Steady-state or transient heat balances for comparable energy demand calculations? A case-study based on a sandwich lightweight structure

Energy demand calculations are very common nowadays due to various regulations and assessment methods around the world. Depending on local regulations they are usually carried out with either simplified steady-state energy balances or with dynamic simulations. Hereby, most stead-state calculations are based on the same temperature difference between inside and outside over a whole heating period or on monthly mean values compared to hourly data for transient calculations. In a case study on a sandwich-lightweight structure it became evident that dynamic calculations with transient weather data show results where the energy demand is approximately up to 50 % lower than steady-state calculations according to a German standard. Therefore, steady-state calculations cannot be recommended without restriction e.g. for sustainability assessment.