Microclimate & Urban Heat Island Modeling D E V S Kir Kiran an Ku Kumar mar The Energy and Resour Resources ces Institute
Approach to Passive design
Micro climate
Geometry
Orientation
Envelope design
Envelope Materials
Microclimate Climate The Sun & Wind Temperature, relative humidity, sky condition, radiation, wind flow Microclimate Water bodies, vegetation, landform, soil condition, wind pattern,
Heat Islands
Understanding heat islands Time (day/ night) Season
Climate
Wind
Topography
Cloud cover
surroundings
UHI Ground cover Building geometry & materials used
Energy use in buildings pollution
Understanding heat islands
Understanding heat islands
Building related parameters •
Albedo (Solar Reflective Index)
•
Green Cover (Leaf Area Index)
•
Building Geometry (Sky view factor)
Solar Reflective Index
Albedo
Albedo
5%
43%
52%
Albedo
Sky View Factor
Building Geometry
Radiant Temperature 39.7⁰C
Radiant Temperature 36.8⁰C
Leaf Area Index
Leaf Area Index
Moot points
Area of treatment
Built Density
Tree Characteristics
Reflective pavements need be considered cautiously in a dense urban scenario as higher cooling loads were observed due to increased larger ground albedo
Roof is the more critical area to change its surface type and reducing the air temperatures
The impa impact ct of heat island in a highly vegetated vegetated environment depends on the tree characteristics
Activity Narrow streets with respect to lower solar exposure is important in case of pedestrian movement
Climate Higher temperatures during winter nights might be helpful in providing human thermal comfort and hence reducing the energy costs
Understanding Understanding UHI •
UHI can be classified as –
Surface Urban heat Island (based on surface temperatures)
–
Atmospheric Urban heat island (based on air temperatures) temperatures)
General UHI Profile
Surface & Atmospheric UHI
•
Concrete paved areas usually result in higher surface temperatures than the air temperature
•
Shaded or moist surfaces show close to the air temperatures
Measuring microclimate
Local/ Micro scale
Urban/ Meso scale
•
•
Fixed stations are usually preferred –
Temperature probe kept at 1.21.5m from ground
Traverse automobile measurements are usually preferred
Measuring microclimate
Thermo-hygro data logger
WBGT Heat Stress Meter
IR- Thermometer
High resolution infrared camera
Effect of Vegetation •
Roof area
:22.7%
•
Road Area
:0%
•
Green Area/ open Area
: 77.3%
•
Urban area
•
Highly vegetated area with all matured trees
•
Less Built up
2-4m
Effect of Vegetation
•
The maximum day time temperature recorded at highly vegetated IISc is 2.4degC lower compared to less vegetated Palace Road
•
Night temperatures recorded at IISc are 1.5degC higher than palace road
Effect of Water body •
Roof area
:32.5%
•
Road Area
:15.8%
•
Water body Area
:34.1%
•
Green Area/ open Area
:17.6%
•
Urban area/ city center
•
Development around a water body
•
Less open area and medium vegetation
2-4m
Effect of water body
•
•
Almost 3 degC lower air temperatures observed at Ulsoor lake during night Higher relative humidity & lower temperatures makes the locations cooler compared to other areas
Impact of reflective roofs and roof gardens
•
Reduction in peak air temperature –
1.5⁰C incase of Reflective roof
–
1.9⁰C incase of Green roofs
ENVI-met •
Developed by Michael Bruse of the University of Bochum, Germany
•
Three- dimensional computer model that simulates surface-plant-air interactions within urban environments
•
Fluid dynamic characteristics such as air flow and turbulence
•
Thermodynamic process that takes place at the ground surface, walls, roofs and plants
The major prognostic variables of the model are wind speed and direction, air temperature, humidity and radiative fluxes
Why Microclimate modeling? •
To develop scientific knowledge based recommendations for sustainable urban development policies –
setbacks,
–
roof top solar pv,
–
reflective roofs,
–
vegetation requirements,
–
development density ratios
–
Imperviousness factors etc..,
ENVI-met
Atmosphere Air temperature, relative humidity Wind Turbulence Radiate Fluxes Pollutant Dispersion
Soil Surface and Soil temperature Water bodies and ponds Soil water content Vegetation water supply
Built Environment Vegetation Model
Building geometry, walls
3D plant Geometry
Building Materials
Foliage Temperature
Building Physics
Exchange Processes with environment
Green walls & Roof systems
Vegetation health
Building energy performance
ENVI-met
Software installation requirements
ENVI-met •
The tool works in two steps –
First is editing the Area input file to provide information on building, soil and vegetation
–
In the second step editing the configuration file to provide the information about site’s geographical location, temperature, wind movement, humidity and other required output parameters would be entered into the tool
Input file •
The input file that is prepared can be edited into each cell of the model
•
The resolution of cells can be as large as 10m and as fine as 0.5m
•
The program has modules of working areas up to 250X250 cells
•
To minimize boundary effects which may distort the output data, the model uses an area of nesting grids around the core of the model
•
The tool takes information about the day of simulation from input data and adjusts the sun position accordingly
Example
Input Data Parameter
High reflective roof case
Heat Transmittance (U-Value) of roof
3.74W/m2K (for RCC with Brickbat coba)
Reflectance of roof
0.9
Reflectance of wall
0.8
Simulation time
14.03.2016 & 06:00:00
Simulation interval and duration
1hr & 24hrs
Wind speed & Direction
3 m/s & SW
Ambient Temperature
28.0○C
Relative Humidity
70.%
Indoor Building Temperature
27.0○C
Start Bar
Main Screen
Area Input file Configura tion file
Output Visualization
Help
Tool Bar Selection options
Model Settings
Area input sheet
Background settings
Model Analyser overiview
Model Settings
Give same name for input as well as configuration file
Save the file in C:\ENVImet31\ with extension .cf
Check only what is required
Check for errors; Fix the errors
Run Simulation
Analyse and extract data from here
