TL;DR

A rising approach temperature means heat transfer is degrading. On the condenser side this is almost always tube fouling. On the evaporator side it can also be low refrigerant charge. Calculate both approach temperatures from the operating log and address the affected side.

What you might see

evaporator approach temperature above 1 degree C
condenser approach temperature above 2 degrees C
chiller running at higher power for same cooling load
chilled water temperature not meeting setpoint under partial load

Likely causes

Tap to mark as ruled out

Fouled evaporator or condenser tubes reducing the effective heat transfer coefficient
Low refrigerant charge reducing the evaporator wetted tube area
Reduced water flow on either the chilled water or condenser water side
Improperly balanced refrigerant distribution inside the evaporator shell

Required tools

Chiller controls access (Trane Tracer panel)
Calibrated thermometers for water side temperatures
Tube brush cleaning kit (for condenser or evaporator cleaning)

Safety first

Evaporator tube access requires isolating and draining the chilled water circuit. Confirm isolation before opening the water box.
Refrigerant charge verification requires EPA Section 608 certification.

Procedure

7 steps · ~60 min

1
Calculate the evaporator approach temperature: chilled water leaving temperature minus saturated evaporating temperature. Record the value.[1]
2
Calculate the condenser approach temperature: saturated condensing temperature minus condenser leaving water temperature. Record the value.[1]
3
Compare both values to the baseline from the last tube cleaning. An increase of more than 0.5 degrees C in either is significant.
4
Verify chilled water flow rate at the evaporator and condenser water flow at the condenser. Compare to design flow from the original commissioning report.
5
If condenser approach is elevated, schedule a condenser tube cleaning (see the high-discharge-pressure procedure on this machine).
6
If evaporator approach is elevated and flow is normal, a Trane-certified technician should check refrigerant charge and evaporator liquid level.
7
After tube cleaning or refrigerant correction, record the new baseline approach temperatures for future trending.

Sources

Trane CenTraVac Chiller Operation and Maintenance Manual, Trane (Trane Technologies)
Trane CenTraVac Operation and Maintenance Manual, approach temperature analysis and heat exchanger maintenance (general)
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