ONLINE BRUSSELS HERITAGE - ONE-DAY SEMINAR - 11/12/2014

idea of the scale we can expect regarding energy-efficiency and costs. Additional audits will provide more information and provide a clearer picture of the qualities of the houses and the financial means needed to realise the energy policy of these social housing residences. The return on investment time (ROI) plays a crucial role in decisions, both short-term and medium-term. “Medium-term” means a term which is reconcilable with the 2040-2050 energy goals.

On the one hand, the estimated costs of the works (as described in detail in the management plan] are taken into account when calculating the ROI. On the other hand, the obtained energy saving also plays a role in both the ROI and the energy costs. The energy saving is the difference between the current consumption and the estimated future consumption. Over the years, it has become ever clearer that energy use models can divert greatly from actual consumption. Old, non-insulated buildings appear to draw their energy performance from other, undocumented qualities. They consume much less (up to 3 or 4 times less) than what can be expected based on the calculations. In the past, this has also been found to apply to the houses of the Le Logis and Floréal garden cities. In the energy audit of the two aforementioned houses, it was therefore conservatively assumed that the houses consume 2.5 times less than indicated by the calculations⁵. This difference between actual and calculated consumption also leads to a difference between the ROI based on the actual consumption and that based on the theoretical, calculated consumption.

With the goals for 2040-2050 in mind, the following conclusion can be made based on a preliminary evaluation of the energy efficiency of the measures provided in the management plan:

• A 50% reduction in energy consumption with a selection of measures

a) with an ROI of less than 50 years,

Fig . 6

Various measures are presented on the plans for a specific type of house.

44 | The listed houses of the Le Logis and Floréal garden cities