This paper describes four simulation models, which reproduce energy and temperature measurements of occupied buildings very well. These buildings represent small to medium size residential low-energy buildings of different construction type, which are typical for mid-Europe. For the simulation, the software TRNSYS is used. The reproduction of measured energy and temperatures in time steps of 15 minutes is well suited for precise predictions on heating energy demand and comfort of the buildings and modifications of them. Results are used to develop generalized guidelines for the efficiency of energy saving measures, which are helpful for an advanced design and evaluation of low-energy buildings.