Compressors I PDF

Compressors I RACM-130 Learning Objectives Demonstrate knowledge of compressors, their components and operation. Demonstrate knowledge of the fundamental principles of compressors. Heart of the System The compressor is considered to be the heart of the refrigeration system. Creat...

Compressors I RACM-130 Learning Objectives Demonstrate knowledge of compressors, their components and operation. Demonstrate knowledge of the fundamental principles of compressors. Heart of the System The compressor is considered to be the heart of the refrigeration system. Creates a pressure difference, allowing the refrigerant to flow from high pressure to low pressure. Increases suction pressure level to discharge pressure level. Ex. 5 PSIG suction pressure, 170 PSIG discharge pressure. The pressure increase is 165 PSIG. Vapor pump – liquid is not compressible. Positive Displacement Most compressors we see are the positive displacement type. A compressor that draws suction vapor into a cylinder/chamber that reduces its volume and through compression, increases the vapor pressure/temperature. Reciprocating Compressor Basics Positive displacement Piston – creates the pressure. Crankshaft – drives the piston. Connecting rod – transfers the rotational motion into linear motion. Not the most efficient, due to clearance volume. The Basics of Reciprocating Compressor for Refrigerator｜How Refrigerator Compressor Works Scroll Compressor Basics Fixed scroll – stays stationary and attached to compressor body. Orbiting scroll – orbits during operation, creating the compression. Discharge check valve – stops refrigerant from entering during the off cycle. Can handle small amounts of liquid, as the orbiting scroll can lift axially. If compression ratio gets too high, the orbiting scroll will also separate axially. Copeland Scroll™ Compressors for Refrigeration Applications Rotary Compressor Basics Crankshaft fully rotates rollers unlike the scroll that orbits. Vane separates high and low side in compression chamber. Positive displacement. The Evolution of LG's Rotary Compressor for Air conditio ner Screw Compressor Basics Instead of a piston and cylinder, two screw type gears are used to squeeze the refrigerant vapor. Positive displacement. Used in large commercial industrial systems. https://www.youtube.com/watch?v=YMFe7saE-_E Centrifugal Compressor Basics Non – positive displacement type. Compress the refrigerant using an impeller that spins the refrigerant outward, radially. Inlet guide vanes draw gas into the center of the impeller, where it is spun outward with centrifugal force. Centrifugal Compressors - Chillers HVAC Semi Hermetic Housing Semi Hermetic – serviceable. Bolt on heads allow for gasket and plate replacements. Hermetic Housing A hermetic compressors housing is welded. Also know as tin can type compressor. Usually never get repaired, just replaced. Open Drive Compressor An open drive compressor is a compressor in a mechanically sealed body. The drive motor is attached at the shaft end with a coupling. Designed to be repaired. Needs shaft seal. Can be belt driven. Can be direct drive. Motor Windings Single Phase (PSC) Start – Common – Run windings. Start to run reading will have the highest resistance. Start to common will have the second highest resistance. Run to common will have the lowest resistance reading. Start to common + run to common = start to run. Motor Windings PSC Internal/External Overloads Internal/external overloads will break common winding, killing power to the motor. When taking the resistance readings, you will see resistance from start to run, but OL from R to C or S to C. Motor Windings 3 Phase All resistance values from each winding are equal. Ex. T1 to T2 = 1.8 Ohms, T2 to T3 = 1.8 Ohms, T1 to T3 = 1.8 Ohms. Overloads break each leg of power. If only one leg was removed, the motor will be single phasing and can get damaged. Motor Windings 3 Phase Compression Ratio Absolute Discharge / Absolute Suction Discharge pressure + 14.7 PSI = absolute discharge Suction pressure + 14.7 PSI = absolute suction The higher the ratio, the more work required by the compressor to move around the refrigerant. Ex. 418 PSIG discharge, 118 PSIG suction, what is the compression ratio? 418 + 14.7 = 432.7 118 + 14.7 = 132.7 432.7/132.7 = 3.2:1 Splash Lubrication Found in smaller compressors without oil pumps/delivery systems. Compressor oil is splashed around by using the crankshaft or connecting rods to scoop the oil from the sump every rotation. Oil Pump Feed System Used on larger compressors. Pump used to force feed oil Lubricates bearings/crankshaft/connecting rods. Typically mounted to at the end of the compressor crankshaft. Can be electronically driven. Cooling the Compressor Suction Gas returning to the compressor cools the motor. Air Cooled – a fan blows air over the compressor housing Water Cooled – a copper coil piping around with compressor housing, water circulates and cools the compressor. Common Electrical Failures Shorted/grounded winding. Moisture contamination. Oil turns acidic and eats at motor windings. * Proper evacuation is critical * Overheating of motor windings due to lack of suction gas. Ex. T1 to G = 142 ohms. Common Mechanical Failures Oil return issue resulting in mechanical failure. Springs in reciprocating compressor, causing motor knock. Reed valves faulty, causing high discharge pressure to go into the low-pressure suction chamber. Scroll plate wearing from lack of oil. Discharge check valve worn causing flooded starts. Compressors Recap Air Conditioning Compressor Basics Diagnosing a Locked Compressor 3D