Condensate Collector Pan Heating

Abstract

A refrigerant evaporator defrost mechanism having improved control means for keeping the drain pan heater energized for a predetermined delay period following termination of the defrost cycle. The prolonged heating of the pan prevents ice from forming as might impede flow of condensate into the drain.

Description

BACKGROUND OF THE INVENTION

In refrigeration systems having a defrosting cycle it is common practice to provide a drain pan under the evaporator to collect melted ice and also to provide a heater for the drain pan.

SUMMARY OF THE INVENTION

In accordance with the invention a heater for the drain pan for a refrigeration system having a defrosting cycle is provided with control means which functions to maintain the heater energized for a period of time after termination of a defrosting cycle. The incomplete melting of ice in the drain pan, the re-solidification of melting ice, the freeze up of water in a cold drain and the over flow of condensate are thereby prevented and the free flow of melted ice through a drain line connected to the drain pan is assured.

THE DRAWINGS

FIG. 1 schematically illustrates a refrigeration system using a defrost mechanism of this invention.

FIG. 2 is an electrical circuit diagram illustrating one way of controlling the FIG. 1 system.

FIG. 3 illustrates a second defrost mechanism employable in the invention.

FIG. 4 is an electrical circuit diagram illustrating a control mechanism useful in the invention.

FIG. 1

FIG. 1 shows a conventional refrigeration system comprising a refrigerant compressor 10, condenser 12 and evaporator 14. During normal run operation the compressor discharges high pressure -- high temperature refrigerant gas into line 16, through reversing valve 18, and into line 20 leading to air-cooled condenser 12; illustrative pressure-temperature values may be in excess of 175 p.s.i. and 125.degree. F. Liquified refrigerant is passed from the condenser through check valve 21 and expansion valve 22 into evaporator 14.

Evaporator 14 discharges low pressure-low temperature refrigerant gas to the compressor through a path comprising suction line 26, reversing valve 18, and suction line 27. Illustrative pressure-temperature values may be 25 p.s.i. and 25.degree. F; for certain applications the temperature can be as low as minus 40.degree. F. Evaporator fan 28 and condenser fan 52 move air across the respective coils to keep the evaporation and condensing processes ongoing.

Fan 52 may be controlled by a switch 53 responsive to condenser temperature or pressure; fan 28 may be selectively controlled by a manual switch 29 (FIG. 2) or a wall thermostat 33. Thermostat 33 is shown controlling a relay coil 35, which operates a relay switch 31 to energize fan 28 in response to a call for cooling. Relay coil 35 also may be used to control a second relay switch 37 which energizes the compressor during normal run periods.

INITIATING THE DEFROST CYCLE

During normal run operation atmospheric frost builds up on the fins of evaporator 14. The frost is removed by altering the position of reversing valve 18 so that hot gas line 16 connects with the evaporator and line 27 connects with the condenser. Valve 18 is operated to the defrost position by a conventional timer 30 which periodically energizes a FIG. 2 circuit comprising power line 32, branch line 34, relay coil 36, and power line 38. Relay 36 includes three normally open switches 40, 42 and 44. Closure of switch 40 energizes compressor 10 through a circuit comprising branch line 46, junction 48, and line 50. Closure of switch 42 energizes condenser fan 52 through a circuit comprising line 54. Closure of switch 44 energizes the motor or solenoid portion of reverser valve 18 through a circuit comprising line 56.

As valve 18 shifts from its illustrated normal run position to the defrost position line 16 connects with line 26 and line 27 connects with line 20. Therefore high pressure-high temperature gas flows from line 16 through valve 18, line 26, and into evaporator 14 to melt frost which has accumulated on the evaporator fin surfaces. Refrigerant flows out of evaporator 14 through check valve 58, expansion valve 23, coil 12, line 20, valve 18 and line 27 back to the compressor. During the defrost cycle coil 12 acts as an evaporator to vaporize refrigerant prior to its passage back to the compressor. Fan 52 is energized through a circuit comprising switch 42.

HEATING THE CONDENSATE COLLECTOR

As the defrost cycle proceeds condensate gravitates from evaporator 14 into condensate collector 62, which is warmed by an electric resistance heater 64. A suction line switch 66 is arranged to control heater 64 so that the heater is energized whenever the suction line temperature or pressure is above a predetermined value somewhere between normal high side and low side values, as for example a temperature of 120.degree. F or a pressure of 140 p.s.i. During the defrost cycle (and for a short period thereafter) switch 66 energizes heater 64 through a circuit comprising power line 32, branch line 68, the switch, line 70, the heater, and branch line 72. Switch 66 keeps the evaporator fan 28 off during the defrost cycle, and for a short period thereafter.

TERMINATION OF DEFROST CYCLE

When coil 14 has been sufficiently defrosted the circuit through timer switch 30 is interrupted, either because of the lapse of time, an increase in evaporator coil temperature, or other characteristic commonly used to terminate a defrost cycle. Various suitable defrost termination devices are shown for example in U.S. Pat. No. 3,033,005 issued to E.W. Zearfoss on May 8, 1962 and U.S. Pat. No. 3,335,576 issued to D.S. Phillips on Aug. 15, 1967. The defrost termination mechanism is intended to be associated in the line 34 circuit so that it can deenergize relay coil 36 when substantially all of the frost on coil 14 has been melted. Deenergization of relay coil 36 opens switches 40, 42 and 44, and thus deenergizes compressor 10, condenser fan 52, and the motor for reverser valve 18. A conventional spring in the valve motor 18 drive train causes the reverser valve to return to return to its FIG. 1 position.

DISCONTINUING THE COLLECTOR PAN HEAT CYCLE

After termination of the defrost cycle the pressure-temperature differential between suction line 26 and coil 12 tends to equalize. For example, suction line 26 may cool from a temperature of 125.degree. F down to some lower temperature for example 100.degree. F; similarly the line 26 pressure may drop from about 175 p.s.i. down to about 140 p.s.i. At these lower temperatures or pressures switch 66 deenergizes the circuit through heater 64. At somewhat lower temperature-pressure values switch 66 completes a circuit comprising line 68 and fan 28 (providing either switch 31 or switch 29 is closed).

Evaporator fan 28 and condensate collector heater 64 are in electrical parallelism so that the heater alone is energized when the suction line temperature or pressure is above a predetermined value, and the fan alone is energized when the suction line temperature or pressure is below a predetermined value. The switch 66 differential may be adjusted or chosen to provide a predetermined time delay between termination of the defrost cycle (deenergization of relay coil 36) and deenergization of heater 64. During this time delay period heater 64 continues to heat the condensate collector 62 so that particles of ice in the collector pan may be melted, and so that water still dripping from coil 14 is prevented from freezing in the pan and thereby clogging the drain. During the delay period switch 66 prevents evaporator fan 28 from running; the fan is thereby prevented from blowing condensate off of the coil 14 fin edges, or removing heat from the coil surfaces, or otherwise interfering with condensate formation and disposal. It is believed that in some cases the prolonged warming of the collector pan may make possible the attainment of shorter defrost cycles in that the evaporator coil can return to its normal run condition without waiting for complete melting of ice particles in the pan and/or flow of condensate into the drain.

FIG. 3

FIG. 3 illustrates a conventional refrigeration system wherein a single compressor 10 and single condenser 12 are employed in conjunction with a plurality of separate evaporators 14a and 14b. The drawing shows two evaporators, but in practice several evaporators would usually be provided for the enclosure or enclosures.

Evaporators 14a and 14b are in parallel flow relation as respects refrigerant flow. Therefore, either evaporator can be hot-gas defrosted while the other is on normal run operation. Normal run for all evaporators involves compression of gas in compressor 10, passage of hot gas through line 30 to condenser 12, and passage of condensed refrigerant into main line 40 which serves branch lines leading to different ones of the evaporators.

Evaporator 14a is connected in a branch circuit which includes a normally open solenoid valve 22a, thermostatic expansion valve 24a, check valve 58a, the evaporator, and evaporator pressure regulator 90a. Commonly regulator 90a is a bellows-operated valve or diaphragm-operated valve having its bellows or diaphragm exposed to pressures in line 92a in a manner to inversely control the throttling action of a valve element, thus providing a relatively constant suction pressure during normal operations and/or defrost periods.

Line 92a connects with another branch line 94a containing a normally closed solenoid valve 96a. During normal run operation the solenoids for valves 22a and 96a are de-energized so that valve 22a is open and valve 96a is closed. Refrigerant can flow through a circuit comprising valves 22a and 24a, evaporator 14a, and regulator 90a (assuming a sufficiently high temperature for the sensing bulb of valve 24a). This would be the so-called normal run operation.

Defrosting of evaporator 14a is initiated by energizing the solenoids for valves 22a and 96a. The consequent opening of valve 96a and closing of valve 24a allows hot gas to flow through a circuit comprising line 30, auxiliary line 98, valve 96a, evaporator 14a, check valve 58a, and line 100 leading to the other evaporator 14b. The gas gives up heat to the frost on the fins of evaporator 14a, thereby melting the frost; the refrigerant gas is condensed in evaporator 14a and later evaporated as it passes through evaporator 14b (or one of the other evaporators in the system).

During the defrost cycle a certain portion of the hot gas in line 94a can conceivably flow leftwardly through line 92a and regulator 90a. However the regulator responds to the high pressure to substantially completely throttle the leftward flow; in practice little or no hot gas will escape through the regulator.

Termination of the defrost cycle by time, temperature, etc. is such as to de-energize the solenoids for valves 22a and 96a, thus returning evaporator 14a to the normal run condition. The connector line 94a between valve 96a and evaporator 14a may have a pressure switch or temperature switch 66a connected thereto for responding to changing line pressures or temperatures. As the defrost cycle is terminated the refrigerant in line 92a gradually cools from the relatively high condensing temperature down to a relatively low temperature representative of normal evaporator conditions. The temperature change may be used to actuate switch 66a for halting the collector pan heating action in the same way as described in connection with FIG. 1.

The system is preferably such that only one of the evaporators 14a, 14b etc., is on defrost at any one time. Such selective defrosting is preferably controlled by the timer or timers. The present invention is concerned with defrost of multi-evaporator systems only to the extent that such systems include mechanisms for keeping the drain pans warm after termination of the defrost cycle.

FIG. 4

FIG. 4 illustrates a control circuit for an electrically energized defrosting unit used on a non-reversible refrigeration system. In this case the defrost system is not the hot-gas type but is instead the electrical heater type wherein an electric heater 45 is positioned on or adjacent the evaporator to melt frost accumulations. Initiation of the defrost cycle involves closing the contacts in timer 30 and consequent energization of the relay coil 36. This action closes contacts 44 which energize the evaporator coil heater 45. At the same time contacts 47 are closed to energize small heater coil 49. When heated, coil 49 produces a downward warping of bimetal switch 65 for energizing condensate collector pan heater 64. Coil 49 and switch 65 constitute a time delay generally designated by numeral 102.

When the contacts in timer 30 are opened to terminate the defrost cycle the coil heater 45 is immediately de-energized; contacts 47 then open to produce a controlled slow cooling of heater 49 and a delayed de-energization of heater 64. During the delay period following opening of contacts 47 the heater 64 keeps the pan warm to deter ice formations in the pan and/or in the drain.

It will be seen that the invention involves various different ways of delaying the shut-down of the condensate collector heater following termination of the defrost cycle. During the delay period the collector continues to be emptied of condensate to thereby minimize problems relating to incomplete melting of ice particle, re-solidification of melted condensate, plug-up of the collector drain, freeze-up of water in a cold drain line, or overflow of condensate from the collector.

Claims

I claim:

1. In a defrost mechanism for a refrigerant evaporator equipped with a condensate collector, a valve for diverting high side hot gas through the evaporator to defrost same, and an electric heater for warming the condensate collector: the improvement comprising switch means responsive to suction line temperature or pressure for energizing the heater while the suction line temperature or pressure is above its normal run value, whereby the collector is warmed for a period of time after termination of the defrost cycle.

2. The mechanism of claim 1 wherein the evaporator is equipped with a fan, and the heater and fan are in electrical parallel connection with one another and in series connection with the switch means, whereby the switch means prevents the fan from operating while the heater is warming the collector.

3. The mechanism of claim 1 wherein the switch means deenergizes the heater when the suction line temperature or pressure drops a predetermined amount below the normal high side values.

4. In a defrost mechanism for a refrigerant evaporator equipped with an evaporator fan, a defrost controller operable to cause hot refrigerant gas to pass through the evaporator to melt ice formations on the evaporator coil, said controller including means operable to terminate the melting operation when substantially all of the ice has been melted, a condensate collector associated with the evaporator to receive melted condensate, and a heater for warming the collector to deter ice formations therein: the improvement comprising means causing the heater to be energized and the evaporator fan to be off during the melting operation, and means causing the heater to remain energized and the fan to remain off for a predetermined time after termination of the melting operation.

5. The mechanism of claim 4 wherein the last mentioned means comprises a switch responsive to pressure or temperature in the evaporator.

6. The mechanism of claim 5 wherein the switch (1) energizes the heater when the evaporator pressure-temperature approaches normal high side values, and (2) energizes the fan when the evaporator pressure-temperature approaches normal low side values.

7. In a defrost mechanism for a refrigerant evaporator having a condensate collector, means for heating the evaporator to cause condensate to be deposited in the collector, and means for warming the collector to prevent solidification of the collected condensate; the improvement comprising control means for keeping the collector warming means energized for an anti-icer delay period following return of the evaporator to normal run operation.

8. The mechanism of claim 7 wherein the evaporator is equipped with a fan, and the improved control means includes means for keeping the fan off during the anti-icer delay period.