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Free cooling: what it is, how it works and where it is used

Free cooling is a system capable of harnessing the temperature difference with the external environment to cool indoor spaces without using refrigeration systems

As the summer season approaches and temperatures rise, air conditioning is increasingly used. Sometimes air conditioning is used excessively, becoming a health risk and an issue in terms of energy consumption.

To reduce the excessive use of cooling systems and contain energy costs, there are solutions that make the most of external climatic conditions, especially when they are more comfortable than the indoor environment.

One of these solutions is the technology free cooling, a system of natural air conditioning achievable even through a simple mechanical ventilation system.

Mechanical ventilation is an important resource for effectively addressing indoor pollution issues and preventing potential health risks for building occupants.

Moreover, the best controlled mechanical ventilation systems are equipped with free cooling. It is essential to also know the appropriate tools to optimally design this type of systems. In fact, only with a BIM software for MEP plant design you can you effectively manage all project phases, from conception to construction.

What is Free Cooling

Free cooling allows cooling indoor spaces by using only external renewal air, at times when it is more comfortable than the internal air. It exploits the temperature difference with the external environment to cool indoor spaces, without the need to use refrigeration systems and therefore consuming less energy.

It is a technology widely used in industrial settings, shopping centers, data centers, and sports facilities, but it is also spreading in residential environments.

In fact, in residential settings, this mechanism can be especially useful in summer, for example at night when the external temperature is cooler than the indoor temperature, but also during the transitional seasons.

There are 2 types of natural cooling:

  • direct free cooling: occurs when external air is introduced directly into an indoor environment that has a higher temperature than the external one. For example, through the use of a mechanical ventilation system;
  • indirect free cooling: occurs when the temperature of the cold source is transferred to the internal distribution circuit through a heat exchanger. For example, in geothermal systems, it is possible to isolate the heat pump and interact, through an exchanger, the internal distribution circuit with the mixture coming from the ground at ground temperature. The heat pump will not consume electrical energy: the free cooling of the spaces is carried out without electricity input.

Direct Free Cooling

This type of system can be implemented with both variable and constant air volume systems and is particularly suitable for Mediterranean regions, where humidity rarely exceeds 70% for most of the year.

Direct free cooling is the most chosen by large commercial spaces that need to remain cool even when heavily crowded: external air, generally cooler than the internal one, circulates in the spaces, contributing to oxygenate and refresh the visitors’ stay. By its nature, direct free cooling is also suitable for transitional seasons.

Indirect Free Cooling

In this type of system, the water in the distribution circuit is cooled using two sources: a geothermal system with a heat pump or external air.

In geothermal systems with radiant panel distribution, it is possible to naturally cool the spaces by circulating the water returning from the geothermal probes in the radiant panels, isolating the heat pump with a bypass. The temperature acquired from the ground is transferred to the distribution circuit through a simple heat exchanger.

External air can also be used to cool the system’s water, but in this case, there must be favorable climatic conditions without excessively high external temperatures.

Controlled Mechanical Ventilation with Free Cooling

Controlled Mechanical Ventilation (CMV) is a system designed to ensure air exchange between the interior and exterior of buildings. During this process, the main parameters influencing air quality, such as temperature and humidity, are managed and maintained.

The operation of these systems is simple: indoor air is sent out by passing it first through a heat exchanger that retains part of the heat.

The next step involves taking the outside air and bringing it back in. Even the outside air passes through the same heat exchanger as before, which will transfer the previously stored heat to it.

During summer periods characterized by intense heat, high humidity becomes a critical factor that accentuates the perception of heat. Most controlled mechanical ventilation systems are equipped with dehumidification devices that help mitigate this effect.

Controlled ventilation systems with free cooling allow for effective exchange of summer hot air, especially during night hours, leveraging natural cooling and dehumidification of external air. This technology exploits the temperature difference between indoor and outdoor environments to ensure comfort without the need for air conditioning.

Through the adoption of this technology, the system automatically adjusts the heat exchanger activity based on the external air temperature, significantly reducing energy consumption. CMV systems not only ensure air quality in indoor environments but also offer a concrete opportunity to reduce energy consumption associated with summer cooling.

Furthermore, the energy consumption of CMV systems with free cooling is much lower than traditional air conditioning systems, even those with the best energy ratings, making them a highly energy-efficient solution.

Free Cooling: Advantages and Disadvantages

The system of free cooling exploits only the temperature difference with the external environment.

Therefore, a free cooling system does not require a particular refrigeration system, i.e., machines designed to facilitate heat exchange. Therefore, thanks to its operation with zero energy consumption for air conditioning, it also allows for significant savings on bills.

Moreover, it is a system based on simple technology that requires low maintenance, mainly related to the periodic cleaning of the radiator.

Among the disadvantages, there is a reduced dissipating power compared to other systems, resulting in less effective heat dissipation and its dependence on environmental conditions. Furthermore, it is always necessary to provide dedicated air conditioning systems properly set up to take into account the free cooling system.

Adopting this technology, where the climate allows it, therefore presupposes a higher initial investment compared to that required by systems with direct expansion or chilled water without free cooling, which is often discarded due to the widespread short-sightedness in evaluating long-term economic returns.