Using in-situ U-value measurements to inform retrofit
The Arc, Winchester
The Arc is a public, multi-use cultural space in the heart of Winchester’s conservation area, comprising a Grade II* listed building and modern extension.
Its original, Italianate-style building dates to 1815 and includes the original, double-height Winchester Library and offices. An extension built in 2006 increased the original footprint to 2,800m², and encompasses a performance hall, learning spaces, art gallery and café.
The building is managed by Hampshire Cultural Trust on behalf of Hampshire County Council, and is one of the estate’s most challenging buildings to decarbonise. Beyond Carbon was commissioned - alongside Hive and SKP3 - to create a decarbonisation plan to meet the Trust’s strategic goal to reach net zero by 2030 across scope 1 and 2 carbon emissions.
The key aim of the study was to establish feasibility of meeting net zero via fabric and services retrofit. The team took a pragmatic approach to proposing retrofit solutions given additional constraints of minimising capital expenditure and keeping the building in-use throughout the works.
Beyond Carbon’s approach to retrofit modelling typically begins with creation of a steady-state model in PHPP. Accurate U-values are a vital input to the modelling process as they help calibrate the ‘existing’ energy model, the foundation from which retrofit upgrades can then be modelled. U-values are assumed based on a variety of sources: planning documents, architectural drawings, observations during site visits, typical U-values based on the building’s age and construction, or sometimes opening-up works.
An accurate energy model at the start of the process provides important data to inform retrofit proposals, potentially mitigating the need for deeper fabric interventions, and in turn reducing the potential size of a heat pump installation to replace gas boilers.
To replace these U-value assumptions on The Arc, we collaborated with Build Test Solutions to use their Heat3D U-value measurement technology to carry out unobtrusive U-value measurements across the building.
Build Test Solutions conducting in-situ U-value measurements with their Heat3D technology
Test results
The speed of Heat3D allowed for five sets of measurements in one day, and the data revealed some unexpected insights:
In the modern extension, the rendered stair area achieved a U-value of 0.26 W/m²K – better than designed – and the learning space measured 0.38 W/m²K. However, the performance hall’s 0.66 W/m²K was 89% worse than the assumed SAP (standard assessment procedure) U-value, indicating an issue. Opening-up works were proposed for this space to identify defects in the construction that may be causing thermal bypass.
Results in the older areas of the building were a pleasant surprise. The first-floor meeting room achieved a U-value of 0.74 W/m²K, with 0.81 W/m²K for the staff office – 56% and 52% better than the assumed SAP U-value for the age and construction, respectively. Here, the results confirmed that costly and disruptive intervention would not be necessary in the original part of the building.
Outcome
The measured U-value data produced a closely calibrated energy model of the building - verified against energy bills - and therefore gave us confidence in our retrofit recommendations. Build Test Solution’s in-situ U-value measurements not only helped us identify energy efficiency improvements to tackle the worst-offending areas, but revealed that measures in the original part of the building wouldn’t need to be invasive or costly.
For clients like HCT looking to address heritage buildings, the measurement data allows us to take an informed view and propose a pragmatic and cost-effective approach to retrofit.
Read more detail about the Heat3D approach on Build Test Solution’s website, here, and contact us if you’d like to talk about our strategic approach to decarbonising heritage buildings.