Greenhouse Air Humidity Research Articles

Study of Microclimate and Sapling Citrus Plant Transpiration in Tunnel Greenhouse Under Mediterranean Conditions

Abstract In Mediterranean basin, citrus culture is expanding rapidly with a growing demand for high-quality saplings. Protected cultivation with fine microclimate conditions control is the best process of citrus saplings growing with the required quality. In this context, the developed microclimate of a tunnel citrus saplings greenhouse and its effects on plant activity parameters, such as leaf temperature and transpiration, were investigated. The findings show that the temperatures of air and plant leaves inside the greenhouse are highly variable between 6 °C and 33 °C and from 8 °C to 30 °C, respectively. Results also show that greenhouse air humidity is very high – more than 80%. The analysis of plant transpiration based on greenhouse microclimate conditions and leaf temperature reveals that (i) plant transpiration varies throughout the day (between 1.9 and 65.7 mg m−2·s−1); (ii) leaf temperature simulation can be used as an indirect indicator of plant water stress; and (iii) the simulated temperature difference between the leaves and the internal air of the greenhouse can be used to define the minimum threshold air temperature for proper plant development under the greenhouse conditions.

Modeling and analysis of greenhouse environmental factors in north China based on path analysis and stepwise regression

To explore the relationship between environmental factors in a greenhouse on sunny/cloudy days, an environmental factor model was developed using path analysis and stepwise regression analysis. The environmental factors studied include greenhouse air temperature (GAT), greenhouse air humidity (GAH), soil temperature (ST), soil humidity (SH), greenhouse radiation (GR), and carbon dioxide concentration (CDC). The results showed that on a sunny day, the models can describe the GAT and GAH well (R2=0.957, 0.936), and the model’s tested determination coefficient was above 0.87. However, due to the delay and other main control factors of ST and SH, the models’ determination coefficient was poor (R2=0.587, 0.625). However, there was a fifth-order polynomial fitting relationship between ST and SH (R2=0.817). On a cloudy day, the coupling effect between dependent variables and environmental factors was well described (R2 ? 0.97). The model test results for GAT and ST were better (R2=0.997, 0.981), and the GAH and SH model test results were also good (R2=0.789,0.882). In summary, the established coupling model of greenhouse environmental factors was suitable for simple greenhouse environment prediction, allowing greenhouse managers to easily predict greenhouse environmental change trends and reduce the cost of testing, laying a foundation for the subsequent establishment of a simpler, more accurate greenhouse factor model.

Using CFD to improve the irrigation strategy for growing ornamental plants inside a greenhouse

In order to cope with water scarcity, improved water management should be implemented to reduce water inputs without affecting production. A better quantifying of the heat and water vapour transfers in response to water restriction is thus needed. Distributed climate models, with the addition of transfers through the substrate-plant-atmosphere continuum calculation is a useful tool. However, such models have generally been established for plants grown in well-watered conditions. This study aimed to simulate the transpiration of plants grown in pots and the resulting microclimate in a greenhouse compartment under different irrigation regimes. An experiment was conducted on New Guinea impatiens grown in containers on shelves, in a 100-m2 greenhouse compartment. A 2D transient CFD model was implemented, including a specific sub-model taking into account the water transport in the substrate-plant-atmosphere continuum, as well as the resulting crop interactions with the greenhouse climate for both well-watered and restricted water conditions. The substrate water content was calculated from the water balance. Special care was paid to model the stomatal resistance. Simulation results showed the model ability to correctly predict transpiration, air and leaf temperatures, as well as greenhouse air humidity for both irrigation conditions. Different irrigation scenarios were then tested by reducing the water supply from 100 to 50% of the substrate retention capacity. Simulations allow assessing the model responses on plant transpiration, growing media water potential and climate distribution inside the greenhouse. Consequently, the CFD model could be useful to define an irrigation strategy for a better water input management.

Modeling greenhouse air humidity by means of artificial neural network and principal component analysis

A back propagation neural network (BPNN) based on principal component analysis (PCA) was proposed for modeling the internal greenhouse humidity in winter of North China. The environment factors influencing the inside humidity include outside air temperature and humidity, wind speed, solar radiation, inside air temperature, open angle of top vent and side vent, and open ration of sunshade curtain, which were all collected as data samples. Through PCA of these data samples, 4 main factors were extracted, and the relationship between the main factors and the original data was discussed. Taking the principal component values as the input of BPNN, the model showed a good performance. A comparison was made between the performances of the BPNN based on PCA and the stepwise regression method with 20 data samples which had not been used to establish the NN model, and the prediction of stepwise regression method was less accurate than the BPNN based on PCA.

Effect of greenhouse ventilation on humidity of inside air and in leaf boundary-layer

After preliminary studies demonstrated that greenhouse air humidity increased considerably close to the lower leaf surface, particularly during daytime when crop transpiration is maximum, we have focused in this study on the consequences of greenhouse ventilation on the decoupling between outside and inside climate and between the latter and the climate in the neighbourhood of the leaves. The theory of moisture transfer within the leaf boundary-layer is first outlined and a model for the air temperature and humidity distribution reviewed. We have investigated also experimentally the ventilation dependence of inside air climate and of the climate in the leaf boundary-layer in two greenhouse tomato crop tunnels differing only in their ventilation conditions. We have demonstrated that wind speed and vent opening govern greenhouse ventilation flux and the resulting inside air speed, which determines inside air humidity, more particularly in the leaf boundary-layer and at leaf level. Inside air speed is also much higher in the area situated near the vent openings than in the centre of the tunnel and consequently inside climate and leaf boundary-layer climates near the vents or the open gable ends are more tightly coupled to outside conditions. Finally, implications of these findings are considered for biological control of whiteflies using myco-insecticides from the point of view of the tunnel ventilation, transpiration activity and crop growth systems.

Measurement of canopy transpiration or evapotranspiration in greenhouses by means of a simple vapour balance model

Canopy transpiration of a greenhouse crop was calculated by means of a simple vapour balance model based on the vapour loss from the greenhouse by ventilation and condensation. The vapour loss by ventilation was calculated from the greenhouse air humidity and ambient humidity and the volume flux of air from the greenhouse. Vapour loss by condensation was calculated from the greenhouse air humidity, glass temperature and the greenhouse air temperature. Two corrections are required for the condensation model: the maximum possible condensation on the cover has to be allowed for, and in summer a correction is applied for the thermal expansion coefficient. Comparison of measured and calculated canopy transpiration shows that this method is suitable to calculate canopy transpiration on a daily as well as on an hourly basis. However, in the region of transpiration rates below 0.1 kg m −2 h −1 the accuracy decreases. This might be improved by a more accurate ventilation rate model.