Cep / Cep,nr (Primary energy consumption)

The Cep and Cep,nr measure a building's primary energy consumption over one year, in kWhEP/m².year. The Cep aggregates all primary energy (renewable or non-renewable) related to regulated uses; the Cep,nr only considers the non-renewable portion. These two indicators, central to the RE2020 regulation, are used to verify project compliance, compare different options (building envelope, systems, renewable energy sources), and guide a credible energy/carbon trajectory.

Cep / Cep,nr: operational definition

The regulatory scope covers, depending on the type of building, heating, cooling, domestic hot water, lighting and auxiliary equipment (pumps/fans/BMS). Final energy consumption (kWh) is converted into primary energy using coefficients specific to each energy source, then related to the reference surface area.

Cep = sum of kWhEP of all uses.

Cep,nr = same logic, but only counting the non-renewable part.

Practical consequences: improving the building envelope (low Ubat, treated bridges), choosing efficient systems (heat pumps, recovery, variable speed drives), controlling (BMS, schedules) and promoting local self-production of energy (to reduce grid demand) are the major levers to lower Cep and especially Cep,nr.

Read and optimize Cep / Cep,nr in project

What Cep / Cep,nr actually measure (and compare)

• Building envelope efficiency: heat loss, managed free heat gains, summer/winter comfort.
• System performance: yields, regulations, flow rates/ΔT, recovery.
• Energy mix: impact varies depending on the source and conversion into primary energy.
• Control: schedules/instructions, sequencing, peak shaving via BMS.

Limits to keep in mind

• Conventional indicators: actual uses (densities, times) may diverge.
• Auxiliaries and perimeters: depending on the buildings, not everything is always counted the same way.
• A good label alone does not guarantee controlled OPEX without monitoring.

Key points to consider for effective action

• First envelope: EWI, low Uw joinery, treated Ψ/χ bridges → Ubat ↓.
• Energy-efficient systems: low temperature emitters, heat recovery, variable speed drives, balancing.
• Control: optimized water law, realistic schedules, remote meter reading and BMS alarms.
• Local energy: sizing self-consumption according to the load profile (not just the available surface area).
• Measurement & verification: compare calculations with meter readings (kWh useful/electric) to correct any deviations.

Anecdote — “Kwh put back in order in La Rochelle”

In La Rochelle, a mixed-use building aimed for RE2020 compliance, but its Cep,nr (primary energy consumption) was problematic. The team first lowered Ubat (by treating electrical panels and adding external insulation to the gable ends), then adjusted the heating curve and sequenced the morning heating cycles via the building management system. Finally, self-consumption was aligned with the load curve (prioritizing domestic hot water and ventilation during the day). The result of the recalculation: a significant decrease in Cep and Cep,nr, without oversizing the equipment. The building manager summarized: "We weren't looking for more kWh; we were mainly focused on avoiding excess kWh."