# Asphal Heat Recovery Application for Sustainable Green Energy
## 1 Introduction  
Human activities have affected around 75% of the global non-iced terrestrial environment [1]. Although urban areas occupy a small area equivalent to about 0.5% of the global surface of the planet [2], more than half of the world's population (with an estimated growth of up to 66% by 2050) currently lives in urban areas [3] and asphalt-covered surfaces are increasing. Asphalt is the main material used as a finish for road surfaces and parking areas for vehicles. Its color leads to heat absorption and an increase in surface temperature. On the basis of measurements, it was observed that the temperature of the asphalted surfaces can reach values as high as 72 \({}^{\circ}\)C on a usual day [4]. This contributes to the intensification of the effect known as the \"urban heat island effect\" or UHI [5]. The effect of the UHI has significant consequences on the quality of life of city occupants and is the source of a significant number of environmental problems in urban areas. Thus, it has been observed that with intensification of the UHI effect, emissions of volatile organic compounds increase [6], and these have a negative impact on pedestrian health [7]. Another negative effect observed apart from increased urban heat island effect is generated by the impact on the strength of internal structure of the asphalt layer. It was shown that at high temperatures, plastic deformations occur with damage to the structure of the material, thus leading to a rapid decrease in its lifespan and implicitly to an increase in the operating and maintenance costs of asphalted surfaces [8]. Reference [9] shows the negative influence that high temperatures have on the lifespan of the asphalt layer in terms of decreasing the lifespan of the asphalt from 20 years for a surface temperature of 57 degrees Celsius to only an 8-years lifespan for a surface temperature of 70 degrees Celsius. Other studies have focused on the effect of thermalradiation generated by an asphalt layer and the additional consumption generated by building air conditioning systems [10]. Given the available thermal potential, a number of applications can be identified in which the thermal energy recovered from the asphalt layer can be used through Asphalt Mounted Solar Collectors [CSA]. Thus, an industrial application in which we can use this technology is the use of fluid that crosses the asphalt layer to heat digesters that aim to generate anaerobic methane gas (given that this technology requires a temperature of around 30-35 \({}^{\circ}\)C [11] for optimal operation). Digesters are used to \"treat\" wastewater that is rich in organic matter, which is the case in most municipal domestic wastewater treatment plants. [12]. It is known that this fermentation process uses thermal energy [13] resulting from the cogeneration process in order to achieve optimal parameters. This thermal energy may be capitalized by selling to other consumers if we use a CSA-type system in the hot season to cover the necessary process' thermal energy. Another way of use is coupling with geothermal storage systems so that it can be used to defrost critical areas of highways or bridges [14] without using fossil fuels or chemically or mechanically aggressive materials for the asphalt layer. Implementation in such a way leads to reduction of operating costs and emissions due to the use of fossil fuels. Another applicability is the operation of ground-to-water heat pump heating systems with vertical boreholes. It has been observed that the COP (coefficient of performance) of the heat pump decreases by up to 50% [15] after 10 years in situations in which the thermal loads during the heating and cooling period are not balanced, and Romania is also in this situation from a meteorological point of view. The CSA solution could be used for thermal regeneration of vertical boreholes [14] in order to help increase and maintain the energy efficiency of these types of heat pumps. Such an implementation would also implicitly reduce the payback time of the investment by reducing operating costs.