WO2009096620A1

WO2009096620A1 - A method and an apparatus for protecting a compressor of an air-conditioning system

Info

Publication number: WO2009096620A1
Application number: PCT/KR2008/000637
Authority: WO
Inventors: Moon Hee Lee
Original assignee: Carrier Corp
Current assignee: Carrier Corp
Priority date: 2008-02-01
Filing date: 2008-02-01
Publication date: 2009-08-06
Anticipated expiration: 2010-08-01
Also published as: KR20100115757A

Abstract

The present application discloses a method for protecting a compressor of an air-conditioning system comprising; sensing connection of a power of the air-conditioning system, starting the operation of the crankcase heater, detecting the temperature by the ambient temperature sensor, determining a pre-heating time of the compressor based on the ambient temperature detected by the ambient temperature sensor, continuing the pre-heating of the compressor by the crankcase heater during the determined pre-heating time of the compressor, and starting the operation of the compressor when the determined pre-heating time of the compressor is over.

Description

A METHOD AND AN APPARATUS FOR PROTECTING A COMPRESSOR OF AN AIR-CONDITIONING SYSTEM Technical Field

[1] The present invention relates to a method and an apparatus for protecting a compressor of an air-conditioning system, in particular, a method and an apparatus for protecting a compressor of an air-conditioning system by increasing the temperature in the compressor to prevent dilution of oil. Background Art

[2] The refrigerant discharged from a compressor is condensed in a condenser. The condensed refrigerant is expanded in an expansion device and then evaporated in an evaporator. Accumulators are positioned on the suction side of the compressor in order to filter the liquid-phase refrigerants which have not been evaporated in the evaporator, thereby preventing the liquid-phase refrigerant from flowing into the compressor.

[3] Refrigerants and the oil used as a lubricant for the compressor of an air-conditioner are freely miscible. During normal operation of the air-conditioner, due to the operating pressures and temperatures, the oil in the sump of the compressor is substantially free of refrigerant. Further, an accumulator prevents the inflow of the liquid- phase refrigerants into the compressor. However, when the compressor is shut off, the refrigerant in the air-conditioner tends to migrate and condense in the coldest parts of the system. For example, when a system is shut down on a cool night, the temperature of indoor is higher than that of outdoor. Thus, the refrigerant in the system will tend to migrate to the cooler outdoor coil and the compressor. In the morning as the outdoor temperature goes up, the outdoor coil will warm up much quicker than the compressor because the thermal capacity of the compressor is larger than that of the outdoor coil. As a result, the refrigerant which had condensed in the outdoor coil will migrate to the compressor.

[4] As such, crankcase heaters have been designed to solve the problem of liquid refrigerating migrating into the crankcase or sump of a compressor during a shut-down cycle of an air-conditioner. Such crankcase heaters are normally energized continuously even though they are only necessary when the liquid-phase refrigerants flow into the compressor. Such heaters may be electrical resistance elements which are installed directly in the sump of the compressor, or may be wrapped around the outer surface of the compressor casing so that it enables heat transfer to the oil stored in the simp.

[5] When the air-conditioner turns on, crankcase heaters are energized and evaporate the liquid-phase refrigerants to protect the compressor. However, if the air-conditioner is not used for a long time, users may remove power to the air conditioning by merely unplugging the air conditioning system unit. During this period, the operation of crankcase heater stops since crankcase heater is unable to operate without power. As a result, the liquid-phase refrigerants flow into the compressor and dilute oil.

[6] Diluted oil along with the liquid refrigerant reduces the ability to lubricate the compressor bearings and other operating parts when the compressor is in operation at start-up. Refrigerant dissolves into the oil as time goes on. In this case, the affinity between the refrigerants and many of the lubricants used therewith causes oil dilution and attendant loss of lubrication. Further, as the liquid is essentially incompressible, the presence of the liquid refrigerant can result in very high pressures and stresses in the compressor. Therefore, lesser amounts of the liquid refrigerant can wash away lubrication oil films present on the operating parts.

[7] As such, if the user starts the air-conditioner again which has been shut down for a long time, the motor of the compressor rotates with the liquid refrigerant and thus causes failure of the compressor as described above. Disclosure of Invention Technical Problem

[8] The present invention is to solve the above -noted problems in the art, where it provides a method and an apparatus for protecting a compressor of an air-conditioning system by eliminating the liquid refrigerant in the compressor by pre-heating the compressor during a predetermined time based on the ambient temperature, when the air-conditioner is operated again after being shut down for a long time. Technical Solution

[9] In order to achieve the above objective, the present invention is embodied to a method for protecting a compressor of an air-conditioning system. The method comprises sensing connection of a power of the air-conditioning system, starting the operation of the crankcase heater, detecting the temperature by an ambient temperature sensor, determining a pre-heating time of the compressor based on the ambient temperature detected by the ambient temperature sensor, continuing the pre-heating of the compressor by the crankcase heater during the determined pre-heating time of the compressor, and starting the operation of the compressor when the determined pre- heating time of the compressor is over.

[10] Further, the present invention embodies an apparatus for protecting a compressor of an air-conditioning system. The apparatus comprises a crankcase heater heating the bottom part of the compressor, an ambient temperature sensor detecting the outdoor temperature, and a control unit connected to the crankcase heater and the ambient temperature sensor for controlling the crankcase heater. The control unit comprises a preheating time determination part determining a pre -heating time of the compressor based on the temperature detected by the ambient temperature sensor, a crankcase heater driving part continuing the pre-heating of the compressor by the crankcase heater during the determined pre-heating time of the compressor, and a compressor driving part starting the operation of the compressor once it is determined that the preheating time of compressor is over.

[11] The method and apparatus for protecting a compressor of an air-conditioner can be applied to a variable capacity compressor compressing refrigerant depending on a duty control signal which determines a loading time and an unloading time.

Advantageous Effects

[12] The present invention prevents dilution of oil with the compressor refrigerant. Thus, the ability to lubricate is maintained and thereby the lifespan of the compressor is enhanced and the compressor failure is prevented. In particular, since a variable capacity compressor used in a large capacity air-conditioner requires significant costs for repairing or replacing parts, the method for protecting a compressor according to the present invention is significant. Further, the air-conditioner according to the present invention pre -heats the compressor during the required pre-heating time based on the ambient temperature by properly predicting the required pre-heating time for starting the compressor. Thus, the present invention provides a more efficient use of an air-conditioning system compared to those requiring pre-heating the compressor for a long time. Brief Description of the Drawings

[13] Figure 1 is a schematic diagram illustrating an air conditioner according to an embodiment of the present invention.

[14] Figure 2 is a control flow chart illustrating a method for protecting a compressor of an air-conditioner according to an embodiment of the present invention.

[15] Figure 3 is an oil dilution chart illustrating the relationship between the inlet pressure of the compressor and the temperature of the bottom part of the compressor according to an embodiment of the present invention.

[16] Figure 4 is a diagram illustrating the testing method for obtaining a pre -heating time of a crankcase heater corresponding to the outdoor temperature based on the oil dilution chart of Figure 3 according to an embodiment of the present invention.

[17] Figure 5 is a diagram illustrating the relationship between the outdoor temperature and the pre -heating time of a crankcase heater according to an embodiment of the present invention.

[18] Figure 6 is a schematic diagram illustrating the control unit according to an embodiment of the present invention. Best Mode for Carrying Out the Invention

[19] The present invention is described in detail below with reference to the accompanying drawings.

[20] Fig. 1 is a schematic diagram illustrating an air conditioner according to an embodiment of the present invention. An air conditioner (1) comprises an outdoor unit (10) and an indoor unit (20) As shown in Fig. 1, one outdoor unit (10) can be connected to one or more indoor units (20) The outdoor unit (10) comprises a compressor (2), an accumulator (4), an outdoor electromotor valve (5), an outdoor heat exchanger (6), an outdoor fan (7), an outdoor fan motor (8), and a direction control valve (9) A compressor (2) comprises a crankcase heater (11), an inlet port (14), and a discharge port (15) An ambient temperature sensor (3) is installed on the outdoor heat exchanger (6) The indoor unit (20) comprises an indoor heat exchanger (21), an indoor fan (22), an indoor fan motor (23), and an indoor electromotor valve (24)

[21] The air conditioner (1) according to an embodiment of the present invention further comprises a control unit (30) The control unit (30) determines a pre-heating time of the compressor (2) by the crankcase heater (11) based on the ambient temperature measured at the ambient temperature sensor (3) and controls the compressor (2) to start after the pre-heating time. The control unit (30) also controls the operation of fan motors (8, 23) or electromotor valves (5, 24)

[22] According to an embodiment of the present invention, the compressor (2) can be a variable capacity compressor. A variable capacity compressor may further comprise a pulse width modulated valve (12) and a bypass conduit (13) compared to a conventional compressor. A conventional variable revolution compressor can vary its capacity by an inverter control in such a way that the revolution of a motor is controlled by varying the frequency of the current applied to the motor. However, the conventional variable revolution compressor had certain problems in that the re- volution of the motor cannot be controlled with a desirable response and accuracy because the rotating motor has to be controlled directly. Further, since the revolution of the motor is frequently varied, vibrations and noises occur, and thereby the lifespan of compressor is reduced.

[23] The variable capacity compressor (2) periodically experiences the loading state discharging the refrigerant and unloading state not discharging the refrigerant during its operation. The ratio of the loading time and unloading time is controlled by a pulse width modulation method. A bypass conduit (13) connecting the upper portion of the compressor (2) to an inlet port (14) is installed to the casing of the compressor. A Pulse Width Modulated (PWM) Valve (12) is installed on the bypass conduit (13) When the pulse width modulated valve (12) is closed and thus the bypass conduit (13) is closed, the compressor (2) discharges the refrigerant. This state is referred to as "a loading." In this state, the compressor (2) is operated at 100% capacity. In contrast, when the pulse width modulated valve (12) is open and thus the bypass conduit (13) is open, the compressor (2) does not discharge the refrigerant. This state is referred to as "an unloading." In this state, the compressor (2) is operated at 0% capacity.

[24] The compressor (2) repeats loading and unloading while the motor of the compressor rotates at a constant speed regardless of the loading and unloading. However, the compressor operates at between 0% and 100% capacity in accordance with the ratio of the loading and the unloading.

[25] Fig. 2 is a control flow chart illustrating a method for protecting a compressor of an air-conditioner according to an embodiment of the present invention. The method is described with reference to Fig. 2. When an air-conditioner (1) turns on, control unit (30) senses connection of power of the air-conditioning system (Step Sl), and a crankcase heater (11) starts the operation (Step S2) An ambient temperature sensor (3) measures the temperature (Step S3) For example, a thermistor can be used as an ambient temperature sensor. Fig. 2 illustrates that an ambient temperature sensor measures the temperature after the crankcase heater (11) starts to operate. However, these two steps can be performed in a reverse order or simultaneously.

[26] A control unit (30) determines a pre-heating time of the compressor (2) by a crankcase heater (11) based on the ambient temperature, which required the oil in the oil simp of the compressor be placed within a safe area (Step S4) The "safe area" in the description of the present specification and claims means a safe region where it is substantially free of the liquid refrigerant. There is thus little concern for damaging the compressor when the compressor of the air-conditioner starts to operate. [27] The control unit (30) determines whether the operating time of the crankcase heater

(11) exceeds the pre-heating time of the compressor determined in Step 4 (Step 5) If the pre-heating time is passed, the control unit starts to operate the compressor of the air-conditioner.

[28] Fig. 3 illustrates an oil dilution chart according to the inlet pressure of the compressor and the temperature of the bottom part of the compressor. The X-axis indicates the inlet pressure of the compressor expressed by kg/cπf and the Y-axis indicates the temperature of the bottom part of the compressor expressed by ⁰C, in the chart. The chart shows a safe area, an unsafe area, and an intermediate area. The "unsafe area" refers to the region where starting the compressor is not desirable since a substantial amount of the liquid refrigerant is present in the compressor and oil is diluted. The "intermediate area" becomes a safe area during the heating operation. However, that area becomes an unsafe area during the cooling operation since a high super heating is necessary at the inlet of the compressor during the cooling operation. The pre-heating time of the compressor is the time that the oil in the compressor reaches to a safe area, either during the heating operation or the cooling operation. However, the pre-heating time can be determined as the time that the oil in the compressor reaches a safe area during the cooling operation but merely reaches to an intermediate area during the cooling operation.

[29] Under the constant inlet pressure of the compressor (for example, 3.30 kg/cm²), as the temperature of the bottom part of the compressor increases, the oil moves to the safe area since the liquid refrigerant is promoted to evaporate ( see arrow P) For example, if the inlet pressure of the compressor is 2.30 kg/cnfand the temperature of bottom part of the compressor is 12.22°C (point A), the oil is within the safe area. Therefore, there is no risk of damage in the compressor for starting the operation of the compressor. However, if the inlet pressure of the compressor is 4.30 kg/cnfand the temperature of bottom part of the compressor is -7.78°C (point B), the oil is within the unsafe area. At this time, pre-heating by the crankcase heater is necessary before starting the operation of the compressor.

[30] Fig. 4 is a diagram illustrating the testing method obtaining the pre-heating time of the crankcase heater corresponding to the outdoor temperature on oil dilution chart of Fig. 3. The above test is conducted in a chamber which can maintain the interior temperature constant. The test sequence is as follows. At first, an air-conditioner (1) with a compressor (2) is placed in the chamber while maintaining the temperature in the chamber constant. The inlet pressure of the compressor (2) and the temperature of the bottom part of the compressor are measured. The temperature of the bottom part of the compressor is measured around the oil sunp of the compressor. And then, the inlet pressure of the compressor and the temperature of the bottom part of the compressor are measured continuously while a crankcase heater (11) pre-heats the compressor (2) The test result like Fig. 4 is obtained if the measured inlet pressure of the compressor and temperature of the bottom part of the compressor are displayed. [31] As shown in Fig. 4, it can be noted that the temperature of the bottom part of the compressor is gradually increased while the inlet pressure of the compressor is rarely deviated, as crankcase heater (11) performs pre-heating. Therefore, a trace of the inlet pressure of the compressor and the temperature of the bottom part of the compressor becomes a line facing upward on the chart by the pre-heating of the crankcase heater

(H)

[32] Lines indicated by (a), (b), (c), (d), and (e) are the test results where the ambient temperatures are -1O⁰C, -5°C, 0⁰C, 5⁰C, 10⁰C, respectively. When the crankcase heater (11) starts to heat, the temperature of the bottom part of the compressor is identical to ambient temperature. As can be seen from the location of the starting point of lines (a), (b), (c), (d), and (e), the oil in a compressor of an air-conditioner, which has been stopped for a long time, is placed in the unsafe area. The lines (a), (b), (c), (d), and (e) are minimun movement sections for reaching from the unsafe area to the safe area. The consuming time to move this section is determined as the pre-heating time of the compressor.

[33] Fig. 5 illustrates an example of the pre-heating time based on the ambient temperature, which is determined by the above test. Fig. 5 illustrates the test result for an air-conditioner with an 1 IkW system capacity. As the ambient temperature becomes lower, the amount of the liquid refrigerant is larger and thereby a longer pre-heating time is necessary. As seen in Fig. 5, it can be noted that when the ambient temperature is 1O⁰C, the pre-heating time is about 30 minutes. However, the pre-heating time is about 40 minutes at O⁰C, and about 56 minutes at -10⁰C. As such, the pre-heating time increases as the ambient temperature decreases.

[34] The pre-heating time of the compressor corresponding to the ambient temperature can be varied according to the capacity of the air-conditioner, size or type of the compressor, the compressing method and the like. Thus, the pre-heating time of the compressor is obtained experimentally for each type of the air-conditioner. The mapping data of the pre-heating time based on the ambient temperature, obtained by the above test, can be stored in a storage medrun (not shown) in the air-conditioner (1) The storage mediun (not shown) can be provided in the control unit (30) or be embodied to a separate memory device outside the control unit.

[35] Fig. 6 illustrates the control unit (30) according to an embodiment of the present invention. The control unit (30) comprises a pre-heating time determination part (31) for determining the pre-heating time of the compressor based on the temperature measured by an ambient temperature sensor (3), a crankcase heater driving part (32) continuing the pre-heating of the compressor by the crankcase heater during the determined pre-heating time of the compressor, a compressor driving part (33) staring the operation of the compressor when determined as the pre-heating time of compressor is over. Further, the control unit (30) may include a pulse width modulated valve control part (34) for determining the ratio of the loading time and the unloading time of the pulse width modulated valve (12), a fan motor driving part (35) for controlling the drive of the indoor and outdoor fan motors (8, 23), and an electromotor valve driving part (36) for controlling the drive of the indoor and outdoor electromotor valves (5, 24) Mapping data of the pre-heating time based on the ambient temperature can be stored in a storage mediun (not shown) in the pre-heating time determination part (31) However, as described above, the storage medium can be embodied to a separate memory device outside the control unit (30)

[36] Although the invention has been described in detail for the purpose of illustration, it is understood that such detail is solely for that purpose, and variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention which is defined by the claims that follow.

Claims

[1] A method for protecting a compressor of an air-conditioning system having the compressor, a crankcase heater, an ambient temperature sensor detecting outdoor temperature, and a control unit connected to the crankcase heater and the ambient temperature sensor for controlling the crankcase heater, comprising: sensing connection of a power of the air-conditioning system; detecting a temperature by the ambient temperature sensor; determining a pre-heating time of the compressor based on the temperature detected.

[2] The method of Claim 1, further comprising: starting an operation of the crankcase heater when the power of the air- conditioning system is supplied.

[3] The method of Claim 1, further comprising: continuing the pre-heating of the compressor by the crankcase heater during the determined pre-heating time of the compressor; and starting an operation of the compressor when the determined pre-heating time of the compressor is over.

[4] The method of Claim 1 , wherein the pre-heating time of the compressor is a minimum time for oil to reach a safe area that is substantially free of the liquid refrigerant.

[5] The method of Claim 1, wherein the pre-heating time of the compressor is determined based on mapping data stored in a storage medium.

[6] The method of any one of Claims 1 to 5, where the compressor is a variable capacity compressor compressing a refrigerant depending on a duty control signal which determines a loading time and an unloading time.

[7] An apparatus for protecting a compressor of an air-conditioning system, comprising: a crankcase heater for heating a portion of the compressor; an ambient temperature sensor for detecting a temperature; a control unit connected to the crankcase heater and the ambient temperature sensor for controlling the crankcase heater; wherein the control unit comprises a pre-heating time determination part for determining a pre-heating time of the compressor based on the temperature detected by the ambient temperature sensor and a crankcase heater driving part for pre-heating of the compressor by the crankcase heater during the determined pre-heating time of the compressor. [8] The apparatus of Claim 7, wherein the pre-heating time of the compressor is a minimun time for oil to reach a safe area that is substantially free of the liquid refrigerant. [9] The apparatus of Claim 7, wherein the ambient temperature sensor is a thermistor. [10] The apparatus of Claim 7, wherein the ambient temperature sensor is installed on an outdoor portion of the air-conditioning system. [11] The apparatus of Claim 10, wherein the ambient temperature sensor is installed on an outdoor heat exchanger. [12] The apparatus of Claim 7, wherein the crankcase heater is comprised of resistance elements installed in an oil sump directly to enable heat transfer to the oil stored in the sunp. [13] The apparatus of Claim 7, wherein the crankcase heater is comprised of resistance elements wrapped around an outer surface of a compressor casing to enable heat transfer to the oil stored in a sunp. [14] The apparatus of any one of Claims 7 to 13, where the compressor is a variable capacity compressor compressing a refrigerant depending on a duty control signal which determines a loading time and an unloading time.