Increasing urbanization and the effects of climate change will bring new challenges for cities, such as energy saving and supply of renewable energy, preventing urban heat islands and water retention to deal with more frequent downpours. A major urban surface, the surface of roofs, is nowadays hardly exploited and could be used to make cities more ‘future proof’ or resilient. Many Dutch municipalities have become aware that the use of green roofs as opposed to bituminous roofs positively contributes to these challenges and are stimulating building-owners to retrofit their building with green roofs. This study aims at comparing costs and benefits of roof types, focused on green roofs (intensive and extensive) both on building- and city scale. Core question is the balance between costs and benefits for both scales, given varying local conditions. Which policy measures might be needed in the future in order to apply green roofs strategically in regard to local demands? To answer this question the balance of costs and benefits of green roofs is divided into a public and an individual part. Both balances use a strengths, weaknesses, opportunities and threats framework to determine the chance of success for the application of green roofs, considering that the balance for green roofs on an individual scale influences the balance on a public scale. The outcome of this combined analyses in the conclusion verifies that a responsible policy and a local approach towards green roofs is necessary to prepare the city sufficiently for future climate changes. http://dx.doi.org/10.13044/j.sdewes.d6.0225
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This paper assesses wind resource characteristics and energy yield for micro wind turbines integrated on noise barriers. An experimental set-up with sonic anemometers placed on top of the barrier in reference positions is realized. The effect on wind speed magnitude, inflow angle and turbulence intensity is analysed. The annual energy yield of a micro wind turbine is estimated and compared using data from a micro-wind turbine wind tunnel experiment and field data. Electrical energy costs are discussed as well as structural integration cost reduction and the potential energy yield could decrease costs. It was found that instantaneous wind direction towards the barrier and the height of observation play an influential role for the results. Wind speed increases in perpendicular flows while decreases in parallel flow, by +35% down to −20% from the reference. The azimuth of the noise barrier expressed in wind field rotation angles was found to be influential resulted in 50%–130% changes with respect to annual energy yield. A micro wind turbine (0.375 kW) would produce between 100 and 600 kWh annually. Finally, cost analysis with cost reductions due to integration and the energy yield changes due to the barrier, show a LCOE reduction at 60%–90% of the reference value. https://doi.org/10.1016/j.jweia.2020.104206
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Blue-green roofs have been utilized and studied for their enhanced water storage capacity compared to conventional roofs or extensive green roofs. Nonetheless, research about the thermal effect of blue-green roofs is lacking. The goal of this research is to study the thermal effect of blue-green roofs in order to assess their potential for shielding the indoor environment from outdoor temperature extremes (cold- and heat-waves). In this field study, we examined the differences between blue-green roofs and conventional gravel roofs from the perspective of the roof surface temperatures and the indoor temperatures in the city of Amsterdam for late 20th century buildings. Temperature sensor (iButtons) values indicate that outside surface temperatures for blue-green roofs are lower in summer and fluctuate less during the whole year than temperatures of conventional roofs. Results show that for three warm periods during summer in 2021 surface substrate temperatures peaked on average 5°C higher for gravel roofs than for blue-green roofs. Second, during both warm and cold periods, the temperature inside the water crate layer was more stable than the roof surface temperatures. During a cold period in winter, minimum water crate layer temperatures remained 3.0 o C higher than other outdoor surface temperatures. Finally, also the variation of the indoor temperature fluctuations of locations with and without blue-green roofs have been studied. Locations with blue-green roofs are less sensitive to outside air temperature changes, as daily temperature fluctuations (standard deviations) were systematically lower compared to conventional roofs for both warm and cold periods.
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