What system characteristic enhances the efficiency of low-pressure chillers?

Operation in a vacuum enhances the efficiency of low-pressure chillers because it allows the refrigerant to evaporate at lower temperatures. In a vacuum system, the pressure is reduced, which lowers the boiling point of the refrigerant. This means that the refrigerant can absorb heat from the chilled water more effectively without needing to operate at high pressures. This not only improves the thermodynamic efficiency of the cooling cycle but also reduces energy consumption, leading to more efficient performance overall.

The other characteristics mentioned, such as high refrigerant pressure, larger compressor size, and increased temperature, do not directly contribute to the efficiency of low-pressure chillers in the same beneficial manner as operation in a vacuum. High refrigerant pressures can lead to increased energy requirements for compression, while larger compressor sizes may not always correlate with efficiency depending on system design. Increased temperature within the system does not enhance efficiency either, as lower temperatures typically help with more effective heat transfer and cooling capabilities.