US 3350895 A
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J. R. HARNISH Nov. 7, 1967 DEFROST MEANS FOR NON-REVERSIBLE REFRIGERATION SYSTEMS Filed Jan. 11, 196e DLC /DLCS FIG. l.
/IRas Rss INVENTOR: JAMES RHARNISH BY f J ,WM
ATTORNEY United States Patent O 3,350,895 DEFROST MEANS FOR NON-REVERSIBLE REFRGERATION SYSTEMS James R. Hamish, Staunton, Va., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Jan. 11, 1966, Ser. No. 519,878 7 Claims. (Cl. 62--197) ABSTRACT F THE DISCLOSURE A refrigeration system includes a compressor, a condenser, a heat exchange coil, an expansion valve, an evaporator and an accumulator connected in series in the order named. A normally closed valve is connected across the expansion valve. When defrosting of the evaporator is required, the normally closed valve is opened, draining liquid from the condenser and the heat exchange coil, which liquid flows through the evaporator into the accumulator where it is stored. After the condenser is emptied, hot gas flows through the heat exchange coil which is arranged to evaporate liquid within the accumulator, some of this gas being condensed within the heat exchange coil as it boils liquid within the accumulator to provide discharge gas to the compressor. The remainder of the hot gas flows through the evaporator where it is condensed, thus providing heat for defrosting the evaporator, the condensed liquid owing into the accumulator where it is evaporated by heat from the heat exchange coil.
This invention relates to the defrosting of evaporators of non-reversible refrigeration systems, and has as objects to simplify and to reduce the cost of the equipment used for defrosting, while providing a rapid defrost without damaging the refrigerant compressors of the systems.
It is Well known that air cooling evaporators which operate at temperatures low enough for frost to form on their surfaces, have to be defrosted periodically. Methods of melting the frost have included spraying water on the surfaces of the evaporators; heating the evaporators with electric heat, and using hot discharge gas from associated compressors.
This invention simplifies and reduces the cost of equipment for defrosting an evaporator of a refrigeration system having a suction line accumulator, and having a heat exchange coil within the accumulator through which refrigerant liquid is flowed on its way to the associated expansion valve, as disclosed in my copending application, Ser, No. 447,008, filed April 9, 1965, now Patent No. 3,264,837, by simply placing a normally closed valve across the expansion valve. The normally closed valve is opened when defrosting is required, and drains liquid out of the associated condenser and the coil within the accumulator, which liquid Hows through the evaporator into the accumulator where it is stored. After the condenser is emptied, discharge gas from the associated compressor flows through the coil within the accumulator where some of it is condensed as it boils off refrigerant liquid within the accumulator to supply suction gas to the compressor. The remainder of the discharge gas flows through the now open, normally closed valve into the evaporator where it condenses and provides heat for melting the frost on the evaporator, the condensed refrigerant flowing from the evaporator into the accumulator where it is evaporated by heat from the heat exchange coil within the accumulator.
An increase in the speed of defrosting can be accomplished by throttling the ow of discharge gas from the compressor. This increases the power required by the compressor, and increases the heat it adds to the refrigerant.
3,350,895 Patented Nov. 7, 1967 This invention will now be described with reference to the annexed drawings, of which:
FIG. 1 is a diagrammatic view of a refrigeration system embodying this invention;
FIGS. 2a and 2b are diagrammatic views of the compressor motor starter, and the fan motor starter respectively, used with the system of FIG. 1;
FIG. 2c is a diagrammatic view of the defrost relay;
FIG. 2d is a diagrammatic View of the timer used to initiate the defrosting of the evaporator of FIG. 1;
FIG. 3 is a simplified electrical circuit schematic showing the electrical controls of the system in the positions they occupy when the system is in normal operation, and
FIG. 4 is an enlarged view in section of the pressure regulator valve which may be used instead of the solenoid operated valve and the by-pass around the latter, in the discharge gas tube of FIG. l.
Referring first to FIG. l of the drawings, a hermetic refrigerant compressor C, driven by an enclosed electric motor CM, is connected by discharge gas tube 10 containing a two-way valve VA, shunted by a flow restrictor 11, to the inlet of condenser 12. The outlet of the condenser 12 is connected by liquid tube 14 to the inlet of heat exchange coil 15 in the lower portion of accumulator 16. The outlet of the coil 15 is connected by tube 17 to the inlet of expansion valve 18, the outlet of which is connected by tube 19 to the inlet of evaporator 20. The outlet of the evaporator 20 is connected by tube 21 to the upper portion of the accumulator 16. The expansion valve 18 is shunted by a valve VB. The valve VB is opened and closed by a solenoid SB, and during normal operation is closed. The valve VA is opened and closed by a solenoid SA, and during normal operation, is open. A fan F driven by an electric motor FM, moves air to be cooled over the evaporator 20.
A pressure regulator valve 39 can be used instead of the valve VA, in the discharge gas tube 10. The valve 39 has a diaphragm chamber 40 with a diaphragm 41 extending thereacross. The outer end of a piston rod 42 is attached to the center of the diaphragm 41, and its inner end is attached to a valve piston 43. The valve 39 has a valve chamber 44, and has a partition 45 extending across its interior `between its inlet and outlet. The partition 45 has a valve opening 46. A coiled spring 48 extends between the center of the diaphragm 41 and the end of extension Stl of the diaphragm chamber 40. The spring 48 biases the piston 43 towards the opening 46, and` valve 39 would be wide open. During defrosting, when the temperature and the pressure would be substantially reduced, the valve 39 would throttle towards closed position, thereby throttling the iiow of discharge gas, and causing the compressor C to require more power.
Preferably, the expansion valve 18 is a subcooling control valve such as is disclosed in detail in the previously mentioned application. The valve 18 has a diaphragm chamber 24, the upper portion of which is connected by a capillary tube 25 to a thermal bulb 26 in.` heat exchange contact with the liquid tube 14, and the lower portion of which is connected by a capillary tube 27 to the interior of the tube 14. The valve 18 responds to the pressure and the temperature of the liquid flowing through the tube 14, and meters liquid to the evaporator 20 at the rate at which it is condensed within the condenser 12, while maintaining a predetermined amount of subcooling of the liquid, which may be F. subcooling at a condensing temperature of 100 F.
The accumulator 16 contains a U-shaped tube 30 having an open end 31, and connected at its other end through suction gas tube 32 to the suction side of the compressor C. Portions of the tubes 14 and 32 are in heat exchange contact.
A defrost limit control DLC responds to the condition (pressure or temperature) of the refrigerant within the evaporator 20, and has a switch DLCS which is closed during normal operation, and which opens when the pressure and the temperature of the refrigerant within the evaporator 20 increase as a result of frost having been melted from the surface of the evaporator.
Referring now to FIGS. 2a-2d of the drawings, starter CMS of the compressor motor CM has a switch CMSS which closes when the starter CMS is energized; starter FMS of the fan motor FM has a switch FMSS which closes when the starter FMS is energized; defrost relay R has normally open switches R3S and R48 which close, and normally closed switches R1S and RZS which open, when the relay R is energized, and a conventional clock driven timer T has a switch TS which closes when defrosting is to be started.
Referring now to FIG. 3 of the drawings which shows the various switches in the positions they occupy during normal operation of the system, the compressor motor CM is connected through the switch CMSS of its starter CMS to electric supply lines L1 and L2, and is energized; the fan motor FM is connected through the switch FMSS of its starter FMS, and is energized; the starter CMS is conected through a conventional starter switch SS to the lines L1 and L2, and is energized; the starter FMS is connected through the switch RIS of the relay R to the lines L1 and L2, and is energized; the relay R is connected through the switch TS of the timer T, shunted by switch R45, and the switch DLCS of the control DLC to the lines L1 and L2, and is deenergized; the solenoid SA is connected through the switch R2S of the relay R to the lines L1 and L2, and is energized, and the solenoid SB is connected through the switch R3S of the relay R to the lines L1 and L2, and is deenergized.
Normal operation The compressor C supplies discharge gas through the tube 10 and the open va-lve VA, shunted by the restrictor 11, into the condenser 12. Liquid flows from the condenser 12 through the tube 14, the coil 15 within the accumulator 16, the expansion valve 18 and the tube 19 into the evaporator 20. The latter is supplied by the valve 18 with more refrigerant than it can evaporate so that unevaporated liquid and gas flow from the evaporator 20 through the tube 21 into the accumulator 16. Gas separated from the liquid within the accumulator 16 enters the open end 31 of the tube 30, and ows through the suction gas tube 32 to the suction side of the compressor C.
Heat from the liquid flowing through the coil evaporates the refrigerant liquid liowing from the evaporator through the tube 21 into the accumulator 16, the liquid being further subcooled by this action. Any refrigerant liquid entering the suction gas tube 32 is evaporated by heat from the liquid flowing through that portion of the tube 14 which is in Contact with the tube 32, the liquid being further subcooled by this action.
So far, the described operation is that disclosed in the previously mentioned application. The novelty of the present invention resides in the defrosting system described in the following.
Defrosting operation The timer T periodically closes its switch TS which energizes through the switch DLCS, the relay R which opens its switches RIS and R2S, and closes its switches RSS and R45. The now open switch RIS deenergizes the fan motor starter FMS which opens its switch FMSS, stopping the fan rnotor FM. The now closed switch R38 energizes the solenoid SB which opens the valve VB, permitting unrestricted flow of refrigerant liquid into the evaporator 20 and from the latter into the accumulator 16, draining the condenser 12 and the coil 15. After the condenser 12 has been drained, discharge gas from the compressor C flows through the coil 15 within which some of the gas is condensed while the coil 15 is evaporating some of the liquid within the accumulator 16, to supply suction gas to the compressor C. The remainder of the discharge gas llows through the valve VB into the evaporator 20 where it is condensed, thus providing heat for melting the frost.
The now closed switch R48 provides a holding circuit around the timer switch TS which opens shortly after it closes.
If it is desired to speed up the melting of the frost, the valve VA or the valve 39 can be used. When the valve VA is used, its solenoid SA is deenergized by the now open switch RZS, and closes the valve VA so that all of the discharge gas has to fiow through the restrictor 11, throttling such gas and thereby increasing the power required by the compressor. The compressor thus adds more heat to the refrigerant which on owing through the evaporator 20, melts the frost on the latter.
If the valve 39 is used, it automatically throttles the discharge gas flow when the refrigerant pressure at the underside of its diaphragm 41 is abnormally low resulting from the frost on the evaporator. The valve 39 has the advantages over the valve VA in that the solenoid SA, the switch R28 and the restrictor 11 are not required, and the valve 39 can easily be adjusted to provide a wide range of settings.
When the frost has melted from the evaporator surface, the resulting rise in the temperature (-or pressure) of the refrigerant within the evaporator, causes the limit control switch DLCS to open, deenergizing the relay R which recloses its switches RIS and R2S, and reopens its switches R3S and R48, restoring the refrigeration system to normal operation.
What is claimed is:
1. In a refrigeration system including a refrigerant compressor, a condenser connected to the discharge side of said compressor, accumulator means, a heat exchange coil arranged to heat liquid within said accumulator means connected to said condenser, an expansion valve connected to said coil, an evaporator connected to said expansion valve and to said accumulator means, and a suction gas tube connecting said accumulator means to the suction side of said compressor, the combination of a normally closed valve connected across said expansion valve, and means for opening said normally closed Valve when defrosting of said evaporator is required.
2. The invention claimed in claim 1 in which said means for opening said normally closed valve includes a solenoid, in which means for initiating defrosting of said evaporator is provided, in which electric supply connections are provided, and in which means including said initiating means is provided for connectng said solenoid to said connections.
3. The invention claimed in claim 1 in which the connection of said compressor to said condenser includes means adjustable from a normal position where it permits free flow of discharge gas to said condenser, to a position where it throttles the flow of discharge gas to said condenser.
4. The invention claimed in claim 3 in which said adjustable means comprises a second, normally closed valve, comprises a restrictor connected across said second valve, comprises a solenoid for opening and closing said second valve, in which electric supply connections are provided, in which means for initiating defrosting of said evaporator is provided, and in which means includ- 5 6 ing said initiating means is provided for connecting said expansion Valve is a subcooling control Valve, and in solenoid to said connections. which said means for adjusting said expansion valve in- 5. The invention claimed in claim 3 in which said cludes means responsive to the pressure of the refrigerant adjustable means comprises a pressure regulator valve, leaving said condenser, and includes means responsive to and in which means is provided for throttling said regu- 5 the temperature of said refrigerant leaving said condenser. lator valve towards closed position when discharge gas pressures are abnormally 10W. References Cited 6. The invention claimed in claim l in which means UNITED STATES PATENTS is provided for adjusting said expansion valve to overfeed said evaporator so that unevaporated refrigerant ows 10 lllfr 62% 215615 from the latter into said accumulator means where it is 2983112 5/1961 Batteiuer 62-156 s a c evaporated by heat from said coil.
7. The invention claimed in claim 6 in which said MEYER PERLIN, Primary Examiner.