Energy Performance of Solid Walls - UK Construction Week · PDF fileEnergy Performance of...
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Transcript of Energy Performance of Solid Walls - UK Construction Week · PDF fileEnergy Performance of...
Part of the BRE Trust
Energy Performance of Solid Walls Funded by BEIS
Project overview
John Riley
Director, Housing Stock performance,
BRE
What is the SWI research project?
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.
Understanding why solid wall insulation in housing may
not save as much as anticipated
What is the potential for SWI?
Why doesn’t SWI achieve the predicted savings?
Why is there a gap between calculated and measured consumption?
Are the measured & calculated U-
values correct?
Do we understand what
the occupants are doing?
How can we better predict savings?
Can we give energy
surveyors the right tools and
info?
Does SWI perform as expected?
Are there risks with SWI?
Can we identify them?
Can we mitigate them?
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
What have we found so far?
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-valuesa
W/m²K
Ratio of
(Mean measured U-value)
(Typical RdSAP
U-value)
Solid wall, standardb 85 1.57
1.90 2.1 0.75
Why there is a large difference between the RdSAP
and calculated values.
Is there a problem with the measurements?
Hot box tests and modelling
+5% to
measured
values
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
Solid wall U-values measure lower than currently
assumed (2.1 W/m2K)
On site investigations provide clues to why
this might be the case
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%.
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.
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.
Moisture content
Standard
assumption
Fieldwork data
Moisture content by
volume
5% ~1% (Brick)
~2% (Mortar)
• 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
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/m2K.
Lab work allows us to study these effects in a controlled
environment – NPL hot box
The construction process for the test walls (Test wall 3)
Also investigating the people - Those studied do not
achieve the assumed heating regimes
10% lower
20% lower weekdays
50% lower weekends
Site visits identifying poor practice: Unintended
consequences are not well understood by the industry or
controlled for
Cost minimisation seems to be the main driver in most
cases observed
Next steps
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
Part of the BRE Trust
Energy Performance of Solid Walls Funded by BEIS
Project overview
John Riley
Director, Housing Stock performance,
BRE