Refrigeration mechanical diagnostic protection and control device

Abstract

In vapor compression refrigeration systems a mechanism and method are provided for protecting a compressor from failures related to lack of superheat, loss of lubricating oil and other system malfunctions. Also provided is a mean of monitoring system conditions and providing service personnel with a quick manner of diagnosing problems.

Description

BACKGROUND OF THE INVENTION [0001] The present invention relates to refrigeration, air conditioning and heat pumps and more particularly to a method and apparatus for monitoring and controlling system pressures, temperatures, and superheat and subcooling. [0002] In the operation of refrigeration and air conditioning systems, the cooling effect is provided by the change in state of the refrigerant from a liquid to a gas in the evaporator of the system. The gaseous refrigerant is compressed by a compressor and is condensed to a liquid state in a condenser before passing through an expansion valve upon being returned to the evaporator. [0003] The failure of a compressor is usually very costly. Most compressor failures can be traced back to one of the following system conditions: “refrigerant floodback”, “flooded starts”, “slugging”, excessively high discharge temperature or loss of lubricating oil. [0004]“Refrigerant floodback” results when liquid refrigerant returns to the compressor ...

AI Technical Summary

Benefits of technology

[0015] Accordingly it is the object of the present invention to protect a refrigeration system or air conditioner compressor against adverse operating conditions such as floodback, slugging, excessively high discharge temperature and loss of oil. The present invention will also protect the system against high refrigerant line pressure and low refrigerant line pressure.

[0016] This and other objects of the present invention are attained by monitoring and controlling the system pressures (high and low), temperatures (both system and ambient), superheat and subcooling. The present invention uses a microprocessor to sense pressure inputs using pressure transducers (example: 4-20 mili-amp, 0-10 Volt DC, or resistance) for high side and low side pressures. Temperature sensors are connected to the liquid line, the suction line and positioned to sense outdoor ambient temperature. This information is conveyed to the microprocessor. With this information the firmware installed in the microprocessor can calculate the superheat, subcooling, discharge temperature, high side pressure, low side pressure and outdoor temperature. Through the use of control relays the microprocessor can protect the compressor from mechanical failure from the previously mentioned conditions.

[0018] It is also the purpose of this invention to assist a service technician in determining the present state of the refrigeration system and in rapidly determining what fault condition(s) may have occurred. This is done through the use of a bank of LED indicators showing the present superheat temperature status (“OK”, “WARNING” or “FAILURE”), the low pressure condition, high pressure condition, discharge temp condition, and sensor status. This bank of LEDs represents the first line of diagnosis, allowing even moderately skilled individuals to quickly determine the system's condition and / or reasons for failure. In the past this would have entailed the connection of a set of test gauges to service ports on the refrigeration system, allowing some refrigerant to escape to the environment as well as possibly allowing non-condensables to enter the system.

[0021] The invention also allows for condenser fan cycling (either vari-speed or simply ON / OFF) to maintain a head pressure range in low ambient conditions. Under high ambient conditions when proper subcooling is difficult to maintain, the invention can energize an auxiliary subcooling device.

[0024] In addition to system protection from low superheat, the present invention uses the collected data to further increase system efficiency by providing a method of increasing subcooling under heavy load conditions or decreasing subcooling when needed.

[0025] An electrical device monitors the mechanical aspects of standard refrigeration and air conditioning systems. The device protects these systems by calculating temperature, pressure, superheat, sub-cooling, ambient temperature and controlling system components. The device provides an easy, graphic representation of system conditions and faults for rapid verification of satisfactory operating parameters. Further detailed system conditions are provided for more extensive examination through use of digital read-outs.

Problems solved by technology

The failure of a compressor is usually very costly.

Most compressor failures can be traced back to one of the following system conditions: “refrigerant floodback”, “flooded starts”, “slugging”, excessively high discharge temperature or loss of lubricating oil.

The lubricant oil becomes mixed with refrigerant to the point that it cannot properly lubricate the load bearing surfaces.

When the compressor starts, the diluted oil cannot properly lubricate the load bearing surfaces causing erratic wear.

In the case of excessively high discharge temperature the compressor head and cylinders become so hot that the oil loses its ability to lubricate properly.

This causes rings, pistons and cylinders to wear resulting in “blow by”, leaking valves and metal debris in the oil.

Loss of oil is the result of insufficient oil in the crankcase to properly lubricate the load bearing surfaces.

The result is the system superheat.

Another cause for concern is introduction of foreign materials from the gauge set into the system.

This device does not monitor or display other system parameters such as temperature and pressure.

Further it does not provide simple system status indicators for the actual condition of superheat.

This device also relies on analog to digital converters for refrigerant pressure sensing, a method with inherent inaccuracies that would not provide the level of accurate control required with a refrigeration system under heavy load conditions.

These devices, however, only address one or two dangerous systems conditions and fail to provide and adequate level of compressor protection.

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