How an energy performance certificate (CPE) is calculated under Mc 001-2022

For many owners, the energy performance certificate (CPE) remains a bureaucratic document obtained in a hurry before a sale or a lease. For the energy auditor who prepares it, however, it is the result of a process with well-defined steps, in which every wrongly entered piece of data carries straight into the energy class shown on the certificate. This article reviews the legal framework, the data required and the methodological stages of the calculation, without going into the calculation formulas themselves — these belong to the technical standards that the methodology uses as its basis.

What the CPE is and what the law says

The certificate is made mandatory by Law no. 372/2005 on the energy performance of buildings, republished. The law provides that the certificate is prepared for buildings that are constructed, sold, leased or subject to major renovations, as well as for buildings owned by public authorities or frequently visited by the public, with a useful floor area of over 250 sq m. The document must be made available to the buyer or tenant before the contract is signed, and for a new building it is presented at the acceptance on completion of the works. The certificate is valid for 10 years from the date of issue, except where a major renovation subsequently changes the building's energy consumption, in which case a new certificate is required.

Law 372/2005 also provides, in art. 5, that the line ministry prepares and approves by order the technical regulation on the calculation methodology. That regulation is Mc 001-2022, approved by Order MDLPA no. 16/2023, published in the Official Gazette no. 46 of 17 January 2023. As a general rule, the order entered into force 30 days after publication, with one exception: a few sub-chapters of the annex — those on the thermal envelope and on the assessment of energy consumption — had an application period of 180 days from publication, to give the industry time to adapt. Mc 001-2022 replaces the old Mc 001-2006 methodology and is structured modularly, so it can be applied both to an independently assessed apartment and to a building with complex installations shared by several units.

The content of the certificate is set by the same order: the energy class, the total specific primary energy consumption, the CO₂ emission index, the share from renewable sources, the calculated values of final and primary energy consumption, as well as recommendations for reducing consumption, with the estimated savings and associated costs.

What data is needed for a correct calculation

A correct calculation always starts from a complete survey of the building, not from assumptions. The data that goes into the calculation falls, broadly, into three categories:

• Administrative and identification data — the address, the year of construction, the use of the building or building unit, the height regime, the climate zone in which the building is located (relevant for the reference temperatures used later in the calculation).
• Building envelope — the areas and composition of the envelope elements (exterior walls, floors, roof, windows and doors), including any thermal rehabilitation work already carried out, in part or in full, as well as the structural thermal bridges.
• Building installations — the heating system, domestic hot water preparation, ventilation, air conditioning where it exists, lighting for non-residential buildings, with the type of equipment, its age and the efficiencies declared by the manufacturer or found on site.

This data forms the base on which the methodology is applied; its quality determines, in turn, how close the calculated result is to the real energy behaviour of the building.

Methodological stages of an audit

At the level of the process, regardless of the tool used, an energy audit follows a sequence of stages:

1. Collecting field data — the site visit, measurements, photographs, identifying the existing technical documentation (technical file, design, energy bills from previous periods, where available for comparison). 2. Characterising the thermal envelope — determining the areas and thermal resistances of the envelope elements, based on the identified constructive compositions. 3. Characterising the installations — describing the heating, domestic hot water, ventilation and, where applicable, air conditioning and lighting systems. 4. Calculating energy demand and consumption — determining, according to the methodology, the building's energy demand for each use (heating, hot water, ventilation, etc.) and converting it into final energy consumption, then into primary energy, through the conversion factors specific to each energy carrier. 5. Assigning the energy class — comparing the calculated result with the thresholds that define the A→G rating scale, set by the methodology for each building type. 6. Generating the certificate documents — the certificate itself, together with the annexes that detail the input data and the recommendations for reducing consumption, as well as the calculation brief that justifies the result.

For the technical details of each stage — the heat transfer coefficients, the energy conversion factors, the exact calculation method for each energy carrier — the Mc 001-2022 methodology relies on the SR EN ISO 52000 series of European standards, together with other related SR EN standards. These standards are commercial documents, available for purchase from ASRO, and their content cannot be freely reproduced; the auditor who applies them must have legal access to them.

Frequent data-collection errors

Most deviations of the final result from the real behaviour of the building come not from the calculation itself but from the data entered at the start:

• Roughly measured envelope areas, especially in old buildings, without an up-to-date survey, where differences from the original design can be significant.
• Ignoring thermal bridges or treating them generically, although they influence the heat demand.
• Confusing the climate zone or using incorrect reference temperatures for the site.
• Outdated installation data — a recently replaced boiler that was not recorded, or efficiencies estimated instead of the real ones declared by the manufacturer.
• Ignoring partial rehabilitation work — insulating a single facade or partially replacing windows and doors, not correctly recorded in the survey.
• No check against real consumption, where bills are available, as a plausibility benchmark for the calculated result.

Each of these errors carries straight into the energy class shown, and therefore into a document that the owner later uses in transactions.

The role of dedicated software

A dedicated software tool does not replace the field survey or the professional liability of the attested auditor — these remain entirely the auditor's. What well-built software can do is reduce the risk of human error in the repetitive stages: validating the consistency of the data entered (areas, orientations, types of building elements), correctly applying the conversion factors set by the methodology, generating the final documents — the certificate, Annex 1 and Annex 2, the calculation brief — in a standardised format consistent with the requirements of Order MDLPA 16/2023, and keeping a verifiable archive of the input data for each certificate issued.

It is important to state that no software on the market, including Zephren, has official validation from MDLPA — legal responsibility for the correctness of the certificate remains entirely with the attested energy auditor who signs it.

For auditors who want to reduce the time spent on the administrative part of an audit and generate the CPE documents from a single data flow entered once, the structure above — from data collection to generating Annex 1+2 and the calculation brief — can be followed digitally in the Zephren calculation program.