THE ENERGY FUTURE OF EXISTING BUILDINGS IN BRUSSELS: BETWEEN PRESERVATION AND PERFORMANCE

The audit techniques

The audit of the eleven buildings was carried out by Centre Urbain using PAE (EnergyAudit Procedure] software, currently used by auditing firms. It is interesting to be able to analyse and critique this PAE method and the results that it provides. The main point is the difference between the reality of the building's occupation and what the calculation takes into consideration. A factor of 2, or indeed often far higher, is often diagnosed for a single-family house. The occupancy scenario - how the rooms are actually used - is a decisive factor, even more so if the renovation is intended to be cost effective. By over-estimating the costs of renovation, the payback periods calculated become too long. In most of the cases examined, the PAE software calculates a payback period that exceeds the lifespan of the renovation solutions, and this is in the best-case scenarios. These findings can be interpreted in a number of ways:

- The required level (U value) is too high;

- The solutions envisaged are not suited to the consumption profiles of old buildings; or

- The software is not appropriate for energy audits of old buildings.

DEFINITION OF A RENOVATION PROJECT OR FINDING A BETTER BALANCE

Winter comfort is often the sine qua non of renovation. This is the criterion that takes precedence in the standard calculations. However, the measures taken for winter comfort must not counter summer comfort. For example, interior insulation of solid walls may compromise the benefits that they provide in the summer. In the same vein, it is necessary to anticipate the problems that may be created by the renovation work.

Furthermore, there is also one essential element missing in the reasoning applied to renovations: the behaviour of users. This means understanding that people's behaviour is unpredictable and does not follow a pattern. The sociology of the building must be taken into account when dealing with a renovation. Without the residents' support, the energy saving objectives being sought will remain out of reach.

Fig. 10

Example of a PAE audit, carried out on a neoclassical building. The payback periods calculated are long. If the economic actors do not see any financial benefit in undertaking energy efficiency works, the overall objective of a 20% reduction does not seem to be achievable. There is a high chance of the grants being misappropriated and fuelling a windfall effect (© Centre Urbain).

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