Effectively reducing energy costs with Free Cooling
During data center operations, reducing energy costs while maintaining the cooling capacity is one of the main goals. Here, Free Cooling offers the largest possible savings. STULZ has decades of experience delivering Free Cooling projects worldwide. This long-standing experience allows us to address the diverse requirements of different climates and regions with precision and reliability. Our scalable cooling systems are tailored to the unique conditions of each location, ensuring optimal performance and efficiency. Whether in temperate, tropical, or extreme environments, STULZ offers the right solution for every application—developed individually and implemented with accuracy.
What is the difference between direct and indirect Free Cooling?
With Direct Free Cooling, filtered outside air is used directly to cool the data center. This makes it highly energy-efficient, but it does require broader tolerances for temperature and humidity. With Indirect Free Cooling, the outside air does not enter the data center. Instead, cooling takes place through a separate system, for example using a water/glycol mixture, keeping the indoor air completely separated from the outside air. The main difference is therefore how outside air is used: directly in the space or indirectly through a heat exchange system.
Types of Free Cooling
Direct Free Cooling allows outside air to enter the room directly, where it is further treated by filtration systems to ensure indoor air quality. This highly efficient approach is especially effective when outdoor conditions are favorable, as its performance is influenced by the quality of the outside air.
To fully leverage this method, wider tolerances in temperature and humidity levels are required.
Benefits:
- Maximum energy efficiency thanks to the direct use of Free Cooling
- Excellent system scalability – no hydraulics (pipework, pumps, valves)
- Lower investment costs compared with conventional Indirect Free Cooling systems
- Much lower energy requirement than all conventional systems
Indirect Free Cooling uses outside air indirectly for air conditioning through a heat exchanger. This approach keeps the sensitive interior of the building isolated from outdoor air, ensuring reliability and consistent cooling performance.
Indirect Dynamic Free Cooling from STULZ is a hybrid system that combines Indirect Free Cooling with dynamic control for maximum efficiency.
Benefits:
- Minimal compressor running time
- Switching operation and control according to actual heat load
- Maximized periods of Free Cooling
- Automatic selection of the optimum operating mode without a fixed Free Cooling start value
- Minimized operating costs
More about STULZ Free Cooling
Free Cooling can operate in different modes depending on ambient conditions and system configuration. Each mode optimizes energy efficiency by adjusting components such as compressors, pumps, and fans. Below is an overview of the main operating modes. By combining these modes intelligently, STULZ systems ensure maximum energy savings and reliable cooling performance under all conditions.
Operating modes
| Free Cooling | Extended Free Cooling* | Mixed mode | Compressor mode | |
|---|---|---|---|---|
| Compressor | Off | Off | Variable | On |
| Standby unit | On | On | On | Off |
| Fan | Set point | Max. | Set Point | Set point |
| Pumps | Variable | Max. | Max. | Min. |
| CRAC | CW: Variable / DX: Off | CW: Max. / DX: Off | CW: Variable/ DX: Staged | CW: Off / DX: Max. |
| Dry cooler fans | Variable | Max. | Max. | Variable |
*What is Extended Free Cooling?
Extended Free Cooling is available in Indirect Dynamic Free Cooling systems. In this mode, variable-speed pumps and dry coolers with fan speed control maintain cooling capacity by increasing airflow. This extends Free Cooling operation and reduces operating costs to an absolute minimum.
Calculate your Free Cooling potential
Free Cooling Calculator for STULZ Chiller systems