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Researchers in Niger have proposed using photovoltaics to power evaporative cooling greenhouses. The proposed experimental solution uses locally manufactured panels and can reportedly compete with commercial counterparts.
A group of researchers from Abdou Moumouni University in Niger has proposed using photovoltaics to power evaporative cooling greenhouses (ECG) in the African Sahel region.
ECGs are a type of greenhouse that cools plants through the natural process of evaporation. The evaporation process is done by pumping water over special wet pads while fans blow air through them.
“In the dry and hot climatic conditions of the Sahel, cooling is necessary to maintain a favorable microclimate,” explains the research group. “To avoid the expensive and unsustainable conventional cooling system in the Sahel with grid-connected air conditioning or by generators powered by carbonated fossil fuel, a stand-alone photovoltaic system was used to power the evaporative cooling system, i.e. the pumping and water distribution and fans.
The experimental setup was located in the south-west of Niger and covered an area of ??50 m2, with a height of 3.66 m and a roof pitch of 15 degrees. The water pumping and fans were powered by six photovoltaic modules of 260 W each, using a 5 kVA inverter. Four batteries of 150 Ah each were also used to allow trouble-free operation in case of lack of irradiation.
As for wet pads, the academics compared two different types in the same system. One was the commercially available Celdek pads (C-pads), while the other was the locally manufactured Hyphaene thebaica fiber pads (HF-pads). In both cases, the pads were inserted along the sides of the greenhouse, with a fan for each pad.
“The field climatic parameters recorded in situ and the thermophysical data obtained in the laboratory prototype and from the installed PV-ECG were used to evaluate the alternative cooling potential of the HF panels compared to the conventional C panel,” the academics explain. “Key cooling performances of the greenhouse were derived from established thermodynamic energy and mass balance equations.”
Additionally, after collecting data from the actual greenhouse and conducting laboratory investigation of the pads, a computational fluid dynamics (CFD) analysis was performed to obtain a general understanding of the cooling fluid distribution in the greenhouse. Both the numerical model and the experimental data collection were carried out in the warm and dry seasons, with inlet temperatures of 35 ºC to 45 ºC and a relative humidity of 10% to 15%.
“The cooler that uses HF-pad allows the microclimate to be maintained below 25 ºC, with a maximum humidity rate of up to 80%, in adverse environmental conditions,” the team stressed. “HF-pad had the highest cooling coefficient of performance (COP = 9 vs. 6 for C-pad), the best cost-effectiveness ratio (CER = 5; 4 times less than C-pad) and the highest outlet temperature.” low (20.0 ºC)”.
The scientists also highlighted that, due to the higher velocity of the exhaust air, the C-pad cooler spread cold air up to 1.25 m further than its counterpart, creating a higher pressure in the atmosphere, with twice the kinetic energy. turbulent.
The group concluded that the HF pad achieved cooling performance that rivaled that of conventional pads. “Optimizing the high-frequency pad structure and scaling the technology to an industrial level can improve thermal and economic performance,” they added.
Their findings were presented in “ Improving the sustainability and effectiveness of photovoltaic evaporative cooling greenhouse in the Sahel ,” published in Scientific Reports . |
