Patent Publication Number: US-6705100-B2

Title: Purge

Description:
This is a divisional of application Ser. No. 10/015,971, filed Oct. 22, 2001, now U.S. Pat. No. 6,564,564. 
    
    
     BACKGROUND OF THE INVENTION 
     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. 
     While the Purifier™ purge has been an industry leader for many years, there are improvements in improving the efficiency of its operation and reducing the percentage of condensable gases escaping with the release of noncondensable gases. 
     SUMMARY OF THE INVENTION 
     It is an object, feature and advantage of the present invention to solve the problems of the prior art purge systems. 
     It is an object, feature and advantage of the present invention to provide a purge tank for condensing condensable gases and accumulating noncondensable gases where the purge tank includes baffles. 
     It is a further object and feature of the present invention that these baffles comprise flat copper discs brazed directly to the top and bottom of an evaporator coil located within the purge tank. 
     It is an object, feature and advantage of the present invention to increase the rate of removal of noncondensable gases. 
     It is a further object, feature and advantage of the present invention to modulate the pumpout compressor flow capacity. In one embodiment, this is accomplished by cycling the compressor or its flow components. Cycling flow components includes controlling a pumpout solenoid valve on the suction side of a pumpout compressor during a pumpout cycle. 
     It is a further object, feature and advantage of the present invention that the solenoid valve be pulsed on and off when the pumpout cycle is initiated so that an adaptive setpoint for the pumpout compressor capacity can be adjusted to full capacity when a feedback sensor indicates that a need for full capacity exists. 
     It is a still further object, feature and advantage of the present invention that the value of a feedback sensor be measured and compared to a setpoint value to determine whether the pumpout cycle should be initiated, continue or cease. 
     It is an object, feature and advantage of the present invention to provide adaptive pumpout setpoints that vary during the pumpout cycle. 
     It is a further object, feature and advantage of the present invention that these adaptive pumpout setpoints be determined as a function of the temperature of condensed liquid refrigerant being returned to the chiller system. 
     The present invention provides a purging device for a system accumulating condensable and non-condensable gases. The purging device comprises: a purge tank; an inlet connection to the purge tank for receiving the condensable and non-condensable gases from the system and directing said gases into the purge tank; refrigeration means associated with the purge tank for condensing the non-condensable gases into a condensed form; header space in the purge tank for accumulating the non-condensable gases; a first outlet connection for returning the condensed gases from the purge tank to the system; a second outlet for controllably removing the accumulated non-condensable gases from the header space; and a baffle in the purge tank for providing a controlled flow space for the condensable and non-condensable gases and providing a quiet zone in the header spacer. 
     The present invention also provides a device for separating non-condensable gases from condensable gases. The device comprises: a separation tank having an inlet and an outlet; a heater located in proximity with the separation tank and providing a source for heating the tank; a substance having an affinity for one of the condensable gases and a heat exchanger located within the separation tank in heat exchange relationship with the heater and the substance. The substance is located within the separation tank between the inlet and the outlet so as to capture the gas for which the substances affinity lies. The substance releases the captured gas in response to the application of heat by the heater, and/or reduction of pressure by connection to the low pressure point of the chiller. 
     The present invention additionally provides a method of determining a setpoint for a purge system. The method comprises the steps of: determining a chiller condensing temperature based upon a temperature of condensed liquid being returned from the purge system to a system being purged; determining a pumpout initiate setpoint as a function of the purge liquid temperature. 
     The present invention further provides a method of determining a setpoint for a purge system. The method comprises the steps of: determining a chiller condensing temperature based upon a temperature of condensed liquid being returned from the purge system to a system being purged; determining a pumpout terminate setpoint as a function of the purge liquid temperature. 
     The present invention still further provides a method of determining setpoints for a purge system. The method comprises the steps of: determining a chiller condensing temperature based upon a temperature of condensed liquid being returned from the purge system to a system being purged; determining a pumpout initiate setpoint as a function of a purge operating condition; and determining a pumpout terminate setpoint as a function of the purge operating condition. 
     The present invention moreover provides a method of controlling the pumpout of a purge tank which contains non-condensable gases extracted from a refrigeration system. The method comprising the steps of: pulsing an outlet control valve for a predetermined amount of time; determining a pumpout initiate setpoint; measuring temperature associated with the purge tank; comparing the measured temperature with the initiate setpoint; initiating continuous pumpout if the suction temperature is less than the initiate setpoint; determining a terminate setpoint; and comparing the suction temperature to the terminate setpoint and terminating pumpout if the measured temperature is greater than the terminate setpoint. 
     The present invention yet further provides a method of adaptively controlling the operation of refrigeration system. The method comprises the steps of: monitoring the operation of a chiller to determine the time when the chiller is on and the time when the chiller is off; monitoring the operation of a purge system removing non-condensable gases from the chiller to determine when the chiller is pumping out non-condensable gases in terms of when the chiller is on and off; and adaptively modifying the control of the purge in response to the monitored data. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     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. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     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. 
     The purge tank  20  includes a float switch  40  to measure and detect the accumulation of liquid refrigerant in a bottom area  42  of the purge tank  20 . The float switch  40  inhibits operation if liquid accumulates. 
     The purge tank also includes a header space  44  wherein noncondensable gases accumulate after the operation of the evaporator  22  condenses the condensable gases into a liquid form. The purge tank  20  includes a header outlet  46  and a header outlet line  48  to allow the noncondensable gases to be removed from the header space  44 . A pumpout solenoid valve  50  is provided in the header line  48  to control the removal of the noncondensable gases. A pumpout compressor  52  is located in the header line  48  so as to provide a motivating force for the removal of the noncondensable gases from the header space  44 . 
     The header line  48  leads to a separation tank  60  filled with a substance having an affinity for a condensable gas. Preferably, the separation tank  60  is filled with an activated carbon having an affinity for many system refrigerants including CFC11, CFC113 and HCFC123. The separation tank  60  includes an inlet  62 , an outlet  64  and an electric heater  66  located within the separation tank  60 . The separation tank  60  is filled with the carbon  68  and a heat exchanger  70  is operably connected between the heater  66  and the carbon  68  to enhance the heat exchange relationship therebetween. The separation tank  60  also includes a temperature sensor  72  to measure the temperature within the separation tank  60  and control the operation of the electric heater  66 . The outlet  64  of the separation tank  60  includes connections to an exhaust line  80  under the control of an exhaust valve  82 , to a pressure relief line  84  under the control of a pressure relief device  86 , and a second return line  88  under the control of a regeneration valve  90  and an isolation valve  92 . The second return line  88  preferably returns to an evaporator  94  of the chiller system  13 . The exhaust line  80  is connected to a chiller vent line or an area of safe exhaust  96 . 
     The purge tank  20  includes baffles  100  and  102  respectively located in an upper area  104  and a lower area  106  of the purge tank  20 . The baffles  100 ,  102  act to provide a controlled flow space for the condensable and noncondensable gases and a quiet zone in the header space where the non-condensable gases may accumulate. In operation, the baffles  100 ,  102  also serve to direct the gases into condensing contact with the coil  23 . The baffles  100  and  102  are preferably braised, welded or otherwise affixed to the copper coil  23  of the evaporator  22  within the purge tank  20 . 
     In operation, the purge system  10  is turned on and the purge evaporator  22  condenses the condensable gases present in the purge tank  20 , transforming or coalescing the condensable gases into a liquid form which then returns through the return line  16  to the chiller system  13 . The partial vacuum created within the purge tank  20  causes more condensable and noncondensable gases to enter through the supply line  14  to the purge tank  20  where the condensable gases continue to condense into liquid form and return to the chiller system  13 . Eventually the header space  44  begins to fill with noncondensable gases and begins to effect the efficiency and operation of the purge evaporator  22  as measured by the temperature sensor  34  (or other detection means such as a pressure sensor or the like). At such time, a pumpout cycle may be initiated. In a pumpout cycle, the normally closed valve  50  and  82  are opened and the pumpout compressor  52  is turned on to cause the noncondensable gases to flow out the header line  48  into the separation tank  60 . In the separation tank  60 , any condensable gases still flowing with the noncondensable gases are attracted to the activated carbon  68  in the separation tank  60  and bond thereto, leaving only the purified noncondensable gases to flow out the now open exhaust valve  82  to the vent area  96 . 
     The actual pumpout control is described with respect to the flow chart  120  of FIG.  2 . 
     The pumpout cycle begins at step  122  and proceeds to step  124  where initiate and terminate setpoints are calculated. The initiate setpoint and the terminate setpoints are calculated as a function of the purge liquid temperature measured by the temperature sensor  38  in the return line  16 . Preferably the initiate setpoint is equal to the measured purge liquid temperature minus 50° F., whereas the terminate setpoint is determined by the purge liquid temperature minus 40° F. Of course, a person of ordinary skill in the art will recognize that other methods of calculating these setpoints may be employed. 
     Periodically, the accumulated condensables with their affinity for the carbon  68  must be regenerated so that the carbon can be purified to improve its efficiency and so that the refrigerant condensables may be returned to the chiller system  13 . This is accomplished by activating the electric heater  66  under the control of the temperature sensor  72 . The addition of considerable heat and reduction of pressure to the carbon  68  in the separation tank  60  acts to break the affinity between the carbon  68  and the refrigerant gases. These gases are then drawn through the line  88  through the now open valve  90  and back to the chiller evaporator  94 . 
     At step  126  a determination is made as to whether a regeneration cycle is in progress regenerating the carbon  68  in the separation tank  60 . Only if such a process is not ongoing will the flow chart  120  continue to step  128 . 
     At step  128  the determination is made that the purge refrigeration circuit  32  is on. If so, then at step  130 , the temperature measured by sensor  34  is compared to the initiate setpoint. If the measured temperature is less than the initiate setpoint, then the pumpout control continues to step  132 . 
     At step  132 , the valve  82  is opened, the pumpout compressor  52  is turned on, and a short delay is indicated by step  134 . After this delay, preferably of 5 seconds amount of time, the valve  50  is pulsed at step  136  to an open position for 20 seconds, then pulse closed for 20 seconds and the cycle then repeated one more time followed by a short delay. After this delay, the suction temperature is compared at step  138  to the terminate setpoint. If the suction temperature is greater than the terminate setpoint, then the pumpout cycle is ended at step  140  by closing the valve  82  and turning off the pumpout compressor  52 . 
     However, if the step  138  did not determine that the suction temperature was greater than the terminate setpoint, then the valve  50  is opened at step  142  and the pumpout cycle continues in a cycle of steps  138 ,  142  and  144 . Step  144  causes step  146  to be implemented every 10 minutes. Step  146  recalculates the initiate and terminate setpoints using the same method as they were initially calculated at step  124  as a function of the liquid temperature measured by the sensor  38 . This of course, causes the termination at step  138  to vary as setpoints, are periodically updated and causes the overall purge pumpout cycle to operate much more efficiently and quickly.