Setting the benchmark: Wilmott Dixon's Energy Synergy

R eflecting its vision of better-performing buildings for society and the environment, CIBSE expanded its annual awards this year to include two new categories: Building Performance Evaluation – Practice; and Building Performance Evaluation – Product or Innovation of the Year. Contractor Willmott Dixon won both the Building Performance Evaluation – Practice and the CIBSE Next Generation of Building Performance Award with its Energy Synergy building performance management service. Designed to monitor operational energy and close the performance gap between design and in-use operation, judges hailed Energy Synergy as an excellent example of building performance monitoring and said it demonstrated best practice in a 'reliable, replicable and scalable way'. The system now monitors 50 projects and those with 12 or more months of data show an average 15% better-than-predicted performance compared with TM54 projections. Bassaleg School, South Wales, exemplifies the exceptional results that can be achieved. Actual energy use is 21% less than predicted at design stage, which has resulted in annual energy savings of 327,204kWh, savings of 65.11 tonnes CO₂e, and a £98,161 reduction in energy bills. Under the hood Energy Synergy monitors all aspects of operational energy performance, including heating, ventilation, small power and DHW. The process is integrated into a BMS to capture energy-use data, typically over a three-year, post-occupancy period. The service enhances customers' BMS rather than replaces it, and clients retain full ownership and control of data. There are three stages to the Energy Synergy service. Stage 1 is CIBSE TM54 performance modelling, where engineers work with CIBSE-affiliated consultants to develop achievable energy benchmarks. Stage 2 is BMS integration and comprehensive metering. Sub-metering, and measurement and verification after construction, are key to closing the performance gap. Stage 3 is the creation of an AI-supported dashboard, which allows users to identify inefficiencies and optimise performance. Hollycroft Primary School, Leicestershire, benefited from this monitoring when data revealed a mechanical failure in a pump, which was causing inadequate hot-water circulation. By isolating this specific component failure, the school avoided a wider performance decline and restored occupant comfort. Among the other projects using Energy Synergy is Ysgol Gynradd Glyn-Coch in Wales, which opens this month. This 300-pupil, two-storey primary school, designed by architect Stride Treglown, brings together pupils from two existing schools, and includes a nursery and community hub. The school was part of the UK Net Zero Carbon Buildings Standard (UK NZCBS) pilot scheme, under which contractors and engineering teams tested the standard's draft framework on real-world projects. The UK NZCBS is a science-backed framework that provides unified, verifiable performance limits aligned with the UK's 1.5°C carbon budgets. It covers 15 building types, including education buildings (see panel, 'Limits and targets for schools'). The school is being built to the Passivhaus standard and will be certified. The methodology focuses on energy efficiency, exceptional thermal comfort and superior indoor air quality through fabric-first design principles. The design features an air source heat pump for space heating, while ventilation with heat recovery is provided by two AHUs and four mechanical ventilation with heat recovery units. Under Version 1 of the UK NZCBS, Passivhaus certification is recognised as a 'deemed to satisfy' route at practical completion for direct space heating – Passivhaus's core threshold of 15kWh· m-2 per year satisfies the UK NZCBS limit – and energy-use intensity (EUI). The school's space heating demand is predicted at 13kWh· m-2·yr and is currently on track to be lower still. Passivhaus's strict quality assurance ensures that the predicted design EUI in the Passivhaus Planning Package (PHPP) energy modelling service closely matches the actual metered EUI on site. 'As the school was already targeting Passivhaus certification, this gave us a comfortable buffer against the standard's operational energy limit,' says Doug Drewniak, principal sustainability manager, building performance, at Willmott Dixon. Achieving the 2025 NZCBS embodied carbon limit for schools of 530kgCO2 ·m–² was more challenging – for example, when more structural steel than expected was required to support AHUs that had to be placed on the roof. 'A slender timber-frame structure and floor plans not quite stacking vertically meant we needed extra structural steel,' says Drewniak. This meant the upfront embodied carbon figure increased, as did the thermal bridging value in PHPP, resulting in a small operational energy penalty. Drewniak said the project benefited significantly from having a single consultant/coordinator leading the process and requiring assessments. 'Issues were overcome by our excellent consultant Mark Morant, from Arda Consulting. In this case, he coordinated a robust detail with the design team at the external wall junction to minimise thermal bridging and airtightness risk.' Another 'operational reality' was the higher energy demand linked to Wales' universal free-school meals policy. The compact Passivhaus form meant there was not enough room on the roof to install the PVs that would have offset the extra energy needed to provide hot dinners. A collaborative solution was found by installing additional panels in a south-facing canopy, says Drewniak. 'The performance gap between design and in-use operation is not inevitable' Lightening the loads TM54 was the bridge between design and in use, according to Drewniak. While PHPP models the envelope to ensure minimal heat escapes, TM54 models how human behaviour, equipment and occupancy schedules consume energy within that completed building. The real challenge of UK NZCBS is not the fabric, but the extra loads from catering, ICT, external lighting and community use outside of school hours, adds Drewniak, who says using TM54 to predict energy use in realistic scenarios enables an achievable target to be set. 'Without allowing for operational factors or realistic building-use scenarios, there's a real risk of a performance gap.' The second step in Energy Synergy is to create a metering process that measures and manages energy performance in use, and verifies that the TM54 design-stage target is being met. Operational data from this system can be submitted to the UK NZCBS portal to verify that a building is net zero aligned. 'At Willmott Dixon, we've been running TM54 as the benchmark behind Energy Synergy for years. To now have a standard that is finally driving in-use performance feels like our approach has been vindicated', says Drewniak, who would like as-built data used to inform design modelling in Energy Synergy. 'Closing the feedback loop is big on the agenda for us in the coming years, especially if we can leverage AI to assist that process,' he says. Through Energy Synergy, Willmott Dixon has demonstrated that the performance gap is not inevitable. Upfront embodied carbon: Caps emissions from raw material extraction, transport and construction up to practical completion (Modules A1-A5). Schools cap is 530kgCO 2 e·m -2 GIA for 2025. e·m GIA for 2025. Energy use intensity school limit: 45kWh·m – ² per year GIA for 2025. Includes heating, lighting, hot water and plug loads. ² per year GIA for 2025. Includes heating, lighting, hot water and plug loads. Fossil fuels: zero onsite combustion for heating, hot water or cooking. Envelope efficiency: the standard has strict mandates to ensure low energy demand for space heating (typically ≤ 15–20kWh·m – ² per year). ² per year). Renewable generation: there is a minimum requirement based on roof footprint (typically ≥ 80% usable roof footprint). Refrigerants and water: Caps refrigerant global warming potential (GWP), at 677kgCO 2 e·kg–¹ per system, and refrigerant leakage rates, and sets operational water benchmarks litres per person per day.