GB2188136A - Air conditioning system and method of operation - Google Patents

Abstract

An air conditioning system 10 has a compressor 14, an indoor heat exchanger coil 22, an outdoor heat exchanger coil 28, an accumulator 20, and two controlled valves 32 and 46. The valve 32 can be set to connect the compressor outlet line 34 to either of the coils 22 and 28, the compressor inlet line 21 then being connected respectively to the other exchanger coil. The valve 46 can be opened to provide unrestricted flow between the coils 22 and 28, or closed so that only restricted flow through one or the other of two bypassing metering valves 42 and 44 is possible. To transport condensed refrigerant quickly from one of the coils 22 and 28 to the other at start up of an operating cycle, the valve 46 is temporarily opened and the valve 32 set to allow the compressor to blow the condensed refrigerant from the one coil to the other. <IMAGE>

Description

SPECIFICATION Air conditioning system and method of operation The invention disclosed herein pertains broadly to the field of refrigeration and more specificallyto systems and methods for commencing an operating cycle of a refrigeration device to minimize the cyclic losses caused by non-steady state operation.

Increased energy costs have caused an increasing demand for efficient heating and cooling systems of all types and sizes. Heat pumps have rapidly gained in popularity, in large part as a result of the efficiency of heat pumps as compared with conventional heating systems. The efficiencies of heat pumps themselves also have been improved, primarily by improving the efficiencies of the compressors, fans and motors used in the heat pump. Larger coils are used in newer heat pump designs to improve seasonal performance by increasing the steady state operating efficiency.

In steady state operation of an air conditioning system approximately 65 - 80% of the refrigerant charge is located in the high pressure side ofthe system. During extended periods of off-time much of of the refrigerant will migrate to the evaporator, in thatthe evaporator is generally at a lower ambient temperature than the condenser. At the start ofthe next operating cycle the excess refrigerant charge in the low side of the system must be pumped to the high side of the system to achieve steady state operation. Liquid refrigerant in the evaporator flows to the accumulator, the suction pressure drops to a value lowenough to vaporizethe liquid, andthe compressorpumpsthe vaporto the condenser.This process can take several minutes, during which time the air conditioning system does not operate at steady state capacity. The cyclic losses are greater in systems having largercoil sizes as a result of the greater amount of refrigerant charge in such systems. In a typical heat pump the period during which refrigerant is being pumped from the evaporator to the condenser to achieve steady state operation may be six minutes or longer.

Asimilarproblem occurs during a defrost cycle of a heat pump, both upon initiation of the defrost cycle and upon termination thereof and resumption of heating mode operation. When the cycle is reversed, both at the start and at the completion of a defrost cycle, refrigerant is flooded to the accumulatorto be gradually boiled therefrom to achieve steady state operation. Thus, the heating efficiency of the heat pump is reduced by the inefficiencies resulting from improper refrigerant location when heat exchanger functions are reversed at the commencement ofthe defrost cycle and at the resumption of heating mode operation. The time required for defrost is lengthened as a result of the cyclic loss at the start of a defrost cycle, and the amount of supplemental heat required is increased due to both cyclic losses.

Isolating each coil with solenoid valves substantially reduces the migration of refrigerant during the off-cycle caused by temperature differences. While normal cyclic losses caused by refrigerant migration can be reduced in this manner, no reduction is achieved in the cyclic losses of the defrost cycle which occur because of reversal of heat exchanger functions and the resultant mislocation of refrigerant. Additionally, as a result ofthe large pressure differential across the compressor at start-up, a hard-start kit must be included in such a system. The cost savings from cyclic loss reductions do not generally justify the additional equipment required when the coils are isolated by solenoid valves.

It is therefore one of the principal objects ofthe present invention to provide an air conditioning system and a method for operating the system which result in rapid attainment of a steady state operating condition, thereby significantly reducing cyclic losses caused by non-steady state operation.

Another object of the present invention is to provide an air conditioning system and a method for operating the system which eliminate the need for an accumulator and compensate for refrigerant migration without requiring hard-start kits.

Afurther object of the present invention is to provide a method for operating an air conditioning device which substantially reduces cyclic losses in a heat pump occurring as a result of non-steady state operation caused by improper refrigerant location due to reversal of heat exchanger functions, both at commencement of a defrost cycle and at resumption of normal heating mode operation.

These and other objects are achieved in the present invention by providing a bi-flow expansion valve assembly in the refrigerant line between the heat exchangers of a conventional air conditioning device. A reversing valve is provided in the discharge line from the compressor, and at the start of a cycle the reversing valve is adjusted to a position for directing refrigerant flow opposite to the direction of the desired operating mode. The bi-flow expansion valve assembly is opened to provide virtually unrestricted flow th rough the refrigerant line between the heat exchangers. Liquid refrigerant from the evaporator-to-be is flooded to the condenser-to-be, and the bi-flow expansion valve assembly is closed to a metering condition.The reversing valve is adjusted for directing refrigerant in the proper direction for the desired operating mode, and normal operation is commenced.

In a heat pump, at the commencement of a defrost cycle,the bi4lowexpansion valve assembly is opened to permit refrigerant to flood from the indoor coil to the outdoor coil. The reversing valve is then switched to the defrost mode, the bi-flow expansion valve assembly is adjusted to a refrigerant metering condition and defrost ensues. Upon completion of the defrost cycle the bi-flow expansion valve assembly is again opened to permit vi rtual Iy unrestricted flow th rough the refrigerant line, the liquid refrigerant is flooded to the indoor coil, the reversing valve is adjusted to the heating mode of operation and the bi-flow expansion valve assembly is closed to a refrigerant metering condition.

These and other objects of the present invention will become apparent from the following detailed description and the accompanying drawing.

Figure lisa schematic view of a heat pump having a bi-flow expansion valve assembly for operating in accordance with the methods ofthe present invention.

Detailed description of the preferred embodiments Referring now more specifically to the drawing, numeral 10 designates a heat pump of substantially conventional design, but having a bi-flow expansion valve assembly 12 which enables the heat pump to operate according to the methods ofthe present invention. The bi-flow expansion valve assembly replaces the expansion devices and checkvalves typically found in the refrigerant line between the heat exchangers of a heat pump. The operation of the bi-flow expansion valve assembly will be described more fully hereinafter. The heat pump also includes a compressor 14, an indoor heat exchanger assembly 16 and an outdoor heat exchanger assembly 18.An accumulator 20 is provided in the compressor suction line 21; however, it is contemplated that operating an air conditioning device using the present methods may obviate the need for an accumulator.

Indoor heat exchanger assembly 16 includes a refrigerant-to-air heat exchange coil 22 and a fan 24, and the assembly is also shown with a backup electrical resistant heating coil 26. Outdoor heat exchanger assembly 18 includes a refrigerant-to-air heat exchange coil 28 anda fan 30. The indoorand outdoor heat exchanger assemblies are of conventional design and will not be described further herein. A reversing valve 32 is connected to the compressor discharge port by a refrigerant line 34,tothecompressorsuction port by suction line 21 and to coils 22 and 28 by refrigerant lines 36 and 38, respectively.The reversing valve is also of conventional design for directing high pressure refrigerantvaporfrom the compressor to either the indoorcoil during heating mode operation ortothe outdoorcoilforcooling mode operation orfor defrost, and for returning refrigerant from the coil operating as an evaporator to the compressor.

A refrigerant line 40 is disposed between the indoor coil 22 and the outdoor coil 28, and the aforementioned bi-flow expansion valve assembly 12 is disposed in the refrigerant line 40. Although the bi-flow expansion valve assembly may encompass many different valve structures co-operating in function, ore single complexvalve capable of unrestricted flowtherethrough and metered flow in either direction, schematically the assembly has been shown to include metering passages 42 and 44 for metering refrigeranttherethrough along paths toward, respectively, the indoor coil 22 and the outdoor coil 28.Asolenoid valve 46 or the like is disposed in the line 40, and valve 46 may be opened to permit unrestricted refrigerantflowtherethrough in line 40, or may be closed to cause refrigerant to flow only through either the metering orifice 42 or the metering orifice 44, which are connected to refrigerant line 40 by branch lines 48 and 50 bypassingtheflowthrough path ofthevalve assemblycontaining solenoid valve 46.

With the basic structure of a heat pump ofthe invention having been fully described, operation of the heat pump in accordance with the methods of the present invention will now be described more completely, with respectto each operating mode.

At the start of a cooling mode cycle, refrigerantwill havemigratedtotheindoorcoil 22 as a result of the cooler ambienttemperatures in the indoor unit. For steady state operation approximately 65 to 80% of the refrigerant should be located in the high pressure side including outdoorcoil 28. To rapidly achieve this condition at the commencement of the operating cycle, the bi-flow expansion valve assembly 12 is adjusted to a flow-through, unrestricted condition wherein valve 46 is opened, and refrigerant flow is restricted only by the capacity of line 40. Reversing valve 32 is adjusted to the position for heating mode operation wherein high pressure refrigerant vapor is directed to the indoor coil 22.The compressor is started, and the excess liquid refrigerant in the indoor coil is rapidly pumped through the bi-flow expansion valve assembly to the outdoor coil. When the liquid refrigerant has been pumped out of the indoor coil, which may take only a matter of seconds, the bi-flow expansion valve assembly 12 is adjusted to a metering condition wherein the flow-through passage having valve 46 is closed. Reversing valve 32 is adjusted to the proper position for cooling mode operation wherein the refrigerant vapor is directed to the outdoor coil.

Conventional cooling mode operation then follows.

During heating mode operation a reverse procedure to that just described for cooling mode operation is followed. Excess liquid refrigerant will have migrated to the outdoor coil which is at a lower ambienttemperaturethan the indoor coil. At initiation of a heating cycle the reversing valve 32 is adjusted to a cooling mode operating position, the bi-flow expansion valve assembly 12 is adjusted to an unrestricted flow condition wherein valve 46 is fully opened and the compressor is started to flood refrigerant from the outdoor coil to the indoor coil.

After thins is accomplished, the bi-flow expansion valve assembly is adjusted to a refrigerant metering condition wherein valve 46 is closed. the reversing valve is adjusted to heating mode operation and a conventional heating cycle follows. Again, the refrigerant has been properly located in the heat pump within a matter of seconds, thereby eliminating the often-encountered many minutes of non-steady state operation found in conventional systems.

When a defrost cycle is required, initiallythe reversing valve is in a position for heating mode operation and normallythecompressorwill be operating. With the reversing valve remaining in the position for heating mode operation, the bi-flow expansion valve assembly is adjusted to an unrestricted flow condition wherein valve 46 isfully opened, the compressor continues operating and refrigerantfrom the indoor coil is pumped rapidly to the outdoor coil. The bi-flow expansion valve assembly is then adjusted to a refrigerant metering condition, reversing valve 32 is adjusted to a cooling mode operating condition for defrost and the defrost cycle follows.Upon completion ofthe defrost cycle, the reversing valve 32 is left in the position for cooling or defrost mode operation, bi-flow expansion valve assembly 12 is adjusted to an unrestrictedflowcondition and the liquid refrigerant is pumped rapidly from the outdoor coil to the indoor coil. The bi-flow expansion valve assembly is adjusted to afluid metering position, and the reversing valve is adjusted to a heating mode operating position to complete the cycle.

Substantial energy savings can result from using the present methods, particularly during the defrost mode in that many minutes of non-steady state operation are eliminated, both at the commencement of a defrost cycle and at resumption of a heating mode cycle. The defrost cycle is made more efficient, thereby reducing the amount of time required for defrost and reducing the required back-up heat. Basic cooling and heating cycles are made more efficient by reducing cyclic losses, thereby reducing on-cycle times and decreasing energy consumption.

The present invention works equally as well in a cooling-onlyairconditioning system. In such a system a reversing valve and bi-flow expansion valve assembly must be added to the system. At the start of each cooling cycle the system operates as described previously herein for the cooling cycle of a heat pump.

It is also contemplated thatthe bi-flow expansion valveassemblycan be used to control the amountof superheat leaving the evaporator. Asolid state controller can be used to optimize su perheat to existing operating conditions as well as to control the system at the start of operating cycles. Thus, in addition to improving overall system efficiency by minimizing non-steady state operating times, the present invention can also be used to improve steady state operation and further increase the efficiency of an air conditioning system.

Although an air conditioning system and a method for the operation thereof have been shown and described in detail herein with particular reference to a heat pump system, it should be understood that various modifications may be made without departing from the scope ofthe present invention.

Claims (12)

1. A method for rapidly achieving steady state operation of an air conditioning device having a compressor, a condenser and an evaporator, said method comprising the steps at start up of: a. providing a substantially unrestricted path for the flow of refrigerant from the evaporator to the condenser; b. flooding refrigerant from the evaporator to the condenserthrough the unrestricted path; and c. providing a restricted path for metering refrigerantflowfromthe condensertothe evaporator.

2. The method defined in claim 1 in which said flooding step is performed by operating the compressor and directing compressed refrigerant vaportherefrom to the evaporator.

3. The method defined in claim 1 which further includes the steps of: a. providing a substantially unrestricted path for the flow of refrigerant from the condenser to the evaporator; b. flooding refrigerantfromthecondensertothe evaporator; c. providing a restricted path for metering refrigerant flow from the evaporator to the condenser; d. operating the compressor and directing compressed refrigerant vapor from the compressor to the evaporatorto defrost the evaporator; and e. repeating the steps of: i. providing a substantially unrestricted path for the flow of refrigerant from the evaporator to the condenser; ii. flooding refrigerant from the evaporatorto the condensor; iii. providing a restricted path for metering refrigerant flow from the condenser to the evaporator.

4. The method defined in claim 3 in which said flooding steps are performed by operating the compressor and directing compressor refrigerant vapor to the one of said condenser and evaporator from which refrigerant is flooded.

5. Amethodforoperating an airconditioning device having a compressor; an evaporator; a condenser; refrigerant lines disposed between the compressor and the condenser, between the evaporator and the compressor and between the evaporatorand the condenser; a first valve means disposed in the refrigerant line between the evaporator and the condenser, the valve means having aflow-through portion openedforan operating condition in which refrigerant can flow through said valve means substantially unrestricted by the valve means between the evaporator and the condenser, and a metering portion restricted when the valve means is in a condition in which the flow of refrigerant is metered between the condenser and the evaporator; and a reversing valve having first and second operating conditions for directing refrigerantvaporfrom the compressorto the condenserortheevaporator; said method comprising the steps of a. placing the firstvalve means in the flow-through operating condition; b. adjusting the reversing valve to direct refrigerant vapor from the compressor to the evaporator; c. operating the compressor to pump excess liquid refrigerant from the evaporator to the condenser throughtheflow-through portion ofthefirstvalve means; d. placing the first valve means in the restricted operating condition for metering refrigerantflow from the condenser to the evaporator; and e. adjusting the reversing valve to direct refrigerantvaporfrom the compressortothe condenser.

6. The methodforoperating an air conditioning device as defined in claimS, said method further including the steps of: a. placing thefirstvalve means in theflow-through operating condition while maintaining the reversing valve in a condition to pump refrigerant vaporto the condenser; b. pumping the excess liquid refrigerant from the condenserto the evaporator; c. placing the first valve means in the flow metering condition for metering refrigerant flow from the evaporatorto the condenser; d. adjusting the reversing valve to direct refrigerantvaporfrom the compressor to the evaporator for defrosting the evaporator;; e. reopening the first valve means to permit unrestricted refrigerant flow from the evaporatorto the condenser, while maintaining the reversing valve in a condition to pump refrigerant vapor to the evaporator; f. pumping excess liquid refrigerant from the evaporatorto the condenser; g. returning the first valve means to a restricted operating condition for metering refrigerantflow from the condenserto the evaporator; and h. repositioning the reversing valve to direct refrigerantvaporfrom the compressor to the condenser.

7. A method for operating a heat pump having indoor and outdoor heat exchangers functioning alternatively as the evaporator and the condenser during cooling and heating modes respectively; a compressor; refrigerant lines disposed between the heat exchangers and the compressor; a reversing valve having first and second positions for directing refrigerantfrom the compressor to the outdoor heat exchanger in a first operating mode and to the indoor heat exchanger in the second operating mode, respectively; and a bi-flow expansion valve assembly in a refrigerant line between the indoor and outdoor heat exchangers for metering refrigerant flow in either direction between the heat exchangers and for providing substantially unrestricted refrigerant flow through the refrigerant line between the heat exchangers; said method comprising the steps of: a. placing the reversing valve in the position for directing refrigerant vapor to the heat exchanger which will function as an evaporator during the desired operating mode; b. adjusting the bi-flow expansion valve assembly to permit virtually unrestricted refrigerant flow between the heat exchangers; c. operating the compressor to flood liquid refrigerant from the heat exchanger which will function as the evaporator during the desired operating mode to the heat exchanger which will function as the condenser during the desired operating mode; d. placing the bi-flow expansion valve in a position for metering refrigerant flow between the heat exchangers; and e. placing the reversing valve in the position for directing refrigerantvaporto the heat exchanger which will function as a condenser during the desired mode of operating.

8. The method for operating a heat pump as defined in claim 7 wherein the heat pump is operating in the second operating mode with the indoor heat exchangerfunctioning as a condenser and the outdoor heat exchangerfunctioning as an evaporator, said method further comprising the steps of: a. adjusting the bi-flow expansion valve assembly for unrestricted flowtherethrough from the indoor heat exchangerto the outdoor heat exchangerwhile maintaining the reversing valve in the second operating mode; b. flooding refrigerant from the indoor heat exchanger to the outdoor heat exchangerthrough the bi-flow expansion valve assembly;; c. placing the reversing valve in the first operating mode and adjusting the bi-flow expansion valve assembly for metering refrigerant flow from the outdoor heat exchanger to the indoor heat exchanger; d. operatingthecompressortodefrosttheoutdoor heat exchanger; e. re-adjusting the bi-flow expansion valve assembly to permit unrestricted flow through the refrigerant line from the outdoor heat exchangerto the indoor heat exchanger while maintaining the reversing valve in the first operating mode; f. flooding refrigerantfrom the outdoor heat exchanger to the indoor heat exchangerthrough the bi-flow expansion valve assembly; and g. returning the reversing valve to the second operating mode and the bi-flow expansion valve assembly to the condition for metering refrigerant flow from the indoor heat exchanger to the outdoor heat exchanger.

9. A method for defrosting a heat pump having an evaporator; a condenser; a compressor; refrigerant lines disposed between the compressor and the evaporator, between the compressor and the condenser, and between the evaporator and the condenser; and restriction means for metering refrigerant flow in paths from the evaporator to the condenser and from the condenser to the evaporator; said method comprising the sequential steps of: a. unrestricting the flow of refrigerant in a path from the condenser to the evaporator; b. flooding liquid refrigerant from the condenser to the evaporator; c. restricting the flow of refrigerant in a path from the evaporator to the condenser; d. operating the heat pump in a conventional defrost mode, by directing refrigerantvaporfrom the compressor to the evaporator; e. unrestricting the flow of refrigerant in a path from the evaporator to the condenser; f. flooding refrigerantfrom the evaporator to the condenser; g. restricting the flow of refrigerant in a path from the condenser to the evaporator; and h. resuming conventional heat pump operation.

10. In an air conditioning device having first and second heat exchangers, one of said heat exchangers operating as an evaporator and the other of said heat exchangers operating as a condenser; a compressor; refrigerant lines disposed between the heat exchangers and between the compressor and the heat exchangers; and a reversing valvefor directing refrigerant from the compressorto either of said heat exchangers, the improvement comprising: means initiated for a short time period at start up to cause flooding of refrigerant from said heat exchanger operating as a evaporatorto said heat exchanger operating as a condenser.

11. The air conditioning device defined in claim 10, wherein said flooding means includes a bi-flow expansion valve assembly disposed in the refrigerant line between said first and second heat exchangers having a first path therethrough for metering the flow of refrigerant between said first and second heat exchangers and second path therethrough for allowing the flow of refrigerant between said first and second heat exchangers substantially unrestricted by said bi-flow expansion valve assembly.

12. A method for rapidly achieving steady state operation of a heat pump system having a low pressure portion and a high pressure portion, said method comprising the sequential steps at start up of: a. providing a substantially unrestricted path for the flow of refrigerant from the low pressure portion ofthe systems to the high pressure portion of the systems; b. flooding refrigerant from said low pressure portion of the system to said high pressure portion of the system; and c. providing a restricted path for metering refrigerantflowfrom the high pressure portion of the system to the low pressure portion ofthe system.