Energy and Economic Performance of Plant-Shaded Building Façade in Hot Arid Climate
4. Cost Benefit Analysis
1/4th of the façade is plant shaded so the increment applies to 25% of the rent.
Added property value of tested space due to greening = 0.04× 3500 × 0.25 = 35 US$
Local cost of electricity = 320 AED/MWh = 87.12 US$/MWh Energy cost savings = 87.12× 0.37 = 32.23 US$/year
Total savings = saving on rental + energy cost saving = 35 + 32.23 = 67.23 US$/year Payback period = 696/67.23 = approx. 10 years
Table 2. Cost and benefits of the plant-shaded wall per tested space.
Category Cost in US$
(1 US$ = 3.67 AED) Category Benefit
Initial cost of plants and growing media 240 US$ Energy savings 32.23 US$/year
Installation cost 132 US$ Added property value 35 US$/year
Initial cost of irrigation system 55.2 US$ Air quality improvement Ignored
Water cost for irrigation 40.8 US$/year Carbon reduction Ignored
Maintenance cost 108 US$/year Street noise reduction Ignored
Plantation space use cost 120 US$/year Urban heat island Ignored
Total cost 58 US$/m2 Total Benefit 67.23
Tested façade area per floor = 12 m2
Total cost for the tested façade per floor (12×58) 696 US$ Payback Period 10 years
As shown in Table 2, the plant-shaded wall system is economically sustainable with a payback period of 10 years. The payback period employs unsubsidized local electricity rate. The most favorable economic conditions take place when the payback period is low. In comparison with other greenery techniques, where the payback periods are usually higher than 10 years, e.g., 14–20 years for indirect green façade combined with planter boxes and steel mesh [28,30]. The authors expect to achieve a reduced payback period once the social and environmental benefits are included as subject of future study to make the use of greening systems financially viable.
5. Conclusions
The use of vegetation on and around building façades has gained increasing popularity in many cities for improving thermal performance in buildings and reducing negative environmental impacts.
Plant-shaded wall technique was tested in Al-Ain, the Garden City, to increase energy efficiency and reduce cooling load in residential buildings. The study finds that plant-shaded façades can reduce the yearly cooling energy by up to 0.37 MWh compared to the unshaded façades. An indoor temperature reduction of 12◦C at the peak time and 2◦C on average on a 24-h basis was achieved in the month of July. The decreased temperature was achieved by the shading and insulation effect of low-conductivity plant foliage that rendered less thermal energy gain eventually reducing cooling demand of the building. The economic analysis reveals that the payback period of plant-shaded greenery system was 10 years, in the case of unsubsidized energy tariffs. A further reduction of the payback period is expected once the environmental savings are included, which is a subject for future study.
Acknowledgments: The authors would like to express their appreciations to the College of Engineering at the UAE University for funding this research project.
Author Contributions: Mahmoud Haggag envisioned the idea; Ahmed Hassan and Mahmoud Haggag conducted the experiments; Ahmed Hassan analyzed the results; and Ghulam Qadir collected the literature survey. The paper was written as a joint effort.
Conflicts of Interest: The Authors confirm no conflict of interest.
Appendix A
-10 0 10 20 30
12:06 AM 9:26 AM 6:46 PM 4:06 AM 1:26 PM 10:46 PM 8:06 AM 5:26 PM 2:46 AM 12:06 PM 9:26 PM 6:46 AM 4:06 PM 1:26 AM 10:46 AM 8:06 PM 5:26 AM 2:46 PM 12:06 AM 9:26 AM 6:46 PM 4:06 AM
Temperature reduction (°C)
Time External Surface
-10 0 10 20 30
12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM
Temperature reduction (°C)
Time Internal Surface
-10 0 10 20 30
12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM 12:00 AM
Temperature reduction (°C)
Time Indoor ambient
Figure A1. Temperature reductions (◦C) in external surface, internal surface & ambient temperature.
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