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  • Writer's pictureKaren Fletcher

The SectorScope report: Low carbon retrofit

On 14th September, Mitsubishi Electric hosted a seminar in London as part of its On the Road to Net Zero series. The presentations focused on how building owners can decarbonise their existing buildings, particularly large office spaces.

Opening the seminar, Mitsubishi Electric’s Commercial Product Group Director, Phil Ord noted: “Even though the decarbonisation of the UK electricity grid is progressing, we still face a considerable challenge. We must think about how we will decarbonise our existing building stock. This means considering how we would heat a building like the Gherkin, for example, without gas boilers.”

He also highlighted the problem of balancing the costs of retrofitting for Net Zero with the benefits, and how building owners can make these complex decisions.

This is exactly the question that the UK Green Building Council (UKGBC) has been addressing in its latest research – a cost evaluation study into commercial retrofit measures. The study, which is due to be published in full later in 2023, is part of the UKGBC’s Advancing Net Zero programme (launched in 2018). Its goal is to drive carbon emission reductions from the built environment with the overarching mission for the UK built environment to achieve net zero carbon by 2050.

The aim of the study is to create a basis for building a business case for commercial building retrofits that reduce the carbon footprint of buildings. Speaking at the event, UKGBC Senior Advisor, Anna Hollyman, said: “There are huge opportunities for easy wins to optimise the performance of buildings. But we are past the point where incremental change will make an impact. Radical change is the key.”

The UKGBC’s research is spotlighting large commercial offices. The reason for this is the impact they have energy use and emissions. “Just 7% of UK non-domestic buildings are over 1,000m2 in size, but they are responsible for 53% of total non-domestic energy consumption,” explained Hollyman.

However, even thought these large offices represent only 7% of the office stock by number, they make up 50% of the floor area. Tackling the energy and carbon performance of the largest buildings therefore has a greater potential impact on the footprint of the commercial building sector.

The work carried out by the UKGBC is at a draft stage, however it has highlighted several important lessons:

* Retrofitting buildings for Net Zero is an iterative process. That is, it shouldn’t be regarded as a ‘one-off’, but a long-term and constant optimisation of building performance. At every stage, collecting data on energy use is vital to understand what’s working and where new improvements can be found.

* The UKGBC categorises retrofit as ‘Light’ or ‘Deep’. Each has different time, cost and carbon reduction implications.

Light retrofit examples:

* Occupancy sensors

* Lighting upgrades

* Circadian lighting

* Packaged MEP

* Optimised building controls

* Low energy office appliances

Deep retrofit examples

* Floor and ceiling insulation upgrades

* Façade replacement

* Major plant replacement

* There is no requirement to make an either/or choice between light or deep retrofit. Each building owner must plan their approach to retrofitting. It may be easier to start with light retrofit steps. Bear in mind that carbon reduction is cumulative – carbon saved right now will continue to be saved for years into the future. Therefore even small steps can make a difference.

* The UKGBC refers to ‘trigger points’ for building owners which can provide useful timings for retrofit projects. A trigger point may be a change of tenants or something more fundamental such as the change in Minimum Energy Efficiency Standards in 2030.

* Anna Hollyman also pointed out that there are other reasons to undertake building retrofits which should be part of a business case for investment. Wider environmental considerations include climate adaptation and resilience, for example thinking about the risks of overheating in the building. Other benefits include improved occupant health and wellbeing from improved indoor environments.

Final figures are due to be published by the UKGBC research group at the end of 2023. However, indications so far are that, unsurprisingly, deep retrofit projects such as changes to the building fabric are more costly but have a significant impact on building energy and carbon performance. However, light retrofit steps such as decarbonising heating systems by switching to heat pumps carry less capital cost and can provide useful first steps on the road to Net Zero buildings.

Mitsubishi Electric’s Zero Carbon Design Manager, Chris Newman highlighted this point in a presentation on bivalent solutions with heat pumps working in tandem with gas boilers.

He noted that the challenge of replacing all boilers with heat pumps in a large commercial office building may not be practical. Issues of timing and space for new equipment may be particularly pressing in this market. However, by replacing one boiler, for example, with an electric heat pump, he demonstrated that significant carbon (and energy) savings can be made.

The bivalent approach requires some considered engineering planning, but the benefits for commercial building owners can be substantial – providing a way to take the first steps towards lower carbon and electric heating with managed approach over time.

For more information on the Mitsubishi Electric Road to Net Zero programme visit:

And for information on the UK Green Building Council Advancing Net Zero campaign and related research, see:


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