Patent Description:
In HVAC&R systems, a refrigerant gas is compressed by a compressor and then delivered to the condenser. The refrigerant vapor delivered to the condenser enters into a heat exchange relationship with a fluid, e.g., air or water, and undergoes a phase change to a refrigerant liquid. The liquid refrigerant from the condenser flows through a corresponding expansion device(s) to an evaporator. The liquid refrigerant in the evaporator enters into a heat exchange relationship with another fluid, e.g. air, water or other process fluid, and undergoes a phase change to a refrigerant vapor. The other fluid flowing through the evaporator is chilled or cooled as a result of the heat-exchange relationship with the refrigerant and can then be used to cool an enclosed space. Finally, the vapor refrigerant in the evaporator returns to the compressor to complete the cycle.

In an air-cooled condenser, the refrigerant flowing through the condenser can exchange heat with circulating air generated by an air moving device such as a fan or blower. Since circulating air is used for heat exchange in an air-cooled condenser, the performance and efficiency of the condenser, and ultimately the HVAC&R system, is subject to the ambient temperature of the air that is being circulated through the condenser. As the ambient air temperature increases, the condensing temperature (and pressure) of the refrigerant in the condenser also increases. At very high ambient air temperatures, i.e., air temperatures greater than <NUM> degrees Celsius (°C) (<NUM> degrees Fahrenheit (°F)), the performance and efficiency of the HVAC&R system can decrease due to higher condensing temperatures (and pressures) caused by the very high ambient air temperatures.

<CIT> relates to a conventional vapor compression system having a multi-stage cooling system capable of providing a plurality of cooling capacities. The cooling system comprises a plurality of independently operable compressors, wherein the cooling system is configured to operate the compressors to provide a cooling capacity corresponding to the heat load of a space to be cooled. A condenser structure of the cooling system has a plurality of individual condenser coils. Each condenser coil has an independent refrigerant path receiving compressed refrigerant from one of the compressors. An evaporator structure of the cooling system has a plurality of individual evaporator coils. Each evaporator coil has an independent refrigerant path receiving condensed refrigerant from a corresponding condenser coil via an expansion mechanism and returning the refrigerant to an input of a corresponding compressor.

Therefore, what is needed is an air-cooled condenser that can operate at a lower condensing temperature at very high ambient air temperatures to maintain desired HVAC&R system performance and efficiency.

One advantage of the present invention is a more compact system design in terms of footprint and/or volume when compared to systems of similar capacity.

Another advantage of the present invention is increased system capacity at very high ambient air temperatures.

Still another advantage of the present invention is the ability to equalize compressor motor loads when using economizers.

A further advantage of the present invention is the ability to use fewer fans to circulate air through the condenser which results in lower fan noise associated with the condenser.

Yet a further advantage of the present invention is more efficient use of the condenser surface by more closely correlating ambient air temperature and condensing temperature.

Other advantages of the present invention include lower cost, improved system efficiency and a lighter weight unit.

Referring to <FIG>, an exemplary environment for a heating, ventilation, air conditioning and refrigeration (HVAC&R) system <NUM> in a building <NUM> for a typical commercial setting is shown. HVAC&R system <NUM> may include a compressor incorporated into a rooftop unit <NUM> that may supply a chilled liquid that may be used to cool building <NUM>. HVAC&R system <NUM> may also include a boiler <NUM> to supply a heated liquid that may be used to heat building <NUM>, and an air distribution system that circulates air through building <NUM>. The air distribution system may include an air return duct <NUM>, an air supply duct <NUM> and an air handler <NUM>. Air handler <NUM> may include a heat exchanger (not shown) that is connected to boiler <NUM> and rooftop unit <NUM> by conduits <NUM>. The heat exchanger (not shown) in air handler <NUM> may receive either heated liquid from boiler <NUM> or chilled liquid from rooftop unit <NUM> depending on the mode of operation of HVAC&R system <NUM>. HVAC&R system <NUM> is shown with a separate air handler <NUM> on each floor of building <NUM>. However, several air handlers <NUM> may service more than one floor, or one air handler may service all of the floors.

HVAC&R system <NUM> can include an air-cooled condenser for the exchange of heat with the refrigerant used in HVAC&R system <NUM>. To more efficiently use the heat transfer surface of an air-cooled condenser in HVAC&R system <NUM>, the refrigerant temperature in the condenser can be correlated or matched to the temperature of the air circulating through the condenser. In one exemplary embodiment, the air-cooled heat exchanger or condenser can be set up, configured or arranged to have one or more portions with substantially planar sections or coils arranged or positioned in a V-shape. The sections or coils can be stacked or nested and operated at different condensing temperatures, condensing pressure and/or in different refrigerant circuits. The stacked sections or coils can be arranged or positioned so that the air exiting one section or coil enters the other section or coil. Stated differently, the air flow through the sections or coils of the portion of the condenser can be in a series configuration or arrangement. In
another exemplary embodiment, the condenser may have portions with both stacked sections and coils operating at different condensing temperatures or pressures and single sections or coils operating at a single condensing temperature or pressure.

<FIG> shows an exemplary embodiment of a condenser. In the exemplary embodiment of <FIG>, condenser <NUM> has portions <NUM> having separate, stacked sections or coils <NUM>. The outer sections or coils (of the V-shape) of heat exchanger or condenser portion <NUM> can be part of one refrigerant circuit and the inner sections or coils (of the V-shape) of heat exchanger or condenser portion <NUM> can be part of a second refrigerant circuit. The discharge vapor or gas from the compressor(s) can enter each section or coil <NUM> at connections <NUM> at the top and middle of the section or coil <NUM>. The liquid refrigerant can exit each section or coil <NUM> from a connection <NUM> near the bottom of the section or coil <NUM>. In one exemplary embodiment, each section or coil <NUM> can be identical in design, configuration or arrangement with two refrigerant passes through the section or coil <NUM>. However, in other exemplary embodiments, the sections or coils can have different designs, sizes or configurations and a different number of passes of refrigerant. The use of a section or coil <NUM> with two passes results in both inlet and outlet connections being at the same end of the section or coil <NUM> and can provide for the cooler air leaving a subcooling portion of the upstream section or coil to be used by a subcooling portion of the downstream section or coil.

In another exemplary embodiment, a single pass or odd-number pass configuration may be used for each section or coil <NUM> or particular sections or coils <NUM>. The single pass or odd-number pass configuration can result in the corresponding refrigerant headers for the section or coil <NUM> being at opposite ends of the section or coil <NUM> to provide sufficient space for the easy assembly and assembly of the piping connections.

<FIG> shows a partially exploded view of a heat exchanger or condenser <NUM> that may be used in the exemplary HVAC&R system <NUM> shown in <FIG>. Heat exchanger <NUM> may include an upper assembly <NUM> including a shroud <NUM> and one or more fans <NUM>. The heat exchanger sections or coils <NUM> may be positioned beneath shroud <NUM> and may be positioned above or at least partially above other HVAC&R system components, such as a compressor(s), an expansion device, or an evaporator. The heat exchanger sections or coils <NUM> can be mounted using the same or common structural components and can be assembled as part of a packaged unit. Section or coils <NUM> may be positioned at any angle between zero degrees and ninety degrees to provide enhanced airflow through coils <NUM> and to assist with the drainage of liquid from coils <NUM>. In one exemplary embodiment, the stacking of the heat exchanger sections or coils as part of a packaged unit provides for a compact unit that can be shipped in standard shipping containers.

<FIG> show the contrast in condenser refrigerant temperature between a single condenser section configuration and a stacked condenser section configuration. <FIG> shows condenser refrigerant temperature relative to air temperature for a single condenser section or coil configuration. A pinch point, as shown in <FIG>, between the leaving air temperature and the refrigerant temperature limits the condensing temperature of the refrigerant. Increasing condenser heat transfer surface area can provide little or no improvement in theoretical condensing temperature because the refrigerant temperature is limited by the leaving air temperature at the pinch point. In addition, the extra air-side pressure drop from the added heat transfer surface area can reduce air flow and can eventually result in a higher condensing temperature. Thus, there is a practical limit to the amount of heat transfer that can be obtained from a single coil or section for a given fan.

In contrast, <FIG>, shows condenser refrigerant temperature relative to air temperature for a stacked condenser section or coil configuration used with two refrigerant circuits and having series air flow. The upstream refrigerant circuit (and condenser section) has half the heat transfer load and thus sees a lower leaving air temperature, which permits the use of a much lower condensing temperature. The downstream refrigerant circuit (and condenser section) perform about the same as the single condenser section shown in <FIG>. The downstream refrigerant circuit or section in <FIG> can have a higher entering refrigerant temperature, but the leaving refrigerant temperature is almost unchanged (relative to <FIG>), moreover, the downstream refrigerant circuit or section has half the heat transfer load. The result of using the two refrigerant circuits or condenser sections is a large reduction in the average condensing temperature for the two refrigerant circuits or condenser sections. The series air flow configuration for the stacked condenser sections can effectively reduce the thermodynamic limit to the condensing temperature because the heat exchange better approximates a counter-flow arrangement.

The sections or coils <NUM> can be implemented with microchannel or multichannel coils or heat exchangers. Microchannel or multichannel coils can have the advantage of compact size, light weight, low air-side pressure drop, and low material cost. The microchannel or multichannel coils or sections can circulate refrigerant through two or more tube sections, each of which has two more tubes, passageways or channels for the flow of refrigerant. The tube section can have a cross-sectional shape in the form or a rectangle, parallelogram, trapezoid, ellipse, oval or other similar geometric shape. The tubes in the tube section can have a cross-sectional shape in the form of a rectangle, square, circle, oval, ellipse, triangle, trapezoid, parallelogram or other suitable geometric shape. In one embodiment, the tubes in the tube section can have a size, e.g., width or diameter, of between about a half (<NUM>) millimeter (mm) to about a three (<NUM>) millimeters (mm). In another embodiment, the tubes in the tube section can have a size, e.g., width or diameter, of about one (<NUM>) millimeter (mm).

According to the invention, the sections or coils <NUM> are implemented with round-tube plate-fin coils. According to the invention, the fins of the round-tube plate-fin coils are split so that there is no conduction path between the two refrigerant circuits or coils, but to use a common tube sheet. The result is two separate coils from a thermal standpoint, but mechanically they appear as single unit. Another configuration according to the invention is to make a round-tube coil where the refrigerant circuits share the fins and where there may be conduction through the fins between the two circuits or coils that is limited by the inclusion of a thermal break (such as a slit) in the fin design. In still another exemplary embodiment falling outside of the scope of the claims, the round-tube coil condensers can be configured to have the desuperheating sections downstream of both condensing sections and the subcooling sections upstream of both condensing sections to provide the optimum thermal performance.

<FIG> show different exemplary vapor compression systems for HVAC&R system <NUM> that incorporate or use a stacked condenser sections or coils. The vapor compression systems can circulate a refrigerant through one or more independent or separate circuits starting with compressors <NUM> and including a condenser <NUM> having stacked sections or coils, expansion device(s) <NUM>, and an evaporator or liquid chiller <NUM>. The vapor compression systems can also include a control panel that can include an analog to digital (A/D) converter, a microprocessor, a non-volatile memory, and an interface board. Some examples of fluids that may be used as refrigerants in the vapor compression systems are hydrofluorocarbon (HFC) based refrigerants, for example, R-410A, R-<NUM>, R-134a, hydrofluoro olefin (HFO), "natural" refrigerants like ammonia (NH3), R-<NUM>, carbon dioxide (COz), R-<NUM>, or hydrocarbon based refrigerants, water vapor or any other suitable type of refrigerant. In one exemplary embodiment, the same refrigerant can be circulated in all of the circuit in the vapor compression system. However, in other embodiments, different refrigerants can be circulated in separate refrigerant circuits.

Compressors <NUM> can have a fixed Vi (volume ratio or volume index), i.e., the ratio of suction volume to discharge volume, or the compressors <NUM> can have a variable Vi. In addition, compressors <NUM> for each circuit may have the same Vi or the Vi for the compressors <NUM> may be different. The motors used with compressors <NUM> can be powered by a variable speed drive (VSD) or can be powered directly from an alternating current (AC) or direct current (DC) power source. The VSD, if used, receives AC power having a particular fixed line voltage and fixed line frequency from the AC power source and provides power to the motor having a variable voltage and frequency. The motor can include any type of electric motor that can be powered by a VSD or directly from an AC or DC power source. The motor can be any other suitable motor type, for example, a switched reluctance motor, an induction motor, or an electronically commutated permanent magnet motor. The output capacity of compressors <NUM> may be based upon the corresponding operating speeds of compressors <NUM>, which operating speeds are dependent on the output speed of the motor driven by the VSD. In an another exemplary embodiment, other drive mechanisms such as steam or gas turbines or engines and associated components can be used to drive the compressors <NUM>.

Compressors <NUM> compress a refrigerant vapor and deliver the compressed vapor to the separate condenser sections or coils of condenser <NUM> through separate discharge passages. Condenser <NUM> can have an upstream section or coil <NUM> and a downstream section or coil <NUM> relative to the direction of air flow through the condenser. The upstream section or coil <NUM> can operate at lower condenser temperatures and pressures relative to the downstream section or coil <NUM>. The refrigerant vapor delivered by compressors <NUM> to upstream section or coil <NUM> and downstream section or coil <NUM> transfers heat to air circulated by fan(s) <NUM>. The refrigerant vapor condenses to a refrigerant liquid in both upstream section or coil <NUM> and downstream section or coil <NUM> as a result of the heat transfer with the air. In addition, upstream section or coil <NUM> and downstream section or coil <NUM> may also include a sub-cooler for the liquid refrigerant. The liquid refrigerant from upstream section or coil <NUM> and downstream section or coil <NUM> flows through expansion device(s) <NUM> to evaporator <NUM>. The liquid refrigerant delivered to evaporator <NUM> absorbs heat from a process fluid, e.g., water, air, ethylene glycol, calcium chloride brine, sodium chloride brine or other suitable type of fluid, to chill or lower the temperature of the process fluid and undergoes a phase change to a refrigerant vapor. The vapor refrigerant exits evaporator <NUM> and returns to compressors <NUM> by suction lines to complete the circuit or cycle. Depending on the number of circuits implemented in a particular vapor compression system, evaporator <NUM> may have one or more vessels. Further, even if multiple circuits are used for a particular vapor compression system, the evaporator may still use a single vessel that can maintain the separate refrigerant circuits for heat transfer.

In one exemplary embodiment, compressors <NUM> can be selected to not have the same Vi. In other words, one compressor <NUM> can have a high Vi (relative to the other compressor) and the other compressor <NUM> can have a low Vi (relative to the other compressor). The low Vi compressor can be connected to the upstream section or coil <NUM> having the lower condensing temperature. As shown in <FIG>, the temperature of the air for the downstream condenser section or coil <NUM> is greater than the temperature of the air for the upstream condenser section or coil <NUM>. Thus, the difference in airflow temperature permits the refrigerant from the high Vi compressor to condense in the downstream condenser section or coil <NUM> at a higher condensing temperature and/or pressure than the refrigerant from the low Vi compressor in the upstream condenser section or coil <NUM>. Using the low Vi compressor with the upstream condenser section or coil <NUM> operating at the lower condensing temperature can improve full-load efficiency for the vapor compression system. In addition, part-load efficiency of the vapor compression system can be improved when only the low Vi compressor is operated. In one particular exemplary embodiment, the low Vi compressor can be a centrifugal compressor and the high Vi compressor can be a positive displacement compressor such as a screw compressor.

In one particular exemplary embodiment, the compressor for the refrigerant circuit with the upstream coil can be a variable-speed centrifugal compressor and the high Vi compressor with the downstream coil can be a positive displacement compressor such as a screw compressor. The compressor pairing in this embodiment improves the high-ambient temperature capability of the system since the compressor configuration reduces the discharge pressures required on the centrifugal compressor. The discharge pressure that a centrifugal compressor can achieve is generally limited by a maximum ratio of compressor suction and discharge pressures for given compressor design. The centrifugal compressor can be a hermetic two-stage compressor with variable-speed direct-drive and magnetic bearings. High part-load efficiency for the system can be obtained by operating the centrifugal compressor by itself, i.e., the screw compressor is not operated, at part-load conditions.

<FIG> shows a vapor compression system with multiple compressors supplying a single refrigerant circuit. The vapor compression system of <FIG> uses check valves <NUM> or other similar valves to isolate refrigerant flow so that only a single compressor may be operated. In addition, an orifice <NUM> is used at the output of the condenser <NUM> to equalize the pressure of the refrigerants exiting the upstream section or coil <NUM> and downstream section or coil <NUM>. The working pressure of the refrigerant line between condenser <NUM> and expansion device <NUM> can be lower than what the working pressure would be if a separate connection was used for the downstream section or coil <NUM>. The lower working pressure enables additional components in the liquid line between condenser <NUM> and expansion device <NUM>, for example, a filter/drier or sight glass, to be configured and operated for lower pressures. The compressors used for the separate refrigerant circuits may have the same Vi or different Vi. In the vapor compression system of <FIG>, compressors <NUM> can be scroll compressors.

<FIG> shows a vapor compression system with multiple separate refrigerant circuits and separate evaporator sections for each circuit that are used to cool air directly for the HVAC&R system <NUM>. The compressors used for the separate refrigerant circuits may have the same Vi or different Vi. In the vapor compression system of <FIG>, the vapor compression system can be used in a packaged rooftop unit.

<FIG> shows a vapor compression system with multiple separate refrigerant circuits using a single evaporator vessel. The compressors used for the separate refrigerant circuits may have the same Vi or may have a different Vi. In an exemplary embodiment of the vapor compression system of <FIG>, the vapor compression system can be used for chillers or chilled liquid systems and incorporate scroll compressors.

In the exemplary embodiments shown in <FIG>, the vapor compression circuits can include one or more intermediate or economizer circuits incorporated between condenser <NUM> and expansion devices <NUM>. The intermediate or economizer circuits can be utilized to provide increased cooling capacity for a given evaporator size and can increase efficiency and performance of the vapor compression system. The intermediate circuits can have an inlet line(s) that can be either connected directly to or can be in fluid communication with one or both of upstream section or coil <NUM> and downstream section or coil <NUM>. The inlet line(s) can include an expansion device(s) <NUM> positioned upstream of an intermediate vessel. Expansion device <NUM> operates to lower the pressure of the refrigerant from the upstream section or coil <NUM> and/or downstream section or coil <NUM> to an intermediate pressure, resulting in the flashing of some of the refrigerant to a vapor. The flashed refrigerant at an intermediate pressure can be reintroduced into the corresponding compressor <NUM> for that particular circuit. Since intermediate pressure refrigerant vapor is returned to compressor <NUM>, the refrigerant vapor requires less compression, thereby increasing overall efficiency for the vapor compression system. The remaining liquid refrigerant, at the intermediate pressure, from expansion device <NUM> is at a lower enthalpy which can facilitate heat transfer. Expansion devices <NUM> can receive the intermediate pressure refrigerant from the intermediate vessel and expand the lower enthalpy liquid refrigerant to evaporator pressure. The refrigerant enters the evaporator <NUM> with lower enthalpy, thereby increasing the cooling effect in systems with economizing circuits versus non-economized systems in which the refrigerant is expanded directly from the condenser.

The intermediate vessel can be a flash tank <NUM>, also referred to as a flash intercooler, or the intermediate vessel can be configured as a heat exchanger <NUM>, also referred to as a "surface economizer. " Flash tank <NUM> may be used to separate the vapor from the liquid received from expansion device <NUM> and may also permit further expansion of the liquid. The vapor may be drawn by compressor <NUM> from flash tank <NUM> through an auxiliary refrigerant line to the suction inlet, a port at a pressure intermediate between suction and discharge or an intermediate stage of compression. In one exemplary embodiment, a solenoid valve <NUM> can be positioned in the auxiliary refrigerant line between the compressor <NUM> and flash tank <NUM> to regulate flow of refrigerant from the flash tank <NUM> to the compressor <NUM>. The liquid that collects in the flash tank <NUM> is at a lower enthalpy from the expansion process. The liquid from flash tank <NUM> flows to the expansion device <NUM> and then to evaporator <NUM>. Heat exchanger <NUM> can be used to transfer heat between refrigerants at two different pressures. The exchange of heat between the refrigerants in heat exchanger <NUM> can be used to subcool one of the refrigerants in heat exchanger <NUM> and at least partially evaporate the other refrigerant in heat exchanger <NUM>.

<FIG> shows a vapor compression system with multiple separate refrigerant circuits each incorporating an intermediate or economizer circuit. Each of the upstream section or coil <NUM> and downstream section or coil <NUM> can be fluidly connected to an expansion device <NUM> that is fluidly connected to a flash tank <NUM>. The expansion devices <NUM> can be used to adjust the operating pressure of the economizers. The compressors used for the separate refrigerant circuits may have the same Vi or different Vi. In an exemplary embodiment using a high Vi compressor connected to the downstream section or coil <NUM> and a low Vi compressor connected to the upstream section or coil <NUM>, the vapor refrigerant from the flash tank <NUM> connected to the downstream section or coil <NUM> can be provided to the high Vi compressor at a higher pressure to reduce motor loading on the high Vi compressor.

<FIG> shows a vapor compression system similar to the vapor compression system of <FIG> except that a heat exchanger is incorporated into the intermediate or economizer circuits. The upstream section or coil <NUM> can be fluidly connected to expansion device <NUM> that is fluidly connected heat exchanger <NUM> and then flash tank <NUM>. The downstream section or coil <NUM> can be fluidly connected to heat exchanger <NUM> that is fluidly connected to expansion device <NUM> and then flash tank <NUM>. The compressors used for the separate refrigerant circuits may have the same Vi or different Vi.

<FIG> shows a vapor compression system similar to the vapor compression system of <FIG> except that an additional or second heat exchanger is incorporated into the intermediate or economizer circuit connected to the downstream section or coil <NUM>. The liquid refrigerant from the downstream section or coil <NUM> is split into two separate passageways and provided to a second heat exchanger <NUM>. One of the passageways can incorporate an expansion device <NUM> before the liquid refrigerant enters the second heat exchanger <NUM>. The output of the second heat exchanger <NUM> corresponding to the input passageway with the expansion device <NUM> can be provided to the compressor <NUM> supplying the downstream section or coil <NUM> at a port corresponding to a higher pressure in compressor <NUM> separate from the port connected to flash tank <NUM>. The other output from second heat exchanger <NUM> can enter the first heat exchanger as described in <FIG>. The compressors used for the separate refrigerant circuits may have the same Vi or different Vi.

<FIG> shows a vapor compression system with multiple separate refrigerant circuits each incorporating an intermediate or economizer circuit. The upstream section or coil <NUM> can be fluidly connected to expansion device <NUM> that is fluidly connected heat exchanger <NUM> and then flash tank <NUM>. The downstream section or coil <NUM> can be fluidly connected to heat exchanger <NUM> that is fluidly connected to expansion device <NUM> and then evaporator <NUM>. The compressors used for the separate refrigerant circuits may have the same Vi or different Vi. Heat exchanger <NUM> can use the refrigerant from the upstream section or coil <NUM> to cool the refrigerant liquid from for the downstream section or coil <NUM>. By cooling the refrigerant liquid from the downstream section or coil <NUM>, the motor load on the compressor <NUM> connected to the downstream section or coil <NUM> can be reduced and equalized with the motor load on the compressor <NUM> connected to the upstream section or coil <NUM>.

<FIG> shows a vapor compression system similar to the vapor compression system of <FIG> except that an additional flash tank is incorporated into the intermediate or economizer circuit connected to the downstream section or coil <NUM>. The liquid refrigerant from the downstream section or coil <NUM> is fluidly connected to an expansion device <NUM> that is fluidly connected to a flash tank <NUM>. The liquid refrigerant from flash tank <NUM> can be provided to heat exchanger <NUM> as described with respect to <FIG>. The vapor refrigerant from flash tank <NUM> can be provided to the compressor <NUM> supplying the downstream section or coil <NUM>. The compressors used for the separate refrigerant circuits may have the same Vi or different Vi.

In one exemplary embodiment using high and low Vi compressors, economizer load can be shifted from the circuit with the high Vi compressor operating at the higher condenser pressure to the circuit with the low Vi compressor operating at the lower condenser pressure to equalize compressor loading and improve capacity at high ambient temperatures.

<FIG> compares system efficiency with the stacked condenser coil configuration to the system efficiency with a single condenser coil configuration. Both condenser coil configurations use <NUM> deep microchannel heat exchanger coils. For the purpose of the analysis, a vapor compression system configured as shown in <FIG> was used. In addition, both compressors have the same Vi design, i.e., a high Vi design. As shown in <FIG>, about the same system efficiency can be obtained using only <NUM> fans with the stacked condenser coil configuration as can be obtained using <NUM> fans with the single condenser coil configuration, which can result in an improvement of about <NUM>% in system efficiency. In addition, higher efficiency levels can be achieved over the single condenser coil configuration with the use of additional fans. <FIG> shows the relationship between system efficiency and system cost. The results in <FIG> are based on the same system configurations as in <FIG>. As shown in <FIG>, more efficient systems can be obtained using the stacked condenser coil configuration for the same cost as single condenser coil configuration. Furthermore, the stacked condenser coil configuration can provide a reduction cost compared to a single condenser coil configuration for a particular design efficiency.

In an exemplary embodiment, the condenser can be expanded to have more than two condenser sections or coils operating at different pressures. In general, the incremental performance improvement is smaller with each additional section and condensing pressure.

In another exemplary embodiment, each of the compressors may be a single-stage compressor, such as a screw compressor, reciprocating compressor, centrifugal compressor, rotary compressor, swing link compressor, scroll compressor, turbine compressor, or any other suitable compressor, although any single-stage or multi-stage compressor can be used.

In a further exemplary embodiment, the expansion devices may be any suitable expansion device including expansion valves such as electronic expansion valves or thermal expansion valves, capillary tubes or orifices.

In another exemplary embodiment, each compressor can include tandem, trio, or other multiple-compressor configurations that share a single refrigerant circuit and act as a single compressor system. For example, scroll compressors can be configured in a multiple compressor configuration, i.e., two or more compressors can be connected in a single refrigerant circuit. In the scroll compressor example, capacity control can be achieved by staging compressors in the multiple compressor configuration. In addition, a multiple compressor configuration can include other associated components such as valves to regulate flow. In still another exemplary embodiment, compressors having different design Vi may also share the same refrigerant circuit.

In other exemplary embodiments, the vapor compression system may have other configurations. For example, additional economizers may be incorporated to the circuits to further improve efficiency. The optimum economizer configuration depends on the efficiency and capacity improvement relative to the cost.

Claim 1:
A vapor compression system (<NUM>) comprising:
- a first circuit to circulate a refrigerant comprising a first compressor (<NUM>), first condenser (<NUM>, <NUM>) and first evaporator (<NUM>) in fluid communication;
a second circuit to circulate a refrigerant comprising a second compressor (<NUM>), second condenser (<NUM>, <NUM>) and second evaporator (<NUM>) in fluid communication;
- both the first evaporator (<NUM>) and the second evaporator (<NUM>) exchanging heat with a process fluid in a common vessel;
- at least one air moving device (<NUM>) to circulate air through both the first condenser (<NUM>, <NUM>) and the second condenser (<NUM>, <NUM>);
- the first condenser (<NUM>, <NUM>) and the second condenser (<NUM>, <NUM>) each comprising at least one substantially planar section; and
- a condensing temperature of the refrigerant in the first condenser (<NUM>, <NUM>) is different from a condensing temperature of the refrigerant in the second condenser (<NUM>, <NUM>),
whereby
- the at least one substantially planar section of the first condenser (<NUM>, <NUM>) being positioned next to and substantially parallel to the at least one substantially planar section of the second condenser (<NUM>, <NUM>);
the at least one substantially planar section of the first condenser (<NUM>, <NUM>) and the at least one substantially planar section of the second condenser (<NUM>, <NUM>) are positioned to have air circulated through the at least one substantially planar section of the first condenser (<NUM>, <NUM>) and then through the at least one substantially planar section of the second condenser (<NUM>, <NUM>); characterized in that:
- the at least one substantially planar section of the first condenser (<NUM>, <NUM>) and the at least one substantially planar section of the second condenser (<NUM>, <NUM>) are separate, stacked coils (<NUM>), and the coils (<NUM>) are round-tube plate-fin coils; and
- the at least one substantially planar section of the first condenser (<NUM>, <NUM>) is thermally separate from the at least one substantially planar section of the second condenser (<NUM>, <NUM>) either via respective fins of the first condenser (<NUM>, <NUM>) being split from respective fins of the second condenser (<NUM>, <NUM>) to interrupt a conduction path there between or via inclusion of a thermal break, such as a slit, in common fins shared by the first condenser (<NUM>, <NUM>) and the second condenser (<NUM>, <NUM>) to limit conduction there between.