Answer:
Heat recovery ventilation systems allow R-2000 homes to maintain high indoor air quality without excessive additional energy costs. They consist of 2 separate air-handling systems - one collects and exhausts stale indoor air, the other draws in fresh outdoor air and distributes it throughout the home. At the core of an HRV is the heat transfer module. Both exhaust and fresh-air streams pass through the module and the heat from the exhaust air is used to pre-heat the fresh air system (only the heat is transferred; the 2 air streams remain physically separate).

Displacement ventilation is a technique used in many green buildings. Air is not recirculated or mixed. Instead it is introduced near the floor before gradually migrating upward to exhaust vents near the ceiling. This ‘stack effect' is optimized through careful design.  An exhaust fan is often included to provide accurate control of the ventilation rate.

House as a System - Energy Reduction Through Integrated Design: