Energy Performance of Solid Walls Funded by BEIS. Project overview. John Riley Director, Housing Stock performance, BRE. Part of the BRE Trust

Transcription

1 Energy Performance of Solid Walls Funded by BEIS Project overview John Riley Director, Housing Stock performance, BRE Part of the BRE Trust

2 What is the SWI research project?

3 What is a solid wall home? Found in older homes in the UK (pre-1930s, depending on region) Mix of stretcher and header bricks (compared to stretcher only cavity walls) Approximately one-third of English Homes are solid walled.

4 Understanding why solid wall insulation in housing may not save as much as anticipated

5 What is the potential for SWI? Why doesn t SWI achieve the predicted savings? Are there risks with SWI? Why is there a gap between calculated and measured consumption? How can we better predict savings? Can we identify them? Can we mitigate them? Are the measured & calculated U- values correct? Do we understand what the occupants are doing? Can we give energy surveyors the right tools and info? Does SWI perform as expected?

6 Six work packages 1 Literature review Desk study 2 Existing wall performance Fieldwork & lab tests 3 Pre-, post-insulation study: Understanding the gap Fieldwork & occupant survey 4 Measurement and calculation method Hot-box & field tests, desk study of calculation 5 Unintended consequences Review of evidence, observations, route-map 6 A system for more accurate U-value estimation Classification database, product review & competition

7 What have we found so far?

8 Existing results (2012 work by BRE) Wall type Number of cases Measured U- values: mean W/m²K * Calculated (theoretical) U-values: Mean W/m²K * Typical RdSAP U-values a W/m²K Ratio of (Mean measured U-value) (Typical RdSAP U-value) Solid wall, standard b Why there is a large difference between the RdSAP and calculated values.

9 Is there a problem with the measurements? Hot box tests and modelling +5% to measured values

10 More fieldwork: In-situ U-values Measurement of U-values 120 properties Two weeks measurement period Heat flux plates (transducers) High specification data logger Floor to ceiling poles to pressure fix to wall

11 Solid wall U-values measure lower than currently assumed (2.1 W/m 2 K)

12 On site investigations provide clues to why this might be the case

13 Mortar fill In standard calculation methods assumed that all joints are filled. But full fill is not the usual situation. On average: Space between stretchers are 67% full. Perpends were 70%.

14 Frogs Frogs are not accounted for in standard U-value calculations. Fieldwork: When laid frog down it is very seldom filled. When laid frog up it is usually filled.

15 Split headers and broken bricks Standard calculations take no account of broken or split bricks forming part of the wall. Fieldwork» Around 10% of locations showed some evidence of broken or split bricks being used.

16 Moisture content Thermal conductivity of the materials in the wall are strongly dependent upon moisture content Brick and mortar samples from the field were tested The walls are drier than have usually been assumed Moisture content by volume Standard assumption Fieldwork data 5% ~1% (Brick) ~2% (Mortar)

17 Producing a new U-value Taken together, these findings can help explain why U- values are lower than originally thought Lower moisture content Air gaps between bricks Presence of air filled frogs Broken bricks and snapped headers Taking all of these into account produces calculated U- values of ~1.7 W/m 2 K.

18 Lab work allows us to study these effects in a controlled environment NPL hot box

19 The construction process for the test walls (Test wall 3)

20 Also investigating the people - Those studied do not achieve the assumed heating regimes 10% lower 20% lower weekdays 50% lower weekends

21 Site visits identifying poor practice: Unintended consequences are not well understood by the industry or controlled for

22 Cost minimisation seems to be the main driver in most cases observed

23 Next steps

24 Next steps Integration of laboratory and field test results Final analysis Outputs Reporting and conclusions Solid wall U-value default database. Updating SAP and BREDEM. Further work On-going monitoring Monitoring historical cases Further fieldwork

25 Energy Performance of Solid Walls Funded by BEIS Project overview John Riley Director, Housing Stock performance, BRE Part of the BRE Trust