Glossary of Terms

  1. Approach: The difference in temperature between the heat exchange fluids, typically either the leaving water temperature, or air temperature, and the saturated (liquid) refrigerant temperature.
  2. Evaporator Approach = Leaving Chilled Water Temperature – Saturated Refrigerant Evaporating Temperature
  3. WC Condenser Approach = Saturated Refrigerant Condensing Temperature – Leaving Condenser Water Temperature
  4. AC Condenser Approach = Saturated Refrigerant Condensing Temperature – Ambient Air Temperature
  5. Saturated Refrigerant Evaporating Temperature: The temperature at which the refrigerant changes state, at that particular pressure, from a liquid to a vapour, i.e. the temperature at which the liquid evaporates.
  6. Saturated Refrigerant Condensing Temperature: The temperature at which the refrigerant changes state, at that particular pressure, from a vapour to a liquid, i.e. the temperature at which the vapour condenses.
  7. Delta T: The difference in temperature between the entering and leaving water temperatures.
  8. Chilled Water Delta T: Entering Chilled Water Temperature – Leaving Chilled Water Temperature
  9. Condenser Water Delta T: Entering Condenser Water Temperature – Leaving Condenser Water Temperature
  10. Specific Heat: the ability of a fluid to absorb and transport heat
  11. Specific Gravity: The density of the water as compared to water
  12. Viscosity: The ability of a fluid to flow
  13. Thermal Conductivity: The rate of heat transfer possible
  14. Evaporator Pressure: The pressure of the refrigerant found within the Evaporator
  15. Condenser Pressure: The pressure of the refrigerant found within the Condenser
  16. Suction Pressure: The pressure of the refrigerant at the suction inlet of the compressor.
  17. Discharge Pressure: The pressure of the refrigerant at the discharge outlet of the compressor.
  18. Superheat: The difference in temperature between the saturated refrigerant temperature, and the temperature of the refrigerant vapour that has risen above this point. See examples for Suction Superheat, and Discharge superheat.
  19. Suction Superheat: The difference between the Saturated Refrigerant Evaporating Temperature, and the temperature at the compressor suction inlet.
  20. Discharge Superheat: The difference between the temperature of the gas at the outlet of the compressors discharge, and the saturation temperature for the condenser.
  21. Delta P / Water Side Pressure Drop: The difference in water pressure between the water entering the heat exchanger, and the water leaving the heat exchanger. This may be affected to some degree by fouling, or by a seal issue at the water box divider, but most typically, if this has deviated from design, it would be due to a change in the flow rate, as the flow rate and the pressure drop are directly linked.
  22. Subcooling: The difference in temperature between the refrigerant liquid temperature, and the saturated temperature for the refrigerant at the condensing pressure.
  23. Voltage: The average voltage of the three readings of the voltage between each phase of the incoming supply voltage (i.e. measure between Phase 1 and 2, Phase 2 and 3, and Phase 3 and 1, add them together, then divide by 3).
  24. Water Cooled Condenser: A heat exchanger designed as the condenser for the chiller that removes heat from refrigerant vapour and transfers it to the condenser water running through the tubes within it. The Compressor discharges refrigerant vapour into this heat exchanger, which then condenses on the outside of the tubes, transferring heat out of the refrigerant, into the water, as the refrigerant vapour is at a hotter temperature than the water temperature within the tubes. The difference in temperature between these two being called the WC Condenser Approach.
  25. DX / Direct Expansion Evaporator: A Heat Exchanger Designed as the evaporator, or main functioning part of the chiller, that removes heat from the chilled water by transferring it into the refrigerant. This heat exchanger has refrigerant running through the tubes, and the water surrounding all the tubes, typically being forced to travel through the chiller in a zig zag pattern due to internal baffles within the heat exchanger. As the water that is surrounding each tube is warmer than the liquid refrigerant within the tubes, the refrigerant evaporates, absorbing heat from the chilled water, by changing state from a liquid to a vapour, which is then sucked out of the evaporator by the compressor, before being discharged into the Condenser.
  26. Flooded Evaporator: A Heat Exchanger Designed as the evaporator, or main functioning part of the chiller, that removes heat from the chilled water by transferring it into the refrigerant. This heat exchanger has water running through the tubes, and the refrigerant surrounds all the tubes, As the water within each tube is warmer than the liquid refrigerant surrounding the tubes, the refrigerant evaporates, absorbing heat from the chilled water, by changing state from a liquid to a vapour, which is then sucked out of the evaporator by the compressor, before being discharged into the Condenser.