Abstract:
A refrigeration device includes a radiator, an evaporator, a compressor, a heater and a control device. The radiator causes a refrigerant to radiate heat. The evaporator causes the refrigerant to evaporate. The compressor compresses the refrigerant circulating between the radiator and the evaporator. The heater heats lubricating oil in the compressor. The control device controls the heater so that an oil temperature of the lubricating oil in the compressor reaches an oil temperature target value obtained by adding a predetermined temperature to saturation temperature of the refrigerant in the compressor.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a refrigeration device in which a refrigerant is compressed by a compressor. 
       BACKGROUND ART 
       [0002]    Conventionally, as air-conditioning devices for transferring heat between indoors and outdoors, there have been air-conditioning devices comprising a usage-side heat exchanger disposed indoors and a heat-source-side heat exchanger disposed outdoors. In an air-conditioning device of such description, in order to transfer heat, one of the usage-side heat exchanger and the heat-source-side heat exchanger is used as a radiator, and the other is used as an evaporator. For example, in air-conditioning devices of such description, a refrigerant is circulated between the usage-side heat exchanger and the heat-source-side heat exchanger and heat is transferred; therefore, a refrigeration device is generally configured using a compressor for compressing the refrigerant, and the usage-side heat exchanger and the heat-source-side heat exchanger (radiator and evaporator). 
         [0003]    In a refrigeration device of this type, if the lubricating oil temperature (hereafter referred to as “oil temperature”) is low when the pressure in the crank case is under a fixed condition when the compressor is stopped, the proportion of the refrigerant dissolving into the lubricating oil in the crank case increases. Under additional conditions such as a long-term shutdown of the compressor and/or a change in the temperature of the refrigerant or temperature of external air, the phenomenon that we call “refrigerant stagnation” occurs, and a large amount of the refrigerant solves into the lubricating oil in the compressor under the refrigerant stagnation. When the refrigerant stagnates into the lubricating oil, e.g., the viscosity of the lubricating oil decreases and the performance of the lubricating oil decreases. 
         [0004]    Accordingly, in order to prevent refrigerant stagnation in the compressor, measures have conventionally been taken to mount a heater to the crank case and warm the compressor and prevent the refrigerant from stagnating even when the compressor is stopped. There are also instances in which the lubricating oil in the compressor is warmed by motor coil heating using open-phase energization. 
         [0005]    However, energizing the heater to warm the compressor presents a problem in that a given amount of power (standby power) is consumed, increasing the amount of power consumed by the refrigeration device. 
       SUMMARY OF THE INVENTION 
     Technical Problem  
       [0006]    In order to cut the standby power consumed by the compressor, e.g., each of Patent Literature 1 (JP-A 2001-73952) or Patent Literature 2 (Japanese Patent No. 4111246) discloses a technique for determining, on the basis of the refrigerant temperature or the external air temperature, periods in which heating by the compressor heater is not necessary, controlling the heater, and cutting the standby power. 
         [0007]    In the techniques in Patent Literature 1 and Patent Literature 2, although it is possible to cut the standby power, there remains scope for further cutting the standby power. In addition, since control is not performed on the basis of the amount of the refrigerant solved into the lubricating oil in the compressor, there may be instances in which heating by the heater is insufficient. 
         [0008]    Meanwhile, according to prior art disclosed in Patent Literature 3 (JP-A 9-170826), the compressor heater is controlled on the basis of the concentration of oil in the mixture of the lubricating oil and the refrigerant (i.e., proportion of lubricating oil in the mixture). However, the heater control disclosed in Patent Literature 3 involves a complex calculation for obtaining the current oil concentration from curves indicating the solubility characteristics of the refrigerant and the lubricating oil, and is not practical. For example, in the technique in Patent Literature 3, the curve indicating the solubility characteristics has to be obtained every time there is a change in the refrigerant and/or lubricating oil type and/or combination and/or a condition. Therefore, not only will there be an increase in cost required to acquire data from which the solubility curve is obtained and/or the amount of work required to obtain a regression formula created from the data, but there will also be an increase in calculation load, such as an increase in the amount of data processed by a microcomputer during actuation. 
         [0009]    An object of the present invention is to provide, at a low cost, a refrigeration device in which an appropriate oil concentration or oil viscosity can be readily maintained with regards to lubricating oil in a compressor and in which a cut in standby power can be achieved. 
       Solution to Problem  
       [0010]    A refrigeration device according to a first aspect of the present invention comprises a radiator for causing a refrigerant to radiate heat, an evaporator for causing the refrigerant to evaporate, a compressor for compressing the refrigerant circulating between the radiator and the evaporator, a heater for heating lubricating oil in the compressor and a control device for controlling the heater. The control device controls the heater so that the oil temperature of the lubricating oil in the compressor reaches an oil temperature target value obtained by adding a predetermined temperature to the saturation temperature of the refrigerant in the compressor. 
         [0011]    According to the refrigeration device of the first aspect, controlling the heater using the oil temperature target value for the lubricating oil and the current oil temperature makes it possible to control the heater in a simple manner using temperature as a parameter. Since the predetermined temperature is added to the saturation temperature of the refrigerant, it is possible to minimize the refrigerant from dissolving into the lubricating oil when the temperature of the external air or the like does not reach the saturation temperature of the refrigerant, and readily maintain the oil concentration and/or oil viscosity. in addition, since the heater can be switched ON/OFF on the basis of the saturation temperature of the refrigerant, the heater can be switched OFF when heating is unnecessary without being affected by external air conditions or the like, and a cut in standby power can be achieved. 
         [0012]    A refrigeration device according to a second aspect of the present invention is the refrigerant device according to the first aspect, and further comprises a refrigerant pressure detector for detecting the pressure of the refrigerant in the compressor. The oil temperature target value is set, using the predetermined temperature, to a temperature of a mixture of the lubricating oil and the refrigerant at which the oil concentration or the oil viscosity at solubility equilibrium at the pressure of the refrigerant is within a predetermined set range. 
         [0013]    According to the refrigeration device of the second aspect, the oil temperature target value is set, using the predetermined temperature to a temperature of the mixture at which the oil concentration and/or the oil viscosity at the pressure of the refrigerant is within a predetermined set range, whereby the heater is controlled in a manner that enables the standby power to be cut while preventing a state in which heating by the heater is insufficient. 
         [0014]    A refrigeration device according to a third aspect of the present invention is the refrigeration device according to the second aspect, wherein the oil temperature target value is set, using the predetermined temperature, to the temperature of the mixture of the lubricating oil and the refrigerant at which the oil concentration or the oil viscosity at solubility equilibrium at the pressure of the refrigerant is at a predetermined set value. 
         [0015]    According to the refrigeration device of the third aspect, the heater can be controlled so as to result in an oil temperature at which an oil concentration or oil viscosity is maintained a fixed condition, 
         [0016]    A refrigeration device according to a fourth aspect of the present invention is the refrigeration device according to any of the first through third aspects, wherein the control device holds the predetermined temperature as data for each of the saturation temperatures. 
         [0017]    According to the refrigeration device of the fourth aspect, it is possible to use the data to omit the workload for, e.g., the calculation performed by the control device. 
         [0018]    A refrigeration device according to a fifth aspect of the present invention is the refrigerant device according to any of the first through fourth aspect, and further comprises a temperature detector for measuring the oil temperature of the lubricating oil in the compressor and outputting the oil temperature to the control device or measurement devices for performing a measurement relating to a parameter for estimating the oil temperature of the lubricating oil in the compressor and outputting the result of the measurement to the control device. 
         [0019]    According to the refrigeration device of the fifth aspect, providing the dedicated temperature detector or the measuring device for measuring the oil temperature of the lubricating oil in the compressor makes it possible to detect the oil temperature of the lubricating oil in the compressor in a relatively accurate manner. 
         [0020]    A refrigeration device according to a sixth aspect of the present invention is the refrigeration device according to a fifth aspect, wherein the control device performs, when the refrigeration device is being launched, a selection between normal start-up and special start-up for refrigerant stagnation on the basis of the oil temperature of the lubricating oil and the oil temperature target value. 
         [0021]    According to the refrigeration device of the sixth aspect, it is possible to appropriately make a selection between normal start-up and special start-up, therefore improving the reliability of the compressor. 
         [0022]    A refrigeration device according to a seventh aspect of the present invention is the refrigeration device according to the sixth aspect, wherein the special start-up includes a plurality of special start-ups for refrigerant stagnation having different settings from each other. When selecting the special start-up instead of the normal start-up, the control device performs a selection from the special start-ups on the basis of the oil temperature of the lubricating oil and the oil temperature target value. 
         [0023]    According to the refrigeration device of the seventh aspect, it is possible to select a more appropriate special start-up on the basis of the oil temperature and the oil temperature target value, and the reliability is improved compared to an instance in which no selection of the special start-up is available. 
         [0024]    A refrigeration device according to an eighth aspect of the present invention is the refrigeration device according to the sixth or seventh aspects, wherein at the initial start-up after a power supply fed to the refrigeration device from the exterior is switched ON, the control device selects, according to test operation implementation history, whether to perform a test operation or to perform the special start-up. 
         [0025]    According to the refrigeration device of the eighth aspect, the control device can be used to switch between test operation and stagnation operation, making it possible to perform a test operation of the refrigeration device as required at the site of usage and the like. 
       Effect Of The Invention  
       [0026]    In the refrigeration device according to the first aspect of the present invention, performing control using the saturation temperature and the predetermined temperature simplifies the control and therefore makes it possible to minimize cost, while also making it possible to maintain an appropriate oil concentration or oil viscosity with regards to the lubricating oil in the compressor and achieve a cut in the standby power. 
         [0027]    In the refrigeration device according to the second aspect of the present invention, it is possible to avoid performing a control that results in an unnecessarily high oil concentration or oil viscosity, therefore improving the effect of cutting the standby power. 
         [0028]    In the refrigeration device according to the third aspect of the present invention, it is possible to cut the standby power while maintaining a uniform oil concentration or oil viscosity. 
         [0029]    In the refrigeration device according to the fourth aspect of the present invention, it is possible for the control device to control the heater at a high speed, and the speed of response of the compressor to a change in situation is increased. From another perspective, it is possible to suppress an increase in the calculation region used in the control. 
         [0030]    In the refrigeration device according to the fifth aspect of the present invention, control can be performed accurately on the basis of an accurate lubricating oil temperature. 
         [0031]    In the refrigeration device according to the sixth aspect of the present invention, special start-up can be performed in an appropriate manner when special start-up is necessary, and the reliability is improved. 
         [0032]    In the refrigeration device according to the seventh aspect of the present invention, it is possible to select the appropriate special start-up and thereby improve reliability. 
         [0033]    In the refrigeration device according to the eighth aspect of the present invention, it is possible to switch between test operation and special start-up, and installation of the refrigeration device is made easier. In addition, unnecessary stagnation operation can be avoided. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]      FIG. 1  is a refrigerant circuit diagram illustrating the configuration of an air-conditioning device according to an embodiment of the present invention; 
           [0035]      FIG. 2  is a partially cutaway perspective view illustrating the configuration of a compressor; 
           [0036]      FIG. 3  is a flow chart illustrating heater control by a control device; 
           [0037]      FIG. 4  is a graph showing the relationship between the saturation temperature and the oil temperature offset value; 
           [0038]      FIG. 5  is a graph showing the relationship between the refrigerant pressure, the degree of solubility, and the temperature of the mixture; 
           [0039]      FIG. 6  is a schematic diagram illustrating the setting of the oil temperature offset value; 
           [0040]      FIG. 7  is a graph illustrating the effect of the refrigeration device according to a first embodiment; 
           [0041]      FIG. 8  is a flow chart illustrating heater control by a conventional control device; 
           [0042]      FIG. 9  is a schematic diagram illustrating heater control by a conventional control device; and 
           [0043]      FIG. 10  is a flow chart illustrating heater control by a control device according to a second embodiment, 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0044]    Embodiments of the present invention will now be described with reference to the accompanying drawings. Embodiments of the compressor according to the present invention are not limited to that described below, and can be modified without departing from the scope of the present invention. 
       First Embodiment  
       [0045]    (1) Configuration of Refrigeration Device 
         [0046]    (1-1) Refrigerant Circuit 
         [0047]      FIG. 1  is a refrigerant circuit diagram showing the configuration of an air-conditioning device  10  in which a refrigeration device according to a first embodiment of the present invention is employed. The air-conditioning device  10  comprises a usage-side unit  20  installed indoors, and a heat-source-side unit  30  installed outdoors. An indoor heat exchanger  21  and an indoor fan  22  are disposed in the usage-side unit  20 . An outdoor heat exchanger  31 , an outdoor fan  32 , an electric valve  33 , an accumulator  34 , a four-way switching valve  35 , and a compressor  40  are disposed in the heat-source-side unit  30 . 
         [0048]    The air-conditioning device  10  in  FIG. 1  comprises the four-way switching valve  35 , and the four-way switching valve  35  enables switching between a cooling operation in which the indoor space is cooled and a heating operation in which the indoor space is heated. During a cooling operation, the indoor heat exchanger  21  functions as an evaporator and the outdoor heat exchanger  31  functions as a radiator. During a heating operation, in contrast, the indoor heat exchanger  21  functions as a radiator and the outdoor heat exchanger  31  functions as an evaporator. 
         [0049]    The four-way switching valve  35  has four ports, from a first port to a fourth port. In the four-way switching valve  35 , the first and second ports are connected and the third and fourth ports are connected during cooling, and the first and third ports are connected and the second and fourth ports are connected during heating. A discharge pipe  42  of the compressor  40  is connected to the first port of the four-way switching valve  35 , one end of the outdoor heat exchanger  31  is connected to the second port, one end of the indoor heat exchanger  21  is connected to the third port, and an intake pipe of the accumulator  34  is connected to the fourth port. 
         [0050]    The connections between parts of the usage-side unit  20  and the heat-source-side unit  30  other than the four-way switching valve  35  in the air-conditioning device  10  are as follows. Specifically, one end of the electric valve  33  is connected to the other end of the outdoor heat exchanger  31 . The other end of the indoor heat exchanger  21  is connected to the other end of the electric valve  33 . A discharge pipe of the accumulator  34  is connected to an intake pipe  43  of the compressor  40 . 
         [0051]    (1-2) Configuration of the Compressor 
         [0052]      FIG. 2  is a partially cutaway perspective view of the compressor  40 . The discharge pipe  42  is mounted on a side part of a cylindrical casing  41 , and an intake pipe  43  is mounted on an upper part. A scroll  44  is provided below the intake pipe  43 , and a motor  45  for driving the scroll  44  is provided below the scroll  44 . A configuration is present so that lubricating oil  70  accumulates at a bottom part  41   a  of the cylindrical casing  41 , and a crank case heater  46  is mounted so as to be wound onto the bottom part  41   a  of the casing  41 . An oil temperature detector  62  is mounted on the bottom part  41   a  in which the lubricating oil  70  accumulates. 
         [0053]    (1-3) Control Device and Measurement Instruments 
         [0054]    As shown in  FIG. 1 , the air-conditioning device  10  also comprises a control device  50  for controlling the operation of the air-conditioning device  10  and a variety of measurement instruments. Measurement instruments relating to controlling the crank case heater  46  of the compressor  40  are indicated herein; many of the other measurement instruments will not be described. The control device  50  comprises a microcomputer comprising, e.g., a central processing unit (CPU)  50   a , a memory  50   b , and the like. The control device  50  is connected to a fan motor  22   a  of the indoor fan  22 , a fan motor  32   a  of the outdoor fan  32 , the electric valve  33 , the four-way switching valve  35 , and the motor  45  and the crank case heater  46  of the compressor  40 . A refrigerant pressure detector  61  for measuring the pressure in the intake pipe  43  of the compressor  40 , an oil temperature detector  62  for detecting the temperature of the lubricating oil  70  in the compressor  40 , an external air temperature detector  63  for detecting the external air temperature, and a heat exchange temperature detector  64  for detecting the temperature of the indoor heat exchanger  21 , are connected to the control device  50 . 
         [0055]    (2) Control of Crank Heater 
         [0056]    A description will now be given with regards to control of the crank case heater  46  performed by the control device  50  along the flow chart shown in  FIG. 3 . The control device  50  controls the motor  45  of the compressor  40  and therefore has information relating to the states of the compressor  40  during actuation and stoppage. 
         [0057]    In a state in which the compressor  40  is stopped, the control device  50  first receives a result of detection by the refrigerant pressure detector  61  and calculates the saturation temperature in the compressor  40  (step S 10 ). As long as the refrigerant pressure LP is known, the saturation temperature T r  of the refrigerant can be easily calculated from the relationship between the refrigerant pressure and the saturation temperature using a conventionally well-known method. For example, the control device  50  stores a formula fa indicating the relationship between the refrigerant pressure LP and the saturation gas temperature (hereafter referred to as the saturation temperature T r ), and calculates the saturation temperature T r  using the formula fit. 
         [0058]    Next, the control device  50  adds a predetermined temperature (hereafter referred to as an oil temperature offset value) to the saturation temperature T r  obtained in step S 10  and calculates an oil temperature target value T so . The oil temperature offset value is determined on the basis of data stored in the memory  50   b  of the control device  50  (step S 11 ). A more detailed description of the oil temperature offset value will be given further below. 
         [0059]      FIG. 4  is a graph showing the relationship between the saturation temperature Tr and the oil temperature offset value. The graph shown in  FIG. 4  varies according to the oil concentration C so .  FIG. 4  shows two plots representing an instance in which the oil concentration C so  is 60% (, the refrigerant concentration is 40%) and an instance in which the oil concentration C so  is 70% (i.e., the refrigerant concentration is 30%). For example, if the oil concentration C so  of the refrigeration device in the air-conditioning device  10  is set to 60%, the data corresponding to the lower side plots (the concentration C so  is 60%) in  FIG. 4  is used, and no other data is used. If the saturation temperature T r  obtained in step S 10  is 5° C., the oil temperature offset value is determined to be Tos1° C. from point P 1 . Therefore, the oil temperature target value T so  is determined to be 5° C. +Tos1° C. (saturation temperature T r  oil temperature offset value). The graph shown in  FIG. 4  is approximated, e.g., by simple quadratic formula fb, and the control device  50  calculates the oil temperature target value T so  from the values for the oil concentration C so  and the saturation temperature T r . With regards to the formula fb (T r ), a formula is made available for each value for the oil concentration C so . A formula is selected according to the value for the oil concentration C so , and the oil temperature target value T so  is calculated from the value for the saturation temperature T r  using the selected formula fb (T r ). 
         [0060]    The control device  50  detects the oil temperature of the lubricating oil  70  in the compressor  40  using the oil temperature detector  62  (step S 12 ). The oil temperature detector  62  may be installed so as to directly detect the oil temperature of the lubricating oil  70 , but is mounted on the bottom part  41   a  of the casing  41  in this instance. The location at which the oil temperature detector  62  is installed may be, e.g., a side part of the compressor  40 , as long as the location is in the vicinity of an oil reservoir. Therefore, the control device  50  substitutes the detected temperature T b  detected by the oil temperature detector  62  into a simple compensation formula fc and detects the oil temperature T o  by the formula fc. The compensation formula fc can be derived from, e.g., an actual measurement performed with regards to a result of detection by the oil temperature detector  62  and a value detected through directly inserting a temperature sensor into the lubricating oil  70 . 
         [0061]    In step S 13 , the control device  50  compares the oil temperature target value T so  and the oil temperature T o  with each other. If the oil temperature T o  has not reached the oil temperature target value T so , the flow proceeds to step S 14 , the crank case heater  46  is put in an ON state, and the flow returns to step S 10 . If, upon the oil temperature target value T so  and the oil temperature T o  being compared with each other in step S 13 , the oil temperature T o  has reached the oil temperature target value T so , the control device  50  proceeds to step S 15 , the crank case heater . 46  is put in an OFF state, and the flow returns to step S 10 . 
         [0062]    Through performing control of such description, the control device  50  is able to control the crank case heater  46  so that the oil temperature T o  satisfies the oil temperature target value T so  during the compressor  40  is stopped. 
         [0063]    (3) Oil Temperature Offset Value 
         [0064]    As described above, the refrigeration device as an example of the air-conditioning device  10  is configured so that the control device  50  performs a control enabling the state in which the oil temperature T o  of the lubricating oil  70  reaches the oil temperature target value T so  to be maintained while the compressor  40  is stopped. The oil temperature target value T so  is established from the saturation temperature T r +the oil temperature offset value. 
         [0065]    The oil temperature offset value is set such that the oil temperature target value T so  is set to the temperature of a mixture of the lubricating oil  70  and the refrigerant at which the oil concentration at solubility equilibrium at refrigerant pressure LP assumes a predetermined set value. 
         [0066]    This matter will now be described using  FIG. 5 .  FIG. 5  is a graph showing the relationship between the refrigerant pressure LP in an equilibrium state, the temperature of the mixture of the lubricating oil  70  and the refrigerant (hereafter referred to as the liquid temperature) and the refrigerant solubility. Points Ps 1 , Ps 2 , Ps 3 , and Ps 4  shown in  FIG. 5  corresponds to points P 1 , P 2 , P 3 , and P 4  in  FIG. 4 , respectively. 
         [0067]    In the graph shown in  FIG. 5 , point Ps 1  is a point at which, in a state in which the pressure is α1 and the liquid temperature is β1 at solubility equilibrium, the oil concentration is 60% (i.e., the refrigerant solubility is 40%). As shown in  FIG. 6 , when the crank case heater  46  is left without being put in an ON state in the state ST 1  at point Ps 1 , the liquid temperature changes from the current liquid temperature β1 to a refrigerant saturation temperature T rα1  at which the equilibrium state ST 2  is maintained at pressure α1. At this time, the refrigerant further solves into the lubricating oil, and the oil concentration decreases from 60%. In other words, in order to maintain the oil concentration at 60%, the liquid temperature is held at β1. 
         [0068]    Therefore, the oil temperature offset value is derived from (liquid temperature at which the oil concentration is 60% at pressure α1 at solubility equilibrium)−(refrigerant saturation temperature at pressure α1), i.e., β1−T rα1 . A description will now be given for the method for determining the oil temperature offset value for each refrigerant saturation temperature using  FIGS. 4 and 5 . With regards to the oil concentration, a desired set value for the oil concentration is determined for each refrigeration device from the viewpoint of reliability and cutting standby power. Therefore, for a refrigeration device in which, e.g., the oil concentration is set to 60%, the relationship between a straight line parallel to the vertical axis at which the solubility is 40% (hereafter referred to as the 40% line) and each of curves L 1 , L 2 , L 3 , L 4 , etc. is examined. It follows that the solubility curve with which the 40% line intersects at point Ps 2  corresponding to pressure α2 is L 2 , the solubility curve with which the 40% line intersects at point Ps 3  corresponding to pressure α3 is L 3 , and the solubility curve with which the 40% line intersects at point Ps 4  corresponding to pressure α4 is L 4 . Meanwhile, the temperature of an imaginary solubility curve indicated by a two-dot chain tine passing through point P th2  at which the oil temperature and the saturation temperature are equal at pressure α 2  is T rα2 . Similarly, the temperature of an imaginary solubility curve passing through point P th3  corresponding to pressure α3 is T rα3  and the temperature of an imaginary solubility curve passing through point P th4  corresponding to pressure α4 is T rα4 . Therefore, the oil temperature offset value for pressure α 2  is a value obtained by subtracting temperature T rα2  from temperature β4 indicated by curve L 2 . Similarly, the oil temperature offset value is, tier pressure α3, a value obtained by subtracting temperature T rα3  from temperature β3 indicated by curve L 3 , and for pressure α4, a value obtained by subtracting temperature T rα4  from temperature β4 indicated by curve L 4 . 
         [0069]    As described above, the oil temperature offset value is one that is determined as a single value once the pressure of the refrigerant in the compressor  40  is determined. In addition, the oil temperature offset value can be obtained in advance once the graph shown in  FIG. 5  is established. 
         [0070]    Points P 1 , P 2 , P 3 , and P 4  in the graph shown in  FIG. 4  are obtained by plotting the oil temperature offset values for four saturation temperatures obtained from the graph in  FIG. 5 . For example, the method of least squares or a similar method is applied with regards to each of the obtained points P 1 , P 2 , P 3 , and P 4 , and the gaps between the points are filled to complete the graph showing the relationship between the saturation temperature and the oil temperature offset value. Approximation formulae representing the curves in the graph shown in  FIG. 4  are stored, as data, in the memory  50   b  of the control device  50 . 
         [0071]    (4) Characteristics 
         [0072]    (4-1) 
         [0073]    As described above, the refrigeration device as an example of the air-conditioning device  10  is configured so as to comprise the indoor heat exchanger  21  (radiator or evaporator), the outdoor heat exchanger  31  (evaporator or radiator), the compressor  40 , the crank case heater  46 , the control device  50 , the refrigerant pressure detector  61 , and the oil temperature detector  62 . The control device  50  controls the heater so that the oil temperature T o  of the lubricating oil in the compressor  40  reaches the oil temperature target value T so  obtained by adding the oil temperature offset value (predetermined temperature) to the saturation temperature T r  of the refrigerant in the compressor  40 . 
         [0074]    For example, in the techniques shown in Patent Literature 1 and 2, the crank case heater may be in an ON state even in a high-oil-concentration section as shown in  FIG. 7 . Specifically, when the external air temperature is increasing from a low state in which it is necessary for the crank case heater to be in an ON state, even if the oil concentration has become sufficiently high for there to be no need for the crank case heater to be in an ON state, the prevailing circumstances are maintained until the external air temperature is such that the crank case heater is to be turned off; therefore, the ON state may be maintained irrespective of the oil concentration 
         [0075]    However, in the control device  50  according to the abovementioned first embodiment, the oil temperature target value T so  is set, according to the oil temperature offset value (predetermined temperature), to a temperature of the mixture of the lubricating oil  70  and the refrigerant (e.g., β1 to β4, etc.) at which the oil concentration at solubility equilibrium at pressure of the refrigerant in the compressor  40  is at a predetermined set value (e.g., 60%). Therefore, the control device  50  can control the crank case heater  46  according to the oil concentration without the heater control being affected by the external air temperature, and it is possible to cut the standby power without the crank case heater  46  being in an ON state in the high-oil-concentration section. The control device  50  can control the crank case heater  46  so as to obtain an oil temperature at which a fixed oil concentration is maintained, 
         [0076]    Patent Literature 3 also discloses a technique for similarly controlling the crank case heater so as to maintain the oil concentration. However, in the technique in Patent Literature 3, the solubility of the oil in the compressor is calculated from solubility characteristics to obtain the target oil concentration, requiring a complex calculation, increasing the cost of the refrigeration device, and slowing the speed of response.  FIG. 8  is a flow chart showing the conventional heater control according to the oil concentration disclosed in Patent Literature 3.  FIG. 9  is a graph schematically showing solubility characteristics in order to illustrate the conventional heater control. In the conventional heater control, a solubility calculator calculates the solubility X from pressure Pa in the compressor detected by a shell interior pressure detector and temperature T1 detected by the oil temperature detector (step S 20 ). Then, it is determined whether or not the calculated solubility X is higher than a set solubility X0 (step S 21 ). If the calculated solubility is lower than the set solubility X0, as with the case of Xa, the heater is put in an OFF state (step S 23 ), and if the calculated solubility is higher than the set solubility X0, as with the case of Xb, the heater is put in an ON state (see  FIG. 9 ). 
         [0077]    As described above, the conventional heater control in Patent Literature 3 looks superficially simple, but is not simple in reality.  FIG. 9  is depicted so as to be partially deformed in order to facilitate comprehension. In the heater control in Patent Literature 3, it is necessary to search for the heater-OFF point Px 4  while modifying the solubility curve such as from curve L 11  to curves L 12 , L 13 , and L 14 . For example, while the pressure and liquid temperature at the calculated solubility Xb are Ph and T1, when the compressor is then warmed using the crank. case heater, the pressure and the temperature subsequently measured would have changed to e.g., pressure Pc and temperature T2. It follows that curve L 11  cannot be used as the solubility curve, and it is necessary to modify the solubility curve to curve L 12 . Moreover, since it is necessary to search for point Px 2  on curve L 12 , it is necessary to return to step S 20 , re-perform the complex calculation using the solubility calculator, and calculate a solubility Xc. Thus, as the lubricating oil is heated using the crank case heater, the temperature changes from T1 to T2, T3, and T4, and the pressure also changes with every measurement such as from Pb to Pc, Pd, and Pe due to the effect of environmental temperature or the like, making it necessary to modify the solubility curve from L 11  to L 12 , L 13 , and L 14 . Since solubility Xa, Xb, Xc, Xd, Xe, etc. cannot be obtained without performing a complex calculation using the two parameters of refrigerant pressure and oil temperature, the calculation takes time and the response is slower. In addition, there are diverse combinations of the refrigerant and the lubricating oil, the solubility curve must be prepared for each of the temperatures, and designing requires a large amount of workload, 
         [0078]    In contrast, as shown in  FIG. 4 , in the refrigeration device according to the first embodiment above, even if there is a change in the temperature of the lubricating oil  70  and the refrigerant pressure due to the crank case heater  46  being switched ON or OFF, the oil temperature offset value can be obtained, using a single, simple formula representing the curves in  FIG. 4 , from the saturation temperature T r  obtained from the temperature of the lubricating oil  70  and the refrigerant pressure. In other words, the control device  50  according to the above first embodiment is not required to hold the solubility curve information, and the calculation involved in heater control can be simplified. In addition, even if the types of lubricating oil and refrigerant change, and it becomes necessary to newly acquire data such as that shown in  FIG. 4  to be held by the control device  50 , it is only necessary for the oil temperature offset value and the saturation temperature in relation to a predetermined set value for the oil concentration (e.g., 60%) to be established. Therefore, there is no need to hold a solubility curve as data, and the design workload is reduced. While in the above first embodiment, a description was given for an instance in which ON/OFF control is performed, since, in the air-conditioning device  10  according to the present embodiment, temperature is the only parameter according to which the control device  50  controls the crank case heater  46 , it is also easy to arrive at a configuration in which proportionality control or the like is used to reduce the time taken to reach the oil temperature target value T so . 
         [0079]    (4-2) 
         [0080]    In addition, the amount of data stored by the memory  50   b  of the control device  50  is smaller. As long as an oil temperature offset value (predetermined temperature) is held as data for each saturation temperature shown in  FIG. 4 , the memory capacity and/or calculation load required for, e.g., the calculation by the control device  50  can be omitted. It is thereby possible for the control device  50  to control the crank case heater  46  at a high speed, and the speed of response of the compressor  40  to a change in situation is increased. 
         [0081]    (5) Modification Examples 
         [0082]    (5-1) 
         [0083]    The relationship between the oil temperature offset value and the saturation temperature held by the control device  50  may be represented by a curve or a straight line corresponding to an oil concentration in a predetermined set range, e.g., 60 to 65%, instead of a curve corresponding to an oil concentration of 60%. For example, line LN in  FIG. 4  falls within a set oil concentration range of 60 to 65%. On the side at which the saturation temperature is relatively low, the straight line LN is nearer a curve showing the relationship between the oil temperature offset value and the saturation temperature for which the set oil concentration value is 65%, and on the side at which the saturation temperature is relatively high, the straight line LN is nearer a curve showing the relationship between the oil temperature offset value and the saturation temperature for which the set oil concentration value is 60%. 
         [0084]    The control device  50  performing a control using a straight line LN of such description will result in the oil concentration being controlled to a range that has a moderate width (e.g., 60 to 65%). However, a control performed within such a range is sufficient. It is also possible to adopt a setting so that the set oil concentration value changes within a predetermined setting range due to another reason. When the straight line LN is used, the oil temperature offset value is obtained by proportional calculation from the saturation temperature, simplifying the control. 
         [0085]    (5-2) 
         [0086]    In the first embodiment above, as shown in  FIG. 4 , using the oil concentration as the set value, the relationship between the oil temperature offset value and the saturation temperature at which the oil concentration is within a predetermined set range or at a predetermined set value is obtained, and the control device  50  controls the crank case heater  46  using the obtained relationship. 
         [0087]    However, an oil viscosity value may be used instead of an oil concentration value with regards to the predetermined set range or the predetermined set value used when obtaining the relationship between the saturation temperature and the oil temperature offset value. An original purpose of controlling the crank case heater  46  so that the oil concentration is within a predetermined set range or at a predetermined set value is to prevent a decrease in oil viscosity. Therefore, heater control may be performed so as to directly achieve this purpose. The oil temperature offset value can be established, in an instance in which oil viscosity is used, in a similar manner to that in the instance in which oil concentration is used. 
         [0088]    (5-3) 
         [0089]    In the first embodiment above, a description was given for an instance in which the oil temperature detector  62  detects the oil temperature of the lubricating oil  70  in the compressor  40 . However, the oil temperature of the lubricating oil  70  may be estimated from a result of detection by another measurement device. For example, the oil temperature may be estimated through further increasing the accuracy by correcting the result of detection by the oil temperature detector  62  with, e.g., the temperature of external air surrounding the compressor  40  and/or the temperature of the indoor heat exchanger  21 . Alternatively, the oil temperature of the lubricating oil  70  in the compressor  40  may be estimated from a result of measurement by another measurement instrument for performing a measurement in relation to a parameter for estimating the oil temperature of the lubricating oil  70 , without using the oil temperature detector  62 . 
         [0090]    (5-4) 
         [0091]    In the first embodiment above, the control device  50  performs ON/OFF control of the crank case heater  46 . However, the control device  50  may perform a control so as to change the amount of heating according to the oil temperature offset value. For example, there may be an instance in which the oil temperature offset value becomes negative when there is a sharp change in the pressure in the compressor  40 . In such an instance, a modification may be performed that the amount of heating is greater than in an instance in which the oil temperature offset value is positive. 
         [0092]    (5-5) 
         [0093]    In the first embodiment above, the refrigerant pressure detector  61  is mounted on the intake pipe  43 , and the pressure of the refrigerant in the compressor  40  is measured on the side of the intake pipe  43 . However, in an instance in which the pressure of the refrigerant in the compressor  40  can be measured more satisfactorily on the side of the discharge pipe  12  than on the side of the intake pipe  43 , the pressure may be detected upon mounting, on the intake pipe  43 , the refrigerant pressure detector  61  on the discharge pipe  42 . 
         [0094]    (5-6) 
         [0095]    In the first embodiment above, the saturation gas temperature is used as the saturation temperature. However, the saturation liquid temperature may be used as the saturation temperature. 
         [0096]    (5-7) 
         [0097]    In the first embodiment above, the lubricating oil  70  is warmed using the crank case heater  46 . However, the heater for warming the lubricating oil  70  is not limited to the crank case heater  46 . For example, motor coil heating using open-phase energization may be used as a method for warming the lubricating oil  70 ; in such an instance, a motor cod is used as the heater for warming the lubricating oil  70 . In such an instance, the control device  50  performs, as heater control, ON/OFF control of motor coil heating using open-phase energization. 
       Second Embodiment  
       [0098]    (6) Overview of Refrigeration Device 
         [0099]    In the first embodiment above, a description was given with regards to controlling the heater while the refrigeration device of the air-conditioning device  10  is being supplied with power and the refrigeration device of the air-conditioning device  10  is maintaining an power-on state. However, situations in which the refrigeration device of the air-conditioning device  10  may be placed include a state in which the power supply of the air-conditioning device  10  is cut. In a compressor  40  that is stopped for a long period of time in a state in which the power supply is cut, the refrigeration oil in the compressor  40  cannot be heated, and a large amount of the refrigerant may solve into the refrigeration oil due to a change in the external air temperature. An air-conditioning device  10  according to a second embodiment described below is configured so as to make it possible to perform a control to prevent defects caused by a decrease in viscosity due to a large amount of refrigerant dissolving into the refrigeration oil when the power supply is switched back on after the power supply has been cut. 
         [0100]    A refrigeration device according to the second embodiment may be configured in a similar manner to the refrigeration device of the air-conditioning device  10  according to the first embodiment. Therefore, the following description of the refrigeration device according to the second embodiment will focus on the control performed when the power supply is switched back on after the power supply has been cut, with the configuration of the refrigeration device according to the second embodiment being the same as that of the refrigeration device of the air-conditioning device  10  according to the first embodiment. 
         [0101]    (7) Heater Control 
         [0102]    FIG  10  is a flow-chart showing the actuation of heater control during start-up of the refrigeration device according to the second embodiment. The control of constant oil concentration in step S 31  is the control described in the first embodiment, and indicates heater control other than that corresponding to start-up. In other words, steps S 32  to S 37  are subroutines of the heater control according to the first embodiment. Therefore, steps S 32  to S 37  may be performed at an appropriate point in time in the heater control according to the first embodiment. 
         [0103]    At start-up, it is determined whether or not the breaker is being switched ON for the first time (step S 32 ). This corresponds to determining whether or not the start-up is one in which a test operation is performed. If the breaker being switched ON is for the first time, a test operation is generally thought to be necessary. Therefore, if the breaker is being switched on for the first time, the flow proceeds to step S 33 . In step S 33 , it is determined whether or not a test operation implementation flag is ON. If the test operation is implemented, the test operation implementation flag is switched ON. This test operation implementation flag is stored, e.g., in the memory  50   b  of the control device  50 . If the test operation implementation flag is OFF, the test operation has not yet been implemented, so the test operation is implemented (step S 34 ). If the test operation implementation flag is not OFF, the test operation has already been implemented, so special start-up for the refrigerant stagnation is performed (step S 35 ). Special start-up is one that is performed upon modifying the setting from that corresponding to normal start-up to a setting that is more suited to a state in which a large amount of the refrigerant has solved into the lubricating oil in the compressor (refrigerant stagnation state). Instances in which it is determined that the breaker is being switched ON for the first time may include, e.g., an instance in which no power has been supplied to the air-conditioning device  10  at all due to a power cut or the like. Following the test operation in step S 34  and the special start-up in step S 35 , an operation such as a cooling operation or a heating operation is performed (step S 39 ). Then, the control device  50  stops the operation of the air-conditioning device  10  when, e.g., the control device  50  receives an instruction to stop the operation (step S 40 ). Heater control other than that corresponding to start-up is performed after the operation has stopped (step S 31 ). 
         [0104]    On the other hand, if, at start-up, it is determined that the breaker is not being switched ON for the first time (step S 32 ), it is determined whether or not (To−Tr) is equal to or less than a target offset value. The target offset value is a value obtained by subtracting the saturation temperature T r  from the oil temperature target value T so  at which the target oil concentration is achieved, and is one that is continually calculated and renewed according to the change in situation (at predetermined time intervals). If (To−Tr) is greater than the target offset value, the target oil concentration is realized, so normal start-up is performed (step S 38 ). 
         [0105]    If it is determined in step S 36  that (To−Tr) is equal to or smaller than the target offset value, the control device  50  performs level-differentiated special start-up set according to the value of ΔT (step S 37 ). Here, ΔT corresponds to {target offset value—(To−Tr)}. For example, if ΔT is such that 0≦ΔT≦5° C., low-level special start-up is performed, and if ΔT&gt;5° C., high-level special start-up is performed. More so than that for the low-level special start-up, the setting for the high-level special start-up is more suitable for start-up in an instance in which more than a predetermined amount of the refrigerant has solved into the lubricating oil in the compressor. 
         [0106]    A description of the determining performed in step S 36  using a specific example is as Wows. First, the pressure of the refrigerant and the oil temperature are read from the intersection on the graph at the target oil concentration, and the oil temperature offset value is obtained. For example, intersections Ps 1 , Ps 2 , Ps 3 , and Ps 4  between the line corresponding to an oil concentration of 60% (solubility of 40 wt %) and equal-oil-temperature lines in  FIG. 5  are read. The pressure at the intersections are converted to saturation temperatures T r  and subtracted from the oil temperature T o  to obtain (To−Tr). 
         [0107]    Thus, since values are directly read from a graph obtained through actual experiments or the like (i.e., since the values are directly derived from the actual relationship between the refrigerant pressure, the oil temperature, and the target oil concentration), the relationship between all parameters used in heater control performed by the control device  50  is reproduced to a high degree of accuracy. 
         [0108]    In addition, if the in-dome oil amount (100%) held by the compressor  40  is clearly known, the oil surface height can be calculated in reverse from the target oil concentration. Therefore, in an instance in which there is a likelihood of a terminal insulation fault caused the terminal being immersed in the lubricating oil during start-up, it is also possible to modify the target oil concentration and cause the control device  50  to perform a control so as to avoid the insulation fault. 
         [0109]    (7) Characteristics 
         [0110]    (7-1) 
         [0111]    As described above, the control device  50  of the air-conditioning device  10  according to the second embodiment performs, at start-up, a selection between normal start-up and special start-up on the basis of (To−Tr) and the target offset value (example of the oil temperature of the lubricating oil and the oil temperature target value) (step S 36 ). Since a selection can be made between normal start-up and special start-up, when special start-up is necessary, it is possible to proceed to step S 37  and perform special start-up, improving reliability. 
         [0112]    (7-2) 
         [0113]    If the special start-up is selected instead of normal start-up, the control device  50  selects the high-level special start-up or the low-level special start-up (examples of a plurality of special start-ups) on the basis of ΔT (example of the oil temperature of the lubricating oil and the oil temperature target value) (step S 37 ). Since an appropriate special start-up can be thus selected, it is possible to select a more appropriate special start-up and start-up the compressor  40  compared to an instance in which no selection of special start-up is possible, further improving the reliability. 
         [0114]    (7-3) 
         [0115]    At the initial start-up after the power supply ted to the air-conditioning device  10  from the exterior is switched ON, the control device  50  selects, according to test operation implementation history, whether to perform a test operation or to perform a special start-up (step S 33 ). Since the control device  50  can be used to switch between test operation and stagnation operation, it is possible to perform a test operation of the refrigeration device as required at the site of use and the like. It is thereby possible, through performing a test operation, to avoid having to perform an unnecessary special start-up, facilitating the refrigeration device installation. 
         [0116]    (8) Modification Examples 
         [0117]    (8-1) 
         [0118]    In the second embodiment above, even when it is determined in step S 33  that the test operation has been completed, the state after the stoppage is not known; therefore, special start-up is performed instead of normal start-up. However, it is possible to further apply, with regards to the special start-up, the high-level special start-up set in step S 37 . 
         [0119]    In addition, when the condition for entering step S 35  is satisfied, a measure for increasing the target oil concentration can also be taken. 
       REFERENCE SIGNS LIST 
       [0120]      10  Air-conditioning device 
         [0121]      21  Indoor heat exchanger 
         [0122]      31  Outdoor heat exchanger 
         [0123]      40  Compressor 
         [0124]      46  Crank case heater 
         [0125]      50  Control device 
         [0126]      61  Refrigerant pressure detector 
         [0127]      62  Oil temperature detector 
       PRIOR ART LITERATURE 
       [0128]    Patent Literature 
         [0129]    Patent Literature 1 JP-A 2001-73952 
         [0130]    Patent Literature 2 Japanese Patent No. 4111246 
         [0131]    Patent Literature 3 JP-A 9-170826