Unit 21 & 23 Review

Low temperature food storage applications typically have a temperature range of ________.

0 and -20 Degrees Fahrenheit

For every 1 degree rise in suction gas temperature returning to the compressor, there will be a _____ degree rise in the compressor's discharge temperature.

1

In a water-cooled system that recirculates water through a cooling tower, the refrigerant in the condenser typically condenses at ______ above the leaving water temperature.

10°F

A 2-ton wastewater system that operates approximately 16 hours per day would use about _______ gallons of water per day.

2880

A 10-ton water-cooled system that recirculates water through a cooling tower averages 16 hours of run time per day. The amount of water that would be circulated in a day would be about ________ gallons.

28800

A medium-temperature refrigeration box typically operates within what temperature range?

28°F to 40°F

When a standard-efficiency air-cooled condenser is used, the condensing refrigerant will normally be _______ above the ambient air temperature.

30°F

A typical water-cooling tower can cool the water to within ______ of the ambient air wet-bulb temperature.

7°F to 8°F

On a system that uses condenser flooding to control head pressure during low ambient conditions, the receiver should be sized so that it is ___________.

80% full when it contains the entire system charge

A refrigeration system's evaporator typically runs at about ________ of superheat.

8°F to 12°F

What does a high evaporator superheat indicate?

A starved evaporator

When is the most heat removed from the refrigerant in the condensing process?

During the change in state from a vapor to a liquid

The difference in temperature between the boiling refrigerant temperature and the evaporator outlet temperature is known as ___________.

Evaporator Superheat

Condensing temperatures can be reduced by reducing the condenser surface area. T/F

False

Natural-convection evaporators use a blower to force or induce air over the coil to improve the efficiency of the heat exchange. T/F

False

What is commonly used to defrost the ice from a low-temperature evaporator?

Hot gas or electric resistance heat defrost.

Which of the following is not a function of an evaporator efficiency control?

Regulates condensate removal by activating a condensate pump.

Why are some water-cooled condensers cleaned with brushes and others with chemicals?

Some condenser tubes are not straight and will not allow brushes to pass through them.

Why is a multicircuit evaporator used?

To reduce pressure drop through larger evaporators.

When moisture is removed from the air, latent heat is removed. T/F

True

An evaporator that does not operate flooded is thought of as what type of evaporator?

a dry type evaporator

Low ambient controls are used on ___________ to maintain head pressure during low ambient conditions.

air-cooled condensers

When liquid refrigerant floods the compressor crankcase, the oil level in the crankcase can drop causing _______.

bearing washout

Refrigerant in the evaporator ___________.

changes from liquid to vapor

A device that passes outside air over water to remove the system heat is a ________

cooling tower

Natural draft, forced draft, and evaporative are all types of __________.

cooling towers

The three materials of which air-cooled condensers are normally made are __________.

copper, aluminum, and steel

When the hot discharge gas enters the compressor, it is first _________.

desuperheated

Any refrigerant receiver should be able to hold all of the system's charge and still have a 25% vapor head for safety. T/F

false

Flooded evaporators typically use a(n) ________ type of expansion device.

float

When a refrigerated space has been allowed to warm up considerably, the system must ________.

go through a hot pulldown

Due to the seasonal temperature variations of municipal water, a wastewater system ___________.

has no definite refrigerant-to-water temperature relationship

Low-temperature evaporator coils __________.

have fewer fins per inch than medium temperature evaporator coils

Condenser flooding is accomplished by _____________ in both mild and cold weather to keep the head pressure constant.

having enough refrigerant in the system to flood the condenser

The greater the difference in temperature between the evaporator and the air being cooled, ______________.

he more moisture will be removed from the air

Fan cycling, air shutters or dampers, condenser flooding, and variable-frequency drive (VFD) condenser fan motors are all methods for controlling __________.

head pressure

A system that uses heat from the compressor discharge line to provide heated air or water to a conditioned space is called a(n) __________ system.

heat reclaim

Two common methods for defrosting a low temperature evaporator are __________.

hot gas and electric heat

When an evaporator experiences a heat-load increase, the suction pressure ___________.

increases

A finned-tube evaporator equipped with fans is called a(n) ________ evaporator.

induced- or forced-draft

What is the function of the evaporator in the refrigeration system?

it absorbs heat into the refrigeration system.

Air-cooled condensers are ____________.

less efficient than water-cooled condensers

On a system that uses a floating head pressure, _______________.

less system heat is available for heat reclaim coils

Flooding the compressor crankcase with liquid refrigerant can cause ________.

oil foaming

A low evaporator superheat may indicate a(n) ____________.

overcharge

A __________ can be piped into the high-side of the system to cycle the condenser fan on and off during a low ambient condition.

pressure control

An outdoor air-cooled condenser that has a vertical coil can be affected by the ___________.

prevailing winds

A medium-temperature evaporator uses a(n)_________ defrost method.

random or off cycle

One of the differences between air-cooled and water-cooled condensers is the _____________.

refrigerant condensing temperature

When the evaporator removes heat from the air and lowers the temperature of the air, _________.

sensible heat is removed from the air

The type of condenser that has straight copper tubes that are fastened into an end sheet within a steel shell that is typically used in large installations is the _________ condenser.

shell and tube

The sensible heat that is added to a saturated vapor after all of the liquid has boiled away is referred to as ________.

superheat

What determines the pressure on the low-pressure side of the system?

the boiling temperature of the refrigerant in the evaporator.

The difference in the amount of heat (in Btu/lb) that the refrigerant contains at the point where it enters the evaporator and the point at which it leaves the evaporator is known as _________.

the net refrigeration effect

The best heat exchange occurs between ___________.

two liquids

After heat is absorbed into the water in a water-cooled condenser, the water can be _______________.

wasted down the drain or sent to a cooling tower

__________ systems use water once, it is then piped to a drain.

wastewater

The component that varies the flow of water through a water-cooled condenser to maintain a stable head pressure is called a(n) ______________.

water-regulating valve

A water-cooling tower capacity is governed by what aspect of the ambient air?

wet bulb temperature

Low-temperature refrigeration systems typically operate at what temperature range?

−20°F to 0°F