Free Cooling

Indirect Free Cooling with the STULZ Explorer

The STULZ Explorer range is available in Free Cooling version, which allows significant energy savings, mainly in cold and temperate climates.

Free Cooling. Energy Saving.

Free Cooling uses the external air to cool the fluid and may entirely replace the cooling circuit, enabling the compressors to be switched off.

Operating modes

Compressor operation: In the case of high outside temperatures, the throughflow of the chilled water through the Free Cooling coil is blocked. The entire cooling capacity is generated with the help of the compressor.

Mixed mode: In the case of outside temperatures below the water inlet temperature, part of the cooling capacity is generated via the Free Cooling coil. The residual heat is dissipated via the refrigerant circuit.

Free Cooling: Depending on the water and outside temperature, the chilled water is exclusively cooled with the help of the outdoor temperature. Only the fans of the chiller are operated. The energy requirement is thus significantly reduced and the operating costs are minimized.

The STULZ Explorer range in particular

WPAmini: The maximized surface of the FreeCooling coils enables the WPAmini to switchover into the Mix- or FC-mode very early. The chiller operating in Mix- or FC-mode reduces the compressor runtimes and thereby reduces the energy consumption to a minimum.

WPAmini product page

WPA: The Free Cooling circuit of the WPA Explorer comprises copper-aluminum heat exchangers. A 3-way valve controlled by the STULZ controller ensures maximum performance and minimizes the operating time of the compressors.

The operating times of the compressors can be minimized by the use of a Free Cooling circuit.

WPA product page

WSA: The Free Cooling circuit of the WSA Explorer comprises copper-aluminum heat exchangers. Two 2-way valves controlled by the STULZ controller regulate the flow of the chilled water through the Free Cooling coil.

Operating costs can be reduced by use of the 2-way valves due to comparatively low pressure drops in the chilled water circuit. In addition, operating times and compressor utilization can be minimized by use of a Free Cooling circuit.

WSA product page



Dynamic Diagram

And what about you?

The interaction of compressor cooling and free cooling is directly dependent on factors such as installation location, cold water temperature and temperature spread and is therefore decisive for efficient operation. Try out which parts of the compressor, mixed and free cooling mode are used at your installation site:


  1. Select the desired location.

  3. Set the temperatures at the cold water inlet and outlet to the desired values.

  5. The switch-over points of the operating modes adapt dynamically to your settings.




Contact us

Holsteiner Chaussee 283
22457 Hamburg 

Central Office: +49 40-5585-0
Fax: +49 40-5585-352

Contact us
To top