The Use of Reflective and Permeable Pavements as a Potential Practice for Heat Island Mitigation and Stormwater Management

Transcription

1 The Use of Reflective and Permeable Pavements as a Potential Practice for Heat Island Mitigation and Stormwater Management H. Li 1*, J. T. Harvey 2, T. J. Holland 3 and M. Kayhanian 4 1, 2 University of California Pavement Research Center, Department of Civil and Environmental Engineering, University of California, Davis, CA California Department of Transportation, Sacramento, CA Department of Civil and Environmental Engineering, University of California, Davis, CA * hili@ucdavis.edu, 2 jtharvey@ucdavis.edu, 3 t.joe.holland@dot.ca.gov, 4 mdkayhanian@ucdavis.edu * (ph), (fax) A Supplementary material A.1 Diurnal variation of surface temperatures of different pavements It is revealed previously that the highest and lowest pavement temperatures happen at the pavement surface. The critical pavement surface temperatures have a great influence on the near-surface air temperature and consequently affect the human thermal comfort and air quality. To further examine the diurnal variation of pavement surface temperature in different seasons, the surface temperatures of three different pavements (concrete C1, paver A1 and asphalt B1) in one clear sunny day of each season are plotted in Figure A.1. The weather data (ambient air temperature, wind speed and solar radiation), which were measured from a nearby weather station at around 2 m high from ground, are also presented in Figure A.1 for reference. 1

2 Temperature ( C) C1_Surf ace A1_Surf ace B1_Surf ace Air Temp. Wind Speed Solar Radiation (a) Winter Solar Radiation W m 2 Temperature ( C) C1_Surf ace A1_Surf ace B1_Surf ace Air Temp. Wind Speed Solar Radiation (b) Spring Solar Radiation W m 2 Temperature ( C) /16 1/17 C1_Surf ace A1_Surf ace B1_Surf ace Air Temp. Wind Speed Solar Radiation (c) Summer Solar Radiation W m 2 Temperature ( C) /6 4/7 C1_Surf ace A1_Surf ace B1_Surf ace Air Temp. Wind Speed Solar Radiation (d) Fall Solar Radiation W m /1 7/ /17 1/18 Figure A.1. Diurnal variation of surface temperatures and weather data in one day of each season. [Weather data (Air Temp., Wind Speed and Solar Radiation) were measured from a nearby weather station at around 2 m high from ground.] (Wind Speed shown in the left y axis in m/s) It is clearly shown that there are differences in temperature for different pavements, especially around noon with high solar radiation intensity. The black asphalt pavement (B1) has higher surface temperature than concrete (C1) and paver (A1) pavements with light color. The temperature of paver pavement is slightly higher than that of concrete. The surface temperature of the asphalt pavement (B1) reaches up to almost 7 C (158 F) in summer (Figure A.1(c)), compared to 5 C (122 F) of the concrete pavement (C1). The differences of peak temperatures between asphalt (B1) and concrete (C1) pavements are about 1 to 2 C, depending on the weather conditions and seasons. During nighttime, the surface temperatures of the three pavements are very close to each other, but still higher than the ambient air temperature by 2 to 1 C. The difference in surface temperatures between asphalt and concrete pavements is determined mainly by the color of pavement surfaces (i.e. the solar reflectivity or albedo). The higher the albedo of 2

3 pavement is, the more the solar radiation is reflected and the less is absorbed by the surface, which will produce a lower surface temperature. The asphalt pavement has a darker color and consequently a lower albedo and a higher surface temperature, compared to the concrete pavement. The difference of surface temperatures between them is higher (~2 vs. ~1 C) during summer with a high solar radiation [peak intensity of ~1 W/m 2 in Figure A.1(c)] than winter with a low solar radiation [peak intensity of ~5 W/m 2 in Figure A.1(a)]. This implies that increasing the albedo is an effective strategy to reduce the surface temperature, especially for the climates and seasons with high solar radiation. A.2 Seasonal variation of surface temperatures of different pavements To comprehensively evaluate the thermal performance of different pavements, it is of great significance to examine the seasonal change of surface temperatures in one year. The daily maximal and minimal surface temperatures of concrete (C1), paver (A1) and asphalt (B1) pavements over one year are extracted and plotted in Figure A.2, along with daily maximal and minimal ambient air temperatures for reference. As observed previously, the changes of daily maximal and minimal pavement surface temperatures follow the similar pattern as the ambient air temperature. The pavement surface temperatures are generally higher than the ambient air temperature over the year round, even for the daily minimal temperature during winter [Figure A.2(b)]. The daily maximal surface temperature of asphalt pavement (B1) is higher than the concrete (C1) and paver (A1) pavements and as well the ambient air temperature. The temperature differences between them are higher during summer than winter due to the difference in solar radiation of different seasons. During summer, the daily maximal surface temperature of asphalt pavement (B1) is around 2 C higher than the concrete (C1), and around 16 C higher than paver (A1) pavements and about 3 C higher than the ambient air temperature. During winter, the daily maximal surface temperature of asphalt pavement (B1) is around 1 C higher than the concrete (C1), and around 8 C higher than paver (A1) pavements and about 15 C higher than the ambient air temperature. There are no significant differences in the nighttime daily minimal surface temperatures between the three pavements for both summer and winter, which are about 1 C and 5 C higher than the ambient air temperature for summer and winter, respectively. 3

4 Temperature ( C) Max. Air Temp. Max. C1 Surface Temp. Max. A1 Surface Temp. Max. B1 Surface Temp Temperature ( F) -1 (a) Max Temperature ( C) 9/1/11 11/5/11 12/3/11 2/24/12 4/21/12 6/16/ Min. Air Temp. Min. C1 Surface Temp. Min. A1 Surface Temp. Min. B1 Surface Temp Temperature ( F) -1 (b) Min /1/11 11/5/11 12/3/11 2/24/12 4/21/12 6/16/12 Figure A.2. Daily max. and min. air temperatures and pavement surface temperatures over one year. [Concrete (C1), paver (A1) and asphalt (B1) pavements] (date format: mm/dd/yy) A.3 Thermal images of experimental pavement sections: comparison of dry and wet conditions Thermal images were taken during the irrigation experiment at different times for Jul/9/212, Jul/1/212 and Jul/11/212 for all the experimental sections along with the optical images. The water tables were monitored using small monitoring wells for the six permeable experimental sections after irrigation. The weather data were also monitored using a nearby weather station. From 3: pm Jul/1/212, water was irrigated into the permeable test sections. The irrigation was continued until each permeable pavement section was filled up with water at around 1: am Jul/11/212. After irrigation stopped, the water tables would drop over time due to the nature processes of infiltration 4

5 and evaporation. The water tables were monitored using small wells for each permeable section and are presented in Figure A.5. Water table from pavement surface (cm) A2 A3 B2 B3 C2 C3 Figure A.3. Water tables in the monitoring wells for six permeable sections after irrigation. The weather data during the experiment period were also monitored and are shown in Figure A.4. It is noted that the air temperature was increasing in the three days. The solar radiation was keeping constant for the period. The wind speed was increasing slightly and the relative humidity was decreasing slightly. 5

6 4 Air Temperature 2. Wind Speed 35 Air Temperature (C) Wind Speed (m/s) Solar Radiation (W/m2) /9/12 7/1/12 7/11/12 7/12/12 Solar Radiation Relative Humidity (%) /9/12 7/1/12 7/11/12 7/12/1 Relative Humidity /9/12 7/1/12 7/11/12 7/12/ /9/12 7/1/12 7/11/12 7/12/1 Figure A.4. Weather data during the experiment period (no rain). The thermal images at Jul/1/212 are presented in Figure A.5, along with the optical images. When water was being applied into the permeable pavements (Figure A.5), the temperatures of the pavement portions with water were as low as ~3 C, which were much lower than the pavement portion without water. This implies that watering can be an effective way to lower down the pavement temperature in summer. Comparison of thermal images of six permeable pavements under dry, watering and wet conditions is presented in Figure A.6. As observed previously, under the watering condition (Jul/1/212) the pavements had much lower temperatures than under the dry condition (Jul /9/212). Even in the third day (Jul /11/212) without watering but with higher air temperature (see Figure A.4), the pavements still showed lower temperatures at 4 pm (25 hours after watering) by 2 to 7 C compared to those in the second 6

7 day, without considering the higher air temperature on the third day (Jul /11/212, see Figure A.4) due to evaporative cooling of some moisture existing in pavements. This implies that watering can effectively lower the pavement surface temperatures using cool water, and evaporation of some moisture existing in pavements also can help produce a low pavement temperature. The specific cooling effect depends on the evaporation rate on the pavement. 7

8 C: Concrete C1 C2 C3 B: Asphalt B1 B2 B3 A: Paver A1 A2 A3 (a) Optical images N C: Concrete 45 C 62 C 52 C C1 C2 C3 B: Asphalt 63 C 67 C 66 C B1 B2 B3 A: Paver 51 C 55 C 53 C A1 A2 A3 N (b) Thermal images of different pavements during watering (16:) (lighter is hotter) Figure A.5. Optical and thermal images of experimental sections on Jul/1/212. 8

9 Jul/9 (dry) Jul/1 (watering) Jul/11 (wet) 25 hours after watering C2 59 C 62 C 55 C C3 5 C 52 C 49 C B2 66 C 67 C 65 C B3 65 C 66 C 64 C 52 C 55 C 5 C A2 A3 53 C 5 C 49 C Figure A.6. Comparison of thermal images of surface temperature of permeable pavements under different conditions (16: Jul/9 through Jul/11). (lighter is hotter) 9