Purge

#A purge system is required on all subatmospheric refrigeration systems, and may be used on non-subatmospheric systems, to remove air, moisture and other noncondensable gases that leak or otherwise enter into the system. The present invention is directed to improvements in such purge systems to reduce the emissions of condensable gases that may accompany the purging or release of the non-condensable gases from the system.

#For example, refrigeration systems such as centrifugal chillers, including, for example, the CenTraVac® centrifugal chillers manufactured by The Trane Company, a Division of American Standard Inc., utilize low pressure refrigerants such as CFC11, CFC113, HCFC123 and multi-pressure refrigerants such as CFC-114 and CFC245A to operate at less than atmospheric pressure, either at all times or under a set of operating or standdown conditions. Since the chillers are operating at subatmospheric pressures, air and moisture may leak into the machine through these low pressure areas. Once the air and moisture and other non-condensables enter the chiller, the noncondensables accumulate in the condenser portion of the chiller during machine operation. The non-condensable gases in the condenser reduces the ability of the condenser to condense refrigerant, which in turn results in an increased condenser pressure, and thereby results in lower chiller efficiency and capacity.

#A purge device is a device mounted externally to the chiller. The purge device, in its simplest form, consists of a tank, inlet and outlet connections and valves, and an arrangement for cooling the tank. The arrangement for cooling the tank can be a refrigeration system but may also be a source of cold water or other fluid, a fan system, or even cooled refrigerant from the system being purged. The evaporator or cooling coil of the purge refrigeration system is located within the purge tank and is called the purge evaporator. The purge tank is connected to the chiller system by supply and refrigerant lines through which refrigerant may freely flow. The supply line is typically connected to the condenser and the return line may be connected to the condenser or to the evaporator depending upon the inclusion of a device to maintain system pressures. The purge evaporator includes a coil representing a cold condensing surface to the chiller refrigerant entering the tank through the supply line. When the purge refrigeration unit is running, refrigerant from the chiller condenser is attracted to the cold surface of the purge evaporator in the purge tank. When the gaseous refrigerant contacts the cool surface of the purge evaporator coil, the gaseous refrigerant condenses into a liquid, leaving a partial vacuum behind. More refrigerant vapor from the chiller condenser migrates to the purge tank to fill this vacuum. The liquid refrigerant condensed in the purge tank returns to the chiller system via the return line. Any noncondensables in the vapor from the chiller do not condense in the purge tank and are left behind to fill more and more header space in the purge tank. Increasing quantities of noncondensables accumulating in the purge tank act to reduce the heat transfer efficiency of the evaporator coil, and the leaving temperature will begin to decrease in response thereto. The leaving temperature is monitored by the unit controls, which will activate a pumpout cycle to remove accumulated noncondensables from the purge tank. When enough noncondensables have been removed, the increasing purge compressor suction temperature will terminate the pumpout cycle. Such a system is implemented by Trane and sold under the trademark Purifier™, and is further described in U.S. Pat. No. 5,031,410 to Plzak et al., the disclosures of which are commonly owned and which are incorporated by reference herein.

#FIG. 1 is a schematic drawing of a purge system in accordance with the present invention.

#FIG. 2 is a flow chart of pumpout control logic in accordance with the present invention.

#FIG. 1 shows a purge system 10 connected to the condenser 12 of a chiller system 13 by a supply line 14 and a return line 16. Isolation valves 18 are included in each of the supply and return lines 14, 16.

#The purge system 10 includes a purge tank 20 to which the supply line 14 and the return line 16 connect. The purge tank 20 is a sealed tank enclosing a heat exchanger acting as an evaporator 22. The evaporator 22 may be implemented as a copper coil 23. The evaporator 22 is preferably part of a refrigeration system 32 including the evaporator, a compressor 24, condenser 26 and an expansion device 28 all serially linked by refrigeration tubing 30 into a refrigeration circuit to form the refrigeration system 32.

#The refrigeration system 32 includes a temperature sensor 34 located in the tubing 30 in proximity to the evaporator outlet 36. A liquid temperature sensor 38 is provided in the return line 16 to measure the temperature of liquid refrigerant condensed by the evaporator 22 and being returned to the condenser 12. In an alternative arrangement, this temperature information may be obtained from a temperature sensor (not shown) in the condenser sump when the chiller is on, and from an evaporator temperature sensor (not shown) when the chiller is off.