Software Limitations

unusually severe and long lasting, were used to construct the boundary conditions for the simulation. A cloudless January 15 with a medium wind speed (0.5m/s in 8m above ground) was chosen as the worstcase scenario date for the simulation. With this set-up, the simulated day's irradiation is at its highest, and the amount of cooling provided by wind is minimal.

The simulation began at 9 a.m. and ended at 10 p.m. Just the average extreme heat hour results, i.e., 2 PM, are considered in the discussion that follows.

The scale of the plan changes depending on how many pixels are used in the program. For the selected area to fit in the model of 180 X 200, each pixel represents 4 meters in the plan. The true condition file was created, and four different scenarios were proposed around it. The true condition file is the one that is the closest to the current situation, while the other scenarios use mitigation strategies that promote the use of renewable energy.

Simulator settings were applied once the models had been created in the map area and transferred into the simulation settings. Pavement and asphalt are included in the map region along with a variety of building types and heights. The 3D model is being created at the same time as the 2D plan in the case. Because the buildings' heights vary, a scale factor has been used to the 3D to provide a lighter model.

Using the ENVI-Area met's Input file editor, the model was rotated by -20° clockwise to match the main development direction of the roadways. A thicker grid towards the ground allows for higher precision in identifying edge effects since the grid has a fixed spacing on the x and y - axis but is telescopic on the z axis (1.20 m is the mean value). As a result, the model's maximum height is 36 m (1.20 30 m). For the model to be numerically stable, the height of the highest building must be at least twice as high as this value. With three types of façade materials (Appendix) and a mix of good and moderate insulation at heights ranging from 18 meters to 36 meters, buildings in the model are taken into consideration for the study. Different plant varieties have been used to model the vegetation. For the most part, the area has been paved with typical soil, with the significant exception of the main road, which is paved with asphalt.

All the models use the same basic inputs for their simulations. However, because of the proposed complexity, the values for each case model differ. Each model had a total 6-hour profile set for the same period, and the simulations predicted 48 hours of downtime. Due to the large size of each model, the simulation took on average 50 hours to finish.

Software Limitations ENVI-met is continually being developed, and it is getting new features all the time. Although it comes close to accurately simulating reality, ENVI-met does have certain (significant) drawbacks.

The following is a brief list of ENVI-met's most significant limitations:

• Precipitation in model: ENVI-met is unable to simulate precipitation or temperatures below zero degrees • Radiation: In the model area, the radiative fluxes have been neglected. - The above and down diffuse radiation scattering is termed isotropic.

- plants have little impact on diffuse short-wave radiation. To put it differently: When light travels through vegetation, it is not absorbed and is not converted to diffuse light (i.e., no scattering of direct short-wave radiation). - the soil and vegetation scattering short wave radiation upwards are not considered. - However, it is determined by taking an average temperature of all the leaves and surfaces within a given field of view, not just those that are directly exposed to incoming long wave radiation. - In locations with colder surfaces (such as a small inner courtyard), the high frequency radiation budget is overstated, while near warmer surfaces, it is undervalued.

• Soil model: The irrigation of soil/plants cannot be replicated at this time. • Turbulence (k): There is evidence to suggest that the typical ENVI-met k-closure overestimates turbulence generation when applied to flows around buildings, when acceleration and deceleration are high. ENVI-met simulations frequently exhibit this behavior. Several k closing adjustments have been proposed to address or at least reduce this issue. The Kato Launder modification (Kato and

Launder, 1993) appears to be the most often utilized and gives the best outcomes (Huttner n.d.). This change was also tested in ENVI-met, but it was not adopted because it only marginally reduced the value of k near stagnation points, but it also increased the likelihood of numerical instabilities in the simulations (Huttner n.d.).

A complete reprogramming of ENVI-met would be required for other ways of closing turbulent kinetic energy, such as Large Eddy Simulation or Direct Numerical Simulation (DNS), and these approaches will not be applicable to ENVI-met for the near future.

• Materials: When trying to use a wide range of materials on different surfaces, the model ran into several issues. For the program to be more effective, the materials must be improved (in this scenario, the facade materials & the solar panel implementation to improve the heat fluxes) (Appendix)

• Poly crystalline photovoltaic (PV) solar roof panels: Properties of photovoltaic solar panel module components are taken into consideration for the model simulation. These components are horizontally installed in an open system above a roof surface and vertically installed on the facade of the building. These components' input parameters are entered manually because the software does not provide the Solar Panel materials or a default configuration for them. Thus the input for the PV panels is details in the Appendix.

The impact of these inadequacies on the simulations' outcomes is highly dependent on the model's design. However, the user must be aware of the limits of ENVI-met and have at least a basic understanding of atmospheric physics to evaluate the quality of a simulation.

The Proposals & Discussion

The Proposals and Discussions

Four possible configurations of the model have been evaluated for analyzing the impact of the key tools to reduce the effects of urban microclimate:

• Total Site area – 26.61 Acres (10.7 Hectares) • Total four proposals are taken in consideration • With each alternative case and their results, the best is recommended – Solar Panels on Façade +

Green Roof • Simulation is done for the warmest month in Sydney by selecting extreme heat day and time as per

City of Sydney 2020 records

Figure 8: Plans showing the 2D plans for actual condition (left) of the site and proposed site (right)