US3364692A

US3364692A - Refrigeration systems having aircooled condenser coils

Info

Publication number: US3364692A
Application number: US605693A
Authority: US
Inventors: James C Reynolds
Original assignee: Westinghouse Electric Corp
Current assignee: YORK-LUXAIRE Inc A CORP OF DE
Priority date: 1966-12-29
Filing date: 1966-12-29
Publication date: 1968-01-23
Anticipated expiration: 1985-01-23

Description

Jan. 23, 1968 J. c. REYNOLDS 3,364,692

REFRIGERATION SYSTEMS HAVING AIR-COOLED CONDENSER COILS Filed Dec. 29, 1966 P Sheets-Sheet 1 F|G.l. |o P082 PCS! 20 HPCS ACCUMULATOR o EFM CFM

CF CONDENSER HERMETIC EVAPORAT R COMPRESSOR con. 0

SUBCOOLING CONTROL VALVE INVENTOR= JAMES C.REYNOLDS, BY WJQW ATTORNEY Jan. 23, 1968 .1. c. REYNOLDS REFRIGERATION SYSTEMS HAVING AIR-COOLED CONDENSER COlLS 2 Sheets-$heet Filed Dec. 29, 1966 CGNDENSER EVAPORATOR COlL-- l8 COIL W \m a w 2 n ii O 1 Z 6 D;

ENVENTGF? JAMES C Bvwmmi ATTOWflEY United States Patent 3,364,692 REFRIGERATlGN SYSTEMS HAVING AIR- COQLED CONDENSER COILS James C. Reynolds, Staunton, Va., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Dec. 29, 1966, Ser. No. 605,693 16 Claims. (Cl. 62184) ABSTRACT OF THE DlSCLCSURE A control responsive to the temperature or the pressure of the refrigerant at the evaporator of a refrigeration system, acts to decrease the speed of the motor of the condenser fan of the system when the temperature and the pressure of the refrigerant at the evaporator decrease, and vice versa. Another control responsive to the temperature or the pressure of the discharge gas of the system, acts to speed up the condenser fan motor when the discharge gas pressure increases to closely approach that at which the switch of the high pressure cut-out of the system would open.

This invention relates to refrigeration systems having air-cooled condenser coils, and has as an object to control the speeds of fans used for moving air over such coils, in accordance with the temperatures or pressures of refrigerants at the evaporator coils of such systems.

As is well known, at low outdoor temperatures, the refrigerant pressures in air-cooled condensers decrease until there may insufiicient pressure at the associated expansion devices to properly operate the latter, resulting in erratic control, and in starving evaporator coils so that condensed moisture freezes on their surfaces. Many so-called low ambient controls responsive to condenser temperatures or pressures, or to outdoor temperatures, have been proposed for overcoming this problem. Such controls have included means for adjusting dampers of a condenser coil as disclosed in Patent No. 2,958,208; have included means for varying the number of fans moving air over a condenser coil as disclosed in Patent No. 3,112,620; have included liquid pumps as disclosed in latent No. 2,244,312, and have included means for varying the speeds of condenser fans as disclosed in Patent Nos. 2,705,404, 2,952,991 and 3,196,629.

This invention takes into account that low evaporator loads as well as low outdoor temperatures can cause evaporators to become starved, and provides a control circuit for adjusting the speed of a condenser fan in accor-dance with the temperature or the pressure of the refrigerant at an associated evaporator.

This invention also takes into account that reducing the speed of a condenser fan may result in such a high head pressure that the switch of the usual high pressure cut-out may open and stop the motor of the associated refrigerant compressor, and provides a control for increasing the condenser fan speed when the head pressure approaches that at which the cut-out switch would open.

This invention will now be described with reference to the annexed drawings, of which:

FIG. 1 is a diagrammatic view of a refrigeration system embodyin this invention;

FIGS. 2, 3 and 4 are diagrammatic views of the starters of the compressor motor; the evaporator fan motor, and the condenser fan motor respectively;

FIG. 5 is a diagrammatic view of the thermostat used;

FIG. 6 is a circuit schematic showing the controls of the compressor and fan motors;

FIG. 7 is a fragmentary diagrammatic view showing a modification of FIG. 1;

3,364,692 Patented Jan. 23, 1968 FIG. 8 is a fragmentary circuit schematic showing FIG. 6 modified in accordance with FIG. 7;

FIG. 9 is a fragmentary diagrammatic view showing another modification of FIG. 1, and

FIG. 10 is a fragmentary circuit schematic showing FIG. 6 modified in accordance with FIG. 9.

Referring first to FIG. 1 which shows a refrigeration system generally similar to that disclosed in Patent No. 3,264,837 of J. R. Harnish, a conventional, hermetic refrigerant compressor C, driven by an enclosed electric motor CM, has its outlet connected by discharge gas tube 16 containing a conventional high pressure cut-out HPC having a normally closed switch HPCS, and containing a pressure control PC having a normally closed switch PCSl and a normally open switch PCS2, to One end of condenser coil 11. The other end of the coil 11 is connected by liquid tube 12 to one end of heat exchange coil 13 within accumulator 15. The other end of the coil 13 is connected by tube '16 to the inlet of subcooling control valve 17, the outlet of which is connected by tube 17 to one end of evaporator coil 18. The other end of the coil 18 is connected by tube 19 to the upper portion of the accumulator 14. The latter is connected by suction gas tube 20 to the inlet of the compressor C.

A fan CF driven by a shaded-pole motor CFM, moves outdoor air over the surface of the condenser coil 11. A fan EF driven by an electric motor EFM, moves indoor air over the surface of the evaporator coil 18.

The subcooling control valve 16, the details of which are disclosed in the previously mentioned patent of J. Hamish, has a diaphragm chamber 22, the outer portion of which is connected by capillary tube 23 to thermal bulb 24 in heat exchange contact with the liquid tube 12, and the inner portion of which is connected by capillary tube 25 to the interior of the tube 12, Instead of using the capillary tube 25, the valve 16 could be internally equalized since the pressure drop across the coil 13 is insignificant. The valve 16 responds through the capillary tube 23 and the thermal bulb 24 to the temperature of the liquid within the tube 12, and responds through the capillary tube 25 to the pressure of the liquid within the tube 12, and is adjusted as disclosed in the previously mentioned Harnish patent, to meter refrigerant to the evaporator coil 18 at the rate at which the refrigerant is condensed in the condenser coil 11, while maintaining a predetermined amount of subcooling of the refrigerant liquid, which may be 10 F. subcooling, at a condensing temperature of 100 F. As the subcooling decreases, more liquid is backed up in the coil 11 by the valve 16 to increase the subcooling, and vice versa.

A NTC (negative temperature coetficient of resistance) thermistor Tl-Il is in heat exchange contact with the tube 19 at the outlet of the evaporator coil 18, although it could be in contact with a return bend of the coil 18, or in contact with the tube 17 at the inlet of the coil 18. Another NTC thermistor TH2 is in heat exchange contact with the discharge gas tube 10.

Referring now to FIGS. 2, 3, 4 and 5, compressor motor starter CMS has an energizing coil 29, and has switches CMSS which close when the coil 29 is energized; evaporator fan motor starter EFMS has an energizing coil 30, and has switches EFMSS which close when the coil 30 is energized; condenser fan motor starter CFMS has an energizing coil 31, and has switches CFMSSI and CFMSS2 which close when the coil 31 is energized, and thermostat T respectively, has a normally open switch TS which closes when the thermostat T calls for cooling.

Referring now to FIG. 6, stator winding 28 of the fan motor CFM is connected through the switch CFMSSI to AC line L1, and is connected in series with diode 33, wire 34, silicon controlled rectifier SCR, wire 35, diode 36 and the switch CFMSSZ to AC line L2. The

diodes

33 and 36 are connected with

diodes

37 and 38 in a fullwave rectifier bridge B. The rectifier SCR, as is well known, is a solid state switch, and controls AC to the motor CFM as a function of the phase angle at which it is fired by its gate circuit. When fired, it conducts until the voltage at its anode decreases to zero voltage at the end of each half-cycle. The junction of the

diodes

36 and 37 is negative, and is connected to the wire and to the cathode of the rectifier SCR. The junction of the

diodes

33 and 38 is positive, and is connected to the wire 34, and to the anode of the rectifier SCR. The wire 34 is connected through resistor 40 to wire 41 which is connected through resistor 42 to base terminal 43 of unijunction transistor 44, the other base terminal 45 of which is connected by resistor 46 to the wire 35, and to gate 47 of the rectifier SCR. Variable resistor 48 is connected to the wire 41, and in series with capacitor 49 to the wire 35, their junction being connected to control electrode 50 of the transistor 44. The thermistor TH1 is connected to the positive wire 41, and in series with variable resistor 51 to the negative wire 35, their junction being connected through the switch PCSI of the pressure control PC, and the diode 54 to the junction of the resistor 48 and the capacitor 49. The thermistor TH2 is connected to the wire 41, and in series with variable resistor 58 to the wire 35, their junction being connected through the switch PCS2 of the control PC, to the diode 54. A Zener diode 55 is connected to the

wires

41 and 35, and clamps the voltage between them to a fixed level.

The

resistors

51 and 58 are adjustable to control the operating points of the thermistors TH1 and THZ respectively, and the resistor 48 is adjustable to fix the speed range of the condenser fan motor CFM.

The speed control circuit described so far in connection with FIG. 6, except for the use of two thermistors, is conventional, and is similar to the circuit disclosed on page 132 of the GE SCR manual, Third Edition.

The compressor motor starter coil 29 is connected in series with the switch HPCS of the high pressure cut-out HPC, and the switch TS of the thermostat T to the lines L1 and L2. The coil 30 of the evaporator fan motor starter is connected in series with the switch TS to the lines L1 and L2. The coil 31 of the condenser fan motor starter is connected in series with the switch TS to the lines L1 and L2. The compressor motor CM is connected through the switches CMSS to the lines L1 and L2. The evaporator fan motor EFM is connected through the switches EFMSS to the lines L1 and L2.

OPERATION OF FIGS. 1 AND 6 When the thermostat T calls for cooling, it closes its switch TS, energizing through the closed switch HPCS, the compressor motor starter CMS which closes its switches CMSS, starting the compressor motor CM. The closed switch TS also energizes the evaporator fan motor starter EFMS which closes its switches EFMSS, starting the evaporator fan motor EFM. The closed switch TS also energizes the condenser fan motor starter CFMS which closes its switches CFMSSI and CFMSSZ, starting the condenser fan motor CFM. The compressor C supplies discharge gas through the cut-out HPC, the tube 10 and the control PC into the condenser coil 11. Liquid flows from the coil 11 through the tube 12, the heat exchange coil 13 within the accumulator 14, and the tube 15 into the subcooling control valve 16. Refrigerant expanded within the valve 16 flow through the tube 17 into the evaporator coil 18, overfeeding the latter. Gas and unevaporated refrigerant liquid fiow from the coil 18 through the tube 19 into the accumulator 14. Gas separated from the liquid within the accumulator 14 flows through the suction gas tube 20 to the suction inlet of the compressor C.

Heat from the high pressure liquid flowing through the coil 13 within the accumulator 14, evaporates the excess liquid supplied from the evaporator coil 18 into the accumulator 14, the high pressure liquid being subcooled by this action. Any refrigerant liquid flowing through the suction gas tube 20 is evaporated by the heat exchange contact of the latter with the liquid tube 12, the liquid flowing through the latter being further subcooled by this action.

At evaporator temperatures above, for example, 34 F., the components of the control circuit of FIG. 6 have such characteristics that the fan motor CFM operates at full speed. Below 34 F., the fan motor CFM speed decreases with faliing evaporator temperature, reaching a minimum speed at, for example, 28 F.

The pulsating DC voltage supplied from the rectifier bridge B through the wire 34, the resistor 40, the Wire 41, and the resistor 48 to the capacitor 49 and the control electrode 50 of the transistor 44, is insufiicient to cause the transistor 44 to conduct. The latter conducts during each half-cycle when additional positive voltage is supplied from the junction of the thermistor TH1 and the resistor 51, through the diode 54 to the capacitor 49 and the control electrode 50 of the transistor 44, and added to the DC voltage supplied through the resistor 48, as will be described in the following.

The thermistor TH1 and the resistor 51 form a voltage divider, the positive DC voltage at their junction increasing with decreasing resistance of the thermistor TH1 caused by increases in its temperature, and vice versa. At temperatures above 34 F., the resistance of the thermistor TH1 is sufficiently small that the voltage supplied from its junction with resistor 51, through the diode 54 to the capacitor 49 is sufiicient to provide sufficient additional voltage at the control electrode 50 of the transistor 44 to cause the latter to conduct early during each half-cycle. When the transistor 44 conducts, it discharges the capacitor 49 into the gate 47 of the rectifier SCR, causing the latter to conduct early during each half-cycle, and to energize the condenser fan motor CFM so that it operates at full speed.

When the evaporator temperature and the corresponding temperature of the thermistor TH1 decrease below 34 F., the resistance of the thermistor TH1 increases, decreasing the voltage supplied through the diode 54 to the capacitor 49 so that the transistor 44 and the rectifier SCR conduct later during each half-cycle, decreasing the speed of the fan motor CFM in accordance with the decrease in evaporator temperature down to an evaporator temperature of 28 F. At the latter temperature, the speed of the motor CFM decreases to a minimum. The reduction in the speed of the condenser fan motor reduces the cooling of the condenser coil 11, increasing the condenser and evaporator pressures.

Since the subcooling control valve 16 backs up liquid within the condenser coil 11 for maintaining subcooling, decreasing the cooling of the condenser coil l l by reducing the speed of its fan motor CFM, results in the valve 16 backing up more liquid within the condenser coil to satisfy the subcooling requirements. This may result in such a reduction of the active condenser surface that there may be a rise in the head pressure sufficient to cause the switch HPCS of the high pressure cut-out HPC to open and stop the compressor motor CM. To prevent this, the control now to be described is used. When the head pressure approaches closely the pressure at which the switch HPCS would open, the pressure control PC opens its switch PCSl and closes its switch PCS2. The now open switch PCSI disconnects the thermistor TH1 from the diode 54. The now closed switch PCS2 connects the thermistor THZ to the diode 54. The thermistor TH2 and the resistor 58 form a voltage divider, the voltage at their junction increasing with increasing temperature of the thermistor TH2, and vice versa. The thermistor THZ responds to the temperature of the discharge gas fiowing through the tube 10, which temperature varies conformably with the pressure of thedischarge gas. The resistor 58 is adjusted to cause its junction with the thermistor TH2 to deliver a higher voltage to the diode 54 than the junction of the thermistor TH1 and the resistor 51 delivered when just before the switch PCSl opened, so that the transistor 44 and the rectifier SCR conduct earlier during each half-cycle than when the switch PCSI was closed, and cause the speed of the condenser fan motor CFM to increase. If the head pressure should increase further, the temperature of the discharge gas would increase in proportion, and the thermistor THZ would cause a further increase in the speed of the motor CFM.

It is well known that the temperature and the pressure of refrigerant at an evaporator vary conformably so that a pressure responsive control can be substituted for a temperature responsive control, and vice versa. The modification of FIG. 1 shown by FIG. 7, omits the thermistor THl, and substitutes therefor an equivalent pressure responsive control consisting of a modulating pressurestat 61: connected in the tube 19 at the outlet of the evaporator coil 18. The pressurestat 60 has a bellows 61 connected to slider 62 of resistor 63, the resistance of the latter decreasing with increase in refrigerant pressure, and vice versa. The modification of FIG. 6 shown by FIG. 8, omits the thermistor THl, and substitutes therefor the resistor 63, the resistance of which decreases with increasing temperature and pressure of the refrigerant at the evaporator coil 18, and vice versa, and operates in the modification of FIG. 6 in the same manner as does the th rmistor THI of FIG. 6.

It is also well known that the temperature and the pressure of discharge gas vary conformably so that a pressure responsive control can be substituted for a temperature responsive control, and vice versa. The modification of FIG. 1 shown by FIG. 9, omits the thermistor THZ, and substitutes therefor an equivalent pressure responsive control consisting of a modulating pressurestat -65 connected in the discharge gas tube 19 at the inlet of the condenser coil 11. The pressurestat 65 has a bellows 66 connected to slider 67 of resistor 68, the resistance of the latter decreasing with increase in discharge gas pressure, and vice versa. The modification of FIG. 6 shown by FlG. 10, omits the thermistor THZ, and substitutes therefor the resistor 68, the resistance of which decreases with increasing temperature and pressure of the discharge gas, and vice versa, and operates in the modification of FIG. 6 shown by FIG. 10, in the same manner as does the thermistor TH2 of FIG. 6.

While this invention has been described in connection with a system using a subcooling control valve as an expansion valve, it applies to systems using other forms of expansion means.

Use of this invention will result in operation at minimum discharge pressures with resulting low power consumption through a broad range of condenser entering air temperatures, and/or decreasing evaporator loads. What is more important is that this invention will prevent freezing of an evaporator coil under both lower than normal condenser air temperatures, and lighter evaporator loads than has been accomplished in prior systems.

What is claimed is:

1. A refrigeration system comprising a refrigerant compressor, a condenser coil, expansion means, and an evaporator connected in series in a refrigeration circuit; a fan for moving air over the surface of said condenser coil; an electric motor for driving said fan; AC supply connections; a solid-state switch; means connecting said switch and said motor in series to said connections; said switch having a gate; means for causing said switch to conduct during portions of half-cycles when current is applied to said gate; and means including means responsive to the condition of the refrigerant at said evaporator for applying current to said gate to cause said switch to conduct during sufificient portions of half-cycles to cause said motor to operate at full speed when the temperature of the refrigerant at said evaporator is above a predetermined temperature, and to cause said switch to conduct during portions of half-cycles on decreases in the temperature of the refrigerant at said evaporator below said predetermined temperature, which decrease conformably with said decreases to cause the speed of said motor to decrease conformably with said decreases.

2. A system as claimed in claim 1 in which said means for supplying current to said gate is arranged to cause said switch to conduct during shorter periods of halfcycles on decreases in the temperature at said evaporator down to a lower predetermined temperature to cause the speed of said motor to decrease until said lower temperature is reached, and then for causing said switch to conduct for substantially constant portions of half-cycles on further decreases in the temperature of the refrigerant at said evaporator to cause said motor to operate at a minimum speed.

3. A system as claimed in claim 2 in which said responsive means comprises a thermistor.

4. A system as claimed in claim 2 in which said responsive means comprises pressure responsive means, and a resistor, the resistance of which is varied by said pressure responsive means.

5. A system as claimed in claim 1 in which said responsive means comprises a thermistor.

6. A system as claimed in claim 1 in which said responsive means comprises pressure responsive means, and a resistor, the resistance of which is varied by said pressure responsive means.

7. A system as claimed in claim 1 in which said circuit between said compressor and said condenser coil includes a high pressure cut-out having a normally closed switch that opens when there is abnormal pressure at said cutout; in which there is provided normally inoperative means responsive to the condition of the refrigerant in said circuit between said compressor and said condenser coil; in which said means for applying current to said gate includes said inoperative means when the latter is operative, and which causes said switch to conduct during portions of half-cycles which increase with increases in the temperature of the refrigerant at said normally inoperative means; and in which there is provided in said circuit between said compressor and said condenser coil, pressure responsive means for rendering inoperative said first mentioned responsive means, and for rendering operative said inoperative means when the pressure at said cut-out increases to approach the pressure at which said cut-out switch opens, said inoperative means, when rendered operative, applying current to said gate to cause said switch to conduct during longer portions of half-cycles than when said first mentioned responsive means was operative, for causing the speed of said motor to increase.

8. A system as claimed in claim 7 in which said first mentioned responsive means is arranged to cause said switch to conduct during shorter periods of half-cycles on decreases in the temperature or" the refrigerant at said evaporator down to a lower predetermined temperature for causing the speed of said motor to decrease until said lower temperature is reached, and then to conduct for substantially constant portions of half-cycles on further decreases in the temperature of the refrigerant at said evaporator, for causing said motor to operate at a minimum speed.

9. A system as claimed in claim 8 in which said first and second responsive means comprise thermistors.

10. A system as claimed in claim 8 in which said first and second mentioned responsive means comprise pressure responsive means, and resistors, the resistances of which are varied by said pressure responsive means.

11. A system as claimed in claim 7 in which said first and second mentioned responsive means comprise thermistors,

12. A system as claimed in claim 7 in which said first and second mentioned responsive means comprise pressure responsive means, and resistors, the resistances of which are varied by said pressure responsive means.

13. A refrigeration system comprising a refrigerant compressor, a high pressure cut-out, a condenser coil, expansion means, and an evaporator connected in series in a refrigeration circuit, said cut-out having a normally closed switch which opens when there is abnormal pressure at said cut-out; a fan for moving air over the surface of said condenser coil; an electric motor for driving said fan; AC supply connections; a solid-state switch; means connecting said switch and said motor in series to said connections; said switch having a gate; means for causing said switch to conduct during portions of halfcycles when current is applied to said gate; means including normally operative means for applying current to said gate to cause said switch to conduct and energize said motor; said means for applying current to said gate including normally inoperative means responsive to the condition of the refrigerant in said circuit between said compressor and said condenser coil; and means for rendering operative said inoperative means and for rendering inoperative said operative means when the pressure at said cut-out approaches the pressure at which said switch opens; said inoperative means when rendered operative being arranged to apply current to said gate to cause said switch to conduct during longer portions of half-cycles than when said operative means was operative, for causing the speed of said motor to increase.

14. A system as claimed in claim 13 in which said normally inoperative means comprises a thermistor.

15. A system as claimed in claim 13 in which said normally inoperative means comprises pressure responsive means, and a resistor, the resistance of which is varied by said pressure responsive means.

16. In a refrigeration system including a refrigerant compressor; a condenser coil; a fan for moving air over the surface of said coil; an electric motor for driving said fan; a discharge gas tube including a high pressure cutout connecting said compressor to said coil, said cut-out having a normally closed switch that opens when the pressure of the discharge gas increases to an abnormally high pressure; expansion means connected to said coil; an evaporator connected to said expansion means; and an energizing circuit for said motor; the improvement comprising means including means responsive to the condition of the discharge gas flowing through said tube, and including means connected in said circuit for increasing the speed of said motor when the pressure of the discharge gas approaches that at which said switch opens.

References Cited UNITED STATES PATENTS 3,152,455 10/1964 Ware 62-184 3,293,876 12/1966 Geisler 62184 WILLIAM J. WYE, Primary Examiner.