Articles
COOLING NEED OF GREENHOUSES IN SEMI-ARID HOT WATER-SCARCE KUTCH REGION OF NORTH-WEST INDIA
Article number
1054_2
Pages
31 – 38
Language
English
Abstract
Cooling, which is achievable in greenhouses of the semi-arid Kutch region of north-west India by shading, natural ventilation and water consumption when a fan pad is used, was studied via a simulation model.
This was done to increase the availability of information on the effectiveness of these measures under local climate conditions.
Natural ventilation alone limited the rise of temperature inside over the ambient (ΔTmax) to 2-4°C, over a major part of the year.
With 50% shading alone on top, the ΔTmax range was 6-11°C over a major part of the year.
With the two measures combined, the ΔTmax range was 1 to 3°C. Natural ventilation was very effective due to (a) high wind speeds particularly in the afternoons, (b) the efficient configuration of vents (one on the ridge, and two on the sides) and (c) high vent area (total unscreened vent area was 25% of the floor). The actual measurement of the light intensity inside an experimental greenhouse with 50% shade net showed that it was still adequate for plant growth and shading could be increased by a further small amount.
With these measures, the inside temperature could be kept close to the ambient over seven months.
This may in part be the reason growers in the area increasingly prefer open-vent units with shade nets.
Also, such units require low investment and have lower operational costs.
Simulations also showed that fan pad cooling was required for at least five, possibly seven, months with several hours of operation each day to keep the inside close to 32°C. In April, for instance, fan pad operation will span 10 h and consume 9.3 L m-2 day-1 of water.
Water is scarce in the region and this may in part be the reason for the abandonment of fan-pad-cooled greenhouses some years ago.
The information generated suggests that the expansion and sustainability of greenhouse cultivation in such a region calls for a design-approach different from that used for colder regions of the world.
Here, full use should be made of shading and natural ventilation.
More efficient evaporative cooling techniques such as fogging should be tried out, along with shade and ventilation.
Although, not discussed here, cost-effective solar-powered brackish-water desalination would also be an integral part of sustainable greenhouses for semi-arid climates.
This was done to increase the availability of information on the effectiveness of these measures under local climate conditions.
Natural ventilation alone limited the rise of temperature inside over the ambient (ΔTmax) to 2-4°C, over a major part of the year.
With 50% shading alone on top, the ΔTmax range was 6-11°C over a major part of the year.
With the two measures combined, the ΔTmax range was 1 to 3°C. Natural ventilation was very effective due to (a) high wind speeds particularly in the afternoons, (b) the efficient configuration of vents (one on the ridge, and two on the sides) and (c) high vent area (total unscreened vent area was 25% of the floor). The actual measurement of the light intensity inside an experimental greenhouse with 50% shade net showed that it was still adequate for plant growth and shading could be increased by a further small amount.
With these measures, the inside temperature could be kept close to the ambient over seven months.
This may in part be the reason growers in the area increasingly prefer open-vent units with shade nets.
Also, such units require low investment and have lower operational costs.
Simulations also showed that fan pad cooling was required for at least five, possibly seven, months with several hours of operation each day to keep the inside close to 32°C. In April, for instance, fan pad operation will span 10 h and consume 9.3 L m-2 day-1 of water.
Water is scarce in the region and this may in part be the reason for the abandonment of fan-pad-cooled greenhouses some years ago.
The information generated suggests that the expansion and sustainability of greenhouse cultivation in such a region calls for a design-approach different from that used for colder regions of the world.
Here, full use should be made of shading and natural ventilation.
More efficient evaporative cooling techniques such as fogging should be tried out, along with shade and ventilation.
Although, not discussed here, cost-effective solar-powered brackish-water desalination would also be an integral part of sustainable greenhouses for semi-arid climates.
Authors
G. Sharan
Keywords
temperature, natural ventilation, shading, fan pad cooling, water consumption
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