Combination of Forced Ventilation and Fogging Systems for Cooling Greenhouses

Arbel, A.; Barak, M.; Shklyar, A.

doi:10.1016/s1537-5110(02)00216-7

Cited by 96 publications

(49 citation statements)

References 3 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…It is worth mentioning that no significant differences were found between the strategy of 12 s every 4min and 8 s every 4min; this result suggests that it is better to increase the cycle frequency than the fogging time in each cycle to increment flux. Studies varying the fogging rate have been conducted in the past (Arbel et al, 2003): the wet bulb temperature did not change significantly with an increase of the fogging rate, as this temperature mainly depends on the heat supply and the ventilation air supply.…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Cooling strategies for greenhouses in summer: Control of fogging by pulse width modulation

Perdigones

Garcı́a

Romero

et al. 2008

Biosystems Engineering

View full text Add to dashboard Cite

The possibilities for improving the control of greenhouse fogging systems, were studied by comparing several combinations of ventilation cooling techniques, shade screening and low-pressure fogging. The study was divided into three parts: experiments, modelling and simulations.In the first part of the paper, ten combinations of five cooling techniques were tested during the summers of 2002 and 2003 in a 132 m 2 greenhouse with a steel structure and a single-layer methacrylate cover located in Madrid, Spain. An analysis of variance of the climatic parameters was carried out to determine which combinations produced significant differences in inside temperature or relative humidity. Comparing the values for the inside to outside temperature difference, the combination of a shade screen and above-screen fogging achieved a difference in temperature almost the same as that for under-screen fogging, but the relative humidity was significantly lower.In the second part of the study a dynamic model was developed (2002) and validated (2003). The mean absolute error obtained for inside temperature was similar in the fit and the validation and it was less than 1.5 °C in both cases.The model was used to simulate the inside air temperature for a fog system working without shading, and above and under a shade screen. Control algorithms were developed for reducing system water consumption. In the three cases a simple on/off control with a fixed fogging cycle was compared with a pulse width modulation (PWM) strategy, in which the duration of the fogging pulse was increased as a function of inside temperature. The strategies with PWM applied to the fog system were able to reduce water consumption by 8-15% with respect to the strategies with a fixed fogging cycle.

show abstract

Section: Resultsmentioning

confidence: 99%

“…Other studies analysed a range of variables in a combination of fogging and forced ventilation with fans on both sides of the greenhouse (e.g. Arbel et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

Cooling strategies for greenhouses in summer: Control of fogging by pulse width modulation

Perdigones

Garcı́a

Romero

et al. 2008

Biosystems Engineering

View full text Add to dashboard Cite

show abstract

“…Sabeh humidity; and waste of water -to prevent blockage of wet pad water bleed is necessary," Arabel et al 3 . Sprinkling uses large surfaces (blankets) for faster evaporation installed overhead in greenhouses and wetted by mist nozzles.…”

Section: Literature Reviewmentioning

confidence: 99%

Cropping in Semi-arid North-west India in Greenhouse with Ground Coupling Shading and Natural Ventilation for Environmental Control

Sharan¹,

Madhavan²

2010

IJSLE

View full text Add to dashboard Cite

-Research is ongoing to develop greenhouse technologies which economically control water and energy in order to improve farming in water-scarce, hot, semi-arid regions of north-west India. A greenhouse under investigation was coupled to earth-tubeheat-exchangers (ETHE) and also had provisions for shading, natural ventilation and mist nozzles. Tomatoes were grown in the greenhouse. In the cooler months, a regime of natural ventilation and top shading kept the greenhouse temperature close to ambient temperature. Mist was not used. Evaporation and later transpiration may have aided cooling. This cooling effort became less effective in warmer periods as the cooling load increased and dense foliage appeared to hinder ventilation. Forced ventilation via ETHE and top shading was then implemented. Inside temperature occasionally rose 2-3 °C above the ambient temperature. Cropping could be done through the spring and early summer. Heating was affectively achieved with ETHE in cold nights of December and January keeping the inside temperatures well above 12°C. Yields were 68 t/ha -nearly twice the open field production, while the water used (266 mm) was nearly half of the open-fields usage. This appears to be a promising new way to improve livelihoods from farming.

show abstract

“…The most desirable distribution of relative humidity was derived from the wind speed of 0.5 m·s -1 (Case 6). Arbel et al 4 reported that the entry velocity of the air into the greenhouse should not exceed about 0.5 m·s -1 in order to obtain uniform environmental conditions in the greenhouse.…”

Section: Simulation For a Multi-span Glasshousementioning

confidence: 99%

CFD Modeling to Improve the Design of a Fog System for Cooling Greenhouses

Kim

Giacomelii

Yoon

et al. 2007

JARQ

View full text Add to dashboard Cite

Evaporative cooling systems have been developed to provide the desired conditions for plant growth in the greenhouses during hot seasons. The fog system performs better than the pad-and-fan system with respect to uniform distribution of temperature and relative humidity in the greenhouse. The appropriate combination of air and water supply depends on the environmental conditions, such as solar radiation, ambient temperature and relative humidity, and is essential for maintaining the desired conditions in the greenhouse 3 . The fog-cooling system supplies water droplets in diameters of 2-60 µm so as to enhance the heat and mass exchange between the water and the air 5 . Ventilation is an important factor since the water spray evaporates along with the movement by airflow. Most studies on fog-cooling systems used forced ventilation systems 3,4 . Natural ventilation is normally achieved by air exchanges through multiple controlled openings. Wind is generally the primary driving force in natural ventilation systems. System design and subsequent field-testing are very difficult due to the variations of environmental factors, wind velocity and direction, solar radiation, outside temperature, etc. AbstractA CFD model was developed to simulate the air temperature and relative humidity distribution in greenhouses adopting fog-cooling systems using FLUENT. The developed model was validated using the data from a fog-cooling experiment in a single-span greenhouse without plants. The measured and simulated air temperatures varied from 0.1 to 1.4ºC and the differences of relative humidity varied 0.3-6.0%. The validated model was then used to evaluate the design of a fog-cooling system in a multi-span glasshouse. The optimal system design was determined in terms of the cooling efficiency and the special uniformity of air temperature and relative humidity. The simulations demonstrated that the best performance of the cooling system occurred when the fog nozzles were located at the height of 2.3 m above the floor and at a distance of 1.9 m from the sidewalls with uniform row-to-row spacing of 3.7 m. The most effective location of the nozzles was within the air entry from the sidewall ventilator inlets of the greenhouse. However, it was important not to wet the sidewalls with the fog. This study suggested that the CFD model developed could be a useful tool to design and evaluate the fog-cooling systems in greenhouses with various configurations. Discipline: Agricultural facilitiesAdditional key words: CFD, fog-cooling system, glasshouse, natural ventilation, wind speed JARQ 41 (4), 283 -290 (2007) http://www.jircas.affrc.go.jp This research was carried out under the US-Japan collaborative project on analysis and control of greenhouse environment for efficient crop production under semiarid climate.

show abstract

Combination of Forced Ventilation and Fogging Systems for Cooling Greenhouses

Cited by 96 publications

References 3 publications

Cooling strategies for greenhouses in summer: Control of fogging by pulse width modulation

Cooling strategies for greenhouses in summer: Control of fogging by pulse width modulation

Cropping in Semi-arid North-west India in Greenhouse with Ground Coupling Shading and Natural Ventilation for Environmental Control

CFD Modeling to Improve the Design of a Fog System for Cooling Greenhouses

Contact Info

Product

Resources

About