US2949750A - Heat exchange system of the evaporative type with means for maintaining liquid supply line pressure - Google Patents

Description

EVAPORATIVE TYPE WITH MEANS FOR MAINTAINING LIQUID SUPPLY LINE PRESSURE Filed May 28, 1956 INVENTOR jLATTQRNEYQ f United States Patent HEAT EXCHANGE SYSTEM OF THE EVAPORA- TIVE TYPE WITH MEANS FOR MAINTAINING LIQUID SUPPLY LINE PRESSURE Daniel E. Kramer, Trenton, N.J., assignor to Mercer Engineering 'Co., Trenton, N.J., a co-partnerslrip Filed May 28, 1956, Ser. No. 587,609 4 Claims. (Cl. 62-196) This invention relates to a Heat Exchange System of the Evaporative Type with Means for Maintaining Liquid Supply Line Pressure, and has for an object to provide such a system which comprises the usual compressor, condenser, with or without a separate receiver, evaporator, and refrigerant pressure reducing device associated with the evaporator, all interconnected in a series circuit, and in which the condenser is of the air cooled or evaporative type, with means for maintaining satisfactory operative pressure in the liquid refrigerant supply line adjacent the said pressure reducing device, regardless of ambient temperature at the condenser.

Another object is to provide such a system in which the maintenance of said pressure is accomplished without resorting to varying the height of liquid refrigerant in the condenser to regulate its functional capacity by decreasing or increasing its effective area of internal heat exchange surface.

Another object is to provide such a system in which the maintenance of said pressure is accomplished without the necessity of increasing the load or charge of refrigerant in the system beyond that necessary for normal operation in refrigerating cycles.

Another object is to provide such a system in which the maintenance of said pressure is accomplished by the provision of means, preferably mechanical, for forcing refrigerant from the receiver or condenser to the pressure reducing device immediately following fall in condenser pressure to a degree which is inadequate for the feeding of refrigerant to the pressure reducing device at a pressure suflicient for proper performance of the latter.

Another object is to provide such a system in which said pressure is maintained by the provision of a pump arranged to force refrigerant from the receiver or condenser to the pressure reducing device, the activity of the pump being subject to condenser pressure.

Another object is to provide such a system in which maintenance of said pressure is accomplished while condenser pressure remains in correspondence with ambient temperature at the condenser.

Another object is to provide such a system which is adapted to take economic advantage of low condensing temperatures due to ambient conditions while maintaining full refrigerating effect through positive supply of refrigerant to the pressure reducing device at desired elevated pressure.

A further object is to provide such a system which is simple in arrangement and of low cost in construction, due largely to the employment of elements which are readily available commercially and do not require special design or fabrication.

A further object is to provide certain improvements in the form, construction and arrangement of the several parts, whereby the above named objects and others inherent in the invention may be effectively attained.

In brief summary, the invention comprehends a refrigerating or air conditioning heat exchange system of the evaporative type, which is designed and adapted for operation with an air cooled or evaporative condenser that may be exposed to outdoor ambient atmosphere, the said system being so constructed and arranged that, even under seasonal or geographic conditions in which the condenser is subjected to low, and even extremely low, temperatures, satisfactory operating pressure adjacent the usual pressure reducing device, such as a thermostatic expansion valve, is maintained without loading or charging the system with an amount of refrigerant in excess of that required for normal operation for the purpose of varying condenser capacity and pressure by greater or less flooding of the condenser with liquid refrigerant. The functional and economic advantages of this system are attained essentially by the provision of a refrigerant pump located in the supply conduit between the receiver or condenser and thermostatic expansion valve, the operation of which pump is controlled by a pressure switch, or the like, in communication With the high side of the system between compressor and pump, so that the latter is activated for supplying refrigerant under adequate pressure to the thermostatic expansion valve immediately following any reduction of said high side pressure below a predetermined minimum. The pump has associated therewith a relief valve, or the like, to obviate undesirably high pressure of the refrigerant fed to the thermostatic expansion valve; and provision is also made for return of refrigerant to the receiver or condenser.

A practical embodiment of the invention is diagrammatically represented in the accompanying drawing, to which reference will hereinafter be made.

In heat exchange engineering directed to the refrigeration and air conditioning industry, as exemplified in compression type systems, it is a Well known fact that the high side pressure is related to the condensing temperature, which latter is dependent upon the relative temperature of the condensing coolant. Thus, if air is the coolant as in air cooled and evaporative condensers, a sharp fall in ambient temperature at the condenser can lead to such a decrease in the high side pressure of the system as to lessen its operative capacity, particularly by curtailing refrigerant flow at satisfactory pressure through the thermostatic expansion Valve, or the like, positioned adjacent the inlet of the evaporator, due to reduction in pressure differential across the valve. This condition also notably restricts hot gas defrosting of the evaporator. It is also well understood by engineers in this field that the functioning characteristics of the evaporator and the condenser differ essentially in that more flooding of the former with liquid refrigerant enhances its capacity, while increased flooding of the latter has the opposite effect.

Inventors in this field have taken advantage of the foregoing factors by embodying in systems of this nature means for automatically varying the level of liquid refrigerant within the condenser in response to changes in its ambient temperature, in order to provide control of high side pressure and prevent fall below a predetermined minimum especially at the thermostatic expansion valve or its equivalent pressure reducing device; thereby promoting effectiveness of the said valve and evaporator as well as efiicient defrosting capability. These advances have been of practical commercial importance due largely to recent rapid increases in the use of air cooled condensers in all year operating systems wherein the condenser is located outdoors for the purpose of enjoying the coolest ambient atmosphere in warm seasons and days, which location necessarily also subjects the condenser to low, and frequently frigid, temperatures in cold seasons or days and in cold geographical locations.

However, the value of the aforesaid developments has not risen to heights commensurate with substantial perfection, due largely to the fact that the flooding of the condenser with liquid refrigerant has required the presence in the system of a load or charge of refrigerant exceeding that necessary for circulation therethrough in the normal operation of the system. It will be clear that, if ambient conditions at the outdoors condenser call for any substantial flooding of the latter with liquid refrigerant, and especially if such conditions prevail for a considerable period, there will be an appreciable, or more than appreciable, volume of liquid refrigerant that is, in effect, stored within the condenser and idle insofar as the normal operation of the system is concerned. Refiigerants in common use are quite costly, so that the economic loss entailed by the charging of the system with more refrigerant than needed for normal circulatory operation in order to provide the quantity which rests idly in the condenser as above explained is readily discernible. This expense is greatly magnified in connection with large tonnage systems; and a further expense is incurred by the necessary increase in size of receiver in order that the latter may accommodate under warm ambient conditions the quanity of excess refrigerant that is stored in the condenser during colder ambient conditions. Moreover, the risk involved in the use of refrigerant naturally increases with the volume of refrigerant charged into the system, and there is frequently objection to such risk by the owner of the system or by the person or concern which may be providing warranty servicing of the system. Finally, as a result of inaccuracy or uncertainty with respect to correct charging of the system with refrigerant, a certain extent of defective operation sometimes occur when the condenser ambient temperature falls below the estimated low temperature for which the system has been charged. Thus, for example, if a system is charged to provide desired high side pressure when the ambient temperature falls as low as plus 10 R, an unexpected further fall to, for instance, R, will cause more than the designed amount of refrigerant to flood into the condenser and rob the receiver and supply line to the evaporator with the result of starving the latter and reducing to an undesirable degree its refrigeration effect.

The present invention is calculated to eliminate the above described imperfections in previous practice as well as to offer inherent advantages of its own.

Referring to the embodiment of the invention illustrated in the accompanying drawing, the system includes a compressor 1 which is actuated by the usual motor (not shown). The discharge of the compressor travels through a conduit 2 to the inlet of condenser 3, shown as of an air cooled type, that is fitted with the customary fan and motor unit 4. The outlet of the condenser is connected by a conduit 5 with a receiver 6; and the latter communicates by the refrigerant supply conduit 7 with a pressure reducing device such as a thermostatic expansion valve 8 that is diagrammatically indicated as controlled by the usual feeler bulb and capillary tube; which valve is connected, as shown, with the inlet of an evaporator 9 with which is associated a fan and motor unit 10 in accordance with approved practice. The outlet of the evaporator is in refrigerant flow communication through a suction conduit 11 with the intake of the compressor 1, thus completing the normal refrigeration circuit of a compression type system. The compressor, condenser, receiver, thermostatic expansion valve, and evaporator may be of any well known and approved form, and their details will not be herein set forth as the same constitute no feature of the present invention.

. A significant element of this system resides in the interpositioning of a fluid pump 12 in the supply line 7 between receiver 6 and expansion valve 8, the said pump being preferably located close to the receiver and slightly below the level of the latter. The exact character of the pump is not an item of importance, although it is desirably of the positive displacement type and functionally capable of delivering suitable refrigerant such, for instance, as Freon-IZ or Freon-22, at a pressure of from 70 to 100 pounds per square inch. The pump is designed to be driven by a suitable motor (not shown) operatively associated therewith, and electric current for the motor is provided through wires 13, 14, which receive their power from any appropriate source such, for instance, as commercial supply, generator, or battery conventionally indicated at 15. The wires 13, 14, are connected with a pressure switch 16 of any appropriate design which is in communication with discharge conduit 2 through a tube 17 so that the actuation of the switch is subject to condenser pressure as reflected in the said discharge conduit, the arrangement being such that fall in such pressure below a predetermined degree will close the switch and complete the electric circuit to operate the pump 12 and thereby force refrigerant from the receiver to the expansion valve 8, and thence to the evaporator.

A by-pass 18 in the supply conduit 7 spans the pump 12 in order to provide for free refrigerant flow from receiver to expansion valve without passage through the pump if the latter be so constructed as to hinder or prevent flow therethrough when idle, and a check valve 19 serves to halt reverse flow through the by-pass. A branch conduit 20 leads from the supply conduit 7 at a point between the pump and the expansion valve, to the conduit 5 or, if preferred, directly to the receiver, the said branch conduit serving the purpose of returning to the receiver any excess of refrigerant delivered by the pump toward the expansion valve, and in this branch conduit is positioned a relief valve 21 of suitable design which obviates any build-up of pressure in the supply conduit 7 to an undesirably high point which could impose upon the expansion valve 8,refrigerant in excess of the demand of the valve for satisfactory performance. Any gas bubbles which may be formed during passage of refrigerant through the relief valve 21 will be separated from the liquid portion of the refrigerant during travel through branch conduit 20 and also in the receiver, so that the refrigerant flowing to the pump from the receiver remains mainly, if not entirely, in liquid phase.

In the operation of the system, and assuming that the air cooled condenser 3 is located so as to be subject to out of doors temperature, whenever the ambient temperature at the condenser falls to such a degree that the condenser pressure would fail to supply an adequate amount of refrigerant at adequate pressure to the expansion valve 8, the said fall in condenser pressure will at once close switch 16 and activate the motor of pump 12 with the result of immediately providing a supply of refrigerant to the expansion valve in satisfactory amount and at satisfactory pressure so that the pressure diiferential across the valve will insure full operative refrigerant flow to the evaporator. It will be understood that the pressure switch 16 will be set by the installing engineer or the operator in charge so that it will be closed upon fall in condenser pressure to a point below which the particular system in hand would not continue in fully satisfactory operation. When the operation of the pump has served to reestablish the functional efiiciency of the system to that desired, the consequent increase in condenser pressure will open switch 16 and interrupt the current supply to the pump motor so that the system may resume normal operation without pump activity. The pressure at which the switch is set to operate will naturally vary with difierent installations but, for the sake of a concrete illustration, I have found that a setting which causes the switch to close and activate the pump at a condenser pressure of 70 pounds per square inch, and to open and deactivate the pump at pounds per square inch, has proved satisfactory. V

1' ul b noted that the system will usually have the well known pressure switch connected with the low side or suction conduit of the system for governing the compressor motor so as to start the latter when conditions in the space being chilled by the evaporator call for a supply of refrigerant and to stop the motor when the conditions in the said space have been satisfied. Consequently, it may frequently, if not usually, be desirable for the electric circuit to include both the motor of pump 12 and the compressor motor so that the two run and cease running together. I have found that, when a system is running with on and off-cycles of the compressor, the pump 12 will feed refrigerant to the expansion valve 8 with great rapidity at the institution of compressor on-cycles, and thus avoid fall of evaporator pressure which might lead to the stopping of the compressor motor by the low side pressure switch above mentioned. An arrangement as just described is illustrated in the drawing, the compressor motor 22 being shown as connected at 23 to the compressor, and by wires 24, 2,5, with the wire 26 that extendsfrom power source 15 to switch 16, and to wire 13 that joins the power source with pump 12. Wire 26 is broken for mating with a bellows switch denoted generally by 27 which is in communication by a tube 28 with suction conduit 11, as usual. It will be understood that the shown control of switch 27 by suction pressure is conventional and that cycling of the compressor may be controlled in other ways, also well known, as by the temperature of the chamber in which the evaporator is positioned or some other system characteristic adapted to this purpose.

The foregoing is believed to make it evident that this extremely uncomplicated system provides well for attainment of the objects hereinabove detailed, mainly through the incorporation of means which, independently of condenser pressure, serves to maintain the pressure in the refrigerant supply conduit adjacent the pressure reducing device above a predetermined minimum, and that it possesses the very substantial economic value of functioning according to its design without the need for any over loading or over charging of the system with expensive refrigerant. When I refer herein and in the claims to the pump 12 as being controlled by condenser pressure, I mean the high side pressure of the system between the compressor and the pump, as explained in column 2, lines 15 through 26 above.

While the embodiment of the invention illustrated in the accompanying drawing and heretofore described presents the features which essentially characterize the invention as incorporated in a system of the compression type which includes a receiver separate from the condenser, the invention is also adaptable for incorporation in systems which are devoid of a separate receiver, and likewise is well suited to incorporation in systems that comprise low pressure means for feeding liquid refrigerant to the evaporator such, for instance, as the supply line leading from subcooler drum to evaporator in the well known two stage system, and the supply line leading from the low stage receiver to the evaporator in the also well known cascade system. Furthermore, the availability of the invention is not restricted to systems of the compression type but extends to absorption systems. Accordingly, while claims specifically directed to the incorporation of the invention in such additional systems are not included in this application, it is my intention that the claims herein which are phrased in language generically sufficient to cover such various embodiments of the invention shall be thus construed as to their scope.

It will also be understood that various changes may be resorted to in the form, construction and arrangement of the several parts of the apparatus without departing from the spirit or the scope of the invention; and hence I do not intend to be limited to details herein shown or described except as the same may be included in the claims or be required by disclosures of the prior art.

What I claim is:

1. In a heat exchange system of the evaporative type having a circuit for refrigerant flow including cycling compressor, condenser, receiver, refrigerant pressure reducing device, and evaporator, all operatively interconnected by conduits, positively driven means in the conduit between receiver and pressure reducing device for forcing refrigerant to the said pressure reducing device during on-cycles of the compressor whenever condenser pressure falls below a predetermined degree, and means automatically controlled by the condenser pressure for activating and deactivating said positively driven means.

2. A system as defined in claim 1, in which the activating and deactivating means is a switch operatively connected with the high side of the system between the compressor and the said positively driven means, said switch being responsive to pressure in the said high side.

3. A system as defined in claim 1, in which the positively driven means is a pump, and which also includes a branch conduit establishing refrigerant flow communication between the output side of the pump and the receiver for returning to the latter excess refrigerant delivered by the pump.

4. A system as defined in claim 3, which also includes a relief valve in the said branch conduit for preventing refrigerant delivery to the pressure reducing device at excessive pressure.

Pfau Oct. 26, 1915 Newton June 3, 1941

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