Abstract
Semiarid climate regions have great potential for productivity due to large amounts of solar radiation throughout year. However, these regions also have disadvantages, such as excessive air temperature and limited water use. Optimizing the ventilation rate and evapotranspiration during fog cooling in combination with natural ventilation will provide more favorable growing conditions for plants in a semiarid climate and allow less water use. A single-span greenhouse at The University of Arizona was used to investigate the fog cooling performance on clear days with excessively high air temperature.The environmental conditions and the natural ventilation rate were measured. The performance of fog cooling in combination with natural ventilation was compared with pad-and-fan cooling. Fog cooling and pad-and-fan cooling used 24 g m-2 min-1 and 41 g m-2 min-1 of water, respectively. The air relative humidity for fog cooling was slightly higher than that for pad-and-fan cooling, at approximately 35%.An English version of Visual VETH (ventilation-evapotranspiration-temperature-humidity) software was also developed. A cooling strategy devised for semiarid greenhouses found that the air relative humidity inside a greenhouse decreased with an increase in ventilation rate as expected from simulation based on steady-state energy balance equations, while the water use for fog cooling increased.A simple and unique control algorithm for fogging and ventilation inlet openings demonstrated the possibility of maintaining relative humidity and air temperature simultaneously within a desirable range while reducing the water use for fog cooling. The tomato plant canopy transpiration rate and the water balance relative to the natural ventilation rate in a fog-cooled greenhouse were also investigated. The transpiration rate increased linearly with an increase in vapor pressure deficit (VPD) of the air. At a lower ventilation rate made possible by reducing the ventilation inlet openings, total water use in the greenhouse decreased by 13% and relative humidity increased as was expected from the steady-state energy balance simulation. The decrease in canopy transpiration resulted from the decrease in VPD, and was at a magnitude greater than that of the fog evaporation rate under similar experimental conditions with relatively high humidity in the range of 70-94%. By optimizing the natural ventilation rate, the greenhouse could be effectively cooled with less water use. Arizona can be considered a model analogous to many other semiarid climate conditions. Due to the long history of greenhouse technology development, the application of greenhouse crop production to an area with excessive radiation and dry air remains a relatively new effort. We believe that our efforts will contribute not only to the American Southwest but also to enhancing the application of greenhouse technology for crop production in these climate regions worldwide, including Mexico, China, the Middle East and Africa.
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Claims 9
Claim · model-written summary
Fog cooling used less water than pad-and-fan cooling.
- Taxon
- tomato plant
Solanum lycopersicume1 - Treatment
- Fog coolinge0
- Outcome
- watere0
- Value
- 24 g m-2 min-1e0
- Qualifier
- 41 g m-2 min-1e0
- Comparator
- pad-and-fan coolinge0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Fog cooling and pad-and-fan cooling used 24 g m-2 min-1 and 41 g m-2 min-1 of water, respectively”
e1“The tomato plant canopy transpiration rate”
Claim · model-written summary
Air relative humidity was slightly higher with fog cooling than pad-and-fan cooling.
- Taxon
- tomato plantSolanum lycopersicume1
- Treatment
- fog coolinge0
- Outcome
- air relative humiditye0
- Direction
- highere0
- Value
- approximately 35%e0
- Comparator
- pad-and-fan coolinge0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The air relative humidity for fog cooling was slightly higher than that for pad-and-fan cooling, at approximately 35%”
e1“The tomato plant canopy transpiration rate”
Claim · model-written summary
Simulated greenhouse air relative humidity declined with increasing ventilation rate.
- Taxon
- tomato plantSolanum lycopersicume1
- Treatment
- ventilation ratee0
- Outcome
- air relative humidity inside a greenhousee0
- Direction
- decreasede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the air relative humidity inside a greenhouse decreased with an increase in ventilation rate as expected from simulation based on steady-state energy balance equations”
e1“The tomato plant canopy transpiration rate”
Claim · model-written summary
Water use for fog cooling increased with ventilation rate.
- Taxon
- tomato plantSolanum lycopersicume2
- Treatment
- ventilation ratee1
- Outcome
- water use for fog coolinge0
- Direction
- increasede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“while the water use for fog cooling increased”
e1“the air relative humidity inside a greenhouse decreased with an increase in ventilation rate as expected from simulation based on steady-state energy balance equations, while the water use for fog cooling increased”
e2“The tomato plant canopy transpiration rate”
Claim · model-written summary
The control algorithm could maintain humidity and temperature in a desirable range while reducing fog water use.
- Outcome
- maintaining relative humidity and air temperature simultaneously within a desirable range while reducing the water use for fog coolinge0
- Comparator
- fogging and ventilation inlet openingse0
Not reportedValue
Verbatim
e0“A simple and unique control algorithm for fogging and ventilation inlet openings demonstrated the possibility of maintaining relative humidity and air temperature simultaneously within a desirable range while reducing the water use for fog cooling”
Claim · model-written summary
Tomato canopy transpiration increased linearly with vapor pressure deficit.
- Taxon
- tomato plantSolanum lycopersicume0
- Treatment
- vapor pressure deficit (VPD) of the aire1
- Outcome
- transpiration ratee1
- Direction
- increased linearlye1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The tomato plant canopy transpiration rate”
e1“The transpiration rate increased linearly with an increase in vapor pressure deficit (VPD) of the air”
Claim · model-written summary
Lower ventilation decreased total greenhouse water use by 13%.
- Taxon
- tomato plantSolanum lycopersicume1
- Treatment
- lower ventilation ratee0
- Outcome
- total water use in the greenhousee0
- Direction
- decreasede0
- Value
- 13%e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“At a lower ventilation rate made possible by reducing the ventilation inlet openings, total water use in the greenhouse decreased by 13%”
e1“The tomato plant canopy transpiration rate”
Claim · model-written summary
Lower ventilation increased greenhouse relative humidity.
- Taxon
- tomato plantSolanum lycopersicume1
- Treatment
- lower ventilation ratee0
- Outcome
- relative humiditye0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“At a lower ventilation rate made possible by reducing the ventilation inlet openings, total water use in the greenhouse decreased by 13% and relative humidity increased”
e1“The tomato plant canopy transpiration rate”
Claim · model-written summary
Reduced VPD caused a decrease in canopy transpiration greater than the decrease in fog evaporation.
- Taxon
- tomato plantSolanum lycopersicume1
- Outcome
- decrease in canopy transpiratione0
- Value
- 70-94%e0
- Qualifier
- decrease in VPDe0
- Comparator
- fog evaporation ratee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The decrease in canopy transpiration resulted from the decrease in VPD, and was at a magnitude greater than that of the fog evaporation rate under similar experimental conditions with relatively high humidity in the range of 70-94%”
e1“The tomato plant canopy transpiration rate”