High Approach RTAC

Issue:

Why does one circuit have a high approach and the other circuit have a good approach?

Resolution:

RTAC Chillers: 

Approach temperature is the difference between the leaving water temperature and the saturated evaporator refrigerant temperature for that respective circuit.  Approach temperature indicates the effectiveness of the heat exchanger.  The lower the number the better the heat transfer.  High approach temperatures can be a result of having too much oil or glycol in the chilled water loop, inadequate water flow, or having fouled tubes in a falling film/flooded evaporator.

• If one circuit has a high approach temperature and the other circuit has an acceptable approach, it is advisable to inspect the oil strainer on the oil return line. This line runs from the bottom of the evaporator to the bottom of the compressor. If there is a restriction in this line, it can result in the accumulation of oil in the evaporator.
• It is also recommended to check the oil level in the circuit. To do so, operate the circuit at minimum load for 45 minutes, then shut it down and wait for 30 minutes before checking the oil level in the oil separator.
• Insufficient water flow can negatively impact the evaporator approach temperature, leading to poor approach temperatures in both circuits.
• The evaporator approach can be affected by the performance of the Liquid Level Sensor (LLS) and the Expansion Valve (EXV).

GLYCOL:  When using glycol, TechView Setpoint View setting for "Freeze Inhibitor Present" must be set to "YES" to prevent nuisance diagnostics for "High Approach".

Other Question/Problem/Cause Statements:

• Why does one circuit have a high approach and the other circuit have a good approach?
• Approach Temperature?
• Evaporator Approach?

Facts:

• One circuit has approach less than 5 degrees F and other circuit has 10 degrees F approach temperature
• Air-Cooled Chiller (Pueblo) (RTAC)