Urban context and climate change impact on the thermal performance and ventilation of residential buildings: a case-study in Athens

Joint conference with the 11th TightVent Conference and the 9th Venticool ConferenceUrban settings and climate change both impact energy use, thermal comfort and ventilation of buildings. This is more noticeable in hot urban areas where the urban heat island effect is more pronounced; also, in densely built urban areas where thermal comfort in naturally ventilated buildings is affected by changes in natural ventilation rates because of surrounding obstructions. In some cases, overshadowing might alleviate the impact. This paper presents a study of changes in energy demand in residential buildings considering the overlapping effect of climate change and urban heat island intensity in Athens representing a hot European climate and a dense urban setting. The case study building is a real residential building in an urban canyon in central Athens with data obtained from the PRELUDE H2020 project. The impact of urban parameters on air temperature wind speed and solar overshadowing was considered. Urban air temperature was calculated by using the Urban Weather Generator which includes a number of indices such as site coverage, façade to site ratio and average building height; it also considers the building construction materials as well as anthropogenic heat emissions by the operation of the buildings. Urban wind speed was modified using the URBVENT urban canyon model for the computation of wind speed; this model was validated by its proposers in 2005 by measurements in Athens. Solar overshadowing was calculated for the case-study building considering the surrounding buildings. Current-urban and future-urban weather files were generated, and simulations were run considering energy demand and indoor thermal comfort. The thermal simulation results show that in the hot European climate of Athens with densely built urban areas and for a building within an urban canyon, current weather files which include overshadowing, urban heat island and canyon wind will increase the cooling demand by 24% in comparison to using a typical current weather file. However total energy demand (heating and cooling) increased only 3% for lower floors and 12% for higher floors due to the reduction of heating demand. Simulations using future weather files indicated a 66% increase of cooling demand in comparison to using a typical weather file. Future total energy demand increased by 32% for higher floors and 13% for lower floors. If the building is free floating an adaptive thermal comfort analysis indicated that only 25% of the summertime will be comfortable in comparison to the 50% prediction by the current typical weather file. Therefore, the use a suitable weather file to include urban external conditions in thermal simulations is essential for more accurate predictions of energy demand and internal avoidance of overheating in free-floating buildings.European Union’s Horizon 2020 research and innovation programme under Grant Agreement N° 958345 for the PRELUDE project (https://preludeproject.eu)

Innovating together for just and green urban transitions: Stories from Urban ReLeaf Cities

Nature-based solutions in urban environments can provide cooling effects, decrease air pollution, and improve mental health, amongst others important ecosystem services and health-related benefits. Ambitious plans, such as the pledge to plant 3 billion trees in the EU, the European Green Deal, or the Green City Accord support this direction. Their implementation, however, requires transformative changes on the ground to overcome business as usual approaches. The Urban ReLeaf project delivers change by bringing public authorities and citizen groups together to shape green infrastructure actions in their cities. Six pilot cities co-create citizen-centric innovations for the democratisation of urban greenspace monitoring and the wider policy making process in pursuit of urban climate resilience. This poster showcases the stories of the six cities and their approaches to participatory, and data-driven decision making. Athens is undergoing a greening transformation with a new, citizen-powered tree registry providing critical data for better management of greenspaces. Cascais engages citizens in sharing perceptions and thermal comfort levels while using greenspaces to validate the effectiveness of its parks. Meanwhile in Dundee, a city facing increasing grey infrastructure in deprived areas, actions to enhance the accessibility of greenspaces are co-developed with citizens and stakeholders. Mannheim has a heat action plan to safeguard its most vulnerable residents but has identified critical data gaps. Citizen observations of trees and thermal comfort, when integrated with official data streams, will aid the delivery of climate adaptation measures. Riga engages diverse audiences to address concerns about air pollution and greenspace usage, to ensure better informed policies. Finally, in Utrecht, data on temperature, humidity and heat stress, collected by and for citizens, will help them reduce the urban heat island effect and shape effective mitigation strategies

Seismic resistance of traditional timber-frame hımış

Hımış structures have hardly ever found as extensive a role as other traditional timber housing, such as those originating from Japan or Central Europe, within the wide discourse on the seismic performance of timber-frame architecture that has gained significant momentum in the last few decades owing to advancing testing technologies. While the hımış construction technique was perhaps not born as a result of a conscious search for a seismically resistant building form, it was soon widely appreciated for its structural features advantageous under seismic loading - especially from the sixteenth century when it has become a well-established construction technique in part of the Balkans and in today’s Turkey. Despite widely available anecdotal information based on post-disaster studies regarding its performance under earthquakes, robust quantitative data on the seismic behaviour of these structures were practically non-existent until quite recently, and are still somewhat limited. However, we are now able to confirm that hımış constructions do have intrinsic qualities that are very beneficial under seismic action. This paper aims to make a brief review of the current state of our knowledge on structural performance of hımış buildings under earthquake loading, with specific emphasis on infill/cladding techniques, connection details and energy dissipation characteristics