School of Energy & Environment

To date the majority of investigations into the performance of amorphous silicon photovoltaic systems have been limited to single sites, and therefore the conclusions from such studies are unlikely to be as generic as they might at first appear. This paper compares data collected from different systems across the world in Brazil, Hong Kong, Spain, Switzerland, and the United Kingdom. All systems have been operating for a number of years, and are employing double junction amorphous silicon devices of a similar age manufactured by RWE Solar.

Water is in short supply with countries vying for access to river heads. Hong Kong (HK) is no different. It relies on supply from Mainland China with other cities rivalling access. Yet there is still no great impetus for water conservation. This paper reports on progress in setting up a pilot biological wastewater treatment plant and a PV-powered UV-LED disinfection system plus a feasibility study carried out in conjunction with a local developer investigating the application of the treated water for irrigation. The objective is to incorporate the systems within a small-scale community for its contribution to water and energy conservation as well as establish the parameters for replication in other countries with potential up-scaling for urban application. r

An experimental investigation was carried out to determine the effect of trees on buildings' micro-climate. Parameters of thermal conditions were measured between September 2010 and February 2011 in and around two typical buildings located on a university campus. One of the buildings is shaded on the south eastern side by trees while the other is not. Indoor air temperature, outdoor air temperature and wall temperature were measured, while ancillary wind and solar radiation data were collected from the campus' meteorological station. Comparisons on air temperature and wall temperature as measured inside and outside the shaded and unshaded buildings were made. Air temperatures were higher and for longer hours throughout the study period inside the un-shaded building. Indoor-outdoor temperature differences show a peak of 5.4°C for the un-shaded building while the tree-shaded did not exceed 2.4°C. The results show that tree-shading constitutes an excellent passive cooling system for buildings, potentially enhances thermal control and conserves energy in buildings.

This study investigates the effect of tree-shading on energy demand in two similar buildings. Outdoor and indoor air temperature was measured simultaneously for a period of 6 months. Five different base temperatures ranging from 20 • C to 25 • C were chosen and used to calculate cooling degree-days. Degreeday and cooling/warming rate methods were used to estimate cooling energy requirements for the two buildings. Indoor and outdoor cooling degree days were observed to be more for the un-shaded buildings compared to the tree-shaded one. Indoor warming and cooling rate show that the un-shaded building warms earlier and faster than the tree-shaded. Results indicate that tree-shading can save up to 34,500 NGN (US$218) on energy costs. The study shows the role of greening in reducing energy demand in buildings.

Nigerian agriculture is mainly rain-fed and basically dependent on the vagaries of weather especially rainfall. Nigeria today has about forty-four (44) weather observation stations which provide measurement of rainfall amount for different locations across the country. Hence, this study investigates change detection in rainfall pattern over each climatic zone of Nigeria. Data were collected for 90 years period for all the weather observation stations in Nigeria, while a subdivision was made to three (3) non-overlapping climate period of 30 years i.e. 1910-1939, 1940-1969 and 1970-1999. Statistical methods were utilized to justify any change in the average monthly and annual rainfall trend using probability density function and non-parametric tests such as the Pettitt test, Wilcoxon signed-rank test and paired sample test. Results show common change points and transitions from dry to wet (upward shift) in all climatic zones. Statistical tests performed on the data show that rainfall variation over each climatic zone is significant (po 0.05) between pairs of climate periods. Suggestions were therefore made at the end of the study on the use of the contained information for socio-economic improvement and agricultural development of the zones.

This study assessed thermal conditions in and around two typical buildings on a university campus in Akure, Nigeria. One of the buildings was shaded by trees, while the other was unshaded. The aim is to
evaluate the effect of vegetation (tree shading) on indoor and outdoor thermal comfort. Air temperature
and relative humidity were measured simultaneously inside and outside both buildings for six months
(September 2010 to February 2011). Results show that the unshaded building is generally less com-
fortable in comparison with the tree-shaded one, especially during the daytime. The unshaded building
becomes less comfortable as early as 10:00h during the dry season, and that can even extend till
around 18:00h during the wet season. Also, the outdoor area around the tree-shaded building is
more thermally comfortable than around the unshaded one, irrespective of the season. A strong rela-
tionship between outdoor and indoor comfort conditions, irrespective of seasonal or diurnal variations
and thermal comfort index, also emerged. While the positive role of tree shading in thermal comfort is
not new, this study contributes additional evidence from an understudied sub-Saharan African region
like Nigeria. It points to the need for tree planting (greening) as a means to improve thermal comfort in
Nigerian cities.

Well-positioned and configured vegetation barriers
(VBs) have been suggested as one of the green infrastructures
that could improve near-road (local) air quality. This is because
of their influence on the underlying mechanisms: dispersion
and mass removal (by deposition). Some studies have
investigated air quality improvement by near-road vegetation
barrier using the dispersion-related method while few studies
have done the same using the deposition-related method.
However, decision making on vegetation barrier’s configuration
and placement for need-based maximum benefit requires
a combined assessment with both methods which are not commonly
found in a single study. In the present study, we
employed a computational fluid dynamics model, ENVI-met,
to evaluate the air quality benefit of near-road vegetation barrier
using an integrated dispersion–deposition approach. A technique
based on distance between source (road) and point of
peak concentration before dwindling concentration downwind
begins referred to as Bdistance to maximum concentration
(DMC)^ has been proposed to determine optimum position
from source and thickness of vegetation barrier for improved
dispersion and deposition-based benefit, respectively.
Generally, a higher volume of vegetation barrier increases the  overall mass removal while it weakens dispersion of pollutant
within the same domain. Hence, the benefit of roadside vegetation
barrier is need-based and can be expressed as either
higher mass deposition or higher mass dispersion. Finally, recommendations
on applications of our findings were presented.

The potential use of rainwater harvesting in conjunction with miscellaneous water supplies and a rooftop
garden with rainwater harvesting facility for temperature reduction have been evaluated in this study for
Hong Kong. Various water applications such as toilet flushing and areal climate controls have been
systematically considered depending on the availability of seawater toilet flushing using the Geographic
Information System (GIS). For water supplies, the district Area Precipitation per Demand Ratio (APDR)
has been calculated to quantify the rainwater utilization potential of each administrative district in Hong
Kong. Districts with freshwater toilet flushing prove to have higher potential for rainwater harvest and
utilization compared to the areas with seawater toilet flushing. Furthermore, the effectiveness of using
rainwater harvesting for miscellaneous water supplies in Hong Kong and Tokyo has been analyzed and
compared; this revives serious consideration of diurnal and seasonal patterns of rainfall in applying such
technology. In terms of the cooling effect, the implementation of a rooftop rainwater harvesting garden
has been evaluated using the ENVI-met model. Our results show that a temperature drop of 1.3
C has
been observed due to the rainwater layer in the rain garden. This study provides valuable insight into the
applicability of the rainwater harvesting for sustainable water management practice in a highly urbanized
city.

Many previous studies have investigated the role of urban greening (especially trees) on thermal comfort condition of open spaces while its influence in street canyons has, however, received relatively lower research attention. In this study, numerical experiments involving street canyons of varying aspect ratio(ARB) with embedded trees of varying aspect ratio (ART), leaf area index (LAI), leaf area density (LAD)distribution and trunk height under different wind conditions were conducted using a micro-meteorological model, ENVI-met. Employing physiological equivalent temperature (PET), the in-canyon thermal comfort was characterized. Results show variable magnitude of PET reduction (DPET)with trees of different vertical LAD distribution even though they are of similar LAI. While larger tree-covered area (TCA) ensures improved thermal comfort, the magnitude varies with tree-planting pattern. Between the tree-planting patterns in TCA = 0.6,DPET with double-rows is higher than centre tree-planting. Between eastern and western side tree-planting (TCA = 0.3), the former is more temporally effective than the latter. Furthermore, strong oblique wind condition (“without trees”) was found to be more efficient in improving thermal comfort than t rees under calm perpendicular wind,reinstating the importance of desirable ventilation in achieving a thermally comfortable environment.However, vegetation offers improved PET reduction under calmer perpendicular than stronger oblique wind condition. Finally, recommendations on applications of our key findings were presented.

Numerical experiments involving street canyons of varying aspect ratio with traffic-induced pollutants (PM 2.5) and implanted trees of varying aspect ratio, leaf area index, leaf area density distribution, trunk height, tree-covered area, and tree planting pattern under different wind conditions were conducted using a computational fluid dynamics (CFD) model, ENVI-met. Various aspects of dispersion and deposition were investigated , which include the influence of various tree configurations and wind condition on dispersion within the street canyon , pollutant mass at the free stream layer and street canyon, and comparison between mass removal by surface (leaf) depo-sition and mass enhancement due to the presence of trees. Results revealed that concentration level was enhanced especially within pedestrian level in street canyons with trees relative to their tree-free counterparts. Additionally, we found a dependence of the magnitude of concentration increase (within pedestrian level) and decrease (above pedestrian level) due to tree configuration and wind condition. Furthermore, we realized that only ∼0.1–3 % of PM 2.5 was dispersed to the free stream layer while a larger percentage (∼97 %) remained in the canyon, regardless of its aspect ratio, prevailing wind condition, and either tree-free or with tree (of various configuration). Lastly, results indicate that pollutant removal due to deposition on leaf surfaces is potentially sufficient to counterbalance the enhancement of PM 2.5 by such trees under some tree planting scenarios and wind conditions

To enhance the quality of human life in a rapidly urbanized world plagued with high transportation, the masterful contribution of improved urban and local air quality cannot be overemphasized. In order to reduce human exposure to near-road air pollution, several approaches including the installation of roadside structural barriers especially in open street areas, such as city entrances are being applied. In the present study, the air quality around real world and idealized green infrastructures was investigated by means of numerical simulation and a short field measurement campaign. Fair agreement was found between ENVI-met modelled and measured particulate matter's concentration data around a realistic vegetation barrier indicating a fair representation of reality in the model. Several numerical experiments were conducted to investigate the influence of barrier type (vegetation/hedge and green wall) and dimensions on near-road air quality. The results show different horizontal/vertical patterns and magnitudes of upwind and downwind relative concentration (with and without a barrier) depending on wind condition, barrier type and dimension. Furthermore, an integrated dispersion-deposition approach was employed to assess the impact on air quality of near-road vegetation barrier. At last, recommendations to city and urban planners on the implementation of roadside structural barriers were made.

Using field measurement and numerical simulation techniques, this study assessed the impact of tree-shading on indoor and outdoor summer thermal conditions of two similar buildings at the Federal University of Technology Akure (FUTA), Nigeria. One of the buildings was shaded by trees, while the other was unshaded. For the numerical simulation, outdoor micro-climate model, ENVI-met and Building Energy Simulation (BES) program, EnergyPlus were integrated. This modelling approach was validated using simultaneously observed air temperature and relative humidity data inside and outside both buildings during the summer period (September–November) of year 2010. Model performance statistics results indicate reasonable agreement between simulated and observed micro-climatic data at the indoor and outdoor of both buildings. The integrated models captured the evolution and magnitude of a warm-humid micro-climate of West Africa sub-region and impact of tree-shades on local thermal comfort. Furthermore, micro-scale relationship between non-radiation based thermal comfort indices (Temperature-Humidity Index, THI and Wet Bulb Globe Temperature, WBGT) and Physiological Equivalent Temperature, PET at the interior and exterior of both buildings was investigated. Result suggests preference of WBGT to THI for the assessment of local thermal condition where technical instrumenta-tion (required for PET estimation) and/or model capability is lacking irrespective of shading condition and environment (indoor or outdoor).

Tree-planting is one of the veritable tools for combating urban heat island and improving thermal comfort in the wake of global warming and urbanization. However, trees of different species and morphological properties have variable solar attenuation capacity and consequently, thermal comfort regulation potential. Besides, the shadow-cast effect by buildings helps in reducing pedestrian radiant load and consequently improves thermal comfort especially in high-density cities even though ventilation is reduced. Therefore, a holistic and contextual understanding of tree-planting and shadow-casting can help in designing climate-proof cities. In this study, we employed the ENVI-met model to better understand the interaction between these two forms of shading (trees and buildings) on the pedestrians' thermal comfort in Hong Kong and the influence of one over the other. The impact of different urban densities on the thermal comfort improvement potential by eight (8) common tree-species in Hong Kong was specifically studied. Results show that shallow canyons are susceptible to worse thermal condition when compared to their deeper counterparts with similar aspect ratio value. Of all tree configuration parameters, leaf area index, tree height and trunk height are most influential in improving and aggravating daytime and nighttime thermal comfort, respectively. We also found that trees' effectiveness in improving daytime thermal comfort reduces with increasing urban density and vice-versa for nighttime. For the reference of planners and landscape architects, this study recommends tall trees of low canopy density with high trunk in deeper canyons and vice-versa for shallow canyons and open-areas.

This paper presents a parametric study on the effect of four green-roof types on outdoor/indoor temperature and cooling demand under four different climates and three urban densities using co-simulation approach with ENVI-met and EnergyPlus. Results reveal an outdoor nighttime warming effect of not more than 0.2 • C which is most obvious with the semi-extensive while the outdoor and indoor cooling effect ranges between 0.05–0.6 • C and 0.4–1.4 • C, respectively depending on the green-roof type, urban density and time of the day. These daytime temperature reductions also vary per prevailing climates and follow this order: hot-dry, hot (or warm)-humid, and temperate which can be explained by the interplay between solar intensity/air temperature and relative humidity between the regions. In a hot-humid region, the evaporative cooling potential of greenery is dampened when compared to hot-dry region. This is also true for region with low solar intensity and humidity like the temperate region. In terms of cooling demand reduction, 5.2% was observed in hot-dry climate on the hottest day of the year with full-intensive green-roof while the least saving of 0.1% was found with semi-extensive green-roof in temperate climate. In general, for both outdoor temperature and cooling demand reduction, semi-intensive green-roof was found more effective than its full-extensive counterpart while the higher spatial green-roof is most important for indoor temperature reduction irrespective of the leaf density of the greenery. Therefore, the intent of green-roof installation should be a determining factor for the type and spatial extent to be implemented.

A B S T R A C T
To improve outdoor thermal environment and reduce indoor energy use, passive techniques including façade greenery have been suggested. In high-density cities like Hong Kong, buildings' surface area is much greater than the roof and ground surface areas combined, offering a huge vertical surface platform for greening. However, scientific evidence to assert the thermal benefit from this greening option especially at neighborhood scale is still very few. Therefore, this study was designed to provide such evidence using results from validated ENVI-met model simulation. Thereafter, parametric study was conducted to investigate the quantity and location of facade greening required for potential air cooling and thermal comfort improvement of a neighborhood of varying densities. Model validation results revealed an acceptable modelling of facade surface temperature, air temperature , relative humidity and wall-emitted long-wave fluxes. From the parametric study, we found that 30–50% of facades in the high-density urban setting of Hong Kong must be greened to potentially cause ∼1 °C reduction in both daytime and nighttime air temperature while the same could help improve daytime pedestrian thermal comfort by at least one thermal class. We also established that higher greened facade ratio will be required to obtain similar thermal benefits in low and medium density urban settings. Also, realized benefits at pedestrians' height can be enhanced when the vertical greening facilities are placed along podium than tower heights. Lastly, practicable urban planning recommendations were presented for the attention of urban planners and landscape architects.

Using a validated ENVI-met model, a parametric study was conducted to investigate the thermal and energy saving benefits in a selected neighbourhood with its current greenery coverage ratio (GCR) of 7.2%, compared to the recommended 30%. To provide information for efficient tree species selection, nine scenarios were tested for the case of 30% GCR. In eight of them, only one tree species was used in each case. The trees represent the eight most common species in Hong Kong. The remaining one featured a mix of tree species. In comparison with the reference case (no trees), results revealed a reduction in maximum temperature of 0.4°C and 0.5-1.0°C under the current and 30% GCR situations respectively; and a decrease in average Physiological Equivalent Temperature of 1.6°C and 3.3-5.0°C. The area coverage of "Very Hot" thermal sensation reduced from ∼60% in the reference case to ∼50% with the current GCR and 17-21% with 30% GCR. Lastly, a decrease in cooling energy of 1500 kWh per typical summer day was observed with the current GCR, which increased to ∼1900-3000 kWh with 30% GCR, equivalent to 200-450 US$ savings within the 500 × 500 m 2 domain. The variations in the estimated benefits between the 30% GCR scenarios reflect the importance of species-specific analysis. Statistical analysis revealed leaf area index was the main driver of the observed benefits, followed by trunk height, tree height and crown diameter. Our findings will encourage city planners and citizens to take actions for urban greening.

Nigerian agriculture is mainly rain-fed and basically dependent on the vagaries of weather especially rainfall. Nigeria today has about forty-four (44) weather observation stations which provide measurement of rainfall amount for different locations across the country. Hence, this study investigates change detection in rainfall pattern over each climatic zone of Nigeria. Data were collected for 90 years (1910-1999) period for all the weather observation stations in Nigeria, while a subdivision was made to three (3) non-overlapping climate period of 30 years i.

This study investigates the effect of tree-shading on energy demand in two similar buildings. Outdoor and indoor air temperature was measured simultaneously for a period of 6 months. Five different base temperatures ranging from 20 • C to 25 • C were chosen and used to calculate cooling degree-days. Degreeday and cooling/warming rate methods were used to estimate cooling energy requirements for the two buildings. Indoor and outdoor cooling degree days were observed to be more for the un-shaded buildings compared to the tree-shaded one. Indoor warming and cooling rate show that the un-shaded building warms earlier and faster than the tree-shaded. Results indicate that tree-shading can save up to 34,500 NGN (US$218) on energy costs. The study shows the role of greening in reducing energy demand in buildings.