Measurement and simulation of climate inside Almer�a-type greenhouses using computational fluid dynamics

Molina-Aiz, F.D.; Valera, D.L.; Martínez, Antonio Jesús Álvarez

doi:10.1016/j.agrformet.2004.03.009

Cited by 105 publications

(42 citation statements)

References 27 publications

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“…Corp., Bourne, MA, USA) placed at heights of 1 and 2 m. These fixed devices allowed temperature measurement in a range of -40°C to 70°C with an accuracy of ± 0.18°C. They were all programmed to register data at 0.5 Hz and were protected against direct solar radiation with passive solar radiation open boxes, allowing natural air movement around the sensors (Molina-Aiz et al, 2004). From the data of inside humidity we can obtain the specific humidity q and correct the sonic anemometer temperature T s using the following expression :…”

Section: Instrumentationmentioning

confidence: 99%

Microclimate evaluation of a new design of insect-proof screens in a Mediterranean greenhouse

López-Martínez

Valera

Molina-Aiz

et al. 2014

Span. j. agric. res.

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This work studies natural ventilation in a Mediterranean greenhouse, comparing a new experimental screen of 13×30 threads cm-2 (porosity 39.0%) with a commercial control screen of 10×20 threads cm-2 (porosity 33.5%). In addition, both screens were tested in a wind tunnel to determine the discharge coefficients Cd of the greenhouse side and roof vents, which proved to be 0.16 for the commercial control screen and 0.18 for the experimental screen at both vents. These values represent a theoretical increase of 11% (Cd,φ-10×20 /Cd,φ-13×30 = 0.89) in the natural ventilation capacity of the greenhouse when the experimental screen is used. The greenhouse was divided into two separate sections allowing us to analyze natural ventilation in both sectors simultaneously. Air velocity was measured in the lateral and roof vents with two 3D and six 2D sonic anemometers. Using the commercial control screen there was an average reduction of 16% in ventilation rate, and an average increase of 0.5ºC in the average indoor air temperature, compared to the experimental screen. In addition, the ventilation efficiency ηT was higher with the experimental screen (mean value of 0.9) than with the control (mean value 0.6). We have designed an experimental insect-proof screen (13×30 threads cm-2) with smaller thread diameter, higher thread density, smaller pore size and higher porosity than are used in most commercial meshes. All of these factors promote natural ventilation and improve the greenhouse microclimate.

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Section: Instrumentationmentioning

confidence: 99%

Microclimate evaluation of a new design of insect-proof screens in a Mediterranean greenhouse

López-Martínez

Valera

Molina-Aiz

et al. 2014

Span. j. agric. res.

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“…However, it requires extremely hermetic greenhouse structures to ensure that all incoming air passes through the evaporative pads along part or the whole of the side wall, with powerful extractor fans being placed along the opposite wall to provide the required suction ( Figure 1). The Almería-type greenhouse [7], which accounts for 94.7% of the greenhouse area in southeast Spain, is not hermetic, and as a result growers have opted for the installation of the fog system, which is better suited to such structures [8]. According to López et al [6], in a greenhouse equipped with evaporative pads a difference in temperature of up to 11.6 °C was recorded with respect to a naturally ventilated greenhouse, whereas using the fog system this difference was 10.4 °C.…”

Section: Introductionmentioning

confidence: 99%

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

2014

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Abstract: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, 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 . 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.

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“…Portanto, nem mesmo a instabilidade atmosférica, oriunda da aproximação das frentes frias durante o período experimental, foi capaz de intensificar o movimento do ar no interior da casa de vegetação. Resultados semelhantes, relacionados a baixos valores de velocidade do ar em ambientes protegidos, também foram relatados por Wang et al (1999), Boulard et al (2004), Molina-Aiz et al (2004) e Bartzanas et al (2005).…”

Section: Resultsunclassified

“…ou valores extremamente baixos, como os observados em ambiente protegido (Wang et al, 1999;Boulard et al, 2004;Molina-Aiz et al, 2004;Bartzanas et al, 2005). Com a utilização do fator de desacoplamento, é importante observar que a velocidade do ar não é mais necessária para a estimativa do termo r a .…”

Section: Penman-monteith Modificado Para Ambientes Protegidos (Pmap)unclassified

Coeficiente de cultura da alface hidropônica baseado no conceito de graus-dia

et al. 2010

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Degree-day-based crop coefficient for hydroponic lettuceThe main objective in this work was to propose the adoption of a thermal crop coefficient by using accumulated degree-days after transplanting to estimate lettuce daily evapotranspiration (ET c ) for the cultivars Grand Rapids, Regina and Great Lakes in a NFT hydroponic system under protected environment. Subsequently, the adjusted model to the observed values of K c was used for estimating ET c during the growing period after transplanting with the following methods: Penman-Monteith parameterized by FAO in 1998 (PMF); Penman-Monteith modified for aerodynamic characteristics in protected environment (PMAP); simplified Penman-Monteith (PMAPS); Priestley-Taylor (PT); solar radiation (RS); and simplified solar radiation (RSS). It was verified that the sigmoid model with four parameters fitted well to observed values of K c ,giving adjusted coefficients of determination of 0,9874, 0,9784 and 0,9767 for cultivars Grand Rapids, Regina and Great Lakes, respectively. As far as daily ET c estimates are concerned, the methods PMF, PMAP and RS presented better statistical performance as compared to the methods PMAPS, PT and RSS, regardless of the evaluated cultivar. However, the method PMF systematically underestimated ET c in the lettuce initial growth period. Coeficiente de cultura da alface hidropônica baseado no conceito de graus-dia O objetivo principal deste trabalho foi propor a adoção de um coeficiente de cultura térmico, com a aplicação do conceito de graus-dia acumulados após o transplantio, para estimativa da evapotranspiração diária (ET c ) dos cultivares de alface Grand Rapids, Regina e Great Lakes em sistema hidropônico do tipo NFT ("nutrient film technique"), em ambiente protegido. Posteriormente, o modelo matemático ajustado aos valores observados de K c (coeficiente de cultura) foi utilizado para a estimativa de ET c no período pós-transplantio por meio dos métodos: Penman-Monteith parametrizado pela FAO, em 1998 (PMF); Penman-Monteith modificado para condições aerodinâmicas, características de ambientes protegidos (PMAP); Penman-Monteith para ambiente protegido simplificado (PMAPS); Priestley-Taylor (PT); Radiação solar (RS); e Radiação solar simplificado (RSS). Verificou-se que o modelo sigmoidal com quatro parâmetros ajustou-se bem aos valores observados de K c , proporcionando coeficientes de determinação ajustados de 0,99, 0,98 e 0,98 para os cultivares Grand Rapids, Regina e Great Lakes, respectivamente. No que se refere às estimativas diárias de ET c , os métodos PMF, PMAP e RS apresentaram melhor desempenho estatístico em relação aos métodos PMAPS, PT e RSS, independentemente do cultivar avaliado. No entanto, o método PMF subestimou sistematicamente a ET c no período inicial de crescimento da alface.Palavras chave: Cultivo protegido, tempo térmico, técnica de circulação laminar de nutrientes.

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Measurement and simulation of climate inside Almer�a-type greenhouses using computational fluid dynamics

Cited by 105 publications

References 27 publications

Microclimate evaluation of a new design of insect-proof screens in a Mediterranean greenhouse

Microclimate evaluation of a new design of insect-proof screens in a Mediterranean greenhouse

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

Coeficiente de cultura da alface hidropônica baseado no conceito de graus-dia

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