Balancing environmental impact, energy use and thermal comfort: Optimizing insulation levels for The Mobble with standard HVAC and personal comfort systems

Abstract

The energy crisis in the 1970s led to increasingly stricter building codes, resulting in the currently required nearly zero-energy buildings. Nonetheless, the energy saving potential of further increasing insulation packages decreases as a result of the inverse correlation of thermal transmittance with insulation thickness. Therefore, a balance is required between the potential energy savings and the material impact using Life Cycle Assessment (LCA). This balance is studied for a demonstration building called ‘The Mobble’. For the LCA, the Ecoinvent database and impact assessment method ReCiPe H/A (2016) are used. For the potential energy savings dynamic energy simulations are run in Modelica/Dymola. To ensure equal comfort, thermal comfort is modelled using Human Thermal Module. An optimisation using the trade-off between material impact and operational energy by considering the optimal insulation thickness is executed on three levels: (1) building envelope (insulation, glazing type), (2) HVAC system efficiency (constant, demand based, personal comfort systems) and (3) electricity mix. This additionally enables to assess the robustness of imposing strict insulation requirements in e.g. building codes. The results show that even when extremely advanced demand based systems are adopted, the optimal insulation thickness ranges between 22 cm and 28 cm and is thus hardly affected, neither by user behaviour. However, the choice of energy mix does have a considerable impact on this optimal insulation thickness, and entails a shift in optimal insulation thickness from 20 cm - 30 cm–10 cm - 20 cm when a lower environmental impact for the electricity mix is considered (compared to the current Belgian electricity mix).