Free cooling: an effective method of energy savings

Do you know what free cooling is? The Guide to Energy Savings (document recognized by RITE 2007) gives us an approximation of what is undoubtedly the best method to save energy. It is a free air cooling system that uses outside air (filtered to remove impurities) to cool the interior of the spaces in a building (instead of recirculating the return air from the systems).

Use of a free cooling system

In addition to economic savings, free cooling improves the indoor air quality of buildings, as using cold air from outside to dissipate internal loads increases the flow of outside air. If we want to benefit from this free cooling system, the air conditioning systems of the spaces must also be air systems. Furthermore, the air handling units must be equipped with suitable dampers, fans, and controls, essential for proper control of the installation. A free cooling system must allow, through appropriate control, to select the different situations of internal and climatic loads that can develop, so that action can be taken on the air dampers and equipment. In this way, the supply air will reach suitable hygrometric conditions with the lowest energy cost.

During winter, the main demand of buildings is heating; however, there are spaces with specific characteristics (stores, nightclubs, bars, and restaurants, etc.) that have a high latent and sensible load. If the conditions of the outside air are suitable (we are talking about air that is not excessively polluted), it is possible to use it to cool the spaces and thus avoid having to start a conventional mechanical compression cooling system.

Operating principle

If the enthalpy of the outside air (or the temperature, depending on the control system used) is lower than the enthalpy or temperature of the indoor air, it is more efficient to use outside air instead of recirculating return air from the location (conventional air conditioning system).

There are three types of systems, depending on the control used, namely:

• Free cooling by pure enthalpy control.
• Free cooling by dry temperature control.
• Free cooling by improved enthalpy control.

What does the device consist of? It consists of a system with three air dampers positioned such that the return air damper is in series with both the return and supply air fans. The other two dampers are parallel (the exhaust damper is placed in the return fan circuit and the outside air damper is in the supply fan circuit).

Application in ventilation systems

Given that homes are becoming increasingly airtight, it is extremely important to equip our home with a suitable ventilation system. We must opt for efficient ventilation capable of recovering energy, providing excellent heat renewal, and achieving acoustic, thermal, and airflow balance.

Controlled Mechanical Ventilation (CMV) with Double Flow is a ventilation system that guarantees air quality by extracting stale air from humid rooms (kitchen, bathrooms, restrooms, laundry) while simultaneously ensuring the supply of new filtered air into dry rooms (living room, dining room, bedrooms). Thanks to the heat exchanger, up to 95% of the energy from the exhaust air can be recovered. In summer, the bypass versions utilize free cooling, as they allow the passage of fresh night air (previously filtered) to naturally cool the home.