Rhode Island - Unit 26 Review Questions - Application of Refrigeration Systems
1. The two broad categories of display cases are ___ and ___
Open and closed
15. Large or small compressors on parallel compressor racks, which are usually dedicated to the coldest cases, are called.
both a and c
9. 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
29. What is the critical point of carbon dioxide
31.1 degrees Celsius
31. What is the triple point of carbon dioxide
5.2 atm
19. 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
8. 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
17. 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
2. 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
24. What special valve is used in a refrigerant air drier.
D. hot gas bypass valve
20. How is defrost accomplished when the equipment room is in the back and the medium-temperature fixtures are in the front
EPR valves
21. True or false: the two types of defrost used with low-temperature fixtures are hot gas and electric defrost
False
14. 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
18. 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
28. 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.
30. 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.
22. What special precautions should be taken with drain lines and walk-in coolers.
all of the above
23. What holds up the structure of a walk-in cooler
aluminum of galvinized sheet metal, when panels pull together become a prefabricated structure
3. What are mullion heaters
an electric heater mounted inside the mullion to prevent moisture from forming in humid weather
11. Exactly matching the refrigeration load with the capacity of of refrigeration compressors is referred to as.
capacity control
5. The two methods for rejecting heat from from refrigerated cases are ___ and ___
evaporative condensors and cooling towers
6. When the compressors are located in the equipment room, the piping is routed.
in floor cases or in plastic pipes under the floor
4. The three temperature ranges for refrigeration systems are ___,___, and ___
low, medium, and high
16. A(n) ___ varies the frequency of and electrically altered sine wave, which affects the speed of alternating current motors
power inverter
13. What is the function of the microprocessor-based controller in the parallel systems
processes voltage signals
12. What is the functin of the pressure transducer in parallel compressor systems
signals the controller on the parallel compressor rack for capacity steps
33. Define a natural refrigerant
still used to cool foods today
7. When one large compressor is used, what desirable feature should it have.
suction muffler
10. 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
32. Define a synthetic refrigerant
uses mechanical and chemical processes
