Thesis "EVALUACIÓN TÉCNICA Y ECONÓMICA DE UN SISTEMA EÓLICO DE ENERGIZACIÓN PARA INVERNADEROS AGRÍCOLAS UBICADOS EN CONDICIONES EXTREMAS EN LA XII REGIÓN DE CHILE"
Date
2017
Authors
ANGULO ESPINOZA, JUAN MANUEL
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Abstract
Este trabajo tuvo como fin evaluar y analizar las necesidades energéticas asociadas a la calefacción de un invernadero con un cultivo de tomate en su interior, ubicado en la Región de Magallanes. Con los resultados obtenidos se ha generado información que resulta útil en la búsqueda de medidas de eficiencia energética para el diseño y manejo de estas estructuras en la zona, permitiendo el estudio de distintas alternativas de calefacción.El invernadero considerado es de tipo simétrico y unimodular, con un ángulo de inclinación del techo de 26,5°, cubierta de policarbonato alveolar de 4 mm, estructura de Metalcon, y cuyas dimensiones son 40 m de largo, 6 m de ancho y 3,9 m de alto a nivel de cumbrera. El cálculo de la demanda energética en calefacción, se obtuvo resolviendo un modelo de balance de energía estacionario, para cada hora de un día característico de cada mes del año en la ciudad de Punta Arenas. Las condiciones climatológicas (variables de entrada para resolver el balance), consideradas constantes para cada hora, fueron: radiación solar global horizontal, temperatura y humedad relativa del aire, nubosidad y velocidad del viento. El cultivo interior se considera que tiene un desarrollo foliar máximo durante todo el año.En primer lugar, la demanda energética calculada bajo las condiciones descritas, indican una demanda de 7813 MJ/m2 al año, que para la superficie total del invernadero fue de 1.875 GJ. Las pérdidas por convección entre el aire exterior y la cubierta, son un 21,6% de las pérdidas totales, las pérdidas por radiación infrarroja entre la cubierta y el cielo un 12,4%, por evapotranspiración un 7,5%, por conducción a través del suelo un 24,0% y por ventilación o infiltración de aire un 34,6%.Posteriormente, se hicieron comparaciones para la demanda energética bajo ciertos cambios en las condiciones iniciales, estudiando así la variación obtenida. Primero, se estimó la energía necesaria para calefaccionar el suelo a las temperaturas recomendadas: 14 C° de noche y 16 C° de día, lo que supone un aumento de 6,5% respecto a la demanda total obtenida bajo condiciones estándar. Otra comparación, fue suponer noches despejadas en todos los días del año, lo que incrementa en un 3,2% el valor anual de la demanda inicial, debido a las pérdidas por radiación infrarroja. La tercera comparación se hizo modificando la geometría del invernadero por una de tipo asimétrica, que maximiza la transmisividad a la radiación solar, disminuyendo la demanda anual en un 3,2%, valor que puede alcanzar incluso un 8,4% durante enero, debido a la mayor radiación solar en verano.La cuarta comparación se hizo calculando la tasa de renovaciones de aire para una configuración determinada de ventanas cenitales y laterales. Esto incrementó la demanda en un 26,6% y las pérdidas por ventilación fueron un 45,8% del total, lo que indica que este es un punto crítico en las pérdidas de energía. Por último, se estimó que una mejora de la hermeticidad del invernadero puede disminuir la demanda en un 7,0%, lo que significa una mejora relevante. Con estos resultados se determina que la ventilación y las pérdidas por infiltración tienen una influencia considerable en las pérdidas de calor, por lo que se sugiere estudiar métodos de control en las renovaciones de aire en los invernaderos de la XII Región, para hacerla de la manera más eficiente posible.Por último, se calculó la potencia necesaria en calefacción al combinar las condiciones climáticas de temperatura, viento y nubosidad, más desfavorables o extremas. La máxima potencia requerida fue de 352,5 W/m2 (84,61 kW para la superficie total del invernadero). Al evaluar el invernadero bajo las condiciones más altas de temperatura, se determina que la ventilación natural es suficiente para no superar la máxima biológica del cultivo.
The present work was aimed to analyze and evaluate the different energetic demand associated to the heating of a greenhouse with a tomato crop in it, located in the Magallanes region. The obtained results provides useful information for the search of energetic efficiency measures for the design and handling of this type of structures in the area, allowing the study of different heating alternatives.The considered greenhouse is an unimodular and symmetric type, with an inclination roof angle of 26,5°, a 4mm alveolar polycarbonate cover, a Metalcon structure with overall dimensions of 40m large, 6m wide, and 3,9m high. The energy demand calculates in heating, was obtained solving a stationary energy balance model for each hour of a specific day per month in the city of Punta Arenas. The climate conditions (input variables to solve the balance model) considerated as constants for each hour, were: horizontal global solar radiation, temperature and relative air humidity, cloudiness and wind speed. The Indoor cultivation is considered to have a maximum leaf development throughout the year.First, the energy demand was calculated under the above described conditions, denominated “standard conditions”, obtaining a demand of 7813 MJ/m2 per year, which for the total surface of the greenhouse was 1.875 GJ. Convective losses between the external air and the cover were 21,6% of the total losses, the losses by infrared radiation between the cover and the ceiling were 12,4%, by evapotranspiration were 7,5%, by ground conduction were 24,0% and by ventilation or air infiltration were 34,6%.Second, comparisons were made for energy demand under certain changes in the initial conditions in order to study the variation obtained. First, estimating the energy needed to heat the soil to the recommended temperatures: 14 C ° at night and 16 C ° during the day, which means an increase of 6,5% regarding the total demand obtained under the standard conditions. Another comparison was to assume clear nights every night of the year, which increases the annual value of the energy demand by 3,2%, due to the losses by infrared radiation. Third, another comparison was made by the greenhouse geometry modification, from a symmetric type to an asymmetric one, which maximizes the transmissivity to the solar radiation, decreasing the annual energy demand by 3,2%, value that could go as high as 8,4% during January due to a highest solar radiation in summer.The fourth comparison was made by calculating the rate of air renewals for a given configuration of zenith and side windows. This increased energy demand by 26,6% and ventilation losses were 45,8% of the total, indicating that this is a critical point regarding energy losses. Then, it was estimated that an improvement of the greenhouse air tightness can reduce the energy demand by 7,0%, which means a relevant improvement. With these results, it is determined that ventilation and infiltration losses have a considerable influence on heat losses, so it is suggested to study control methods in air renewals in the greenhouses of Region XII, in order to the process more efficiently.Finally, the required power in heating was calculated by combining the most unfavorable or extreme climatic conditions of temperature, wind and cloudiness. The maximum required power was 352,5 W/ m2 (84,6 kW for the total greenhouse area). When evaluating the greenhouse under the highest temperature conditions, it is determined that the natural ventilation is sufficient to not exceed the biological maximum of the crop.
The present work was aimed to analyze and evaluate the different energetic demand associated to the heating of a greenhouse with a tomato crop in it, located in the Magallanes region. The obtained results provides useful information for the search of energetic efficiency measures for the design and handling of this type of structures in the area, allowing the study of different heating alternatives.The considered greenhouse is an unimodular and symmetric type, with an inclination roof angle of 26,5°, a 4mm alveolar polycarbonate cover, a Metalcon structure with overall dimensions of 40m large, 6m wide, and 3,9m high. The energy demand calculates in heating, was obtained solving a stationary energy balance model for each hour of a specific day per month in the city of Punta Arenas. The climate conditions (input variables to solve the balance model) considerated as constants for each hour, were: horizontal global solar radiation, temperature and relative air humidity, cloudiness and wind speed. The Indoor cultivation is considered to have a maximum leaf development throughout the year.First, the energy demand was calculated under the above described conditions, denominated “standard conditions”, obtaining a demand of 7813 MJ/m2 per year, which for the total surface of the greenhouse was 1.875 GJ. Convective losses between the external air and the cover were 21,6% of the total losses, the losses by infrared radiation between the cover and the ceiling were 12,4%, by evapotranspiration were 7,5%, by ground conduction were 24,0% and by ventilation or air infiltration were 34,6%.Second, comparisons were made for energy demand under certain changes in the initial conditions in order to study the variation obtained. First, estimating the energy needed to heat the soil to the recommended temperatures: 14 C ° at night and 16 C ° during the day, which means an increase of 6,5% regarding the total demand obtained under the standard conditions. Another comparison was to assume clear nights every night of the year, which increases the annual value of the energy demand by 3,2%, due to the losses by infrared radiation. Third, another comparison was made by the greenhouse geometry modification, from a symmetric type to an asymmetric one, which maximizes the transmissivity to the solar radiation, decreasing the annual energy demand by 3,2%, value that could go as high as 8,4% during January due to a highest solar radiation in summer.The fourth comparison was made by calculating the rate of air renewals for a given configuration of zenith and side windows. This increased energy demand by 26,6% and ventilation losses were 45,8% of the total, indicating that this is a critical point regarding energy losses. Then, it was estimated that an improvement of the greenhouse air tightness can reduce the energy demand by 7,0%, which means a relevant improvement. With these results, it is determined that ventilation and infiltration losses have a considerable influence on heat losses, so it is suggested to study control methods in air renewals in the greenhouses of Region XII, in order to the process more efficiently.Finally, the required power in heating was calculated by combining the most unfavorable or extreme climatic conditions of temperature, wind and cloudiness. The maximum required power was 352,5 W/ m2 (84,6 kW for the total greenhouse area). When evaluating the greenhouse under the highest temperature conditions, it is determined that the natural ventilation is sufficient to not exceed the biological maximum of the crop.
Description
Catalogado desde la version PDF de la tesis.
Keywords
CALCULO DE POTENCIA , DEMANDA ENERGETICA MEDICIONES , ENERGIA EOLICA , INVERNADEROS CALEFACCION , REGION DE MAGALLANES CHILE