How to estimate realistic energy savings in Energy Performance Certificates

Given the fact that most MS use fixed or other kinds of default values as boundary condi-tion input for energy performance calculations, it is not surprising that the calculated energy performance differs from the measured energy consumption. As a consequence, the calculated energy savings due to suggested building energy upgrading in the EPC will also deviate from the actual achieved energy savings.
Adjusting input boundary condition to the actual values, will often result in realistic (compa-rable with measured energy consumption) calculated energy demands. This even happens in simple, quasi stationary calculation tools using monthly average values.
The optimum solution for energy performance certificates and calculating realistic energy savings is to have two calculations. One calculation, using default values to calculate the label itself, and one with actual input parameters for calculating energy performance before and after implementing energy saving measures. Actual values though, may be diffi-cult to identify, so there is a need to make adaptations to reality easy. Even if actual values are available, there are still issues that cause calculated energy savings to differ from the obtained savings. These are the prebound effect, i.e. before refurbishment users of poor energy efficient building are using less energy than predicted and the rebound effect where users of energy refurbished efficient buildings are using more energy than predict-ed, therefore the amount of energy saved is lower.
Fixing the boundary conditions for the national standard EP calculations is highly important for the calculated energy performance and hence the EP requirement level that MS set. It has great influence on the EP if there are 2 or 4 persons in a house, and the same goes for the rest of the standard parameters that constitute the boundary conditions for the cal-culations. Buildings subject to different loads will perform differently under different boundary conditions. The first part of the double session demonstrated the influence of boundary conditions on calculations of the same building subject to the variation of boundary conditions (except climate data) and highlight differences in boundary conditions used in different MS.