Circularity and Energy Performance in the Built Environment: In-Depth Notes

Learning Objectives

  • Describe the relevance of reducing energy use in buildings.
  • List the heat losses and gains that occur in a building.
  • Calculate basic transmission heat losses.

Overview of Energy Use in Buildings

  • Energy Consumption:
    • Buildings account for 30% of final energy consumption globally.
    • In the EU, 42% of total energy use in 2021 was attributed to buildings.
    • Over 1/3 of EU's energy-related greenhouse gas emissions come from the building sector.
    • Approximately 80% of energy used in EU households is for heating, cooling, and hot water.

Importance of Reducing Energy Use

  • Fossil Fuel Depletion:
    • Reducing reliance on fossil fuels is critical due to limited natural resources.
  • Environmental Impact:
    • Carbon emissions from fossil fuels contribute to climate change.
    • Air pollution from fossil fuel combustion can lead to health issues such as:
    • Asthma
    • Cancer
    • Heart disease
    • Premature mortality
    • Neurological disorders (e.g., autism spectrum disorder, Alzheimer’s disease)
  • Economic and Health Benefits:
    • Reducing energy consumption can mitigate public health risks and improve workforce productivity.

Key Directives and Standards

  • Energy Performance of Buildings Directive (EPBD):
    • A European Union directive aimed at improving the energy efficiency of buildings.
    • Initial version enacted in 2002, with revisions aimed at achieving a 60% reduction in building sector emissions by 2030 compared to 2015 levels and striving for climate neutrality by 2050.
    • Introduction of Energy Performance Certificates (EPCs) to assess and certify the energy efficiency of buildings.
  • Sustainability Certifications:
    • Broader assessments are conducted beyond energy performance, including certifications like LEED and BREEAM.

Energy Use Definitions

  • Nearly Zero-Energy Building (NZEB):
    • A building with high energy performance where the required energy is covered significantly by renewable sources, especially those produced on-site or nearby.

Understanding Heat Balance in Buildings

  • Heat Balance Equation: heta{in} ext{ (indoor temperature) } ightarrow heta{out} ext{ (outdoor temperature) }
    • Heat losses can be categorized into:
    • Transmission Losses ($ ext{Φ}_t$): Heat loss through walls, windows, etc.
    • Ventilation Losses ($ ext{Φ}_v$): Heat loss due to air exchange with outside.
    • Internal Gains ($ ext{Φ}_i$): Heat gains from occupants and equipment.
    • Solar Gains ($ ext{Φ}_s$): Heat gain from solar radiation.

Calculating Heat Losses

  • Transmission Heat Losses Formula:
    ext{Φ}t = A imes U imes ( hetai - heta_e)

    • Where:
    • A = Surface area (m²)
    • U = Thermal transmittance (W/m²K)
    • heta_i = Indoor air temperature (°C)
    • heta_e = Outdoor air temperature (°C)

  • Fourier’s Law for Conduction:
    q = -k rac{dT}{dx}
    where:

    • q = heat flux (W/m²)
    • k = thermal conductivity (W/mK)
    • dT/dx = temperature gradient (K/m)

Efficiency in Design

  • Strategies for Energy-Efficient Design:
    • Optimize insulation to minimize heat losses.
    • Incorporate natural ventilation strategies to balance indoor air quality and energy use.
    • Use energy modeling to predict and optimize performance based on heat balances.

Conclusion

  • Understanding the principles of heat balance and energy performance is crucial in constructing buildings that are both sustainable and healthy for their occupants. By implementing effective designs and adhering to established standards, the built environment can significantly reduce energy consumption and its associated impacts.