1. Building for the climate - The impact of heat mitigation strategies on thermal comfort in Melbourne's suburbs
Joseph Oppedisano, Nigel Tapper, Andrew Coutts
CRC for Water Sensitive Cities
School of Earth Atmosphere and Environment, Monash University
Background
Urban warmth, climate change and climatic variability continue to exacerbate challenges posed to the urban environment and heat-related illnesses. In January 2009 Victoria experienced a heatwave with temperatures °C above normal climatic conditions leading to a 34 fold increase in heat related illnesses and 374 excess deaths (Department of Health, 2012). Therefore, it is becoming increasingly important to establish heat mitigation strategies in urban areas and implement them successfully. Loughnan, Carroll and Tapper (2014) emphasize that the relationship between housing and heat wave resilience emerge from numerous factors including housing design and adaptation. Residential dwellings can have a significant impact upon reducing the severity of heatwaves through improving the materials used in the building envelope and Urban Green Infrastructure (UGI) used on site. Consequently, residents could remain in a state of thermal comfort and reduce their reliance upon artificial heating and cooling. This study aimed to examine and quantify the potential benefits of UGI using two building material schedules in townhouses that typify the urban infill phenomenon in Melbourne, Australia.
Energy Conservation during the January 2014 heat wave % %
Figure 1. The average reduction in artificial cooling recorded following temperatures exceeding 35 °C during the 15th January to 18th January 2014 heatwave
Indoor temperature changes during Jan 2014 heat wave
28.7 °C
Methods
A series of building design scenarios were examined to compare heat wave resilience using DesignBuilder and EnergyPlus software.
Construction materials schedule
1. As Constructed - The actual materials used in the dwellings (used as the ‘control scenario’) including an insulation and glazing schedule that is compliant with the NatHERS 6-star energy rating.
2. Best Practice - Thermally efficient construction materials used including double glazed, low emissivity windows, improved insulation ratings for the external walls and ceiling, wooden window frames, overhang shadings and reflective slats.
Combined with Urban Green Infrastructure °C
Figure 2. The average reduction in daily maximum indoor temperature recorded following dry-bulb temperatures exceeding 35 °C during the 15th January to 18th January 2014 heatwave
Direct solar gains during the January 2014 heat wave
kWh
1. Control
2. Green Roof
Figure 3. The average reduction in direct solar gains recorded following dry-bulb temperatures exceeding 35 °C during the 15th January to 18th January 2014 heatwave
Discussion & Conclusion
Both UGI and best practice materials can increase resilience by improving both indoor thermal comfort and energy conservation. The greatest temperature reduction was achieved with a combination of best practice materials and a green roof which reduced average indoor temperatures by 3 °C during heatwave conditions.
Green roofs were the most effective green infrastructure strategy for improved indoor heat mitigation followed by green walls and both share a positive impact upon indoor thermal comfort and energy conservation.
Improving the building materials was more effective in improving indoor thermal comfort and energy conservation than implementing green infrastructure. The use of best practice materials reduced the extent that UGI improved indoor climate.
Tree shadings were important in reducing direct solar gains; both thermally efficient materials and tree shadings can combine to reduce factors contributing to heat stress from direct solar irradiance (Carter et al., 2006).
In turn, residents can experience a greater extent of liveability within their home given the context of increased building density and propensity for extreme heat events. Benefits could help increase the uptake of UGI in a domestic context in low to medium density developments.
3. Green Walls
4. Tree Shadings
Results
During the January 15th-18th heat wave:
Green roofs reduced average indoor temperatures by 1.1 °C °C with natural ventilation conditions.
Green walls reduced average indoor temperatures by 0.2 °C – 0.6 °C with natural ventilation conditions.
Tree shadings had a negligible effect on average indoor temperatures but consistently reduced direct solar gains by 18% even with local shading from the best practice materials schedule.
Best practice materials reduced indoor temperatures by 2.8 °C.
Energy conservation was improved by up to 18% with a green roof and 16% for green wall dwellings when combined with best practice materials.
References
DEPARTMENT OF HEALTH January 2009 Heatwaves in Victoria: an Assessment of Health Impacts. In Department of Health (ed.). Melbourne, Victoria.
LOUGHNAN, M., CARROLL, M. & TAPPER, N. J The relationship between housing and heat wave resilience in older people. International Journal of Biometeorology.
CARTER, R., CHEUVRONT, S. N. & SAWKA, M. N Heat Related Illnesses. Sports Science Exchange, 19.