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Journal of Arid Land  2021, Vol. 13 Issue (4): 375-387    DOI: 10.1007/s40333-021-0060-y
Research article     
Water, land, and energy use efficiencies and financial evaluation of air conditioner cooled greenhouses based on field experiments
Ibtihal AL-MANTHRIA1, Abdulrahim M AL-ISMAILIA1,*(), Hemesiri KOTAGAMAB2, Mumtaz KHANC3, L H Janitha JEEWANTHAD4,5
1Department of Soils, Water and Agricultural Engineering, Sultan Qaboos University, Muscat PC123, Oman
2Department of Natural Resource Economics, Sultan Qaboos University, Muscat PC123, Oman
3Department of Plant Science, College of Agricultural and Marine Sciences, Sultan Qaboos University, Muscat PC123, Oman
4Centre for Future Materials, University of Southern Queensland, Toowoomba QLD 4350, Australia
5School of Mechanical and Electrical Engineering, University of Southern Queensland, Toowoomba QLD 4350, Australia
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Abstract  

High temperature and humidity can be controlled in greenhouses by using mechanical refrigeration cooling system such as air conditioner (AC) in warm and humid regions. This study aims to evaluate the techno-financial aspects of the AC-cooled greenhouse as compared to the evaporative cooled (EV-cooled) greenhouse in winter and summer seasons. Two quonset single-span prototype greenhouses were built in the Agriculture Experiment Station of Sultan Qaboos University, Oman, with dimensions of 6.0 m long and 3.0 m wide. The AC-cooled greenhouse was covered by a rockwool insulated polyethylene plastic sheet and light emitting diodes (LED) lights were used as a source of light, while the EV-cooled greenhouse was covered by a transparent polyethylene sheet and sunlight was used as light source. Three cultivars of high-value lettuce were grown for experimentation. To evaluate the technical efficiency of greenhouse performance, we conducted measures on land use efficiency (LUE), water use efficiency (WUE), gross water use efficiency (GWUE) and energy use efficiency (EUE). Financial analysis was conducted to compare the profitability of both greenhouses. The results showed that the LUE in winter were 10.10 and 14.50 kg/m2 for the AC- and EV-cooled greenhouses, respectively. However, the values reduced near to 6.80 kg/m2 in both greenhouses in summer. The WUE of the AC-cooled greenhouse was higher than that of the EV-cooled greenhouse by 3.8% in winter and 26.8% in summer. The GWUE was used to measure the total yield to the total greenhouse water consumption including irrigation and cooling water; it was higher in the AC-cooled greenhouse than in the EV-cooled greenhouse in both summer and winter seasons by almost 98.0%-99.4%. The EUE in the EV-cooled greenhouse was higher in both seasons. Financial analysis showed that in winter, gross return, net return and benefit-to-cost ratio were better in the EV-cooled greenhouse, while in summer, those were higher in the AC-cooled greenhouse. The values of internal rate of return in the AC- and EV-cooled greenhouses were 63.4% and 129.3%, respectively. In both greenhouses, lettuce investment was highly sensitive to changes in price, yield and energy cost. The financial performance of the AC-cooled greenhouse in summer was better than that of the EV-cooled greenhouse and the pattern was opposite in winter. Finally, more studies on the optimum LED light intensity for any particular crop have to be conducted over different growing seasons in order to enhance the yield quantity and quality of crop.



Key wordsland use efficiency      energy use efficiency      water use efficiency      gross water use efficiency      financial evaluation      air conditioner cooled greenhouse      evaporative cooled greenhouse     
Received: 15 March 2020      Published: 10 April 2021
Corresponding Authors: Abdulrahim M AL-ISMAILIA     E-mail: abdrahim@squ.edu.om
About author: * Abdulrahim M Al-ISMAILIA (E-mail: abdrahim@squ.edu.om)
Cite this article:

Ibtihal AL-MANTHRIA, Abdulrahim M AL-ISMAILIA, Hemesiri KOTAGAMAB, Mumtaz KHANC, L H Janitha JEEWANTHAD. Water, land, and energy use efficiencies and financial evaluation of air conditioner cooled greenhouses based on field experiments. Journal of Arid Land, 2021, 13(4): 375-387.

URL:

http://jal.xjegi.com/10.1007/s40333-021-0060-y     OR     http://jal.xjegi.com/Y2021/V13/I4/375

Fig. 1 Illustration of evaporative-cooled (EV-cooled) prototype greenhouse (a) and air conditioner-cooled (AC-cooled) prototype greenhouse (b). The EV-cooled greenhouse is equipped with a fan (A)-pad (B) evaporative cooling system, 200 μm? thick polyethylene plastic sheet (C), and two hydroponic irrigation system frames (D); the AC-cooled greenhouse is equipped with an air conditioner (E), 50 mm thick rockwool insulation material sheet and double layers of polyethylene plastic sheets (F), a small fan (G), two hydroponic irrigation system frames (D), and four different height levels red and blue light emitting diodes (LED) lights (H).
Input/output Unit Energy equivalent Reference
per unit input/output (MJ/hm2)
Energy input Human labour h 1.96 Singh et al. (2002)
Rotavator 2.35 Alam et al. (2005)
Knapsack sprayer 1.40 Gezer et al. (2003)
Seed kg 1.00 Taki et al. (2012)
Diesel-oil L 56.31 Singh and Kamal (2012)
Electricity kW·h 3.60 Ozkan et al. (2011)
Water for irrigation/cooling m3 1.02 Yaldiz et al. (1993)
Nitrogen kg 60.60 Singh et al. (2002)
Phosphorus kg 11.10 Singh et al. (2002)
Potassium kg 6.70 Singh et al. (2002)
Sulfate kg 1.12 Mohammadi and Omid (2010)
Calcium kg 1.12 Mohammadi and Omid (2010)
Micro-nutrients kg 120.00 Banaeian et al. (2011)
Farm yard manure kg 0.30 Taki et al. (2012)
Pesticides kg 196.00 Kuswardhani et al. (2013)
Fungicides kg 168.00 Kuswardhani et al. (2013)
Energy output Crop yield (lettuce) kg 1.20 Hatirli et al. (2005)
Table 1 Energy equivalents of different input and output values used in agricultural production
Performance index AC-cooled greenhouse EV-cooled greenhouse
Yield per cultivation period (kg) 151.50 217.50
LUE (kg/m2) 10.10 14.50
WUE (kg/m3) 100.32 96.52
GWUE (kg/m3) 100.32 1.98
EUE 0.08 0.10
Table 2 Performance of the AC-cooled greenhouse and EV-cooled greenhouse in winter
Item Lifetime (a) Initial investment cost (USD) Annualized investment cost (USD)
Hydroponic irrigation
system frames
20 1664.00 24.18
PVC accessories 20 36.40 0.52
Aluminum door 10 312.00 7.07
Rockwool sheet with double layers of polyethylene sheets 5 299.00 11.83
Water tank 20 55.90 0.81
Foot valve 3 5.72 0.36
Electrical 1.5 mm wires 10 52.00 1.17
Cooling fans 20 156.00 2.26
AC cooling system 10 390.00 6.80
Irrigation pump 5 23.40 0.93
Binding wires 7 5.20 0.16
Electrical panel enclosure 20 52.00 0.75
LED lights 13 1950.00 36.71
Electrical accessories 5 26.00 1.01
Hydroponic irrigation
system
20 1248.00 18.12
Installation 20 1170.00 17.00
Water meter* 5 39.00 1.53
Thermocouple wires* 10 1916.20 43.40
Watt meter* 5 67.60 2.68
PAR meter* 10 1625.00 36.79
RHT sensor* 10 1235.00 27.98
Anemometer* 20 1326.00 19.27
pH/EC meter 10 156.00 3.53
Total 13810.42** 288.94
Table 3 Initial capital and annualized investments of an AC-cooled greenhouse (18 m2) with lettuce production in winter
Item Lifetime (a) Initial investment cost (USD) Annualized investment cost (USD)
Hydroponic irrigation
system frames
20 1664.00 24.18
PVC accessories 20 36.40 0.52
Aluminum door 10 312.00 7.07
Polyethylene plastic sheet 5 65.00 2.57
Water tank 20 55.90 0.81
Foot valve 3 5.72 0.36
Electrical 1.5 mm wires 10 52.00 1.17
Two cooling fans 20 312.00 4.52
Cooling pads 5 143.00 5.67
Irrigation pump 5 23.40 0.93
Binding wires 7 5.20 0.16
Electrical panel enclose 20 52.00 0.75
Electrical accessories 5 26.00 1.04
Hydroponic irrigation system 20 1248.00 18.12
Installation 20 1170.00 17.00
Water meter 5 39.00 1.53
Thermocouple wires 10 1916.20 43.40
Watt meter 5 67.60 2.68
PAR meter 10 1625.00 36.79
RHT sensor 10 1235.00 27.98
Anemometer 20 1326.00 19.27
pH/EC meter 10 156.00 3.53
Total 11535.42** 220.10
Table 4 Initial capital and annualized investments of an EV-cooled greenhouse with lettuce production in winter
Cost and return components AC-cooled greenhouse EV-cooled greenhouse
Total yield in winter (kg) 780.00 1305.00
Price (USD/kg) 4.68 4.68
Gross value of production (USD) 3650.40 6107.40
Variable cost of production (USD) 959.09 1207.44
Fixed cost of production (USD) 266.94 220.06
Total cost of production (USD) 1226.03 1427.50
Per kilogram cost of production (USD/kg) 1.56 1.09
Gross return (USD) 2691.31 4899.96
Net return (USD) 2424.37 4679.89
Benefit-to-cost ratio 2.98 4.28
Financial productivity (kg/USD) 0.63 0.92
Table 5 Agricultural budgets of the AC- and EV-cooled greenhouses in winter
Performance index AC-cooled greenhouse EV-cooled greenhouse
Yield per cultivation period (kg) 102.00 103.20
LUE (kg/m2) 6.80 6.88
WUE (kg/m3) 41.83 30.61
GWUE (kg/m3) 47.77 0.29
EUE 0.03 0.05
Table 6 Performance of the AC- and EV-cooled greenhouses in summer
Cost and return components AC-cooled greenhouse EV-cooled greenhouse
Total yield in summer (kg) 612.00 619.20
Price (USD/kg) 5.20 5.20
Gross value of production (USD) 3182.40 3219.84
Variable cost of production (USD) 1074.68 1603.68
Fixed cost of production (USD) 266.94 220.06
Total cost of production (USD) 1341.62 1823.74
Per kilogram cost of production (USD/kg) 2.18 2.94
Gross return (USD) 2107.71 1616.16
Net return (USD) 1840.77 1396.10
Benefit-to-cost ratio 2.37 1.77
Financial productivity (kg/USD) 0.46 0.34
Table 7 Agricultural budgets of the AC- and EV-cooled greenhouses in summer
Fig. 2 Relationships of the internal rate of return (IRR) with sale price, yield and electricity cost after subsidy in the AC-cooled greenhouse (a, b and c, respectively) and EV-cooled greenhouse (d, e and f, respectively)
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