Energy and Economic Evaluation of Green Roofs for Residential Buildings in Hot-Humid Climates
- Develop a green roof model for a selected four bedroom residential building with the help of DesignBuilder software.
- Validate the result of the developed model using experimental data.
- Determine the energy saving potential of different green roof options.
- Undertake economic assessment of the developed green roof.
2. Overview of Green Roof Technology
3. Energy Challenges Facing Saudi Arabia
4. Green Roof Model Development
4.1. Validation of the Model
5. Simulation Techniques for Energy Analysis
6. Economic Evaluation
- t is the time period, usually computed yearly.
- Ft the net cash flow for year t, computed as Ft = Bt − Ct.
- Bt represents the inflows or benefits accrued for the year t (which in this study is taken as the cost of Energy-savings in year t and the cost of other potential benefits).
- Ct represents the cost outflows for year t (which in this study is taken as the total operations and maintenance cost for year t).
- C0 represents the initial investment (including all costs of materials and installation).
- p the cost of capital taken as 2% (Source): .
- n is the number of years for which the economic evaluation is desired (40 years for this study).
7. Results and Discussion
7.1. Energy Analysis
7.2. Economic Analysis
Conflicts of Interest
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|Building Features||Description of the Housing|
|Location||Dhahran (26.27 N latitude, 50.15 E longitude, and 17 m above sea level)|
|Orientation||Front Elevation facing East|
|Floor to Floor Height||3.5 m|
|Floor Area||367.3 m2 (Gross); 192.0 m2 (Ground Floor); 175.0 m2 (First Floor)|
|Window to Wall Ratio (WWR)||10%|
|Weather File and relative humidity (RH)||Dhahran: 2012 and 55% relative humidity|
|Exterior Walls||0.016 m Plaster (Dense) + 0.1 m Concrete Block (Medium) + 0.05 m Extruded Polystyrene + 0.1 m Concrete Block (Medium) + 0.013 m Plaster (Lightweight)|
|Roof||0.04 m Concrete Tiles (Roofing) + 0.0002 m Polyethylene (High Density) + 0.05 m Extruded Polystyrene + 0.004 m Bitumen Felt + 0.059 m Cement Screed + 0.3 m Reinforced Concrete (Cast, Dense)|
|Infiltration||1.25 air changes per hour (ACH) (Ground Floor), 0.75 ACH (First Floor)|
|Lighting Power Density||21 W/m2 (Ground Floor); 13 W/m2 (First Floor)|
|Heating, ventilation, and air conditioning (HVAC) System Type||Residential System Direct Expansion (DX) Air Conditioner (AC)|
|Window||0.004 m tinted glass +0.012 m air gap + 0.004 m tinted glass|
|Month||Measured Data KWh/m2||Simulated Data KWh/m2|
|1||Thermal Conductivity (W/(m·K))||0.30|
|2||Height of Plants (m)||0.30|
|3||Leaf Area Index (LAI)||5.00|
|6||Minimum Stomata Resistance (s/m)||50.0|
|7||Maximum Volumetric Moisture Content at Saturation||0.50|
|8||Minimum Residual Volumetric Moisture Content||0.20|
|Installation cost for extensive green roofs (including the soil and equipment needed)||SR 88 per square meter||Local practitioners|
|Annual operations and maintenance cost||Varies||Local practitioners|
|Saudi energy consumption tariff||SR 0.113 /KWh|||
|Longevity benefit||SR 2/m2||[52,53,54,55,56]|
|Green roof enhanced air quality advantage||SR 0.09/m2|||
|Green roof habitat creation advantage||SR 2.5/m2|||
|Mitigation of heat island effect||SR 3/m2||[59,60,61]|
|Option A||Option B||Option C|
|1||Initial investment (C0)||15,429||7715||7715|
|4||Green roof enhanced air quality advantage||15.75||7.88||7.88|
|5||Green roof habitat creation advantage||437.5||218.75||218.75|
|6||Mitigation of heat island effect||525||262.5||262.5|
|7||Cost inflows i.e., total benefit (Bt)||2499.25||1434.13||1467.13|
|8||Cost outflows i.e., operations and maintenance cost (Ct)||1500||1000||1000|
|9||Cash flow (Ft = Bt – Ct)||999.25||434.13||467.13|
|10||Net Present Value (NPV) (40 years)||11,905.96||4160.83||5063.57|
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Mahmoud, A.S.; Asif, M.; Hassanain, M.A.; Babsail, M.O.; Sanni-Anibire, M.O. Energy and Economic Evaluation of Green Roofs for Residential Buildings in Hot-Humid Climates. Buildings 2017, 7, 30. https://doi.org/10.3390/buildings7020030
Mahmoud AS, Asif M, Hassanain MA, Babsail MO, Sanni-Anibire MO. Energy and Economic Evaluation of Green Roofs for Residential Buildings in Hot-Humid Climates. Buildings. 2017; 7(2):30. https://doi.org/10.3390/buildings7020030Chicago/Turabian Style
Mahmoud, Abubakar S., Muhammad Asif, Mohammad A. Hassanain, Mohammad O. Babsail, and Muizz O. Sanni-Anibire. 2017. "Energy and Economic Evaluation of Green Roofs for Residential Buildings in Hot-Humid Climates" Buildings 7, no. 2: 30. https://doi.org/10.3390/buildings7020030