US20080202140A1 - High Side Pressure Regulation For Transcritical Vapor Compression System - Google Patents
High Side Pressure Regulation For Transcritical Vapor Compression System Download PDFInfo
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- US20080202140A1 US20080202140A1 US11/908,629 US90862907A US2008202140A1 US 20080202140 A1 US20080202140 A1 US 20080202140A1 US 90862907 A US90862907 A US 90862907A US 2008202140 A1 US2008202140 A1 US 2008202140A1
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- heat exchanger
- compressor
- flow path
- refrigerant
- expansion device
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- 230000006835 compression Effects 0.000 title abstract description 23
- 238000007906 compression Methods 0.000 title abstract description 23
- 230000033228 biological regulation Effects 0.000 title description 2
- 239000003507 refrigerant Substances 0.000 claims description 15
- 238000011144 upstream manufacturing Methods 0.000 claims description 9
- 238000005057 refrigeration Methods 0.000 claims description 5
- 235000013361 beverage Nutrition 0.000 claims description 4
- 230000003134 recirculating effect Effects 0.000 claims description 2
- 230000007423 decrease Effects 0.000 description 4
- 238000012354 overpressurization Methods 0.000 description 3
- 238000009825 accumulation Methods 0.000 description 2
- 230000008901 benefit Effects 0.000 description 2
- 238000006073 displacement reaction Methods 0.000 description 2
- 238000001704 evaporation Methods 0.000 description 2
- 230000008020 evaporation Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000005457 optimization Methods 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 238000004378 air conditioning Methods 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 238000009530 blood pressure measurement Methods 0.000 description 1
- 238000011217 control strategy Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000008030 elimination Effects 0.000 description 1
- 238000003379 elimination reaction Methods 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 239000012530 fluid Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000000034 method Methods 0.000 description 1
Images
Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B9/00—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point
- F25B9/002—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point characterised by the refrigerant
- F25B9/008—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point characterised by the refrigerant the refrigerant being carbon dioxide
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B2309/00—Gas cycle refrigeration machines
- F25B2309/06—Compression machines, plants or systems characterised by the refrigerant being carbon dioxide
- F25B2309/061—Compression machines, plants or systems characterised by the refrigerant being carbon dioxide with cycle highest pressure above the supercritical pressure
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B2600/00—Control issues
- F25B2600/17—Control issues by controlling the pressure of the condenser
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B2700/00—Sensing or detecting of parameters; Sensors therefor
- F25B2700/19—Pressures
- F25B2700/193—Pressures of the compressor
- F25B2700/1931—Discharge pressures
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B2700/00—Sensing or detecting of parameters; Sensors therefor
- F25B2700/21—Temperatures
- F25B2700/2117—Temperatures of an evaporator
- F25B2700/21171—Temperatures of an evaporator of the fluid cooled by the evaporator
- F25B2700/21172—Temperatures of an evaporator of the fluid cooled by the evaporator at the inlet
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B41/00—Fluid-circulation arrangements
- F25B41/30—Expansion means; Dispositions thereof
- F25B41/385—Dispositions with two or more expansion means arranged in parallel on a refrigerant line leading to the same evaporator
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
- F25D19/00—Arrangement or mounting of refrigeration units with respect to devices or objects to be refrigerated, e.g. infrared detectors
- F25D19/02—Arrangement or mounting of refrigeration units with respect to devices or objects to be refrigerated, e.g. infrared detectors plug-in type
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
- F25D31/00—Other cooling or freezing apparatus
- F25D31/006—Other cooling or freezing apparatus specially adapted for cooling receptacles, e.g. tanks
- F25D31/007—Bottles or cans
Definitions
- the invention relates to refrigeration. More particularly, the invention relates to beverage coolers.
- FIG. 1 schematically shows transcritical vapor compression system 20 utilizing CO 2 as working fluid.
- the system comprises a compressor 22 , a gas cooler 24 , an expansion device 26 , and an evaporator 28 .
- the exemplary gas cooler and evaporator may each take the form of a refrigerant-to-air heat exchanger. Airflows across one or both of these heat exchangers may be forced. For example, one or more fans 30 and 32 may drive respective airflows 34 and 36 across the two heat exchangers.
- a refrigerant flow path 40 includes a suction line extending from an outlet of the evaporator 28 to an inlet 42 of the compressor 22 .
- a discharge line extends from an outlet 44 of the compressor to an inlet of the gas cooler. Additional lines connect the gas cooler outlet to expansion device inlet and expansion device outlet to evaporator inlet.
- the evaporator may be essentially at the cooler interior temperature. It is typically desired to maintain this temperature in a very narrow range regardless of external condition. For example, it may be desired to maintain the interior very close to 37° F. This temperature essentially fixes the steady state compressor suction pressure.
- the energy efficiency of a vapor compression system is usually expressed as a ratio of the system capacity to the energy consumed. Because an increase in pressure typically produces both a higher capacity and a higher energy consumption, the balance between the two will dictate the overall COP. Therefore, there is typically an optimal pressure which yields the highest possible performance.
- An electronic expansion valve is usually used as the device 26 to control the high side pressure to optimize the COP of the CO 2 vapor compression system.
- An electronic expansion valve typically comprises a stepper motor attached to a needle valve to vary the effective valve opening or flow capacity to a large number of possible positions (typically over one hundred). This provides good control of the high side pressure over a large range of operating conditions.
- the opening of the valve is electronically controlled by a controller 50 to match the actual high side pressure to the desired set point.
- This pressure control strategy involves a fairly high cost valve, a sophisticated controller 50 , and a sensor 52 for measuring the high side pressure. This equipment adds a significant amount of cost to the CO 2 vapor compression system, causing the CO 2 vapor compression system to be less attractive compared to an HFC system.
- a fixed expansion device e.g., a fixed orifice or capillary tube
- a fixed expansion device can work well to regulate the system high side pressure to a near optimum pressure.
- the flowrate through a fixed speed and displacement compressor can become relatively high. This high flowrate can cause the high side pressure to exceed a safe limit.
- An expensive expansion device may be eliminated in favor of a less expensive pressure regulator in a CO 2 vapor compression system such as is used in a bottle cooler or small-capacity air conditioner, refrigerator, or other system.
- the potential for overpressurization may be reduced by using an inexpensive, multi-step fixed expansion device based on one or more solenoid valves.
- FIG. 1 is a schematic of a prior art vapor compression system.
- FIG. 2 is a schematic of a first inventive CO 2 vapor compression system.
- FIG. 3 is a schematic of a second inventive CO 2 vapor compression system.
- FIG. 4 is a schematic of a third inventive CO 2 vapor compression system.
- FIG. 5 is a schematic of a fourth inventive CO 2 vapor compression system.
- FIG. 6 is a schematic of a fifth inventive CO 2 vapor compression system.
- FIG. 7 is a schematic of a sixth inventive CO 2 vapor compression system.
- FIG. 8 is a schematic of a seventh inventive CO 2 vapor compression system.
- FIG. 9 is a side schematic view of a display case including a refrigeration and air management cassette.
- FIG. 10 is a view of a refrigeration and air management cassette.
- the current invention relates to high-side pressure optimization for a CO 2 vapor compression system.
- a fixed expansion device e.g., an orifice or capillary tube
- the preset value should be determined such that the CO 2 vapor compression system can achieve the best overall Coefficient of Performance (COP) for the entire operating envelope.
- COP Coefficient of Performance
- the compressor flowrate will be significantly higher than during steady state conditions.
- the high-side pressure should be optimized such that the pulldown cooling capacity of the CO 2 vapor compression system can be maximized, but the flow through the pressure regulator does not exceed the flow through the compressor (so that the system pressure becomes too great).
- This optimal high-side pressure for maximizing capacity is usually higher than the optimal high-side pressure for maximizing the overall COP.
- the expansion device may be configured to have a larger flow capacity during pulldown conditions. A simple multi-position expansion device may provide this. There are a number of ways through which this can be achieved through the use of solenoid valves to enable a two or more position pressure control system.
- FIG. 2 shows a system 60 in which the refrigerant flow path 62 is split into two parallel branches/segments 64 and 66 between the gas cooler 24 outlet and evaporator 28 inlet.
- the first branch 64 has a first fixed expansion device 68 .
- the second branch 66 includes, in series, a solenoid valve 70 and a second fixed expansion device 72 .
- the exemplary solenoid valve 70 has two settings/conditions.
- One setting/condition is a fully closed condition in which no flow may pass along the second branch 66 .
- the second setting/condition is a fully open condition allowing flow to pass through the second branch 66 with a minimal pressure loss across the solenoid valve 70 .
- the solenoid valve 70 is kept fully closed.
- the compressor flowrate is relatively high.
- the solenoid valve 70 is opened, allowing flow through the second fixed expansion device 72 .
- the combination of both expansion devices 68 and 72 regulates the high-side pressure to avoid overpressurization while still delivering good system performance.
- a pulldown condition may be detected by means of one or more temperature sensors 75 and pressure sensor 74 coupled to a controller 76 coupled to control the solenoid valve 70 .
- the controller 76 may also be coupled to the compressor and/or fan(s) to control their respective operation.
- the sensor and controller are not illustrated in the following examples although they may be present.
- FIG. 3 shows a system 80 wherein the refrigerant flow path 82 has two segments/branches 84 and 86 in parallel upstream of a first fixed expansion device 88 .
- the first branch 84 includes a solenoid valve 90 .
- the second branch 86 includes a second fixed expansion device 92 .
- the solenoid valve 90 is closed to prevent flow along the first branch 84 .
- the second branch 86 acts as a bypass with restricted flow passing through the second fixed expansion device 92 before then passing through the first fixed expansion device 88 .
- the solenoid valve 90 is open, allowing an essentially unrestricted flow along the first branch 84 .
- a small additional flow may flow along the second branch 86 , with the combined flow then passing through the first expansion device 88 .
- the first expansion device 88 may be upstream of the branching rather than downstream. Control methods and components (not shown) of this system and those discussed below may be similar to those of the system 60 .
- FIG. 4 shows another system 100 wherein the flow path 102 has first and second segments/branches 104 and 106 between the gas cooler and evaporator.
- a fixed expansion device 108 is located in the first branch 104 .
- a solenoid valve 110 is located in the second branch 106 .
- the solenoid valve 110 combines aspects of a solenoid valve and a fixed expansion device. Specifically, the open condition may still be relatively restricted compared with the open condition of the solenoid valve 90 . Therefore, the pulldown pressure drop through the solenoid valve 110 is significant and the high-side pressure of the system is controlled to the preset constant optimal value by the combination of the solenoid valve 110 and the fixed expansion device. For steady state operation, the solenoid valve 110 is fully closed and all flow passes through the expansion device 108 .
- FIG. 5 shows a branch-less system 120 in which, along the flow path 122 , a solenoid valve 124 and fixed expansion device 126 are located in series.
- the solenoid valve 124 combines aspects of the solenoid valve and a fixed expansion device differently from the valve 1 10 of FIG. 4 .
- the valve element (e.g., the solenoid plunger) of the solenoid valve 124 may have a small orifice so that its closed condition is only a partially closed condition.
- the open condition is an essentially fully open condition with low pressure drop.
- the solenoid valve 124 is in its closed condition passing a relatively low flow and creating a substantial pressure drop (individually and combined with the expansion device 126 ).
- the solenoid valve is open, permitting the flow rate to be dictated essentially solely by the expansion device 126 .
- the series order may be reversed.
- FIG. 6 shows a system 140 combining aspects of the systems 80 and 120 .
- the flow path 142 has two segments/branches 144 and 146 in parallel upstream of a first fixed expansion device 148 .
- the first branch 144 includes a solenoid valve 150 .
- the second branch 146 includes a fixed expansion device 152 .
- the exemplary solenoid valve 150 may, similar to the solenoid valve 124 , have a closed condition that is only partially closed. During pulldown conditions, the solenoid valve 150 is open. During steady state conditions, the valve 150 is closed. In the steady state condition, there is a relatively small flow along each of the branches. During pulldown conditions, a larger flow may pass along the first branch 144 , with a residual flow along the second branch 146 .
- FIG. 7 shows another system 160 wherein the flow path 162 includes a solenoid valve 164 that combines solenoid valve and orifice functions.
- the element of the solenoid valve 144 includes an orifice so that the closed condition is only partially closed.
- the valve 144 is in its closed condition with the orifice passing the relatively small flow.
- the valve is open so that a larger flow is passed.
- FIG. 8 shows a system 180 wherein the flow path 182 includes segments/branches 184 and 186 between the gas cooler and the evaporator.
- a solenoid valve 188 and 190 is located in each of the branches.
- the elements of these solenoid valves may include orifices. Independent control over the valves may provide more than two alternative effective flow restrictions. For example, with different size orifices, the two valves provide up to four different effective restrictions.
- a minimal restriction may be present with both valves open.
- a maximal restriction may be present with both valves closed.
- a pair of intermediate restrictions may be achieved with one of the valves closed and the other open.
- the conduit of the branches may be sized or the valve sized or additional restriction may be present so that with only one valve open there is not essentially free flow.
- An alternative embodiment could feature such valves in series rather than parallel.
- a variety of sensor and/or user inputs may be used to control the solenoid valve(s).
- Direct measurement of the high-side pressure may be made by the sensor 74 . When this pressure exceeds one or more associated thresholds, the controller 76 may cause the valve(s) to assume an associated relatively free-flow condition.
- input may be received from an air temperature sensor.
- the exemplary sensor 75 may be positioned to be exposed to air in or from the cooler interior (e.g., to the flow 36 upstream of the evaporator 28 ). The sensor 75 may form part of a control thermostat. Accordingly, use of such a sensor alone may permit cost savings through the elimination of the pressure sensor 52 or 74 .
- the flow through the system is a direct function of the density of the refrigerant entering the compressor and, to a lesser extent, the pressure ratio of the compressor.
- the inlet density is a direct function of the saturation temperature and superheat of the refrigerant.
- These, in turn, are direct functions of the air temperature, system size, and charge.
- these parameters may be determined in the design stage as a function of air temperature flowing through the evaporator. A correlation can be produced which matches the evaporator air temperature to the refrigerant inlet density.
- the solenoid valve(s) would remain in the open position until the output of the evaporator temperature sensor 75 drops below a predetermined value.
- the solenoid valve or one of the solenoid valves is closed. This can be repeated for systems having multiple solenoid valves further reducing the effective expansion orifice area as the temperature drops so as to maintain a mere optimal pressure in the high pressure portion of the system.
- a high-side pressure is directly measured (e.g., by the sensor 74 ) a different correlation may be used.
- the optimal high-side pressure may be known as a function of evaporator temperature and, optionally, the ambient temperature.
- the solenoid valve or valves may be actuated to maintain the pressure within certain limits.
- FIG. 9 shows an exemplary cooler 200 having a removable cassette 202 containing the refrigerant and air handling systems.
- the exemplary cassette 202 is mounted in a compartment of a base 204 of a housing.
- the housing has an interior volume 206 between left and right side walls, a rear wall/duct 216 , a top wall/duct 218 , a front door 220 , and the base compartment.
- the interior contains a vertical array of shelves 222 holding beverage containers 224 .
- the exemplary cassette 202 draws the air flow 34 through a front grille in the base 224 and discharges the air flow 34 from a rear of the base.
- the cassette may be extractable through the base front by removing or opening the grille.
- the exemplary cassette drives the air flow 36 on a recirculating flow path through the interior 206 via the rear duct 210 and top duct 218 .
- FIG. 10 shows further details of an exemplary cassette 202 .
- the heat exchanger 28 is positioned in a well 240 defined by an insulated wall 242 .
- the heat exchanger i 28 is shown positioned mostly in an upper rear quadrant of the cassette and oriented to pass the air flow 36 generally rearwardly, with an upturn after exiting the heat exchanger so as to discharge from a rear portion o the cassette upper end, a drain 250 may extend through a bottom of the wall 242 to pass water condensed from the flow 36 to a drain pan 252 .
- a water accumulation 254 is shown in the pan 252 .
- the pan 252 is along an air duct 256 passing the flow 34 downstream of the heat exchanger 24 . Exposure of the accumulation 254 to the heated air in the flow 34 may encourage evaporation.
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Abstract
Description
- Benefit is claimed of U.S. patent application Ser. No. 60/663,960, filed Mar. 18, 2005, and entitled “High Side Pressure Regulation for Transcritical Vapor Compression System”, the disclosure of which is incorporated by reference herein as if set forth at length.
- The invention relates to refrigeration. More particularly, the invention relates to beverage coolers.
- As a natural and environmentally benign refrigerant, CO2 (R-744) is attracting significant attention. In most air-conditioning operating ranges, CO2 systems operate in transcritical mode.
FIG. 1 schematically shows transcriticalvapor compression system 20 utilizing CO2 as working fluid. The system comprises acompressor 22, agas cooler 24, anexpansion device 26, and anevaporator 28. The exemplary gas cooler and evaporator may each take the form of a refrigerant-to-air heat exchanger. Airflows across one or both of these heat exchangers may be forced. For example, one ormore fans respective airflows refrigerant flow path 40 includes a suction line extending from an outlet of theevaporator 28 to aninlet 42 of thecompressor 22. A discharge line extends from anoutlet 44 of the compressor to an inlet of the gas cooler. Additional lines connect the gas cooler outlet to expansion device inlet and expansion device outlet to evaporator inlet. - The major difference between transcritical and conventional operation is that heat rejection in the gas cooler is in the supercritical region because the critical temperature for CO2 is 87.8° F. Consequently, pressure is not solely dependent on temperature and this opens additional control and optimization issues for system operation.
- For a fixed gas cooler discharge temperature, as the high side pressure is increased, the exit enthalpy of the refrigerant decreases, yielding a higher differential enthalpy through the gas cooler. The capacity of the gas cooler is a function of the mass flowrate of refrigerant and the enthalpy difference across the gas cooler. For a beverage cooler, the evaporator may be essentially at the cooler interior temperature. It is typically desired to maintain this temperature in a very narrow range regardless of external condition. For example, it may be desired to maintain the interior very close to 37° F. This temperature essentially fixes the steady state compressor suction pressure.
- For a fixed compressor suction pressure, as the high side pressure increases, the amount of energy used by the compressor increases, and the volumetric efficiency of the compressor decreases. When the volumetric efficiency of the compressor decreases, the flowrate through the system decreases. The balance of these two counteracting effects is typically an increase in gas cooler capacity as the high side pressure is increased. However, above a certain pressure the amount of capacity increase becomes very small. Because the expansion device is usually isenthalpic, the evaporator capacity will also typically increase as the high side pressure increases.
- The energy efficiency of a vapor compression system, the Coefficient of Performance (COP), is usually expressed as a ratio of the system capacity to the energy consumed. Because an increase in pressure typically produces both a higher capacity and a higher energy consumption, the balance between the two will dictate the overall COP. Therefore, there is typically an optimal pressure which yields the highest possible performance.
- An electronic expansion valve is usually used as the
device 26 to control the high side pressure to optimize the COP of the CO2 vapor compression system. An electronic expansion valve typically comprises a stepper motor attached to a needle valve to vary the effective valve opening or flow capacity to a large number of possible positions (typically over one hundred). This provides good control of the high side pressure over a large range of operating conditions. The opening of the valve is electronically controlled by acontroller 50 to match the actual high side pressure to the desired set point. This pressure control strategy involves a fairly high cost valve, asophisticated controller 50, and asensor 52 for measuring the high side pressure. This equipment adds a significant amount of cost to the CO2 vapor compression system, causing the CO2 vapor compression system to be less attractive compared to an HFC system. - It is possible to use a fixed expansion device in a transcritical vapor compression system, but this approach has limitations which may cause a loss of performance or functionality. During steady state operation, a fixed expansion device (e.g., a fixed orifice or capillary tube) can work well to regulate the system high side pressure to a near optimum pressure. During pulldown, when the system is started and the evaporation temperature and pressure can be very high, the flowrate through a fixed speed and displacement compressor can become relatively high. This high flowrate can cause the high side pressure to exceed a safe limit.
- An expensive expansion device may be eliminated in favor of a less expensive pressure regulator in a CO2 vapor compression system such as is used in a bottle cooler or small-capacity air conditioner, refrigerator, or other system. The potential for overpressurization may be reduced by using an inexpensive, multi-step fixed expansion device based on one or more solenoid valves.
- The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.
-
FIG. 1 is a schematic of a prior art vapor compression system. -
FIG. 2 is a schematic of a first inventive CO2 vapor compression system. -
FIG. 3 is a schematic of a second inventive CO2 vapor compression system. -
FIG. 4 is a schematic of a third inventive CO2 vapor compression system. -
FIG. 5 is a schematic of a fourth inventive CO2 vapor compression system. -
FIG. 6 is a schematic of a fifth inventive CO2 vapor compression system. -
FIG. 7 is a schematic of a sixth inventive CO2 vapor compression system. -
FIG. 8 is a schematic of a seventh inventive CO2 vapor compression system. -
FIG. 9 is a side schematic view of a display case including a refrigeration and air management cassette. -
FIG. 10 is a view of a refrigeration and air management cassette. - Like reference numbers and designations in the various drawings indicate like elements.
- The current invention relates to high-side pressure optimization for a CO2 vapor compression system. For HVAC & R products which do not have broad operating envelopes, the optimal high side pressures for all operating conditions do not vary much. Therefore, a fixed expansion device (e.g., an orifice or capillary tube) can be used to regulate the high side pressure to a preset constant value for all steady state operating conditions of the CO2 vapor compression system. The preset value should be determined such that the CO2 vapor compression system can achieve the best overall Coefficient of Performance (COP) for the entire operating envelope. Using a fixed expansion device can significantly reduce the cost of the pressure control components in a CO2 vapor compression system.
- For pulldown conditions, the compressor flowrate will be significantly higher than during steady state conditions. The high-side pressure should be optimized such that the pulldown cooling capacity of the CO2 vapor compression system can be maximized, but the flow through the pressure regulator does not exceed the flow through the compressor (so that the system pressure becomes too great). This optimal high-side pressure for maximizing capacity is usually higher than the optimal high-side pressure for maximizing the overall COP. However, because the compressor flowrate is much higher during pulldown conditions than during steady state conditions, the expansion device may be configured to have a larger flow capacity during pulldown conditions. A simple multi-position expansion device may provide this. There are a number of ways through which this can be achieved through the use of solenoid valves to enable a two or more position pressure control system.
- The following examples reflect modifications of the basic system of
FIG. 1 . Accordingly, the same reference numerals are used to identify thecompressor 22,gas cooler 24, andevaporator 28. In any reengineering or remanufacturing situation, these components may be identical to those of the baseline system or may be further modified.FIG. 2 shows asystem 60 in which therefrigerant flow path 62 is split into two parallel branches/segments gas cooler 24 outlet andevaporator 28 inlet. Thefirst branch 64 has a firstfixed expansion device 68. Thesecond branch 66 includes, in series, asolenoid valve 70 and a secondfixed expansion device 72. Although thesolenoid valve 70 is shown upstream of the secondfixed expansion device 72, this order may be reversed. Theexemplary solenoid valve 70 has two settings/conditions. One setting/condition is a fully closed condition in which no flow may pass along thesecond branch 66. The second setting/condition is a fully open condition allowing flow to pass through thesecond branch 66 with a minimal pressure loss across thesolenoid valve 70. - During steady state operating conditions, when the compressor flowrate is relatively low, the
solenoid valve 70 is kept fully closed. During pulldown conditions, the compressor flowrate is relatively high. In order to avoid overpressurization during pulldown, thesolenoid valve 70 is opened, allowing flow through the secondfixed expansion device 72. The combination of bothexpansion devices - In operation, a pulldown condition may be detected by means of one or
more temperature sensors 75 andpressure sensor 74 coupled to acontroller 76 coupled to control thesolenoid valve 70. Thecontroller 76 may also be coupled to the compressor and/or fan(s) to control their respective operation. For ease of illustration, the sensor and controller are not illustrated in the following examples although they may be present. -
FIG. 3 shows asystem 80 wherein therefrigerant flow path 82 has two segments/branches fixed expansion device 88. Thefirst branch 84 includes asolenoid valve 90. Thesecond branch 86 includes a secondfixed expansion device 92. During steady state operating conditions, thesolenoid valve 90 is closed to prevent flow along thefirst branch 84. Thesecond branch 86 acts as a bypass with restricted flow passing through the secondfixed expansion device 92 before then passing through the firstfixed expansion device 88. During pulldown conditions, thesolenoid valve 90 is open, allowing an essentially unrestricted flow along thefirst branch 84. A small additional flow may flow along thesecond branch 86, with the combined flow then passing through thefirst expansion device 88. In alternative embodiments, thefirst expansion device 88 may be upstream of the branching rather than downstream. Control methods and components (not shown) of this system and those discussed below may be similar to those of thesystem 60. -
FIG. 4 shows anothersystem 100 wherein theflow path 102 has first and second segments/branches expansion device 108 is located in thefirst branch 104. Asolenoid valve 110 is located in thesecond branch 106. Thesolenoid valve 110 combines aspects of a solenoid valve and a fixed expansion device. Specifically, the open condition may still be relatively restricted compared with the open condition of thesolenoid valve 90. Therefore, the pulldown pressure drop through thesolenoid valve 110 is significant and the high-side pressure of the system is controlled to the preset constant optimal value by the combination of thesolenoid valve 110 and the fixed expansion device. For steady state operation, thesolenoid valve 110 is fully closed and all flow passes through theexpansion device 108. -
FIG. 5 shows abranch-less system 120 in which, along theflow path 122, asolenoid valve 124 and fixedexpansion device 126 are located in series. Thesolenoid valve 124 combines aspects of the solenoid valve and a fixed expansion device differently from the valve 1 10 ofFIG. 4 . Specifically, the valve element (e.g., the solenoid plunger) of thesolenoid valve 124 may have a small orifice so that its closed condition is only a partially closed condition. The open condition, however, is an essentially fully open condition with low pressure drop. Accordingly, during steady state operating conditions, thesolenoid valve 124 is in its closed condition passing a relatively low flow and creating a substantial pressure drop (individually and combined with the expansion device 126). In the steady state condition, the solenoid valve is open, permitting the flow rate to be dictated essentially solely by theexpansion device 126. As with the other systems, the series order may be reversed. -
FIG. 6 shows asystem 140 combining aspects of thesystems flow path 142 has two segments/branches fixed expansion device 148. Thefirst branch 144 includes asolenoid valve 150. Thesecond branch 146 includes a fixedexpansion device 152. Theexemplary solenoid valve 150 may, similar to thesolenoid valve 124, have a closed condition that is only partially closed. During pulldown conditions, thesolenoid valve 150 is open. During steady state conditions, thevalve 150 is closed. In the steady state condition, there is a relatively small flow along each of the branches. During pulldown conditions, a larger flow may pass along thefirst branch 144, with a residual flow along thesecond branch 146. -
FIG. 7 shows anothersystem 160 wherein theflow path 162 includes asolenoid valve 164 that combines solenoid valve and orifice functions. Specifically, the element of thesolenoid valve 144 includes an orifice so that the closed condition is only partially closed. During steady state conditions, thevalve 144 is in its closed condition with the orifice passing the relatively small flow. During pulldown conditions, the valve is open so that a larger flow is passed. -
FIG. 8 shows asystem 180 wherein theflow path 182 includes segments/branches solenoid valve - A variety of sensor and/or user inputs may be used to control the solenoid valve(s). Direct measurement of the high-side pressure may be made by the
sensor 74. When this pressure exceeds one or more associated thresholds, thecontroller 76 may cause the valve(s) to assume an associated relatively free-flow condition. Alternatively or in addition to high-side pressure measurement would besensor 74, input may be received from an air temperature sensor. Theexemplary sensor 75 may be positioned to be exposed to air in or from the cooler interior (e.g., to theflow 36 upstream of the evaporator 28). Thesensor 75 may form part of a control thermostat. Accordingly, use of such a sensor alone may permit cost savings through the elimination of thepressure sensor - For fixed speed and displacement compressor, the flow through the system is a direct function of the density of the refrigerant entering the compressor and, to a lesser extent, the pressure ratio of the compressor. The inlet density is a direct function of the saturation temperature and superheat of the refrigerant. These, in turn, are direct functions of the air temperature, system size, and charge. For a simple system, these parameters may be determined in the design stage as a function of air temperature flowing through the evaporator. A correlation can be produced which matches the evaporator air temperature to the refrigerant inlet density. In operation, the solenoid valve(s) would remain in the open position until the output of the
evaporator temperature sensor 75 drops below a predetermined value. When this happens, the solenoid valve or one of the solenoid valves is closed. This can be repeated for systems having multiple solenoid valves further reducing the effective expansion orifice area as the temperature drops so as to maintain a mere optimal pressure in the high pressure portion of the system. - If a high-side pressure is directly measured (e.g., by the sensor 74) a different correlation may be used. The optimal high-side pressure may be known as a function of evaporator temperature and, optionally, the ambient temperature. The solenoid valve or valves may be actuated to maintain the pressure within certain limits.
-
FIG. 9 shows anexemplary cooler 200 having aremovable cassette 202 containing the refrigerant and air handling systems. Theexemplary cassette 202 is mounted in a compartment of abase 204 of a housing. The housing has aninterior volume 206 between left and right side walls, a rear wall/duct 216, a top wall/duct 218, afront door 220, and the base compartment. The interior contains a vertical array ofshelves 222 holdingbeverage containers 224. - The
exemplary cassette 202 draws theair flow 34 through a front grille in thebase 224 and discharges theair flow 34 from a rear of the base. The cassette may be extractable through the base front by removing or opening the grille. The exemplary cassette drives theair flow 36 on a recirculating flow path through the interior 206 via therear duct 210 andtop duct 218. -
FIG. 10 shows further details of anexemplary cassette 202. Theheat exchanger 28 is positioned in a well 240 defined by aninsulated wall 242. The heat exchanger i28 is shown positioned mostly in an upper rear quadrant of the cassette and oriented to pass theair flow 36 generally rearwardly, with an upturn after exiting the heat exchanger so as to discharge from a rear portion o the cassette upper end, adrain 250 may extend through a bottom of thewall 242 to pass water condensed from theflow 36 to adrain pan 252. Awater accumulation 254 is shown in thepan 252. Thepan 252 is along anair duct 256 passing theflow 34 downstream of theheat exchanger 24. Exposure of theaccumulation 254 to the heated air in theflow 34 may encourage evaporation. - One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, when implemented as a remanufacturing of an existing system or reengineering of an existing system configuration, details of the existing configuration may influence details of the implementation. Accordingly, other embodiments are within the scope of the following claims.
Claims (11)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US11/908,629 US20080202140A1 (en) | 2005-03-18 | 2005-12-30 | High Side Pressure Regulation For Transcritical Vapor Compression System |
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US66396005P | 2005-03-18 | 2005-03-18 | |
US11/908,629 US20080202140A1 (en) | 2005-03-18 | 2005-12-30 | High Side Pressure Regulation For Transcritical Vapor Compression System |
PCT/US2005/047528 WO2006101566A1 (en) | 2005-03-18 | 2005-12-30 | High side pressure regulation for transcritical vapor compression |
Publications (1)
Publication Number | Publication Date |
---|---|
US20080202140A1 true US20080202140A1 (en) | 2008-08-28 |
Family
ID=37024108
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US11/908,629 Abandoned US20080202140A1 (en) | 2005-03-18 | 2005-12-30 | High Side Pressure Regulation For Transcritical Vapor Compression System |
Country Status (6)
Country | Link |
---|---|
US (1) | US20080202140A1 (en) |
EP (1) | EP1963760A4 (en) |
JP (1) | JP2008533428A (en) |
CN (1) | CN101142450B (en) |
HK (1) | HK1118600A1 (en) |
WO (1) | WO2006101566A1 (en) |
Cited By (5)
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---|---|---|---|---|
US20080256974A1 (en) * | 2005-03-18 | 2008-10-23 | Carrier Commercial Refrigeration, Inc. | Condensate Heat Transfer for Transcritical Carbon Dioxide Refrigeration System |
US20100300127A1 (en) * | 2007-10-17 | 2010-12-02 | Carrier Corporation | Refrigerated Case |
US20130233009A1 (en) * | 2012-03-08 | 2013-09-12 | Toromont Industries Ltd | Co2 refrigeration system for ice-playing surface |
US20150168036A1 (en) * | 2013-12-17 | 2015-06-18 | Lennox Industries Inc. | Managing high pressure events in air conditioners |
CN111351273A (en) * | 2020-04-13 | 2020-06-30 | 宁波奥克斯电气股份有限公司 | Throttling mechanism, air conditioner and throttling control method |
Families Citing this family (2)
Publication number | Priority date | Publication date | Assignee | Title |
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WO2010000088A1 (en) * | 2008-06-30 | 2010-01-07 | Carrier Corporation | Remote refrigeration display case system |
WO2010039630A2 (en) * | 2008-10-01 | 2010-04-08 | Carrier Corporation | High-side pressure control for transcritical refrigeration system |
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Also Published As
Publication number | Publication date |
---|---|
WO2006101566A1 (en) | 2006-09-28 |
EP1963760A1 (en) | 2008-09-03 |
EP1963760A4 (en) | 2011-03-09 |
CN101142450A (en) | 2008-03-12 |
JP2008533428A (en) | 2008-08-21 |
HK1118600A1 (en) | 2009-02-13 |
CN101142450B (en) | 2011-06-22 |
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Legal Events
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AS | Assignment |
Owner name: CARRIER COMMERCIAL REFRIGERATION, INC., NORTH CARO Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:SIENEL, TOBIAS H.;CHEN, YU;REEL/FRAME:017266/0928 Effective date: 20060201 Owner name: CARRIER COMMERCIAL REFRIGERATION, INC.,NORTH CAROL Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:SIENEL, TOBIAS H.;CHEN, YU;REEL/FRAME:017266/0928 Effective date: 20060201 |
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STCB | Information on status: application discontinuation |
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