At operating temperatures above approximately 180 °C. The reasons for this are:
- Safety risks associated with systems not using fixed pipes. At 180 °C, the system pressure has already reached 12 bar, which does not include the pump pressure that depends on the consumer connected to the temperature control unit.
- The seals in the consumer can leak at these high pressures.
- Depending on the acceptable pressure of the consumer, the pressure in the temperature control circuit must be kept to a minimum.
- If no limits are present, water is to be preferred over oil as a heat transfer fluid due to water's significantly better heat transfer properties.