It's all about heat recovery
When developing new and most efficient renewable energy technologies, it is not just about harnessing the sun or the wind and using such technology in our homes or offices. The trick of the trade is to make most of what is given to us by nature and, in doing so, to help reduce our collective environmental impact. This also includes reducing the amount of energy escaping into the environment on a daily basis.
In practice, we distinguish between two types of heat recovery-based ventilation systems, i.e. regenerative and recuperative.
Regenerative systems are applied in unidirectional ventilation systems. The word regeneration means to improve a system by making it more active or efficient, and to retain some desirable properties. This is true of regenerative systems – the energy of outlet air is stored in a ceramic plate of a unidirectional ventilation system, which then transfers the desired properties to the inlet air. Problems with regenerative systems occur in case of large temperature difference of indoor and outdoor air (e.g. indoors: +20°C, outdoors: -10°C). The ceramic plate is heated to +20°C by energy from the outlet air for about 70 seconds. For the next 70 seconds inlet air with a temperature of -10°C enters the room. However, due to the large temperature difference, the plate will not be able to heat the inlet air to +20°C for all 70 seconds. That is why regenerative systems incur greater heat losses than recuperative systems.
Recuperative systems are applied in bidirectional ventilation systems. In engineering and the energy industry, the word recuperation describes a technical process for recovering energy and heat. Thus, in the case of recuperative bidirectional ventilation systems, the outlet air simultaneously and continuously transfers its properties to the inlet air in the heat exchanger (the system heats or cools fresh air with the energy of the outlet air) without interruptions or interim storing of energy in a plate. The efficiency of heat transfer of a heat recovery system is essential, as it tells us how much energy it will save. This is indicated by the thermal efficiency rate (%).