Recovery can be achieved with different product technologies (multifunction units, VRF systems, rooftop units and zephir units). Each technology offers a different type of recovery.

Recover the thermal energy in the stale air extracted from rooms, which would otherwise be lost, to ensure indoor air quality while avoiding energy waste. This is the job of the heat recovery system, a component now present in most air renewal units, which over the years has evolved significantly, thus becoming more and more highly efficient.

What is a heat recovery system and how does it work?

As the word itself implies, heat recovery systems are “technological devices” that transfer heat between two fluids (air or water). In the specific case of ventilation systems, this transfer occurs between two air flows: the heat is recovered from the flow of the exhaust air in the indoor environment to the outside, and then transferred to the inlet air flow. It is no coincidence that with controlled mechanical ventilation, which is the most popular solution for achieving correct and constant air exchange in rooms without having to open the windows, as much as 80-90% of the heat in the air can be recovered before it is expelled.


Cross-flow heat recovery technology

Cross-flow heat recovery systems are among the most popular air-to-air recovery systems and can be combined with heating or cooling coils to reduce the amount of energy required to maintain indoor conditions. They usually consist of specially designed metal plates (aluminium or steel) that are assembled together and which allow heat to be transferred, either by convection or radiation, from the exhaust air to the clean air from outside, without the two flows ever coming into contact.

This type of heat recovery system is normally fitted with a bypass damper, which excludes some or even all of the inlet outside air from the recovery treatment. The reason? To avoid the risk of frost during the winter or simply to use free-cooling, i.e. “natural” cooling achieved when the outdoor air temperature is low enough not to require further treatment. Cross-flow recovery systems are capable of recovering between 40 and 70% of the heat and in some cases can achieve nearly 80% efficiency.


Transferring moisture with the enthalpy heat recovery system

In controlled mechanical ventilation systems, one often hears about the enthalpy heat recovery system. What does it mean and what is the difference compared to standard systems mentioned before? This device not only recovers the sensible thermal energy, i.e. heat, from the exhaust air flow, but also the moisture value. The result in this case is twofold: on the one hand, overall efficiency is increased, and on the other hand, the inlet air does not become too dry. Enthalpy heat recovery systems are also made of porous materials, as they must transfer not only heat but also vapour from the outlet air to the inlet air and vice versa.

Heat recovery becomes even more efficient: thermodynamic recovery

The cross-flow heat recovery system, and also the single-flow one, are commonly referred to as static because they don’t involve any moving  part. To increase the overall efficiency of the system, many air handling units feature a second energy recovery system. In this case, we are talking about units with thermodynamic recovery, in which the first static recovery system is combined with a second active system, created with a heat pump refrigerant circuit.

The static cross-flow recovery system transfers heat from the exhaust air to the fresh air, while the heat pump refrigerant circuit starts up to support the former when the indoor and outdoor air temperature conditions require it. The result is a significant energy saving combined with improved thermo-hygrometric comfort and air quality. 

Clivet: air renewal solutions for every need

The thermodynamic heat recovery system is an essential component in solutions designed by Clivet to ensure correct and continuous air exchange and perfect filtration in residential applications and in large commercial and industrial buildings.

ELFOFresh EVO, for example, is the perfect controlled mechanical ventilation unit for rooms measuring between 90 and 250 m2 that “take advantage” of full inverter technology with active thermodynamic recovery to supply air that is warmer than the ambient air in heating mode and cooler and more dehumidified in cooling mode. The result is the achievement of 85% of the building’s thermal demand, which even rises to 100% in mid-season. Its refrigerant circuit is also environmentally friendly because it uses R32 refrigerant gas, while highly efficient electronic filters with iFD technology can be provided for excellent purification of the inlet air.

Active thermodynamic recovery achieves its peak performance and is an essential element in ZEPHIR3, Clivet’s air renewal unit that combines the entire fresh air system into a single, fully autonomous unit, which is capable of purifying and ensuring precise control of air inlet conditions. Available in six sizes, with air flow-rate ranging from 1,300 to 14,000 m3/h, ZEPHIR3 ensures, thanks to its full inverter active thermodynamic recovery system, savings of up to 50% in primary energy consumption, as well as greatly simplifying the design and installation of the system, making it the perfect solution for commercial & industrial sectors.