HVAC Unit 26 Application of Refrigeration Systems Review Questions

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

- Even parallel systems have compressors of equal sizes and are made for refrigeration loads that are relatively constant or have known increases and decreases in capacity. - Uneven parallel system are used with systems that have widely varying loads. pg 558

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 the formation of acid in the entire system - Extensive cleanup procedure required pg 557

What holds up the structure of a walk-in cooler?

1-4 inch thick panels are made of foam insulation sandwiched in-between galvanized sheet metal or aluminum. pg 569

What is the special valve used in a refrigerated air drier?

A hot gas bypass valve. It monitors the pressure in the evaporator and allows hot gas to enter the suction line at any time there is no or reduced load in the evaporator. pg 581

Explain the function and advantages of a secondary-fluid system.

A secondary fluid is an antifreeze fluid that is cooled by a primary refrigerant, which is then circulated by pumps throughout the refrigeration system to absorb heat. Advantages- it allows the amount of HFC or HCFC in a refrigeration system to be decreased. It is a zero ODP and is non-toxic. It eliminates long liquid and suction lines. pg 561

When one large compressor is used, what desirable feature should it have?

A three-way heat reclaim valve. pg 553

When the compressors are located in the equipment room, the piping is routed:

A) in floor chases or in plastic pipes under the floor. pg 564

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

By using a timer clock and a liquid-line solenoid. For medium temperature, it can use off-cycle defrost. The clock can deactivate the solenoid and an automatic pumpdown will remove the refrigerant for a predetermined amount of time. The fans will continue to run and the ambient temperature will defrost the coil. pg 565

The two methods for rejecting heat from refrigerated cases are ______ and ______.

Condensing unit built inside the box or a remote condensing unit. pg 550

Exactly matching the refrigeration load with the capacity of refrigeration compressors is referred to as:

D) Load matching pg 557

Large or small compressors on parallel compressor racks, which are usually dedicated to the coldest cases, are called:

D) both A and C Satellite compressors and booster compressors pg 559

What special precautions should be taken with drain lines in walk-in coolers?

Heat must be provided to keep the condensate from freezing in low temperature coolers. Line piped to a drain must have a trap to prevent the atmosphere from being pulled into the cooler. They should be downsloped. pg 571

The three temperature ranges for refrigeration systems are ______, _______ and _______.

High, medium and low pg 549

An _____ varies the frequency of an electronically altered sine wave, which affects the speed of alternating current motors.

Inverter pg 559

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

It receives signals from the pressure transducer. pg 557

What is the function of the pressure transducer in parallel compressor systems?

It senses the refrigeration load and sends signals to a microprocessor control board that turns on and off compressors so that their capacity matches the refrigeration load. pg 557

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

It uses a small centrifugal pump to pressurize liquid entering the liquid line. This pressurized amount is equivalent to the pressure loss between the condenser outlet and the TXV inlet. Advantages - It allows the saturation temperature to be raised while the actual liquid temperature remains the same. The liquid becomes subcooled and will not flash if exposed to pressure drops in the liquid line. It also gives the condenser more internal volume to condense refrigerant. pg 563

What type of defrost is normally used for vending machine medium-temperature applications?

Off cycle defrost. It may be timed if the system does not get enough off time to complete a defrost. pg 574

Explain how the oil separator, oil reservoir, pressure differential valve, and oil level regulators work.

Oil separator - located in the common discharge line, it separates oil from the refrigerant and pumps it to an oil reservoir. Oil reservoir - can be combined with the oil separator, it holds oil that was separated by the oil separator. Pressure differential valve - It is located in the oil reservoir and ensures that the oil reservoir is pressurized each time an oil regulator is opened. Oil level regulators - it senses the oil level in the compressor's crankcase and adds oil if necessary. It senses the oil level by means of a float. pg 559

The two broad categories of display cases are _____ and ____.

Open display and closed display pg 549

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

Parallel compressor systems apply two or more compressors to a common suction header, a common discharge header and a common receiver. Advantages are - load matching, most important - diversification - flexibility - higher efficiencies - lower operating costs pg 556

Three advantages of unitary, stand-alone refrigeration modules in supermarket refrigeration are _____, ______ and ______.

Reduced refrigerant charge 75% less piping Lower installation costs pg 564

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

Refrigerated air is heavy and settles to the bottom of the case. Air patterns are formed to created air curtains that keeps the cooler air from leaving the case and controlled. pg 550

What are mullion heaters?

They are heaters made of resistance-type wire that runs just under the surface of the cabinet. They keep moisture from forming on the sides of the refrigeration cabinet. pg 568

T or F - The two types of defrosts used with low-temperature fixtures are hot gas and electric defrost.

True pg 565