Unit 24

The pressure drop for R-22 due to vertical lift in a liquid line is approximately:

0.5 psi per foot of lift.

For most systems, the minimum velocity in a vertical suction line is:

1,000-1,500 ft per minute.

A system using R-404a has an evaporation temperature of 20°F. If the line length is 100 ft and a 7/8 in line is used, what is the maximum capacity of the system?

2 tons

An R-22 system has a 28-ft lift and a 7 psi pressure drop in the liquid line due to vertical lift. If the liquid leaves the condenser at 244 psi, what is the pressure at the top of the vertical lift?

223 psi

An R-22 system has a 6 psi pressure drop in the liquid line and leaves the condenser at 218 psi. If the pressure at the top of the vertical lift is 199 psi, what is the height of the vertical lift?

26 ft

For most systems, the minimum velocity in a horizontal suction line is:

500-750 ft per minute.

A system using R-404a has an evaporation temperature of 0°F. If the line length is 100 ft and the system needs a capacity of 2 tons, what size line should be used?

7/8 in

The maximum pressure drop for a suction line should not exceed:

A corresponding saturation temperature drop of 2°F.

Flash gas in the liquid line can be identified by:

A significant temperature drop in the liquid line temperature.

Oil accumulation in the evaporator:

Acts as an insulator reducing the heat transfer of the coil.

Which of the following modifications would alleviate the stress on a compressor in a long-line system?

Adding a compressor hard-start kit

Which of the following modifications would alleviate refrigerant migration in a long-line system?

Adding a liquid line solenoid

In a parallel compressor system, oil does not return at the same rate to all of the compressors because:

All the compressors do not operate for the same length of time.

What is an oil lift?

An oil lift is a trap at the bottom of a vertical suction riser.

Oversized suction lines:

Can cause poor oil return because of low refrigerant velocity.

Undersized suction lines:

Can reduce system efficiency because of a high pressure drop.

Which of the following statements is TRUE about double risers within suction lines?

During part-load operation, refrigerant is forced through the smaller riser.

The hot gas lines need to be insulated:

If they are exposed to cold temperatures that could cause the refrigerant to condense in the line.

Liquid lines need to be insulated:

If they travel through an unusually hot space.

What is considered a long-line application for residential air conditioning?

Lines exceeding 80ft in length or with a vertical rise of more than 20 ft

One difference between refrigerant piping practices for air-conditioning systems and refrigerant piping practices for commercial refrigeration systems is that:

Most air-conditioning manufacturers do not recommend oil traps.

Refrigerant piping must be able to adequately carry both refrigerant and:

Oil.

The factors must be considered when sizing the discharge line are:

Pressure drop and velocity.

Besides improving efficiency, insulating the suction line:

Prevents moisture from condensing on the line.

The refrigerant line whose sizing has the most effect on the compressor's compression ratio is the:

Suction line.

Which pair of factors most directly affects the maximum allowable pressure drop within a system?

Temperature of refrigerant and type of refrigerant

Which of the following statements is TRUE about these systems?

The R-410a system can operate at twice the suction line pressure drop of the R-134 system.

When installing a double riser in a commercial refrigeration system, which of the following statements is TRUE?

The combined areas of the risers should be equal to the area of the suction line.

Refrigerant oil flow through the liquid line in not a problem because:

The oil mixes with the liquid refrigerant.

Modifications such as adding a liquid-line solenoid at the outdoor unit, using a hard shutoff thermal expansion valve at the evaporator, and adding a compressor hard-start kit are recommended when:

The refrigerant line length is over 80 ft.

Why are vertical suction risers often smaller than the horizontal runs on the same suction line?

The risers are sized smaller to maintain a minimum velocity to lift the oil.