Chiller Purge Systems: How They Work    

LOW PRESSURE REFRIGERANTS Purge units are most commonly used on negative pressure chillers charged with R11 or R123 refrigerants. During operation, these chillers generate a 15 to 17 inch vacuum in the evaporator, where chilled water is produced. If leaks exist in the seals and joints of the evaporator, air will enter the chiller and create a host of problems. Noncondensible gases entering the evaporator will migrate to the compressor and ultimately collect in the condenser tube bundle. In the condenser, these gases elevate the head pressure against which the compressor discharges. Too high of a head pressure causes the compressor to “surge”, which drastically increases energy consumption and damages expensive compressor components. Noncondensible gases also insulate the tubes and decrease heat exchange efficiency between the condensing water and the refrigerant. Water vapor that likewise leaks into the chiller generates rust and highly reactive aqueous acids that corrode components. A purge unit’s job is to remove noncondensible gases as rapidly as possible. The EnviroPurge mounts permanently to a chiller and continuously draws condenser vapor into its chilled purge vessel. As it is drawn over the vessel’s cooling coil, refrigerant vapor condenses and pools in the bottom of the vessel where it is drawn back to the chiller evaporator by pressure differential. Noncondensible gases separate and rise to the top of the purge vessel. When the microprocessor determines that enough noncondensible gases have been collected, a pump-out cycle is initiated in which the noncondensibles are discharged to the atmosphere with negligible refrigerant loss. HIGH PRESSURE REFRIGERANTS With the growing popularity of high pressure chillers, we see an increasing occurrence of noncondensible gas contamination in R22, R134a, etc. systems. Since these systems rarely operate at negative pressures, improper recovery or evacuation practices are typically to blame. In the past, elimination of air from these refrigerants was difficult. Today, the MiniPurge purges noncondensible gases from high pressure refrigerants quickly and economically. While the EnviroPurge separates noncondensibles by chilling the refrigerant, the MiniPurge uses pressure. An on board compressor actively draws vapor from the chiller condenser (making the process very fast) and compresses it in a separation vessel. Compressed refrigerant vapor condenses in the bottom of the vessel and is forced back to the cooling system. Meanwhile, noncondensible gases separate and rise to the top of the vessel. When the microprocessor determines the most efficient pump-out cycle, the noncondensible gases are expelled, again with negligible refrigerant loss.