reports Building Performance Evaluation Study
Over 100 Buildings Have ‘Gaps’
A study into the operational performance of more than 100 low-energy buildings has found “performance gaps” between design intent and actual carbon emissions of up to a factor of 10.
£8m in Innovate UK grants
…paid for original project teams to fulfill BPE’s original project aims of embedding post-occupation review and analysis skills across the industry, by checking the performance of 48 non-domestic and 59 residential projects over three years – applying consistent monitoring standards.
Results repeated the findings of earlier studies: that poor commissioning, hand-over procedures and clashes between different low energy systems are delivering slow progress towards the industry’s 2025 and 2050 carbon reduction targets.
Almost every non-domestic building had higher carbon emissions than design expectations. Some recorded up to 10 x higher emissions than the Building Emission Rate – calculated as part of gaining Part L compliance.
On-Site Renewables Problem
Nearly two-thirds of the buildings included onsite renewable energy generation to reduce their energy requirements – but two-thirds of this group experienced problems that reduced their energy savings.
… from new homes were two or three times higher than design estimates. For most of the projects, SAP predictions of CO2 varied from 8 to 23 kgCO2/m2 a year. However, in the first year of monitoring, actual carbon emissions mostly varied from 20 to 50 kgCO2/m2 a year.
29 Times More than Design Estimate
One house with a heat pump, solar water heating, PV and heat-recovery ventilation used 29 times more than the design estimate for regulated energy (excluding appliances in the home).
Innovate UK’s Optimism
Despite this, Mat Colmer, Innovate UK project manager reckons that the comprehensive scale and the information fed into the industry gives grounds for optimism that the performance gap could be narrowed in future. It’s not just a group of specialists but industry people who are grappling with the problem. BPE’s underlying data set is available at Building Data Exchange
Social Housing Just As Bad
A parallel BPE meta study of social housing projects by the National Energy Foundation charity found the following particular worrying problems.
- On average, fabric U-values exceeded targets, with nine properties failing to meet the Part L backstop;
- The air tightness of 46% of the BPE test dwellings was below the design intent;
- Commissioning, operation and maintenance-related issues were encountered in a high number of buildings, particularly where these had advanced equipment
- Underheating was less of an issue than overheating, due to high levels of thermal insulation and airtightness, and sub-optimal building design and specification.
In the view of NEF energy specialist, Federico Seguro, “The construction industry continues to wrestle with pinpointing and bridging the gap between the design of buildings and their ‘as-built’ performance; a gap that exists across all building sectors.”
Thermographic Imaging for All
Recommendations from the BPE study included the suggestion that taking thermographic images of completed buildings should be adopted as a regular technique, it having exposed more than one anomaly that was worth investigating. "In particular it was very helpful in evaluating underfloor heating systems, and any system that was not immediately visible or easy to assess. It also helped pinpoint areas where the construction details had not been robust, particularly in areas around windows, doors and vents; and at junctions between building elements or irregular (non-90°) corners.”
KISS – (Keep It Simple, Stupid)
Calling for more robust and simple controls for renewables equipment such as solar hot water systems, PV and ground or air source heat pumps, the report observes that “renewable energy systems, which are often increasingly complex, can contribute to the performance gap between as-designed and actual energy use. Projects also found it difficult to commission uncovered problems, and manage the controls for multiple renewables.”
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