Sunless city swelters in summer

Buildings in Greece’s second largest city are sunless, energy-consuming places, hostile to humans and the environment, incompatible with climatic conditions, surrounded by industrial pollution, heat and humidity that become unbearable in the summer, according to a Thessaloniki University survey. A perfect example of how not to design a city, the northern port of Thessaloniki has industries situated to windward (in the northwest), sending airborne pollution over the city. This is exacerbated by the layout of the main roads and buildings, which blocks any air that does circulate. The roads were not built in the same direction as the prevailing winds, which would have facilitated the flow of air and the channeling of airborne pollutants out of residential areas. In fact, the beneficial effects of the wind were ignored completely. The sea breeze from the Thermaic Gulf, which would have improved the environment and cooled the atmosphere, is obstructed by a high wall of eight-floor buildings along the coast road, with only a few side streets and squares through which air can circulate. No sunlight Moreover, high-density construction whereby tall buildings are constructed in cramped rows facing each other across narrow streets mean that not much sunlight filters through. For example, along Thessaloniki’s main roads (Egnatia, Tsimiski, Mitropoleos) where buildings are eight floors high, the roads need to be 53 meters wide with a north-south orientation, if all floors in the buildings are to receive sunlight in December, 44 meters wide for sunlight in January and 32 meters wide for sunlight as of February and onward. Yet they are only 30, 25 or 15 meters wide, and none of them positioned properly to let in light. Therefore a building facing northeast only receives sunlight for about an hour every morning. Clearly, the problem of insufficient sunlight not only results in poor energy efficiency and carbon dioxide absorption but poor health conditions for the residents. Thessaloniki does not have many buildings facing south and those that do exist are shaded by the buildings opposite them. Consequently, only the top floors receive direct sunlight. Building materials such as concrete and asphalt and the absence of sufficient greenery and open spaces also contribute to the city overheating. Plants attract 80 percent of the sun’s radiation, bringing down air temperature and creating humidity. The same applies to the soil. As it absorbs solar radiation, it transforms it into heat, contributing to the evaporation of natural humidity, thereby reducing outside temperatures and that of the soil. As there is very little vegetation and very few open spaces in Thessaloniki, overheating occurs, intensified by human-generated heat waste and pollution, creating the «heat island» effect [when temperatures are higher than in surrounding areas]. According to measurements taken during the summer of 2000, large variations in temperature were recorded between the center of the city, in the suburb of Panorama on the heights above the city and at points in between the two, over a total distance of just 7 kilometers. These differences ranged from 10.18 to 14.5 degrees Celsius during a single day and 7.8-11.40 during the night. The greatest difference from the center was recorded in Panorama, due to its height above sea-level, low-density construction, denser vegetation and greater number of open spaces. Makedonomachon Square As it is not feasible to redesign the urban landscape, it is even more important to protect, restore and conserve existing free spaces and to look for new areas to make use of. Such spaces exist, and this was the goal of the survey by the Laboratory for Construction Physics at Thessaloniki University’s Department of Building Science and Technology, led by Associate Professor Niovi Chrysomallidou, within the framework of the research program Rediscovering Urban Realms and Urban Spaces (RUROS), with the participation of another eight European universities. Makedonomachon Square is just one example of the importance of open spaces. The microclimate in the square was measured during the first week of September 2001 and compared with measurements by the Environmental Department’s meteorological station at the corner of Venizelou and Egnatia streets, just 500 meters away. During daylight hours, the maximum temperature difference (1-1.5 degrees Celsius) occurred just before noon, indicating that Macedonomachon Square is clearly cooler at night, not only because of the relative increase in wind variations but due to the reduction in the amount of heat stored in the surface of the square. This is a considerable difference, if one takes into account the close proximity of the two points. During midday and the early afternoon hours the difference is not as marked, but even then, the shade created by the trees, the low level of reflection from planted areas, the cooling action of the plants and the exchange of air masses keeps the temperature in the square about one degree cooler than in Venizelou Street. The increased air flow also has a clear effect on the humidity level of the square, where it is about 10 percent lower than that in Venizelou Street.