Deck 47: High-Pressure, Low-Pressure, and Absorption Chilled-Water Systems

Question 1

High pressure chillers use either air- or water-cooled condensers.

Answer 1

True

Question 2

When a chiller using a low-pressure refrigerant is operating, the low pressure side of the system ____.

A) always shows a positive pressure
B) is always in a vacuum
C) contains a mixture of oil and air
D) rejects oxygen and moisture

Answer 2

B

Question 3

Speeds up to ____ rpm are used in centrifugal compressors.

A) 15,000
B) 20,000
C) 25,000
D) 30,000

Answer 3

D

Question 4

Direct expansion evaporators have ____.

A) expansion joints between sections of the evaporator
B) an established superheat at the outlet of the evaporator
C) subcooling at the outlet of the evaporator
D) an established superheat at the inlet of the evaporator

Question 5

A centrifugal compressor uses ____ for capacity control.

A) guide vanes
B) block vanes
C) guide blocks
D) control vanes

Question 6

A chiller typically cools ____________________ (what liquid?) for the purpose of air conditioning.

Question 7

The compressors used in low pressure chillers are the ____ type.

A) reciprocating
B) scroll
C) screw
D) centrifugal

Question 8

In centrifugal compressors, capacity control is accomplished by the use of ___________________________________ at the impeller inlet.

Question 9

A purge unit ____.

A) helps to provide subcooling in the condenser
B) helps to provide superheat in the suction line
C) relieves non-condensable gases from the system to the atmosphere
D) provides capacity control

Question 10

Electronic starters are much smaller than conventional starters.

Question 11

Thermostatic expansion valves are the only metering devices used in high pressure chillers.

Question 12

A reciprocating compressor with six cylinders, three banks of two cylinders each, can have its capacity reduced by unloading to ____% of full capacity.

A) 12.5
B) 25
C) 33-1/3
D) 50

Question 13

A benefit of operating a compressor unloaded is ____.

A) reduced energy costs
B) reduced compression ratios
C) increased cooling
D) both a and b

Question 14

Low pressure chillers use either air- or water-cooled condensers.

Question 15

The pressure difference in a low-pressure chiller is produced by a(n) ____________________ compressor.

Question 16

When referring to evaporators, the terms "direct expansion" and "dry type" can be used interchangeably.

Question 17

The evaporator of a chiller can be used to absorb heat from ____.

A) water
B) a solution of water and polyethylene glycol
C) the refrigerant
D) both a and b

Question 18

Two basic categories of chillers are the ____.

A) compression cycle and absorption
B) purge and absorption
C) absorption and lithium bromide
D) purge and lithium bromide

Question 19

Lithium bromide is ideal for use in absorption systems because it is non-corrosive.

Question 20

To unload a reciprocating compressor, hot gas bypass across the cylinder is the best method.

Question 21

Centrifugal compressors are designed with the lubrication isolated from the refrigerant vapor. Why?

Question 22

Explain how absorption refrigeration is different compression refrigeration.

Question 23

In a lithium bromide system, the refrigerant boils at 40°F. What is the corresponding absolute pressure required?

Question 24

The device that automatically helps to remove non-condensables from a chiller is called a(n) ____________________.

Question 25

What is the reason to use cylinder unloading in high pressure chillers?

Question 26

The pressure difference in an absorption chiller where the source of energy is steam or hot water is produced with the use of a(n) ____________________ solution.

Question 27

Why are multiple smaller compressors sometimes preferred over one large compressor?

Question 28

Name two methods commonly used to unload a reciprocating compressor.

Question 29

The refrigerant in an absorption chiller whose source of energy is steam or hot water is ____________________.

Question 30

Why are open-drive compressors often started up for a short time in the off season?

Question 31

What is accomplished by having a compressor that is equipped with unloaders?

Question 32

How is the capacity of a screw compressor controlled?

Question 33

The ends of a chiller evaporator are closed off by standard or marine boxes. What is the difference?

Question 34

Explain the difference, with respect to superheat, between a dry type evaporator and a flooded evaporator.

Question 35

Since there are no "valves" in a scroll compressor, what must be done to prevent refrigerant from flowing backward when the compressor cycles off?