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).

Traditional HVAC systems provide a uniform indoor climate for the whole building or space, whereas the occupants each have their own comfort preferences. The result is suboptimal comfort for the occupants on the one hand, with at best up to 5 % of dissatisfied, and energy losses due to control on the safe side by the building operators. Personalised conditioning systems (PCS) do not aim to heat, cool or ventilate the space but to deliver the heat, cold and fresh air directly to the occupant. This paper provides a systematic assessment about the energy saving potential and potential comfort gains that can be achieved by implementing localized and personal HVAC systems in home environments. Using the Human Thermal Module software that allows to study the thermal sensation and thermoregulation under transient and asymmetric environmental conditions, the energy saving potential was evaluated in TRNSYS, and for a case study with different user behavior patterns it was shown that comfortable micro-climates can be achieved by means of heated chairs for an air temperature as low as 17°C, and the total annual energy savings amount to 30% in winter conditions and 70% in summer conditions.

Today, strict insulation requirements apply. Nevertheless, the inverse correlation of thermal conductivity with insulation thickness leads to decreasing energy savings with increasing insulation packages. Therefore, a balance between potential energy savings and environmental impact due to additional materials using Life Cycle Assessment (LCA) needs to be strived for. This balance is sought for a case study called ‘The Mobble’ i.e. a flexible, modular, and circular building system developed by a student team from Ghent University. Through an iterative design process supported by LCA, comfort and dynamic energy simulations efforts are made to design an energy-efficient and low impact module with an agreeable indoor environment. First, material choices are made based on LCA and the material impact of a 5-module home is calculated. Second, energy calculations are executed in Modelica/Dymola. For this, three possible energy reductions are explored: insulating the building, altering the working regime of the HVAC system and lowering the setpoint temperature while maintaining comfort by using personal comfort systems (PCS). The results support PCS as a possible energy conservation measure and indicate that reducing operational energy does not shift the environmental burden to the additional materials’ production. However, these environmental saving effects decrease as the operational share decreases.