Energy Efficiency in Greenhouse Evaporative Cooling Techniques: Cooling Boxes versus Cellulose Pads

Evaporative cooling systems using a combination of evaporative pads and extractor fans require greenhouses to be hermetic. The greatest concentration of greenhouses in the world is located in southeast Spain, but these tend not to be hermetic structures and consequently can only rely on fogging systems as evaporative cooling techniques. Evaporative cooling boxes provide an alternative to such systems. Using a low-speed wind tunnel, the present work has compared the performance of this system with four pads of differing geometry and thickness manufactured by two different companies. The results obtained show that the plastic packing in the cooling unit produces a pressure drop of 11.05 Pa at 2 m·s−1, which is between 51.27% and 94.87% lower than that produced by the cellulose pads. This pressure drop was not influenced by increases in the water flow. The evaporative cooling boxes presented greater saturation efficiency at the same flow, namely 82.63%, as opposed to an average figure of 65% for the cellulose pads; and also had a lower specific consumption of water, at around 3.05 L·h−1·m−2·°C−1. Consequently, we conclude that evaporative cooling boxes are a good option for cooling non-hermetic greenhouses such as those most frequently used in the Mediterranean basin

Design and Testing of a Structural Monitoring System in an Almería-Type Tensioned Structure Greenhouse

Greenhouse cultivation has gained a special importance in recent years and become the basis of the economy in south-eastern Spain. The structures used are light and, due to weather events, often collapse completely or partially, which has generated interest in the study of these unique buildings. This study presents a load and displacement monitoring system that was designed, and full scale tested, in an Almería-type greenhouse with a tensioned wire structure. The loads and displacements measured under real load conditions were recorded for multiple time periods. The traction force on the roof cables decreased up to 22% for a temperature increase of 30 °C, and the compression force decreased up to 16.1% on the columns or pillars for a temperature and wind speed increase of 25.8 °C and 1.9 m/s respectively. The results show that the structure is susceptible to daily temperature changes and, to a lesser extent, wind throughout the test. The monitoring system, which uses load cells to measure loads and machine vision techniques to measure displacements, is appropriate for use in different types of greenhouses

Thermography and Sonic Anemometry to Analyze Air Heaters in Mediterranean Greenhouses

The present work has developed a methodology based on thermography and sonic anemometry for studying the microclimate in Mediterranean greenhouses equipped with air heaters and polyethylene distribution ducts to distribute the warm air. Sonic anemometry allows us to identify the airflow pattern generated by the heaters and to analyze the temperature distribution inside the greenhouse, while thermography provides accurate crop temperature data. Air distribution by means of perforated polyethylene ducts at ground level, widely used in Mediterranean-type greenhouses, can generate heterogeneous temperature distributions inside the greenhouse when the system is not correctly designed. The system analyzed in this work used a polyethylene duct with a row of hot air outlet holes (all of equal diameter) that expel warm air toward the ground to avoid plant damage. We have observed that this design (the most widely used in Almería’s greenhouses) produces stagnation of hot air in the highest part of the structure, reducing the heating of the crop zone. Using 88 kW heating power (146.7 W∙m−2) the temperature inside the greenhouse is maintained 7.2 to 11.2 °C above the outside temperature. The crop temperature (17.6 to 19.9 °C) was maintained above the minimum recommended value of 10 °C

Application of Semi-Empirical Ventilation Models in A Mediterranean Greenhouse with Opposing Thermal and Wind Effects. Use of Non-Constant Cd (Pressure Drop Coefficient Through the Vents) and Cw (Wind Effect Coefficient)

The present work analyses the natural ventilation of a multi-span greenhouse with one roof vent and two side vents by means of sonic anemometry. Opening the roof vent to windward, one side vent to leeward, and the other side vents to windward (this last vent obstructed by another greenhouse), causes opposing thermal GT (m3 s−1) and wind effects Gw (m3 s−1), as outside air entering the greenhouse through the roof vent circulates downward, contrary to natural convection due to the thermal effect. In our case, the ventilation rate RM (h−1) in a naturally ventilated greenhouse fits a second order polynomial with wind velocity uo (RM = 0.37 uo2 + 0.03 uo + 0.75; R2 = 0.99). The opposing wind and thermal effects mean that ventilation models based on Bernoulli’s equation must be modified in order to add or subtract their effects accordingly—Model 1, in which the flow is driven by the sum of two independent pressure fields GM1=√(∣∣G2T±G2w∣∣) , or Model 2, in which the flow is driven by the sum of two independent fluxes GM2=|GT±Gw| . A linear relationship has been obtained, which allows us to estimate the discharge coefficient of the side vents (CdVS) and roof vent (CdWR) as a function of uo [CdVS = 0.028 uo + 0.028 (R2 = 0.92); CdWR = 0.036 uo + 0.040 (R2 = 0.96)]. The wind effect coefficient Cw was determined by applying models M1 and M2 proved not to remain constant for the different experiments, but varied according to the ratio uo/∆Tio0.5 or δ [CwM1 = exp(−2.693 + 1.160/δ) (R2 = 0.94); CwM2 = exp(−2.128 + 1.264/δ) (R2 = 0.98)]

Dispositivo para medir el comportamiento de cimentaciones ante un esfuerzo de tracción o de comprensión

Número de publicación: ES2221783 A1 (01.01.2005) También publicado como: ES2221783 B1 (16.12.2006) Número de Solicitud: Consulta de Expedientes OEPM (C.E.O.)P200202403 (18.10.2002)Un dispositivo para medir el comportamiento de cimentaciones ante un esfuerzo de tracción o de compresión, que comprende: un bastidor (1, 2); un cilindro hidráulico (3) montado en el bastidor de modo que pueda pivotar alrededor de al menos un eje; medios de acoplamiento mecánico del cilindro hidráulico (3) a la cimentación; medios de medir el esfuerzo ejercido por el cilindro hidráulico sobre la cimentación; medios de medir el desplazamiento de la cimentación bajo el esfuerzo; y medios de alimentación hidráulica del cilindro hidráulico.Universidad de Almería. Universidad de Sevill

The Role of Technology in Greenhouse Agriculture: Towards a Sustainable Intensification in Campo de Dalías (Almería, Spain)

Campo de Dalías, located in southeastern Spain, is the greatest European exponent of greenhouse agriculture. The development of this type of agriculture has led to an exponential economic development of one of the poorest areas of Spain, in a short period of time. Simultaneously, it has brought about a serious alteration of natural resources. This article will study the temporal evolution of changes in land use, and the exploitation of groundwater. Likewise, this study will delve into the technological development in greenhouses (irrigation techniques, new water resources, greenhouse structures or improvement in cultivation techniques) seeking a sustainable intensification of agriculture under plastic. This sustainable intensification also implies the conservation of existing natural areas

Effects of surrounding buildings on air patterns and turbulence in two naturally ventilated mediterranean greenhouses using tri‐sonic anemometry

The aim of the present study is to increase the available information concerning the influence of surrounding buildings on air patterns and turbulence characteristics of the ventilation airflow in greenhouses. With a view to evaluating the possible effect of different obstacles close to greenhouse vents, sonic anemometry has been used. At the side opening, the airflow was mainly horizontal, while at the roof vent it was upward or downward. The vicinity of obstacles to the greenhouse side openings reduced the incoming mean flow up to 79% and increased turbulence. Larger ventilation rates were observed for the leeward roof vent, since the wind impacts directly with the windward side opening without obstacles, with a maximum of 31.6 air exchanges per hour. However, when the roof vent is on the windward side, the wind is partially blocked by another similar greenhouse located upwind, as the outside air enters through the roof vent and exits through the two side openings. In this situation, the maximum ventilation rate observed was 14.5 air exchanges per hour. Natural ventilation was more effective in eliminating heat from the part of the greenhouse with a crop when the air entered through the side openings and exited through the roof vent. In this case, the ventilation efficiency for temperature ( T) was greater than 1. The maximum turbulence levels were associated with low air speeds and were observed mainly at the points located close to the side openings influenced by surrounding buildings. The turbulent energy levels of the airflow were higher at the windward openings without obstacles

Determining the emissivity of the leaves of nine horticultural crops by means of infrared thermography

he present study was carried out with the aim of analysing the variability of the emissivity values of nine of the most characteristic horticultural crops of the greenhouse productive system in the Mediterranean region. A thermographic camera was used for both qualitative and quantitative emissivity measurement by evaluating radiation emission from the leaves. The real temperature of the leaves was also measured with a contact probe in order to calculate emissivity. The differences in emissivity between crops for the upper side of leaves are below standard deviation values, the average values are all close to 0.98. For upper side of leaves we obtained the following average values of emissivity: 0.980 ± 0.010 for Lycopersicum esculentum Mill., 0.978 ± 0.008 for Capsicum annuum L., 0.983 ± 0.008 for Cucumis sativus L., 0.985 ± 0.007 for Cucurbita pepo L., 0.973 ± 0.007 for Solanum melongena L., 0.978 ± 0.006 for Cucumis melo L., 0.981 ± 0.009 for Citrullus lanatus Thunb., 0.983 ± 0.006 for Phaseolus vulgaris L. and 0.983 ± 0.005 for Phaseolus coccineus L. Considerable differences have been observed between the emissivity values on the opposite sides of the leaves in some horticultural crops, such as green bean and particularly red bean, with a difference of 0.029 in the average emissivity value. Emissivity values of 0.98 are recommended as a reference for measuring the temperature of horticultural crops other than those studied here whenever there is no other possibility to determine the emissivity

Aproximación a los factores de diseño de las edificaciones destinadas a albergue de ganado caprino lechero de la provincia de Almería

In the present article are shown the results of a work of investigation centered in fixing the main factors that condition the design of the buildings dedicated lo lodgings of mi/k goals livestock in Almería province, and considering the conceptual principles of the planning of industrial facilities. For that, it has been carried out the characterization of the lodgings of mi/k goats ' livestock of the A1mería province in an integral way. by a sampling of the referred explotations. For that, a questionnaire has been made which includes all the parameters 01' variables of design that can characterize this explitatíons, and later on it has been carried out an multivariate statistical analysis that has allowed lOreduce the number of original variables by a Factorial Analysis, and that it has borne lo establish groups of exploitations with homogeneous characteristics together with the realization of a cluster analysis. By means of this methodology five grollps of f arms with homogeneous characteristics have been obtained. andfive descriptive axes that summarize the entirety of the original quantitative variables have been determined, and that they represent the main design fa ctors that condition the construction of the lodgings. Finally a mathematical model has been formulated that allows discriminating against among each one of the homogeneous groups of farms . allowing to classify any new farm of mi/k goats 'Livestock, and thus lo know which are the design parameters that characterize it and those on which is neccessary to act.En el 'presente artículo se presentan los resultados de un trabajo de investigación centrado en fijar los factores principales más significativos que condicionan el diseño de los edificios destinados a alojamientos de caprino de leche de la provincia de A1mería. considerando los principios conceptuales de la planificación de instalaciones industriales. Para conseguir este objetivo se ha realizado la caracterización de los alojamientos de ganado caprino de leche de la provincia de Almería de una forma integral. mediante muestreo de las referidas explotaciones. Para ello. se ha confeccionado un cuestionario que engloba todos los parámetros o variables de diseño que pueden caracterizar dichas explotaciones. y posteriormente se ha realizado un análisis estadístico multivariante, que ha permitido reducir el número de variables originales mediante un análisis factorial. y que ha conllevado a establecer grupos de explotaciones con características homogéneas junto con la realización de un análisis cluster. Mediante dicha metodología se han obtenido cinco grupos de granjas con características homogéneas. y se han determinado cinco e es descriptivos que resumen la totalidad de las variables cuantitativas originales. y que representan los factores de diseño principales que condicionan la construcción de los alojamientos. Finalmente se ha formulado un modelo matemático que permite discriminar entre cada lino de los grupos homogéneos de granjas. permitiendo clasificar cualquier nueva granja de caprino de leche. y conocer, así, cuales son los parámetros de diseño que la caracteriza y sobre los que hay que actuar

Pad-fan systems in mediterranean greenhouses: determining optimal setup by sonic anemometry

The present work studies the microclimate and airflow inside a greenhouse equipped with a pad-fan cooling system, analyzing several operational alternatives: three ventilation flow rates (18.1 m3 s-1, 20.2 to 23.5 m3 s-1, and 26.3 m3 s-1), and combining the medium flow rate with two interior fans or with a shading screen. The different airflow levels were obtained using a variable frequency drive (VFD) system to control ventilation fans (working at frequencies of 30, 40, and 50 Hz). The use of interior fans increased the velocity and intensity of the turbulent airflow, thus enhancing the mixing of air inside the greenhouse. The lowest fan frequency (30 Hz) reduced the system’s cooling capacity, increasing both the horizontal and vertical temperature gradients compared to the results obtained for the frequencies of 40 and 50 Hz. The system’s cooling capacity increased using the high-level ventilation flow rate or combining the pad-fan with a shading screen. In both situations, we obtained maximum temperature reductions of 3°C compared to the outside air. Different operational alternatives tested on sunny days show greater temperature reductions (4.4°C to 8.1°C) with respect to a similar naturally ventilated greenhouse (the most widespread type in the Mediterranean region). However, on cloudy days, when the outside relative humidity is high, the cooling capacity is more limited. Lack of system maintenance may lead to a considerable loss of efficiency (η), as this value fell from η = 0.82 when the system was installed to η = 0.65 one year later, at the time of this study. Estimated water consumption of the pad-fan system increases with the capacity to increase the water vapor content of the incoming air and with the volumetric flow rate