Heat Recovery: An Essential Element in Energy Savings

The heat recovery unit is an essential element in mechanical ventilation systems with double flow. This article explains how this component works, whose purpose is to increase the energy efficiency of the installation.

The use of a heat recovery unit in ventilation systems makes it possible to utilize the sensible, latent, and excess heat from the installation itself. This leads to a reduction in energy consumption and, consequently, a significant economic savings.

Towards a More Sustainable World

The European Union, through its EU directive 2010/31, aims for the construction of a sustainable and environmentally friendly property stock. To this end, it promotes NZEB, Nearly Zero Energy Building (EECN, Edificios de consumo casi nulo, by its acronym in Spanish). Data from IDEA in its Analysis of Energy Consumption in the Residential Sector in Spain shows that "the energy needs in Spain of the residential sector, in terms of final energy, account for 17% of total final consumption and 25% of electricity demand." To achieve the goal set by the European Union, heat recovery units are essential.

The Technical Building Code (CTE DB HE, Energy Saving) also emphasizes the urgency of reducing energy consumption and insists on the need for rational use of energy in building usage, using renewable energy as much as possible.

How Can I Increase the Efficiency of My Ventilation System?

Thanks to two ventilation systems, reducing energy consumption in your building is possible. These are, on one hand, the Decentralized Double Flow Ventilation System, and on the other hand, the Centralized Double Flow Ventilation System.

In the first case, ideal for rehabilitation projects (due to the minimal space it requires), the equipment is installed on the facade of each dwelling in the building. The system extracts stale air from the rooms and supplies fresh, clean air free from impurities. In the second case, two collective extractors (one supply group and one extraction group) are placed on the building's roof.

In both systems, the heat recovery unit uses the thermal energy from the expelled air to heat the supplied fresh air, allowing for the recovery of up to 94% of the energy.

Efficiency of the Heat Recovery Unit

To know the efficiency of a heat recovery unit, you must first determine the energy that the component is capable of recovering. According to the RITE, in its information document "Energy Saving and Recovery in Air Conditioning Installations," to find the energy (E) that a heat recovery unit can recover, you need to multiply the mass flow rate (mas), the enthalpy difference (Δh) of the air between the inlet and outlet of the unit, and the time it is operating (t). So, E = mas Δh t

The efficiency (ε) of any recovery unit can be obtained by dividing the amount of recovered energy by the maximum recoverable energy. Thus, ε = Amount of recovered energy / Maximum amount of recoverable energy.