US3638446A

US3638446A - Low ambient control of subcooling control valve

Info

Publication number: US3638446A
Application number: US837172A
Authority: US
Inventors: Robert T Palmer
Original assignee: Individual
Current assignee: Individual
Priority date: 1969-06-27
Filing date: 1969-06-27
Publication date: 1972-02-01
Anticipated expiration: 1989-02-01

Abstract

A refrigeration system has a condenser coil cooled by outdoor air, and has a subcooling control valve with its thermal bulb in heat exchange contact with the liquid line from the condenser coil. The bulb is normally heated by an electric heater, and the valve is adjusted to provide a desired amount of subcooling of the liquid when the heat applied to the bulb by the electric heater is maximum. At low outdoor temperatures when the condenser pressure decreases so that a conventional subcooling control valve would not open sufficiently, the electric heat is automatically reduced so that the valve opens wider.

Description

D United States Patent [151 3,638,446 Palmer Feb. 1, 1972 [54] LOW AMBIENT CONTROL OF 3,320,763 5/1967 Hamish ...62/222 X SUBCOOLING CONTROL VALVE 3,350,895 1 1/1967 Hamish ..62/278 X [72] Inventor: flzlgrtogbgalmer, 15 Pleasant St., Sharon, Prim), txanane-r Meyer Peru [22] Filed: June 27, 1969 ABSTRACT [21] A N 837,172 A refrigeration system has a condenser coil cooled by outdoor air, and has a subcooling control valve with its thermal bulb in heat exchange contact with the liquid line from the condenser U-Sa a u s u I s s s 2; valve is adjusted to provide a desired amount of subcooling of l e o are 62/19; the liquid when the heat applied to the bulb by the electric heater is maximum. At low outdoor temperatures when the condenser pressure decreases so that a conventional subcool- [56] References cued ing control valve would not open sufiiciently, the electric heat UNITED STATES PATENTS is automatically reduced so that the valve opens wider.

3,316,730 5/1967 Lauer ..62/ 196 18 Claims, 12 Drawing Figures l5 SUBGOOLING THERMAL BULB B NTROL l2 VALVE l I T CONDENSER 2 2 HEATERH COMPRESSOR 0 CM THERMISTOR UNIT TU EVAPORATOR COIL PATENTED FEB 1 B72 SHEH 1 0F 2 F l G. I. I5 sugggg lg THERMAL BULB B '2 l4 VALVE L CONDENSERT W 22 HEATERH EVAPORATOR COIL COMPRESSOR 0 CM no.4.

Ts CMS Y F|G.2. FIG.3. i SII 0M -s| 2. .TS 1%.32 THERMOSTAT T 82 TH] COMPRESSOR I MOTOR STARTER CMS H SUBCOOLING SUBCOOLING ICONTROL m common. l2 VALVE |2 VALVE lj l7 *l? "THERMISTOR TH? EVAPORATOR 3 con. THERMISTOR TH3-EU-' INVENTOR= ROBERT T. PALMER LOW AMBIENT CONTROL OF SIJIIICOOLING CONTROL VALVE BACKGROUND OF THE INVENTION In refrigeration systems having condenser coils cooled by outdoor air, at low outdoor temperatures, the pressure of the liquid from the condenser coils may be insufficient to properly operate the associated expansion means, resulting in erratic control, and in the starving of associated evaporator coils so that condensed moisture freezes on their surfaces. Many socalled low ambient controls responsive to condenser pressure or temperature, to outdoor temperature, or to evaporator pressure or temperature, have been proposed for solving this problem by increasing liquid pressure. Such controls have adjusted dampers of a condenser coil as disclosed in US. Pat. No. 2,958,208; have varied the number of fans moving air over the surface of a condenser coil as disclosed in US. Pat. No. 3,112,620; have used a liquid pump as disclosed in U.S. Pat. No. 2,244,312, and have adjusted the speeds of condenser fan motors as disclosed in US. Pat. Nos. 2,705,404, 2,952,991, 3,196,629 and 2,364,692.

SUMMARY OF THE INVENTION Subcooiing control valves such as are disclosed in U.S. Pat. Nos. 3,264,837 and 3,367,130 are now widely used as expansion valves in refrigeration systems. Such a valve responds through a thermal bulb in heat exchange contact with a highpressure liquid line, to refrigerant liquid temperature, and responds to liquid pressure within the same line. A decrease in the temperature of the thermal bulb without a corresponding decrease in the liquid pressure, tends to open the valve wider, and vice versa.

A refrigeration system having a condenser coil cooled by outdoor air uses a subcooling control valve as an expansion valve. An electric heater is provided for adding heat to the thermal bulb of the valve. The valve would be factory adjusted to provide the desired amount of subcooling with maximum electric heat applied to the bulb. A control responds to a condition within the system caused by a low outdoor temperature, and a resulting decrease in the pressure within the system, and decreases the electric heat applied to the bulb, causing the valve to open wider.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a diagrammatic view of a refrigeration system embodying this invention;

FIG. 2 is a diagrammatic view of a compressor motor starter used in the system;

FIG. 3 is a diagrammatic view of a cooling control thermostat used in the system;

FIG. 4 is a simplified circuit of the controls of the system;

FIG. 5 is a fragmentary, diagrammatic view of a modification of the system of FIG. ll;

FIG. 6 is a fragmentary, diagrammatic view of another modification of the system of FIG. 1;

FIG. 7 is a fragmentary circuit showing FIG. 4 modified in accordance with FIG. 5;

FIG. 8 is a fragmentary circuit showing FIG. 4 modified in accordance with FIG. 6;

FIG. 9 is a fragmentary, diagrammatic view of a modification of FIG. 5;

FIG. 10 is a fragmentary, diagrammatic view of a modification of FIG. 6;

FIG. II is a fragmentary circuit showing FIG. '7 modified in accordance with FIG. 9, and

FIG. 12 is a fragmentary circuit showing FIG. 8 modified in accordance with FIG. 10.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. i of the drawings, refrigerant compressor C, having an enclosed, electric driving motor CM, is connected by discharge gas tube lit to outdoor condenser coil II. which is connected by liquid tube I2 to the inlet of subcooiing controi valve V. The valve V is disclosed in detail in the previously mentioned US. Pat. No. 3,367,130, and has a diaphragm chamber 114 connected by capillary tube 15 to thermal bulb B in heat exchange contact with the liquid tube I2. The outlet of the valve V is connected by tube 17 to evaporator coil 18 which is connected to suction gas tube 19 which has a portion 20 in heat exchange contact with the liquid tube 112; has another portion 21 out of heat exchange contact with the liquid tube 112, and containing a thermistor unit TU; has another portion 22 in heat exchange contact with the liquid tube 12, and has another portion 23 connected to the suction inlet of the compressor C. The thermistor unit TU is shown in detail by FIG. 3 of the US. Pat. No. 3,444,699, and contains a FTC thermistor 'IHl shown by FIG. 4 of the drawings of this application. An electric heater l-I supplies heat to the thermal bulb B in addition to that supplied by the liquid line I2. The arrows alongside the tubing of FIG. I show the direction of refrigerant flow during operation of the system.

Referring to FIG. 2 of the drawings, compressor motor starter CMS has switches SI and S2 which close when the starter CMS is energized.

Referring to FIG. 3 of the drawings, cooling control thermostat T has a switch TS which closes when the thermostat T calls for cooling.

Referring to FIG. 4- of the drawings, the compressor motor starter CMS is connected in series with the thermostat switch TS to electric supply lines LI and L2; the compressor motor CM is connected in series with the switch SI of the starter CMS to the lines L1 and L2, and the thermistor THI is connected in series with the switch S2 of the starter CMS, and the electric heater H to the lines LI and L2.

Operation of FIGS. 11 and 4 When the thermostat T calls for cooling, it closes its switch TS, connecting the starter CMS to the lines LI and L2. The starter CMS closes its switches SI and S2. The closed switch S1 connects the compressor motor CM to the lines L1 and L2, starting the compressor C. The closed switch S2 connects the thermistor Till and the heater H in series to the lines LI and L2, energizing the heater H, and heating the thermal bulb B. The compressor C supplies discharge gas through the tube 10 into the outdoor condenser coil 11. Refrigerant liquid flows from the iatter through the liquid tube I2 and the subcooling control valve V into the indoor evaporator coil 18. Gas and unevaporated refrigerant liquid flow from the coil 18 through the suction gas tube 19 and its

portions

20, 21, 22 and 23 to the suction inlet of the compressor C. The refrigerant flowing through the tube portion 211 flows through the thermistor unit TU in contact with the thermistor THI.

The thermistor TI-Il heated by current flowing therethrough, is evaporatively cooled by its contact with refrigerant liquid droplets. For most effective cooling of the thermistor THI, the refrigerant contacting it should be supersaturated gas containing about 2 percent liquid, being in the nature of a heavy fog. The upstream (with respect to refrigerant flow from the evaporator coil 18 towards the compressor C) suction gas tube portion 20 in contact with the liquid tube 12 is provided for permitting the evaporator coil 18 to be substantially overfed so that, for example, the refrigerant flowing from the latter may be about 12 percent liquid. The heat exchange between the tube portion 20 and the liquid tube i2 evaporates about 10 percent of the liquid leaving about 2 percent liquid to effectively cool the thermistor THE. By making the tube portion 20 longer so that there would be more heat exchange contact between it and the liquid tube 212, the evaporator coil 18 could be overfed by more than 52 percent. By making the tube portion 20 shorter, there would be less heat exchange between it and the liquid tube 12, and the evaporator coil 18 would be overfed by less than 12 percent. By omitting the tube portion 20, the evaporator coil 18 could be overfed by 2 percent. Some liquid is evaporated in cooling the thermistor THl. Any refrigerant liquid flowing from the thermistor unit TU would be evaporated by the heat exchange between the downstream tube portion 22 and the liquid tube 12.

The heat exchange between the suction

gas tube portions

20 and 22 with the liquid tube 12, between the thermistor THl and the liquid flowing through the thermistor unit TU, provide subcooling of the liquid, which subcooling added to that provided by the valve V greatly increases the refrigerating effect, aiding the valve V in overfeeding the evaporator coil 18 by the desired amount.

The heater H adds heat to the thermal bulb B, and this is taken into account in the factory calibration and adjustment of the valve V. The heat applied by the heater H to the bulb is maximum during normal operation of the system, with the evaporator coil 18 overfed as described in the foregoing. The

evaporator coil 18 is overfed by an amount equal to that of the refrigerant liquid evaporated in other portions of the system.

At low outdoor temperatures, the pressure within the condenser coil 11 decreases, and may become insufficient to cause the valve V to open sufficiently. When this abnormal condition occurs, the amount of refrigerant liquid contacting the thermistor 'II-II decreases below 2 percent, the temperature of the thermistor THl increases, and its electrical resistance increases, decreasing the current flowing through the heater H, and causing the valve V to open wider.

The U.S. Pat. Nos. 3,397,552, and 3,444,699, disclose thermistor units, and suction gas tube to liquid tube contact as ;isclosed herein, but the expansion valves of these patents are not subcooling control valves, and their thermistors control the heat applied to bimetallic diaphragms of other types of expansion valves.

The U.S. Pat. No. 3,388,558, discloses the heating of the thermal bulb of a subcooling control valve by an electric heater, but such heater is turned on only when the compressor of the system stops, and is not turned on during normal operation of the system.

The system of FIGS. 1 and 4 could be embodied in a heat pump in which the operation described in the foregoing is the cooling operation of the heat pump. Such a heat pump could include an accumulator, and a heat exchange coil within an accumulator as disclosed in the previously mentioned U.S. Pat. No. 3,444,699.

Description of FIGS. 5 and 7 The system of FIG. 5 modifies that of FIG. 1 by omitting the upstream suction gas tube portion in contact with the liquid tube 12; by omitting the suction gas tube portion 21 and the thermistor unit TU, and by placing a NTC thermistor TH2 in heat exchange contact with the liquid line 12. The circuit of FIG. 7 modifies that of FIG. 4 by replacing the thermistor THl with the thermistor TH2.

Operation of FIGS. 5 and 7 When the pressure within the liquid line 12 decreases below normal, the temperature of the liquid flowing through the liquid line 12 decreases conformably. The thermistor TH2 responds to the temperature of the liquid line 12 adjacent to the valve V. When the temperature of the thermistor TH2 decreases because of a reduction in pressure, its electrical resistance increases, reducing the current flowing through the heater H, and causing the valve V to open wider.

The thermistor TI-I2 could be placed in contact with the liquid line 12 on the other side of the suction gas tube portion 22 but would have to be calibrated differently since it would not respond to the temperature (through the tube 12) of liquid subcooled by the heat exchange between the tube 12 and the suction gas tube portion 22. The thermistor TH2 could be placed in heat exchange contact with a surface such as a return bend, of the condenser coil 11. The thermistor TH2 could also be exposed to outdoor air so as to respond to the temperature thereof.

Description of Figures 6 and 8 The system of FIG. 6 modifies that of FIG. I by omitting the upstream suction gas tube portion 20 in contact with the liquid tube 12; by omitting the suction gas tube portion 21 and the thermistor unit TU, and by placing a NTC thermistor TH3 in contact with the suction gas tube 19 at the outlet of the evaporator coil 18. The circuit of FIG. 8 modifies that of FIG. 4 by replacing the thermistor TI-Il with the thermistor TI-l3.

Operation of Figures 6 and 8 Description of Figures 9 and 10 The system of FIG. 9 modifies that of FIG. 5 by omitting the thermistor TH2, and replacing it with a pressurestat P1 in the liquid tube 12, the pressurestat Pl having a bellows Bl connected to slider 30 of variable resistor R1.

The system of FIG. 10 modifies that of FIG. 6 by omitting the thermistor TI-I3, and replacing it with a pressurestat P2 in the suction gas tube 19 at the outlet of the evaporator coil 18, the pressurestat P2 having a bellows B2 connected to slider 31 of variable resistor R2.

Description of Figures 11 and 12 The system of FIG. 11 modifies that of FIG. 7 by substituting the resistor R1 for the thermistor TH2.

The system of FIG. 12 modifies that of FIG. 8 by substituting the resistor R2 for the thermistor TH3.

Operation of Figures 9 and 11 When the pressure within the liquid tube 12 decreases below normal, the bellows B1 of the pressurestat PI contracts, and moves the slider 30 of the resistor R1 along the latter to increase its resistancein series with the heater H, reducing the current flowing through the latter, reducing the heat from the latter, and causing the valve V to open wider.

Operation of Figures 10 and 12 When the pressure within the suction gas tube 19 decreases below normal, the bellows B2 of the pressurestat P2 contracts, and moves the slider 31 of the resistor R2 along the latter to increase its resistance in series with the heater H, reducing the current flowing through the latter, reducing the heat from the latter, and causing the valve V to open wider.

The embodiments of FIGS. 5-7 and 6-8 could be incorporated within heat pumps, and the latter could include accumulators as disclosed in the previously mentioned U.S. Pat. No. 3,264,837.

For permitting field adjustments, variable resistors could be placed in series with the thermistors THl, TH2 and THIS, and in series with the resistors R1 and R2,.

Among the advantages of this invention are that it provides a low ambient control that is simpler, less expensive, and more effective than prior low ambient controls.

I claim:

1. In a refrigeration system having a refrigerant compressor, a condenser coil cooled by outdoor air, a liquid tube, a subcooling control valve, an evaporator coil, and a suction gas tube connected in series in the order named, said valve having a thermal bulb in heat exchange contact with said liquid tube, the improvement comprising an electric heater for said bulb, and means for energizing said heater to apply maximum electric heat to said bulb during normal operation of, with normal pressure and temperature within, said system, and for reducing the electric heat applied to said bulb during operation of said system when a low outdoor temperature causes the pressure and temperature within the system to decrease below normal.

2. The improvement claimed in claim 1 in which said means includes temperature-responsive means.

3. The improvement claimed in claim 1 in which said means includes means responsive to the temperature and quantity of refrigerant liquid flowing from said evaporator coil into said suction gas tube.

4. The improvement claimed in claim 3 in which said means responsive to temperature and quantity comprises a thermistor within said suction gas tube.

5. The improvement claimed in claim 1 in which said means includes means responsive to the temperature of the refrigerant liquid within said system, upstream with respect to refrigerant flow, of said suction gas tube.

6. The improvement claimed in claim 5 in which said temperature-responsive means comprises a thermistor.

7. The improvement claimed in claim 1 in which said means includes means responsive to the temperature of the refrigerant between said evaporator coil and said compressor.

8. The improvement claimed in claim 7 in which said means responsive to temperature comprises a thermistor.

9. The improvement claimed in claim 1 in which said means comprises electric supply connections, and variable resistor means connected in series with said heater to said connections.

10. The improvement claimed in claim 9 in which said resistor means comprises a thermistor within said suction gas tube.

11. The improvement claimed in claim 9 in which said resistor means comprises a thermistor responsive to the temperature of the refrigerant between said evaporator coil and said compressor.

12. The improvement claimed in claim 9 in which said resistor means comprises a thermistor responsive to the temperature of the refrigerant liquid within said system, upstream with respect to refrigerant flow, of said suction gas tube.

13. The improvement claimed in claim 9 in which said resistor means comprises a thermistor within said suction gas tube, and in which said suction gas tube is in heat exchange contact with said liquid tube between said thermistor and said evaporator coil.

14. The improvement claimed in claim 13 in which said suction gas tube is in heat exchange contact with said liquid tube between said thermistor and said compressor.

15. The improvement claimed in claim 9 in which said resistor means comprises a thermistor responsive to the temperature and quantity of refrigerant liquid flowing from said evaporator coil into said suction gas tube.

16. The improvement claimed in claim 9 in which means responsive to pressure within said system is provided, and which has means for varying the resistance of said resistor means in accordance with changes in said pressure.

17. The improvement claimed in claim 16 in which said pressure-responsive means responds to pressure within said system between said suction gas tube and said condenser coil.

18. The improvement claimed in claim 16 in which said pressure-responsive 'means responds to pressure within said system between said evaporator coil and said compressor.

Claims

18. The improvement claimed in claim 16 in which said pressure-responsive means responds to pressure within said system between said evaporator coil and said compressor.