Patent Description:
Refrigerant vapor compression systems are commonly used in transport refrigeration systems for refrigerating air supplied to a temperature controlled cargo space of a truck, trailer, container or the like for transporting perishable/frozen items by truck, rail, ship or intermodally.

Traditionally, most of these refrigerant vapor compression systems operate at subcritical refrigerant pressures. However, in recent years greater interest is being shown in "natural" refrigerants, such as carbon dioxide, for use in refrigeration systems instead of HFC refrigerants. Because carbon dioxide has a low critical temperature, most refrigerant vapor compression systems charged with carbon dioxide as the refrigerant are designed for operation in the transcritical pressure regime.

A typical refrigerant vapor compression system includes compression device, a refrigerant heat rejection heat exchanger (functions as a condenser for subcritical operation and as a gas cooler for supercritical operation), a refrigerant heat absorption heat exchanger (functions as an evaporator), and an expansion device disposed upstream, with respect to refrigerant flow, of the refrigerant heat absorption heat exchanger and downstream of the refrigerant heat rejection heat exchanger. <CIT> disclosing a refrigerant vapor compression system according to the preamble of independent claim <NUM> discloses a heat pump system capable of improving cycle efficiency in the processing of the heat load performed by a secondary refrigerant. A heat pump circuit through which carbon dioxide refrigerant is circulating has a low-stage-side compression mechanism, a high-stage-side compression mechanism, an expansion mechanism, and an evaporator. An air-warming circuit through which water as a secondary refrigerant circulates has a radiator. The air-warming circuit through which water as an air-warming heat medium circulates has an intermediate-pressure-side branching channel and a high-pressure-side branching channel which are parallel to each other.

A refrigerant vapor compression system according to the present invention is provided by independent claim <NUM>. The refrigerant vapor compression system includes a compression device having at least a first compression stage and a second compression stage arranged in series refrigerant flow relationship. A first refrigerant heat rejection heat exchanger is disposed downstream with respect to refrigerant flow of the second compression stage for passing the refrigerant in heat exchange relationship with a flow of a first secondary fluid. A first refrigerant intercooler is disposed intermediate the first compression stage and the second compression stage for passing the refrigerant passing from the first compression stage to the second compression stage in heat exchange relationship with the flow of the first secondary fluid. An economizer circuit includes a vapor line in fluid communication with a suction inlet to the second compression stage. A second refrigerant heat rejection heat exchanger is disposed intermediate with respect to refrigerant flow of the second compression stage and the first refrigerant heat rejection heat exchanger. A second refrigerant intercooler is disposed intermediate the first compression stage and the second compression stage for passing the refrigerant from the first compression stage to the second compression stage in heat exchange relationship with a second secondary fluid, characterized in that: the first refrigerant intercooler is disposed downstream of the first refrigerant heat rejection heat exchanger with respect to the flow of the first secondary fluid; and the second refrigerant intercooler is disposed downstream with respect to refrigerant flow of the vapor line.

Optionally, the first refrigerant heat rejection heat exchanger includes a round tube plat fin heat exchanger or a louver fin mini-channel flat tube heat exchanger.

Optionally, the first refrigerant intercooler includes a round tube plat fin heat exchanger or a louver fin mini-channel flat tube heat exchanger.

Optionally, the second refrigerant heat rejection heat exchanger includes a brazed plate heat exchanger, a tube-on-tube heat exchanger or a tube-in-tube heat exchanger.

Optionally, the second refrigerant intercooler includes a tube-on-tube heat exchanger or a tube-in-tube heat exchanger.

Optionally, the first secondary fluid includes air and the second secondary fluid includes a brine.

Optionally, a pump is operatively associated with the second refrigerant heat rejection heat exchanger and with the second refrigerant intercooler for moving a flow of the second secondary fluid first through the second refrigerant heat rejection heat exchanger and thence through the second refrigerant intercooler.

Optionally, the economizer circuit includes a flash tank economizer disposed between the first refrigerant heat rejection heat exchanger and a heat absorption heat exchanger.

Optionally, at least one fan is operatively associated with the first refrigerant heat rejection heat exchanger and with the first refrigerant intercooler for moving a flow of air first through the first refrigerant heat rejection heat exchanger and thence through the first refrigerant intercooler.

<FIG> illustrates an example refrigerated container <NUM> having a temperature controlled cargo space <NUM> the atmosphere of which is refrigerated by operation of a refrigeration unit <NUM> associated with the cargo space <NUM>. In the depicted example of the refrigerated container <NUM>, the refrigeration unit <NUM> is mounted in a wall of the refrigerated container <NUM>, typically in the front wall <NUM> in conventional practice. However, the refrigeration unit <NUM> may be mounted in the roof, floor or other walls of the refrigerated container <NUM>. Additionally, the refrigerated container <NUM> has at least one access door <NUM> through which perishable goods, such as, for example, fresh or frozen food products, may be loaded into and removed from the cargo space <NUM> of the refrigerated container <NUM>.

<FIG> schematically illustrate various example refrigerant vapor compression systems <NUM>-<NUM> through <NUM>-<NUM> suitable for use in the refrigeration unit <NUM> for refrigerating air drawn from and supplied back to the temperature controlled cargo space <NUM>. The refrigerant vapor compression systems <NUM>-<NUM> through <NUM>-<NUM> operate in either an air-cooled mode or a water/brine-cooled mode as discussed further below. Although the refrigerant vapor compression systems <NUM>-<NUM> through <NUM>-<NUM> will be described herein in connection with a refrigerated container <NUM> of the type commonly used for transporting perishable goods by ship, by rail, by land or intermodally, it is to be understood that the refrigerant vapor compression systems <NUM>-<NUM> through <NUM>-<NUM> may also be used in refrigeration units for refrigerating the cargo space of a truck, a trailer or the like for transporting perishable goods. The refrigerant vapor compression systems <NUM>-<NUM> through <NUM>-<NUM> are also suitable for use in conditioning air to be supplied to a climate controlled comfort zone within a residence, office building, hospital, school, restaurant or other facility. The refrigerant vapor compression systems <NUM>-<NUM> through <NUM>-<NUM> could also be employed in refrigerating air supplied to display cases, merchandisers, freezer cabinets, cold rooms or other perishable and frozen product storage areas in commercial establishments.

<FIG> illustrates an example vapor compression system <NUM>-<NUM> according to the present invention. The refrigerant vapor compression system <NUM>-<NUM> includes a compression device having a first compression stage 22A having an outlet discharge port fluidly coupled to an inlet on an air-cooled refrigerant intercooler <NUM> through a refrigerant line <NUM>. The first compression stage 22A compresses the refrigerant vapor from a lower pressure to an intermediate pressure. An outlet of the air-cooled refrigerant intercooler <NUM> is fluidly coupled to a suction port on a second compression stage 22B of the compression device through a refrigerant line <NUM>. The refrigerant line <NUM> is also in fluid communication with a second intercooler <NUM> located fluidly downstream of the air-cooled refrigerant intercooler <NUM> and upstream of the second compression stage 22B. The second compression stage 22B compresses the fluid from the intermediate pressure to a higher pressure. The first and second compressor stages 22A, 22B may be scroll compressors, screw compressors, reciprocating compressors, rotary compressors or any other type of compressor or a combination of any such compressors.

A discharge port on the second compression stage 22B is fluidly coupled to a refrigerant inlet on a refrigerant heat rejection heat exchanger <NUM>, also referred to herein as a gas cooler, through a refrigerant line <NUM>. The refrigerant line <NUM> is also in fluid communication with a second refrigerant heat rejection heat exchanger <NUM> located fluidly downstream of the second compression stage 22B and upstream of the air-cooled refrigerant heat rejection heat exchanger <NUM>. During air-cooled mode, a fan <NUM> is positioned adjacent the refrigerant heat rejection heat exchanger <NUM> and the air-cooled refrigerant intercooler <NUM> for passing secondary fluid (air) over the refrigerant heat rejection heat exchanger <NUM> and the air-cooled refrigerant intercooler <NUM>. The air-cooled refrigerant intercooler <NUM> may comprise, for example, a round tube plate fin heat exchanger or a louver fin mini-channel flat tube heat exchanger.

An outlet on the refrigerant heat rejection heat exchanger <NUM> is fluidly coupled to a refrigerant heat absorption heat exchanger <NUM>, also referred to herein as an evaporator, through a refrigerant line <NUM>. The refrigerant line <NUM> also includes a primary expansion device <NUM>, such as an electronic expansion valve or a thermostatic expansion valve, operatively associated with the evaporator <NUM>.

The refrigerant heat rejection heat exchanger <NUM> may comprise a finned tube heat exchanger through which hot, high pressure refrigerant discharged from the second compression stage 22B (i.e. the final compression charge) passes in heat exchange relationship with a secondary fluid, most commonly ambient air drawn through the refrigerant heat rejection heat exchanger <NUM> by the fan(s) <NUM>. The refrigerant heat rejection heat exchanger <NUM> may comprise, for example, a round tube plate fin heat exchanger or a louver fin mini-channel flat tube heat exchanger.

The evaporator <NUM> may also comprise a finned tube coil heat exchanger, such as a fin and round tube heat exchanger coil or a fin and flat mini-channel tube heat exchanger. The evaporator <NUM> functions as a refrigerant evaporator whether the refrigerant vapor compression system is operating in a transcritical cycle or a subcritical cycle. Before entering the evaporator <NUM>, the refrigerant passing through refrigerant line <NUM> traverses the primary expansion device <NUM>, such as, for example, an electronic expansion valve or a thermostatic expansion valve, and expands to a lower pressure and a lower temperature to enter the evaporator <NUM>. As two-phase refrigerant traverses the evaporator <NUM>, the refrigerant passes in heat exchange relationship with a heating fluid whereby the refrigerant is evaporated. The low pressure vapor refrigerant leaving the evaporator <NUM> passes through a refrigerant line <NUM> to a suction inlet on the first compression stage 22A. The heating fluid may be air drawn by an associated fan(s) <NUM> from a climate controlled environment, such as a perishable/frozen cargo storage zone associated with a transport refrigeration unit, or a food display or storage area of a commercial establishment, or a building comfort zone associated with an air conditioning system, to be cooled, and generally also dehumidified, and thence returned to a climate controlled environment.

The refrigerant vapor compression system <NUM>-<NUM> further includes an economizer circuit <NUM> associated with the primary refrigerant circuit. The economizer circuit <NUM> includes a flash tank economizer <NUM>, an economizer circuit expansion device <NUM>, and a vapor injection line <NUM> in refrigerant flow communication with an intermediate pressure stage of the compression process through the refrigerant line <NUM>. The economizer circuit expansion device <NUM> may, for example, be an electronic expansion valve, a thermostatic expansion valve or an adjustable orifice expansion device.

As shown in <FIG>, the flash tank economizer <NUM> is disposed in the refrigerant line <NUM> between the refrigerant heat rejection heat exchanger <NUM> and the primary expansion device <NUM>. The economizer circuit expansion device <NUM> is disposed in the refrigerant line <NUM> upstream of the flash tank economizer <NUM>. The flash tank economizer <NUM> defines a chamber <NUM> into which expanded refrigerant having traversed the economizer circuit expansion device <NUM> enters and separates into a liquid refrigerant portion and a vapor refrigerant portion.

The liquid refrigerant collects in the lower portion of chamber <NUM> and is metered therefrom through the downstream leg of the refrigerant line <NUM> by the primary expansion device <NUM> to flow to the evaporator <NUM>. The vapor refrigerant collects in the upper portion of chamber <NUM> above the liquid refrigerant and passes therefrom through the vapor injection line <NUM> for injection of refrigerant vapor into an intermediate stage of the compression process. In the depicted embodiments, the vapor injection line <NUM> communicates with the refrigerant line <NUM> downstream of the air-cooled intercooler <NUM> and upstream of the inlet of the second compression stage 22B. A check valve (not shown) may be disposed in the vapor injection line <NUM> upstream of its connection with the refrigerant line <NUM> to prevent backflow through the vapor injection line <NUM>. It is to be understood that when the check valve is fully closed, the system works in non-economized mode.

During operation in brine-cooled mode, the refrigerant vapor compression system <NUM>-<NUM> utilizes a second refrigerant heat rejection heat exchanger <NUM> and the second intercooler <NUM> in place of the refrigerant heat rejection heat exchanger <NUM> and the air-cooled refrigerant intercooler <NUM>, respectively. During operation in the brine-cooled mode, the fan <NUM> is not operating such that little to no heat transfer occurs in the refrigerant heat rejection heat exchanger <NUM> and the air-cooled refrigerant intercooler <NUM>. It is to be understood that other liquids, such as for example brines having a glycol or glycol/water mixtures, could be used as the secondary fluid instead of water in the brine-cooled mode.

In the illustrated example, the second refrigeration heat rejection heat exchanger <NUM> comprises a refrigerant-to-liquid heat exchanger having a secondary liquid pass <NUM> and a refrigerant pass <NUM> arranged in heat transfer relationship. The refrigerant pass <NUM> is disposed in the refrigerant line <NUM> and forms part of the primary refrigerant circuit. The secondary liquid pass <NUM> is disposed in a cooling liquid line <NUM> and forms part of the liquid cooling circuit. The secondary fluid pass <NUM> and the refrigerant pass <NUM> of the second refrigerant heat rejection heat exchanger <NUM> may be arranged in a parallel flow heat exchange relationship or in a counter flow heat exchange relationship, as desired. The second refrigerant heat rejection heat exchanger <NUM> may be a brazed plate heat exchanger, a tube-in-tube heat exchanger or a tube-on-tube heat exchanger.

The second intercooler <NUM> comprises a refrigerant-to-liquid heat exchanger having a secondary fluid pass <NUM> and a refrigerant pass <NUM> arranged in heat transfer relationship. The refrigerant pass <NUM> is disposed in refrigerant line <NUM> that interconnects the air-cooled refrigerant intercooler <NUM> in refrigerant flow communication with the second compression stage 22B and forms part of the primary refrigerant circuit. The second intercooler <NUM> is also located downstream of the refrigerant flow from the vapor injection line <NUM>.

In operation, refrigerant passes through the refrigerant pass <NUM> of the second intercooler <NUM> in heat exchange relationship with the secondary fluid, for example water, passing through the secondary liquid pass <NUM> whereby the refrigerant is cooled interstage of the first compression stage 22A and the second compression stage 22B. The secondary fluid pass <NUM> and the refrigerant pass <NUM> of the second intercooler <NUM> are arranged in a counter flow heat exchange relationship. The second intercooler <NUM> comprises a tube-in-tube heat exchanger or a tube-on-tube heat exchanger. One feature of this configuration is improved packaging in the refrigeration unit <NUM>.

As depicted in <FIG>, the second intercooler <NUM> is disposed downstream to the second refrigerant heat rejection heat exchanger <NUM> with respect to the secondary cooling liquid line <NUM>. The cooling water, or other secondary cooling liquid, is pumped through the secondary cooling liquid line <NUM> by an associated pump <NUM> to first flow through the secondary fluid pass <NUM> in heat exchange relationship with the refrigerant flowing through the refrigerant pass <NUM> of the second refrigerant heat rejection heat exchanger <NUM> and then through the secondary liquid pass <NUM> in heat exchange relationship with the refrigerant flowing through the refrigerant pass <NUM> of the second intercooler <NUM>. In this arrangement, the refrigerant in the second heat rejection heat exchanger <NUM> and the second refrigerant intercooler <NUM> can be cooled with a single-circuit brine fluid flow, instead of two-circuits brine fluid flow.

<FIG> illustrates a refrigerant vapor compression system <NUM>-<NUM>, not in accordance with the present invention, that is similar to the refrigerant vapor compression system <NUM>-<NUM> except where described below or show in the Figures. In the system <NUM>-<NUM>, the second intercooler <NUM> is located upstream of the air-cooled refrigerant intercooler <NUM> and associated with the refrigerant line <NUM> such that heat transfers from refrigerant in the refrigerant pass <NUM> to the secondary fluid pass <NUM> prior to the refrigerant reaching the air-cooled refrigerant intercooler <NUM>.

<FIG> illustrates a refrigerant vapor compression system <NUM>-<NUM>, not in accordance with the present invention, that is similar to the refrigerant vapor compression system <NUM>-<NUM> except where described below or shown in the Figures. In the system <NUM>-<NUM>, the second intercooler <NUM> is located upstream of the air-cooled refrigerant intercooler <NUM> and associated with the refrigerant line <NUM> such that heat transfers from refrigerant in the refrigerant pass <NUM> to the secondary fluid pass <NUM> prior to the refrigerant reaching the air-cooled refrigerant intercooler <NUM>. Additionally, the second intercooler <NUM> is not a tube-on-tube or a tube-in-tube heat exchange in this configuration.

<FIG> illustrates a refrigerant vapor compression system <NUM>-<NUM>, not in accordance with the present invention, that is similar to the refrigerant vapor compression system <NUM>-<NUM> except where described below or shown in the Figures. In particular, the system <NUM>-<NUM> does not include the second intercooler <NUM>.

<FIG> illustrates a refrigerant vapor compression system <NUM>-<NUM>, not in accordance with the present invention, that is similar to the refrigerant vapor compression system <NUM>-<NUM> except where described below or shown in the Figures. In the system <NUM>-<NUM>, the second refrigerant heat rejection heat exchanger <NUM> is located fluidly downstream of the refrigerant heat rejection heat exchanger <NUM> in the refrigerant line <NUM> and the second intercooler <NUM> is located downstream of the air-cooled refrigerant intercooler <NUM> in the refrigerant line <NUM>.

It should also be understood that although a particular component arrangement is disclosed and illustrated in these exemplary embodiments, other arrangements could also benefit from the teachings of this invention.

Claim 1:
A refrigerant vapor compression system (<NUM>) comprising:
a compression device having at least a first compression stage (22A) and a second compression stage (22B) arranged in series refrigerant flow relationship;
a first refrigerant heat rejection heat exchanger (<NUM>) disposed downstream with respect to refrigerant flow of the second compression stage (22B) for passing the refrigerant in heat exchange relationship with a flow of a first secondary fluid;
a first refrigerant intercooler (<NUM>) disposed intermediate the first compression stage (22A) and the second compression stage (22B) for passing the refrigerant passing from the first compression stage (22A) to the second compression stage (22B) in heat exchange relationship with the flow of the first secondary fluid;
an economizer circuit (<NUM>) including a vapor line (<NUM>) in fluid communication with a suction inlet to the second compression stage (22B);
a second refrigerant heat rejection heat exchanger (<NUM>) disposed intermediate with respect to refrigerant flow of the second compression stage (22B) and the first refrigerant heat rejection heat exchanger (<NUM>); and
a second refrigerant intercooler (<NUM>) disposed intermediate the first compression stage (22A) and the second compression stage (22B) and in heat exchange relationship with a second secondary fluid,
characterized in that:
the first refrigerant intercooler (<NUM>) is disposed downstream of the first refrigerant heat rejection heat exchanger (<NUM>) with respect to the flow of the first secondary fluid; and
the second refrigerant intercooler (<NUM>) is disposed downstream with respect to refrigerant flow of the vapor line (<NUM>) for passing the refrigerant from the first compression stage (22A) to the second compression stage (22B).