Unit 24

What would be the pressure drop due to the weight of refrigerant in a 30ft tall liquid line containing R-410A refrigerant at 100 degree?

.43x30= 12.90 psi drop

What two factors affect the hot gas line size?

1. Pressure drop 2. Velocity

What are 2 major functions of refrigerant piping?

1. Provides a passageway for the circulation of refrigerant 2. Provides passageway for oil

What are the two common reasons the suction line is insulated?

1. To keep the suction line from absorbing ambient air 2. Keep moisture from condensing on the line

How is the maximum pressure drop for a suction line determined?

1. Type of refrigerant 2. Temp. Of refrigerant

What two factors does the amount of pressure drop require?

1. Type of refrigerant 2. Temp. Of refrigerant

If the condenser pressure of the above system is 300 psig, how much subcooling will be required to offset the pressure drop created by the vertical lift?

100-93= 8 degree

What pressure drop should the engineer use on the nomograph if the equivalent length for the suction line in the above system is 75ft?

100/75 x 1psig= 1.33psi

What is the most common range for minimum velocities in a risers carrying refrigerant vapor?

1000-1500 feet per minute

Standard practice has been to design gas lines for a maximum pressure drop roughly to equal to how much of a saturation's temp drop?

2 degree

Use figure 24-13 to determine the total equivalent length of a 50ft section of 1 3/8in line with four 90 degree elbows and one angle valve.

2.4 x 9= 9.6 + 22.5 + 50= 82.1 total equivalent feet.

What is the minimum recommended velocity for a 2 5/8in suction riser in a low temp. System using R-22?

2010 feet per minute.

Use figure 24-25 to determine the refrigerant velocity through a 7/8in suction line in a walk-in cooler with a capacity of 2 tons an evaporator saturation temp. Of 20 degree and a condenser saturation temp. Of 100 degree

2900 ft per min

What is the most common range for minimum velocities in a horizontal line carrying refrigerant vapor?

500-750 feet per minute

What is liquid slugging?

A momentary return of a quantity of liquid to an operating compressor.

How can flash gas be spotted in a liquid line?

A significant temperature drop in the liquid line

List the system modifications that need to be made for a long-line residential AC application.

Adding liquid line solenoid at the outdoor unit. Using a hard shutoff TEV at the evaporator. Adding compressor crankcase heater. Compressor hard start kit.

What can be done to prevent refrigerant from being drained or migrating back to the compressor during the off cycle?

Do pitch horizontal lines

Why might the hot gas line need to be insulated?

If it's exposed to cold temperatures

Why may the liquid line need to be insulated?

If the travel through an unusually hot space

Why is it important to keep oil level balanced between parallel compressors?

If too low or high can damage the compressor.

What will excessive flow resistance do to the pressure drop?

Increase

What effect does oil have on a systems coil?

It lubricates it

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

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

What problems are cause by undersized suction line?

Loss of efficiency

According to figure 24-31 what would be the recommended support spacing for 2 1/8 type L copper pipe?

Maximum is 10 ft

What problems are caused by oversized suction lines?

Prevent oil returning to the compressor

An engineer wishes to select a suction line that will have a maximum pressure drop that is equivalent to a 2 degree saturation temp. Drop what would the pressure drop be for an R-134a system operating with a 0 degree saturation temp.

R-134A at 0 degree saturation is 6.5 psig. R-134A at 2 degree saturation is 5.5psig 6.5- 5.5= 1psig drop for a 2 degree saturation temp. Drop

Why are suction risers sized differently for systems with capacity control than for systems without capacity control?

Risers are sized smaller on systems with capacity controls to maintain a minimum velocity

Which piping pressure drop has the greatest effect on the compressors compression ratio?

Suction pressure drop

Why are oil lifts needed in tall vertical refrigerant risers?

The oil lift will fill with oil.

Why is refrigerant oil flow through the liquid line not a problem?

The oil mixes with the refrigerant

Excessively large piping causes low refrigerant flow velocity. True or False

True