Assessment of evaporative cooling efficiency in greenhouses equiped with wetted porous plates

Abstract

The main objective of this study was to experimentally validate a mechanistic model for predicting the cooling efficiency (η) of wetted porous plates built with expanded clay. The expanded clay material was physically characterized by specific mass, surface area, and volume. The model was validated with dry bulb temperature (Tdb, °C) and air relative humidity (RH, %) data, which were continuously monitored in two different points, upstream and downstream the direction of the air passing through the porous plate. Data collection was carried out consecutively for a period of 10 days, between 11:00 a.m. and 4:00 p.m. Average values for η, simulated and observed, were 74.8 ± 7.4% and 68.3 ± 8.3%, respectively. Based on the developed model, it was observed that η was higher than 40% for Tdb > 30 °C and constant RH at 45%. The simulation for predictions indicates that the increase in the air temperature greater than 20 °C may affect negatively the production in greenhouses from states located in tropical and subtropical countries as Minas Gerais, Brazil, if some design criteria in the evaporative cooling system are not revised.Keywords: Greenhouse; mathematical modeling; simulation; heat and mass transfer.Evaluación de la eficiencia de equipos de enfriamiento evaporativo usando placas porosas en invernaderos Resumen El objetivo principal de este estudio fue validar experimentalmente un modelo mecánistico para predecir la eficacia de enfriamiento (η) de placas porosas construidas con arcilla expandida. El material de arcilla expandida fue físicamente caracterizado encontrando su masa específica, área superficial y volumen. El modelo fue validado con datos de temperatura de bulbo seco (Tdb, ° C) y humedad relativa del aire (humedad relativa,%) que fueron continuamente monitoreados en dos puntos diferentes, en contra y a favor de la dirección del aire que pasa a través de la placa porosa. La recolección de datos se llevó a cabo de forma consecutiva durante un período de 10 días entre las 11:00 y 4:00 p.m. Los valores medios de η, simulados y observados, fueron 74,8 ± 7,4% y 68,3 ± 8,3%, respectivamente. Basado en el modelo desarrollado, se observó que η fue mayor del 40% para Tdb> 30 ° C y HR constante en 45%. La simulación indicó que el aumento de la temperatura del aire puede afectar negativamente la producción en invernaderos en Estados como Minas Gerais, Brazil, si no se revisan algunos criterios de diseño en el sistema de enfriamiento por evaporación.Palabras clave: Invernadero; modelo matemático; simulación; transferencia de calor y masa.

Effect of Utilization of Different Materials and Thicknesses Evaporative Cooling Pad On Cooling Efficiency in Greenhouses in Hot-Arid Regions

“…Likewise, the air velocity through the pads was seen to change at various points. According to Flávio et al (2017) and Al-Amri (2000), air velocity impacts the path that air takes and the amount of time it spends in touch with the moisture source. In evaporative cooling pads, the latent heat absorbed by the water as it changes from liquid to vapor is taken from both the air passing through the media and the water left in the media.…”

Evaluation of the Coolnet Placement Distance to Direct Evaporative Cooling to Increase Potato Seed Production in Aeroponic Systems with Root Zone Cooling in the Lowlands

“…High air temperatures of more than 25-30 °C tend to increase stem length and branching but reduce leaf size and leaf area. An increase in air temperature of greater than 20 °C can hurt crop production in greenhouses for countries located in tropical and subtropical countries (Alves-Damasceno et al, 2017).…”

Comfort and energy consumption in a hybrid tunnel-type broiler barn in different bioclimatic zones of Brazil

“…However, this effect is null when the temperature of the dry bulb is equal to the body temperature of the bird, and there is a need to use evaporative cooling methods. The use of these systems allows the reduction of the temperature of the dry bulb up to 11°C in some regions, particularly in Brazil, the average of this reduction is 6°C [12][13][14]. The evaporative cooling systems have been used in thermal environmental control applications to improve human, plant and animals comfort conditions [15].…”