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Zack Gill

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Energiesprong performance in the UK – our top 10 findings (part 1)

With spiralling energy costs and unprecedented heatwaves, rapid scale up of retrofit has never been more urgent. And, as an industry, we must come together and share learning if this is to be successful.

Which is why we’re excited to be sharing our first performance report – detailing the performance of 69 homes retrofitted using the Energiesprong whole house retrofit model across six UK social housing schemes.

Energiesprong explained

Energiesprong is a revolutionary approach to domestic energy retrofit that has now been applied to 173 properties across nine schemes in the UK, with more to follow in 2022/23. These projects are led by the housing provider and the main contractor, with Energiesprong UK providing technical advice and market development.

The Energiesprong approach aims to fully insulate homes using offsite manufactured wall and roof panels in conjunction with pre-assembled ‘energy pods’ - creating warmer, more desirable places to live that are partly financed by energy and maintenance savings.

In the UK – due to the immaturity of the market – some of these pilot projects have used more traditional technologies and methods of insulation. We are taking the learning from these schemes and sharing widely as the industry gears up to deliver offsite retrofit and energy innovation at scale.

Guaranteed performance is at the heart of the Energiesprong model

One of the innovations that underpins the model is that the contractor (Solution Provider) signs a performance guarantee, ensuring that the in-use energy use and generation are in line with the approved design. The only way to provide this guarantee is to closely monitor the energy consumption and other metrics after the project is complete.

The Performance Guarantee encompasses the following elements (and more) with corresponding, typical, targets defined for each scheme. These targets apply per property across a scheme.

So, what has our performance report found?

Properties are meeting their targets - with a massively reduced impact on the grid

1. Properties retrofitted using the Energiesprong model do, on average, meet their targets (in particular regarding fabric efficiency) showing that the increased focus on outcomes and the guarantee is starting to work

The performance analysis shows the fabric solutions appear to be working well, generally within ±15% of the design target. Furthermore, space heating targets below 50 kWh/m2 are typically being met, in line with the pilot project performance targets.

This shows that the increased focus on performance outcomes by the Solution Provider teams are working and furthermore that monitoring, verification and the performance guarantee all help to focus efforts on real-world performance.

2. Energiesprong properties (even those with high consumption) are having a massively reduced impact on the grid compared to local homes – 70%+ less energy on average. There’s huge potential for deep retrofit to overcome our demand and supply issues…

Results show that these retrofitted homes are using more than 70% less energy on average compared to typical UK dwellings (according to Ofgem typical domestic consumption values (TDCVs) and government postcode-level energy consumption estimates). And this is despite residents taking increased comfort by having higher temperatures and having higher energy consumption than expected on their plug loads.

For instance, even the home with the highest monitored grid electricity import value (5,565 kWh/yr) is using 43% less total energy than the lowest TDCV figure (9,800 kWh/yr) and 56% less than the local postcode average (12,693 kWh/yr). And that’s even before accounting for the electrical energy being exported to the grid...

The benefit of retrofitting homes in the UK to reduce demand on the utility grid is clear. And because we have data, we can start to understand how to move all homes to be nearer to the highest performers.

Energy systems have the potential to go even further

The purpose of monitoring is to learn from these pilots and prototypes. One area for improvement is energy system elements which are performing a bit worse than designed (albeit typically within 10% of their design targets).

3. PV should be maximised on every project (it typically represents best value for money!)

Resident electricity consumption (i.e. for appliances, cooking and lighting) was found to be approximately 30% higher than the comfort plan allowance. However, it is estimated that only ~1 kWp additional PV (per property) would be required to offset this increased consumption.

Note: The comfort plan charge is a fixed fee that replaces the resident's gas bill and helps pay for the retrofit, allowing the housing provider to retrofit more homes.

With improvements to PV technology (i.e. significantly increased outputs from individual panels), this may be feasible to achieve on future projects without increasing the physical system size (which is important where the whole roof has been used already for PV).

It is always recommended and encouraged that Solution Providers maximise the size of PV array installed on any project, regardless of the specific project targets, as it is generally attractive both economically and in terms of meeting the performance specification.

Furthermore, solar systems are not performing quite as well as designed and modelled, which is due primarily to archetypal design processes not accounting for variations on individual properties, but could also indicate poor installation, commissioning, or design. Alternative and emerging technologies could improve this, such as looking at optimisation and micro inverters to improve solar performance.

4. Heat pump performance needs to be better understood and improved upon.

Where data was available, an average heat pump seasonal coefficient of performance (SCOP) of 2.44 was measured compared to a typical design target of 2.6. While this underperformance is estimated only to add approximately 100 kWh to the annual electricity demand of a typical Energiesprong  project in the UK, we are striving for more examples where heat pumps exceed their performance expectations.

Possible causes for this underperformance include (but are not limited to); inefficient operation (i.e. short intervals with high temperature changes), high energy consumption (due to increased internal temperatures), colder than average external temperatures, and sub-optimal setup and commissioning.

On average, the performance of monitored heat pumps is within acceptable design tolerances. However, increasing the SCOP (either via equipment selection, operation, and/or setup and commissioning) is desirable for future projects and so, like other metrics, we will continue to strive towards consistently exceeding design targets and then replicating high performance systems.

There is an overarching question whether we have sufficient capability on these technologies within the industry. But we believe that the combination of the Energiesprong performance guarantee and ongoing monitoring are enabling a transition towards consistently high-performance systems.

We need this feedback to instigate better commissioning, operation, component selection etc. and to ensure resolution of issues is made when they arise. This is a significant opportunity for improvement to create even better performance in the future!

Tenants have higher energy consumption than expected

5. Some like it hot! Retrofitted homes have the potential to massively improve health and wellbeing for residents but should our expectations of winter comfort change…?

On average, the retrofitted properties are operating 2°C warmer than the Energiesprong specification accounts for and so homes are using more space heating energy than anticipated.

This “take back” by the residents can be seen as a positive finding as it suggests that residents can now afford to heat their homes to desirable levels and are choosing to do so.

However, for national net-zero and zero-carbon targets to be met, we have to be mindful that better controls and feedback may be required to encourage residents to use efficient heating profiles and optimise their energy consumption.

That said, compared to typical housing, these retrofitted homes are using on average 70% less energy than local averages, and so despite the increased temperature (and occupant comfort) there is still a dramatic energy saving due to the combination of measures installed. Deep retrofit like this provides great potential to minimise the impact of unintended consequences!

6. We need to collect more resident feedback to complement these energy performance findings and we have a detailed survey in action now

Resident energy consumption is hugely variable. While even the resident using most energy is still using 43% less than similar homes in the same area (showing that the Energiesprong retrofit has minimised the impact), it is still essential to understand why there is such a variation to ensure that energy bills are affordable even after the comfort charge is applied.  

We also need to ensure that residents are satisfied with all other elements of the retrofit and identify any areas for improvement.

To tackle this, we are now using detailed resident surveys (which comply with BS40101:2022 on Building Performance Evaluation and PAS2035:2019 on Retrofit Coordination) to understand more about how tenants are using the home.  

Pre-works monitoring was not available for the pilots but is always sought on future projects to help understand tenant choice. Anecdotally there are incidences of tenants with heating on and windows open, but equally, high tenant consumption could be due to back up electric heating which would indicate a challenge with the heating system, lack of information or simplicity of controls.

All of these are issues which could (and should) be tackled by the Solution Provider, so we need to continue to support them on this.

In the next part of this blog, we explore why we think improved monitoring is vital for the success of future Energiesprong projects and what else we will recommend doing differently for future projects. Read Part 2.

Download our performance report for the full details:

We’d like to thank our partners and funders for supporting the schemes, monitoring and analysis outlined in this report:

Engie (now Equans), Exeter City Council, Melius Homes, Mi-Space, Moat, Nottingham City Homes, North Devon Homes, Sanctuary and Sutton Housing Partnership.

Department of Business, Energy and Industrial Strategy, ERDF, Interreg NWE and the Mayor of London