NZEB: a step forward or backward for energy efficiency?

Building thermal regulations have evolved over the last few decades in different European countries by tightening the thermal performance requirements of buildings to asymptotic levels of performance that will now be expensive to exceed.

The main challenge now lies in the effective and radical improvement of the thermal performance of old buildings. This is a technical and financial challenge that cities must seriously address.

Nevertheless, at the same time, it is not forbidden to think about an additional step to be proposed for new buildings. This is the object of NZEB (nearly zero energy buildings). In addition to a first-class thermal performance, these buildings will have to generate electricity so that their electricity consumption, seen from the distribution network, continues to decline.

Does this emerging standard offer an ideal continuity to the current thermal regulations?

In the field of electricity generation, the most suitable renewable technology for buildings today is solar photovoltaics. Depending on the cases I have dealt with or accessed to, between 12% and 20% of the buildings have a roof adapted to receive an efficient installation of solar photovoltaic. The others are poorly oriented or are in the shade of other buildings for much of the day.

In 80% of the cases, the NZEB standard will impose a very poorly performing generation plant, whereas in other cases the well-oriented roofs will only be used partially.

This suggests a sharing of generation capacities imposed by the NZEB standard between buildings: either the standard applies to a group of buildings, a district, or it requires, as already exists, the production of certificates. These certificates are granted to any building incorporating an electricity generating installation and the certificates corresponding to the integrated excess capacity are transferable to other buildings not benefiting from favourable conditions to integrate a local production.

The same applies to the production of thermal energy from renewable sources. They are more efficient when they are shared.

Depending on how it is implemented, the NZEB standard can prove to be a fantastic lever for the development of renewable energies and energy performance or a disastrous mechanism for the development of inefficient installations.

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