Empirical assessment of calculated and actual heating energy use in Hellenic residential buildings

The ratio of actual to calculated primary energy consumption using the processed EPC data from over 8500 dwellings, averages 0.56 (i.e. 44% lower energy use than calculated). Findings from field surveys of occupant behavioural changes in the operation of space heating systems, confirm poor indoor thermal comfort conditions resulting from reduced operating hours of space heating, lower thermostat settings etc., which deviate significantly from normative calculation assumptions. Other field data on actual energy use before and after refurbishment provide additional insight for adapting the predicted savings as a result of common retrofit actions. Popular measures include for older buildings the installation of double glazed windows, the replacement of heat production systems and roof thermal insulation. On average, the weather corrected actual primary heating energy savings are about 21% by installing double glazed windows and about 18% by replacing an oil-fired boiler with a new natural gas unit. The application of the results with a building stock model illustrates that future energy and emission targets could be reached with the conservative adaptation factors, but will mandate combined measures and more aggressive modernization rates using an average trend scenario.