– Klaas Calle –
For residential high-rise, the facade is the most important part of the building envelope. Therefore, and because of the high need for renovation of this type of buildings in Belgium, a model was developed to quickly evaluate facade renovation strategies for a specific building. The model uses pareto-optimisation to balance the initial investment to renovate and insulate the building, versus the cost for heating and cooling the building over a 30 year period.
The financial analysis is based on the net present value, and next to the initial investment, fuel costs, maintenance and residual value are taken into account. The model is applied to a case study project “Kielpark” in Antwerp, Belgium.
Firstly, all thermal and financial data on the considered renovation strategies, the existing building envelope, and financial forecasts (inflation, oil price, interest) are entered into a simple spread sheet. Subsequently, all possible combinations of strategies to renovate the windows, walls, floors, roofs, airtightness… are calculated with Matlab in terms of investment, energy use and net present value over time.
In the next step, all hundreds or thousands of combinations are run through a Pareto optimization to find an optimal balance between the total actual costs and the thermal performance of the facade for the different economic forecasts. For example in the case of Kielpark, it was concluded that for ETICS thicker insulation packages are cost effective, whereas for concrete sandwich panels the increased cost for longer anchors leads to rather poorly insulated cost-optimal solutions.
Finally, although the window frames and the glass have a significant impact on the overall U-value, it was found that the initial investment could not be compensated for by the reduction in energy use over time.