UHI: implications for architecture and urban design

Transcription

1 UHI: implications for architecture and urban design Ardeshir Mahdavi University Professor and Director Department of Building Physics and Building Ecology Vienna University of Technology, Austria

2 Climate is changing Temperature in eastern Austria next 30 years 1.3 Khigher than last 80 years. Summer temperatures in urban areas up to 2.5 K higher. A. Mahdavi - UHI: implications for architecture and urban design 2

3 Cities face the Urban Heat Island effect Source:

4 Implications energy and environment Buildings use ca. 40% energy use for heating, cooling, ventilation, lighting. Climate change and urban heat island effect further increase buildings' energy demand (particularly cooling)

5 Implications energy and environment 70 heating demand reduction 600% cooling demand increase Relative deviation Heating energy demand [%] B3 B1 B2 Relative deviation Cooling energy demand [%] 500% % 300% 200% 100% B1 B2 B % % -10% Relative deviation HDD [%] % -30% 40% 110% 180% 250% 320% 390% 460% Relative deviation CDH [%] A. Mahdavi - UHI: implications for architecture and urban design 5

6 Implications human health and comfort Urban heat waves Heat stroke stagnant atmospheric conditions trap pollutants in the air, which can trigger respiratory problems for many people.

7 Mitigation and adaptation 1. Historical precedents 2. New buildings/settlements 3. Existing buildings/settlements

8 Historical precedents

9 Historical precedents

10 Historical precedents

11 Historical precedents

12 Day-Night Temperature Difference

13 Day-Night Temperature Difference

14 Evaporative Cooling Effect

15 Historical precedents

16 Historical precedents

17 Historical precedents

18 Historical precedents

19 Historical precedents

20 Historical precedents

21 New buildings/settlements: a new development area Questions: Area 1 Area 2 Thermal performance of housing and office areas for current and future microclimatic condition Alternative building designs (surface designs, effect of trees)

22 Selected Buildings Area 1 Area 2 Apartment/office distribution of selected building block Area 1: 95% apartment 5% office Area 2: 60% apartment 40% office U-value: external walls and roof 0.11 U-value: windows 1.1 Glazing area as percentage of facade area 30 Internal gains apartments: 3; offices: 4 Occupancy density apartments: 33; offices: 14

23 Scenarios Scenario Roof Façade Trees GG_T Green Green Yes GG_N Green Green No GW_T Green White Yes GW_N Green White No GD_T Green Dark Yes GD_N Green Dark No PW_T Pebble White Yes PW_N Pebble White No A. Mahdavi - UHI: implications for architecture and urban design 23

24 Results Building designs Heating load [kwh.m -2.a -1 ] T N Cooling load [kwh.m -2.a -1 ] T N 0 0 GG GW GD PW GG GW GD PW Heating load-reduction [%] Cooling load-reduction [%] GG GW GD PW GG GW GD PW A. Mahdavi - UHI: implications for architecture and urban design 24

25 Results Climatic assumptions Year HDD CDH Present Future Heating load [kwh.m -2.a -1 ] T N Cooling load [kwh.m -2.a -1 ] T N 0 GW present GW future 0 GW present GW future

26 Results Overheating Mean overheating [K] T N Mean overheating [K] GG GW GD PW 0 GW present GW future T N T_with blinds N_with blinds 26

27 Existing building stock The case of Austria: Existing building stock = dominant energy sink Annual construction rate of new buildings ca 1% of existing building stock Almost 85% of existing buildings in Vienna older than 30 years

28 Active cooling (air-conditioning) implications A. Mahdavi - UHI: implications for architecture and urban design 28

29 Cooling via temperature gradient and thermal mass Maximum acceptable indoor temperature Temperature Time Outdoor temperature

30 Implementation in an existing office building

31 Shading and ventilation control (office) Temperature [ o C] OH m = n i= 1 θi θr n 00:00 06:00 12:00 18:00 00:00 Scenario Ventilation Shading (window opening in %) Time day S0 night S1 S2 S3 S0 S4 3 1S5 NoS6 S1 3 1 Yes θ e S Yes S3 Scenarios 30 S0 S130 S2 Yes S3 S4 S5 S6 S4 OH m [K] Yes S5 Rank Yes S Yes 31

32 R1 R2 R3

33 R1 R2 R3

34 Mitigation and adaptation 1. Efficient land/space usage 2. Reduction of vehicular traffic 3. Renewable (low-carbon) energy 4. Greenery, water, and solar control 5. Climatically responsive architecture 6. Passive environmental controls A. Mahdavi - UHI: implications for architecture and urban design 34

35 UHI: implications for architecture and urban design Ardeshir Mahdavi University Professor and Director Department of Building Physics and Building Ecology Vienna University of Technology, Austria