Condensation in the insulating glass unit is a sign that something is wrong and is unacceptable. It can occur in case of depressurization of the insulating glass unit or low quality of the absorbent in the spacer.
Fogging of the insulating glass unit from the inside facing the room is a sign of high moisture and not enough ventilation. With very low outside temperatures during the winter, due to the higher temperature differences, it is more likely condensation to appear in the lower parts of the insulating glass unit. The existence of rolled down inside blinds, heavy curtains, and a wide window sill that obstruct the heated air are also helping the condensation to appear.
In contrast of the double glazing, the pressure qualities of the plastic and the aluminium window systems are much better. They put a stop to the uncontrolled air ventilation of the rooms caused by bad paddings. For healthy environment, comfort and depending on the needs, the ventilation processes can and should be controlled. Most proper way of ventilation is the short and intensive one, when the windows are wide open to create air stream for 10 minutes. This way the inner air with its higher moisture is exchanger for a fresh new air from the outside, without losing the accumulated in the walls and the furniture heat. If the ventilation is weaker and for a longer time the air exchange is slower and the walls and the furnite lose their heat which results in more energy needed to reach the levels of comfort again.