US3482416A - Refrigerating system designed for commercial freezers and refrigerators - Google Patents

Description

Dec. 9, 1969 D. E. KRAMER 3,432,416

REFRIGERATING SYSTEM DESIGNED FOR COMMERCIAL FREEZERS AND REFRIGERATQRS Filed May 10, 1968 5 Sheets-Sheet 1 ATTORNEYS Dec. 9, 1969 D. E. KRAMER REFRIGERATING SYSTEM DESIGNED FOR COMMERCIAL FREEZERS AND REFRIGERATORS 3 Sheets-Sheet 2 Filed May 10, 1968 MJ'%?% M BY 4% w 7 FEG.4

ATTORNEY Dec. 9. 1969 D. E. KRAMER 9 REFRIGERATING SYSTEM DESIGNED FOR COMMERCIAL FREEZERS AND REFRIGERATORS Filed May 10, 1968 3 Sheets-Sheet 5 ATTORNEY United States Patent REFRIGERATING SYSTEM DESIGNED FOR COM- MERCIAL FREEZERS AND REFRIGERATORS Daniel E. Kramer, Yardley, Pa., assignor to Kramer Trenton Co., Trenton, N.J., a corporation of New Jersey Filed May 10, 1968, Ser. No. 728,175 Int. Cl. F25b 41/00, 47/00 US. Cl. 62-278 8 Claims ABSTRACT OF THE DISCLOSURE A small sized low temperature refrigerating system, packaged and precharged with a limited amount of refrigerant using a capillary tube as a pressure and temperature reducing device in place of the usual thermostatic expansion valve, with a low temperature suction-cooled welded hermetic compressor capable of automatically performing the initial pull-down of the freezer box to zero or lower temperature as well as speedy hot gas defrosts FIELD OF THE INVENTION The field of this invention is concerned largely with indoor cold storage rooms which are fitted with refrigeration systems having motor-compressors of the hermetic low temperature type.

BRIEF DESCRIPTION OF THE DRAWING A practical embodiment of the invention is represented in the accompanying drawings, in which:

FIG. 1 represents a diagrammatic layout of the refrigeration system;

FIG. 2 represents, on a larger scale, a partly broken view of the low side with the low side receiver, holdback valve and metering tube therewithin;

FIG. 3 represents a similar view at right angles to FIG. 2;

FIG. 4 represents an external side view of the same;

FIG. 5 represents a detail top view partly in section of the cold storage freezer box and the refrigeration system in place; and

FIG. 6 represents a detail view at right angles to FIG. 5.

As is well known, there are difficulties in the operation of refrigerator-s, often referred to as freezer boxes, in which the desired temperature is zero F. or lower that calls for an evaporating temperature of say fifteen degrees F. below zero or lower, due to stoppage or cut-out of the compressor by heat load particularly at the time of initial starting that requires the so-called pull down of the temperature of the box in which the evaporator is located which may need a day or more, as well as the brief pull downs of temperature following hot gas defrostings of the evaporator that occur, say, about four to eight times each day.

Another difficulty resides in the fact that, for the sake of economy, these low temperature compressors are equipped with comparatively low motive power per unit volume of compressor displacement as compared, for instance, with air conditioning compressors. This renders "ice the low temperature compressors more susceptible to the stoppage or cut-out on overload above mentioned.

Again, a problem has arisen touching the duration of defrosting times. This depends almost entirely on the availability of adequate refrigerant charge in the defrosting circuit and the availability of an adequate amount of heat, either stored or generated, or both, within the defrosting circuit. The duration of this operation in a low temperature system (eg, zero F. freezer box temperature which means an evaporating temperature of approximately fifteen degrees F. below zero) is extremely important because the longer the duration the greater Will be the rise in temperature within the box due not only to heat imparted by the hot defrosting gas, even though the evaporator fan or blower is idle, but also due to heat leakage through the walls of the box from the warmer ambient. It has been found that the duration is often as long as thirty minutes which is apt to be injurious to the food stored in the box and also, of course, places a greater burden on the compressor motor in performing the pull down following each defrost. Indeed, there is a law in several of the States limiting the freezer temperature to zero F. or lower, so that the duration of defrosting is highly important and must be limited in order to ensure compliance with the so-called Zero Code Ordinances.

The refrigeration system of the present invention, about to be described, obviates the above mentioned diificulties or problems, and inherently possesses other features of value.

Turning now to the drawings, and at first to FIG. 1:

The compressor is denoted by 1. It is of the welded suction cooled hermetic type in which the dome or wrapper has no gaskets that might lead to slow leaks and also houses both the motor and compressor body thus providing several heated surfaces (i.e. rotor, stator, compressor, oil charge and dome) for the reevaporation of any liquid particles of refrigerant entrained in the suction stream during defrosting before the said particles can enter the compression chamber; whereas the bolted type is not only subject to leaks but provides nothing more than the heat of the motor compartment for reevaporation of the above mentioned particles before they enter the compression chamber. The matter of leaks is of extreme concern in a precharged system using a limited amount of refrigerant.

The condenser is marked 2, and a conduit leading from the compressor discharge to the condenser inlet bears the reference numeral 3.

Directly connecting the condenser outlet with the evaporator 4, without the intervention of a receiver, is a capillary tube marked 5, which acts as a pressure and temperature reducing device to cause the refrigerant to enter the evaporator as a cold mixture of liquid and vapor (largely liquid) for the usual purpose of chilling the evaporator coils. The length and internal diameter of this capillary tube is suited to the power of the refrigeration system as well as the degree of temperature of the refrigerant entering the evaporator and is predetermined by calculation and test before the system is shipped for installation. A filter drier 6 is preferably inserted at the condenser outlet for the refrigerant flowing to the capillary.

As the particular construction of the condenser is not concerned with this invention, the same is not described or shown except to say that it has the usual coils and the customary fan and motor unit.

From the outlet of the evaporator the suction conduit 7 leads to the compressor inlet and in this conduit is positioned a low side receiver 8. The purpose of this receiver is to catch over spills of liquid refrigerant from the evaporator and hold the same long enough to permit the liquid to leak slowly back into the suction stream of vapor that passes through the said receiver on the way to the compressor. For this slow leakage there is provided a metering tube 9 which connects the bottom of this receiver with the continuation of the suction conduit therebeyond. It is similar to a capillary and, as it is external, can be determined as to length and internal diameter during assembly of the system and be modified if test shows the need.

Another, and very critical, function of this receiver occurs during defrosting when a mixture of condensed refrigerant and vapor enters the same from the evaporator and separates, with the vapor continuing to flow through the suction conduit toward the compressor while the liquid settles in the bottom of the receiver to be metered through the tube 9 back into the suction conduit just mentioned.

Another element in the suction conduit is a holdback valve 10. This is of the outlet pressure regulating type and is designed to maintain a maximum crankcase pressure above which the low temperature compressor might cut out on overload. Thus it is fully open during normal refrigeration but throttles (similarly to an expansion valve) during and immediately after each defrosting cycle when higher pressure refrigerant flows from the evaporator toward the compressor intake. The liquid entering the holdback valve generates flash gas on being reduced in pressure and temperature. Also the residual particles of liquid refrigerant are further vaporized by the heat content of the returning warm vapor, thus chilling and saturating the suction stream entering the compressor dome.

As the refrigerant mixture during defrosting cycles drops rapidly in temperature while passing through the holdback valve, the stream is capable of picking up a maximum amount of heat from the relatively hot motor-compressor assembly (rotor, stator, compressor, oil charge and dome) which results in complete vaporization that avoids any slugging of the compressor valves during defrosting and post-defrost, leading to fast defrosting with much less mass flow of refrigerant than would be required in the absence of the holdback valve.

To accomplish defrosting the hot gas discharge conduit 3 of the compressor has a branch conduit 11, which leads directly to the evaporator 4, and the path of the compressor discharge (either to the condenser or to the evaporator) is controlled by a three way solenoid valve 12. This conduit 11 is so shaped as to have a section marked 11', which lies close to (preferably in contact) and in heat exchange relation with the suction conduit 7, and the outlet of the holdback valve, the main and very important purpose of which is to defrost the suction conduit at that point. It may be here noted that the action of the holdback valve is essential in the initial pull down of the temperature of the freezer box without overloading the low temperature compressor, and in making possible a rapid and automatic defrost operation without injuriously handicapping the functioning of the compressor.

The initial pull down in a capillary system such as this, having a low temperature compressor, places a severe load on the compressor because, in some cases, such as a walk-in freezer, the pull down might require several days, but with a holdback valve as above described, the action becomes automatic and the pull down does not call for any manual attention and does not adversely affect the compressor.

Attention is further directed to a portion of the suction conduit beyond the portion at the outlet of the low side receiver which is in heat exchange relation to the hot gas line at that section. This further portion of the suction conduit is marked 7' and it will be observed that it is in mutual heat exchange relation with a portion of the capillary tube which bears the reference numeral This serves to heat the refrigerant that is flowing to the compressor and simultaneously to cool the refrigerant moving through the capillary tube to the evaporator. Thus it may be said that the suction conduit involves two purposes or functions, one being due to its heat exchange relation with the hot gas conduit which may begin at the inlet of the holdback valve, and the other to its mutual heat exchange relation with the capillary tube beyond the holdback valve and toward the compressor.

For the most efficient operation the system is so charged with refrigerant as almost to flood the evaporator, especially when under full heat load (e.g. summer) conditions. Another requirement for this full charge of refrigerant is to satisfy the condenser and maintain a liquid seal at the inlet of the capillary tube to avoid the presence of bubbles in the refrigerant fed to the evaporator by the said tube. This may lead to overspills from the evaporator (above mentioned) but the receiver 8 will, as previously indicated, catch the overspill and cause the liquid to leak slowly back into the vapor suction stream.

It should further be noted that during defrost practically the entire charge of refrigerant is in the defrosting circuit and at high pressure and relatively high (i.e. above 32 F.) temperature. As the termination of a defrosting cycle approaches, this liquid is at its highest level in the low side receiver, but the above described holdback valve makes possible the completion of the defrost as well as the resumption of the normal refrigeration cycle, including the post-defrost refrigerant and evaporator pull down, without overloading the low temperature compressor or slugging of the latter or oil dilution, so that the entire defrost and and post-defrost operation becomes not only automatic but also safe and rapid.

Defrosting operations may be controlled by timer clock alone so that they are both started and stopped by the clock; or they may be controlled by clock and thermostat so as to be initiated by the former and terminated by the latter, all as is well understood in this art. And further, the start may depend on the basis of compressor operating time-lapse (see Frie US. Patent No. 2,463,027) but he temperature terminated. In this the compressor would usually be in operation so that the action of the three-way valve 12 would cause the refrigerant supply to flow into the defrosting circuit through conduit 11 which would be supplemented 'by the gradual flow of residual liquid in the condenser through the capillary tube toward the lower temperature (pressure) evaporator, thus transferring practically all of the refrigerant in the system into the defrosting circuit which is of most importance at the start of defrosting when the maximum amount of refrigerant is desired to accelerate the defrost. Of course, the fan and motor units of both the evaporator and condenser are inactive during the defrosting cycle.

Toward the end of the defrost operation the vapor flowing from the evaporator into the suction conduit is superheated and the liquid level in its receiver is at the highest point. When the said defrost is completed the three-way solenoid valve closes the defrosting conduit and opens the conduit to the condenser thus initiating the post-defrost-temperature-pressure pull down -of the liquid in the evaporator and low side receiver. As soon as the evaporator has been chilled to a predetermined degree of temperature its motor-fan unit re-starts putting the system back on the normal refrigerating cycle. It may be added that, during the post-defrost period, the refrigerant liquid in the said receiver gradually reevaporates and is fed back into the system for normal refrigeration without overloading the low temperature compressor.

As above noted, the showing of FIG. 1, is merely diagrammatic, and it should be stated that, in practice, the low side receiver 8, with its metering tube 9, and the holdback valve 10, are actually located within or very close to the housing of the evaporator 4 and thus are within the freezer box (to be described) instead of in the warmer ambient exterior thereto. This likewise applies to the heat exchange portion 11' of the hot gas conduit 11.

The reason for the placing of these parts within the freezer box is to avoid the picking up of an excessive amount of heat from the suction conduit and the warm air moving through the condenser and over the compressor, thus avoiding the complication of insulation (and repair thereof) of these parts, as well as providing for water dripping into the drain pan of the evaporator along with the coils of the latter during defrosting. Thus the capacity of the system is not lessened by any of the factors just named.

FIGS. 2, 3 and 4 serve to illustrate the arrangement of the low side receiver, its metering tube, the holdback valve, and the heat transfer portion 11 of the hot gas conduit within the housing of the evaporator 4.

Turning at first to FIG. 4, which shows the low side exteriorly and standing on its back, the casing or enclosure is fitted with a top cover 13 and with a bottom cover 14 which latter serves as a drain pan and is hinged at 15 in order readily to be opened for periodic cleaning. The opening in the top cover for the suction conduit and hot gas conduit is marked 16.

FIG. 3 shows one view of the interior arrangement and it is deemed suflicient simply to apply their numerals to the pertinent elements, with the low side receiver marked 8; its metering tube 9; the holdback valve 10; and the portion of the hot gas line in heat transfer relation to the valve and the suction conduit 11'. It will also be observed that the hot gas line extends along the bottom of the evaporator to heat the drip pan, this portion of the hot gas line being marked 11 The remainder of FIG. 3, and FIG. 2 which shows the parts at a different angle, illustrate the usual coils, etc. of the evaporator that it is regarded as unnecessary to explain or number, other than to note that the hot gas line for defrosting the evaporator coils has a vertical loop, numbered 11 adjacent the said coils.

The system of this invention is produced as a complete apparatus, precharged with refrigerant, tested, packaged, and shipped entirely ready for installation and operation by the mere act of connection with a source of electrical current. I prefer to embody it in the form of the now well known Straddle system though of small enough size to be suited for installation in a freezer box that is preferably located in a suitable room or space in a building. Such installation is represented in FIGS. 5 and 6 of the drawings to which reference will now be made.

In FIG. 5, a portion of the wall of the building or room in which the freezer box is located is denoted by 17, while a portion of the freezer box wall bears the reference numeral 18.

The high side of the system which incorporates the usual elements and is described in some detail above is marked 19, and the low side with its usual and additional contents is indicated by 20. These two sides are supported and united by a pair of arms 21, 21, that are preferably composed of angle iron to provide in their angle for reception of the several conduits that, as usual, constitute parts of the system.

The arrangement just described causes the system to straddle the wall of the freezer box-hence its name. It should be added that, in cases the system is installed while the freezer box is in course of construction, the system is hung in position before that wall of the box is finished; while in other cases when the system is installed after completion of the freezer box, the arms 21, 21, are made detachable from one side of the system and are passed through small holes made in the freezer walls and then attached to the side from which they were separated. The arms 21, 21, may be strengthened by a brace 22, if desired.

As FIG. 6 merely shows the installed system at another angle it is regarded as snfficient to apply the same numerals to the high and low sides and to the freezer box wall, together with the marking of the floor of the room in which the box is located as 23 and the ceiling thereof as 24 when the compressor is located indoors.

The evaporator housing shown in the drawings is formed With a curved face that allows for the convenient positioning of the low side receiver, the holdback valve and the immediately adjacent portion of the hot gas conduit actually within the evaporator housing. However, in cases where the said housing has a fiat face, the said parts will be outside the housing though closely enough thereto to be over the heated drip pan that will be slightly extended for this purpose and the said low side receiver, holdback valve and the immediately adjacent portion of the hot gas conduit will still be located within the freezer box.

It is thought that the foregoing adequately discloses this invention, but I wish it to be understood that various changes may be made in the construction and arrangement of the several parts without departing from the scope of the invention, and hence, I do not intend to be limited to details of the drawings or specification except as the details are included in the claims or such limitation is required by disclosures of the prior art.

What I claim is:

1. In a low temperature refrigeration system for commercial freezer boxes, having a hermetic motor-compressor, a condenser connected therewith, an evaporator having a drain pan, a suction conduit connecting the outlet of the evaporator coils with the intake of the compressor, and a low side receiver, the improvement which comprises the provision of an outlet pressure regu lating valve positioned in the said conduit and connected with the outlet of the said low side receiver, a capillary tube directly connecting the condenser with the inlet of the evaporator, a metering tube connecting the receiver with the suction conduit at a point between the receiver and the said valve, and the positioning of the said receiver over the drain pan.

2. A system as defined in claim 1, which also includes a hot gas conduit connecting the compressor with the inlet of the evaporator for defrosting the latter.

3. A system as defined in claim 2 which also includes an automatic valve for intermittently closing and opening the connections of the compressor with the condenser and the evaporator.

4. A system as defined in claim 1 in which the motorcompressor is of the welded type.

5. A system as defined in claim 1 in which the evaporator is provided with a demountable bottom serving as a drain pan.

6. A system as defined in claim 2 in which the hot gas conduit is in heat exchange relation with the drain pan.

7. A system as defined in claim 2 in which the hot gas conduit is in heat exchange relation with the portion of the suction conduit adjacent the outlet of the low side receiver.

8. A system as defined in claim 7 in which a portion of the suction conduit further from the outlet pressure regulating valve is in mutual heat exchange relation with the capillary tube.

References Cited UNITED STATES PATENTS

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