COZEB I, II & III – Cost-optimal energy performance levels for Wallonia

October 6, 2016


Period:  2012 – 2013 (COZEB I), 2013 – 2015 (COZEB II), 2016 – present (COZEB III)
Client:  SPW-DGO4


Following a comprehensive study performed by 3E (in collaboration with ULg and UMons), the consortium recently analysed cost-effective energy renovation strategies for Walloon real estate (houses, apartment buildings, offices…) (COZEB II). The aim was to define the cost-optimal energy performance level (according to EPB requirements) amongst several combinations of energy efficiency measures (COZEB I).

The most effective renovation strategy, resulting in a significant decrease (50 to 80%) of primary energy use includes:

  • Deep renovation of the exterior walls, windows roof and floor of single family houses built up till 1984, up to an energy performance level similar to that of a passive house
  • Roof insulation for each type of single family houseto a corresponding U value of 0.20 W/m²K and for low compacity office buildings built in the 70’s () to a corresponding U value of 0.24 W/m²K.
  • Deep renovation of the exterior walls, windows, roof and floor of large office buildings built up till 1945 to a level corresponding to the EPB requirements of 2014.

The study also highlighted:

  • The lock-in effect for single houses built between 1985 and 2008,for which deep energy renovation of exterior walls is hardly cost-effective (considering the assumptions made)
  • The cost-optimal energy renovation of apartment buildings would result in a 65% decrease of the specific primary energy use indicator (Espec)
  • The cost-optimal energy renovation of existing schools would only result in a 20 % decrease of primary energy use
  • Beyond the energy renovation of the buildings envelope (the sole strategy allowing a significant long-term decrease of the energy demand of a building), a gradual renewal of HVAC systems (especially in office buildings) is essential to reach a 50 to 80% decrease in primary energy use in a cost-effective way
  • A deep renovation (windows, roof, walls, floor) could result in a 60% decrease in specific primary energy use for each type of building assessed.

In 2016, 3E, ULg and IT developer Hemmis will fully automate cost-optimal calculations in EPB, as well as the sensitivity analysis of the main assumptions, allowing future EPB cost-optimum calculations to be carried out directly by the Walloon energy administration (COZEB III).