Refrigeration System With Subcooler

Abstract

A secondary or booster refrigeration system associated with a primary refrigeration system so that high temperature liquid refrigerant of the primary system is itself subcooled by refrigeration after it has been condensed. The secondary or booster refrigeration system is situated so that the evaporation coil is in heat exchange relation with that portion of the primary refrigeration circuit carrying the condensed liquid refrigerant. Optionally, the secondary or booster refrigeration system may itself be liquid subcooled by heat exchange with the suction line of the primary refrigeration system. Operational control of the secondary refrigeration system is achieved by means responsive to the temperature and/or humidity in the space cooled by the primary refrigeration system and/or the ambient temperature in the vicinity of the condenser of the primary refrigeration system.

Parent Case Text

This is a continuation-in-part of my copending application Ser. No. 204,554, filed Dec. 3, 1971, now abandoned.

Description

BACKGROUND

1. Field of the Invention

The present invention relates to refrigeration systems and more particularly to improved refrigeration booster apparatus and method for increasing the capacity of a refrigeration system.

2. The Prior Art

In refrigeration systems, gaseous refrigerant is compressed by a compressor so as to maintain the refrigerant under substantial pressure. This compression step results in raising the temperature of the refrigerant. Thereafter, the compressed gaseous refrigerant is condensed, usually by a heat exchange-type condenser, into liquid form. The liquid refrigerant is then evaporated in an evaporation coil. The evaporation is a cooling or refrigerating step which results in decreasing the temperature around the evaporation coil to a low point.

The temperature at which the gaseous refrigerant is condensed to liquid is called the condensing temperature. The term "subcooling" as used in this specification means any reduction of the temperature of liquid refrigerant below its condensing temperature. Historically, varieties of ways have been used to produce greater refrigerating capacity in the evaporation coil. A common approach is that of increasing the volume of refrigerant to be handled by the refrigeration system. For example, the compressor for the refrigeration system should have a capacity of about one-half to ten horsepower per ton (12,000 BTUs per hour heat) depending upon how low a temperature is desired in the evaporating coil. If the evaporating coil is operating at, for example, -20.degree.F and it is desired to reduce the temperature in the evaporating coil to -40.degree.F, normally the compressor is replaced by a larger compressor or a compound compressor system which is connected in series so that the compression capacity is substantially increased. It should be observed that the capacity of the compressors must be increased by as much as 50 percent to reduce the temperature in the evaporating coil the addition 20.degree. from -20.degree.F to -40.degree.F because of the difficulty of removing heat from an already low temperature site.

Increasing the compression capacity and refrigerant volume of the refrigeration system has some distinct disadvantages. For example, the costs involved with purchasing compressors having 50 percent greater capacity or in acquiring another compressor system and the attendant increased refrigeration lines, power supplies and the like to handle the greater refrigerant volume makes this method extremely expensive. Moreover, if it is desired to increase the capacity of an existing refrigeration system using prior art techniques, all of the refrigeration lines in the system must be replaced with larger lines so that the additional volume of refrigerant can be accommodated or the efficiency of the system is adversely affected.

The expense and inconvenience of this requirement can be best illustrated by referring to the example of grocery store freezer units which normally have the refrigeration lines buried in the floor and traversing substantial distances to frozen food cases located at various locations around the grocery store. When it is desired to increase the refrigerating capacity of the system servicing the freezer units, the floors must be broken up to expose the refrigeration lines to accommodate replacement of the refrigeration lines.

As an alternative to increasing the compression capacity and refrigerant flow rate, several prior art techniques have improved the efficiency of a refrigeration system by reducing the superheat existing in the compressed gaseous refrigerant between the compressor and the condenser. For example, see U.S. Pat. No. 2,960,837. This approach improves only the capacity of the condenser.

Where cascade or large capacity refrigeration systems are used to obtain low evaporation coil temperatures, it is also common to endeavor to improve the efficiency of the refrigeration system by reducing the condensing temperature of compressed gaseous refrigerant to liquid refrigerant. Examples of this technique can be found in U.S. Pat. Nos. 2,680,956 and 2,453,823. From the mentioned patents and numerous other prior art sources, it is known to be conventional to couple a refrigeration system with the condenser of a second refrigeration system to improve the condensation process.

Nevertheless, it is well-known that regardless of how low the temperature is reduced in the condenser, the temperature of the condensed liquid emerging from the condenser will always be approximately the condensation temperature of the particular refrigerant used. Accordingly, even though refrigeration systems are used to reduce the temperature in the condenser, the condensed liquid refrigerant will nevertheless emerge from the condenser at approximately the condensing temperature of the refrigerant.

In previously known attempts to increase the capacity of refrigeration systems, suction gas has been brought into heat exchange with the condensed refrigerant for subcooling purposes. While suction gas-liquid heat exchangers are frequently used, it is well-known that they are limited in their subcooling ability to about one-third of the temperature difference between the entering liquid and the entering gas. Moreover, a pressure drop inevitably results in the suction line because of the heat exchanger thereby reducing the efficiency of the compressor.

A persistent problem in using conventional refrigeration circuits for food storage and other temperature-sensitive units has been the dehydration of food. It has been found that dehydration is greatest when the difference between the temperature of the evaporation coil and the air in the unit is large. One explanation for dehydration in this circumstance is that moisture in the unit accumulates on the coil as frost thereby continuously drawing moisture from the food storage unit.

In climates where there are large temperature differences in summer and winter, conventional refrigeration systems must have sufficient capacity to operate at a desired low temperature even in the heat of summer. Accordingly, when cold winter temperatures occur, the conventional systems have excess capacity which, in addition to the increased expense of operation and maintenance, undesirably creates temperatures in the evaporation coil so low that dehydration inevitably results.

In many instances, a refrigeration system is used principally to maintain a desired low temperature with very little fluctuation in the work load requirement placed upon it. With this knowledge, it is possible to very closely design the refrigeration system thus greatly reducing the equipment costs for such a system. However, certain excessive load requirements may be placed upon the refrigeration system and thus exceed the refrigeration system's capacity for handling such a load requirement. An example of such an unusual circumstance that may confront an existing refrigeration system would be by placement of a large quantity of material requiring cooling or very high ambient temperatures in the vicinity of the condenser coils thus lowering the capacity of the refrigeration system. It is, therefore, suggested that another distinct advantage of this invention is that of modifying an existing refrigeration system with a smaller, less expensive refrigeration system which would be selectively controlled to act as a booster for the existing refrigeration system. In this way, it is possible to operate the existing or primary refrigeration system as a temperature maintenance system but being able also to increase the refrigeration capacity of the existing system.

High humidity conditions within the cooling chamber would cause increased condensation or frost accumulation on the evaporator coils and would place an increased work requirement on the existing refrigeration system. A condition of high ambient temperature coupled with a high relative humidity would create a demand upon the capacity of the system.

However, continued operation of the secondary refrigeration system under all circumstances would not only be unnecessary but wasteful. For example, very low humidity conditions within the cooling chamber result in excessive moisture being removed from the products within the cooling chamber by condensation on very cold evaporation coil surfaces thus causing undesirable dehydration sometimes called freezer burn. Such a circumstance would arise, for example, if there were a condition of low ambient temperatures within the vicinity of a condenser coil thereby greatly increasing the thermal capacity, hence the thermal efficiency of the entire unit.

BRIEF SUMMARY AND OBJECTS OF THE INVENTION

It has been found according to the present invention that a high temperature liquid line in a main refrigeration system can be subcooled with a small auxiliary or booster refrigeration system to increase the refrigeration effect of the existing volume of refrigerant so that the capacity of the refrigeration system is increased without increasing the volume of refrigerant handled by the system. Because the booster system operates on the high temperature liquid line, where temperature is most easily and efficiently reduced, the heat in the high temperature liquid line can be removed with a much smaller compressor capacity than would be required if the main refrigeration system itself were enlarged to produce the same increase in refrigerating effect. Accordingly, when the subcoded liquid passes through the expansion valve into the evaporating coil, surprising increases in refrigeration capacity can be obtained without large, expensive compressors and without replacing coolant lines. Moreover, the auxiliary system can be selectively shut down without interference with the main system so as to minimize dehydration of food, where desired.

Operational control of the secondary or booster refrigeration system is achieved by monitoring preselected conditions affecting the capacity of the primary refrigeration system and selectively activating or deactivating the secondary refrigeration system in response to these conditions.

It is, therefore, a primary object of the present invention to provide an improved refrigeration system.

It is another primary object of the present invention to provide novel method and apparatus for subcooling the high temperature liquid line of a refrigeration system to achieve increased capacity in the system.

One still further valuable object of the present invention is to provide method and apparatus for improving the capacity of an existing refrigeration system without at the same time requiring replacement or supplementation of the compression capacity or refrigerant volume circulated.

An even further object of this invention is to provide a primary refrigeration system and a secondary refrigeration system acting in liquid sub-cooling relation therewith wherein operation of the secondary refrigeration system is determined by temperatures within the conditioned space of the primary refrigeration system.

Another object of this invention is to provide a primary refrigeration system and a secondary refrigeration system acting in liquid sub-cooling relation therewith wherein operation of the secondary refrigeration system is determined by ambient temperatures in the vicinity of the condenser coils of the primary refrigeration system.

Still another object of this invention is to provide a primary refrigeration system and a secondary refrigeration system acting in liquid sub-cooling relation therewith wherein operation of the secondary refrigeration system is determined by humidity within the conditioned space of the primary refrigeration system.

These and other objects and features of the present invention will become more fully apparent from the following description and appended claims taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is a schematic circuit diagram illustrating primary and secondary refrigeration circuits in heat exchange one with another according to the presently preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference is now made to the FIGURE illustrating presently preferred embodiments of the invention. It is pointed out that all temperatures used in this specification are for illustrative purposes and are only representative of any of a wide range of applicable temperatures, depending upon the size and refrigerant capacity of the system and the type of refrigerant used.

A primary refrigeration circuit generally designated 10 includes a refrigerant compressor 12 which may be of any suitable conventional compressor having a desired capacity. Refrigerant vapor compressed by the compressor 12 is transferred through conduit 14 at a temperature of, for example, 200.degree.F to a condenser 16. Any suitable type of condenser can be used which has the ability to reduce the temperature of the refrigerant vapor to its condensing temperature of, for example, 130.degree.F and to remove its heat of vaporization sufficient to transform the high pressure refrigerant vapor in conduit 14 to a liquid as the refrigerant emerges in line 18. Most commonly, condensers are of the heat-exchange variety which use fluids, such as water or air, to remove heat energy from the refrigerant in line 14 sufficiently to accommodate condensation. However, if desired, the condenser 16 may also be refrigeration cooled as, for example, illustrated and described in U.S. Pat. No. 2,680,956.

The liquid refrigerant emerges from the condenser 16 in line 18 at, for example, about 125.degree.F. Thereafter, the liquid refrigerant is exposed to the evaporation coil 20 of the secondary refrigeration system generally designated 22 for the purpose and in a manner hereinafter more fully described.

Commonly, liquid refrigerant is conducted to a conventional heat exchanger 26 disposed in heat exchange relation with suction line 28. The liquid refrigerant, emerging from the heat exchanger 26 is subcooled by the heat exchange and then conducted to an expansion valve 30. The liquid refrigerant is allowed to expand to vapor through the expansion valve 30 into the evaporation coil 32. Alternatively, other suitable liquid flow control devices could be used in lieu of expansion valves. The vaporization of the liquid by the expansion step and consequent absorption of its heat of vaporization is the principal cooling step in the refrigeration cycle and results in a substantial reduction of temperature in the area surrounding the expansion coil 32. Significantly, the higher the temperature of the liquid refrigerant at the expansion valve 30 the more pounds of refrigerant that must be vaporized to maintain the evaporation coil 32 at, for example, -40.degree.F.

Accordingly, the location of the heat exchanger 26 on the suction line 28 takes advantage of the low temperature of the vaporized refrigerant existing in the suction line 28 to subcool the liquid refrigerant with the vaporized refrigerant as it emerges from the evaporating coil 32. Nevertheless, the use of the heat exchanger 26 is not essential in a refrigeration system nor is it essential in the illustrated embodiment of this invention. Alternatively, the line 18 could be connected directly to the expansion valve 30.

The expansion valve 30 is thermostatically operated by a thermal control element 34 in a conventional manner. The thermal control element 34 is sensitive to the temperature in the suction line and the pressure of the system in the evaporator coil 32. Thermal control element 34 controls the opening in the expansion valve 30 so as to determine the admission of refrigerant to the evaporation coil 32 and simultaneously preclude passage of liquid refrigerant to compressor 12 where it could cause considerable damage.

The vaporized refrigerant in the suction line 28 absorbs heat from liquid refrigerant in line 18 by the heat exchange relation in heat exchanger 26 and is thereafter returned to the intake or suction port of the compressor 12. The description of the foregoing primary refrigeration circuit relates to conventional refrigeration systems, except that portion affected by the secondary refrigeration circuit 22, which will now be more fully described.

A compressor 40 compresses refrigerant which is thereafter conducted in conduit 42 to a conventional condenser 44. The condenser 44 may be similar to condenser 16, if desired. Refrigerant emerging from the condenser 44 is in liquid form and may be further cooled by contact with suction line 28. The liquid subcooling is easily accomplished by conducting the condensed liquid refrigerant from line 42 to a heat exchanger 60, situated at suction line 28. The liquid is subcooled by the suction gas which is at about -10.degree.F. The subcooled liquid is then passed to the expansion valve 48. This technique advantageously subcools the liquid from, for example, about 125.degree.F to 80.degree.F. Heat exchanger 60 is optional and the liquid refrigerant from the secondary condenser 44 could be passed directly into expansion valve 48. Preferably, evaporation coil 20 is situated in heat exchange relation with the line 18 of the refrigeration circuit 10. Alternatively, the evaporation coil 20 could be disposed in heat exchange relation with line 29. The admission of the liquid refrigerant through the expansion valve 48 to the evaporation coil 20 is determined by the thermal control element 50. Thermal control element 50 is situated adjacent the suction line 52 of compressor 40. It is clear that the refrigeration circuit 22 is closed with respect to circuit 10 and different types of refrigerant can be used for each circuit if desired.

The heat available in line 42 of the booster system 22 can be used, if desired. For example, where used with frozen food fixtures, moisture condensation, frost or uncomfortably cold surfaces for contact can be prevented by using the heat in line 42. Thus, the use of separate heaters and the like can be avoided. The use of heat in this manner may, in some cases, eliminate the need for or reduce the size of condenser 44.

Using a refrigerated subcooling booster 22 has been found to have surprising and advantageous effects upon the refrigeration circuit 10. It has been found, for example, that heat can be removed from line 18 or 29 with a far smaller compressor and lower horsepower requirements than would be necessary to remove the same amount of heat at the evaporation coil 32 by increasing the size of circuit 10. This is true because refrigeration systems are more efficient at removing heat at the high temperature of about 125.degree.F than at very low temperatures, for example, -40.degree.F. Accordingly, when the liquid refrigerant in line 18 is subcooled by refrigeration of circuit 22 to, for example, 30.degree.F, the refrigerating effect of each pound of liquid refrigerant fed to the evaporating coil 32 is substantially increased.

The advantage of using the secondary or booster refrigeration system 22 will be more fully understood by continued reference to the drawing. First, existing refrigeration systems can be improved to have substantially greater capacity without acquiring larger compressors or without implementing a cascade-type compressor system. In addition, the refrigeration lines will not need to be replaced to accommodate larger refrigerant flow rates. Moreover, because it is much more efficient to remove heat in a high temperature line than in a low temperature line, the horsepower requirement to remove heat through system 22 is much lower than that required to remove the same amount of heat by increasing the size of system 10 alone. Thus, costs of improving the refrigeration system are substantially reduced.

One advantage of the above-described invention is in making it possible for one to adjust the refrigeration system to balance the coil-ambient temperature and to compensate for difference in seasonal temperatures in which the system operates. Thus, in geographic areas where a wide range of temperatures is encountered during the year, the sub-cooling booster may be selectively switched on during the periods when the ambient temperature surrounding the main condenser 16 is relatively high such as during the summer months. During winter months the booster system 22 may be switched off, thereby conserving operational costs during the period when the main system is more efficient.

Where a system is designed for dehumidified storage as required by some products, the booster 22 can most efficiently facilitate that design and provide a means of controlling the relative humidity by cycling the booster system off to maintain a control point of relative humidity. The humidity is reduced when the booster system is on.

The conditions which affect the capacity of the primary system are monitored with conventional monitoring devices including, for example, thermostats, humidistats, thermometers, hygrometers and the like (not shown). These sensing devices are preferably connected to a suitable control terminal 62. The operational state of the secondary refrigeration system 22 is desirably controlled through control terminal 62.

In operation, the secondary system 22 is off when the temperature in the conditioned space is adequately maintained by the primary system. However, when the temperature in the conditioned space is raised significantly, the temperature change will be sensed and indicated at the control terminal. The secondary system is then actuated to boost the capacity of the primary system. Similarly, when the capacity of the primary system is reduced due to high ambient temperatures at the primary condenser, that condition appears at the control terminal and the secondary system is energized. Moreover, the operating costs for removal of a given quantity of heat is less with both the primary and secondary systems operating than normally incurred by a single system having the same capacity. Thus, this embodiment of the invention is desirable whenever control of humidity within the space is desirable.

In the event the humidity in the conditioned space is reduced to a detrimental level, operation of the secondary system will be terminated to avoid dehydration. Under some circumstances, the existence of low humidity and need for increased capacity in the primary system may require a priority determination as to whether the humidity or temperature sensors control the operation of the secondary system 22. The determination of priority will likely turn on the nature of goods in the conditioned space. Under most circumstances, temperature should control and the effect of the humidity monitor is made subservient to the temperature monitors according to techniques well-known in the art. However, where humidity considerations are of primary concern, temperature conditions can be made subservient.

The invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiment is to be considered in all respects only as illustrative and not restrictive and the scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims

What is claimed and desired to be secured by United States Letters Patent is:

1. A method of modifying an existing refrigeration system to increase the refrigeration capacity thereof, the existing system comprising a compressor, condensor and evaporator, the evaporator comprising an expansion device and acting to cool a conditioned space, comprising the steps of:

providing a secondary refrigeration system;

placing the evaporation coil of the secondary refrigeration circuit in heat exchange relationship with condensed liquid refrigerant of the existing refrigeration system upstream of the existing system evaporator expansion device;

monitoring temperature in at least one of (1) the existing system conditioned space and (2) the existing condenser environment; and

initiating the secondary refrigeration system when the monitored temperature reaches a predetermined upper limit to boost the capacity of the existing system to reduce the temperature in the conditioned space.

2. A method of modifying an existing refrigeration system as defined in claim 1 wherein said monitoring step comprises sensing a preselected upper temperature limit and thereafter generating an initiating signal to automatically energize the secondary refrigeration system.

3. A method of modifying an existing refrigeration system as defined in claim 1 wherein said monitoring step comprises sensing a preselected lower temperature limit and thereafter generating a signal to automatically de-energize the secondary refrigeration system.

4. A method as defined in claim 1 wherein said monitoring step further comprises monitoring the humidity in the conditioned space and where said initiating step comprises initiating the secondary refrigeration system when the monitored humidity reaches a predetermined upper limit.

5. A method of boosting the capacity of an existing refrigeration system to cool a conditioned space without substantially altering the components of the system, the steps of:

sensing at least one of the conditions of (1) temperature and (2) humidity in the existing conditioned space; providing a secondary compressor, secondary condenser, and a secondary closed loop refrigerant path, each of which is completely independent of the existing refrigeration system; situating a secondary evaporator forming part of the secondary closed loop refrigerant path in heat exchange relation with the portion of the existing system upstream from the primary evaporator expansion device which carries only liquified refrigerant at a temperature which is not more than the condensing temperature of the existing system; and continuously subcooling the existing liquified refrigerant with the secondary evaporator substantially below its condensing temperature until the condition sensed in the existing conditioned space reaches a predetermined limit.

6. A refrigeration system for cooling a conditioned space comprising a primary refrigeration system comprising a primary compressor, primary condenser, and primary evaporation coil and associated expansion device located in the conditioned space and having a discrete body of refrigerant; and a secondary refrigeration system comprising a secondary compressor, secondary condenser, and secondary evaporation coil and having a second discrete body of refrigerant, said evaporation coil of the secondary refrigeration system being in heat exchange relation with the portion of the primary refrigeration system between the condenser and the expansion device of the evaporation coil; means for monitoring temperature in at least one of (1) the primary system conditioned space and (2) the primary condenser environment; and means for initiating the secondary refrigeration system when the monitored temperature reaches a predetermined upper limit.

7. A refrigeration system for cooling a conditioned space as defined in claim 6 comprising means for sensing a preselected upper temperature limit and thereafter generating an initiating signal to automatically energize the secondary refrigeration system.

8. A refrigeration system for cooling a conditioned space as defined in claim 6 comprising means for sensing a preselected lower temperature limit and thereafter generating a signal to automatically de-energize the secondary refrigeration system.

9. A refrigeration system for cooling a conditioned space comprising a primary refrigeration system comprising a primary compressor, primary condenser, and primary evaporation coil located in the conditioned space and having a discrete body of refrigerant; and a secondary refrigeration system comprising a secondary compressor, secondary condenser, and secondary evaporation coil and having a discrete body of refrigerant, said secondary evaporation coil being in heat exchange relation with the portion of the primary refrigeration system between the condenser and the evaporation coil; means for monitoring humidity in the conditioned space; and means for initiating the secondary refrigeration system when the monitored humidity reaches a predetermined upper limit.

10. A refrigeration system for cooling a conditioned space comprising a primary refrigeration system as defined in claim 9 comprising means for monitoring humidity in the conditioned space and means for de-energizing the secondary refrigeration system when the monitored humidity reaches a predetermined lower limit.

11. A refrigeration system for cooling a conditioned space comprising a primary refrigeration system comprising a primary compressor, primary condenser, and primary evaporation coil located in the conditioned space and having a discrete body of refrigerant; and a secondary refrigeration system comprising a secondary compressor, secondary condenser, and secondary evaporation coil and having a second discrete body of refrigerant; said evaporation coil of the secondary refrigeration system being in heat exchange relation with the portion of the primary refrigeration system between the condenser and the evaporation coil; means for monitoring at least one of the conditions affecting the capacity of the primary system, the conditions comprising humidity in the primary conditioned space, temperature in the primary conditioned space and temperature of the environment of the primary condenser; means for initiating the secondary refrigeration system when the monitored conditions reach the predetermined upper limit; and means for terminating the operation of the secondary system when the monitored conditions reach a predetermined lower limit.