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Journal of Arid Land  2021, Vol. 13 Issue (4): 388-396    DOI: 10.1007/s40333-021-0057-6
Research article     
Potential reduction in water consumption of greenhouse evaporative coolers in arid areas via earth-tube heat exchangers
Abdulrahim M AL-ISMAILI1,*(), Moustafa A FADEL2, Hemantha JAYASURIYA1, L H Janitha JEEWANTHA3, Adel AL-MAHDOURI1, Talal AL-SHUKEILI1
1Department of Soils, Water and Agricultural Engineering, Sultan Qaboos University, Muscat PC123, Oman
2Department of Arid land Agriculture, United Arab Emirates University, Al-Ain 17555, United Arab Emirates
3Centre for Future Materials & School of Mechanical and Electrical Engineering, University of Southern Queensland, Toowoomba QLD 4350, Australia
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This study aimed to explore the potential of developing a novel cooling system combining a greenhouse and an earth-tube heat exchanger (ETHE). In this system, greenhouse air is circulated through the underneath soil mass to use the deep-soil cooling effect. This was achieved through the following steps. First, soil temperature profile inside and outside the cultivated greenhouse was monitored for almost one year to study the possibility of using deep-soil coldness for cooling the greenhouse air. Second, a prototype ETHE was built to practically investigate the potential reduction in air temperature as the air flows inside the deep earth pipes. Third, a prototype greenhouse was erected to study the ETHE concept. Results from the first experiment revealed that soil temperature at a soil depth of 2.5 m inside the greenhouse offers good conditions to bury the ETHE. The soil temperature at this soil depth was below the maximum temperature (32°C) that most greenhouse crops can withstand. Results from the prototype ETHE showed a slight reduction in air temperature as it passed through the pipes. From the prototype of the integrated greenhouse and ETHE system, reduction in air temperature was observed as the air passed through the ETHE pipes. At night, the air was heated up across the ETHE pipes, indicating that the ETHE was working as a heater. We concluded from this study that greenhouses in arid climates can be cooled using the ETHE concept which would save a large amount of water that would otherwise be consumed in the evaporative coolers. Further investigations are highly encouraged.

Key wordsearth-tube heat exchanger      greenhouse      fan-pad cooling system      water saving      arid areas     
Received: 15 March 2020      Published: 10 April 2021
Corresponding Authors: Abdulrahim M AL-ISMAILI     E-mail:;
About author: * Abdulrahim M AL-ISMAILI (E-mail:;
Cite this article:

Abdulrahim M AL-ISMAILI, Moustafa A FADEL, Hemantha JAYASURIYA, L H Janitha JEEWANTHA, Adel AL-MAHDOURI, Talal AL-SHUKEILI. Potential reduction in water consumption of greenhouse evaporative coolers in arid areas via earth-tube heat exchangers. Journal of Arid Land, 2021, 13(4): 388-396.

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Fig. 1 Overview of temperature sensor positioning. P1, P2, P3 and P4 represent the soil depths of 0.02, 1.00, 2.00 and 3.00 m, respectively, where thermocouples were installed.
Fig. 2 SolidWorks modeled pipe networks (a) and soil block assembly with pipe network (b)
Fig. 3 Fan-mounting structure
Fig. 4 Designed model of greenhouse and ETHE (earth-tube heat exchanger) system (a), ETHE installation (b), greenhouse framework after refilling the ETHE trench (c) and completed prototype greenhouse and ETHE system (d)
Fig. 5 Locations of the shielded thermocouples at the inlet (a) and outlet (fan side; b) of the greenhouse
Fig. 6 Mid-day soil temperatures for the pits outside (a) and inside (b) the greenhouse. P1, P2, P3 and P4 represent the soil depths of 0.02, 1.00, 2.00 and 3.00 m, respectively. The red dotted line means the maximum tolerable temperature (32°C) for some high value vegetable crops.
Fig. 7 Observed and simulated air temperature inside the earth-tube heat exchanger (ETHE) pipe at the air speed of 3 m/s
Fig. 8 Temperature distribution pattern around ETHE the pipe network composed of one pipe (a) and an array of three (b), seven (c) and eleven (d) pipes. These patterns are taken at the middle of 6.00 m long ETHE pipes.
Fig. 9 ETHE temperature variation of air, soil and inside the ETHE pipe for a 2-d period. Env, temperature of air; In avg, average inlet air temperature to the ETHE; Out avg, average outlet air temperature from the ETHE; Soil (3.00 m), soil temperature at a depth of 3.00 m.
Fig. 10 Temperature differences through the greenhouse (outlet minus inlet) and the ETHE (inlet minus outlet) during the daytime (12:00-18:00) and the nighttime (00:00-06:00) for a 2-d period
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