Multistory Residential Buildings in North Greece: Balancing Between Daylight and Thermal Performance Through Façade Strategies

Challenge
The most typical typology in the Greek urban context is the residential urban multistory building. Most of the existing building stock in the commercial center of Thessaloniki was built before the enforcement of any thermal performance related codes, resulting in poorly performing buildings that are among the biggest energy consumers in the country.

Approach
The limitations of the urban context impose a series of geometrical restrictions, which are among the most essential factors that drive the thermal and visual performance of these buildings. The façade, as the physical boundary between the interior and the exterior conditions and, for this typology, almost the only exposed surface, acts as a critical regulator that drives both thermal and daylight design strategies.

Method
The assessment of the various façade components that primarily relate to the convective or conductive heat gain/loss control leads to the proposal of different configurations according to the orientation and obstruction angle of each studied case. The comparative indicators of the assessment are daylight (illuminance and glare) and energy performance (heating, cooling and lighting loads) leading to a continuous attempt to establish a balance between the two.

Results
An application scheme on a typical example in the center of Thessaloniki in north Greece was able to demonstrate the need for distinct treatment of the façade elements at dissimilar cases in order to achieve a more unified performance among them. The highly obstructed façade parts are behaving as non-solar oriented. The window type and the glazing fraction, as the basic building element of solar radiation transmittance, have the reverse outcome for daylight provision and thermal balance. However, the breakdown of heating, cooling and lighting loads into CO2 emissions highlighted the predominance of cooling loads and their immense need to be minimized.  The featured balcony as a fixed shading device is acting as a reflector that redirects the sun, enhances daylight uniformity and alleviates excess illuminance levels. Its detailed sizing is more crucial for solar oriented façades. Generally, an overhang wider than 1.5m is not any more economically beneficial as it does not further affect the thermal performance of the space. The potential of the glazed balcony on solar-oriented facades is limited compared to its thermal impact on non-solar oriented ones. When the glazed balcony is applied on highly obstructed floors, the decrease of daylight may be substantial.

 Deliverable
The paper reports on a dissertation project undertaken at the Architectural Association School of Architecture toward a master’s degree in Sustainable Environmental Design by the Author. It was originally published in PLEA 2016 proceedings.

Application
Additional applications are expected to give even more design variations regarding the glazing sizes or shading components.

Future
A potential development of supplemental considerations, such as a further investigation on ventilation strategies that pertain to the façade or thermal bridging studies, especially at the balcony location, may use the present study for the elaboration of other applications.

Any generalizations that have been made during the research process allow the applicability of the results even beyond the limits of Thessaloniki. Locations of similar latitudes that comprise comparable climate data—mainly solar radiation availability—may also appertain to the results of this study.

Team Members:
Mili Kyropoulou
Dr. Simos Yannas, Mentor

Research Partner:
Architectural Association School of Architecture in London