Physical Activities Complex

In Figure 5.2, monthly-accumulated solar radiation distribution maps of the PAC building rooftop throughout the year are shown with standardized and uniform legends. According to the maps, the seasonal variation of radiation values can be observed. January and December show the least amount of solar radiation received, while June and July received the greatest levels of solar radiation. Roof corners and edges that are completely shaded throughout the year were evident. In each monthly map, the southern, northern, eastern and main rooftops (labeled in Figure 5.6) receive more solar radiation than other rooftops. In order to explore the detailed spatial variation of solar radiation for each month, different legend ranges were adopted with red areas indicating the greatest amounts of solar radiation received, while green areas represent shadow areas with the least incoming solar radiation. Figure 5.3 shows the monthly maps with map legends displaying different ranges of radiation values. Maximum radiation values in each month show that the radiation values in October, November, December, January, February, and March are much lower than during the rest of the year.

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Figure 5.2 - Monthly solar radiation maps of the Physical Activities Complex (PAC) Building with

standardized legends

In Figure 5.3, it is apparent that edges and corners of the rooftops receive less insolation than the roof center areas throughout the year. Comparing the lower eastern and western rooftops (labeled in Figure 5.6), it was noticeable that the eastern rooftop receives more solar radiation than the western, especially during the winter months. The PAC rooftops with higher elevation show greater insolation received than rooftops with lower elevation, since the taller roof shadows surrounding nearby areas, especially when the angle of incidence decreases. This pattern can be easily noticed from the northern lower rooftop, which is constantly shaded by the main rooftop. However, there is an exception for the lower rooftop of the southern side of the building (namely the southern rooftop), which has an approximately 10° slope with a south orientation. Due to the building’s latitude, this rooftop is not blocked by the taller roof on the northern side (namely the main rooftop) and hence, not obscured by shadow effects. During summer months, the sun’s rays reach the ground at a more perpendicular angle in the northern

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hemisphere than in other seasons, and the insolation amount is higher overall. The main rooftop receives the greatest amount of insolation in June and July, while the southern rooftop tends to receive the greatest insolation, except in June and July due to the increased solar incidence angle in summer.

Figure 5.3 - Monthly solar radiation maps of the Physical Activities Complex (PAC) Building with

different individual legends

Figure 5.4 (A) shows a one-year accumulated solar radiation map of the PAC building under clear-sky conditions. In order to better interpret the one-year accumulated solar radiation map, as well as the monthly-accumulated maps, a standard deviation map providing information about how much variation exists in average incoming solar radiation is shown in Figure 5.4 (B). Overall, the standard deviation values are high, since solar radiation varies widely seasonally.

In Figure 5.4 (A), areas with the highest accumulated insolation amount through the entire year are displayed in red, while the lowest are in green. Specifically, the southern

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rooftop receives the most accumulated solar radiation (around 1300 kWh/m2/yr). As mentioned above, the southern rooftop consistently receives the highest amount of incoming solar radiation; therefore, it shows a very low standard deviation. The standard deviation of the southern rooftop compared to its yearly average radiation is approximately 51,175 WH/m2 to 52,924 WH/m2. Area receiving the second highest amount of insolation over a year is the main rooftop. However, according to the monthly maps and the standard deviation map, the amount of solar radiation that strikes the main rooftop varies greatly within one year. Due to the higher height of the main rooftop, a significant shading effect is caused along the northern lower rooftop and northern rooftop below. The northern rooftop obtains less accumulated insolation compared to rooftops located in the south. The south-most part of the northern rooftop, displayed in red in Figure 5.4 (B), shows the highest variation in one year because shadows caused by taller buildings vary according to seasonal changes in solar angle. The deviation of this part is about 58,171 WH/m2 to 64,557 WH/m2. Areas consistently shaded throughout the year, such as roof corners and roof edges, show the lowest standard deviation.

Figure 5.4 - A: One year accumulated solar radiation map of the PAC building; B: Standard deviation of

solar radiation of the PAC building.

A shadow mask map of the PAC building was produced and shown in Figure 5.5 (A), which shows areas covered by shadow versus areas exposed to the sun. According to the shadow map, there are about 4000 m2 of the rooftop areas that are free of shadow effects throughout the year, while the overall rooftop area is almost 7000 m2. Pixels in light grey

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on the northern rooftop have an 8.3% probability of being shaded, indicating a one-month probability. It appears that potential shadow effects are caused by trees close to the PAC building in December. 4.4% of the PAC rooftop area has shadow probabilities of 16.7% and 25%, and these areas are almost located at the roof edges. Probabilities greater than 25% indicate that areas have more than one season of probability to be blocked from the sun.

In the classified map (Figure 5.5 (B)), areas shown in white are the non-shaded areas. In contrast, areas in black mean that the probability of shadow covering those areas is greater than 75%, indicating that throughout the year over nine months those areas are influenced by shadow effects. Such areas are considered to be completely shaded, and should be avoided for solar panel installation. Areas having 50% to 75% of shadow risks are almost shaded areas, indicating that the areas are shaded more than half of a year. By comparing the shadow mask of the PAC building to its yearly-accumulated solar radiation map, it was verified that areas with high shadow risks do indeed receive much less solar radiation than other areas. Areas classified as unshaded areas are considered as optimal installation places in the present study.

Figure 5.5 - Shadow masks of the PAC building. A: Unclassified shadow mask; B: Classified shadow

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Since dimension and shape of the site should be taken into account when considering suitable installation sites, a minimum area of 1.4 m2 were used to screen appropriate areas for solar panel installation. As a result, roof corners and small discrete shapes may be excluded. In Figure 5.6, areas with less than 25% probability of shading effects are highlighted. The overall dimension of these areas is about 3,705 m2. Associated with the annual solar radiation map, the yearly average radiation output is about 1,162.9 kWh/m2, while the minimum yearly output is 1,023 kWh/m2. If the future installed panels have a conversion efficiency of 15%, which is an average efficiency for typical solar panels (e.g., Bielinskas, 2012), the average annual electricity output would be 174.4 kWh/m2.

Figure 5.6 - Areas on the PAC building rooftop with less than 25% of shadow risks overlaid on an

orthoimage