Refrigeration – With indicator or tester
Reexamination Certificate
2000-03-15
2001-08-14
Tanner, Harry B. (Department: 3744)
Refrigeration
With indicator or tester
C165S011100, C374S043000, C062S129000
Reexamination Certificate
active
06272868
ABSTRACT:
FIELD OF THE INVENTION
The invention pertains to the field of air-cooled chillers, and in particular to a condenser coil performance indicator for an air-cooled chiller.
BACKGROUND OF THE INVENTION
A simplified typical air conditioning or refrigeration cycle includes transferring heat into a refrigerant, pumping the refrigerant to a place where heat can be removed from it, and removing the heat from the refrigerant. A refrigerant is a fluid that picks up heat by evaporating at a low temperature and pressure and gives up heat by condensing at a higher temperature and pressure. In a closed system, the refrigerant is then cycled back to the original location where heat is transferred into it. In a mechanical system, a compressor converts the refrigerant from a low temperature and low pressure fluid to a higher temperature and higher pressure fluid. After the compressor converts the refrigerant, a condenser is used to liquefy the fluid (gas) by cooling during the condensing part of the cycle. In operation, hot discharge gas (refrigerant vapor) from the compressor enters the condenser coil at the top, condenses into a liquid as heat is transferred to the outdoors. The refrigerant then passes through a metering device, such as an expansion valve, where it is converted to a low temperature, low pressure fluid before entering an evaporator.
Condensers typically use either water or air to remove heat from the refrigerant. Air-cooled condensers typically pipe the refrigerant through a coil of ample surface across which air is blown by a fan or induced natural draft. Air-cooled condensers can operate in relatively dusty environments where dust settles on the coil. Too much dust on the coil of a condenser severely degrades the performance of the refrigeration or air conditioning unit. Unit operation becomes more expensive due to the higher input power required. In extreme conditions, a dirty condenser may cause a high-pressure safety trip during hot days. Manufacturers recommend that the condenser coil be kept clean, but it is difficult for a user to tell how often a condenser should be inspected, since the frequency of inspection depends on the environment and the frequency of operation of the unit. Having information concerning condenser coil cleanliness on a real time basis would be useful to the user in optimizing a cleaning schedule.
SUMMARY OF THE INVENTION
Briefly stated, an algorithm calculates, in real time, the overall heat transfer coefficient for an air-cooled chiller system and compares this value to a reference value corresponding to a new machine operating with a clean condenser. Based on this comparison, an indication is displayed to inform a user of the degree of degradation in condenser performance.
According to an embodiment of the invention, a method for determining an operating condition of a condenser coil of a refrigeration system includes checking to see if the system is in a steady operating state; determining the saturated condensing temperature, saturated suction temperature, and ambient air temperature of the system; calculating the total heat rejected in a condenser of the system from values obtained in the preceding steps; calculating a heat transfer coefficient for the system; comparing the calculated heat transfer coefficient to an ideal heat transfer coefficient to obtain a value representing the operating condition of the condenser coil; and outputting a message to a user of the system based on the comparison of the calculated to ideal heat transfer coefficients.
REFERENCES:
patent: 4510576 (1985-04-01), MacArthur et al.
patent: 4885914 (1989-12-01), Pearman
patent: 5083438 (1992-01-01), McMullin
patent: 5333674 (1994-08-01), Czolkoss
patent: 5385202 (1995-01-01), Drosdziok et al.
Grabon Michel Karol
Said Wahl
Carrier Corporation
Tanner Harry B.
Wall Marjama & Bilinski
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