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Thermal performanceand building codes
Thermal performance
• λ wall mix is 0.0697W/m.k
• R-value of 12” wall is 24
• R-value of 20” wall is 40
• Depending on finishes/framing
Hygro-thermal properties
• Hemcrete® does not behave like a lightweight insulation material
• The latent heat of water phase changes within the material contribute to its performance
Thermal mass
• Hemcrete® has the lowest diffusivity of any material
• It is slow to change temperature
• This gives it a thermal inertia like a high thermal mass material
Diffusivity (λ/ρc)• Expanded polystyrene ≈ 18.4 x 10-7 m2/s• Mineral fibre ≈ 14.4 x 10-7 m2/s• Polyisocyanurate ≈ 5.7 x 10-7 m2/s• Polyurethane ≈ 5.6 x 10-7 m2/s• Brick ≈ 4.1 x 10-7 m2/s• AAC ≈ 3.0 x 10-7 m2/s• Insulating aerated blocks ≈ 2.3 x 10-7 m2/s• Timber ≈ 1.6 x 10-7 m2/s• Hemcrete® ≈ 1.4 x 10-7 m2/s• Water (10oC) ≈ 1.4 x 10-7 m2/s
Dynamic thermal performance
→ 187
Q24h [kJ/m2]
→ 146
→ 410
→ 229
( Cement concrete → 3163 )
Effective U-value of 250mm Hemcrete®
• 187,000 J/m2 lost in 24 hours• 1W = 1J/s• There are 86,400 seconds in 24 hours• The temperature difference was 20oC• Real heat loss was 0.11W/m2k• Theoretical U-value is 0.29W/m2k
Amplitude suppressionand phase displacement
Dampening factor Time shiftat 25 cm at 25 cm
25cm= 1-(25cm/ init) 25cm= tmax,25cm- tmax,init
[-] [h]Material______________________________________________
LHC – “Wall” mixture 98,5 15
Wood 98,8 16
Cellular concrete 95 10,5
Mineral wool 77,5 6
CEM concrete 89,5 7
Air-tightness
• The monlithic nature of Hemcrete® makes it inherently air tight
• There are no complicated details/junctions
• Figures below 2m3/m2/hr at 50 pascals are achievable
Comfort and Health
• High vapour permeability and absorption coefficicient allow Hemcrete® to buffer high humidity, combat condensation and improve air quality
• Low effusivity makes Hemcrete® walls feel wall and make the internal environment feel comfortable
Thermal bridging
• The timbers within a Hemcrete® wall do not behave as thermal bridges.
• This gives Hemcrete® a significant advantage over most other construction materials
Thermal bridging• U-value of a 500mm Hemcrete® wall
(ignoring the timber frame) is 0.134 W/m2.K
• Including 15% timber framing reduces the U-value to 0.137 W/m2.K
• Difference is 0.003 W/m2.K
• Rounding error is bigger than this difference
The Lime Technology Office
Before
Sprayed Hemcrete®
Spray Limetec® render
The finished office
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External Temperature
External recorded temperature – April to September 2007
Addition of 24hourly average external temperature trend line
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External Temperature 24Hr Average (External)
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Existing Office External Temperature
24Hr Average (External)
Existing offices (monitored June onward) showing high internal temperature swing
By comparison, the Hemcrete offices show a low internal temperature swing, which is characteristic of heavyweight structures.
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Tradical Hemcrete Office Existing Office
External Temperature 24Hr Average (External)
The finished office
Tradical® Hemcrete®
• Good thermal conductivity – 0.07 W/m.K
• No thermal bridging
• Low diffusivity
• Low effusivity
Structure
• Tradical® Hemcrete® is not a structural material. The structural requirements are performed by the frame.
• The Hemcrete® stiffens the frame
Tradical®Hemcrete® is nonstructural
ModCell Hemp
Modular panelTypically 3m x 2m
Fast-track constructionOff-site construction
Can be structural
Fire Safety
• Tests have been carried out at the CSTB in France
• 250mm thick wall constructed of blocks made from Tradical® Hemcrete®
• The mortar joints failed after 1hr 40 mins• UK tests on a solid panel have run for 3hrs
45 mins• Full testing to run in February 2009
The best way to predict the future, is to create it !
