3.6 The Computer Software Validation
3.6.1 The Validation of the Outdoor Microclimate Simulation Software ENVI-Met
In order to validate the accuracy of the selected microclimate simulation software ENVI-Met v.4.1, a pilot study was conducted to collect the field microclimate data required to be compared with data generated as a simulation results. The pilot study was conducted in the selected case study location on 26th of February, 2017.The site located in Dubai, in The Greens compound of mid-rise buildings.
The chosen site consists of eight buildings as a combination of G+4 and G+7 buildings. The dimensions of the G+4 buildings are 25m*60m, and the dimensions of G+7 buildings are 25m*30m. The average height of each floor is 4m and the total height of each type of buildings is 20m and 32m, respectively. Figure 3.16 shows the selected area for software validation. The main street and canyon of the block is 20 m in width, while the setback between the buildings is 10m. Four types of plants were observed that forms the landscaped
127 and planting area in the setback canyon between the buildings. In addition of the few number of plants are distributed in the main canyon/ street between the buildings. Figure 3.17 shows the location of the measurement tool in the main canyon.
Figure 3.16:The canyon in the case study area for software validation(Author, 2108)
3.6.1.1 The Microclimate Measurement Tool and Data Collection
The tool that is used for the microclimate data measurements and collection is the 4-in-1 Environmental Meter-model 45170.This tool allows to measure four of the microclimate parameters at specific point. The parameters that can be measured using this tool covers: Air Temperature, Relative Humidity, Air flow and light level. The tool is an ergonomic pocket size housing, with a LCD simultaneous display of weather data (Figure 3.17). Furthermore, the tool allows to hold the displayed value and records the Min/Max readings. The range of the measured air temperature by this device is varied between 0° C - 50° C, while it can dedicate the wind velocity from 0.4m/s up to 30m/s. The accuracy of the device for air temperature and wind velocity is ±3% and ±1.2 ° C respectively. In this research, the data collected for the software validation covers the air temperature over12 hours. The data was collected from specific point in the chosen site at a level of 1.4m, and it is compared with
128 receptor data generated using the ENVI-Met v.4.1 at the same level using the ᵒC unit (Figure 3.17).
Figure 3.17: The location and the tool used for microclimate data measurements (Author, 2108)
3.6.1.2 The Simulation Model, Process and Results
The indicated site was modelled using the ENVI-Met software v.4.1. The grid dimensions selected is 80*40*40 to represent the x,y,z dimensions of the model respectively. The cell size selected is x=5, y=5 and z=2. The weather file has been chosen from the built-in weather files that indicates the sun path and solar access of the location of Dubai, UAE. In addition to the block of the buildings mentioned previously, the site consists of four types of planets in general. The plants were represented by using the built-in vegetation types in the ENVI-Met v. 4.1 database. The first type is (AC) Acacia with a height of 2m and crown width of 3m.
The second type is (PI) Pine Tree with a height of 4m and crown width of 5m. The (ZI) Zitrusbaum is the third type with a height of 4m and crown width of 3m. The fourth type is (A3) KL.Robinie with a height of 12 m and crown width of 7 m.
The initial setting data used for running the software covers location indication, air temperature, relative humidity, wind speed and direction. The initial temperature of starting the simulation process is 21ᵒC, wind speed is 3m/s, and the relative humidity is 64 %.
129 Other values related to planet and soil specifications are kept according to the default data built in the software file database. The simulated model and the measured data is illustrated in detail in appendix A.1. The microclimate parameter selected for software validation is the air temperature, and one receptor is indicated in the model to represent the exact location of the site station. The data collected at level of 1.4 m over 12 hours of measurement starting from 7:00 am to 7:00 pm, with a records of air temperature at the beginning of each hour. The simulation starting time has been chosen is 4:00 am before the sunrise and continuo for 24h to avoid the underestimation data reported by previous studies (Emmanuel and Fernand, 2007). Figure 3.18 illustrates the calibration between the measured and simulated air temperature, and a good and strong correlation is found at the starting and ending of the simulation loop respectively. However, some variation has been observed at the peak time.
Figure 3.18: Measured and simulated data relation for ENVI-Met software validation on 26th of February (Author, 2018)
15 17 19 21 23 25 27
07:00 08:00 09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00
Air Temperature °C
Mesured Data Simulated Data
y = 0.844x + 2.326 R² = 0.862
20.5 21.5 22.5 23.5 24.5
21 21.5 22 22.5 23 23.5 24 24.5 25 25.5 26 26.5
Actual and Simulated Air Temp. °C
Actual and …
130 The variation in the data between 1:00 pm and 5:00 pm may related to the transportation effect on increasing the actual measured air temperature as this is the time of school bus drop off, and this residential area is occupied by families with 2-3 number of children in average.
Furthermore, the validity of the previous versions of the ENVI-Met software has been proven in many studies (Ali-Toudert, 2005; Meng et al., 2012; Al Znafer, 2014). Figure 3.19 shows the strong relation between the measured and the simulated data using the ENVI-Met 3.1 (Tseliou and Tsiros, 2016).
Figure 3.19: ENVI-Met v.3.1 validation (Tseliou and Tsiros, 2016)