Patent Application
20060137369
This invention relates generally to air conditioning systems and, more particularly, to a method and apparatus for determining proper refrigerant charge in such systems.
Maintaining proper refrigerant charge level is essential to the safe and efficient operation of an air conditioning system. Improper charge level, either in deficit or in excess, can cause premature compressor failure. An over-charge in the system results in compressor flooding, which, in turn, may be damaging to the motor and mechanical components. Inadequate refrigerant charge can lead to increased power consumption, thus reducing system capacity and efficiency. Low charge also causes an increase in refrigerant temperature entering the compressor, which may cause thermal over-load of the compressor. Thermal over-load of the compressor can cause degradation of the motor winding insulation, thereby bringing about premature motor failure.
Charge adequacy has traditionally been checked using either the “superheat method” or “subcool method”. For air conditioning systems which use a thermal expansion valve (TXV), or an electronic expansion valve (EXV), the superheat of the refrigerant entering the compressor is normally regulated at a fixed value, while the amount of subcooling of the refrigerant exiting the condenser varies. Consequently, the amount of subcooling is used as an indicator for charge level. Manufacturers often specify a range of subcool values for a properly charged air conditioner. For example, a subcool temperature range between 10 and 15° F. is generally regarded as acceptable in residential cooling equipment. For air conditioning systems that use fixed orifice expansion devices instead of TXVs (or EXVs), the performance of the air conditioner is much more sensitive to refrigerant charge level. Therefore, superheat is often used as an indicator for charge in these types of systems. A manual procedure specified by the manufacturer is used to help the installer to determine the actual charge based on either the superheat or subcooling measurement. Table 1 summarizes the measurements required for assessing the proper amount of refrigerant charge.
To facilitate the superheat method, the manufacturer provides a table containing the superheat values corresponding to different combinations of indoor return air wet bulb temperatures and outdoor dry bulb temperatures for a properly charged system. This charging procedure is an empirical technique by which the installer determines the charge level by trial-and-error. The field technician has to look up in a table to see if the measured superheat falls in the correct ranges specified in the table. Often the procedure has to be repeated several times to ensure the superheat stays in a correct range specified in the table. Consequently this is a tedious test procedure, and difficult to apply to air conditioners of different makers, or even for equipment of the same maker where different duct and piping configurations are used. In addition, the calculation of superheat or subcool requires the measurement of compressor suction pressure, which requires intrusive penetration of pipes.
In the subcooling method, as with the superheat method, the manufacturer provides a table listing the liquid line temperature required as a function of the amount of subcooling and the liquid line pressure. Once again, the field technician has to look up in the table provided to see if the measured liquid line temperature falls within the correct ranges specified in the table. Thus, this charging procedure is also an empirical, time-consuming, and a trial-and-error process.
Briefly, in accordance with one aspect of the invention, a simple and inexpensive refrigerant charge inventory indication method and apparatus using temperature measurements only is provided for an air conditioning system.
In accordance with another aspect of the invention, a hand held device includes a single temperature sensor which is used to sequentially sense the indoor wet bulb temperature, the condensing liquid line temperature and the outdoor temperature, and these temperatures are used to calculate a condenser approach temperature difference which, in turn, is compared with predetermined values to determine the refrigerant charge condition of an air conditioning system.
By yet another aspect of the invention, the device includes an absorbent pad that may be moistened for purposes of sensing the indoor wet bulb temperature.
By yet another aspect of the invention, the device includes a strap for securing the temperature sensor against the liquid line for sensing the condensing liquid line temperature.
By yet another aspect of the invention, the device includes a microprocessor for storing the sensed temperatures, comparing them with predetermined stored values, and indicating the charge condition of the system.
In the drawings as hereinafter described, a preferred embodiment is depicted; however, various other modifications and alternate constructions can be made thereto without departing from the true spirit and scope of the invention.
Referring now to
In operation, the refrigerant flowing through the evaporator 14 absorbs the heat in the indoor air being passed over the evaporator coil by the evaporator fan 16, with the cooled air than being circulated back into the indoor air to be cooled. After evaporation, the refrigerant vapor is pressurized in the compressor 11 and the resulting high pressure vapor is condensed into liquid refrigerant at the condenser 12, which rejects the heat in the refrigerant to the outdoor air being circulated over the condenser coil 12 by way of the condenser fan 17. The condensed refrigerant is then expanded by way of an expansion device 13, after which the saturated refrigerant liquid enters the evaporator 14 to continue the cooling process.
In a heat pump, during cooling mode, the process is identical to that as described hereinabove. In the heating mode, the cycle is reversed with the condenser and evaporator of the cooling mode acting as an evaporator and condenser, respectively.
It should be mentioned that the expansion device 13 may be a valve such as a TXV or an EXV which regulates the amount of liquid refrigerant entering the evaporator 14 in response to the superheat condition of the refrigerant entering the compressor 11. It may also be a fixed orifice, such as a capillary tube or the like.
In accordance with the present invention, there are three measured variables needed for assessing the charge level in an air conditioning system. These measured variables are liquid line temperature Tliquid outdoor temperature TOD and indoor wet bulb temperature Twb.
Each of these three temperatures are sensed with a single device having a single sensor and a microprocessor for storing these sensed temperatures, for storing predetermined algorithms and defining parameters for particular systems, and for indicating the charge status as a function of comparison of the sensed data with stored data.
Referring now to
Extending from the upper end of the device 22 is a flange 24 which acts as a shelf for supporting both the temperature sensing device and the liquid refrigerant line from the condenser for purposes of sensing that temperature.
Disposed at an inner edge on the upper side of the flange 24 is a sensor probe 26, which is an elongate cylindrical structure with its upper portion being exposed as shown in
For purposes of sensing the indoor wet bulb temperature Twb, it is necessary to maintain the sensor probe 26 in a wet condition. This is accomplished by placing a cylindrically shaped sock 27 over the sensor probe 26 as shown in
Finally, for purposes of measuring the third required temperature, the liquid line temperature Tliquid, it is necessary to place the sensor probe 26 in direct contact with the condenser liquid line 28 as shown in
Referring now to the front panel 23 of the housing 22 as shown in
In operation, as shown in
The wet sock 27 is then removed and the device as shown in
Finally, the device 21 is taken to the condenser liquid line 28 and is attached to that line as shown in
The processing of the three stored temperatures is accomplished by the CPU 43 by comparing the sensed liquid line temperature Tliquid for a given sensed outdoor temperature TOD and indoor wet bulb temperature Twb with an optimal liquid line temperature Toptimal for the same outdoor temperature and indoor wet bulb temperatures. These optimal values are stored in the read only memory 45 for each of various air conditioning system models as described in U.S. patent application No. (docket no.: 210—706) filed concurrently herewith, assigned to the assignee of the present invention and incorporated herein by reference. When the comparison has been made, the difference between the values calculated on the basis of the sensed temperatures and the values that are representative of an optimal condition will indicate whether the system is undercharged, overcharged or properly charged with refrigerant. The LEDS 32, 33 and 34 are then again used to indicate one of these three possibilities. That is, the circuitry is provided within the device 21 such that if the analysis indicates that a proper charge has been found, then the LED 33 will be automatically lighted. If it is found that refrigerant charge is needed in order to present an optimal condition, then the LED 32 will be lighted to indicate that refrigerant must be added. If it is found that the system is overcharged, then the LED 34 will be lighted to indicate that refrigerant must be removed.
While the present invention has been particularly shown and described with reference to a preferred embodiment as illustrated in the drawings, it will be understood by one skilled in the art that various changes in detail may be effected therein without departing from the true spirit and scope of the invention as defined by the claims.
