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Potential and limitations of
infrared thermography on unventilated walls
Katrien Maroy
Nathan Van Den Bossche, PhD
Marijke Steeman, PhD
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Solution?
75% of all renovation projects
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Practice?
Inspection tools• Destruction• Endoscopy • Thermography?
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Overview
The accuracy of thermographyEmissivity and reflected temperatureCamera useBoundary conditions
Infrared inspection of cavity fillingDynamic simulationsCase studies
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Overview
The accuracy of thermographyEmissivity and reflected temperatureCamera useBoundary conditions
Infrared inspection of cavity fillingDynamic simulationsCase studies
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Emissivity and Reflected temperature
𝑊𝑡𝑜𝑡 = 𝜀.𝑊𝑜𝑏𝑗 + 𝜌.𝑊𝑎𝑚𝑏 + 1 − 𝜏𝑎𝑡𝑚 .𝑊𝑎𝑡𝑚 [W/m²]
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Emissivity and Reflected temperature
𝑊𝑡𝑜𝑡 = 𝜀.𝑊𝑜𝑏𝑗 + 𝜌.𝑊𝑎𝑚𝑏 + 1 − 𝜏𝑎𝑡𝑚 .𝑊𝑎𝑡𝑚 [W/m²]
𝜏𝑎𝑡𝑚 = 1 inλ = 3-5 µm and 8-14 µm
Spectrum of IR-camera
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Emissivity and Reflected temperature
𝑊𝑡𝑜𝑡 = 𝜀.𝑊𝑜𝑏𝑗 + 𝜌.𝑊𝑎𝑚𝑏
Emissivity ε Reflection ρ = 1-ε
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Emissivity and Reflected temperature
𝐸𝑥𝑎𝑚𝑝𝑙𝑒: 𝐵𝑟𝑖𝑐𝑘 → 𝜀 = 0,90
Emissivity ε
𝑊𝑡𝑜𝑡 ~ 90% 𝜃𝑜𝑏𝑗
Reflection ρ = 1-ε
𝑊𝑡𝑜𝑡 ~ 10% 𝜃𝑟𝑒𝑓𝑙
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Emissivity and Reflected temperature
Use correct values!Example: measurements in clear sky
𝜀 = 0,75 𝜀 = 0,75
𝜃𝑟𝑒𝑓𝑙 = −20°𝐶 (−4,0°𝐹) 𝜃𝑟𝑒𝑓𝑙 = −15°𝐶 (5,0°𝐹)
Accuracy difference : 1,2°C (2,16 °F)
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Emissivity and Reflected temperature
In-situ determination
Determine εASTM E1993-99a
Determine θrefl
ASTM C1060-11a
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Overview
The accuracy of thermographyEmissivity and reflected temperatureCamera useBoundary conditions
Infrared inspection of cavity fillingDynamic simulationsCase studies
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Camera use
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Camera use
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Camera use
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Camera use
Different FOV’s of the lens
45°x33,8° 25°x19°
θs = 20,0°C (68,0°F) θs = 19,4°C (67,3°F)
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Camera use
640 X 480 320 X 240
Resolution
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Camera use
Standard deviation: ± 2°C (3,6°F)Noise Equivalent Temperature Difference (NETD)
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Overview
The accuracy of thermographyEmissivity and reflected temperatureCamera useBoundary conditions
Infrared inspection of cavity fillingDynamic simulationsCase studies
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Boundary conditions
θi - θe
> 10°C (18 °F)
Weather conditionsNo sun, no clear sky, no wind
→ How long does the influence remain?
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U = 0,22 W/m²KE = 531,21 J/m²K√s
Boundary conditions
U = 0,22 W/m²KE = 531,21 J/m²K√s
(Van De Vijver, 2014)
U = 1,00 W/m²KE = 531,21 J/m²K√s
U = 0,22 W/m²KE = 32,40 J/m²K√s
U = 0,22 W/m²KE = 32,40 J/m²K√s
U = 0,22 W/m²KE = 2500 J/m²K√s
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Boundary conditions
(Van De Vijver, 2014)
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Boundary conditions
(Van De Vijver, 2014)
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Boundary conditions
(Van De Vijver, 2014)
4 hours waiting in heavy clouded windless weather
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Boundary conditions
(Van De Vijver, 2014)
17 hours waiting in heavy clouded windless weather
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Overview
The accuracy of thermographyEmissivity and reflected temperatureCamera useBoundary conditions
Infrared inspection of cavity fillingDynamic simulationsCase studies
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Dynamic simulations
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Dynamic simulations
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32
52
72
92
112
0
10
20
30
40
50
Surf
ace
tem
per
atu
re (
°F)
Surf
ace
tem
per
atu
res
(°C
)
Thermal bridge
Dynamic simulations
Maximal sun radiation, Clear sky, No wind
13 h 22 h
Cooling down
Air inclusion
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104
109
114
40
42
44
46
12h 13h 14h 15h 16h 17h
Dynamic simulations
Maximal sun radiation, Clear sky, No wind
104
109
114
40
42
44
46
12h 13h 14h 15h 16h 17h
[°C] [°F]
[°C] [°F]
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17.6
23.6
29.6
35.6
41.6
-8
-4
0
4
8
21h 3h 9h 15h 21h
No sun, Clear sky vs. fully clouded, No wind
Dynamic simulations
17.6
23.6
29.6
35.6
41.6
-8
-4
0
4
8
21h 3h 9h 15h 21h
[°C][°F]
θse,tb - θse,wall =1,4°C (2,52°F) θse,air - θse,wall =0,4°C (0,72°F)
Clear sky
Clear sky
[°C][°F]
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17.6
23.6
29.6
35.6
41.6
-8
-4
0
4
8
21h 3h 9h 15h 21h
No sun, Fully clouded and Wind (4 m/s) vs. No Wind
Dynamic simulations
27.6
32.6
37.6
42.6
0
4
8
21h 3h 9h 15h 21h
θse,tb - θse,wall =1,4°C (2,52°F)
θse,air - θse,wall =0,4°C (0,72°F)
[°C]
[°F]
[°C] [°F]
Wind 4 m/s
Wind 4 m/s
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Dynamic simulations
Only waiting times after sun radiation necessary
Timber frame
Filled cavity wall
Non-filledcavity wall
Partially filled cavity wall
11400 kJ/m² 0 – 1,5h 3,5 – 7h 2 – 6,5h 3,5 – 7h
8400 kJ/m² 0 – 1h 2 – 6h 0,2 –5h 2 – 6h
5600 kJ/m² 0h 0 – 4,5h 0 – 3,5h 0 – 4,5h
2750 kJ/m² 0h 0 – 2h 0 – 0,5h 0 – 2h
0 kJ/m² 0 – 0,2h 0 – 1h 0 – 0,2h 0 – 1h
+ Temperature difference > 10°C (18°F) across the wall
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Dynamic simulations
In practice:Go measure in wintertime, before sunrise
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Overview
The accuracy of thermographyEmissivity and reflected temperatureCamera useBoundary conditions
Infrared inspection of cavity fillingDynamic simulationsCase studies
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Case studies
(Beulque, 2014)
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Case studies
Common flaws
• Poor or lacking measurement data of the cavity width• Ignorance towards the minimum cavity width (< 5 cm or 1,96”)• Insufficient number of bore holes • Incorrect glue flow rate of the EPS pearls• Incomplete filling at corners and cavity interruptions• Missing bore holes due to vegetation or cables• Open parpens at the top • Parpens and openings in the inner cavity leaf during cavity
filling
Which of these flaws are detectable with thermography?
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Case studies
Know what you can expect Execution report
Vegetation during cavity filling work→ no bore holes→ insufficient filling locally
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Case studies
Know what you can expect Execution report
Filling with EPS-pearlsGlue stacked at the corners
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Case studies
Know what you can expect Execution report
Open parpens
EPS pearls escaped through openings in the inner cavity wallUmeasured = 0,476 W/m²K (+26%)Ucalc = 0,377 W/m²K
Chimney effect?
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Conclusion
Yes, thermography has potentialGeneral overviewThermal bridges are clearly visible • Avoid sun and θi-θe > 10°C (18°F)• Predictable locations and shape (above windows, at floors,…)
However, do not draw direct conclusionsThe ease by which thermal deficiencies are recognized depends on:Type, shape, geometry of the building, condition of the surface, location of the pattern, prior weather conditions…….
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Conclusion
Yes, thermography has potentialGeneral overviewThermal bridges are clearly visible • Avoid sun and θi-θe > 10°C (18°F)• Predictable locations and shape (above windows, at floors,…)
To indicate the location for further research with• An endoscopy• Destructive research
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Potential and limitations of
infrared thermography on unventilated walls
Katrien Maroy
Nathan Van Den Bossche, PhD
Marijke Steeman, PhD