The scope of this document is to analyse and discuss the distribution of the main climatic parameters, ambient temperature, wind speed, surface temperature, outdoor thermal comfort, in the 14 different precincts for future climate in 2050 under non-mitigation and full mitigation conditions.

Project description

Overheating of cities is causing serious energy, environmental and health problems and it has a serious impact on the whole economic and cultural life of cities. To counterbalance the impact of high urban temperatures several mitigation technologies have been proposed, developed and implemented. Monitoring of several large-scale urban projects involving the application of mitigation technologies has demonstrated the possibility decreasing the peak ambient temperature of the precincts up to 2.5 °C.

Analysis reveals that the magnitude of the overheating depends on many parameters of which the more important are: The layout and the characteristics of the buildings and open spaces, the type of the materials used, the released anthropogenic heat, the land use, the climatic conditions, etc.

The main objectives of the study are:

  • To investigate the impact of building height, street width, aspect ratio, built area ratio, orientation and dimensions of open spaces to the distribution of the ambient and surface temperature as well as on thermal comfort conditions in open spaces.
  • To propose appropriate adaptation and mitigation technologies to decrease the energy consumption of buildings and quantify their impact.
  • To assess the current impact of the above parameters on the energy consumption of buildings in a precinct.
  • To evaluate the impact of the cooling potential of the common mitigation technologies influenced by the layout and characteristics of precincts.
  • To propose advanced mitigation techniques aiming to decrease the amplitude of urban overheating through the proper design of buildings and precincts.

The methodology described below was followed:

  1. A total of 14 residential typologies have been used to provide a logical categorisation of residential areas that can support micro-climatic and energy consumption analyses.
  2. Mesoscale climatic models have been used to simulate the climatic conditions in the Sydney area for the actual land use and climatic conditions, as well as for the future climate and land use in 2050.
  3. Microscale simulations to predict the distribution of the main climatic parameters, ambient temperature, wind speed, surface temperature, outdoor thermal comfort, in the 14 different precincts were carried out for representative days of the summer period using the previously defined climatic data for the scenario of 2050 under non-mitigation and full mitigation conditions.

The results and conclusion have shown that:

To evaluate the cooling potential of each of the 14 considered precincts, a new parameter called ‘Gradient of the Temperature Decrease along the Precinct Axis’, GTD, was developed.

  • For the scenarios including mitigation GTD, varies between 0.01 K/m to 0.004 K/m. 
  • For the scenarios without mitigation GTD, varies between 0.0093 K/m to 0.0024 K/m.
  • The maximum expected temperature difference between precincts of about 40,000 m2, employing the same mitigation measures, caused by different layout and characteristics of the buildings and open spaces, may be close to 0.9 °C for a reference ambient temperature of 32 °C, and a wind speed of about 2 m/sec. 
  • The maximum expected temperature difference between precincts of about 40,000 m2, without any mitigation measure, is close to 1.5 °C, for a reference ambient temperature of 33 °C, and a wind speed of about 2 m/sec.
  • The cooling potential caused by an appropriate layout of the precincts is decreasing when mitigation technologies are used, compared to the cooling potential of the same precinct without mitigation, because the utilisability factor.  
  • Analysis of the results shows that advection is the major mechanism to transfer heat to the precincts. There is a strong relation between the flux of heat because of the wind and the GTD values. 
  • There is a strong correlation between the GTD of all the precincts with and without mitigation, and the corresponding average aspect ratio, (Height of buildings to Width of streets), of the precincts. The higher the aspect ratio of the precinct the lower the Cooling Capacity This is expected, as: a) the application of cool roofs in high rise buildings has a lower impact and b) wind speed in canyons of high aspect ratios is quite higher and corresponds to a much higher advection rate.
  • There is a strong correlation between the ratio of the average wind speed in the precinct, V(average), and the incident wind speed in the limits of the precinct, Vinc, with the average aspect ratio of the precinct, H/W.
  • The layout and the characteristics of the precincts may affect the cooling energy consumption of a building of same orientation and same thermal characteristics up to 6 %.
  • The layout and the characteristics of the precincts may affect the total cooling energy consumption per square meter, of all buildings in a precinct, with different orientation and façade and thermal characteristics up to 53 % when buildings are extremely well shaded, or up to 93 % when the shading coefficient is average.

Project participants

Project Leader: Scientia Prof Mattheos Santamouris
Research team: Dr Shamila Haddad, Samira Garshasbi, Dr Carlos Bartesaghi Koc, Dr Riccardo Paolini

Contact person

Prof Mattheos Santamouris, m.santamouris@unsw.edu.au

Links

https://apo.org.au/sites/default/files/resource-files/2019/05/apo-nid243866-1368861.pdf