We distinguish three main types of a free cooling chiller. Systems using auxiliary heat exchangers use separate additional heat exchangers. Most often, plate-type heat exchangers are used. In winter, the required heat load in the cold water circuit is provided by the water from the cooling towers. It is supplied through auxiliary heat exchangers without the use of chillers.
Systems Using Refrigerant Gas
These systems are rarely used. In cases where the condenser water temperature can be reached below the required cold water temperature, the chiller works as a thermosyphon.
- Low-temperature condenser water condenses the gaseous refrigerant in the condenser. It is then directed to the evaporator by gravity or by means of an auxiliary pump.
- The high-temperature cooling water causes the refrigerant to evaporate in the evaporator. The differential pressure between the evaporator and the condenser allows the gas to return to the condenser.
- In this system, the flows between the evaporator and the condenser are provided through bypass channels. There is no need to operate a compressor.
Systems using refrigerant gas may not be used in all refrigeration systems. And in those systems in which they are used, the capacity of free cooling units is limited to 10-30% of the design capacity of the chiller. The capacity of the free cooling units depends on the rated capacity and the difference between the required water temperature and the condensing water temperature.
Systems Using Closed-circuit Cooling Towers
Closed-circuit cooling towers are common in free cooling systems. It eliminates the risk of contamination, unlike open-circuit systems. During the summer, when the equipment of the main cooling group is in operation, the condenser water supplied from the cooling towers circulates in a closed-loop. In winter, when only free cooling systems are in operation, the water supplied from the cooling towers circulates in the cold water circuit in a closed loop.