Patent Description:
Many vapor compression systems using low vapor pressure refrigerants include purge units for removing noncondensable contaminants from the system. A flow is diverted from the main refrigerant flowpath and passed into a purge tank where it is cooled to condense refrigerant while leaving noncondensable contaminants in vapor form. The vapor may be vented or pumped out of the vessel (e.g., to atmosphere). The purge unit may operate intermittently.

The condensing heat may be removed by a secondary vapor compression system. The secondary vapor compression system may have its own recirculating refrigerant flowpath proceeding downstream from a compressor to a heat rejection heat exchanger, an expansion device, a heat absorption heat exchanger providing the cooling for the purge tank, and then returning to the compressor.

One particular vapor compression system is used as a chiller to produce chilled water. An exemplary chiller uses a hermetic centrifugal compressor. The exemplary unit comprises a standalone combination of the compressor, a heat rejection heat exchanger, an expansion device, an evaporator unit, and various additional components. Exemplary compressors are electric motor-driven hermetic or semi-hermetic compressors.

<CIT> discloses chiller systems using low pressure refrigerant. <CIT> defines "low pressure refrigerant" refrigerant as having a liquid phase saturation pressure below about <NUM> psi (<NUM> kPa) at <NUM>°F (<NUM>) and gives an example of low pressure refrigerant as R245fa. It also references use of "medium pressure refrigerant" which it defines as having a liquid phase saturation pressure between <NUM> psia (<NUM> kPa) and <NUM> psia (<NUM> kPa) at <NUM>°F (<NUM>). A further recent low pressure refrigerant is HFO R1233zd(e).

Also, international patent application <CIT>, discloses use of phase change material in association with an evaporator of a refrigeration system. Exemplary phase change materials include paraffin waxes, fatty acids from natural oils, and inorganic salt solutions. The exemplary phase change material has a melting temperature (from solid to liquid) at which it absorbs heat while maintaining a substantially constant temperature. In other words, as the phase change material is heated up from a temperature below the melting temperature to the melting temperature, the temperature of the phase change material rises accordingly. However, when the phase change material reaches its melting temperature, the temperature of the phase change material remains substantially the same as it absorbs heat, before all the phase change material becomes liquid. <CIT> discloses a purge unit for dehydrating gas such as air which is to be compressed for the use in a laboratory or industrial apparatus. The purge unit comprises a thermoelectric module for cooling the gas and a means for separating the cooled gas and the condensable elements.

A first aspect of the invention involves a purge unit as defined in claim <NUM>. It comprises a vessel having an inlet, a return port, a first path between the inlet and the return port, a purge port, and a second path between the inlet and the purge port. One or more thermoelectric units are positioned to be in thermal communication with at least the first path. The purge unit comprises one or more additional thermoelectric units positioned to transfer the heat absorbed by the one or more thermoelectric units. A phase change material is positioned to receive heat absorbed by the one or more thermoelectric units from the first path.

The purge unit may comprise a power supply coupled to the one or more thermoelectric units to, in at least a first mode, cause the one or more thermoelectric units to absorb heat from refrigerant along the first path.

The one or more additional thermoelectric units may be positioned to transfer the heat absorbed by the one or more thermoelectric units to an environment.

The purge unit may comprise: a heat exchange fluid flowpath having a first leg in thermal exchange relation with the one or more thermoelectric units and one or more additional thermoelectric units; and a pump along the heat exchange fluid flowpath.

The one or more additional thermoelectric units may be positioned to exchange heat between the heat exchange fluid flowpath and ambient air.

A heat exchange fluid along the heat exchange fluid flowpath may comprise at least <NUM>% by weight one or more of water and glycol.

The vessel may be an inner vessel, the purge unit may comprise an outer vessel containing the inner vessel, and the phase change material may be in a space between the outer vessel and the inner vessel.

The one or more thermoelectric units may be mounted to the inner vessel, the one or more additional thermoelectric units may be mounted to the outer vessel, and one or more finned heat sinks of the one or more thermoelectric units and one or more finned heat sinks of the one or more additional thermoelectric units may be immersed in the phase change material.

The one or more finned heat sinks of the one or more thermoelectric units and the one or more finned heat sinks of the one or more additional thermoelectric units may have interleaved fins.

The phase change material may comprise material selected from the group consisting of paraffin waxes, fatty acids from natural oils, and inorganic salt solutions.

The phase change material may have a melting temperature of -<NUM> to <NUM>.

A second aspect of the invention involves a vapor compression system comprising the purge unit of the foregoing aspect and comprises: a compressor having a suction port and a discharge port; a first heat exchanger coupled to the discharge port to receive refrigerant driven in a downstream direction along a refrigerant flowpath in a first operational condition; an expansion device downstream of the first heat exchanger along the refrigerant flowpath in the first operational condition; a second heat exchanger downstream of the expansion device and coupled to the suction port to return refrigerant in the first operational condition; and said purge unit wherein: the inlet is coupled to the refrigerant flowpath to receive refrigerant; and the return port is coupled to the refrigerant flowpath to return refrigerant.

The purge port may be vented to atmosphere.

A refrigerant charge may comprise at least <NUM>% by weight an HFO having a liquid phase saturation pressure below <NUM> kPa at <NUM>.

A controller may be configured to operate the purge unit to, in a first mode, apply a voltage to the one or more thermoelectric units to cool the received refrigerant to condense the refrigerant.

A third aspect of the invention involves a method for operating the system of the second aspect, the method comprising: operating the purge unit to, in a first mode, apply a voltage to the one or more thermoelectric units to cool the received refrigerant to condense the refrigerant.

The performance of the state of art purge designs suffers when lower pressure refrigerants are used (which is the case for low global warming potential (GWP) refrigerants). R1233zd(E), for example, has a saturated pressure of around <NUM>. 56psia (183kPa) at <NUM>°F (<NUM>). In order to achieve a separation ratio of above <NUM> (a high tier performance as an example), the vapor pressure for the R1233zd(E) refrigerant would be as low as <NUM>. 133psia (<NUM> divided by <NUM>) (<NUM>. 92kPa) which corresponds to a saturation temperature of roughly -<NUM>°F (-<NUM>). As a rough estimate, this means that if a mixture of air and R1233zd(E) in a tank held at -<NUM>°F (-<NUM>), the gas phase has greater than <NUM>% air and less than <NUM>% of R1233zd(E) and the liquid phase is pure R1233zd(E). To achieve the level of separation (i.e. vapor pressure differences and temperature lift), the state of the art designs require high cost systems.

<FIG> shows a vapor compression system <NUM>. The exemplary vapor compression system <NUM> is a chiller system. The system <NUM> includes a compressor <NUM> having a suction port (inlet) <NUM> fed by a suction line <NUM> and a discharge port (outlet) <NUM> feeding a discharge line <NUM>. The system further includes a first heat exchanger <NUM> having a refrigerant inlet connected to the discharge line. In a normal operating mode, the first heat exchanger <NUM> is a heat rejection heat exchanger (e.g., a condenser). In an exemplary system based upon an existing chiller, the heat exchanger <NUM> is a refrigerant-water heat exchanger in a condenser unit where the refrigerant is cooled and condensed by an external water flow <NUM> (inlet), <NUM>' (outlet).

The system further includes a second heat exchanger <NUM> (in the normal mode a heat absorption heat exchanger or evaporator) having a refrigerant outlet connected to the suction line. In the exemplary chiller system, the heat absorption exchanger <NUM> is a refrigerant-water heat exchanger for chilling a chilled water flow <NUM> (inlet), <NUM>' (outlet). An expansion device <NUM> is downstream of a refrigerant outlet of the heat rejection heat exchanger <NUM> and upstream of a refrigerant inlet of the heat absorption heat exchanger <NUM> along the normal mode main refrigerant flowpath <NUM> (the flowpath being partially surrounded by associated lines/piping, etc. and including the suction line <NUM>, discharge line <NUM>, and intermediate line <NUM>). The exemplary refrigerant-water heat exchangers <NUM> and <NUM> comprise tube bundles (not shown) carrying water flow and in heat exchange relation with refrigerant passing around the bundles within the shells or the tubes of the heat exchangers. The heat exchangers have water inlets <NUM>, <NUM> and outlets <NUM>, <NUM>.

An exemplary compressor is a centrifugal compressor having a housing assembly (housing) <NUM>. The housing assembly contains an electric motor <NUM> and one or more working elements (not shown; e.g., impeller(s) for a centrifugal compressor, scroll(s) for a scroll compressor, rotors for a screw compressor, or piston(s) for a reciprocating compressor) drivable by the electric motor in the first mode to draw fluid (refrigerant) in through the suction port, compress the fluid, and discharge the fluid from the discharge port.

The exemplary centrifugal working element(s) comprise a rotating impeller directly driven by the motor about an axis. Alternative centrifugal compressors may have a transmission coupling the motor to the impeller(s). Alternative drive systems include compressors having a drive shaft passing through a shaft seal to engage external drive means (e.g., electric or other motor).

<FIG> further shows a purge unit <NUM> for removing contaminant gases from the refrigerant. The exemplary purge unit comprises an inlet (inlet port) <NUM> for receiving refrigerant from the remainder of the system (e.g., diverted from the main/primary flowpath <NUM>) and a first outlet (outlet port) <NUM> for returning refrigerant to the remainder of the system (e.g., to the evaporator). For purposes of reference, the inlet port <NUM> is arbitrarily identified as the inlet port of an inlet valve <NUM> and the first outlet <NUM> (a liquid outlet or return outlet or port as is discussed below) is identified as the outlet port of an outlet valve <NUM>. A second outlet <NUM> may be a purge or vent outlet or port for discharging a flow <NUM> of contaminant gases. The second outlet <NUM> is arbitrarily identified as the outlet port of a second outlet valve <NUM>.

Other locations may be alternatively identified as the inlet or outlets. In the exemplary embodiment, the inlet <NUM> receives the refrigerant from the condenser along a line <NUM> extending along a flowpath <NUM> from a port <NUM>. The purge unit returns the refrigerant from the outlet <NUM> along a line <NUM> (e.g., along a flowpath <NUM> to a port <NUM> on the evaporator). As in a conventional purge unit, the refrigerant is returned from the outlet <NUM> directly to the main flowpath. As is discussed further below, the flowpath <NUM> branches off the main flowpath <NUM> and the flowpath <NUM> branches off the flowpath <NUM> so that a bypass flowpath includes the flowpaths <NUM> and <NUM>.

The purge unit <NUM> comprises a purge tank <NUM> having an inlet (inlet port) <NUM> positioned to receive refrigerant from the outlet of the valve <NUM>; a first outlet (outlet port) <NUM> (a liquid outlet port as discussed below) positioned to pass liquid along the flowpath <NUM>; and a second outlet (outlet port) <NUM> (a purge or vent port as discussed below) positioned to pass the flow <NUM> to the inlet of the valve <NUM>.

The inlet flow <NUM> contains refrigerant and contaminants. In the purge tank <NUM> (<FIG>), the inlet flow is cooled to condense out liquid <NUM> and leave a headspace <NUM> thereabove containing gas. The liquid is refrigerant with similarly condensable contaminants. The gas consists essentially (if not entirely) of other contaminants (e.g., air) which are not as easily condensed as the refrigerant.

A discharge (exhaust) flowpath <NUM> from the port <NUM> to the outlet <NUM> may pass along a discharge (exhaust) line <NUM> and through a pump (not shown) and one or more valves <NUM>. The valves serve to eliminate leaking of refrigerant to atmosphere. As does the flowpath <NUM>, the flowpath <NUM> branches off from the flowpath <NUM> which serves as a common trunk.

To condense refrigerant in the purge tank, means for cooling the inlet flow <NUM> in the purge tank <NUM> are provided. The exemplary means comprises solid state heat pumps (SSHP) (also known as thermoelectric cooling units or Peltier coolers). More particularly, the exemplary means comprises two stages of such SSHP units. A first stage of SSHP units <NUM> directly extracts heat from the refrigerant. A second stage of SSHP units <NUM> may further pass the heat extracted by the first stage to a cooling medium. One exemplary cooling medium is an external airflow <NUM> (e.g., ambient air of the external environment). An alternative cooling medium may be an external water flow. This water flow may be part of the same flow or a flow from the same source as the flow <NUM> used to cool the condenser. Depending on configuration, such flows may be either unforced flows or forced flows (via fan or pump depending on the state).

To increase the capacity and/or stabilize purge unit operation, a phase change material (PCM) <NUM> used. For example, the second stage of heat pumps may lack the capacity to extract/lift all the heat extracted by the first stage. Thus, the latent heat of melting of the PCM may be chosen to supplement any cooling available from the second stage during a cycle of the first stage. In the exemplary implementation, a phase change material is used to mitigate temperature at an interstage of the two solid state heat pump stages. An exemplary phase change material has a melting point (at standard or ambient pressure) in a range of -<NUM> to <NUM>, more particularly, -<NUM> to <NUM> or <NUM> to <NUM> or <NUM> to <NUM>. Exemplary phase change materials include paraffin waxes, fatty acids from natural oils, and inorganic salt solutions. The particular melting point of the PCM may be selected in view of the ambient temperature to which heat is rejected and the desired cooling temperature in the vessel for condensing refrigerant. In one example, the desired internal temperature of the unit condensing the refrigerant is -<NUM> and the ambient temperature is <NUM> for a temperature lift of <NUM>. In view of the available capacity of the first stage units, an SSHP melting point of approximately <NUM> or the broader values above may be selected.

In the <FIG> configuration, the phase change material <NUM> is contained in the space between an outer tank or vessel <NUM> and an inner tank or vessel <NUM> within the outer tank. Alternatively characterized, these may be regarded as two walls of a dual-wall tank or vessel <NUM>. The ports <NUM>, <NUM>, and <NUM> communicate with respective corresponding ports <NUM>, <NUM>, <NUM> of the inner tank (e.g., via having conduit segments passing through the space between the tanks). Thus, the liquid refrigerant accumulation <NUM> is in a lower portion/base of the inner tank <NUM> and the headspace <NUM> is a headspace of the inner tank <NUM>.

To facilitate heat transfer, the heat pumps of the two stages may be provided with heat transfer surfaces (e.g., fin arrays) at both sides of the solid state heat pump unit. In the exemplary implementation of generally cylindrical tanks (e.g., with one or two domed ends) each stage of solid state heat pumps comprises a plurality of heat pumps circumferentially and vertically arrayed. The <FIG> purge unit shows each stage as comprising four vertically arrayed circumferential rings of heat pumps with <FIG> showing each ring including twelve heat pumps. These counts are merely illustrative.

Each of the heat pump units has a first side <NUM>, <NUM> and a second side <NUM>, <NUM>. In normal operational modes of each stage of the units, the first side <NUM>, <NUM> is a cold side and the second side <NUM>, <NUM> is a hot side. Each of the units <NUM>, <NUM> is electrically connected to an electric power source <NUM> (<FIG>). The exemplary power source <NUM> is a DC power supply having terminals <NUM> and <NUM> coupled by wiring (not shown) to the units <NUM>, <NUM> in known fashion. If independent control is desired, this may be accomplished by switching (not shown) and/or by having multiple power supplies or multiple independently controllable sets of terminals from a given power supply. If certain alternative modes are desired, the heat flow direction may be reversed by reversing polarity to the units of the desired stage.

In the exemplary embodiment, the first sides <NUM> of the units <NUM> are in thermal communication with heat transfer fins <NUM> of a heat sink <NUM>. In the exemplary embodiment, there is a single circumferential array of heat transfer fins <NUM> secured radially along the inner surface of the sidewall of the inner tank <NUM>. Thus, thermal communication between the first sides <NUM> and the fins <NUM> is through the inner tank sidewall. Accordingly, exemplary material for the inner tank is thermally conductive such as an alloy. In the exemplary embodiment, the remaining sets of heat transfer fins are individually associated with the units <NUM> and <NUM>. Thus, the first side of each heat pump unit <NUM> is in thermal communication with a heat sink <NUM> having an array of fins <NUM>; the second side of each heat pump unit <NUM> is in thermal communication with a heat sink <NUM> having an array of fins <NUM>; and the second side <NUM> of each heat pump unit <NUM> is in thermal communication with a heat sink <NUM> having an array of fins <NUM>.

In the exemplary illustrated <FIG> configuration, an inlet tube <NUM> passes downward to an outlet near the bottom of the vessel to discharge the refrigerant-contaminant mixture. A purge outlet tube <NUM> (e.g., a beginning of the flowpath <NUM>) has an inlet in the headspace. As gas passes upward in heat exchange relation with the fins <NUM> of the heat exchanger <NUM>, it is cooled causing droplets of refrigerant to condense and fall to the refrigerant accumulation <NUM> or withdrawal/return to the main flowpath <NUM>. For ease of illustration, the tubes <NUM> and <NUM> are not shown in the remaining views.

In the exemplary embodiment, the first sides <NUM> of the heat pump units <NUM> are mounted to the exterior surface of the sidewall of the outer tank <NUM> and thermally communicate therethrough to the associated heat sink <NUM>.

Within the space between the vessels, the fins of the heat sinks <NUM> and <NUM> are interleaved with each other. In this exemplary example, the fins of each heat sink <NUM> are interleaved with the fins of exactly one other heat sink <NUM>. The exemplary interleaving leaves sufficient space between the fins to accommodate phase change material <NUM>.

Various other features (whether illustrated or not) may be as are used in conventional purge systems. These may include a variety of sensors, ports, pumps, and the like. For example, <FIG> further shows an optional filter/dryer unit <NUM> in the return line from the port <NUM> to the flowpath <NUM>. Among likely sensors would be a sensor such as a float switch for determining liquid level in the purge tank/vessel. <FIG> also shows an additional valve <NUM> upstream of the filter/dryer unit <NUM> to provide further flexibility in isolating system components (e.g., allowing closure of the valves <NUM> and <NUM> to isolate the filter/dryer unit for purposes such as replacement).

<FIG> further shows a controller <NUM>. The controller may receive user inputs from an input device (e.g., switches, keyboard, or the like) and sensors (not shown, e.g., pressure sensors and temperature sensors at various system locations). The controller may be coupled to the sensors and controllable system components (e.g., valves, the bearings, the compressor motor, vane actuators, and the like) via control lines (e.g., hardwired or wireless communication paths). The controller may include one or more: processors; memory (e.g., for storing program information for execution by the processor to perform the operational methods and for storing data used or generated by the program(s)); and hardware interface devices (e.g., ports) for interfacing with input/output devices and controllable system components.

The purge unit may be controlled by the controller <NUM> by methods similar to those already used in existing purge units. A main "on" or running mode may involve operating both stages of SSHP units <NUM>, <NUM> to respectively extract heat from the refrigerant and, in turn, pass that heat to the environment. More specifically, given the functioning of the PCM, the second stage of units <NUM> may extract only a portion of the heat initially and then later extract the remainder (e.g., in a recharge mode after the first stage is shut off). A variant "on" mode may operate only the first stage. This may represent an initial condition or a low load condition wherein the phase change material may absorb sufficient heat without use of the second stage. It might also be used where there is insufficient power to desirably operate the second stage. Similarly, the recharge mode could involve running only the second stage units to solidify the phase change material when extraction of heat from the refrigerant in the purge unit is not needed.

Further modes involve operating one or both stages or subgroups of units thereof with reversed polarity relative to the "on" modes. For example, this may be used to put heat into the vessel interior to heat the air or other contaminant to increase pressure and/or aid in its evacuation. For example, reverse polarity of the units <NUM> may put heat into the gas in the vessel and raise pressure. Simultaneously, this cools the PCM and may help in its resolidification. This may reduce or eliminate the need to use the second stage units <NUM> for recharging. Thus, a first such variation on a "purge" mode may involve running only the units <NUM>. A second variation that most speedily recharges might involve operating the units <NUM> with a reversed polarity while operating the units <NUM> with the normal "on" mode polarity. However, if such mode variations are not sufficient to provide the desired amount of heat to the gas, a third variation might involve running both stages reversed relative to the "on" mode so that the second stage of units <NUM> puts heat into the PCM for the first stage of units <NUM> to further transfer to the air. The controller may select amongst these mode variations based upon sensed and/or user-entered conditions.

Accordingly, an exemplary purge cycle may start with the inlet valve <NUM> closed, the second outlet valve <NUM> closed and one or both of the valves <NUM> and <NUM> closed (to block the liquid outlet and fully isolate the purged unit from the main flowpath <NUM>). When a purge cycle is needed (e.g., determined by similar logic used in current purge systems) the controller <NUM> may open the inlet valve <NUM> and initiate the appropriate "on" mode. This initiates cooling of refrigerant-contaminant mixture along portions of paths between the inlet and the purge and return ports (e.g., along an intersection of those paths). The controller <NUM> may then command closure of the inlet valve <NUM>. There may be a lag or lead of the valve closure and any termination of the "on" mode. However, at some point, after the closure of the valve <NUM>, the controller will open the valves <NUM> and <NUM> to pass liquid refrigerant along the flowpath <NUM> back to the main flowpath <NUM>. When sufficient refrigerant has been returned (e.g., as determined by the controller <NUM> responsive to level sensors or the like) the valves <NUM> and <NUM> may be re-closed by the controller in preparation for operation in the appropriate "purge" mode of the SSHP stages. The heat pump stages may be operated to heat the contaminant in the vessel and raise pressure of the headspace to a purging pressure. The exemplary pressure may be raised to an exemplary value in the range of <NUM>%-<NUM>% of the condensing pressure in an exemplary system without a pump. Alternative systems might use a pump along the flowpath <NUM> to evacuate air. Upon determining sufficient purge pressure, the controller may open the valve <NUM> to allow the air to purge. Thereafter (e.g., after pressure drops to a threshold value) the valve <NUM> may be closed. Any recharge may then complete in preparation for the next purge cycle.

As is discussed above, an exemplary water-cooled purge unit may have the flows <NUM> be forced or unforced water flows. In an exemplary forced flow situation, a further tank (not shown) surrounds the illustrated tanks and passes a water flow from a water inlet to a water outlet. The water flow <NUM> passes over the heat sinks <NUM> to absorb heat from the second stage units. Other heat exchanger and heat sink configurations are possible as are other configurations of SSHP units.

Among variations are purge systems (e.g., <NUM>, <FIG>) that further physically separate the SSHP stages (if two or more stages are used) and/or the PCM (if any). For example, the two exemplary stages may be at different locations along a heat transfer fluid loop (flowpath) <NUM>. An exemplary heat transfer fluid loop is a liquid loop and comprises at least <NUM>% by weight of one or more of water and glycol as a heat transfer fluid. A pump <NUM> may pump the fluid in recirculating fashion along the loop. A purge vessel <NUM> may be along the loop having an inlet port <NUM>, a return port <NUM>, and a purge port <NUM>. Refrigerant within the vessel may be in heat exchange relation with one side of SSHP unit(s) <NUM> of the first stage of two stages (or the only stage of a single-stage system). The heat transfer fluid loop may be in heat exchange relation with the other side of said SSHP units of the first stage.

For ease of illustration, the exemplary first stage units <NUM> are shown arrayed upstream-to-downstream between two side-by-side portions of a vessel or simply flat between two vessels. However, other configurations might involve concentric tanks as in the first embodiment.

At a remote location, heat may be extracted from the heat transfer fluid loop. An exemplary extraction may also be via SSHP units with a second stage of SSHP unit(s) <NUM> having one side in heat exchange relation with the heat exchange fluid loop and the other side in heat exchange relation (e.g., in heat exchanger vessel <NUM>) with a second flow or body of forced or unforced heat exchange fluid <NUM> acting as a thermal sink (e.g., ambient air of the environment or cooling water). As noted above for the first stage units <NUM>, the second stage units <NUM> may be arrayed in any of numerous possible configurations including a flat array between two side-by-side volumes or between spaces associated with two concentric vessels.

In addition to or independently of the presence of the second stage SSHP units, a PCM <NUM> may be located somewhere along the heat transfer fluid loop. An exemplary PCM may be located in a heat exchanger <NUM> in communication with the heat transfer fluid loop. This may be integrated with one of the SSHP stages or separate from both. An exemplary separate location is downstream of the first stage. An exemplary pump position is upstream of the first stage.

Further variations may involve using the PCM as the heat transfer fluid in a heat transfer fluid loop. For example, the heat exchanger <NUM> of <FIG> may be replaced by a vessel serving as a buffer for storing some of the PCM. In such a system, it may be desirable to avoid full solidification of the PCM in any location that would interfere with system operation. For example, it may be particularly desirable to avoid full solidification anywhere outside of the purge vessel <NUM>. However, for some purposes, it might also be desirable to avoid full solidification in the purge vessel <NUM>. Accordingly, the control system may monitor temperature (via appropriate sensors not shown) at various locations along the heat transfer fluid loop <NUM> to avoid such complete solidification. For example, the PCM state would either be pure liquid or a slurry at all locations along the loop <NUM>. If necessary, the thermoelectric units <NUM> or <NUM> could be used to add heat to avoid such full solidification. In such a loop <NUM>, the PCM may be one or more of the materials noted above. A mixture of several miscible PCM may have advantages in avoiding full solidification.

The purge system and its use may have one or more of several advantages relative to purge systems using vapor compression cycles. First, the thermoelectric purge system may provide a low cost purge system, particularly for low pressure/low GWP refrigerants. In addition to savings on the cooling hardware, there may be savings related to control. It may be easier to configure/program control hardware for the thermoelectric units to provide desired purge condensing conditions. This may entail simpler control hardware and/or fewer sensors, actuators, and the like. Second, it may provide enhanced adaptability (e.g., the same model of thermoelectric purge system or at least major components thereof may be used with vapor compression systems having different refrigerants or otherwise having different purge condensing requirements such as temperatures and capacities). Such adaptability or adjustability may be achieved by control of voltage to the thermoelectric units, by selection of PCM properties, or by control of other components of the purge unit if present. Third, the thermoelectric purge system may offer compactness or other packaging flexibility.

The use of "first", "second", and the like in the description and following claims is for differentiation within the claim only and does not necessarily indicate relative or absolute importance or temporal order. Similarly, the exemplary referenced directions merely establish a frame of reference and do not require any absolute orientation relative to a user. For example, the compressor front may well be at the rear of some larger system in which it is situated.

Claim 1:
A purge unit (<NUM>; <NUM>) comprising:
a vessel (<NUM>; <NUM>) having:
an inlet (<NUM>; <NUM>);
a return port (<NUM>; <NUM>), a first path between the inlet and the return port; and
a purge port (<NUM>; <NUM>), a second path between the inlet and the purge port; and
one or more thermoelectric units (<NUM>) positioned to be in thermal communication with at least the first path, characterised in that
one or more additional thermoelectric units (<NUM>) are positioned to transfer the heat absorbed by the one or more thermoelectric units (<NUM>); and in that
a phase change material (<NUM>) is positioned to receive heat absorbed by the one or more thermoelectric units from the first path.