PurposeAs the global population keeps increasing with its associated urbanisation and climate change issues being experienced in various degrees worldwide, there is the need to find mitigating measures to improve thermal conditions within spaces. The study aimed to evaluate green roofs to determine whether they could provide thermal comfort within residential buildings.Design/methodology/approachForty-two-year weather data were retrieved from the Kumasi weather station to establish the pattern of the climatic variables. Furthermore, an experiment was conducted by constructing test cells to determine the potential of vegetation/green roofs on temperature development within spaces. This approach led to a simulation-based exploration of the thermal performance of the test cells to probe variables that could lead to the reduction in temperature after the models in the software (design-builder) had been validated.FindingsThe results on the 42 years (1976–2018) weather data showed a significant (p = 0.05) mean temperature increment of 2.0 °C. The constructed test cell with Setcreasea purpurea (Purple Heart) vegetation showed an annual mean temperature reduction of 0.4 °C (p = 0.05). In addition, the exploration using the simulation application showed combinations of various soil depth (70–500 mm) and leaf area indices (leaf area index of 2–5) having a potential to lower indoor temperature by 1.5 °C and its associated reduction in energy use. The option of green roofs as a valuable alternative to conventional roofs, given their potential in mitigating climate change, must be encouraged. A survey of occupants in six selected neighbourhoods in Kumasi showed varying subjective perceptions of several green issues (24–98%) and increases in temperature values because of the loss of greenery in the city.Originality/valueEmpirical data that point to the significant reduction of indoor temperature values and a subsequent reduction in energy use have been unearthed. Therefore, built environment professionals together with city authorities could invest in these sustainable measures to help humanity.

Apart from the ever- increasing population of most tropical urban cities, high ambient temperature, deteriorated comfort conditions, highly polluted environments are but a few of the problems these cities are confronted with. In the long run, increase energy demands both for production and the provision of comfortable spaces becomes necessary even though it’s a very scarce resource. It is widely known that Urban heat island (UHI) can significantly affect building’s thermal performance and as such, this study was conducted to find out how green roof which is a mitigating factor can reduce the thermal discomfort in indoor spaces. By means of dynamic simulation in EnergyPlus software, a numerical comparative analysis between eight scenarios was done in a tropical climate of Ghana, taking into account climatological, thermal, and hydrological variables. Two factors: Leaf Area Index (LAI) and Soil depth were the main determinants of the comparative analysis.  From the results, 5 out of the 8 scenarios was seen to all have performed better leading to a 1.5°C temperature reduction. Out of the 5, LAI5/70-150mm and LAI2/500mm suggest that at every point, there could be a reduction in indoor temperature if either LAI is larger or substrate depth is deep. A larger LAI and a deeper depth could also produce a favorable results (LAI5/500mm) though after a certain threshold, their effect weakens. Based on the findings, it is highly recommended that green roofs becomes part of the solution towards the fight against indoor thermal discomfort and not mechanical ventilation which could have a dire consequence on an already scare resource which is energy.

The current study assessed the city of Kumasi, Ghana to find out the extent of urban heat and the views of the populace about their climate. Both the subjective and objective approaches were utilized in the study. Secondary data from the Meteorological Survey Department in Kumasi covering temperature and relative humidity values for a 42- year period (1976 - 2018) was retrieved and used in the analysis to find the trend of urban heat phenomenon. Alongside, a developed questionnaire had a response from 2,083 people. The findings reveal among other things that there’s a 2ºC rise in mean annual temperature from 1976 to 2018. Additionally, the data shows that the past 4 years have had high mean temperature values. Subjectively, 1, 271 residence representing 61% voted in the “slightly warm-hot” range on the thermal sensation scale. Majority of the respondents across all the ages indicated how uncomfortable their outdoor spaces have become in recent times. 36% of the respondents attributed this discomfort to the lack of greenery with over 95% across all ages indicating that Kumasi city has lost its greenery and green spaces to buildings and other infrastructural activities. Whiles climate change and global warming have both become a global menace, the onus lies on individual countries and for that matter, various city authorities to make a conscious effort in planning our cities with greenery to alleviate the menace we already find ourselves. A conscious effort to retrieve and restore encroached green spaces must be undertaken by the city authorities while the parks and gardens division ought to be efficiently resourced to manage our green spaces.

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.

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