Post on 22-Aug-2018
transcript
Introduction Content
This lecture will:
• Identify fabric heat transfer paths
• Explain the concept of thermal bridging
• Illustrate the types of thermal bridges
• Cover the requirements under Building
Regulations Part L
• Provide examples of thermal bridges using
case studies
Fabric Heat Transfer Paths
• Plane elements
• Thermal bridges
• Air permeability (not covered in this lecture)
• Thermal Bypasses (should be designed out)
𝐻 = 𝐴×𝑈 + ℓ×Ψ+ χ
Fabric Heat Transfer Heat Transmission Coefficient
Plane elements Point thermal bridges
Linear thermal bridges
(W/K)
Thermal Bridges Temperature Factors
• Used to assess risk of surface condensation or
mould growth
• Based on lowest surface temperature (Tsi)
• Expressed as ƒRsi
• Must be > ƒCRsi in BR IP 1/06
ƒ𝑅𝑠𝑖 =𝑇𝑠𝑖 − 𝑇𝑒𝑇𝑖 − 𝑇𝑒
Building Regulations Part L Requirements
• Insulation must be reasonably continuous over
whole building envelope
• No reasonably avoided thermal bridges in
insulation layers
Building Regulations Part L Options
• Accredited Construction Details
• Numerical Modelling (thermal modelling)
• No specific quantification of thermal bridges
• A mixed approach is permitted
Building Regulations Part L Approved Design Details
• Approved Design Details set out by DCLG or
recognised by DCLG
• Builder must demonstrate that an appropriate
system of site inspection is in place
Building Regulations Part L Thermal Modelling
• Calculated by a person with suitable expertise
and experience
• In accordance with BR 497
• Builder must demonstrate that an appropriate
system of site inspection is in place
Building Regulations Part L No Specific Quantification
• Default Ψ-values from SAP
• Use default y-value of 0.15
Building Regulations Part L National Calculation Methodology
• The Government’s Standard Assessment
Procedure (SAP)
• Simplified Building Energy Model (SBEM)
• Dynamic Simulation Modelling (DSM)
Building Regulations Part L National Calculation Methodology
𝐻𝑇𝐵 = ℓ ×Ψ
𝐻𝑇𝐵 = 𝑦 𝐴𝑒𝑥𝑝
𝑦 =ℓ × Ψ
𝐴𝑒𝑥𝑝
Single parameter used where values for individual bridges are not used
Aexp = Total heat loss area (m2)
Code for Sustainable Homes
• CSH assessment informed by SAP
• Category 1: Energy and Carbon Dioxide
Emissions
• Dwelling CO2 Emissions Rate (DER)
• Fabric Energy Efficiency (FEE)
Building Regulations Part L
Normal Corner
Design Case Study
This case study will:
• Demonstrate the effect on thermal bridging
when increasing the levels of insulation to a
normal corner
Normal Corner
Design Case Study
• Insulation λ = 0.020 W/mK
• 50mm insulation in base model
• Increased to 75mm and 100mm
Normal Corner: U-values
Design Case Study
Insulation
Thickness: Increase: U-value (W/m2K): Improvement:
50 0.27
75 50% 0.21 22%
100 100% 0.17 37%
Based on Blocks λ = 0.110 W/mK
Normal Corner: Ψ-values
Design Case Study
Insulation
Thickness: Increase: Ψ (W/mK): Improvement:
50 0.052
75 50% 0.043 16%
100 100% 0.038 27%
Based on Blocks λ = 0.110 W/mK
Normal Corner: Temperature Factors
Design Case Study
Insulation
Thickness: Increase: ƒRsi: Improvement:
50 0.957
75 50% 0.967 1%
100 100% 0.973 2%
Forensic Case Study 1 Lintel Detail
ƒCRsi = 0.750
ƒRsi = 0.671
Risk of surface condensation
and mould growth
Exceeds
Regulatory
limit
Summary
This lecture has:
• Identified fabric heat transfer paths
• Explained the concept of thermal bridging
• Illustrated the types of thermal bridges
• Covered the requirements under Building
Regulations Part L
• Provided examples of thermal bridges using
case studies
References
Anderson, B. (2006) Conventions for U-value Calculations. BR 443. Watford: Building Research Establishment.
Building Research Establishment. (2011) National Calculation Methodology (NCM) Modelling Guide (for Buildings Other
than Dwellings in England and Wales). Watford: Building Research Establishment.
Department for Communities and Local Government. (2010) Code for Sustainable Homes Technical Guide. London: RIBA
Publishing.
Department for Communities and Local Government. (2007) Accredited Construction Details. Wetherby, Communities and
Local Government Publications.
Department of Energy and Climate Change. (2013) SAP 2012: The Government’s Standard Assessment Procedure for
Energy Rating of Dwellings. Watford: Building Research Establishment.
Energy Saving Trust. (2008) Enhanced Construction Details: Introduction and Use. CE297. London: Energy Saving Trust.
Energy Saving Trust. (2009) Enhanced Construction Details: Thermal Bridging and Airtightness. CE302. London:
Energy Saving Trust.
HM Government. (2013) Approved Document L1A: Conservation of Fuel and Power in New Dwellings. The Building
Regulations 2010. London: NBS.
Ward, T. & Sanders, C. (2007) Conventions for Calculating Linear Thermal Transmittance and Temperature Factors.
BR 497. Watford: Building Research Establishment.
Ward, T. (2006) Assessing the Effects of Thermal Bridging at Junctions and Around Openings. IP 1/06. Watford:
Building Research Establishment.