Refrigeration – With indicator or tester – Diverse function indicators or testers
Reexamination Certificate
2000-03-20
2001-10-30
Tapolcai, William E. (Department: 3744)
Refrigeration
With indicator or tester
Diverse function indicators or testers
C062S129000, C235S487000, C283S115000
Reexamination Certificate
active
06308523
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to a simple field installable/removable indicator which can be used with a field pressure measurement to indicate the degree of subcooling or superheat of the refrigerant contained in the pipe (tubing, or refrigerant-containing component) to which it is attached. More particularly, the present invention relates to a superheat or subcooling test indicator used in vapor compression refrigerators and the like which can be attached to the system and used in conjunction with a pressure measurement via the existing service valve, making the superheat or subcooling calculation easy and fast, without the need to understand the use of a pressure-temperature saturation curve or table. A series of individual temperature indicating liquid crystals or other well-known temperature indicating chemicals or the like are located on a self-adhesive strip. Alternatively a traditional thermometer can also be utilized.
As used herein, “vapor-compression system” and “refrigeration system” refer to refrigerators, heat pumps, air conditioners or any other system which produces a refrigeration or cooling effect using refrigerant evaporation.
At the refrigerant vapor outlet of most evaporators of vapor-compression systems, it is expected that only vapor will be present. The number of degrees that the vapor is warmer than the saturation temperature corresponding to the actual pressure of the vapor is called the “vapor superheat.” The superheat is a measure of how much of the evaporator is effective in the cooling process. A high superheat suggests that much of the evaporator is not being used for evaporation, meaning the refrigerant charge is low. A low vapor superheat suggests that complete evaporation may not occur, which may be indicative of a blocked or reduced airflow over the evaporator, a clogged filter, or a failed blower fan.
At the refrigerant liquid outlet of the condenser, it is expected that only liquid refrigerant will be present. The number of degrees that the refrigerant temperature is cooler than the saturation temperature corresponding to the refrigerant pressure is called the “liquid subcooling.” A high degree of liquid subcooling suggests that much of the condenser is not being used for condensing vapor, but instead is being employed for subcooling, a much less effective mode of heat transfer.
The reason that measurement of actual superheat is desired is that it is well known as the best method to properly charge a vapor-compression system with refrigerant. It is also an excellent check for proper system charge on an operating unit. For example, operation at evaporator superheats above 10° F. typically indicate a low refrigerant charge and at less than 3° F. indicates an overcharged system.
Checking evaporator vapor superheat and condenser liquid subcooling are common maintenance procedures. The calculation of superheat and subcooling requires, however, a pressure/temperature saturation curve (which is specific to the refrigerant in the system), and at least a rudimentary understanding of the thermodynamics of evaporation and condensation. Other more complex approaches have been proposed to avoid the need to understand a pressure/temperature relationship and to calculate the superheat or subcooling for the user.
In U.S. Pat. No. 5,820,262, a refrigerant sensor provides, within a common assembly, pressure, temperature and superheat measurements and calculations with respect to a refrigerant material. The sensor includes a pressure transducer for measuring the pressure of the refrigerant material and a temperature transducer for measuring the temperature of the refrigerant material. The pressure and temperature measurements are used by a microprocessor to calculate the superheat value of the refrigerant material.
Similarly, U.S. Pat. No. 5,627,770 discloses a gage having sensors for observing temperature and pressure. The gage includes a display and an internal computer with a stored program. A data cartridge is separate from the gage but is connected to it with an electrical plug-type connection. The data cartridge has a non-volatile memory on which is stored data relating pressure and saturation temperature of a volatile refrigerant. The stored program contains programming instructions for measuring temperature and pressure from a source, retrieving from the data cartridge saturated temperature data corresponding to the observed pressure, and calculating/displaying superheat or subcooling.
Various low refrigerant charge-detecting devices have been proposed. For example, U.S. Pat. No. 4,545,212 discloses a superheat detector including a semiconductor pressure sensor and a semiconductor temperature sensor. An operational controller converts an output signal from the semiconductor pressure sensor to a value corresponding to a saturation temperature of the refrigerant, and produces an output electrical signal corresponding to superheat condition of the refrigerant by comparison between the saturation temperature and the output from the semiconductor temperature sensor.
U.S. Pat. No. 5,586,445 discloses a low refrigerant charge detection using a combined pressure/temperature sensor, and U.S. Pat. No. 5,457,965 discloses an apparatus for detecting a low level of refrigerant circulating through a motor vehicle refrigerant circuit. The apparatus comprises an electronic logic module, a pressure transducer and a thermistor preferably located in the refrigerant circuit between the compressor and the evaporator. The pressure transducer generates a signal indicative of the refrigerant pressure, from which the module derives a saturation temperature of the refrigerant. The saturation temperature is compared with the measured temperature to determine if a superheat condition exists indicative of low refrigerant charge.
While no simple, passive, non-electronic visual sensors for the direct determination of subcooling or superheat are known, visual sensors or indicators for use in detecting the moisture of a refrigerant in a vapor compression system are known, as seen for example, in U.S. Pat. No. 4,018,061 as well as commercial products by Parker, Alco Controls, Sporlan, Va. KMP, and others.
Other types of visual indicator systems are known for testing the presence and concentration of contaminants in a refrigerant. For example, U.S. Pat. Nos. 4,923,806 and 5,071,768 show apparatus for testing liquid or vapor contaminants in a closed system. Likewise, U.S. Pat. No. 5,377,496 shows an acid contamination indicator for closed loop vapor compression refrigeration systems. A pending patent application describes another indicator sold under the trademark “QwikCheck,” and represents yet another way of visually detecting the presence of acid in a refrigeration system. Another pending patent application sold under the trademark “QwikLook,” discloses another device for visually detecting the presence of moisture in a refrigeration system.
All the prior art devices and methods for automatic determination of superheat or subcooling have one thing in common, namely an electronic device to process the measured pressure and convert it to the corresponding saturation temperature for the specific refrigerant and then compare this temperature to the measured temperature to determine the superheat or subcooling. A discussion of how to manually calculate superheat from the measured temperature and pressure along with a pressure temperature saturation curve is well known in the art and discussed in numerous service manuals.
The 1975 Refrigeration Service Engineers Society (RSES) literature is one such source of instruction and includes a simple pictorial by Sporlan Valve Company on how to check superheat. The calculation of superheat or subcooling is performed manually by
1. measuring the pressure,
2. using a pressure/temperature saturation table or curve to convert this pressure to the corresponding saturation temperature of the refrigerant, then
3. measuring the actual temperature, and
4. calculating the difference between these temperatures to dete
Crowell & Moring LLP
Mainstream Engineering Corporation
Tapolcai William E.
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