If not designed correctly then sure, low energy homes can overheat or be too cold. As with everything, it’s down to getting the design right. For example, a principle of passivhaus is to obtain some winter heating from south facing glazing. The size and orientation of this glazing must be modelled by an expert in the PHPP software to be sure there is no over heating problem – having too large a glazed area on the southern aspect could cause a problem.
An elegant design principle is to have large roof overhangs above upstairs glazing, this way in the summer when the sun is high the glazing is shaded, in the winter when the sun is low, the heat comes through the glazing warming the internal space.
Having large volumes of thermal mass in the building avoids rapid fluctuations in temperature as well, that’s one of the reasons our frame are insulated with heavy weight Warmcel insulation – adding tons of thermal mass and acoustic insulation. The feel of the internal space has to experienced to understand the difference. The performance from Warmcel cannot be obtained by light weight cheaper alternatives such as Rockwool