Determination of the Effect of Green Roofs on Indoor Temperature by the Use of Simulation in a Tropical Landscape

Aims: To use a simulation base exploration to carry out 6 scenarios of green roof construction methods to determine the most efficient in improving indoor thermal comfort.

Study Design: Simulation Design was used as the study design.

Place and Duration of Study: The study was conducted at the Department of Horticulture – Kwame Nkrumah University of Science and Technology located at Kumasi-Ghana between 2016 and 2019.

Methodology: A simulation experimental setup was done to run for 1 year to cover the two seasons in Ghana. Version 5.0.2 Design Builder and Energy Plus 5.8 was used to work on 6 scenarios using leaf area indexes (LAI) of 2 and 5 as well as soil depth (thickness) of (70-150 mm), 200 mm, 300 mm and 500 mm. Also a real life experiment was done at the Department of Horticulture by constructing 9 test cells and using treatments such as Portulaca grandiflora and Setcreasea purpurea to validate the results for the simulation. The time setup for the simulation was from 12.00 am to 11.59 pm.

Results: A leaf area indexes (LAI) of 5 and soil depth of 70 mm-150 mm recorded the lowest simulated temperature ranging from 26.26°C to 29.30°C for scenario one. For scenario two, a leaf area indexes (LAI) of 5 and a soil depth of 200mm recorded the lowest significantly (P≤0.05) indoor temperature in August (26.20°C) and the highest (29.26°C) in March. In February, June and August, significant differences (P≤0.05) were achieved by leaf area indexes (LAI) 5 and soil thickness 500 mm for scenario three. January, March to July indicated significant differences (P≤0.05) between the treatments leaf area indexes (LAI) 2 and soil thickness 300 mm and leaf area indexes (LAI) 5 and soil depth of 300 mm recorded 26.32°C to 29.33°C for August and March respectively for scenario four. A soil depth of 500 mm and leaf area indexes (LAI) of 2 gave significantly (P≤0.05) low temperatures indoors all year (26.27 to 29.32°C) for scenario five and in August leaf area indexes (LAI) 5 and soil thickness of 500 mm recorded the least temperature all year for scenario six.

Conclusion: From the exploration, a soil depth of 70 mm – 150 mm and a LAI of 5, LAI of 5 and soil depth of 200 mm and LAI of 2 and soil depth of 500 mm achieved the lowest temperature and performed better in terms of temperature reduction which will lead to thermal comfort of occupants.