Skanska implemented a 1.4 million ‘green retrofit’ Energy Performance Contract

skanska maple cross


In 2012 Skanska implemented a 1.4 million ‘green retrofit’ Energy Performance Contract (EPC) project at their head-office site, Maple Cross. The project involved the installation of a number of energy efficiency measures including lighting and BMS, as well as renewable energy generation.

Whilst Skanska had clear reduction targets for the project, 40% on total site consumption and 50% on carbon emissions, one of the main focuses of the project, as an EPC, was to ensure a robust Measurement and Verification (M&V) strategy was employed as this formed a critical part of the performance verification. Skanska engaged EEVS, as a leading provider of independent M&V, and used our experience to ensure an accurate and transparent assessment of the project performance.

Typical client profile for this project

The use of an M&V process guided by the IPMVP (International Performance Measurement & Verification Protocol), used by EEVS to evaluate the Skanska project, is increasingly being recognised by the industry as a best practice approach to measure the performance of energy efficiency projects. Independent and IPMVP based M&V can be applied to any energy efficiency project and is of particular value in Energy Performance Contracts (EPCs), where repayments are dependent on a guaranteed level of saving being achieved.

Challenges & Actions

Skanska sought to assess the impact of the project as a whole as well as breaking down the impact of individual measures on energy consumption. Due to the changeable usage of the Maple Cross site, additional fixed loads were introduced to the site following the 2011 baseline year, including an increased IT load and a coffee bar. Whilst sub-metering of these loads was not available, it was essential that the resulting kWh change was accounted for to enable the accurate assessment of the performance of the green retrofit project.  An additional challenge, in order to calculate the total consumption of the site following the project completion, was how to take into account the onsite generation from the PV cells. Generated kWhs were only available as a running total since the PV cells were installed during the commissioning period.

EEVS was able to draw on the experience gained from assessing 100s of energy efficiency projects to provide a pragmatic approach to tackle the issues Skanska faced and to enable the performance of the project to be accurately verified.

Baseline Model
Initially EEVS calculated an accurate baseline consumption model, this allowed the impact of seasonal variables on the site’s energy consumption to be accounted for. The baseline model provided an indication of the ‘expected level’ of consumption had the green retrofit project not taken place. Due to the accuracy of the model, EEVS was able to use this to identify the level of savings achieved following the implementation of each of the individual energy efficiency measures.

Accounting for Additional Fixed Loads
As neither of the additional fixed loads were individually metered, EEVS had to provide an alternative means of calculating their impact on consumption. The following two approaches were used:

  • The impact of the IT load change was identified through inspection of the half-hourly baseload consumption data. The observed half-hourly baseload change was used to calculate a daily kWh impact of the additional IT load. The associated kWh increase was then accounted for within the ‘expected level’ model calculations.
  • EEVS used statistical t-tests to verify whether the introduction of a coffee bar had resulted in a significant change in consumption. These tests identified that the coffee bar had not significantly impacted consumption and therefore the savings of the project and did not need to be accounted for within the Savings Analysis calculations.

Assigning PV Generation

In order to assess the performance of the green retrofit project a means of separating the electricity generated by the PV cells, prior to and following the project completion, needed to be developed to allow total post-retrofit consumption to be calculated.  EEVS used daylight minutes data over the period of operation of the solar cells to provide informed estimates of the kWh production over both periods.

Lessons & Results

The complexities of the Skanska project, which on the surface appeared to limit the ability to assess the effectiveness of the energy efficiency measures, prompted EEVS to develop innovative technical solutions. This approach provided Skanska with a valuable insight into the impact of the green retrofit and also highlighted how the application of good M&V could be used to assess the performance of Skanska’s future projects with their clients.

Engaging the client throughout the M&V and Savings Analysis process was essential in order to ensure that Skanska were clear on the results of the M&V Plan and on the means by which the changes to the site’s load would be accounted for, in the absence of detailed sub-metering. We learnt that discussing our outputs and methodologies for identifying savings at the site as our work progressed, through emails, meetings and calls, was vital in aiding the client’s understanding of the M&V process. Following the positive feedback we received, regarding our support and involvement, we now strive to ensure all our future work engages clients in the same capacity.

EEVS were able to use pragmatic technical solutions whilst applying the principles of the IPMVP to provide Skanska with a Savings Analysis document, which clearly outlined the approaches used to assess the performance of the project. EEVS’ transparent approach, through written reports and discussions with Skanska, ensured that Skanska was confident that the approach used to assess the performance of the project was robust and that EEVS would provide the technical expertise to ensure the performance of future projects could be assessed in an equally robust manner.



EEVS provided Skanska with a methodology able to test for significant fixed changes in energy consumption, such as changes to IT load, and determine their approximate impact. Importantly we managed to do this in the absence of any sub-metering, by analysing the half-hourly data and applying statistical techniques”


At Skanska we are constantly striving to provide more sustainable buildings.  EEVS has provided Measurement and Verification tools and an independent view on the effectiveness of the energy efficiency solutions installed at the Maple Cross site.  We now know how M&V can in turn be used to bring insight to our clients.”

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