Transcritical Refrigeration With Pressure Addition Relief Valve
A refrigeration system (20) includes a pressure addition relief valve (62) in parallel with an expansion device (63).
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Benefit is claimed of U.S. Patent Application 60/663,959, entitled TRANSCRITICAL REFRIGERATION WITH PRESSURE ADDITION RELIEF VALVE, and filed Mar. 18, 2005. Copending International Application docket 05-258-WO, entitled HIGH SIDE PRESSURE REGULATION FOR TRANSCRITICAL VAPOR COMPRESSION SYSTEM and filed on even date herewith, discloses prior art and inventive cooler systems. The present application discloses possible modifications to such systems The disclosures of said two applications are incorporated by reference herein as if set forth at length.
BACKGROUND OF THE INVENTIONThe invention relates to refrigeration. More particularly, the invention relates to transcritical refrigeration systems such as CO2 beverage coolers.
Transcritical vapor compression systems have an extra degree of control freedom when compared to subcritical vapor compression systems. In subcritical systems, pressure in the high and low pressure components of the system are largely controlled by the heat exchanger fluid temperatures. If the system is an air-to-air system, the evaporator pressure is a strong function of the air temperature entering the evaporator, and the condenser pressure is a strong function of the air temperature entering the condenser. This is because these temperatures are closely correlated with the saturation pressures in the heat exchangers. In a transcritical system, the high pressure side of the system does not have any saturation properties, and thus pressure is independent from temperature. It is well known that the choice of the high side pressure has a very strong effect on the performance of the system, and that there is an optimal pressure which provides maximum energy efficiency. This optimal pressure will change as the operating conditions of the unit change. Control of the high side pressure can be achieved in many different ways, but for systems which have fixed speed and volume compressors, the strongest influence is through the expansion device.
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 a controller 50 to match the actual high side pressure to the desired set point. The controller 50 is coupled to a sensor 52 for measuring the high side pressure.
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.
Like reference numbers and designations in the various drawings indicate like elements.
DETAILED DESCRIPTIONA pressure addition relief valve (PARV) may be used in combination with a primary expansion device.
The exemplary valve 68 (
The membrane has a front face/surface 86 normally engaged/sealed to a seat surface 88 of the body main portion 80. The volumes 76 and 78 have respective ports 90 and 92 in the surface 88. The ports 90 and 92 are normally blocked by engagement with membrane front face 86. The engagement may be assisted by a biasing spring 94 if the particular membrane is not sufficiently self sprung (e.g., a film rather than a metal sheet spring). An exemplary biasing spring 94 is a coil compression spring having a first end 96 engaging the backside/face 98 and a second end 100 engaging an underside 102 of the cover 82. A membrane backside volume (backspace) 104 is formed containing the spring. A port 106 in the cover may expose the backside volume 104 to a reference pressure. The reference pressure may be ambient air pressure, may be a vacuum or other sealed fixed pressure (in which case, the port 106 might be omitted), or a pressure dependent upon a system condition (e.g., connected via a conduit 108 to a TXV-type bulb 110 located elsewhere in the system to provide a variable pressure force). This backside pressure serves to maintain the membrane in its closed condition.
The pressures in the high and low pressure volumes 76 and 78 act on the membrane with forces based upon the relative areas of their ports 90 and 92 and in view of mechanical advantage factors such as port positioning. These pressures act counter to the pressure of the backside volume 104. If the relative balance of the
If the effect of combined high pressure and low pressure forces exceed the effect of backside pressure and spring force on the backside of the membrane, then the membrane will flex outward to an open condition (
The PARV is used in combination with a primary expansion device to provide a better mechanism for controlling the high pressure. The primary expansion device can be a simple orifice as discussed further below, or can be another type of expansion device, such as a capillary tube, TXV, EXV, or other valve. For example, a TXV type valve can be used with the bulb sensing the temperature of the exit of the gas cooler or condenser in one embodiment. In another, a dual bulb TXV can be used to sense the air temperature and gas cooler or condenser discharge difference.
In the
An exemplary system design may reflect specific design external (ambient) and internal temperatures. An exemplary design ambient temperature is 90° F. (32° C.). An exemplary design pulldown temperature is 16° F. (−9° C.).
A theoretical optimal control is that which yields the highest possible COP.
A particular area for implementation of the PARV is in bottle coolers, including those which may be positioned outdoors or must have the capability to be outdoors (presenting large variations in ambient temperature).
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.
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
1. A cooler system comprising:
- a compressor (22) for driving a refrigerant along a flow path in at least a first mode of system operation;
- a first heat exchanger (24) along the flow path downstream of the compressor in the first mode so as to act as a gas cooler;
- a second heat exchanger (28) along the flow path upstream of the compressor in the first mode so as to act as an evaporator to cool contents of an interior volume of the system;
- an expansion device (63) in the flow path downstream of the first heat exchanger (24) and upstream of the second heat exchanger (28); and
- a pressure addition relief valve (62) in parallel with the expansion device.
2. The system of claim 1 wherein:
- the pressure addition relief valve (62) is a purely mechanical valve.
3. The system of claim 1 wherein:
- the expansion device (63) is a purely mechanical device.
4. The system of claim 1 wherein:
- the pressure addition relief valve (62) is normally closed and configured to open responsive to a combined force produced by pressures essentially respectively immediately downstream of the first heat exchanger and upstream of the second heat exchanger.
5. The system of claim 4 wherein:
- a bias force acts opposite the combined force, the bias force comprising at least one of: a supplemental spring (94) bias force; a bias force provided by a system condition sensor (110); and a bias force exerted by ambient air pressure.
6. The system of claim 1 wherein:
- the pressure addition relief valve (62) is integral with the expansion device (63).
7. The system of claim 1 wherein:
- the expansion device (63) comprises a fixed orifice (120) in a common body (70) of the pressure addition relief valve.
8. The system of claim 1 wherein:
- the expansion device (63) comprises non-EEV device.
9. The system of claim 1 wherein:
- the pressure addition relief valve comprises a sheet metal spring membrane (84) and no other spring.
10. The system of claim 1 wherein:
- the pressure addition relief valve comprises a membrane (84) and a coil biasing spring (94).
11. The system of claim 1 wherein:
- flowpath portions upstream (76) and downstream (78) of the expansion device have effective counterbias areas of the pressure addition relief valve, the lesser being no less than 10% of the greater.
12. The system of claim 1 being a self-contained externally electrically powered beverage cooler positioned outdoors.
13. The system of claim 1 wherein:
- the refrigerant comprises, in major mass part, CO2; and
- the first and second heat exchangers are refrigerant-air heat exchangers.
14. The system of claim 1 wherein:
- the refrigerant consists essentially of CO2; and
- the first (24) and second (28) heat exchangers are refrigerant-air heat exchangers each having an associated fan (30; 32), an air flow across the first heat exchanger being an external to external flow and an airflow across the second heat exchanger being a recirculating internal flow.
15. The system of claim 1 in combination with said contents which include:
- a plurality of beverage containers in a 0.3-4.0 liter size range.
16. The system of claim 15 being selected from the group consisting of:
- a cash-operated vending machine;
- a transparent door front, closed back, display case; and
- a top access cooler chest.
17. A transcritical CO2 refrigeration system comprising:
- a compressor (22) for driving a refrigerant along a flow path in at least a first mode of system operation;
- a first heat exchanger (24) along the flow path downstream of the compressor in the first mode so as to act as a gas cooler;
- a second heat exchanger (28) along the flow path upstream of the compressor in the first mode so as to act as an evaporator;
- an expansion device (63) in the flow path downstream of the first heat exchanger (24) and upstream of the second heat exchanger (28); and
- a pressure addition relief valve (62) in parallel with the expansion device.
18. A method for operating a transcritical CO2 refrigeration system comprising: wherein:
- compressing and driving a refrigerant along a flow path in at least a first mode of system operation;
- cooling the compressed refrigerant along the flow path downstream of the compressing;
- expanding the cooled refrigerant; and
- heating the expanded refrigerant;
- the expanding comprises a mechanically automated varying of an effective flow restriction based upon an additive combination of forces from pressures respectively upstream and downstream of the restriction.
19. A method for remanufacturing a transcritical CO2 refrigeration system or reengineering a configuration thereof wherein a baseline configuration comprises: the method comprising at least one of:
- a compressor (22) for driving a refrigerant along a flow path in at least a first mode of system operation;
- a first heat exchanger (24) along the flow path downstream of the compressor in the first mode so as to act as a gas cooler;
- a second heat exchanger (28) along the flow path upstream of the compressor in the first mode so as to act as an evaporator; and
- an expansion device (26) in the flow path downstream of the first heat exchanger (24) and upstream of the second heat exchanger (28),
- adding a pressure addition relief valve (62) in parallel with the expansion device (26); and
- replacing the expansion device (26) with a pressure addition relief valve (62) and a structurally different expansion device (63).
Type: Application
Filed: Dec 31, 2005
Publication Date: Aug 7, 2008
Applicant: Carrier Commercial Refrigeration, Inc. (Charlotte, NC)
Inventors: Tobias H. Sienel (East Hampton, MA), Yu Chen (East Hartford, CT), Hans-Joachim Huff (West Hartford, CT), Parmesh Verma (Manchester, CT)
Application Number: 11/908,619
International Classification: F25B 41/04 (20060101); F25B 41/00 (20060101);