen peroxide than the superoxide anion, promoting growth, especially for leaves under water stress. Furthermore, exogenous GB made a greater increment in Heyu 397 than Yindieyu 9, as well as flooding compared to drought. Overall, a GB concentration of 5.0 mM, with a non-toxic effect on well-watered maize, was determined to be optimal for the effective mitigation of water-stress damage to the physiochemical characteristics and growth of maize.

CFD Analysis and Optimization of a Plastic Greenhouse with a Semi-Open Roof in a Tropical Area

A numerical simulation model of a natural ventilation greenhouse is helpful for improving the production and quality of greenhouse crops in tropical areas. Field experiments show that the mean coefficient of variation of indoor light intensity in four seasons was lower than 10.0%. The highest indoor temperature reached 39.3 °C during summer, while the average indoor temperature ranged from 24 °C to 26 °C in the other three seasons. The average relative humidity in the greenhouse ranged from 76% to 87% annually, which was higher and more stable than that in the external environment. A three-dimensional steady-state numerical model of the greenhouse was established based on computational fluid dynamics. Under natural ventilation conditions, the maximum error between the simulated value and the measured value of the temperature in each measuring point was 5.90%. And the average relative error between the simulated and measured values was 3.0% in the range of 0.7−1.5 m of crop cultivation height. Finally, a numerical simulation of adding side windows and expanding the vents was carried out. The results show that these methods can homogenize the airflow distribution in the greenhouse and improve the utilization efficiency of natural ventilation without more mechanical system operations.

Adaptive PI control of temperature with natural ventilation in greenhouses using a bat algorithm variant

This paper presents a self-tuning PI controller to control the temperature of a greenhouse using natural ventilation. The PI controller parameters are adapted according to the changing dynamics of the process, identified with a simplified greenhouse temperature model based on first principles. The time-varying model parameters are estimated online using the random scaling-based bat algorithm. The model is linearized to obtain a first-order transfer function which facilitates the design of the PI controller using well-known tuning methods. Simulated results with real greenhouse data show that the proposed solution could be applied to keep controllers tuned throughout different agri-seasons.

Designing a strategy for cost-effective CO2 enrichment in a ventilated greenhouse based on the photosynthetic photon flux density-net photosynthetic rate curve of cucumber seedlings

Designing a strategy for cost-effective CO₂ enrichment in a ventilated greenhouse based on the photosynthetic photon flux density-net photosynthetic rate curve of cucumber seedlings

The Role of the Relative Humidity on the Development of Downy Mildew Infection of Cucumber in the Greenhouse in Baghdad

This study conducted at the Dujail, north of Baghdad, aims to control the downy mildew disease of cucumber based on the ventilation of greenhouses by making three ventilation holes in the plastic cover, in comparison to cultivation into a regular greenhouse (without ventilation holes). Three approved cucumber hybrid were included in this study; Mustaqbal, Jamilah, and Faris. The infection percentage and disease severity rates were calculated since the onset of the disease on March 21st, 2022 until May 18th, 2022. The results showed that the average temperatures (minimum and maximum) and relative humidity were 5-25 ºC and 97% inside the regular greenhouse were suitable for the Pseudoperonospora cubensis natural infection. The highest percentage of infection and disease severity were 30.81 and 23.33%, respectively, reported into the regular greenhouse (without ventilation), compared with the infection percentage and disease severity in the ventilated greenhouses, which were 1.28 and 6.99%, respectively. The percentages of infection of Mustaqbal, Faris and Jamila in the regular greenhouse (without ventilation) were 31.69, 31.40 and 29.35%, respectively, compared to 1.47, 1.17 and 1.21% noticed in the greenhouses with three ventilation holes for the same cucumber varieties, respectively. This study found that three ventilation holes in plastic cover of the greenhouse reduced the percentage infection and disease severity in cucumber plants, by 95.8 and 70% respectively.

Estimation of Wind Speed Based on Schlieren Machine Vision System Inspired by Greenhouse Top Vent.

Greenhouse ventilation has always been an important concern for agricultural workers. This paper aims to introduce a low-cost wind speed estimating method based on SURF (Speeded Up Robust Feature) feature matching and the schlieren technique for airflow mixing with large temperature differences and density differences like conditions on the vent of the greenhouse. The fluid motion is directly described by the pixel displacement through the fluid kinematics analysis. Combining the algorithm with the corresponding image morphology analysis and SURF feature matching algorithm, the schlieren image with feature points is used to match the changes in air flow images in adjacent frames to estimate the velocity from pixel change. Through experiments, this method is suitable for the speed estimation of turbulent or disturbed fluid images. When the supply air speed remains constant, the method in this article obtains 760 sets of effective feature matching point groups from 150 frames of video, and approximately 500 sets of effective feature matching point groups are within 0.1 difference of the theoretical dimensionless speed. Under the supply conditions of high-frequency wind speed changes and compared with the digital signal of fan speed and data from wind speed sensors, the trend of wind speed changes is basically in line with the actual changes. The estimation error of wind speed is basically within 10%, except when the wind speed supply suddenly stops or the wind speed is 0 m/s. This method involves the ability to estimate the wind speed of air mixing with different densities, but further research is still needed in terms of statistical methods and experimental equipment.

Field measurement of environmental parameters in solar greenhouses and analysis of the application of passive ventilation

Solar greenhouses are passive agricultural facilities that can realize off-season production. The growth of crops in greenhouses is affected by various environmental parameters. Therefore, it is necessary to understand the variations of environmental parameters in solar greenhouses through field testing to improve their internal environment. Through field tests, it was found that the temperature variation in solar greenhouses was positively correlated with the change in solar radiation. When the top vent was opened, the minimum temperature in the greenhouse remained higher than 30 °C. The temperature gradient in the tall-plant greenhouse was twice that in the short-plant greenhouse. The relative humidity at the bottom of the tall-plant greenhouse remained greater than 65%. Top-vent opening for greenhouse ventilation is not conducive to the cooling and dehumidification of these relatively large sized greenhouses tested in this study. Passive ventilation via an integrated solar chimney and earth-air heat exchanger was applied in an experimental solar greenhouse. The results showed that when the passive ventilation was turned on, the indoor air temperature in the horizontal and vertical direction could be maintained in the range of 25 ∼ 28 °C and 25 ∼ 30 °C, respectively. The air temperature in the vertical direction had been decreased by approximately 3.5 to 6.5 °C. The passive ventilation effectively prevented continuous increases in indoor temperature, improved indoor air distribution and was conducive to the normal growth of crops.

Analysis of the Effect of Exhaust Configuration and Shape Parameters of Ventilation Windows on Microclimate in Round Arch Solar Greenhouse

The round-arch solar greenhouse (RASG) is widely used in the alpine and high latitude areas of China for its excellent performance. Common high temperature and high humidity environments have adverse effects on plants. It is extremely important to explore a reasonable and efficient ventilation system. A three-dimensional numerical simulation model of greenhouse ventilation considering crop canopy airflow disturbance was established. A robust statistical analysis to determine the validity of the model was calculated to thoroughly validate its overall performance. Microclimate distribution characteristics of nine kinds of exhaust configuration in greenhouse in summer were analyzed comparatively. It was determined that the highest ventilation efficiency could be achieved by adopting the combined configuration of rolling film at the south corner of the greenhouse and pivoting the window at the north side of the roof. In winter, the opening angle of ventilation window at the north side of the roof was less than 40° to ensure the rapid cooling of the interior of the greenhouse without the crops being affected by the cold environment. Through optimization analysis, the ventilation configuration with a deviation angle of 25° and a width of 900 mm is more reasonable (10 m span). The research results provide theoretical guidance for the design of the ventilation structure in RASG and further improve the sustainable development of the facility’s plant production.

Assessment of waste heat recovery potential in greenhouse ventilation systems using dynamic pinch analysis

A major factor contributing to the energy efficiency of greenhouses is ventilation losses. The present paper aims at developing a systematic method based on dynamic Pinch Analysis (PA) approach to investigate the heat recovery potential of greenhouse ventilation systems. The heat integration possibility of ventilation waste heat is studied over the course of a year for a greenhouse located in Saskatoon, Canada. The analysis is conducted for a system including a heat pump connected to seasonal heat storage, and an air handling unit. In the first step, a greenhouse climate model is developed to provide the required input data for the PA (i.e., greenhouse thermal and dehumidification loads). Then, a clustering technique is proposed to reduce the heat integration scenarios to a manageable size by limiting the analysis to a set of typical days representing the whole year. Finally, dynamic energy targeting is performed using the composite curves concept of PA to find the maximum heat recovery and minimum energy requirements of the greenhouse. The results showed 55% heat recovery potential for the greenhouse under study. Application of the proposed method can help to find realistic estimations on feasible heat recovery ratios and utility and equipment costs in the early stages of the greenhouse design.

Analysis of Heat and Humidity in Single-Slope Greenhouses with Natural Ventilation

A single-slope greenhouse (SSG) is the general name of a kind of agricultural greenhouse facility widely used in China. Microclimate studies for SSGs in Weifang, Shandong Province, are relatively scarce. This paper mainly discusses the test data of nine SSGs including temperature, humidity, solar global radiation intensity, CO2 concentration, wind speed, and vapor pressure deficit (VPD) trend. Moreover, the conservation of quality method is used to estimate the ventilation volume and humidity growth after opening the top vent in the greenhouse. Through the analysis in this paper, for local SSGs, the internal environmental change has commonality but its internal environment is still influenced by many factors, such as plant planting density, internal cover, plant growth height, and vent opening time. In addition, the method in this paper can provide a quantitative tool for calculating and controlling humidity for researchers and greenhouse workers and provide a basis for greenhouse ventilation strategies.

CFD Simulation Study on the Cooling Characteristics of Shading and Natural Ventilation in Greenhouse of a Botanical Garden in Shanghai

Botanical garden greenhouses typically use solar radiation as an important heat source and meanwhile provide light for plants to survive. However, in the summertime, when the solar radiation is too strong, overheating will occur in the greenhouse and natural ventilation assisted with shading is used to cool it down. The modulation strategy of shading is very important not only to indoor temperature but also to the growth of plants. In order to determine the control strategy of the shading area in the design and installation stage, a CFD model of an exhibition greenhouse in Shanghai is established. During summer conditions, under the worst-case scenario of a windless day, the minimum shading area needed under different outdoor comprehensive temperatures is studied, and the correlation curve is fitted to guide the control of the shading to maintain appropriate thermal conditions. The decrease in indoor temperature under different shading areas is also explored when the outdoor comprehensive temperature is 34 °C. The annual carbon emission reduction of the greenhouse is about 500 t CO2, by adopting shading and natural ventilation. This study provides a reference value for shading control and energy saving and emission reduction of a botanical garden greenhouse.

Seawater Greenhouse Equipped with a Novel Solar Humidification-Dehumidification Desalination Unit in MAKRAN Coast: Fabrication and Experimental Study

The purpose of this study is the fabrication and performance evaluation of a new type of solar humidification–dehumidification (HD) desalination unit to supply sufficient fresh water for a seawater greenhouse in the MAKRAN coast in southeast Iran. In the proposed design, a particular type of air-to-air condenser is used. The cold air coming out of the greenhouse ventilation system (fan and pad) in summer and the cold ambient air in winter is used to supply the required cooling of the system. In this way, when cold air passes over the pipes in air-to-air condensers, condensation of water vapor occurs in the moist air inside the pipes, and fresh water is produced. Greenhouse fans, which have an air flow rate of around 20,000 m3/hr, are used to create this air flow. By fabricating two condensers, each using 42 rows of PVC pipes with a diameter of 75 mm, it is possible to produce 400 L of fresh water per day in a 400 m2 greenhouse. The required heating is provided by the solar farm, which includes 96 square meters of flat plate collectors. The steps of unit fabrication are described in detail in this research. However, the effect of greenhouse air temperature and circulating seawater flow rate on freshwater production, energy consumption, and energy intensity are also investigated. By increasing the flow rate of circulating seawater and decreasing the greenhouse air temperature, the production rate of the system increases. When the hot seawater and greenhouse air temperature are 61.7 °C and 26 °C, respectively, the maximum instantaneous production is estimated to be 80 L/h. The energy intensity of the HD desalination unit is varied between 3192 and 4382 kJ/L, and the gain output ratio of the system is around 0.6. The proposed system can be easily paired with conventional greenhouses employing a fan and pad cooling system and produces around 1.25 (L/m2·day) fresh water.

A Soft Sensor to Estimate the Opening of Greenhouse Vents Based on an LSTM-RNN Neural Network.

In greenhouses, sensors are needed to measure the variables of interest. They help farmers and allow automatic controllers to determine control actions to regulate the environmental conditions that favor crop growth. This paper focuses on the problem of the lack of monitoring and control systems in traditional Mediterranean greenhouses. In such greenhouses, most farmers manually operate the opening of the vents to regulate the temperature during the daytime. Therefore, the state of vent opening is not recorded because control systems are not usually installed due to economic reasons. The solution presented in this paper consists of developing a Long Short-Term Memory Recurrent Neural Network (LSTM-RNN) as a soft sensor to estimate vent opening using the measurements of different inside and outside greenhouse climate variables as input data. A dataset from a traditional greenhouse located in Almería (Spain) was used. The data were processed and analyzed to study the relationships between the measured climate variables and the state of vent opening, both statistically (using correlation coefficients) and graphically (with regression analysis). The dataset (with 81 recorded days) was then used to train, validate, and test a set of candidate LSTM-based networks for the soft sensor. The results show that the developed soft sensor can estimate the actual opening of the vents with a mean absolute error of 4.45%, which encourages integrating the soft sensor as part of decision support systems for farmers and using it to calculate other essential variables, such as greenhouse ventilation rate.

Thermodynamics Analysis of a Membrane Distillation Crystallization Ion Recovery System for Hydroponic Greenhouses Assisted with Renewable Energy

Sustaining agricultural demands is a typical problem, particularly in locations afflicted by the scarcity of fresh water, poor farming soil, and hot weather. The main goal of this study is to perform a thermodynamic analysis of an integrated multigeneration system containing a direct contact membrane distillation crystallization system that recovers beneficial hydroponic farming nutrients from seawater using renewable energy resources. A parametric study is carried out to determine the impacts of various factors on the system, such as changing the rate of mass flow rate, recovery ratio, and salinity. This study proposes a novel sustainable multigeneration system for seawater desalination and ions recovery using the direct contact membrane distillation crystallization system to provide the hydroponic solution and greenhouse ventilation using the dual evaporator vapor compression refrigeration system. With overall exergy efficiency and energy efficiency of 41.40%, and 39.80%, respectively, the system requires about 1182.69 kW and 5314.6 kW of electrical and thermal power in total, respectively, to desalinate 5 kg/s of seawater and recover 170 mg/s of Sulfate (SO4), 81.28 mg/s of Magnesium (Mg), 25.48 mg/s of Calcium (Ca), and 24.16 mg/s of Potassium (K), yielding about 4.4 kg/s of a hydroponic solution, and ventilating 25 greenhouses with a volume of 600 m3 of single greenhouse.

Структурно-логічна схема автоматичної системи управління замкнутою системою опалення та вентиляції теплиць

In the process of designing an automatic control system for a closed system of heating and ventilation of greenhouses with air regeneration, a structural and logical control scheme was substantiated and developed, which provides control of technological parameters (temperature, humidity, CO2 concentration, lighting. The structural-logical scheme was created on the basis of the technological map of the cultivation of common oyster mushrooms taking into account changes in temperature, humidity, CO2 concentration and illumination as a function of time. As a result of the study, controlled quantities, control actions, controlled disturbing actions and uncontrolled disturbing actions were determined. The parameters and modes of operation of the device for automatic control of the closed ventilation system are substantiated. The proposed control algorithm must have memory. During the entire technological cycle, the device must remember the values of temperature, humidity, CO2 concentration and lighting in each room and others. According to the type of memory used, the device will be synchronous, as the parameters of the automatic control device (APU) will change at the moment of arrival of synchronizing pulses. Due to the fact that some transient processes are not stable and have an oscillatory character, with the exception of illumination in our case, it is necessary to introduce a delay into the control algorithm for the response of the system to the duration of pulses. All devices and executive devices work on electricity. Conclusions: 1. It was established that from the point of view of automatic control of the temperature of the substrate and air, the system "cultivation room – greenhouse" with a water heating system is a two-volume object. 2. The structural and logical control scheme of the closed heating and ventilation system, which provides for the control of technological parameters (temperature, humidity, CO2 concentration, illumination) in the system, is substantiated and developed.

A temperature and vent opening couple model in solar greenhouses for vegetable cultivation based on dynamic solar heat load using computational fluid dynamics simulations

AbstractThe application of microclimate control technology in solar greenhouses under a dynamic solar heat load is of great significance for current research on energy consumption and clean efficiency in greenhouses. In particular, solar greenhouses use natural ventilation for the rapid exchange of energy and heat inside and outside the greenhouse. In this study, we proposed a coupling between the natural ventilation model and the computational fluid dynamics (CFD) model to investigate the relationship between ventilation and temperature in solar greenhouses, thus providing a more in‐depth understanding of greenhouse ventilation demands. The influence of vents on the greenhouse microclimate was simulated under dynamic solar thermal loads using CFD to propose a coupling between the natural ventilation model and the CFD model to investigate the relationship between ventilation and temperature in solar greenhouses. Furthermore, we analyzed the daily and annual greenhouse micro‐climates to provide a more in‐depth understanding of greenhouse ventilation demands. Results highlighted the impact of the outdoor wind speed and vent opening on greenhouse ventilation rates and temperatures, with a linear relationship between greenhouse ventilation rates and outdoor wind speed. The outdoor wind speed had little effect on the ventilation rate for reduced vent openings, while the indoor temperature decreased as outdoor wind speed increased. The average temperature in the greenhouse was observed to be greatly affected by wind speeds less than 3 m/s. Simultaneously, opening the greenhouse vent resulted in a fall in indoor temperatures, with openings less than 60% causing the greatest reduction, (the maximum temperature drift was determined as 9.33%).Practical ApplicationsWith the ability to conserve energy and reduce pollution, solar greenhouses are crucial to China's contribution and the global agricultural industry. Moreover, they are associated with improvements in the competitiveness of modern agriculture, particularly in the current era of rapidly increasing costs and pollution from fossil fuels and traditional energy. This study provides a basic reference for the natural ventilation of vents in the control of indoor air temperatures under dynamic solar thermal loads. The results can be used as a theoretical basis for the production management of solar greenhouses, and have an important practical significance for the subsequent automation and intelligent control of greenhouse environments.

Signal Assessment Using ML for Evaluation of WSN Framework in Greenhouse Monitoring

Background and Objective: The deployment of a Wireless Sensor Network (WSN) provides a useful aid for monitoring greenhouse-like environments. WSN helps in achieving precision agriculture i.e. more yield can be produced with precise inputs. Before the deployment of a sensor network, it is necessary to explore the communication range of nodes. Communication signals are affected by losses due to stems, fruits, twigs, leaves, infrastructure material, etc. in a greenhouse. So as part of the deployment strategy, signal assessment is required in the greenhouse. Methods: This research work proposes a Machine Learning (ML) based signal assessment for the evaluation of WSN deployment in different structures of a tomato greenhouse. Signal strength is measured for a naturally ventilated greenhouse and a fan-pad ventilated greenhouse. Measurements for the naturally ventilated greenhouse are considered with two case scenarios i.e. with transmitter and receiver in the same lane and with transmitter and receiver in different lanes. Models are developed for measured values and evaluated in terms of correlation and error between measured and model formulated values. Results and Conclusion: For the naturally ventilated greenhouse case scenario 1, correlation increases from 91.83% to 95.42% as the degree increases from 2 to 7. Correlation for naturally ventilated greenhouse case scenario 2 rises from 72.51% at degree 2 to 90.09% at degree 10. For the fan-pad ventilated greenhouse, the model has a more complex fitting because of the spatial variability within the greenhouse. Correlation of the model increases from 79.39% to 84.06 % with an increase in degree from 2 to 11. For the naturally ventilated greenhouse, better correlation is achieved at lower degrees compared to the fan-pad ventilated greenhouse.