Cool roofs and cool pavements for the reefer container yard

Transcription

1 Cool roofs and cool pavements for the reefer container yard Knowledge Area(s): Main Area Sub-area Author(s) Affiliation Jan Christoph Ahting Jacobs University Distribution / Information to: Name Affiliation Cool roofs 08 Aug 27, /10

2 Contents Cool roofs and cool pavements for the reefer container yard Introduction Cool roofs Principle of a cool roof Types and materials Benefits Application scheme for a container terminal Cool pavements Principle of a cool pavement Types and materials Benefits Application scheme for a container terminal Case study: Port of Hakata Conclusions... 9 References Cool roofs 08 Aug 27, /10

3 1 Introduction Urban regions and their surrounding regions do not share a same temperature level. In a town the temperature is several degrees above the temperature in the countryside. This is due to the built environment and the concentration of human activity. That phenomenon is called an urban heat island [1]. A large portion of the town s area is covered with rooftops and pavements. The traditional colors of the material used are dark. In an effort to mitigate the effect of an urban heat island, researchers of today analyze the opportunity to re-design roofs and pavements with bright colors. These can be grouped as cool roofs and cool pavements. In this white paper, the principle of the technology is explained. Furthermore, different types as well as suitable materials are presented. Some of the benefits are then elaborated. For the GreenEfforts idea, it is interesting to take these two technologies into consideration for use on a container terminal. Therefore, an application scheme is added to this white paper. During his research, the author has found a practical example: The Japanese Port of Hakata has installed a cool roof. 2 Cool roofs A cool roof is a roofing system able to reject solar heat and keep roof surfaces cooler under the sun. This is due to the properties of the materials used, which reflect the solar radiation (solar reflectance) and release the heat they have absorbed (infrared remittance). 2.1 Principle of a cool roof Solar energy heats up roof surfaces, no matter if the surface is dark or white colored. The quality of a cool roof depends on its capabilities to reflect light and the efficiency to radiate heat. Good cool roof surfaces are both highly reflective and highly emissive to minimize the amount of light converted into heat and to maximize the amount of heat that is radiated away. Sunlight is reflected more by white roofs than by dark roofs (see Figure 1). Dark roofs reflect up to 20% of incoming sunlight whereas white roofs reflect up to 80%. These roofs therefore turn less sun energy into heat. When the reflectance of a building is increased by means of a white (cool) roof, it can reduce the temperature inside the building significantly [3, 8]. Figure 1: Black roof versus white roof. Source: A Practical Guide to Cool Roofs and Cool Pavements. Source: [3]. In the example both roof types are compared with each other at a given ambient temperature of 37 C. Some advantages of the white roof can be observed: Cool roofs 08 Aug 27, /10

4 Nearly halving the surface temperature Cooling effect on the inner building Mitigating the heat-island-effect of a city Mitigating global warming More advantages will follow in section 2.3. To what extent large scale application of cool roofs influences the ambient temperature, shows an example from Spain. In the Almeria region the density of greenhouses is among the highest of the world. Some 350km² are covered by greenhouses. That roughly corresponds to the area of the city of Bremen which covers 325km². To cool down the inside temperature, farmers whitewash the greenhouses roofs. Over the last 20 years, the overall temperature in the vicinity of the greenhouse area has fallen by 0.3 C whereas temperature has risen in the surrounding regions by 0.5 C [3]. 2.2 Types and materials In general, there are two types of roofs: low-sloped and steep-sloped. A low-sloped roof is flat. To provide for drainage there is little incline. Such roofs are mostly used for commercial, industrial, warehouse, office, retail and multi-family buildings. Therefore, a low-sloped roof might also be used as a shading roof for a reefer container block on a container terminal. Steep-sloped roofs have greater inclines and are mostly installed on residences and retail commercial buildings. To apply the cool roof technology to a low-sloped roof, coatings and singly-ply membranes can be taken into consideration. Coatings have the consistency of thick paint and contain additives that improve their adhesion and durability, for example. To convert an ordinary low-sloped roof into a cool roof, cementitious and elastomeric coatings can be used. Some coatings contain both cement particles and polymers. Being new, cementitious and elastomeric coatings have a solar reflectance of 65% or higher. Their solar emittance is 80% to 90% or more. An additional advantage of elastomeric coatings is their waterproofness. Single-ply membranes that offer a cooling effect are: EPDM (Ethylene Propylene Diene Monomer) CSPE (Chlorosulfonated Polyethylene) PVC (Polyvinyl Chloride) and TPO (Thermoplastic Olefins) [8, 10] 2.3 Benefits Reduced energy use With a cool roof, the building below stays cooler and uses less energy for cooling in summer. Energy savings for residential and commercial buildings are achieved each year, thereby reducing the building s operating costs. Among others, the savings are affected by the local climate, attic configuration, roof reflectance and insulation levels. On the internet there are calculation tools available to compare the energy consumption between cool and traditional roof types. One of them is the Roof Savings Calculator ( Reduced air pollution and greenhouse gas emissions A reduction in energy use as described above leads to a reduced burning of fossil fuels. The effect is that cool roofs contribute to fewer emissions of air pollutants (e.g. NO x ) and greenhouse gases like CO 2. By reducing air pollutant emissions, total air quality will improve, especially ground-level ozone (smog). Improved human health and comfort Cool roofs 08 Aug 27, /10

5 Cool roofs reduce the air temperatures inside of buildings with and without air-conditioning. To install such roofs on residential buildings without air-conditioning can be a means to save lives. During excess heat periods the roofs improve the comfort, especially for elderly house residents, and may help to reduce deaths from excess heat. Extended roof lifetime Generally, roofs wear out and fail for many reasons. Some of these are linked to temperature. The material might degrade faster the higher the temperature. Cool roofs have lower surface temperature than traditional dark roofs. So, cool roofs could be more durable and outlast similar dark roofs [7, 10]. 2.4 Application scheme for a container terminal A cool roof comes into consideration for the reefer storage area on a container terminal. When being stacked, a reefer container requires energy for inside cooling of the cargo. Energy use increases during summer when the container stands in the blazing sun. The idea is to mitigate the heat-up of the reefer by installing a shading roof above the whole reefer storage area (see Figure 2). Figure 2: Shading roof for the reefer container yard. In addition to the cooling effect there is an opportunity to generate energy. The flat surface area of the shading roof offers ideal conditions for the installation of solar collectors. The energy can be directly used to feed the cooling system of the reefer containers. 3 Cool pavements Besides a cool roof, cool pavement is another option to mitigate the urban heat island effect. Both account for a large portion of the land surface in an urban area. But with regard to cool pavements there has not been so much application activity, yet. More research seems to be necessary to uncover the full potential. And potential exists; this applies in particular for car parking areas. Cool roofs 08 Aug 27, /10

6 3.1 Principle of a cool pavement The functional principle of a cool pavement is similar to the one described for cool roofs (see section 2.1). Bright colored surfaces reflect much more sun energy and heat up much more than dark colored surfaces (see Figure 3). Figure 3: Surface temperature of different pavements. Source: [2]. The material properties of pavements cause them to absorb and store a larger amount of heat than vegetated land cover. In comparison to vegetation, the imperviousness of most pavements reduces cooling due to evaporation. This results in considerable hotter temperatures for pavements. During daytime conventional asphalt heats up and stores the heat in its subsurface. At night, with cool surrounding temperatures, the heat is rereleased and contributes to the heat island effect of a city. Cool pavements aim at controlling the pavement s temperature. This can be achieved by the use of a high solar ray reflecting surface, by increasing the cooling ability at night and by the use of a porous structure which cools the pavement through evaporation [1]. 3.2 Types and materials One advantage of a cool pavement is that it can be realized with existing paving technologies. It does not necessarily require new materials. Current cool pavements are those that feature increased solar reflectance or that use a permeable material. So far, the following materials have been investigated if they are suited for cool pavement purpose [1]: Conventional Portland Cement Concrete Pavement Concrete Additives (e.g. slag cement, fly ash) Whitetopping and Ultra-Thin Whitetopping Roller-Compacted Concrete Pavement Light Aggregate in Asphalt Concrete Pavement (e.g. limestone) Chip Seals with Light Aggregate Porous Pavement and Surfaces Color Pigments and Seals Rubberized Asphalt Cool roofs 08 Aug 27, /10

7 3.3 Benefits The heat island mitigation benefits for cool roofs are also valid for cool pavements. But quantifying these benefits for cool pavements is complicated. Over time, the reflectivity of pavement surfaces changes. Shadows are casted by buildings, cars or the surrounding vegetation. In Athens (Greece) a cool pavement was used for new pavement of an area within a city park. An area of 4,500m² was covered with pale yellow paving blocks, replacing the old dark asphalt. Researchers measured an ambient temperature decrease of 1.9 C and a surface temperature decrease of 12^C [5]. Besides the general heat island mitigation benefits that were stated above in section 2.3, cool pavements have some additional benefits [1]: Improvements in water quality Cool pavements can improve the water quality through reduced heating of runoff. Tests carried out with both conventional and cool asphalt paving have shown differences in runoff temperatures of up to 4 C. Noise reduction New asphalt with a porous surface reduces traffic noise significantly. This benefit declines over time, as does its strength and durability in comparison to conventional surfaces. Safety There are two safety benefits with permeable pavements. One the one hand, water spray from moving vehicles is reduced. On the other hand, better water drainage increases traction. Nighttime illumination This benefit brings also side-benefits with it. Cool pavements are often bright colored and include reflective properties. These account for enhanced visibility at night. Side-benefits are connected with the reduced requirements for lighting. The car park of a shopping center might serve as an example. Large shopping malls are often equipped with large car parks. If the whole parking area is painted in bright reflective color, the lighting can be dimmed to a minimum. That will be sufficient to illuminate the whole parking area. Maybe some light towers become obsolete. In the end, it saves not only money and energy but also adds to security and the shopping mall s customer appeal. 3.4 Application scheme for a container terminal Paving the whole area of a container terminal with a cool bright surface material is far too expensive. In addition to that, especially the driveways for van carriers face heavy wear and tear through daily use. This will downsize the good cooling effect of new bright pavement. Therefore cool pavement should be applied only to the reefer storage area and its vicinity (see Figure 4). Cool roofs 08 Aug 27, /10

8 Figure 4: Cool pavement for the reefer container yard (plan view). It would also be conceivable to combine the technologies of a cool roof and a cool pavement on the reefer storage area. But the shading effect of the roof neutralizes the cooling effect of a bright colored pavement. That is why the base area of the roof has to be chosen smaller in size than the base area of the pavement. 4 Case study: Port of Hakata As one of the first ports in the world, the Japanese Port of Hakata has implemented the cool roof technology on its Hakata Island City Container Terminal (HICCT). The Port of Hakata is the port of the city of Fukuoka. Fukuoka is situated in the very south of Japan, sharing the same latitude with Los Angeles and Casablanca. The climatic conditions are similar to the ones in Southern Europe with hot summer temperatures but even more humidity (see Table 1). Table 1: Climate chart for the city of Fukuoka, Japan. Source: [9]. Besides its cooling function, the installed roof has an extra feature. It is retractable. The roof is closed under normal conditions but for cargo operations with a rubber-tyred gantry crane (RTG) it can be opened (see Figure 5). Under normal conditions, the roof is closed. As an example, the working principle is explained by means of an incoming container by truck. The Terminal Operation System (TOS) of the Port of Hakata, called KACCS, receives entrance information from the gate. In the following, the KACCS prompts an opening instruction to the control system of the roof. At the same time, a work instruction is given to the RTG [4]. Cool roofs 08 Aug 27, /10

9 Figure 5: Shading roof for reefer containers at the Port of Hakata. Source: [4]. At Kyushu University, scientists from the Department of Marine Systems Engineering quantified the energy saving effect for the container terminal in Fukuoka. Statistics from Hakata Port Corporation show a monthly average of electricity consumption of 475 MWh with a peak of 560 MWh in the summer of The energy consumption of reefers accounts for about 50% of the overall power consumption at a container terminal [6]. By means of a shading roof, the Port of Hakata aims at cutting down this large proportion of its power consumption. Measurements conducted by the scientists on a summer day in 2013 showed the difference in energy consumption between a reefer with and without sun-shade. Electric energy consumption for a reefer without sunshade was between 7.8 kw and 8.8 kw whereas the consumption of a reefer with sun-shade remained in low range between 6.4 kw and 6.8 kw. Comparing the averages of energy consumption in the case with sun-shade and without sun-shade, the scientists found that the expected electric energy saving potential due to a shading roof is about 12%. 5 Conclusions Cool roofs and cool pavements are positive developments to mitigate the heat island effect in urban areas. White roofs reflect considerably more sunlight than dark roofs which results in lower ambient temperatures under a white cool roof. Other benefits from cool roofs that have been identified in this paper are: Reduced energy use, reduced air pollution and greenhouse gas emissions, improved human health and comfort as well as an extended roof lifetime. For the cool pavement technology the following benefits have been identified: Improvements in water quality, noise reduction, safety as well as nighttime illumination. With respect to the high proportion of energy consumption of reefer containers (approx. 50%) in the overall energy consumption of a container terminal, the cool roof and cool pavement technologies are a means to reduce energy consumption. There is only little practical experience with such technology on a container terminal. A Japanese research group has found that by means of a sun-shading roof, the energy consumption of reefer containers in the Port of Hakata (Japan) can be cut down by about 12%. One can estimate a further cut in energy consumption if cool roofs are used in combination with cool pavements that will cool down the ambient air around the reefer stacking area. Cool roofs 08 Aug 27, /10

10 References [1] Cambridge Systematics, Inc., 2005, Cool Pavement Report EPA Cool Pavements Study Task 5, Available from: < _complete.pdf> [31 March 2014]. [2] Chao, J 2010, Global Model Confirms: Cool Roofs Can Offset Carbon Dioxide Emissions and Mitigate Global Warming, news release, 19 July 2010, Lawrence Berkeley National Laboratory, U.S. Dept. of Energy, Available from: < [29 March 2014] [3] Global Cool Cities Alliance 2012, A Practical Guide to Cool Roofs and Cool Pavements, Available from: < [27 March 2014]. [4] Ishibashi, H 2013, ECO strategies at Hakata Port, Presentation held during the APEC Port Services Network (APSN) Workshop on Green Ports: Time for Action and Innovation, 5 November 2013, Phuket, Thailand, Available from: < [05 March 2014]. [5] Santamouris, M, Galtani, N, Spanou, A et.al. 2012, Using cool paving materials to improve microclimate of urban areas Design realization and results of the flisvos project, Building and Environment, vol. 53, pp [6] Shinoda, T & Budiyanto, MA 2014, Energy Saving Effect of Roof Shade at Reefer Container Storage Yard, Department of Marine Systems Engineering, Kyushu University, Fukuoka, Japan. [7] The University of Melbourne 2011, Cool Roofs: City of Melbourne Research Report, Available from: < [25 March 2014]. [8] Urban, B & Roth, K 2010, Guidelines for Selecting Cool Roofs, study of Fraunhofer Center for Sustainable Energy Systems for the U.S. Department of Energy Building Technologies Program, Available from: < [28 March 2014]. [9] [10] Wong, E 2008, Cool Roofs, Reducing Urban Heat Islands: Compendium of Strategies, U.S. Environmental Protection Agency. Cool roofs 08 Aug 27, /10