HK1141860A1 - Enhanced refrigerant system - Google Patents

Abstract

A refrigerant system providing enhanced performance over a wider range of operating conditions than traditional economized refrigerant systems. The system includes an economizer branch that connects a liquid outlet from a suction accumulator to an economizer inlet port of a compressor unit. The economizer branch includes a liquid refrigerant pump that delivers a non-evaporated liquid refrigerant portion from the suction accumulator into the economizer heat exchanger, where the liquid refrigerant portion evaporates, increasing thermodynamic potential of the main circuit refrigerant also flowing in through the economizer heat exchanger, and a formed vapor stream is delivered into the economizer inlet port of the compressor unit.

Description

Enhanced refrigeration system

Technical Field

The present invention relates to refrigeration systems, and more particularly to refrigeration systems using an economizer (economizer) cycle.

Background

Refrigeration systems are used to control conditions, such as temperature and humidity, in a target space. Some refrigeration systems are configured as heat pumps that perform heating or cooling work on demand. The performance (capacity and/or efficiency) of the refrigeration system can be enhanced by using an economizer cycle. (see patent US6,385,981B1, US6,571,576B 1 and US 7,000,423B 2).

Summary of The Invention

In one aspect, the present invention provides an enhanced refrigeration system including a refrigerant closed-loop circuit including a compressor unit, a heat rejection unit, an economizer heat exchanger, an expansion device, an evaporator unit, and a suction accumulator. The suction accumulator includes an inlet, a vapor outlet, and a liquid outlet. The compressor unit includes a suction port, an economizer inlet port, and a discharge port.

The economizer line provides a path for refrigerant flow to flow between the liquid outlet of the suction accumulator and the economizer inlet port of the compressor unit. The economizer line includes a liquid refrigerant pump and an economizer heat exchanger.

The economizer heat exchanger provides a heat transfer interaction between the refrigerant flow flowing in the economizer line and the refrigerant flow flowing in the main refrigerant loop. The evaporator unit is constructed and operated in such a manner that at least a portion of the refrigerant leaving the evaporator unit is in the liquid phase.

The economizer line liquid refrigerant pump pumps liquid refrigerant, which is at least a portion of the refrigerant flow exiting the evaporator unit, through the economizer line and the economizer heat exchanger. At least a portion of the liquid refrigerant evaporates in the economizer heat exchanger and forms a vapor refrigerant flow in the economizer line that flows into the economizer inlet port of the compressor unit.

The evaporator unit is configured and operable to provide at least some unvaporized liquid refrigerant portion at an evaporator unit outlet. The liquid refrigerant pump delivers this non-evaporated liquid refrigerant portion to the economizer heat exchanger where it is at least partially evaporated and delivered into the economizer inlet port of the compressor unit.

If the enhanced refrigeration system is charged with and operates with subcritical fluid, the heat rejection unit is referred to as a condenser. If the enhanced refrigeration system is charged with and operates with a transcritical refrigerant, the heat rejection unit is referred to as a gas cooler.

The compressor unit, heat rejection unit, expansion device unit, evaporator unit, economizer heat exchanger unit, suction accumulator unit, and/or liquid refrigerant pump unit may all have multiple components, such as a compressor, heat rejection heat exchanger, expansion device, evaporator, suction accumulator, and liquid refrigerant pump, respectively, located within these units.

If the enhanced refrigeration system is used for cooling, the heat rejection unit is an outdoor unit and the evaporator unit is an indoor unit. If the enhanced refrigeration system is used for heating, the heat rejection unit is an indoor unit and the evaporator unit is an outdoor unit.

If the refrigeration system is used as a heat pump, i.e., it is used for heating and cooling, a four-way reversing valve is employed to redirect the refrigerant flow and switch between cooling and heating modes of operation. The four-way reversing valve has a steam inlet, a steam outlet, a first bi-directional flow port, and a second bi-directional flow port. The vapor inlet is connected to a discharge port of the compressor unit. The vapor outlet is connected to the vapor outlet of the suction accumulator. The first bidirectional flow port is connected to the outdoor unit and the second bidirectional flow port is connected to the indoor unit.

Some refrigeration systems may be combined into a single unit. For example, the compressor unit and the heat rejection unit may be assembled as one unit. Also, the expansion device may be combined with an evaporator unit. Further, the liquid refrigerant pump and the suction accumulator may be combined with each other.

The compressor unit may have two compressors, a low pressure compressor and a high pressure compressor, with the economizer inlet port positioned between the two compressors. Each compressor has at least one compression stage. Each compression stage may have a plurality of so-called tandem compressors in parallel. The low pressure compressor and the high pressure compressor may be manufactured and assembled as a single unit or as a single unit.

The economizer heat exchanger can have a counter-flow, co-flow, or cross-flow arrangement. It may also be replaced by a flash tank. The flash tank has a vapor inlet port, a vapor outlet port, and two liquid ports. It provides direct thermal contact between the refrigerant flow flowing in the main refrigerant loop and the refrigerant flow flowing in the economizer line. At least one of the two liquid ports has an expansion device positioned within the primary refrigerant loop upstream of the flash tank. The flash tank and at least one of the two liquid ports constitute a single unit.

If the refrigeration system uses a transcritical refrigerant, the economizer inlet port of the compressor unit may be combined with the discharge port of the compressor unit. In this case, the liquid refrigerant pump will work in parallel with the compressor unit.

The enhanced refrigeration system has the following advantages over conventional economized systems: 1) a portion of the total refrigerant mass flow rate is provided by a liquid pump, which requires substantially lower power input; 2) the total refrigerant mass flow circulating through the refrigeration system is delivered via the evaporator unit, enhancing the capacity of the evaporator; 3) in contrast to conventional systems, the higher the saved pressure, the better the capacity, compressor power, and coefficient of performance (COP); 4) as the ambient temperature decreases, the density of the liquid refrigerant at the pump inlet increases, which together with the pumping capacity compensates for the decrease in heating capacity and COP; and 5) as the ambient temperature increases, the saving pressure increases, thereby reducing the cooling capacity and the degree of COP decrease.

As a result, the enhanced refrigeration system provides enhanced heating and cooling capacity and increased heating and cooling COP over a wider range of operating conditions than conventional economized systems.

The system design results in an improved heating and cooling coefficient of performance (COP) and higher system capacity compared to conventional economized refrigeration systems. In particular, the proposed enhanced refrigeration system provides performance enhancement at lower ambient temperatures in the heating mode of operation and at higher temperatures in the cooling mode of operation.

Embodiments are described in the figures as described below; however, various other modifications and alternative constructions may be additionally made without departing from the true spirit and scope of the invention.

Drawings

The invention may be better understood with reference to the following drawings and claims. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. Within the drawings, like reference numerals are used to indicate like parts throughout the various views. Differences between similar parts may cause these parts to be denoted by different reference numerals. Dissimilar parts are denoted by different reference numerals.

FIG. 1 illustrates a conventional (prior art) refrigeration system including an economizer cycle;

FIG. 2 illustrates a conventional (prior art) heat pump including an economizer cycle;

FIG. 3 illustrates a conventional (prior art) refrigeration system;

FIG. 4 illustrates an enhanced refrigerant system according to the present invention;

FIG. 5 illustrates a pressure-enthalpy diagram of the enhanced refrigeration system;

FIG. 6 shows a graph of boiling point elevation;

FIG. 7A shows an enhanced refrigeration system including sequential multi-stage compression;

FIG. 7B shows an enhanced refrigeration system including parallel multi-stage compression;

FIG. 8A illustrates an enhanced refrigerant system operating with a transcritical refrigerant;

FIG. 8B shows an enhanced refrigerant system including a separate economizer port;

FIG. 8C illustrates an enhanced refrigeration system including a liquid receiver downstream of the condenser with respect to refrigerant flow;

FIG. 8D illustrates an enhanced refrigeration system including a liquid receiver positioned between a condenser and a subcooler;

FIG. 9 illustrates an enhanced heat pump;

fig. 10 shows an enhanced heat pump with a reversing flow arrangement through an economizer heat exchanger.

Fig. 11 shows an enhanced heat pump with a flash tank.

Detailed Description

Refrigeration systems generally comprise a closed-loop circuit of refrigerant with the following components connected in succession: a compressor, a heat rejection unit, an expansion device, an evaporator unit, and typically also a suction accumulator. The evaporator unit provides a heat transfer interaction between the evaporating refrigerant stream at a lower pressure and temperature and a secondary fluid delivered to the climate controlled space, with heat from the secondary fluid being rejected and transferred into the evaporating refrigerant stream. The heat rejection unit provides a heat transfer interaction between a compressed refrigerant stream at a higher pressure and temperature from which heat is rejected to a secondary fluid flowing into the environment and another secondary fluid.

When a conventional (subcritical) refrigerant is used in a refrigeration system, the heat rejection unit is referred to as a condenser. In the condenser, at least a portion of the heated and compressed refrigerant stream is liquefied from the vapor phase. When using transcritical refrigerants, the heat rejection unit is called a gas cooler (see international patent applications WO9007683 and WO 9306423). In the gas cooler, the compressed refrigerant at the higher pressure and temperature is maintained in the vapor phase.

Suction accumulators are often incorporated into refrigeration systems when the flow rate at which liquid refrigerant is delivered to an evaporation unit can cause a thermal load imbalance. The imbalance may result in liquid refrigerant at the evaporator outlet and compressor inlet, which may compromise compressor reliability. Furthermore, a suction accumulator may be applied when a large amount of oil-refrigerant mixture may intermittently accumulate at the evaporator outlet.

The heat pump is intended to start a heating operation or a cooling operation, also called a heating operation mode or a cooling operation mode. The heat pump is constituted by a closed refrigerant circuit having the following components connected in succession: the heat exchanger comprises a compressor, a four-way reversing valve, an outdoor heat exchange unit, an expansion device, an indoor heat exchange unit and a suction accumulator.

In the cooling mode, the four-way reversing valve directs refrigerant flow in such a manner that the outdoor heat exchanger unit functions as a heat rejection unit (as a condenser in subcritical applications or as a gas cooler in transcritical applications). The indoor heat exchanger unit serves as a heat receiving unit as an evaporator providing a cooling work.

In the heating mode, the outdoor heat exchanger unit serves as a heat receiving unit as an evaporator. The indoor unit serves as a heat rejection unit (again as a condenser in subcritical applications or as a gas cooler in transcritical applications), providing heating duty.

When the ambient temperature is lowered for the following reasons, the heating capacity and coefficient of performance (COP) of the heat pump are lowered. As the ambient temperature decreases, the suction pressure and vapor refrigerant density at the compressor suction decrease in response to the decrease in vapor refrigerant pressure due to the decrease in ambient temperature. However, the pressure ratio across the compressor (discharge pressure divided by suction pressure) increases. The increased pressure ratio can lead to a reduction in the volumetric efficiency of the compressor, and this fact, together with the reduced refrigerant density, causes a reduction in the refrigerant mass flow rate and capacity of the overall system. Furthermore, the increased pressure ratio causes the compressor to work harder and consumes more power in order to pump the refrigerant mass unit, causing the COP to drop.

As ambient temperatures increase, the cooling capacity and COP of the heat pump may decrease because the discharge pressure of the compressor, and the pressure ratio associated with the compressor, increases, causing the compressor to operate more difficultly and consume more power. The increased ambient temperature also affects the operation of the heat rejecting heat exchanger, thereby reducing the cooling thermal potential of the refrigerant entering the evaporator.

To limit the heating capacity and the extent of COP reduction, heat pumps employ economizer cycles (see patents US6,385,981B1, US6,571,576B 1 and US 7,000,423B 2). A heat pump with an economizer cycle typically includes a compressor having a suction port and an economizer inlet port, and is made up of a closed refrigerant loop having the following components connected in series: a compressor, a four-way reversing valve, an outdoor heat exchanger unit, an economizer heat exchanger, an expansion device, an indoor heat exchanger unit, and a suction accumulator. Heat pumps typically have a refrigerant circuit branch connecting the heat rejection unit outlet and the compressor economizer inlet port.

The economizer branch includes an economizer expansion device and an economizer heat exchanger. The economizer heat exchanger provides a heat transfer interaction between the refrigerant flow exiting the heat rejection unit and the vaporized refrigerant flow exiting the economizer expansion device expanded to some intermediate (between suction and discharge) pressure and temperature. In the heating mode of operation, this arrangement increases the mass flow rate through the heat rejection unit and enhances (increases) the heating capacity of the heat pump. Furthermore, the compressor power is increased and a sufficient heating COP can be maintained in a certain (but still slightly limited) operating state range.

In the cooling mode, the economizer cycle increases the cooling capacity, but the power required to operate the compressor is also increased, and as a result, the cooling COP generally does not change significantly (unless special configuration or design features are incorporated).

It must be noted that various economized heat pump designs are possible and well known in the art, which provide similar advantages. These design schematics may include heat pumps having an economizer expansion device positioned upstream or downstream with respect to refrigerant flow of the economizer heat exchanger, heat pumps having dual economizer heat exchangers, heat pumps having dual four-way reversing valves, and the like. All of these diagrams are within the scope and can equally benefit from the invention.

The present invention improves the heating and cooling capacity and heating and cooling COP of refrigeration systems such as those described above and provides an enhanced system that operates over a wider range of operating conditions than conventional economized systems.

Fig. 1 illustrates a conventional (prior art) refrigeration system 100 incorporating an economizer cycle. A conventional refrigeration system with an economizer cycle (fig. 1) employs a compressor unit 101 having an economizer inlet port 101 a. The refrigeration system is constituted by a closed refrigerant loop having the following components connected in succession: a compressor unit 101, a heat rejection unit 102, an economizer heat exchanger 103, an expansion device 104, an evaporator unit 105, and a suction accumulator 106. Further, the refrigeration system has an economizer branch 107 fluidly connected to the outlet of the heat rejection unit 102 and positioned downstream of the outlet of the heat rejection unit 102. The economizer branch 107 includes an economizer expansion device 108 and an economizer heat exchanger 103 and leads to an economizer inlet port 101a of the compressor unit 101.

If a subcritical refrigerant is used in the refrigeration system 100, the heat rejection unit 102 is a condenser. The economizer heat exchanger 103 provides a heat transfer interaction between the liquid refrigerant stream flowing in refrigerant line 103a and the vaporized refrigerant stream flowing in refrigerant line 103 b. The heat transfer interaction produces a subcooled refrigerant having a reduced enthalpy at the inlet to the expansion device 104 and an increased cooling thermal potential in the evaporator 105.

If a transcritical refrigerant is used in the refrigeration system 100, the heat rejection unit 102 is a gas cooler. It provides high pressure steam at its outlet at a temperature above but close to the ambient or cooling fluid temperature. In this case, the economizer heat exchanger 103 provides a heat transfer interaction between the vapor refrigerant flow in refrigerant line 103a and the evaporative refrigerant flow, typically in refrigerant line 103 b. The heat transfer interaction provides additional cooling to the vapor refrigerant stream in channel 103 a. It must be noted that the refrigerant thermodynamic state in the refrigerant line 103b after expansion in the economizer expansion device 108 can be supercritical. In this case, the refrigerant is only heated in the economizer heat exchanger 103 during the heat transfer interaction, rather than being vaporized as described above.

If the refrigeration system is used for heating, the heat rejection unit 102 delivers heat into the climate controlled environment and the refrigeration system efficiency in the heating mode of operation is calculated as the ratio of heat rejection capacity to total power input. If the refrigeration system is used for cooling, the evaporation unit 105 provides cooling (and typically also dehumidification) to the conditioned environment, and the system efficiency in the cooling mode of operation is calculated by the cooling COP as the ratio of cooling capacity to total power input. The total power includes the power input of all the operating electrical components, such as the compressor, fan, blower, and pump.

Let us assume that the refrigerant mass flow rate through the evaporator unit 105 is G_o. Thus, the compressor unit 101 receives a refrigerant flow G through its suction port_oAnd discharges equal to (G)_o+G_e) Increase (due to economizer refrigerant flow component G)_e) To the refrigerant flow of (a). Condenser capacity and compressor power are correspondingly increased. Moiety G_eUsually relatively small, but these increments are sufficient to heat the overall effect of the COP.

The refrigerant flow at the outlet of the refrigerant line 103a and at the inlet to the expansion device 104 has a lower enthalpy and therefore the economizer heat exchanger 103 increases the capacity of the evaporator. However, the compressor power also increases to a certain extent, and the overall effect on the cooling COP may not be sufficient.

The lower the economizer pressure, the higher the economizer heat exchanger, evaporator and condenser capacity. On the other hand, the compressor power is also higher. In addition, in fact, the higher the economizer pressure, the lower the economizer heat exchanger, evaporator and condenser capacity and compressor power. Since capacity and power are conflicting factors in the COP equation, the appropriate optimal economizer pressure can be selected based on trade-offs and sensitivity analysis.

Fig. 2 shows a conventional (prior art) heat pump 200 including an economizing cycle. The heat pump is constituted by a closed refrigerant circuit having the following components connected in succession: a compressor unit 101 having an economizer inlet port 101a, a four-way valve 209, an indoor heat exchanger unit 210 functioning as a condenser or as a gas cooler, an expansion device assembly 211, an economizer heat exchanger 103, an expansion device assembly 212, an outdoor heat exchanger unit 213 functioning as an evaporator unit, and a suction accumulator 106. The heat pump has an economizer branch 107 leading from the outlet of the indoor unit 210 through the economizer expansion device 108, the economizer heat exchanger 103 to the economizer inlet port 101a of the compressor unit 101.

The four-way reversing valve 209 has an inlet port 209a, an outlet port 209b, and two bi-directional flow ports 209c and 209 d.

In the heating mode of operation, the bi-directional flow port 209c is an inlet and the bi-directional flow port 209d is an outlet. The four-way valve 209 receives a flow of refrigerant vapor from the outdoor heat exchanger unit 213 (which functions as an evaporator) via the two-way flow port 209c, and directs it into the suction accumulator 106 via the discharge port 209 b. Compressor unit 101 receives this refrigerant vapor stream from suction accumulator 106, compresses it and discharges it via inlet port 209 a. The four-way reversing valve 209 directs the received compressed vapor to an indoor heat exchanger unit 210 (which again functions as a condenser or as a gas cooler) via a bi-directional flow port 209 d. In this case, the expansion device assembly 211 is not actuated; the expansion device of the expansion device assembly 212 expands the refrigerant stream to a lower pressure and temperature.

In the cooling mode of operation, the bi-directional flow port 209c is the outlet and the bi-directional flow port 209d is the inlet. The four-way reversing valve 209 receives a flow of refrigerant vapor from the indoor heat exchanger unit 210 (which now functions as an evaporator) via the bi-directional flow port 209d and directs it into the suction accumulator 106 via the discharge port 209 b. Compressor unit 101 again receives this refrigerant vapor stream from suction accumulator 106, compresses it and discharges it via inlet 209 a. The four-way reversing valve 209 directs the received compressed vapor to the outdoor heat exchanger unit 213 (which functions as a condenser or gas cooler in the cooling mode) via the bi-directional flow port 209 c. In this case, the expansion device assembly 212 is not actuated; the expansion device of the expansion device assembly 211 expands the refrigerant stream to a lower pressure and temperature. As is well known in the art, the expansion device assemblies 211 and 212 include an expansion device and a bypass line around the expansion device, with a check valve positioned on the bypass line and allowing refrigerant flow in only one direction.

As shown in fig. 2 above, the heat pump schematic is exemplary, and many variations and design choices are possible and within the scope of the invention. These options may include, but are not limited to, heat pumps with economizer expansion devices positioned upstream or downstream with respect to refrigerant flow of the economizer heat exchanger 103, heat pumps with dual economizer heat exchangers, heat pumps with dual four-way reversing valves, and the like. All of these diagrams can equally benefit from the invention.

Fig. 3 shows a conventional (prior art) refrigeration system 100 according to the present invention, while fig. 4 shows an enhanced refrigeration system 400 according to the present invention. Referring to fig. 3-4, in accordance with the present invention, an enhanced refrigeration system is comprised of a compressor unit 101, a heat rejection unit 102, a refrigerant line 103a of an economizing heat exchanger 103, an expansion device 104, an evaporator unit 105, and a suction accumulator 106. The economizer branch 107 connects a liquid outlet refrigerant line 315 from the suction accumulator 106 to the economizer inlet port 101a of the compressor unit 101. The economizer branch 107 includes a liquid refrigerant pump 314 and the refrigerant line 103b of the economizer heat exchanger 103.

The compressor unit 101, heat rejection unit 102, expansion device 104, evaporator unit 105, suction accumulator 106, and liquid refrigerant pump 314 may each include associated components such as a compressor, a heat rejection unit, an expansion device, an evaporator, a suction accumulator, and/or a liquid refrigerant pump. The enhanced refrigerant system may have different design choices and enhancement features.

The compressor 101 may be of the open-run type, the semi-hermetic type, or the hermetic type. It may also employ various compression techniques and include oil separators, drain switches, and/or temperature switches. Further, compressor unit 101 may be combined with heat rejection unit 102.

The heat rejection unit 102 may be cooled by air or by any other secondary fluid. The evaporator unit may also cool air or any other secondary fluid. The heat transfer to the secondary fluid may be of the free or forced convection type. Forced convection may be provided by a fan, blower or pump. The expansion device 104 may be part of an evaporator unit 105.

Each of the refrigerant lines 103a and the channels 103b may include a plurality of channels. The flow arrangement in the heat exchanger may be of the counter-flow, co-flow or cross-flow type and is defined by the particular application.

The liquid refrigerant pump 314 may be incorporated into a single unit having a suction accumulator. The pump itself may be of the open-run, semi-enclosed, or enclosed (canned) type, and various pumping techniques may be employed. Further, it may be positioned inside or outside the suction accumulator. Whether it is located inside or outside the suction accumulator, it is possible to attach the pump to the bottom, top or side wall of the suction accumulator.

The compressor unit 101 receives a refrigerant vapor stream at a suction pressure from a suction accumulator 106 and a refrigerant vapor stream from an economizer branch 107 via an economizer inlet 101a at an economizer pressure, which is higher than the suction pressure. The hot compressed vapor stream at the high discharge pressure is delivered to the heat rejection unit 102.

If a subcritical refrigerant is used in the refrigeration system 400, the heat rejection unit 102 is a condenser and the hot compressed vapor refrigerant stream is at least partially liquefied. On the other hand, if a transcritical refrigerant is used, the heat rejection unit 102 is a gas cooler and the hot compressed refrigerant vapor stream is cooled to a temperature near and above ambient or cooling fluid temperature.

Additional cooling is provided to the refrigerant flow at discharge pressure in refrigerant line 103a of the economizer heat exchanger 103 due to evaporation (or/and heating) of the liquid refrigerant flow pumped by the liquid refrigerant pump 314 from the suction accumulator 106 in refrigerant line 103 b. The refrigerant flowing through refrigerant line 103b is at a lower temperature and pressure than the refrigerant flowing through refrigerant line 103 a.

After expansion from discharge pressure to suction pressure in the expansion device 104, the liquid portion of the resulting two-phase refrigerant stream is evaporated in the evaporator unit 105. The evaporator unit 105 is sized, configured, and operated in a manner such that the liquid portion of the refrigerant does not completely evaporate as it flows through the evaporator unit. The unvaporized portion is delivered into the suction accumulator 106 and pumped by pump 314 through the economizer heat exchanger 103. In refrigerant line 103b of the economizer heat exchanger 103, the liquid stream is subjected to evaporation (or/and heating), receiving heat from the refrigerant stream flowing through refrigerant line 103 a. The vaporized (or/and heated) refrigerant is received through the economizer port 101a of the compressor unit 101.

A table comparing refrigerant mass flow rates of a conventional refrigeration system and an enhanced refrigeration system is shown below. The table has the following designations: g₁Represents the mass flow rate, G, at the location of the suction port to the compressor unit 101₂Indicating the mass flow rate at the discharge location of the compressor, G₃Representing the mass flow rate at the outlet position of the evaporator unit, and G₄Representing the mass flow rate at the economizer inlet port 101a location of the compressor unit 101.

G_oAnd G_eRespectively, represent individual mass flow rates that are not necessarily associated with a particular location within a conventional system or enhancement system. G_oRepresenting the mass flow rate for the evaporator line. G_eRepresenting the mass flow rate for the economized line.

For the evaporator line (G) based on the design of each respective refrigeration system_o) Is equal to the mass flow rate value at the outlet position of the evaporator unit of each respective system.

For conventional systems, the mass flow rate values at the evaporator unit outlet location and the compressor suction port are equal. This is not the case for enhanced systems. For the enhanced system, the mass flow rate at the compressor suction port has a value less than the mass flow rate at the evaporator unit outlet location.

The value of the mass flow rate at the discharge position of the compressor is indicated for conventional systems as (G)₂(conventional) ═ G_o+G_e) And for enhanced systems is denoted (G)₂(enhanced) G_o) Equal to the maximum mass flow rate value for each system.

GoIs the mass flow rate through the evaporator in the conventional cycle
	GoIs a traditionMass flow rate through economizer port in cycle

Referring to the relevant "evaporator" row (2) of the table, if we compare the same mass flow rate (G) at the outlet position of the evaporator unit₃(conventional) ═ G₃(enhanced) G_o) The mass flow rate pumped by the compressor unit of the enhancement system, e.g. by the mass flow rate at the location of its suction port (G)₁(boost)) appears to be less than the mass flow rate (G) at the compressor suction port for a conventional system₁(conventional)).

Specifically, for the enhanced system, the mass flow rate at the compressor suction port location is made equal to (G)_o-G_e) (G) of₁(enhanced)) representation. For a conventional system, the mass flow rate on the compressor suction port is equal to (G)₁(conventional) ═ G_o). Thus, the mass flow rate (G) pumped by the compressor of the enhanced system via its suction port₁＝(G_o-G_e) Less than the mass flow rate (G) pumped by the compressor of a conventional system via the suction port_o)。

For enhanced systems, the mass flow rate (G) pumped through the compressor suction port₁＝(G_o-G_e) Smaller than via the enhanced system (G)₃(enhanced) G_o) The mass flow rate (G) pumped by the evaporator outlet_o). This is not the case for conventional systems. For conventional systems, the mass flow rate (G) pumped through the suction port of the compressor₁(conventional)) is equal to the mass flow rate (G) pumped through the evaporator outlet of a conventional system₃(conventional) ═ G_o)。

For the enhanced system, the mass flow rate at the compressor discharge port location is made equal to (G)₁(enhanced) + G_e) And is equal to (G)_o) (G) of₂(enhanced)) which is less than (G) for the compressor discharge port of conventional systems₂(conventional) ═ G_o+G_e)). Thus, the mass flow rate pumped by the compressor of the enhanced system via its discharge port is less than the mass flow rate pumped by the compressor of the conventional system via the discharge port.

For both conventional and enhanced systems, equality of mass flow rates in the evaporation unit is related to equality of evaporator capacity. A decrease in the mass flow rate pumped through the compressor unit of the enhanced system indicates a decrease in the total amount of compressor power required by the enhanced system. Furthermore, pumping liquid refrigerant through a liquid pump requires much less power than compressing an equal mass of vapor, and as a result, the enhanced system produces an increased coefficient of cooling performance (COP).

Referring to row (2) of the associated compressor in the above table, for the enhanced system, G_eThe increased value results in increased cooling capacity. The advantage of the enhanced refrigerant system is a greater increase in G than is allowed by conventional economized systems_eAnd an opportunity to improve system performance.

If we compare the same mass flow rate (G) at the suction port position of the compressor unit₁(conventional) ═ G₁(boost) 1.0), the mass flow rate pumped by the compressor unit of the boosted system, e.g. by the mass flow rate at the discharge port (G) thereof₂(enhanced)) measured, appears to be greater than the mass flow rate (G) of the conventional system on the compressor discharge port₂(conventional)). Furthermore, at the outlet position of the evaporator unit, G₃(enhancement) appears to be greater than the mass flow rate G of the conventional unit at the evaporator unit outlet₃(conventional).

In particular, for the enhanced system, the mass flow rate at the compressor discharge port is set at G_o/(G_o-G_e) (G) of₂(enhanced)) representation. For a conventional system, the mass flow rate at the compressor discharge port location is equal to (G)₂(conventional) ═ G_o+G_e)/G_o＜G_o/(G_o-G_e)). Mass flow rate reduction at evaporator unit outletShows G₃(enhanced) G_o/(G_o-G_e)＜1＝G₃(conventional). Thus, the heat rejection unit 102 and the evaporator unit 105 of the enhanced system have a higher processing capacity than the same units of the conventional system.

The higher the economizer pressure in an enhanced system, the better the performance characteristics of the enhanced system, which is in stark contrast to conventional systems. This means that the enhanced system may require less power to pump refrigerant from the economizer inlet port to the outlet port than conventional systems. This means that the enhanced system will also have COP advantages in both cooling and heating modes of operation.

Equal mass flow rates at the compressor suction indicate that equivalent compressor applications in the enhanced economizer system and the conventional economizer system will be sufficient to support operation of each system. Another advantage of the enhanced refrigeration system is that higher economizer pressures result in higher system capacity and compressor power. As mentioned above, this is not the case for conventional systems.

Referring to row (2) of the relevant condensers in the above table, the comparison shows the same mass flow rate (G) at the discharge location of the compressor unit₂(conventional) ═ G₂(boost) 1.0) (which means equal condenser heat rejection capacity), the mass flow rate pumped by the compressor unit of the boost system, e.g., the mass flow rate at its suction port location (G)₁(boost)) measured, appears to be less than the mass flow rate (G) on the compressor suction port of a conventional system₁(conventional)). At the outlet position of the evaporator unit, G₃(enhancement) appears to be greater than the mass flow rate G at the evaporator unit outlet of a conventional unit₃(conventional).

The above-described advantages provided by the enhanced system allow for a lower discharge-to-economizer pressure ratio that may be associated with increased refrigerant mass flow rate. As a result, mass flow rate (G) for the same economizer₄(enhanced) G₄(conventional) ═ G_e) The boost system has lower required compressor power and increased heatingThe COP. Enhanced system design provides for incorporation of large economizer mass flow rates (G)_e) To improve the performance characteristics of the enhanced refrigeration system to a greater extent than previously described.

Figure 5 illustrates a pressure-enthalpy diagram for the enhanced refrigeration system 500. The pressure-enthalpy diagram 500 demonstrates the following thermodynamic process with respect to a saturation line separating a subcritical refrigerant and a transcritical refrigerant: 501-502 is a compression process from suction pressure to economizer pressure; 502-502B is the mixing process of the vapor fraction arriving via the suction port and the vapor fraction arriving via the economizer inlet port (thermodynamic point of state 510); 502B-503 are compression processes from economizer pressure to discharge pressure; 503-504 is cooling in a gas cooler or condensation in a condenser; 504-504' is an additional cooling process in the conventional economized cycle; 504-505 are additional cooling or subcooling processes in the enhanced refrigeration system; 504 '-504' A and 505-506 are isenthalpic expansion processes in the conventional cycle and the enhanced cycle, respectively; 504' A-501 and 506-507 are evaporation processes in the conventional cycle and the enhanced cycle, respectively; 508-509 is the process of pumping liquid refrigerant in an enhanced cycle; 509-510 is the evaporation process of the economizer branch refrigerant flow.

The thermodynamic state 509 associated with the refrigerant flowing through the economizer branch 107 of the enhanced refrigeration system is at the inlet to the economizer heat exchanger 103. The thermodynamic state 504B associated with the refrigerant flowing through the economizer branch 107 is at the inlet of the economizer heat exchanger of a conventional economizer system. The condition 510 associated with refrigerant flowing through the economizer branch 107 of the enhanced refrigeration system is at the outlet of refrigerant line 103b of the economizer heat exchanger 103. The difference in refrigerant enthalpy in the thermodynamic states 510 and 509 is the heat transfer rate in the economizer heat exchanger between the economizer branch and the main refrigerant circuit of the enhanced system. The difference in refrigerant enthalpy in the thermodynamic state 510 and the state 504B is the heat transfer rate in the economizer heat exchanger between the economizer branch and the main refrigerant circuit in a conventional system. It is apparent that the enhanced cycle has a higher cooling effect potential in the economizer heat exchanger because the refrigerant enthalpy in thermodynamic state 509 is lower than the refrigerant enthalpy in thermodynamic state 504B.

The graph shows that for the enhanced system, the higher the economizer pressure, the higher the heat transfer rate in the economizer heat exchanger. On the other hand, the higher the heat transfer rate, the higher the cooling and heating capacity. Further, the higher the economizer pressure, the lower the compressor power. Thus, as already mentioned during the discussion of fig. 3 and 4, the higher the economizer pressure, the better the performance characteristics of the enhanced system.

The higher the discharge pressure, the more likely it is to increase economizer pressure and improve performance of the intensifier system relative to conventional systems.

The chart of fig. 5 is exemplary and includes an isobaric process for all components except the compressor, pump, and expansion device. However, as the pressure drops, all discharge pressure conditions downstream of the compressor gradually decrease, all suction pressure conditions upstream at the compressor suction gradually increase, and all economizer pressure conditions upstream at the pump discharge gradually increase.

Enhancing system performance by pumping liquid refrigerant from the suction accumulator includes two unique features: 1) when the ambient temperature decreases, the refrigerant density at the pump inlet increases along with the pumping capacity in the heating mode of operation; 2) as the ambient temperature increases, the economizer pressure and heat transfer rate in the economizer heat exchanger also increase in the cooling mode of operation. The fact that the vapor density at the compressor suction decreases as the ambient temperature decreases is in direct contrast to the first feature, thereby reducing the heating capacity and COP of conventional economizer systems. The second feature reduces the negative impact on the performance characteristics of the enhanced refrigerant system at elevated ambient temperatures.

Fig. 6 is a graph 600 of boiling point rise to reduce the risk associated with cavitation that may occur in a liquid refrigerant pump. As shown in fig. 6, X_oilIs the mass concentration of oil, X_refThe refrigerant properties at the expansion device inlet, evaporator inlet, and evaporator outlet. As the liquid refrigerant boils, the mass concentration of oil in the remaining liquid portion of the refrigerant increases along with the boiling point of the oil-refrigerant mixture. The difference between the boiling point of the oil-refrigerant mixture and the evaporation temperature of the pure refrigerant is called boiling point rise. The higher the oil concentration, the greater the boiling point increase. The boiling point increase serves to subcool and protect the pump from cavitation that may affect the reliability of the liquid pump.

FIG. 6 shows a boiling point increase plot 600; if we have 2% oil carry over in the compressor unit and the refrigerant property on the evaporator inlet is 0.2, then the vapor property at the evaporator outlet is 0.95 and we will have 40% oil in the oil-refrigerant mixture in the suction accumulator 106 and hence at the inlet of the liquid pump 314. This provides a sufficient boiling point rise to avoid cavitation.

Fig. 7A shows an enhanced refrigerant system 700 including sequential multi-stage compression. The compressor unit 101 shown in fig. 7A is a multi-stage compression device, which is composed of a low-pressure compressor 719 and a high-pressure compressor 720. Each of these compressors has at least one compression stage. Each compression stage may have a plurality of compressors in parallel (or so-called tandem). An economizer inlet port 101a is positioned between these compressors 719 and 720. Fig. 7A shows compressor unit 101 as a single unit, however, low pressure compressor 719 and high pressure compressor 720 may represent separate compressor units.

Fig. 7B shows an enhanced refrigeration system 710 including parallel multi-stage compression. The compressor unit 101 shown in fig. 7B is composed of two parallel compressors: a high pressure ratio compressor 719 and a low pressure ratio compressor 720. A high pressure ratio compressor is associated with and operates between the suction port and the discharge port. A low pressure ratio compressor is associated with and operates between the economizer inlet port 101a and the discharge port. Each of these compressors has at least one compression stage. Furthermore, each compression stage may have a plurality of compressors in parallel. Fig. 7B shows compressor unit 101 as a single unit, however, high pressure ratio compressor 719 and low pressure ratio compressor 720 may be configured as separate compressor units. The compressors 719 and 720 in fig. 7A and 7B may be equipped with oil separators to recover oil to enable better lubrication of the moving parts of these compressors.

Fig. 8A shows an enhanced refrigeration system 800 charged with and operating with a transcritical refrigerant. The arrangement of fig. 8A is only suitable for systems operating with transcritical refrigerants. This arrangement means that the economizer inlet port 101a is combined with the discharge port 101b of the compressor unit 101. The liquid refrigerant flow from the suction accumulator 106 pumped by the liquid refrigerant pump 314 is fully evaporated in refrigerant line 103b of the economizer heat exchanger 103. Which is then mixed with the hot refrigerant vapor discharged from compressor unit 101. Thus, the flow of liquid refrigerant from the suction accumulator 106 is pumped in parallel with the refrigerant of the compressor 101.

The economizer inlet port 101a can be physically associated with the discharge port 101b, or the economizer branch 107 can be connected to the discharge line 101c downstream of the discharge port 101 b. Further, an economizer inlet port 101a may be combined with the inlet side 102a of the heat rejection unit 102.

The use of conventional subcritical refrigerants in such systems requires that the vapor temperature at the outlet of refrigerant line 103b of economizer heat exchanger 103 be below the condensing temperature in order to take advantage of the latent heat of the liquid refrigerant stream in refrigerant line 103b of economizer heat exchanger 103. This is not feasible and conventional subcritical refrigerants are not suitable for this system arrangement.

Fig. 8B shows an enhanced refrigerant system 810 including a split economizer port 812. Fig. 8C illustrates an enhanced refrigeration system 820 including a liquid receiver 821 positioned downstream of heat rejection unit 102 with respect to refrigerant flow. Fig. 8D illustrates an enhanced refrigeration system 830 that includes a liquid receiver 821 positioned between condenser 102a and subcooler 102 b.

The arrangement in fig. 8B may be applicable to both subcritical refrigerants and transcritical refrigerants. This arrangement means that the economizer inlet port 101a is positioned between the outlet of the heat rejection unit 102 and the inlet to the economizer heat exchanger 103. The liquid refrigerant flow from the suction accumulator 106 pumped by the liquid refrigerant pump 314 is heated in refrigerant line 103b of the economizer heat exchanger 103. Which is then mixed with the refrigerant flow leaving the heat rejection unit 102. The economizer port 101a can be manufactured as a separate device. Further, it may be incorporated into the heat rejection unit 102 or the economizer heat exchanger 103. However, this arrangement has the disadvantage that it does not utilise any latent heat of the economizer flow.

If a conventional subcritical refrigerant is used, a liquid refrigerant receiver 821 may be installed at the outlet of the condenser 102 as shown on fig. 8C. Furthermore, the condenser may be divided into two parts: such as condensing portion 102a and subcooling portion 102b shown on fig. 8D. In this case, the receiver 821 is installed between these portions. If the receiver 821 is employed in the arrangement shown in FIG. 7B, the economizing port 101a may be incorporated into the receiver.

In some embodiments, the compressor is a variable speed compressor. In some embodiments, the compressor is a multi-speed compressor. In some embodiments, the liquid refrigerant pump is a variable speed pump. In some embodiments, the refrigerant pump is a multi-speed pump.

Fig. 9 shows an enhanced heat pump 900. The heat pump is constituted by a closed refrigerant circuit comprising the following components connected in succession: a compressor unit 101 having an economizer inlet port 101a, a four-way reversing valve 209, an indoor heat exchanger unit 210 that functions as a condenser or as a gas cooler, an expansion device 211, an economizer heat exchanger 103, an expansion device 212, an outdoor heat exchanger unit 213 that functions as an evaporator, and a suction accumulator 106. The heat pump has an economizer branch 107 which begins with a suction accumulator 106, passes through a refrigerant line 103b of the economizer heat exchanger 103, and to an economizer inlet port 101a leading to the compressor unit 101.

In the heating mode, the four-way reversing valve 209 enables the outdoor heat exchanger unit 213 to operate as an evaporator and the indoor heat exchanger unit 210 to operate as a condenser or as a gas cooler. Economizer heat exchanger 103 functions as a counter-flow heat exchanger.

In the cooling mode, the four-way selector valve 209 enables the indoor heat exchanger unit 210 to operate as an evaporator and the outdoor heat exchanger unit 213 to operate as a condenser or a gas cooler. Economizer heat exchanger 103 functions as a parallel flow heat exchanger.

Fig. 10 shows an enhanced heat pump 1000 with a return arrangement in an economizer heat exchanger. If the counter-flow arrangement is more efficient for the cooling mode of operation than for the heating mode of operation, the economizer branch 107 is connected to the refrigerant lines 103a and 103b of the economizer heat exchanger 103 as shown in fig. 10. Furthermore, it may be appropriate to have a cross-flow arrangement in the economizer heat exchanger 103 to balance the requirements in the heating and cooling modes of operation.

Fig. 11 shows an enhanced heat pump 1100 with a flash tank. The economizer heat exchanger 103 can be replaced with a flash tank 1116 in fig. 11. The flash tank 1116 is a heat exchanger device that provides direct thermal contact between the refrigerant flow in the economizer branch 107 and the refrigerant flow in the main refrigerant circuit.

The flash tank 1116 is composed of an inlet port 1116a, an outlet port 1116b, and two bi-directional flow ports 1116c and 1116 d. The inlet port 1116a of the economizing branch 107 is fluidly associated with the liquid refrigerant pump 314. The discharge port 1116b of the economizer branch 107 is connected to the economizer inlet port 101a of the compressor 101. The bi-directional flow port 1116c and the indoor heat exchanger unit 210 are connected via the expansion device 1117; the bi-directional flow port 1116d is connected to the outdoor heat exchanger unit 213 via an expansion device 1118.

In the heating mode, the flash tank 1116 is supplied with a flow of liquid refrigerant from the indoor heat exchanger unit 210 via the expansion device 1117 and the two-way flow liquid port 1116 c. The outdoor heat exchanger unit 213 is supplied from the flash tank 1116 via a two-way flow liquid port 1116d and an expansion device 1118.

In the cooling mode, the flash tank 1116 is supplied with a flow of liquid refrigerant from the outdoor heat exchanger unit 213 via the expansion device 1118 and the two-way flow liquid port 1116 d. The indoor heat exchanger unit 210 is supplied from the flash tank 1116 via a bidirectional flow liquid port 1116c and an expansion device 1117.

If the system is designed to operate in only one mode, either heating or cooling, the ports associated with expansion devices 1117 and 1118 would not be designed for bi-directional flow operation and a four-way reversing valve would not be required.

When applicable, the design choices for fig. 7A, 7B, 8A, 8B, and 8C may be applicable to fig. 9-11. Furthermore, the design choices for fig. 9-11 may apply to fig. 7A, 7B, 8A, 8B, 8C, and 8D.

Thus, the enhanced refrigeration system includes the following advantages over conventional economized systems: 1) a portion of the total mass flow is pumped via the liquid refrigerant pump 314, which requires a significantly lower power input; 2) the total mass flow is pumped through the evaporator unit, thereby increasing the evaporator capacity; 3) the higher the saving pressure, the better the cooling and heating capacity, the compressor power and the COP; 4) as the ambient temperature decreases, the liquid refrigerant density at the pump inlet increases along with the pumping capacity, which prevents a decrease in heating capacity and COP; and 5) as the ambient temperature increases, the economizer pressure increases, thereby reducing the cooling capacity and the degree of COP degradation.

As a result, the enhanced refrigeration system provides enhanced heating and cooling capacity and heating and cooling COPs, and enhanced performance over a wider range of operating conditions than conventional economized systems are designed.

Although some embodiments of the present invention have been disclosed in detail, it should be understood that various modifications to its structure may be employed without departing from the spirit of the invention or the scope of the following claims.

Claims (38)

1. An enhanced refrigerant system comprising:

a refrigerant closed-loop circuit including a compressor unit, a heat rejection unit, an economizer heat exchanger, an expansion device, an evaporator unit, and a suction accumulator, the suction accumulator including an inlet, a vapor outlet, and a liquid outlet, the compressor unit including a suction port, an economizer inlet port, and a discharge port;

an economizer branch providing a passage for refrigerant flow to flow between the liquid outlet of the suction accumulator and the economizer inlet port of the compressor unit, the economizer branch including a liquid refrigerant pump and an economizer heat exchanger;

the economizer heat exchanger providing a heat transfer interaction between the refrigerant flow in the economizer branch and the refrigerant flow in the refrigerant closed-loop circuit;

the evaporator unit is configured and operated to provide refrigerant at an outlet thereof such that at least a portion of the refrigerant is in a liquid or non-evaporated phase; and

wherein the liquid refrigerant pump of the economizer branch pumps the liquid refrigerant from the evaporator unit outlet via the economizer branch and the economizer heat exchanger, and wherein at least a portion of the liquid refrigerant evaporates and forms a vapor refrigerant flow in the economizer branch that flows into the economizer inlet port of the compressor unit.

2. An enhanced refrigerant system as recited in claim 1 wherein said enhanced refrigerant system operates in a subcritical cycle and said heat rejection unit functions as a condenser.

3. An enhanced refrigerant system as recited in claim 1 wherein said enhanced refrigerant system operates in a transcritical cycle and said heat rejection unit functions as a gas cooler.

4. An enhanced refrigerant system of claim 1 comprising at least one of:

(a) the heat rejection unit comprises a plurality of individual heat rejection units;

(b) the expansion device comprises a plurality of individual expansion devices;

(c) the evaporator unit comprises a plurality of individual evaporators;

(d) the suction accumulator comprises a plurality of individual suction accumulators;

(e) the liquid refrigerant pump comprises a plurality of individual pumps; and

(f) the economizer heat exchanger comprises a plurality of individual heat exchangers.

5. An enhanced refrigerant system of claim 1 wherein said economizer heat exchanger comprises a plurality of passages.

6. An enhanced refrigerant system of claim 1 wherein said heat rejection unit is an outdoor unit and said evaporator unit is an indoor unit.

7. An enhanced refrigerant system of claim 1 wherein said heat rejection unit is an indoor unit and said evaporator unit is an outdoor unit.

8. An enhanced refrigerant system of claim 6 wherein said refrigerant closed loop circuit includes a four-way reversing valve including a vapor inlet port, a vapor outlet port, a first bi-directional flow port, and a second bi-directional flow port, said vapor inlet port of said four-way reversing valve being connected to said discharge port of said compressor unit, said vapor outlet port of said four-way reversing valve being connected to said suction accumulator, said first bi-directional flow port being connected to said refrigerant closed loop circuit at a location upstream of said outdoor unit, and said second bi-directional flow port being connected to said refrigerant closed loop circuit at a location downstream of said indoor unit.

9. An enhanced refrigerant system of claim 1 wherein said compressor unit and said heat rejection unit are combined into a single unit assembly.

10. An enhanced refrigerant system of claim 1 wherein said expansion device is integrated with said evaporator unit.

11. An enhanced refrigerant system of claim 1 wherein said liquid refrigerant pump and said suction accumulator are combined into a single unit assembly.

12. An enhanced refrigerant system of claim 1 wherein said compressor unit includes a low pressure compressor, a high pressure compressor, and said economizer inlet port positioned between said low pressure compressor and said high pressure compressor; each of the compressors includes at least one compression stage.

13. An enhanced refrigerant system of claim 12 wherein at least one of said at least one compression stage comprises a plurality of compressors in parallel.

14. An enhanced refrigerant system of claim 12 wherein said low pressure compressor and said high pressure compressor are separate compressor units.

15. An enhanced refrigerant system of claim 1 wherein said compressor unit comprises two compressors in parallel, a first compressor providing a refrigerant passage between said economizer inlet port and said discharge port and a second compressor providing a refrigerant passage between said suction port and said discharge port; each of the compressors includes at least one compression stage.

16. An enhanced refrigerant system of claim 15 wherein said first compressor comprises a plurality of compressors in parallel.

17. An enhanced refrigerant system of claim 15 wherein said second compressor comprises a plurality of compressors in parallel.

18. An enhanced refrigerant system of claim 15 wherein said first compressor and said second compressor are separate compressor units.

19. An enhanced refrigerant system of claim 1 wherein said economizer heat exchanger is a counter-flow heat exchanger in the main mode of operation.

20. An enhanced refrigerant system of claim 1 wherein said economizer heat exchanger is a parallel flow heat exchanger in the main mode of operation.

21. An enhanced refrigerant system of claim 1 wherein said economizer heat exchanger is a cross-flow heat exchanger.

22. An enhanced refrigerant system of claim 1 wherein said economizer heat exchanger is a flash tank having a vapor inlet port, a vapor discharge port, and two liquid ports and providing direct thermal contact between refrigerant flow in said refrigerant closed loop circuit and refrigerant flow in said economizer branch.

23. An enhanced refrigerant system of claim 22 wherein at least one of said two liquid ports has an expansion device for said closed refrigerant loop upstream of said flash tank.

24. An enhanced refrigerant system of claim 23 wherein said flash tank and at least one of said two liquid ports are combined into a single unit.

25. An enhanced refrigerant system of claim 1 wherein said enhanced refrigerant system operates in a transcritical cycle and said economizer inlet port of said compressor unit is integrated with said discharge port of said compressor unit.

26. An enhanced refrigerant system of claim 1 wherein the enhanced refrigerant system operates in a transcritical condition and the economizer inlet port of the compressor unit is a separate device positioned downstream of the heat rejection unit and upstream of the economizer heat exchanger.

27. An enhanced refrigerant system of claim 1 wherein said compressor is a variable speed compressor.

28. An enhanced refrigerant system of claim 1 wherein said compressor is a multi-speed compressor.

29. An enhanced refrigerant system of claim 1 wherein said liquid refrigerant pump is a variable speed pump.

30. An enhanced refrigerant system as recited in claim 1 wherein said liquid refrigerant pump is a multi-speed pump.

31. An enhanced refrigerant system of claim 2 wherein a liquid refrigerant receiver is installed at a location downstream of said heat rejection unit.

32. An enhanced refrigerant system of claim 11 wherein said liquid refrigerant pump is positioned below said suction accumulator.

33. An enhanced refrigerant system of claim 11 wherein said liquid refrigerant pump is positioned above said suction accumulator.

34. An enhanced refrigerant system of claim 11 wherein said liquid refrigerant pump is positioned within said suction accumulator.

35. An enhanced refrigerant system of claim 8 wherein said compressor unit, said four-way reversing valve, and said heat rejection unit are combined into a single unit.

36. An enhanced refrigerant system as recited in claim 1 wherein said compressor unit is equipped with an oil separator to return oil to said compressor.

37. An enhanced refrigerant system of claim 1 wherein said heat rejection unit is a mini-channel heat exchanger.

38. An enhanced refrigerant system of claim 1 wherein said evaporator unit is a mini-channel heat exchanger.