Free cooling is a smart way to reduce the energy needed to cool a building by making use of naturally cool outdoor air. When the temperature outside is lower than inside, the ventilation system can bring in more outdoor air to help cool the building, reducing the need for traditional air conditioning and compressors.
This can significantly reduce energy consumption and cooling costs, while also reducing the workload of the mechanical cooling system. Instead of using energy to create all the required cooling, the building takes advantage of cooling that is already available in the outdoor air. At the same time, the system automatically adjusts the amount of outdoor air and mechanical cooling to maintain a comfortable indoor temperature.
In this way, free cooling provides a simple and energy-efficient way to maintain a comfortable indoor environment while reducing the building's overall energy use and operating costs.
Free Cooling vs. Air Conditioning: What's the Difference?
Both free cooling and air conditioning help reducing indoor temperatures, but they use very different methods.
Air conditioning uses mechanical cooling as a refrigeration system. It actively removes heat from the air, allowing the indoor temperature to be reduced even when the outdoor air is too hot for free cooling. Air conditioning requires electricity to remove heat from the air and cool the building. In general this means higher operating costs and greater use of mechanical cooling equipment.
Free cooling, on the other hand, does not require compressors or refrigeration circuits to cool the incoming air first. The ventilation system uses the cooling potential of cool outdoor air. When it is cooler than the indoor air, the ventilation system increases the supply of outdoor air to remove excess heat from the building. This means that free cooling is dependent on outdoor conditions, while air conditioning can provide cooling independently of the outdoor temperature.
The biggest advantage of free cooling is energy efficiency. If it is cool outside, there is little reason to use a lot of electricity to produce cooling mechanically. Instead, the building can take advantage of the naturally cooler outdoor air. This reduces energy consumption, lowers cooling costs, and can also reduce the operating time and workload of the air-conditioning equipment.
These two cooling methods do not have to operate separately, but can complement each other. When outdoor conditions are favourable, free cooling can reduce or even eliminate the need for mechanical cooling. When outdoor air is no longer cool enough, the system can switch to mechanical cooling, if required.
Smart Control for Energy-Efficient Cooling
Cooling buildings can account for a significant share of their energy consumption, particularly during warm weather and periods of high occupancy. Due to climate change, warm periods are occurring more frequently and lasting longer in many places. Consequently, energy-efficient cooling of buildings is becoming increasingly important. Free cooling helps reduce the energy required to cool a building by using the naturally available cooling capacity of outdoor air. When outdoor air is sufficiently cool, the ventilation system can take over (part of) the cooling demand. This reduces the need to operate compressors and other mechanical cooling equipment.
The main benefits include:
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- Lower energy consumption: reduces reliance on mechanical cooling equipment when outdoor conditions are suitable
- Reduced cooling costs: makes use of naturally cool outdoor air to limit the use of energy-intensive cooling systems
- Reduced mechanical cooling load: helps air conditioning systems operate less frequently or for shorter periods
- More efficient ventilation: allows the ventilation system to contribute actively to temperature control, rather than only supplying fresh air
- Improved comfort: helps maintain a comfortable indoor temperature when free cooling is properly controlled
Free cooling is not suitable under all outdoor conditions. If the outdoor air is too hot, supplying more of it may increase the indoor temperature instead of reducing it. A ventilation system therefore needs to determine when free cooling is beneficial and when another cooling strategy is required. Free cooling is particularly useful during spring and autumn, cool summer nights and other periods when outdoor air is cooler than the indoor environment.
Cool by Nature, Controlled by Sentera!
A free cooling controller continuously monitors relevant temperature conditions and automatically activates the supply of cold outdoor air if necessary. This helps ensure that free cooling is activated when it is too warm inside and when outdoor air can provide a useful cooling effect. When the conditions are no longer favourable, free cooling stops automatically. Intelligent control helps prevent unnecessary fan operation and ensures that the cooling strategy adapts to changing indoor and outdoor temperatures.
Sentera's free cooling controller is designed for ventilation and cooling applications in offices, commercial and industrial buildings. The controller combines continuous temperature monitoring, automatic fan speed control, controls for backflow dampers and flexible communication options in one solution.
How does the free cooling controller work?
This controller works fully automatically and continuously monitors indoor and outdoor temperatures using two PT500 temperature sensors. By comparing both temperatures, it determines when outdoor conditions are suitable for free cooling and adjusts the fresh outdoor air supply accordingly.
Free cooling starts when the following conditions are met:
- The indoor temperature is higher than the setpoint
- The indoor temperature is higher than the outdoor temperature
- The outdoor temperature is more than 5 °C
First the backflow dampers open, then the exhaust (and supply) fan start running. There are two control modes available for the fans.
With Variable Fan Speed Control, the fan speed is adjusted in steps according to the temperature difference between indoor and outdoor air. In this mode, free cooling is carried out in an energy-efficient manner. When the difference between indoor and outdoor temperatures is small, the fan speed is deliberately kept low to avoid wasting energy. When temperature differences are greater, the fan speed is increased to make optimal use of the available free cooling potential.
With Fixed Fan Speed Control, the fan operates at a preset speed whenever free cooling is active. In this mode, the aim is to cool as quickly as possible using fresh outdoor air.
The fans stop running when either of the following conditions occur:
- The indoor temperature falls below the setpoint
- The difference between indoor and outdoor temperature falls below 1 °C
- The outdoor temperature falls below 4 °C
There is also the option to control the fans manually, regardless of the temperature readings. The Boost function can temporarily increase the fan speed when a quick air refresh is needed. The boost function can be easily activated by pressing the button on the front panel. The Override Control function allows the automatic settings to be bypassed for a longer period. Override control can only be activated and deactivated via Modbus RTU communication.
How to connect the free cooling controller?
The free cooling controller features one analogue output to control fan speed. It offers the option to either control a supply fan and an exhaust fan or to control only the exhaust fan. If both a supply fan and an exhaust fan are connected, they are controlled via the same analogue signal. The output type is adjustable, supporting 0–10 VDC, 4–20 mA or PWM, making it suitable for different EC motors with an analogue input. It can also control AC fan speed controllers with analogue input or frequency inverters. This free cooling controller can therefore control virtually any type of motor, whether or not in combination with a fan speed controller or a variable frequency drive.
The relay output can be used to open and close the backflow dampers. The time required to open the damper is adjustable, as is the fan coast-down time.
Via the built-in Modbus RTU communication, the free cooling controller can be combined with SenteraWeb Cloud for remote access. Or it can be integrated in a Building Management System (BMS), providing access to measured values, operating status and settings.
The free cooling controller uses two PT500 temperature sensors to measure indoor and outdoor temperatures. These are available in different enclosure types and must be ordered separately.
SenteraWeb cloud
You can monitor, adjust and log the Free cooling controller with the online HVAC portal SenteraWeb. An optional internet gateway is required to connect the Free cooling controller to SenteraWeb. You can connect the gateway via Wi-Fi connection or through a LAN cable.
With SenteraWeb, you can:
- Configure parameter settings of connected devices
- Monitor connected devices
- Update device firmware
- Log data and view it in diagrams
- Export logged data as a CSV file
- Receive alert messages or warnings via email or SMS in case threshold values are exceeded
- Use the day-week scheduler to set specific value ranges at certain moments of the day / week and overrule other output values at predefined times
- Define different users and configurators for each installation
- Create your own, personalised dashboard for your installation
- Print a QR code that gives everyone access to see the dashboard of your installation. This makes it possible to give people insights in the indoor and outdoor temperatures and status of the free cooling process.
Want to let nature do the cooling?