U-Values for Walls & Windows
CHALLENGE: SCALABLE RENOVATION OF RESIDENTIAL BUILDINGS
Deep-retrofit
• Takes months
• Substantial changes
- Wall insulation
- Windows change, etc
• Current renovation rates: 1-1.5%
Major barriers to large-scale renovation:
• Money - building grants, green loans
• Planning - delays, objections
• People - trust issues, reasons to oppose deep-retrofit
• Older buildings - don't know what's in the walls, restrictions on materials/façade
• Diff homeowners - private/social
• Lack of temporary housing
Thermal Envelope • Shell of building
• Consists of walls, widows, roof, floor
• Acts as barrier to:
- Loss of heat (winter)
- Unwanted heat (summer)
- Infiltration/exfiltration
- Moisture penetration/dampness
• Effective thermal env depends on:
- Insulation levels
- Resistance to moisture
- Thermal properties
HEAT TRANSFER
Conduction • Heat transfer due to kinetic collisions/vibration of material molecules
• Main mechanism of energy transfer
- Wall materials, insulation, glass, roof
• From experimentation (Fourier), rate of heat transfer is:
1) Proportional to heat transfer area A
2) Proportional to temp diff across layer ∆𝑇
3) Inversely prop to thickness of layer ∆𝑥
CHALLENGE: SCALABLE RENOVATION OF RESIDENTIAL BUILDINGS
Deep-retrofit
• Takes months
• Substantial changes
- Wall insulation
- Windows change, etc
• Current renovation rates: 1-1.5%
Major barriers to large-scale renovation:
• Money - building grants, green loans
• Planning - delays, objections
• People - trust issues, reasons to oppose deep-retrofit
• Older buildings - don't know what's in the walls, restrictions on materials/façade
• Diff homeowners - private/social
• Lack of temporary housing
Thermal Envelope • Shell of building
• Consists of walls, widows, roof, floor
• Acts as barrier to:
- Loss of heat (winter)
- Unwanted heat (summer)
- Infiltration/exfiltration
- Moisture penetration/dampness
• Effective thermal env depends on:
- Insulation levels
- Resistance to moisture
- Thermal properties
HEAT TRANSFER
Conduction • Heat transfer due to kinetic collisions/vibration of material molecules
• Main mechanism of energy transfer
- Wall materials, insulation, glass, roof
• From experimentation (Fourier), rate of heat transfer is:
1) Proportional to heat transfer area A
2) Proportional to temp diff across layer ∆𝑇
3) Inversely prop to thickness of layer ∆𝑥
