In Mexico, there are regions where the temperature drops below the minimum threshold for tomato cultivation (10 °C), requiring the implementation of auxiliary equipment to heat greenhouse air. The objective of this work was to estimate the energy consumption necessary to maintain climate requirements of a greenhouse located in Texcoco, State of Mexico, by using a model of energy balance implemented on Computational Fluid Dynamics (CFD) simulations. The temperature prediction relied on a numerical model based on CFD, proposing a benchmarking on the position and direction of the heater to estimate its effect on the thermal distribution. Results indicated that heater operation on January 2019, a power of 85.56 kW was needed to keep the greenhouse at 12 °C. Also, simulations indicated that electric heater used was not enough to get a homogeneous temperature inside the greenhouse. To achieve well-distributed thermal conditions, it was necessary to consider both the direction and position of heaters. Consequently, airflow direction became more important than height of the heater in order to homogenize the greenhouse area, given that the thermal gradient was reduced due to reverse heat flows.

No abstract

The expansion of protected agriculture has technological, climatic, and topographic limitations. The agricultural regions of Costa Rica use the greenhouse concept and adapt it to its conditions. The objective of this work was to describe the variation in temperature and humidity in a greenhouse ventilated passively and on land with a more than 45% slope. To evaluate the environment inside the greenhouse, temperature and humidity variations were measured with a weather station installed outside of the greenhouse to measure the external environment. Inside the greenhouse, 17 sensors were placed to measure the temperature (T) and relative humidity (RH). During data recording inside the greenhouse, tomato crops were in the fruit formation stage, and pepper was less than one week old. Six scenarios were tested to determine the air temperature and humidity dynamic under different climatic conditions. An evaluation of the greenhouse environment was carried out employing an analysis of variance of temperature and RH to establish if there are significant differences in the direction of the slope of the cross-section. The uniformity of temperature and RH do not present stratifications derived from wind currents that can affect the effective production of these crops.

This study proposed an indicator to calculate the regional thermal potential from the local temperature. A probabilistic function curve generalized as a complementary error function (erfc) was used to assume that the temperature curve follows the normal distribution and considered only the portion of the curve where the appropriate temperatures for the crop are located (wi). The Greenhouse Thermal Effectiveness (GTE) index was calculated using (a) the data of measured temperature (outside) and simulated values from inside of the greenhouse, and (b) the normal temperature data from five meteorological stations. Estimations of GTE using average daily temperature (°C) throughout the year indicate that, with an annual mean temperature of around 14 °C, the GTE is 2798 degree units and inside the greenhouse its value goes up to 5800. May is when the highest temperatures occur and when the highest amount of GTE units can be accumulated. The range of temperatures in the analyzed stations were from 13 to 21 °C and the GTE calculated per year was from 2000 to 7000. The perspective will be to calculate if this energy will be enough to grow tomatoes (or other crops) without extra energy for heating or cooling. If more energy may be needed, estimating how much would be the next step.

Vapor pressure deficit (VPD) can be used as an indicator to schedule greenhouse irrigation. VPD can be estimated as a function of relative humidity (RH) and temperature (T). The objective of this work was to analyze spatial variation in VPD as an indicator of water stress influenced by concentration of water vapor and intensity of near infrared (NIR). The study was carried out in an empty three-span sawtooth greenhouse with natural ventilation under the local climate in Montecillo, Mexico; these findings established a base value to analyze greenhouse field conditions prior to the influence from a crop. The experimental phase consisted of recording data (3 February 2019–24 February 2019) on temperature, humidity, solar radiation, and wind speed, which were used for developing a model in computational fluid dynamics (CFD). Then, this model was used to estimate VPD, considering changes in mass fraction of water vapor and the intensity of NIR. Scenarios with 50, 70, and 90% external RH were evaluated. It was found that without a crop, temperature was not affected by the variation in the mass fraction of water vapor and the intensity of NIR in the simulated scenarios, each of which generated a thermal gradient within the range of 4 °C. When considering the scenario of 90% external RH, we found the best VPD range along the greenhouse (2–3 kPa) that would be a favorable field condition for crops. Differences between VPD with and without a crop can be used to estimate the water quantity needs for crop growth based on the climate variables examined in this study, where higher VPD values require more water for irrigation.