The performance gap has been, and continues to be, a key obstacle for the UK’s construction industry in meeting the zero-carbon target by 2050.

Whilst the construction is industry making strides by bringing in a tighter definition for Net Zero Carbon (NZC), there is still a large proportion of professionals measuring NZC with EPC ratings.

EPC ratings can be useful for comparing energy efficiency of buildings with the same construction age and primary function, however, they do not reflect the actual operational energy use or running costs of a building.

The graph below from Better Buildings Partnership (BBP) displays EPC bands on the horizontal (x) axis and actual energy data (from over 1,000 properties) on the vertical(y) axis, demonstrating there is no correlation between EPC ratings and actual energy performance of buildings.

Office Energy Intensity by EPC rating 2019/2020 (Source: Better Buildings Partnership)

Standards like NABERS and now the UK Net Zero carbon Building Standard, aim to reduce this performance gap by emphasising design for performance rather than compliance. They ultimately validate the NABERS Energy star rating or NZC status based on actual in-use energy performance. However, these are predominantly voluntary, meaning uptake will remain low until they are adopted within the legislation -especially for minor refurbishments and retrofits where ROI is generally low or inexistent.

EPC ratings are based on a building’s predicted energy use and only based on ‘regulated’ energy consumption, which includes space heating, water heating for domestic use, space cooling, ventilation and fixed lighting. They exclude plug-in appliances, cooking and other unregulated energy uses, which could be significant proportion of the energy use. On 04 Dec 2024, government kicked off an open consultation for reforms to the EPC methodology, looking into the current metrics and even considering operational ratings based off actual energy use.

At Hollis, we advise our clients to steer away from the EPC approach when undertaking Net Zero Carbon Audits and Decarbonisation Plans. EPCs and MEES compliance reports are essential for regulatory purposes and continue to be an important part of our offering. However, the two workstreams must be distinguished based on each client’s ESG drivers and targets.

A recent example highlighting disparity between the two approaches involved a large-scale big-box type retail store measuring circa 150,000sq.ft. (Gross Internal Area). The retailer sells a wide range of products including; electronics, merchandise, household items, and groceries with an on-site restaurant, bakery, hot food counter and butchery. In this case client was particularly concerned about the energy and carbon liability they were inheriting as a part of the overall acquisition. This needed a CIBSE TM 54 operational energy modelling approach rather than EPC.

For the operational energy assessment, our accredited assessor carried out a physical site examination documenting the fabric, plant equipment and fixed services. Additionally, they recorded the number and type of displayed electronics, numbers and makes of refrigerators/freezers, kitchen equipment and other plugged-in loads. A dynamic energy model was then developed using IES VE approved software, incorporating these inputs along with occupancy schedules and diversities based on actual store operating hours and daily forecasted footfall, equipment gains based on the actual equipment information and hours of operation.

Operational Energy Modelling for a 150,000sq.ft. big box retailer (Source: Hollis Global Ltd.)

The graph above shows the disparity between the total Energy Use Intensity (EUI) based on Part L and CIBSE TM 54 methodologies. The most significant difference is between cooling and unregulated energy use, which is 80% higher with CIBSE TM 54 approach. This discrepancy is due to the higher cooling demand during peak occupancy periods and the detailed estimation of energy consumed by plugged-in devices, kitchen equipment etc. For comparison, the CIBSE TM 46 retail benchmarks indicate an EUI of 505kWh/sq.m for large scale food stores.

By undertaking detailed TM 54 modelling, we were able to isolate the major contributors to energy consumption and performed a well-informed interventions study, backed up by in-depth energy modelling, this analysis enabled us to propose a decarbonisation pathway for the asset in line with the CRREM (Carbon Risk Real Estate Monitor) 1.5° pathway. As a result, we were able to delay the stranding by 25 years, helping the asset meet the Greenhouse Gas (GHG) intensity target for 2050.

Do you need expert advice on Net Zero buildings, CIBSE TM 54, CRREM aligned decarbonisation pathways or in need of any energy and carbon modelling?

Get in touch with Deepika Singhal – Head of Building Physics