News + Insights

Playing by the rules – ESOS and MEES

This article originally appeared in the Chartered Institution of Building Services Engineers (CIBSE) Journal – download their April edition here

Sustain’s Amy Dartington and Stuart Gray explain how Unite Students embraced ESOS and MEES to bridge the performance gap

With more than 150 buildings in 28 cities, Unite Students is one of the UK’s leading providers of student accommodation. The business places great importance on carbon management and this – coupled with legal requirements – resulted in the firm embarking on an ambitious programme to achieve an 80% carbon reduction on its buildings by 2050, against its 2014 baseline.

In spring 2015, Unite Students began working with Bristol-based energy and carbon management company Sustain on its compliance with the Energy Savings Opportunity Scheme (ESOS). Sustain has since continued to offer portfolio-wide analysis for Unite in relation to the Private Rented Sector Energy Efficiency Regulations – known in the industry as the minimum energy efficiency standard (MEES).

Between 1 January and 31 December 2014, Unite’s energy spend was £14.7m. For the sites at risk of non-compliance, Sustain identified a potential annual saving of £380,000, allowing them to achieve compliance with MEES.

From compliance to target

Sustain carried out new Energy Performance Certificate (EPC) assessments across Unite Students’ estate. It added the data to the ESOS assessment and created an asset-management database that could be built on with further data relevant to energy management.

ESOS and MEES helped to drive Unite Students’ carbon and energy ambitions, as required by the regulations – an audit across 90% of energy use (ESOS) and EPCs for all buildings (MEES). They also helped it achieve sign-off on exacting carbon-reduction goals; Unite Students has committed to a target with the Science Based Targets Initiative (SBTI), which helps companies determine by how much they must cut their emissions to prevent the worst impacts of climate change.

The work carried out for ESOS gave the board external validation of the opportunities and the costs to deliver the target, as well as the confidence to sign off on carbon-reduction targets in line with the Climate Change Act and current science. Further confidence in the programmatic approach has been generated by the work in response to MEES. This devised the optimum solution for balancing carbon reduction, Simplified Building Energy Model (SBEM) improvement and cost saving, while driving the ambition to get better data on which to base investment decisions.

Once the case is made at a strategic level, building-level business cases are required by ESOS and MEES to ask: What are we spending? Where are the opportunities? How are our buildings performing and how can we improve this cost-effectively? What level of performance do we want? Answers to these can form a robust energy-efficiency programme.


Sustain and Unite Students set out to bridge the performance gap between SBEM-predicted energy consumption and actual, metered consumption. Sustain built a bespoke end-use profile for Unite Students’ buildings, with the same metrics as SBEM, and using a methodology that allowed it to calculate building-specific profiles. It then applied the Energy Conservation Measures (ECMs) to the profile, using known data points and data points sourced from SBEM. The result was a hybrid model that meets compliance and informs investment planning.

Unite Students needs to balance competing demands for the ECMs. Perversely, demand for SBEM improvement can be at odds with that for carbon reduction. In response, Sustain built a simple ranking methodology that normalises competing benefits to a cost per benefit – carbon saving, SBEM score or return on investment (ROI). Each of the metrics is assigned a weighting out of 100, and can be amended to reflect the priorities at any given time. Using the weightings, an ECM is given a score – also out of 100 – relative to the rest of the ECMs for that building. Unite can then use a single metric to evaluate the returns an ECM will achieve relative to all proposed ECMs, tailored to its priorities.

The ESOS and MEES exercises followed the first four of five stages:

Review: Collate and evaluate Unite’s energy performance

Target: Prioritise the worst-performing areas

Identify: Propose solutions to improve performance and comply

Verify: Evaluate and propose programmes to achieve targets

Practice: Solution pipeline flowing through to installation.

We delivered a workshop to present the results, train Unite Students’ staff to use the analysis tool, and discuss the process for implementation, helping Unite develop a new energy-management process that is currently being rolled out. After presenting a list of recommendations provided by ESOS, targets were set to develop business cases and the most efficient way to arrive at installations that satisfy MEES, internal targets, affordability, feasibility and practicality.


Unite has a relatively uniform portfolio of sites; replicable specifications for fit-out allow it to group buildings by building services. Although the sites perform well, the focus for Unite was reducing consumption from the building services, while maintaining a comfortable and flexible environment suitable for the needs and occupation of each student.

We looked at Unite’s space-heating services – researching control strategies and trialling different heaters – as well as the domestic hot water demand, where potential savings could be made with heat pumps.

First, we advised Unite to get a firm understanding of its end-use profile. The vast majority of Unite’s sites have a single half-hourly electric meter, recording space heating (electric heaters), domestic hot water (showers, washing), lighting, small power, and ventilation. Our advice was to target measures to reduce high end-use consumers.

The issue for hot water and space heating was the carbon intensity of grid electricity. Unite was presented with two options: look to increase the efficiency of its services – through heat pumps, for example – or change to a less carbon-intensive fuel such as gas or biomass.

In high-rise accommodation, we advised Unite to look at the current services infrastructure, asking: how much room is in the risers and is there an existing distribution system for domestic hot water? The feasibility of retrofitting a central wet heating system will be the deciding factor in investment appraisals. We advised Unite to review all floorplans with proposed space heating changes to determine where wet distribution systems could be retrofitted with minimal difficulty.

The residential-style use of its buildings means there is a high demand for domestic hot water. Where buildings currently have a central electric water heater, it is practical to consider replacement with a heat pump; this way, Unite can trial the technology without the added complication of the distribution system.

Sustain has highlighted the practicalities of installing the measures to the setup of Unite’s buildings, and using practicality as a factor for evaluating investments. A ‘complexity factor’ is now a recorded data point within Unite’s asset register when surveying its buildings.

Unite Students, with Sustain, used ESOS and MEES to push for a systematic, long-term asset plan. With the firm’s internal targets, the regulations encouraged a new energy-management process, creating a repeatable methodology for designing a programme for action.

Amy Dartington and Stuart Gray are senior associates at energy and carbon management company Sustain.

Share This