1. Roofing Types and Their Effects on the Thermal Properties of Runoff Robert W. Peters, Julie G. Price, Ronald D. Sherrod, Stephen A. Watts, Julia M. Gohlke, Jason T. Kirby, and Matt Winslett University of Alabama at Birmingham (UAB) Birmingham, Alabama Paper presented at the Alabama Water Resources Conference Orange Beach, Alabama September 8–9, 2011

2. Goal of the Research The overall goal of the presented research involving mini-roofs on the University of Alabama at Birmingham (UAB) campus is to identify a suitable roofing material combination which reduces energy cooling costs. Other considerations involve implementation costs, durability, and maintenance. The overall goal of the presented research involving mini-roofs on the University of Alabama at Birmingham (UAB) campus is to identify a suitable roofing material combination which reduces energy cooling costs. Other considerations involve implementation costs, durability, and maintenance.

3. Ongoing UAB Research of Roofing Materials During the past three years, UAB has conducted research to determine an efficient roofing material combination that decreases the building heat load coupled with a minimal environmental impact. During the past three years, UAB has conducted research to determine an efficient roofing material combination that decreases the building heat load coupled with a minimal environmental impact. UAB has been investigating external and internal temperatures to determine a way to lower utility costs. UAB has been investigating external and internal temperatures to determine a way to lower utility costs. UAB is also interested in the interaction of roof temperature and rainfall. UAB is also interested in the interaction of roof temperature and rainfall.

4. Background Heat that is being transferred into the roofing structure is primarily transferred through conduction and convection, affecting building surface and internal temperatures. Heat that is being transferred into the roofing structure is primarily transferred through conduction and convection, affecting building surface and internal temperatures.

5. Rooftop Performance Due to the hot summers prevalent in the southeastern U.S. during which the tempera- tures can approach 100  F, along with conditions of high humidity, it is crucial to have a roof which minimizes cooling costs. Due to the hot summers prevalent in the southeastern U.S. during which the tempera- tures can approach 100  F, along with conditions of high humidity, it is crucial to have a roof which minimizes cooling costs. By increasing the albedo of a structure, we increase how reflective the object is to the solar radiation, which will result in a lower surface temperature and less heat being transferred into the building. By increasing the albedo of a structure, we increase how reflective the object is to the solar radiation, which will result in a lower surface temperature and less heat being transferred into the building. Vegetative roofs have up to 30% of total rooftop cooling being due to plant transpiration. Vegetative roofs have up to 30% of total rooftop cooling being due to plant transpiration.

6. Mini-Roofs During this study, 15 mini-roof combinations were observed for trends in internal temperatures. During this study, 15 mini-roof combinations were observed for trends in internal temperatures. Each mini-roof is 8-ft long x 4-ft wide x 4-ft deep. All roofs are insulated with 2.0-in. of extruded polystyrene. Each mini-roof is 8-ft long x 4-ft wide x 4-ft deep. All roofs are insulated with 2.0-in. of extruded polystyrene.

7. Mini-Roofs (cont’d) Each roof contains an internal temperature sensor to determine the temperature inside the building without air-conditioning; the temperature was recorded every 10- minutes during the past 3+ years. Each roof contains an internal temperature sensor to determine the temperature inside the building without air-conditioning; the temperature was recorded every 10- minutes during the past 3+ years. This data was then automatically sent to a data logger and placed into an Excel file for review later. This data was then automatically sent to a data logger and placed into an Excel file for review later.

8. Photos of Mini-Roofs Roof 10: vegetated roof Roof 8: concrete pavers with white epoxy coating Roof 3: black membrane roofRoof 6: conventional black granular roof

9. Table 1. Mini-Roof Descriptions.

10. Surface Temperature Measurements The surface temperatures of the mini- roofs were measured using an infrared digital thermometer [InfraPro® 4 (P/N 35639-30) Oakton, China]. The temperature range is  25 to 1400 o F (  32 to 760 o C), with an accuracy of  1%. The surface temperatures of the mini- roofs were measured using an infrared digital thermometer [InfraPro® 4 (P/N 35639-30) Oakton, China]. The temperature range is  25 to 1400 o F (  32 to 760 o C), with an accuracy of  1%. Surface temperature measurements were collected during June 2010 on the various roofing materials. Surface temperature measurements were collected during June 2010 on the various roofing materials.

11. Surface Temperature Measurements (cont’d) During the course of the day, roofing surface temperatures ranged from 20.6 o C (69.4 o F) to 82.2 o C (180.0 o F). [Internal temperatures from the mini-roofs, collected in ten minute intervals, had temperatures ranging from 74 ⁰ F to 95 ⁰ F]. During the course of the day, roofing surface temperatures ranged from 20.6 o C (69.4 o F) to 82.2 o C (180.0 o F). [Internal temperatures from the mini-roofs, collected in ten minute intervals, had temperatures ranging from 74 ⁰ F to 95 ⁰ F]. The vegetative mini-roofs exhibit surface temperatures ranging between 21.7 o C to 52.2 o C, while their large counterpart, the pilot roof on top of Hulsey Center, exhibits higher tempera- tures ranging from 31.7 o C to 61.1 o C. The vegetative mini-roofs exhibit surface temperatures ranging between 21.7 o C to 52.2 o C, while their large counterpart, the pilot roof on top of Hulsey Center, exhibits higher tempera- tures ranging from 31.7 o C to 61.1 o C.

12. Mini-Roof Surface Temperature Measurements

13. Typical Temperature Fluctuations during the Study Period

14. Surface Temperature Measurements Because the temperature seemed to vary cyclically during the course of a year, the data was fitted to a sine wave function. Because the temperature seemed to vary cyclically during the course of a year, the data was fitted to a sine wave function. After a Fourier transform of the data and analysis through various software programs, the sine functions for each mini-roof were determined to describe the thermal trends. This function is applied to the exterior surface temperatures for estimation since the interior and exterior surfaces experience the same source of thermal loading. After a Fourier transform of the data and analysis through various software programs, the sine functions for each mini-roof were determined to describe the thermal trends. This function is applied to the exterior surface temperatures for estimation since the interior and exterior surfaces experience the same source of thermal loading. The roofs had amplitudes ranging from 19.5 to 20.7 o and phases angles roughly 4.2 to 4.3 radians. The roofs had amplitudes ranging from 19.5 to 20.7 o and phases angles roughly 4.2 to 4.3 radians.

15. Fitted Sine Wave Regression for a Mini-Roof System

16. General Observations Generally, the darker the roof, the hotter it is at a given time, no lag was observed when compared to a lighter roof of similar composition. Generally, the darker the roof, the hotter it is at a given time, no lag was observed when compared to a lighter roof of similar composition. Roofs of the same type perform roughly the same internally and externally, but roofs of different materials (e.g., green vs. conventional) were statistically different. Roofs of the same type perform roughly the same internally and externally, but roofs of different materials (e.g., green vs. conventional) were statistically different. The differences in roof temperatures are greater in the summer months than any other time of year. The differences in roof temperatures are greater in the summer months than any other time of year.

17. General Observations (cont’d) During the winter, autumn, and spring months, more roofs begin to exhibit similar internal thermal properties due to diurnal temperature and lower radiation thermal input. During the winter, autumn, and spring months, more roofs begin to exhibit similar internal thermal properties due to diurnal temperature and lower radiation thermal input. The rock roofs maintain lowest surface temperatures, and membranous roofs were the hottest with vegetative roofs behaving similar to rock roofs. The rock roofs maintain lowest surface temperatures, and membranous roofs were the hottest with vegetative roofs behaving similar to rock roofs.

18. Modulation of Mini-Roof Temperature Measurements Associated with Rainfall From the surface temperature measurements, rapid cooling due to rain was a very effective temperature regulator. From the surface temperature measurements, rapid cooling due to rain was a very effective temperature regulator. Rainwater has a very high specific heat capacity, which makes water a very effective cooling agent. Rainwater has a very high specific heat capacity, which makes water a very effective cooling agent.

19. Modulation of Mini-Roof Temperature Measurements Associated with Rainfall (cont’d) The precipitation events cause a sudden drop in temperature at random intervals during the year. Such events add to the randomness and noise observed in the graphs of the raw data. The precipitation events cause a sudden drop in temperature at random intervals during the year. Such events add to the randomness and noise observed in the graphs of the raw data.

20. Effect of Rainfall on Surface Temperature of Mini-Roof No.3 Rainfall events occurred on days: June 1, 2, 4, 5 and July 6, 13, and 16.

21. Surface Temperatures on Mini-Roof No.3 (black membrane roof)

22. Effect of Rainfall on Surface Temperature of Mini-Roof No.6 (conventional black granular roof)

23. Surface Temperatures on Mini-Roof No.6

24. Effect of Rainfall on Surface Temperature of Mini-Roof No.8 (concrete pavers with white epoxy coating)

25. Surface Temperatures on Mini-Roof No.8

26. Effect of Rainfall on Surface Temperature of Mini-Roof No.10 (vegetated roof)

27. Surface Temperatures on Mini-Roof No.10

28. Summary and Conclusions The roofs are statistically different energy performance-wise in terms of the temperature amplitude, while the phase angles are statistically the same. The roofs are statistically different energy performance-wise in terms of the temperature amplitude, while the phase angles are statistically the same. Most roofs are significantly different in terms of the average mean roof temperature, but the difference is most pronounced in the summer months due to the higher solar intensity; during the other times of the year, the roofs behave more similarly to one another. Most roofs are significantly different in terms of the average mean roof temperature, but the difference is most pronounced in the summer months due to the higher solar intensity; during the other times of the year, the roofs behave more similarly to one another.

29. Summary and Conclusions (cont’d) The color black absorbs all frequencies of visible light which causes the roof to become hotter than the lighter colored roofing combinations. This property is most well observed in Roof No. 6 which is the hottest roof primarily due to its color and texture. The color black absorbs all frequencies of visible light which causes the roof to become hotter than the lighter colored roofing combinations. This property is most well observed in Roof No. 6 which is the hottest roof primarily due to its color and texture. The coolest roofs were the roofs composed primarily of a rock or stone material and were of light color. The coolest roofs were the roofs composed primarily of a rock or stone material and were of light color. Vegetative roofs resulted in mini-roof surface and internal temperatures comparable to reflective roofs; their performance is enhanced by evapo-transpiration. Vegetative roofs resulted in mini-roof surface and internal temperatures comparable to reflective roofs; their performance is enhanced by evapo-transpiration.

30. Summary and Conclusions (cont’d) Differences in the thermal properties is also a product of the surface area/volume ratio of the roof and not just the material composition itself. Differences in the thermal properties is also a product of the surface area/volume ratio of the roof and not just the material composition itself. Rainfall had a significant effect on the cooling of the mini-roofs: Rainfall had a significant effect on the cooling of the mini-roofs:  For black roofs,  T > 60 o F  For concrete pavers with a white epoxy coating,  T ~ 33 o F  For vegetative roofs,  T ~ 33  40 o F

31. Future Research Directions Expand the research to develop an overall sustainability assessment that will compare different roof types in terms of economic, social and environmental impacts. Expand the research to develop an overall sustainability assessment that will compare different roof types in terms of economic, social and environmental impacts. Investigate quantifiable impacts on the Birmingham urban heat island and air pollution indices and associated quantifiable health outcomes. Investigate quantifiable impacts on the Birmingham urban heat island and air pollution indices and associated quantifiable health outcomes.

32. Future Research Directions (cont’d) Monitor temperature of roof runoff in real- time to identify whether temperature shock loads emanate from discharges into the natural environment (e.g., discharge into ecosystems, etc.). Monitor temperature of roof runoff in real- time to identify whether temperature shock loads emanate from discharges into the natural environment (e.g., discharge into ecosystems, etc.).

33. Acknowledgments The authors acknowledge the technical assistance provided by UAB’s Facilities Management Department in the conduct of this research. The authors acknowledge the technical assistance provided by UAB’s Facilities Management Department in the conduct of this research. The authors also acknowledge the technical assistance of Dr. Ian Hosch for his input on the sine wave analysis of the temperature variations. The authors also acknowledge the technical assistance of Dr. Ian Hosch for his input on the sine wave analysis of the temperature variations.

34. Questions??? Questions???