Heat recovery ventilation (HRV) works separately from your normal heating system. There are ventilation ducts with filters in each room which feed the air in and out of the room and lead to a heat exchanger that is in the loft or on the roof of the building.
A heat recovery system can work via a ventilation system, which is positioned at the top of the building. It works to draw the heat from the outgoing exhaust air and passes it to the air that is coming in instead of just drawing the stale air out and replacing it with fresh air.
The heat exchanger is the center and brains of the heat recovery system, moving stale air through small pipes while drawing in cold air from the outside through other ducts. These two air currents flow passed each other without mixing but the heat is drawn from the old, stale air to the cold air and then fed back down into the pipes and into the rooms. The stale air is then exhausted into the environment, minus the heat.
Technology for heat recovery ventilation systems has improved drastically over time and there are systems that can extract up to 90 percent of the heat from stale air and return it to the fresh air that is circulated back into the total system.
No one system is perfect and different systems may be needed to maximize the value of waste energy and convert it to something useful that can bring down utility costs and reduce the impact on the environment. Along the spectrum of heat recovery systems, heat recovery can be achieved through thermal wheels, plate heat technology, heat pumps or even more complex industrial processes.