Calculate evaporator or condenser chiller approach, or reverse-solve leaving-water and saturated-refrigerant temperatures in °F, °C, or K.

Use saturated refrigerant temperature. Compare approach with the design value at comparable load and flow; it does not diagnose fouling by itself.

Optional settings

Blank omits the comparison. Use a baseline for comparable operating conditions.

Related Calculators

Chiller Approach Temperature Formula

For an evaporator, approach is leaving chilled-water temperature minus saturated evaporating refrigerant temperature. For a condenser, approach is saturated condensing refrigerant temperature minus leaving condenser-water temperature.

AT = Tcw - Tₑᵥ

Variables:

  • AT is the chiller approach temperature
  • Tcw is the chilled water leaving temperature
  • Tev is the evaporator refrigerant temperature

For the evaporator, subtract saturated evaporating temperature from leaving chilled-water temperature. For the condenser, reverse the temperature order: saturated condensing minus leaving condenser water. The calculator can also solve either temperature from a nonnegative approach. Absolute °F/°C/K values and temperature differences use different conversions; 1 K difference equals 1 Δ°C or 1.8 Δ°F.

What is a Chiller Approach Temperature?

Approach is a heat-exchanger temperature difference. Use saturated refrigerant temperature, rather than a superheated suction-line or subcooled liquid-line measurement. Compare it with manufacturer data or a measured baseline at comparable load, flow and conditions. A change alone does not diagnose fouling or establish whole-system efficiency.

How to Calculate Chiller Approach Temperature?

The following steps outline how to calculate the Chiller Approach Temperature.

  1. First, determine the chilled water leaving temperature (Tcw).
  2. Next, determine the evaporator refrigerant temperature (Tev).
  3. Finally, calculate the chiller approach temperature using the formula AT = Tcw - Tev.
  4. After inserting the values and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Chilled Water Leaving Temperature (Tcw) = 7°C

Saturated Evaporator Refrigerant Temperature (Tev) = 2°C. The approach is 7 − 2 = 5 Δ°C (9 Δ°F).