HVACR Unit 13 Quiz & Flashcards on Compressors

Questions and Answers

A common application for centrifugal compressors is?

Commercial water chilling systems (correct)

Residential air conditioning

Refrigerators

Heat pumps

What is a compressor that compresses gas between a fixed spiral and an orbiting spiral?

Scroll compressor

What is a compressor that uses a large off-center rotating shaft and multiple blades that follow the cylinder walls as the shaft rotates?

Rotary blade rotary compressor

What compressor uses an impeller to throw refrigerant from the center outward?

Centrifugal compressor Signup and view all the answers

What compressor uses an offset rolling piston that seals against a blade that remains stationary?

Stationary blade rotary compressor Signup and view all the answers

What do all refrigeration compressors pump?

Only vapor Signup and view all the answers

What is an advantage of open drive compressors?

The motor and compressor can be replaced separately Signup and view all the answers

What lubrication method do reciprocating compressors use with an oil slinger?

Splash lubrication Signup and view all the answers

Which application requires more horsepower to produce a ton of cooling: a 0°F evaporator or a 40°F evaporator?

0°F evaporator, because of the higher pressure difference Signup and view all the answers

How does compressor cylinder unloading reduce the capacity of a reciprocating compressor?

Making the valves in the head inoperative Signup and view all the answers

How can hermetic compressors be characterized?

They have a welded shell, which holds both the compressor and motor Signup and view all the answers

How can semihermetic compressors be characterized?

They have a bolted housing that encloses both the compressor and motor Signup and view all the answers

How does a reciprocating compressor operate?

In a reciprocating compressor, the piston is driven up and down in the cylinder by the connecting rod and crankshaft Signup and view all the answers

How does a two-step scroll compressor achieve capacity reduction?

An internal rotating plate opens and closes two drilled ports in the scroll Signup and view all the answers

In which system does less refrigerant enter the cylinder for each compression cycle, requiring more horsepower for each BTU of cooling?

A low-evaporator-temperature system Signup and view all the answers

What is one technique for improving efficiency and comfort through compressor selection?

Select a compressor with capacity control to match the compressor capacity with the refrigeration load Signup and view all the answers

What type of compressors meet refrigeration needs on trucks, tractor trailers, and shipping containers?

Open-drive compressors Signup and view all the answers

Where are rotary compressors commonly used?

In window units Signup and view all the answers

What is the advantage of compliance in a scroll compressor?

The orbiting scroll can separate and unload to pass a small liquid slug Signup and view all the answers

What is the function of the compressor in the refrigeration cycle?

Raise the pressure and temperature of the refrigerant Signup and view all the answers

What are the major types of compressors listed by mechanical design?

Reciprocating, rotary, scroll, screw, and centrifugal Signup and view all the answers

What is the match of the motor and compressor inside a hermetic compressor?

Is specific for the application of the compressor Signup and view all the answers

Why is the shaft seal on an open compressor more complicated than the gaskets and seals on other parts?

It must seal a shaft that is turning Signup and view all the answers

What seals the small gaps between the screws on a screw compressor?

Oil flooding Signup and view all the answers

What is the space left between the piston and the valve plate of a reciprocating compressor when the piston is at the top of the cylinder called?

The clearance volume Signup and view all the answers

What are the three different design screw compressors?

Single screw with gate rotors, dual screw, and triple screw Signup and view all the answers

What is the lowest percentage of full capacity that a digital scroll can be safely operated for extended periods?

10% Signup and view all the answers

What opens and closes the valves in a reciprocating compressor?

Pressure difference across the valves Signup and view all the answers

What type of compressors contain the compressor and motor together inside a welded steel housing?

Hermetic compressors Signup and view all the answers

Which compressor has a piston that is driven up and down in the cylinder by a connecting rod and crankshaft?

A reciprocating compressor Signup and view all the answers

Which compressor type draws refrigerant gas in through the inlet port into voids created by turning rotors?

A screw compressor Signup and view all the answers

Which of the following compressors is NOT considered a positive-displacement compressor?

Centrifugal Signup and view all the answers

Which of the following has the capacity range for a centrifugal compressor?

Commercial AC Signup and view all the answers

It is TRUE of a medium-temperature refrigeration unit that it requires 1 hp to produce 2/3 ton of cooling.

True Signup and view all the answers

Study Notes

Centrifugal Compressors

Commonly used in commercial water chilling systems.
Operate by throwing refrigerant outward using an impeller.

Scroll Compressors

Function by compressing gas between a fixed spiral and an orbiting spiral.
Capacity is adjustable through an internal rotating plate that manages drilled ports.
Advantage includes the ability to handle small liquid slugs due to compliance in design.

Rotary Compressors

Utilize a large off-center rotating shaft with blades that follow the cylinder walls.
Commonly found in window units and can be classified as rotary blade rotary compressors or stationary blade rotary compressors.

Reciprocating Compressors

Operate through a piston driven up and down by a connecting rod and crankshaft.
Capacity can be decreased by making the valves in the head inoperative (cylinder unloading).
The clearance volume is the space between the piston and the valve plate when the piston is at the top.

Hermetic and Semihermetic Compressors

Hermetic compressors have a welded shell containing both the compressor and motor.
Semihermetic compressors are enclosed in a bolted housing.
Both types feature specific motor-compressor matching for optimal application.

Compression Efficiency

Compressors designed to pump only vapor reduce risk of liquid damage.
Low-evaporator-temperature systems may require more horsepower for cooling due to less refrigerant entering the cylinder.
Digital scroll compressors can operate safely at a minimum capacity of 10% for proper lubrication.

Various Compressor Types

Classifications include reciprocating, rotary, scroll, screw, and centrifugal.
Screw compressors draw refrigerant through turning rotors and rely on oil flooding to seal small gaps.
Centrifugal compressors are not classified as positive-displacement compressors.

Other Key Points

Open-drive compressors allow for separate replacement of the motor and compressor.
Oil slingers provide splash lubrication in reciprocating compressors.
A medium-temperature refrigeration unit typically requires 1 hp to produce 2/3 ton of cooling.

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Description

Test your knowledge on HVACR concepts with these flashcards focused on Unit 13. Each card features important terms and their definitions related to compressors, including centrifugal and scroll compressors. Ideal for students and professionals looking to strengthen their understanding of HVACR systems.

HVACR Unit 13 Flashcards