High side defrost and head pressure controls for refrigeration systems

Feb. 18, 1969 high side

Filed Dec. 22, 1966

CONTKoJ’⁴²⁷·⁸¹⁹

FOR REFRIGERATION SYSTEMS

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SUB-COOLER

Feb. 18, 1969 »™ s_{1DE suaE coktrol}3,427₎₈19

Filed Dec. 22, 1966 ^{F0R refriger}ATION SYSTEMS

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INVENTOR

LELAND L. SEGHETTI

ATTORNEYS

3,427,819

Patented Feb. 18, 1969

United States Patent Office

3,427,819 ^AND HEAD pressure CONTROLS FOR REFRIGERATION SYSTEMS Leland L. Seghetti, Bridgeton, Mo., assignor to Pet Incorporated, St. Louis, Mo., a corporation of Delaware ttc /,. ^FiIeAPec. 22,1966, Ser. No. 603,797

U.S. CI. 62—196 Ji Claims

Int. CI. F25b 41 /00, 39/04 Claims

ABSTRACT OF THE DISCLOSURE

A hot gas percolation device in a liquid refrigerant supply providing a constant source of saturated gas for defrosting evaporators in a refrigeration system, and pressure valves controlling condenser flooding, hot gas percolation, receiver equalizing and liquid line refrigerant flow to balance the high side of the refrigeration system.

and with the liquid refrigerant header connected with several evaporator coil branch lines in the system.

. An object of the present invention is to provide hot gas injector means for producing a constant supply of saturated gas at a predetermined pressure higher than the refrigerant pressure in the liquid header.

Another object is to provide means for controlling both the compressor head pressure and the liquid line pressure regardless of ambient or load conditions whereby optimum operation is achieved.

Another object is to provide means for maintaining the compressor head pressure or condensing pressure in single and multiple condensing unit arrangemets above a predetermmed minimum under various ambient conditions _; and to balance the high side pressure relationship in the receiver and liquid lines to assure optimum system performance during normal refrigeration and saturated gas defrosting.

These and still other objects and advantages of the । present invention will become more apparent hereinafter.

Brief description of the drawings

For illustration and disclosure purposes the invention is embodied in the parts and in the combinations and arrangements of parts hereinafter described. In the accompanying drawings forming a part of the specification and wherein like numerals refer to like parts:

FIG. 1 is a diagrammatic illustration of a typical refrigerahon system embodying one form of the invention

FIG. 2 is a perspective view showing the receiver and refrigerant line connections thereto of the FIG. 1 embodiment, and . FIG. 3 is a diagrammatic illustration showing the high side, of a refrigeration system embodying another form of the invention.

Description of the preferred embodiments

For purposes of disclosure, a closed refrigeration system embodying the invention has been illustrated and will be described as a heavy multiplexing system of the type which might be installed in a supermarket for operating a plurality of separate fixtures, such as refrigerated storage and display cases, but it will be understood and readily apparent to those skilled in the art that such a system can be adapted to other commercial or industrial installations. The terms “high side” and “low side” are used herein in a conventional refrigeration sense to mean the portions of the system from the compressor discharge to the evaporator expansion valves and from the expansion valves to the compressor suction, respectively. . Referring to FIG. 1, the refrigeration system shown is in part conventional and includes a compressor 10 having a suction or low pressure side 11 operating at a predetermined suction pressure and having a discharge or high pressure side 12 with a discharge conduit 13 through which hot compressed gaseous refrigerant is discharged to a condenser 14. The refrigerant is reduced to its condensing temperature and pressure in the condenser 14 which is connected by a conduit 15 to the inlet 16 of a surge-type receiver 17 forming a liquid refrigerant source for operating the system. The outlet 18 of the receiver 17 is connected to a liquid header 19 for conducting liquid refrigerant to branch liquid lines ^or conduits 20 leading to evaporator coils 21 22 23 and 24 associated with the different refrigerated’ fixtures ⁶⁵ ί° ^sh?^WI?)· Although only four evaporator coils are shown in FIG. 1, it will be apparent that numerous other evaporators can be connected into the refrigera2iⁿ22^Stb7a^{DCh liQUid Une 20 Of each} evaporator 21, 22 23 and 24 is provided with a solenoid valve ₇₀ 25, and expansion valves 26 are provided for metering ™ ‘ I^{6 evap}“ ^{in a} conventional manner!

The outlets of the evaporators are connected to three10

Background of the invention

The invention relates to improvements in defrosting refrigeration system evaporators and in high side pressure controls for such systems.

In the past, closed refrigeration systems of the heavy multiplexing type having a single compressor and of the compounded type having two or more compressors have been used in commercial installations, such as supermarkets, for operating a large number of refrigerated fixtures Hot gas defrosting is effective in such installations due to the large amount or “superabundance” of heat produced by. the refrigerated fixtures in excess of the heat load required for defrosting one or more selected fixture evaporator coils during the continued refrigeration of the remaining fixtures However, highly superheated hot gas diverted directly from the compressor discharge to the selected evaporator coils for defrosting has resulted in several adverse conditions including (1) the rapid thermal expansion of components such as refrigerant lines causing breakage and leaks and (2) the excessive derost temperatures to which the evaporator coils are subjected produce fog or steam that is frequently visual in . e refrigerated fixture. It has been proposed that the objectionable or adverse effects of “hot gas” defrosting can -as”^bbut nr!o^y t^theA^USe °^{f desu}P^erheated “saturated _Bas but prior to the present invention the means for producing saturated gas have not been effective or the supply of saturated gas has been so limited that efficient defrosting could not be accomplished.

m&gt;rn-^ISi^a1^ ^kn°^Wn “ ^{the prior art that the} operation of multiplexed or. compounded refrigeration systems is affected by various climatic conditions and that during winter operation, the maintenance of proper pressures in he high side of the system is one of Vprincipal prob lems m the design and engineering thereof. Various wellknown control arrangements are available for maintaining ^ΙΓβά_k^011dt^nslng. Pressures during extreme ambient conditions, but the existing controls are applicable only ^{or have other} deficiencies ⁶⁰which excludes their adaptation from use in a refrigerafrostw ^{PreSent type having saturate}d gas defrosting of the fixture evaporators.

Summary b “^ventl°^{n is} embodied in a refrigeration system avmg means for providing a continuous supply of saturated gas for defrosting evaporators, and having high side control means for maintaining a balanced pressure relationship of the compressor head pressure or condensing pressure with the liquid supply and saturated gas sources

3,427,819

Still referring to the disclosure of the Blake Patent No. 3,150,498, the desirable pressure differential between the gas defrost header 33 and the liquid header 19 is in the range of 10 to 20 p.s.i.g. and preferably about 15 p.s.i.g. The Blake patent also discloses a range of operating head pressures and other means for regulating the defrost arrangement, and reference may be had to said patent for a more complete description of a conventional closed refrigeration system of the compound compressor type in which the present invention may be used. It will be understood that the system as thus far described herein and as described in the Blake patent form examples conventional refrigeration systems in which the present invention is applicable.

Referring particularly to FIGS. 1 and 2, the receiver 17 forming the high side liquid refrigerant source has a large T-connection base with a vertical column 42 forming a gas separating or percolation chamber 43 and also having the inlet and outlet legs or ducts 16 and 18 connected to the conduits 15 and 19, respectively. The surge receiver, according to the present invention, stores a large supply of liquid refrigerant, the normal liquid level being shown by a broken line L and the minimum liquid level being above the vertical column or percolation chamber 43.

As previously mentioned, one feature of this invention is to utilize saturated gas for defrosting the evaporator coils, and in order to maintain a continuous supply of saturated gas in the receiver 17 (and form a by-pass for winter control as will be described), the compressor dis' charge conduit 13 is connected by a conduit 44 through a check or pressure regulating valve 45 to a gas percolation injector 46 connected to the vertical column and having an upturned L-shaped gas discharge line 47 substantially centrally located in the percolation chamber 43. It will be ' noted that the conduit 44 is shown connected to the compressor discharge conduit 13 above the condenser 14 and, therefore, this conduit also is adapted to function as a gas equalizing line between the condenser 14 and the upper portion of the receiver acting through a vacuum breaker or equalizer line 48 and one-way check valve 49 which prevents the flow of superheated gas from the compressor 10 into the top of the receiver 17.

It will be understood that in the design, engineering, sizing and location of refrigeration system components and the climatic or environmental conditions under which the system operates will have a direct affect upon the pressure relationships and the efficient operation of the system. Accordingly, there could be a substantial drop between the compressor head pressure and the condensing pressure, but it is assumed that the system is designed so that such pressure drop is negligible and reference to compressor head pressures will also mean the condensing pressures since it is the latter pressure that is critical. Therefore, another feature of this invention is to provide a refrigerant condensing pressure control for controlling liquid refrigerant flooding within the condenser 14 to maintain a minimum compressor head or condensing pressure particularly during winter conditions, in order to maintain a balance in the pressure relationship of the compressor head pressure with the receiver 17 to provide the desired pressure of saturated gas for defrost and liquid header pressure downstream of the regulating valve 37. A normally open modulating control valve 50 is. interposed in the condenser discharge conduit 15 having a pilot inlet 51 for controlling the modulating operation of the valve 50 through an external control line 52 connected to the compressor discharge line 13 (for disclosure purposes, being shown connected to the conduit 44). In short, I as disclosed, the control valve 50 is directly responsive to the compressor head pressure acting through control line 52 and the pilot unit 51 and modulates or throttles the flow of refrigerant from the condenser 14 into the conduit 15 in response to a drop in compressor head pressure below a predetermined value.

way valves 27 and, under normal refrigerating operation, are connected through these valves and branch suction lines or conduits 28 to a suction header 29 connected to the suction side 11 of the compressor 10 and through which vaporous refrigerant from the evaporators is returned to the compressor 10 to complete the basic refrigeration cycle. Evaporator pressure regulator (EPR) valves 30 are shown interposed in the branch suction lines 28 for illustrating that the suction pressure on the evaporator coils 21, 22, 23 and 24 can be adjusted so that the respective refrigerated fixtures can operate at different temperatures within the range established by the predetermined suction pressure of the compressor

The refrigeration system operates in a conventional manner in that each fixture evaporator absorbs heat from the fixture or its product load thereby heating and vaporizing the refrigerant and resulting in the formation of frost or ice on the evaporator coils. The number of evaporators in the refrigeration system produce a cumulative latent heat load of the refrigerant gas returned to the compressor, and this heat load is in excess of the amount of heat required to defrost one or more of the evaporators 21, 22, 23 and 24 and is sometimes called a “superabundance” of heat.

A main gas defrost header 33 is provided for conducting gaseous refrigerant selectively to the evaporator coils and is connected through branch defrost lines or conduits 34 to the three-way valves 27, the three-way valve for the evaporator 24 being shown in defrost position. In a conventional “hot gas” defrost arrangement, the gas header 33 would be connected to the compressor discharge conduit 13 so that this source of highly superheated hot compressed gaseous refrigerant would be used for selectively defrosting the evaporators 21, 22, 23 or 24. However, a feature of the present invention is to use so-called “saturated gas” for defrosting purposes; that is, the sensible and latent heat of gaseous refrigerant at its normal or desuperheated saturation temperature as will be described more fully hereinafter. Accordingly, the gas defrost header 33 is connected by conduit 33a to the top of the receiver 17 so that gaseous refrigerant will flow through the header 33, the branch line 34 and the three-way valve 27 into the evaporator coil 24 (or another selected evaporator isolated from the normal refrigeration cycle by actuating the threeway valve 27 and solenoid valve 25) for heating the coil to remove the frost or ice accumulation and thereby condensing the refrigerant to a liquid as in a conventional condenser. A unidirectional by-pass or check valve 35 is provided in a by-pass line 36 connecting the inlet of the evaporators to the liquid header 19 in by-pass relation with the expansion valve 26.

In accordance with the teachings of Blake Patent No. 3,150,498 granted on Sept. 29, 1964, the embodiment disclosed in FIG. 1 provides for the return of the liquid refrigerant resulting from the defrost of each evaporator coil into the liquid header 19 through the by-pass line 36 and check valve 35 so that such refrigerant is immediately available for use in the normal operation of the refrigerating evaporators. It is necessary to maintain a pressure differential between the defrost gas header 33 and the liquid header 19 to provide an incentive for the rapid flow of refrigerant through the defrosting evaporator 24 back into the high side of the refrigeration system. Therefore, a pressure reducing or regulating valve 35 is positioned in the liquid header 19 upstream of the branch liquid supply lines 20, and the liquid header 19 is also provided with a sub-cooler 38 for preventing flash gas from occurring as a result of the reduction of liquid line pressure through the pressure regulator valve 37. The sub-cooler 38 has an evaporator coil (not shown) surrounding the liquid header 19 with the coil having an expansion valve 40 and the outlet of the coil being connected by a branch suction line 41 to the suction header 29.

3,427,819

FIG. 3 discloses another form of the invention in which refrigerant condensing pressure control means is applicable to multiple or parallel condenser units 14α and 14b with the modulating control valve 50 being interposed in the conduit 15 downsteam of both condensers. In this embodiment, an inverted condensed liquid drain trap 55 is provided to form a liquid seal between the branch drain lines 15α and 15b of the condensers 14α and 14£&gt;. The liquid seal formed in the drain trap 55 permits independent operation of the condenser units 14α and 14Z&gt; since the operating pressure dorp will differ from one condenser to another when in parallel operation.

The conduit 15 is shown connected through the drain trap 55 to the side of the lower tank portion 56 of a gas separating and percolation device 57 and a conduit 15c connects the bottom of the tank portion 56 to the inlet 16 of the receiver 17. In the precise arrangement shown in FIG. 3, the trap 55 and lower tank portion 56 of the device 57 both perform the function of forming a liquid seal and, therefore, the drain trap could be eliminated. However, in a typical installation in which the condensers 14α and 14Z&gt; may be mounted on a roof and the percolation device 56 and receiver 17 may be mounted in a lower room, the drain trap 55 is an important separate feature. In such an installation, the upper portion of the trap 55 should be vented by a vertical leg to a vent line connected to the upper portion of the receiver 17 as through the equalizer line 48.

The gas separating and percolation device 57 is arranged vertically in lateral disposition to the receiver 17 and the upper portion 58 of the device 57 is connected by a conduit 59 to the top of the receiver. Accordingly, the liquid level L in the receiver 17 is also maintained in the separate gas separating and perculation device 57, and the percolation injector 47 is positioned in the percolation device below the minimum liquid level, as perviously dis- $5 closed in connection with the FIG. 1 embodiment.

During normal refrigeration operation, and depending upon the engineering design and climatic conditions as previously indicated as well as the specific refrigerant employed in the system, the compressor head pressure can vary substantially, such as between 140 p.s.i.g. and 200 p.s.i.g. Similarly, the refrigerant temperature at the compressor discharge 12 will be in the range of 200° F. to 225° F. or above, but much of this high temperature is attributable to superheat. Accordingly, reference will be ⁴⁵had to condensing temperatures and pressures of refrigerant R-22 for disclosing a typical operation of a refrigeration system embodying the present invention.

Assuming that the pressure regulating valve 37 is set to provide a constant downstream pressure of 160 p.s.i.g., as disclosed in the Blake patent, and that a pressure differential of 15 p.s.i.g. across the defrosting evaporator 24 is desirable, then the pressure in the gas defrost header 33 and in the receiver 17 must be maintained at about 175 p.s.i.g. Accordingly, the condensing pressure or compres- 55 sorehead pressure should normally operate at about 180 p.s.i.g. and, at this condensing pressure, the condensing or saturation temperature of R-22 will be about 94.3⁰ F. and at this temperature the superheat and latent heat of condensation will be dissipated so that the condensed 60 liquid refrigerant discharged from the condenser 14 and stored in the receiver 17 will be substantially at the saturation temperature (94.3° F.) and pressure (180 p.s.i.g.). Of course, if a pressure drop to 175 p.s.i.g. occurs across the condenser or in the receiver 17 then the saturation temper- 65 ature of the liquid will be 92.7° F. for R-22. Such pressure drops and variations in compressor head pressure or condensing pressure are normal and to be expected in most refrigeration systems. It will be understood that there will normally be a balanced condition in the receiver 17 and 70 that gaseous refrigerant at saturation temperature and pressure will always be present due to variations in the supply and demand of liquid refrigerant. In normal refrigeration of the fixtures, the evaporators 21, 22, 23 and 24 create the variable demand for liquid refrigerant from 75 the receiver 17, and the normal refrigeration cycle will be understood to all skilled in the art.

During the defrosting of a selected evaporator, saturated gas from the receiver 17 flows through the gas header 33 and evaporator coil 24 into the liquid header 19, as previously described. The normal supply of saturated gas present in the receiver at any time is inadequate to accomplish a complete defrost of the evaporator and, as soon as the saturated gas begins to flow out through the gas header 33, the pressure in the receiver 17 begins to drop causing liquid refrigerant to boil and provide additional gas at saturated temperature for the pressure at which it is formed. However, this additional saturated gas supply is still inadequate for defrosting partially due to the volumetric flow rate of the saturated gas 11 om the receiver. Furthermore, the rapid pressure drop receiver 17 will lower the liquid header pressure ““g ,¹^¹^ to the still refrigerating evaporator coils 21, 22 and 23 and, in general, causes an inbalance in the system operation.

According to the present invention, the valve 45 in the conduit 44 connected to the compressor discharge hne 13 is set to open at about 1 p.s.i.g. to 5 p.s.i.g. pressure differential so that during defrost superheated gaseous refrigerant is metered through the gas percolation injector 47 into the liquid refrigerant supply thereby maintaining the receiver pressure substantially at the condensing pressure and effecting a rapid heat exchange between the gaseous and liquid refrigerant in the receiver 17 to provide a constant supply of desuperheated or saturated gas at the pressure maintained by the valve 45 from the compressor 10.

During usual winter conditions with much colder ambient conditions, the condenser temperature and pressure can drop appreciably so that the liquid discharged from the condenser 14 is sub-cooled. Furthermore, under such winter conditions, the head pressure of the compressor 14 may drop appreciably below the desirable or necessary pressure required for proper operation of the system In order to maintain compressor head pressure above a mmimum of about 175 p.s.i.g., the modulating valve 50 is throttled in response to the head pressure pilot control 51 therefor to restrict the flow of refrigerant from the condenser 14 and result in condenser flooding thereby reducing condenser capacity and tending to maintain the compressor head pressure at or above this predetermined minimum. Sub-cooled liquid from the condenser 14 may by-pass the surge receiver 17 through the inlet and outlet legs 16 and 18 into the liquid header 19 for supplying the evaporators, _which will refrigerate more efficiently with sub-cooled liquid and create a smaller demand from the receiver 17.

„_I,i^F0r4c^{inter erati0n}’^{the conduit 44} and control check rrfriL™ Provides a by-pass flow of superheated gaseous refrigerant from the compressor conduit 13 into the percothA°nrp^Cham^^er?³ °^f-^{the receiver}’ ^thereby maintaining the pressure in the receiver at approximately 1 to 5 p s i g ret^eran/T^r^ ^{head preSSUre}· ^{This flow of} g^aseous f igerant directly from the compressor discharge 13 y percolation through the liquid refrigerant supply in the receiver 17 effects a heat exchange in which the superheat of the gaseous refrigerant is transferred to the liquid refrigerant and a quantity of the liquid is boiled off or vaporized thereby maintaining a constant supply of sat^l'ra ed gas at the normal saturation temperature/pressure of the refrigerant, such gas being available for defrost purposes.

From the foregoing it will be apparent that a balanced condition can be maintained for year-round operation of the refrigeration system, this balanced condition maintaining the compressor head pressure above about 175 p.s.i.g. by controlling the modulating valve 50 to throttle refrigerant flow from the condenser 14 when the head pressure drops below 175 p.s.i.g., the head pressure of the compressor also being essentially maintained in the

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3,427,819 means forming a liquid refrigeration source and a saturated gas source, and a plurality of evaporators connected in parallel between said liquid refrigerant source and said compressor suction side in a normal refrigeration cycle, said evaporators returning vaporous refrigerant having a superabundant latent heat load in excess of the heat load required to defrost any of said evaporators, means for selectively isolating said evaporators from said normal refrigeration cycle and connecting said selected evaporator to said saturated gas source, for defrosting, and other means for returning liquid refrigerant resulting from said defrosting of said selected evaporator into said refrigeration system, the improvement comprising, second means for connecting said compressor discharge side, into said liquid refrigerant source below the minimum liquid level thereof for maintaining the high side pressure in said first means and providing a constant supply of saturated gas for defrosting said evaporators. . .

4. The refrigeration system according to claim 3,. m which said first means comprises a surge receiver having a vertical base column, and said second means comprises a gas injector positioned in said base column and being connected through a valve-controlled conduit to said compressor discharge. . . .

The refrigeration system according to claim 4, m which said valve-controlled conduit includes normally closed valve means adapted to open upon a predetermined pressure drop in said surge receiver. . .

6. The refrigeration system according to claim 4, m receiver 17 (with only a 1 to 5 p.s.i.g. drop) and thereby maintaining the refrigerant pressure in the liquid line 19 above the pressure setting of the pressure regulating valve 37 so that the liquid line pressure downstream of this valve is constantly at 160 p.s.i.g. Furthermore, the minimum receiver pressure of about 170 to 175 p.s.i.g. is the effective pressure under which saturated gas is conducted through the gas defrost header 33 and within the desired 10 to 20 p.s.i. pressure differential across the defrosting evaporator for establishing rapid refrigerant flow through the evaporator into the liquid header 19.

It will be apparent that the receiver 17 forms a primary source of liquid refrigerant and a saturated gas supply for normal refrigeration and defrosting of the evaporators 21, 22, 23 and 24. In the FIG. 3 embodiment the gas separation and percolation device 57 forms a secondary liquid source, but is the primary source of saturated gas. The check valve 49 is set to open at a negligible pressure of about 0.25 p.s.i.g. under unusual climatic conditions such as when a roof-mounted condenser 14 is employed and the warm environment of the receiver 17 in an operating room causes the pressure in the receiver to exceed the condensing pressure. However, the primary function of the check valve 49 is to prevent gas flow directly from the compressor 10 into the top of the receiver 17.

In addition to winter conditions, it will also be apparent that the condensing capacity may have to be reduced by throttling the modulating valve 50 sometimes 6. The retrigerauon ^m ^^ul^e^ed^v‘““the’’top during normal operation of the refrigeration system such 30 which the top of said surge e“ _means^Pas when the compressor 10 is a multicylinder unit having of said condense means ^y_{Q claim 4 in} unloader or capacity control means and the suction load . 52 ? ° _a receiver means and from the evaporators is reduced to cause unloading of which said ^firs^ ™^ans_c ?_{ses a gas separating an}d _.. _ cvfinders. Sato sec^ itfon is Offiv to be means and forming a secondary liquid refrigerant source, said device having a lower tank portion connected between said condenser means and receiver means and an upper portion vented to the top of said receiver means, and a gas injector positioned in said device below the minimum liquid level therein and being connected through a valve-controlled conduit to said compressor discharge. ,. , . _ .

uuecLcu 8. The refrigeration system according to claim 7, insuction 45 eluding means for equalizing the condensing pressure to the saturated gas pressure in the top of said receiver means, said last mentioned means having one-way valve means preventing the flow of hot gaseous refrigerant from said compressor and condenser means into said duurvv.

9. In a refrigeration system having a compressor with discharge and suction sides, condenser means connected to said compressor discharge side, receiver means connser nected to said condenser means and providing a liquid said 55 refrigerant source, a liquid header connected to said receiver means, and a plurality of evaporator means normally connected to said liquid header for receiving liquid refrigerant from said receiver means and returning gaseous refrigerant to said compressor suction side, the tween said condenser and receiver means, said modulating valve means having a pilot control externally connected between said compressor discharge and said condenser means and being directly responsive to compressor head pressure.

10. The refrigeration system according to claim 9, m which said condenser means comprises multiple condenser units having parallel inlet branch lines connected in parallel flow to said compressor means and having outlet branch lines connected in parallel flow by conduit means to said receiver means, and means forming a liquid seal across said branch lines.

e a wmpicMut 11. ^The refrigeration system according to claim 10, in condenser, first 75 which said outlet branch lines are connected by a substanone or more compressor cylinders.

The foregoing description ise given &lt; . . lustration and example, and the invention is only to be limited by the scope of the claims which follow.