A good balanced ventilation system needs to be both stable and flexible
Stable in that the system works as intended irrespective of what happens in the house. Flexible in that the ventilation can be controlled to meet requirements. If there are more people in the housemore ventilation is needed than if the house were empty.
The heat recovery elements will reduce energy consumption and lower the operating costs of the house. Instead of releasing the used, warm air straight into the atmosphere, it passes through a heat recovery unit which enables the exhaust air to heat the cold outdoor air as it comes in. In new installations, heat recovery is often a standard feature, particularly in Scandinavian countries.
Within a mulit-dwelling the needs of the occupants will vary, one person may be cooking and need to ventilate warm humid air whilst another might be cold and need to increase the air temperature. As such a system must be flexible depending on need.In addition since there are many rooms connected by hallways and stairwells the building must be safeguarded for evacuation during a fire and smoke related emergencies.