Chiller Systems

Absorption Chiller Maintenance - Purging Non-condensable Gases

General

All absorption chillers must be purged of non-condensable gases to maintain performance. The three methods used are steam jet, solution jet (or "motorless purge"), or a vacuum pump, with the vacuum pump being by far the most common.

Non-condensable gases migrate to the area of lowest pressure in the absorption chiller (the evaporator) where a small portion of the vapor is extracted and condensed in the purge unit using cooling water. Non-condensable are then evacuated by the vacuum pump. In normal operation, the purge system should operate about one hour a week. The vacuum pump oil level should be observed, maintained, and changed as necessary. Oil purge pump motor bearings should be inspected and replaced, and the belt adjusted as needed. In addition, the vacuum pump should be flooded with oil during seasonal shutdown to prevent internal corrosion.

Purging of non-condensables can be accomplished using a "motorless purge" as shown here. Where motorless purging is used, an optional vacuum pump can also be used for evacuation.

In all cases, the operator should log purge operation and monitor purge operation trends. Increasing purge operation signals increasing in-leakage of air and moisture.