Absorption Chiller Maintenance - Purging Non-condensable Gases
All absorption chillers must be purged of non-condensable gases to maintain
performance. The three methods used are steam jet, solution jet (or "motor
purge"), or a vacuum pump, with the vacuum pump being by far the most
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-condensable can be
accomplished using a "motor less purge". Where motor less 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.