HVAC UNIT 23 COMPRESSORS

Which style of compressor uses belts to turn the compressor?

A. Open drive

Name 5 types of compressors

Reciprocating, screw, rotary, scroll, centrifugal

What are 2 main reasons why a compressor should have modulating capacity control?

Reduces power consumption, produce better humidification controls, and rude compressor cycling along with small compressor starting currents.

What would be done to increase the compressor speed on a belt-driven compressor?

A. Decrease drive pulley size

List the 3 main advantages of having a digital capacity control on a scroll compressor.

Ability to hold a precise temp and humidity level, efficient full-load and part load efficiency, ability to be 30% more efficient than traditional compressor modulation methods, less compressor cycling for longer compressor life, delivery of maximum comfort efficiency, and reliability in one compressor.

What would be considered a higher-than-normal temp for a discharge gas line on a reciprocating compressor?

B. 215 degrees Fahrenheit

What compressor type uses pistons to compress the gas?

B. Reciprocating

Name 2 things in the design of a reciprocating compressor that control the efficiency of the compressor

Clearance volume and bore size

At what speed in rpm does a hermetic compressor normally turn?

D. Both A and B(1750 and 3450)

What lubricates the refrigeration compressor?

D. Oil

Which compressor type uses tapered, machine gear components to trap the gas for compression?

D. Screw

Briefly describe how the digital capacity control for a scroll compressor works.

Digital scroll compressor is a disengaging solenoid valve for bypassing discharge gas to the suction side of the compressor. An energized solenoid valve will unload the compressor by axially separation the scrolls making the compressor capacity zero.

List the main advantage that a discus compressor's valve plate design has over a conventional piston-type compressor.

Discus valve allows closer tolerance inside the compressor cylinder at the top dead-center. The closer tolerance provides more efficiency because pf less clearance volume. It also has a larger bore and allows more gas through the post within a short period of time. Capacity modulation (10-100%) = reduces the suction pressure and temp. Variation of the refrigerated space and provides for a decrease in the compressor cycling rate.

True or false: A compressor can compress a liquid

False

What effect does a slight amount of liquid refrigerant have on a compressor over a long period of time?

Liquid slugging, which causes oil dilution

List 4 main advantages a scroll compressor has over a conventional piston-type compressor.

No volumetric losses through gas re-expansion. Does not have valve losses that contribute to inefficiencies. No valve noise and very soft gas pulsation noises/vibrations. Separation of suction and discharge gases reduce heat transfer loss. Mating scrolls maintain nearly continuous compression and constant leak free contact. Radial movement allows compressor to handle some liquid.

Describe the reciprocating compressor piston, rod, crankshaft, valves, valve plate, head, shaft seal, internal motor overload device, pilot-duty motor overload device, and coupling.

Reciprocating compressor piston- Part of the cylinder assembly exposed to high pressure gas during compression. Rod- Connects the piston to the crankshaft. Crankshaft- Transmits the circular motion of the rods. Valves- At the top of the compressor determines the direction of gas flow. Valve plate- Holds the suction and discharge flapper valves. Head- The component that holds together the cylinder and the assembly of it. Shaft seal- Has a rubber surface so refrigerant and the atmosphere don't mix. Internal motor overload device- Protects the motor from overheating, found right by winding. Pilot-duty motor overload device- Interrupts controlled voltage Coupling- obtains the correct shaft alignment.

Explain how a compressor can be oil free

The centrifugal compressor is oil free because the rotor and the shaft are the only moving parts, the shaft acts as a rotor for the permanent magnet synchronous motor. The motor shaft has magnetically levitated bearings for friction-less operation.

Briefly describe how the scroll compressor compresses refrigerant gas.

There are 2 spiral shaped scrolls that fit inside one another, which is referred to as involute spirals. One of the spirals doesn't move while the other orbits around it.

What can the service tech do to keep the refrigeration system operating at peak efficiency?

They keep the evaporator and condenser running clean to improve compressor ration. they also run the suction pressure as high as practical, and run the discharge as low as practical.

Describe the operation of a compressor

Vapor pump- It increases suction pressure level to the discharge pressure level. Takes a low pressure low temp vapor compresses it into a high pressure, high temp vapor