Unit 26 Review Questions

Three disadvantages of parallel compressor systems are ___,___, and ___

-large leaks will result in the failure of multiple remote units -one motor burnout can result in acid formatin in system -extensive cleanup procedure required

What is the critical point of carbon dioxide

31.1 degrees Celsius

What is the triple point of carbon dioxide

5.2 atm

Three advantages of unitary, stand-alone refrigeration modules in supermarket refrigeration are ____, ____, and ____

75% less piping, lower installion costs, and requires 75% fewer braze points

Exactly matching the refrigeration load with the capacity of of refrigeration compressors is referred to as A. capacity control B. load shedding C. load paralleling D. load matching

A. capacity control

When the compressors are located in the equipment room, the piping is routed A. in floor chases or in plastic pipes under the floor B. in suspended ceilings C. detween the walls D. in back of walls

A. in floor cases or in plastic pipes under the floor

Define a parallel compressor system and list five advantages of these systems

Apply two or more compressors to a common sucion header,a common discharge header, and a common reciever. Five advantages: -load matching -diversification -flexibility -higher efficencies -lower operating costs and -less compressor cycling

When one large compressor is used, what desirable feature should it have A. discharge muffler B. suction muffler C. cylinder unloaders or variable-speed drive D. hot gas bypass

B. suction muffler

Explain the function and advantages of a secondary-fluid system

Circulates antifreeze solution to refrigerated cases and offers many advantages over a conventional refrigeration system

How are conditions maintained in open display cases when there are high shelves

Conditions are maintained because the refrigerated air is heavy and settles to the bottom

What special precautions should be taken with drain lines and walk-in coolers A. freeze protection B. trapping to prevent air from being pulled in C. downward sloping D. all of the above

D. all of the above

Large or small compressors on parallel compressor racks, which are usually dedicated to the coldest cases, are called A. satellite compressors B. remote compressors C. booster compressors D. both a and c

D. both a and c

What special valve is used in a refrigerant air drier A. four way valve B. defrost valve C. three way valve D. hot gas bypass valve

D. hot gas bypass valve

What type of defrost is normally used for vending machine medium-temperature applications A. electric B. hot gas C. off cycle D. none of the above

D. none of the above

How is defrost accomplished when the equipment room is in the back and the medium-temperature fixtures are in the front

EPR valves

True or false: the two types of defrost used with low-temperature fixtures are hot gas and electric defrost

False

Explain how the oil seperator, oil reservoir, presssure differential valve, and oil-level regulators work together to maintain the correct oil level in parallel compressors

From the oil reservoir, the oil passes to the oil-regulator float valve, which is located in the sightglass, level regulator senses crankcase oil levels and opens/ closes as necessary. PDV maintains the pressure differential

Explain the main idea behind pressurized liquid systems, and list their advantages

Offers a different way to subcool liquid refrigerant this helps in overcoming any pressure drops in liquid line to prevent premature flashing of the liquid before entering the metering device

The two broad categories of display cases are ___ and ___

Open and closed

What is meant by carbon dioxide having a critical point

Supercritical carbon dioxide is a fluid state of carbon dioxide where it is held at or above its critical temperature and critical pressure.

What is meant by carbon dioxide having a triple point

The triple point of any substance is the temperature and pressure where solid, liquid and gas forms can all three coexist in equilibrium, i.e. the amount of gas, liquid and solid won't change.

What holds up the structure of a walk-in cooler

aluminum of galvinized sheet metal, when panels pull together become a prefabricated structure

What are mullion heaters

an electric heater mounted inside the mullion to prevent moisture from forming in humid weather

The two methods for rejecting heat from from refrigerated cases are ___ and ___

evaporative condensors and cooling towers

The three temperature ranges for refrigeration systems are ___,___, and ___

low, medium, and high

A(n) ___ varies the frequency of and electrically altered sine wave, which affects the speed of alternating current motors

power inverter

What is the function of the microprocessor-based controller in the parallel systems

processes voltage signals

What is the functin of the pressure transducer in parallel compressor systems

signals the controller on the parallel compressor rack for capacity steps

Define a natural refrigerant

still used to cool foods today

What is the difference between an even and uneven parallel compressor system

uneven is different sized compressors, and all compressors are equal on an even system

Define a synthetic refrigerant

uses mechanical and chemical processes