40% reduction in electricity consumption: energy audit methodology

02

The framework

The -40% target does not have the same technical reality depending on the building. Savings potential varies from 15 to 25 points depending on use, and the wrong initial trade-off costs two to three years of ROI.

We distinguish three profiles with which the audit strategy must align before any recommendation:

• Standard offices (administrative workstations, open floors): lighting and air conditioning are generally the leading consumption items and often account for more than half of the energy bill. These are the fastest levers to activate.
• Intensive-use buildings (data centres, laboratories, trading floors): 60 to 70% of consumption is concentrated on technical equipment and cooling, with PUE as the management indicator.
• Mixed-use buildings (head offices with catering, training, event spaces): an overlay of uses that requires segmentation by functional zone.

The fundamental trade-off concerns the investment/ROI split: immediate-impact actions (LED, presence detection, HVAC control) or an overhaul of primary installations. The gap between the two strategies can be significant depending on the building: quick-win actions offer a fast return, while an overhaul of primary installations maximises long-term gains. The audit must therefore quantify the savings potential item by item, setting the reference year.

When the -40% target is not the right path. On a building renovated after 2015 whose consumption is already below 90 kWh/m²/year in specific electricity, aiming for a further -40% leads to a ROI exceeding 12 years. The absolute-value Cabs pathway becomes more relevant than Crelat. Below 500 m² of auditable surface, the fixed cost of the detailed audit absorbs the gain: a lightweight level 1 audit is sufficient, and we steer you toward that route.

03

Your gains

For the referent and the CFO: an audit that turns into asset value

The audit is not a technical end in itself. It is the supporting document that secures the annual declaration and avoids the penalty provided for in article L174-1 of the French Construction and Housing Code (publication, administrative fine up to 7,500 EUR for a legal entity).

Our deliverable produces three elements directly usable on the platform:

1. Consolidated reference year: reasoned choice between 2010 and 2019. The year declared spontaneously is rarely the optimised year, and a rigorous audit identifies the one that maximises the margin on the Crelat target.
2. Correctly assigned ASSET activity category and sub-category: a wrong assignment shifts the reference Cabs value by 20 to 60 kWh/m²/year.
3. Quantified 2030-2040-2050 pathway in %Crelat and in kWh ef/m²/year Cabs, to enable the regulatory trade-off at each decennial milestone.

For the CFO involved in the file. A properly prepared audit turns the regulatory obligation into an asset-valuation lever. On Kytom operations where the Cabs pathway was adopted, IPMVP option B (volume 1) made it possible to document an energy OPEX reduction of 18 to 32 EUR/m²/year, directly integrable into the rental value calculation. At the scale of an 850 m² head office, this represents 15,300 to 27,200 EUR/year of OPEX avoided, equivalent to a marginal rent over the term of the lease.

04

Real-world case

Three mistakes that wipe out part of the theoretical gains

In the field, three mistakes regularly compromise reaching -40%, and each produces a measurable effect on the regulatory pathway for reducing tertiary-sector consumption. We have documented them on our recent deliveries.

1. Underestimating user behaviour. Even with high-performance equipment, user behaviour can wipe out a significant part of the theoretical gains: screens left on, manual overrides on thermostats, permanent lighting in sparsely occupied zones. We systematically plan a user-support phase over the first 6 months.
2. Sequential approach to interventions. Handling lighting in year 1, HVAC in year 2, control in year 3 generates extra costs (removal-reinstallation, redundant wiring) and regulation inconsistencies between technical packages. We group interventions into 12-week windows to neutralise these extra costs.
3. Neglecting interfaces between utilities. An isolated optimisation of LED lighting reduces the free heat contribution in winter, which can degrade the heating balance in peripheral spaces, an effect often underestimated in package-by-package approaches.

In concrete terms at Kytom, the analysis of interactions is integrated from the preliminary summary design (APS) phase, but only on configurations with 3 or more distinct technical packages. The systemic approach is often presented as a general rule; in practice, it only becomes profitable from three or more distinct technical packages. Below that, a package-by-package audit remains more economical.

05

When not to go ahead

Three configurations where we advise against the -40% audit

Our profession demands commercial honesty: there are cases where the -40% Crelat pathway is not the right trade-off, and where a heavy audit destroys more value than it creates.

Building already high-performing (below 90 kWh/m²/year in specific electricity). The residual savings potential is too thin to absorb the cost of a detailed audit. We recommend the Cabs pathway on absolute value, declared alone, with a lightweight level 1 audit (3 to 5 man-days versus 25 to 40 for a complete audit).

Portfolio below 500 m² of auditable surface, single-utility. The fixed cost of the audit absorbs the expected gain. A simplified technical diagnosis, coupled with LED and presence-detection quick wins, captures 70 to 80% of the savings potential for 20% of the audit budget. This is the trade-off we systematically propose for agencies and small head offices.

Asset disposal planned in less than 24 months. The ROI of a -40% programme unfolds over 5 to 8 years. If the disposal is decided, the investment benefits the acquirer, not the seller. In this case, we steer toward a minimalist compliance audit (secured declaration, no investment) and a valuation memo intended for the acquirer.

In these three configurations, we say so in the first meeting. Better to lose a mission than to deliver an audit that will not serve any purpose: this is also why 1200+ clients have renewed their trust in us since 2006.

06

Method

1. Historical analysis
   We consolidate the reference year between 2010 and 2019, reconcile the EDF/Engie invoices with the time-stamped load curves and prepare the dual Crelat/Cabs calculation. Duration: 2 weeks.
2. On-site diagnosis
   Our engineers map the consumption items by sub-metering, identify the drifts (permanent lighting, HVAC overrides, oversized DHW) and qualify the interfaces between utilities. The deliverable distinguishes quick-win savings potential from structural savings potential, with enforceable kWh/item quantification. Duration: 3 to 4 weeks depending on technical complexity.
3. Scenario modelling
   We build 3 quantified scenarios expressed simultaneously in %Crelat and in kWh ef/m²/year Cabs, with ROI, CAPEX, projected OPEX and documented rental value reduction. This dual reading preserves regulatory optionality at the time of the energy declaration. Duration: 2 to 3 weeks.
4. Works phasing
   We group interventions into 12-week windows to neutralise removal-reinstallation extra costs, coordinate the technical packages (lighting, HVAC, DHW, BMS) and set the IPMVP option B measurement milestones. The action plan is ranked by decreasing ROI. Duration: 1 to 2 weeks.