Trane TRG-TRC011-EN manual Isolation valve

period three

Capacity Control

notes

isolation valve

purge evaporator coil

vacuum pump

purge tank

refrigerant vapor from chiller condenser

liquid refrigerant returning to chiller condenser

Figure 53

This example purge system consists of a purge tank, a small refrigeration system, a pump-out system, and controls. The purge’s refrigeration system includes: a small compressor, an air-cooled condensing coil, an expansion valve, and an evaporator coil located inside of the purge tank.

When the chiller is operating, air migrates to the absorber, the area of the chiller operating at the lowest pressure. In this example purge system, an eductor system moves the air from the absorber to the condenser. Because the purge evaporator operates at a lower temperature and pressure than the chiller condenser, a mixture of refrigerant vapor and air is drawn from the chiller condenser into the purge tank. Inside the purge tank, the refrigerant condenses on the cold tubes of the evaporator coil, collects in the bottom of the purge tank, and returns to the chiller condenser as a liquid.

The air does not condense, but instead accumulates in the top portion of the purge tank. Eventually, enough air accumulates to cover a large portion of the purge evaporator coil. The air insulates this coil, impeding heat transfer and reducing the temperature of the refrigerant inside the purge evaporator coil. When the purge refrigerant temperature drops below the setpoint, a controller signals the need for a pump-out sequence. The controller opens the isolation valves, allowing the air to be pumped out of the purge by a vacuum pump. When the purge refrigerant temperature rises again, the controller closes the isolation valves.

The purge controls can be used to track and record how often pump-out occurs. Excessive purging activity may indicate an air leak or depletion of the corrosion inhibitor. The results can be decreased capacity, increased risk of internal corrosion, and possible crystallization. Leaks can be detected early by comparing pump-out activity over the last 24 hours to the 30-day average.

TRG-TRC011-EN 45