What is the difference between Energy Diagnosis and Energy Performance Certificate?


Emma Potter

An issue that is often the cause of misunderstandings and misunderstandings, namely the difference between Energy Diagnosis (DE) And Energy Performance Certificate (APE).

Such documents, in fact, at first glance could be considered superimposable since they come from same calculation methodology (the UNI TS 11300 standards) and which both measure the energy performance of a building.


L'APE – Energy Performance Certificate is drawn up through a “standard” calculation methodology (asset rating according to UNI TS 11300:2) whose input data are based on a standard use of the building and a standard climate. Therefore, in determining the energy performance for the drafting of an APE is not taken into account in any way of the following factors:

  • user behavior;
  • real climatic conditions.

To draw up an APE, the rules UNI TS 11300:2 in fact, they impose that there are standard conditions inside the building (e.g. the internal temperature during the entire heating period established by the Presidential Decree 412/1993 is constant, equal to 20°C, for 24 h/day) regardless of how the user uses it.

Furthermore, the external climate is that of regulations, i.e external temperatures are those established by decree, which can also differ significantly from the real ones. It is clear that this only represents an ideal modeluseful for being able to more easily compare the energy performance of different buildings.

The objective of energy certification, in fact, is not to indicate an absolute value of the building's energy consumption, but to provide an comparable reference value of potential energy consumption, so as to guide the user towards the purchase of a property instead of another.

A parallel can be made with the car market: the manufacturer provides us with data regarding the consumption of that vehicle, determined in particular laboratory conditions, but even if we know that they will differ from the real ones, they can provide us with indications about the model that we intend to choose. The same happens when we go to buy an appliance.

Energy diagnosis

There Energy Diagnosis (DE) it is instead carried out in operating conditions of the buildingon the basis of the data collected on occupancy, actual use of the systems (continuous or intermittent) and the real climatic conditions, relative to the period considered for the execution of the DE.

In other words, in the case of DE, the regulation requires that the simulation model is capable of reproduce as faithfully as possible the real operating conditions of the building in the years for which consumption is available, so as to make the comparison between the latter and the calculated needs meaningful.

It's obvious that a DE it can be done only on existing and already lived-in buildingsfor which the consumption data of the energy used are available, while a bee it can be edited for any buildingeven of new construction and therefore with consumption data not yet available.