Lennox Refrigerant Piping Flashcards
1
Q
What factors does the design of refrigerant piping systems affect?
A
Capacity and efficiency, reliability, oil management, refrigerant charge, sound level, liquid refrigerant control, modulation effectiveness, and cost.
2
Q
What is the maximum linear (actual) length for a cooling system using HFC−410A?
A
200 ft.
3
Q
What is the maximum linear liquid lift for HFC−410A?
A
60 ft.
4
Q
What is the recommended action for systems with long line sets over 200 linear feet?
A
Not recommended.
5
Q
What is the total equivalent length guideline for HCFC−22 systems?
A
240 feet.
6
Q
What is the maximum linear liquid lift for HCFC−22?
A
50 ft.
7
Q
What is required for installations of 51 to 80 linear feet?
A
Crankcase heater required, non−bleed port TXV preferred.
8
Q
For systems over 20 lbs of refrigerant, how much oil should be added?
A
1 ounce of every 5 lbs of refrigerant.
9
Q
True or False: A liquid line filter drier is required if not factory provided.
A
True.
10
Q
What is the purpose of pressure taps in refrigerant systems?
A
To allow field measurement of saturated pressures for calculating superheats and sub−cooling values.
11
Q
Fill in the blank: Systems should have _______ protection to prevent short cycling.
A
anti−short cycle.
12
Q
What is the function of a sight glass in a liquid line?
A
For visual inspection of the liquid and to determine when all gas bubbles are removed.
13
Q
What is the maximum length vapor riser for HFC−410A in heat pump systems?
A
60 feet.
14
Q
What is the recommended TXV type for systems with suction lines over 50’?
A
Indoor non−bleed adjustable thermostat expansion valves.
15
Q
What is the critical temperature for superheat maintenance at the outdoor unit service valve?
A
Lower than 25°F.
16
Q
What is the maximum linear length for HCFC−22 heat pump systems?
A
150 ft.
17
Q
What should be done if the indoor unit does not have a factory installed TXV?
A
Replace with a compatible TXV.
18
Q
What should be considered when selecting the liquid line size?
A
The rated liquid line size on the outdoor unit and the maximum elevation.
19
Q
For HCFC−22 systems with suction lines 7/8” or smaller, how much oil should be added every 10’ over 50’?
A
3 ounces.
20
Q
For HCFC−22 systems with suction lines 1 1/8” and larger, how much oil should be added every 10’ over 50’?
A
4 ounces.
21
Q
What should be used to size the liquid line when there is a liquid lift?
A
Table 1.
22
Q
What is the required action for systems with 81 to 200 linear feet?
A
Crankcase heater and non−bleed port TXV required.
23
Q
What is the total equivalent length guideline for heat pump systems using HCFC−22?
A
180 feet.
24
Q
What is the maximum length vapor riser for HCFC−22?
A
50 feet.
25
What is the maximum linear liquid lift for R−22?
50 ft
26
What is the maximum linear liquid lift for R−410A?
60 ft
27
What does 'NR' stand for in the context of liquid line sizing?
Not Recommended
28
What is the required liquid line size for a 10 ton R−22 A/C unit with 100 feet of piping?
5/8 inch
29
What is the pressure drop for R−22 vapor lines per 100 ft?
Varies by size
30
Fill in the blank: When line lengths exceed 50 feet, a _______ and crankcase heater are required.
non bleed port TXV
31
What is the preferred vapor line size for a 7.5 ton R−22 unit?
1−3/8 inch O.D.
32
True or False: Vapor risers must be sized to ensure adequate velocity for oil return.
True
33
What must be installed at the bottom of the suction riser for systems with the outdoor unit 5−50 feet above the indoor unit?
One trap
34
What happens if the refrigerant line is oversized?
Increased risk of refrigerant slugging and oil dilution
35
What is the impact of pressure drop in refrigerant lines on system performance?
Decreases capacity and increases power consumption
36
What must be considered for heat pump systems with elevation differences?
Liquid and suction lift
37
What is the maximum vapor riser length?
125 feet
38
What is the impact of high velocities in the refrigerant lines?
Increased sound levels
39
What is the required component for cooling operation below 50° F if an economizer is not used?
Low ambient (head pressure) controls
40
What is the recommended line size for 50−80 linear feet of refrigerant line?
Non bleed port TXV and crankcase heater required
41
Fill in the blank: A _______ drier should be used with heat pump systems.
bi−flow
42
What should be done when line lengths exceed 80 feet in heat pump systems?
Add an expansion valve and an accumulator
43
What is the desirable characteristic for system reliability?
Long compressor life
44
What can cause a starved evaporator when refrigerant lines are undersized?
Refrigerant flashing before the expansion device
45
What is the impact of the amount of refrigerant charge on cost?
It will impact the applied cost
46
What problems can oversized liquid lines cause in compressors?
Refrigerant slugging and oil dilution.
47
What are the consequences of undersized liquid lines?
Loss of capacity, evaporator coil frosting, high superheat.
48
How can oversized suction lines affect a refrigeration system?
They may result in refrigerant velocities being too low to return oil to the compressor.
49
What issues arise from undersized suction lines?
Reduced capacity and high superheat.
50
What is the acceptable pressure drop in the suction line for R−22?
3 PSI.
51
What is the acceptable pressure drop in the suction line for R−410A?
5 PSI.
52
What is the primary function of the liquid line in a refrigeration system?
To deliver a solid column of 100% liquid refrigerant to the expansion device.
53
What must be considered when calculating pressure drop in the liquid line?
Vertical lift and friction loss.
54
What is the maximum acceptable pressure drop in the liquid line for R−22?
30 PSI.
55
What is the maximum acceptable pressure drop in the liquid line for R−410A?
35 PSI.
56
What is a major factor in oil management in refrigeration systems?
Suction and vapor line sizing.
57
For systems with outdoor units 5−50 feet above the indoor unit, what installation is required?
One trap at the bottom of the suction riser.
58
What is the minimum velocity required for oil return in horizontal runs?
800 fpm.
59
What is the minimum velocity required for oil return in vertical suction risers?
1200 fpm.
60
What should be added to R−22 systems with lines over 50 feet?
3 ounces of oil for each 10 feet of line over 50 feet.
61
What should be added to larger suction lines in R−22 systems over 50 feet?
4 ounces of oil for each 10 feet of line above 50 feet.
62
Is additional oil added to R−410A systems?
No.
63
How do elbows and fittings affect refrigerant piping?
They contribute to friction pressure drop.
64
What is the effect of pressure drop in the suction line?
Significantly reduces system capacity and efficiency.
65
What is the maximum allowable pressure drop across the expansion device for R−22?
100 psi.
66
What is the maximum allowable pressure drop across the expansion device for R−410A?
175 psi.
67
What is a major cause of compressor failure?
Liquid slugging.
68
What must be avoided in the liquid line to ensure proper function?
Flash gas.
69
What is the purpose of checking subcooling in a refrigeration system?
To ensure a solid column of liquid at the expansion device.
70
What is the recommended tubing type for lines over 50 feet?
Hard copper refrigeration tubing.
71
What should be used to prevent copper oxides from forming inside copper tubing?
Bleed dry nitrogen during the soldering process.
72
What is the main consideration in sizing liquid lines?
Pressure drop in the lines and pressure drop across the expansion device.
73
What is the effect of vertical liquid lift on pressure drop for R−22?
0.5 pounds per foot.
74
What is the effect of vertical liquid lift on pressure drop for R−410A?
0.43 pounds per foot.
75
What is the maximum allowable pressure drop in the given scenario?
30 psi
## Footnote
This is the limit for the pressure drop in the system.
76
What refrigerant is mentioned in the example for the condensing unit?
R−22
## Footnote
R−22 is a common refrigerant used in air conditioning systems.
77
What is the total equivalent length of piping in the example with a 10 ton system?
98 equivalent feet
## Footnote
This includes the linear length plus equivalent lengths from fittings.
78
What is the pressure drop per 100 feet for a 5/8 inch O.D. line in a 10 ton system?
4.25 psi
## Footnote
This value is crucial for calculating total pressure drop.
79
What is the pressure drop due to lift for R22 in the given example?
20 psi
## Footnote
This is calculated based on a vertical lift of 40 feet.
80
What is the total pressure drop for the selected 5/8 inch line?
25.17 psi
## Footnote
This total includes friction loss, pressure drop due to lift, and filter drier drop.
81
True or False: A ¾ inch O.D. line is a better choice than a 5/8 inch line based on pressure drop.
False
## Footnote
The 5/8 inch line has a lower total pressure drop and uses less refrigerant.
82
What is the minimum suction line velocity required for oil entrainment in horizontal lines?
800 fpm
## Footnote
This is essential for ensuring adequate oil return to the compressor.
83
What is the minimum suction line velocity required for vertical risers?
1200 fpm (preferably 1500 fpm)
## Footnote
Maintaining this velocity helps ensure oil return.
84
What is the capacity loss factor due to pressure drop in the suction line?
1% capacity loss per pound of pressure drop
## Footnote
This helps estimate capacity loss in refrigerant lines.
85
What should be done to minimize liquid migration to the compressor during the off cycle?
Install traps at the bottom of vertical risers
## Footnote
Traps help prevent liquid refrigerant from reaching the compressor.
86
Fill in the blank: The suction line must provide adequate _______ to the compressor.
oil return
## Footnote
Ensuring proper oil return is critical for compressor operation.
87
What is the pressure drop per 100 feet for a 1−1/8 inch O.D. line in a suction line sizing example?
2.8 psi
## Footnote
This value is used for calculating total pressure drop in the example.
88
What is the total equivalent length for the 1−1/8 inch line in the suction line sizing example?
79.4 feet
## Footnote
This includes both the linear length and equivalent lengths from fittings.
89
What percentage of capacity loss is calculated for the 1−1/8 inch line?
approximately 1.5%
## Footnote
This is based on the total equivalent length pressure drop.
90
What is the pressure drop for 25 feet of 1−3/8 inch line?
0.5 psi
## Footnote
This is calculated for assessing capacity loss in the example.
91
What is the pressure drop in the suction line for a 15 ton two-stage condensing unit?
3 psi per 100 feet
## Footnote
This value is used to determine the total friction loss.
92
What should be included in the suction line sizing procedure?
Sketch layout, measure linear length, determine equivalent length of fittings
## Footnote
This ensures accurate calculations for pressure drop.
93
What is the effect of using field-installed components like suction line driers?
They contribute to both pressure drop and capacity loss
## Footnote
Manufacturer’s data should be consulted for specific pressure drop information.
94
What is the total friction loss when multiplying 3/100 by 111 equivalent feet?
3.3 psi
95
What is the friction loss in 25 feet of 1−5/8 inch line?
0.75 psi
96
How is capacity lost in the total equivalent length of the refrigerant line calculated?
1% x (3.3 – 0.75) x 180,000
97
What is the formula to calculate Btuh lost?
Btuh lost = 0.01 x (2.55) x 180,000
98
What is the capacity loss for the line selected?
Approximately 2.55%
99
What is the operating capacity of Lennox two-stage units when on low stage?
Approximately 60% capacity
100
What velocity indicates sufficient oil return to the compressor?
At least 1200 fpm in vertical risers
101
True or False: A single 1−5/8 inch suction riser may be used without double suction risers.
True
102
What is the most desirable type of hot gas bypass kit?
The type that feeds hot gas from the compressor discharge line to a side tap on the distributor in the evaporator coil
103
What is the function of a run-around hot gas bypass?
Reduces flow through the evaporator and suction line
104
Under what condition may double suction risers be required?
If a condensing unit can unload more than 50%
105
When are double suction risers generally not required?
If the suction velocity is high enough to entrain oil at reduced capacity
106
What happens to the trap in double suction risers during partial load operation?
It gradually fills with oil until the second riser is sealed off
107
What is the minimum load capacity for a 10 ton condensing unit?
3.5 tons
108
What pipe size is selected for full load capacity of 10 tons?
1−3/8 inch O.D. pipe
109
What is the pressure drop for a 1−1/8 inch O.D. line with 6.5 tons capacity?
4.5 psi drop per 100 feet
110
What is the total pressure drop for the riser?
1.33 psi
111
What is the capacity lost in the total equivalent length of the refrigerant line?
Approximately 2.5%
112
What is a common pipe size for a 5 ton two-stage system?
1−1/8 inch suction line
113
What is a good rule of thumb for sizing accumulators?
Select an accumulator that can accommodate 2/3 of the total system charge
114
What can happen if liquid refrigerant floods through an air conditioning system?
It may cause damage to the compressor due to liquid slugging or loss of oil
115
Where should the suction accumulator be located?
In the compressor suction line between the evaporator and the compressor
116
What is critical for the proper control of liquid refrigerant under low ambient heating conditions?
Maintaining a balance between sufficient flooding and avoiding excessive flooding
117
What is the purpose of the accumulator during the heating cycle?
To store refrigerant until needed and feed it back to the compressor at an acceptable rate
118
What must be done to operate air conditioning and heat pump systems at rated capacity?
They must be properly charged
119
What is the impact of inadequate subcooling on a unit's capacity?
As much as 8 to 10% of its capacity can be lost
120
How should liquid line temperature relate to condensing temperature to achieve 10°F subcooling?
Liquid line should be 10°F cooler than condensing temperature
121
What should be checked if suction pressure is excessively low?
Filters, air volume, and restrictions in the system
122
What is the required temperature difference for 10°F subcooling?
The liquid line should be 10°F cooler than the condensing temperature.
123
What should be checked if the suction pressure is excessively low?
Check filters, air volume, and for restrictions in the system.
124
What must be done to boost liquid line pressure below 70°F outdoor temperature?
Airflow will need to be restricted.
125
What is the minimum liquid line pressure for R−22 and R−410A?
240 psig for R−22 and 400 psig for R−410A.
126
True or False: Noise and vibration can be completely eliminated in a condensing unit.
False.
127
What is the purpose of a coil of tubing in residential units?
To provide adequate protection against vibration.
128
What happens when the thermostat calls for cooling?
The thermostat energizes the Y circuit, which energizes the control relay.
129
What does the low pressure switch do when the suction line pressure rises to 55 psig?
It closes, energizing the pump down relay and the compressor contactor.
130
What additional components are required for low ambient cooling operation below 50°F?
Lennox low ambient control kits and a crankcase heater.
131
What refrigerant is replacing HCFC−22?
HFC−410A.
132
What is the operating pressure difference between R−22 and R−410A?
R−410A operates at 50% higher pressure than R−22.
133
Fill in the blank: R−410A is a near−azeotropic mixture of ______ and ______ refrigerants.
[R−32] and [R−125]
134
What is the recommended method for charging R−410A systems?
Charging should be done in the liquid phase.
135
What type of oils are used in R−410A systems?
POE oils.
136
What must be done with filter driers when opening an R−410A system?
Change the filter drier.
137
What is the maximum liquid line pressure drop in R−410A systems?
35 PSI, which equates to 6 degrees of subcooling.
138
What is the proper support for refrigerant lines?
Lines must be supported by isolation hangers.
139
True or False: Refrigerant lines can touch structural members.
False.
140
What is the total pressure drop acceptable between the condensing unit and evaporator?
Should be less than 30 psi.
141
What should be included in complex liquid line sizing with multiple evaporators?
The total evaporator load must at least equal the condensing unit capacity.
142
What is required for cooling operation below 30°F?
Lennox low ambient control kit plus a variable speed controller on the outdoor fan(s).
143
What can cause noise in a refrigeration system?
Gas flow, fans, compressor, and mounting.
144
What is the purpose of a wind barrier in low ambient cooling?
To protect the outdoor coil from high prevailing winds.
145
What is the consequence of high prevailing winds on heat pumps?
It can reduce the effectiveness of the defrost cycle.
146
What is the total pressure drop in the refrigerant piping example?
16.77 psi
## Footnote
Acceptable pressure drop for the system.
147
What must the total evaporator load equal in a complex suction line sizing?
Condensing unit capacity
## Footnote
Necessary for efficient operation.
148
What is a requirement for suction lines connected to different evaporators?
Suction line must rise to the top of each coil before joining the main
## Footnote
Prevents gravity draining of oil.
149
How are suction lines sized in systems with multiple evaporators?
Similar to liquid lines, based on tons of refrigerant flowing
## Footnote
Ensures proper capacity and efficiency.
150
What is the equivalent length of a segment in refrigerant piping?
Total length of pipe plus equivalent lengths of fittings
## Footnote
Important for calculating pressure drop.
151
What is the pressure drop per 100 feet for a 1-3/8 inch O.D. suction line with 10 tons capacity?
3.3 psi
## Footnote
Used to calculate total friction loss.
152
Calculate the total friction loss for a segment A to B with 30 equivalent feet.
0.99 psi
## Footnote
Total friction loss calculated from pressure drop rate.
153
What is the pressure drop for a ¾ inch O.D. suction line with 3 tons capacity?
8.5 psi per 100 feet
## Footnote
Significant pressure drop affects capacity.
154
What is the total pressure drop for the 5 ton evaporator?
3.14 psi
## Footnote
Calculated from segments A to B, B to D, and D to E.
155
What is the capacity loss for each pound of pressure lost in the line?
1% capacity loss
## Footnote
Important for evaluating system performance.
156
Fill in the blank: The purpose of the accumulator is to prevent ______ from entering the compressor.
liquid
## Footnote
Ensures safe operation of the compressor.
157
What is the function of the bypass valve in hot gas bypass systems?
To meter liquid refrigerant and hot gas into the suction line
## Footnote
Maintains system performance at reduced capacity.
158
What is the definition of a capillary tube?
Refrigerant metering device consisting of small diameter tubes
## Footnote
Not suitable for long refrigerant lines.
159
What does the term 'flash gas' refer to?
Liquid refrigerant losing temperature and pressure causing gas bubbles
## Footnote
Reduces system efficiency.
160
What is the impact of vertical lift on pressure in a vapor line?
No effect
## Footnote
Relevant for vapor line calculations.
161
What is the function of a filter drier in the refrigerant line?
To filter contaminants and protect the expansion valve and compressor
## Footnote
Essential for system longevity.
162
True or False: A double suction riser is used to improve oil entrainment during reduced capacity operation.
True
## Footnote
Enhances system efficiency during varying loads.
163
What is the typical pressure drop for a 5/8 inch O.D. suction line with 2 tons capacity?
12 psi per 100 feet
## Footnote
Indicates significant pressure loss.
164
What is the effect of using a larger suction line size?
Reduces capacity loss
## Footnote
Important for meeting job requirements.
165
What is the maximum allowable pressure drop?
Amount of pressure drop before flash gas forms
## Footnote
Critical for system design.
166
What is the definition of low ambient temperature?
The use of the compressor for cooling when outdoor temperature is below 50°F.
## Footnote
Field installed kits are required to protect the compressor and ensure proper operation in the event low ambient cooling below 50° F is required.
167
What does the term 'main' refer to in refrigeration systems?
The line which feeds or collects refrigerant from multiple smaller refrigerant lines.
168
What is the maximum allowable pressure drop?
The amount of pressure drop a liquid line can experience before flash gas will begin to form.
## Footnote
Calculated by subtracting the liquid temperature from the saturated liquid temperature and converting the result into a pressure on the R22 saturation chart.
169
If the outdoor unit is charged to operate with 10°F subcooling at 115°F saturated liquid temperature, what is the maximum allowable pressure drop?
35 psi.
170
Define metering device.
Any device which regulates the flow of liquid refrigerant into an evaporator.
171
What is migration in refrigeration systems?
The tendency of refrigerant gas to slowly travel to the coldest part of the piping system during the off-cycle and condense and collect as liquid.
172
What is miscibility?
The ability of two or more substances to mix and form a single homogeneous phase.
173
What are multiple evaporators in refrigeration?
Piping arranged so that a single condenser can operate several evaporators at the same time.
174
What is the purpose of an oil trap?
To trap oil and prevent it from filling the suction line.
175
What is the definition of pressure drop?
The loss of refrigerant pressure experienced in copper pipe, usually expressed in terms of pounds (psi) per 100 feet.
176
What is pump-down control?
A field installed kit consisting of a solenoid valve located in the liquid line before the expansion valve, used to return refrigerant into the condenser at the end of a cooling cycle.
177
What does RFC stand for?
Refrigerant flow control device.
178
What is a riser in refrigeration terminology?
Any length of refrigerant pipe which transports refrigerant vertically upward.
179
What is run-around hot gas bypass?
A type of hot gas bypass system that diverts hot discharge gas and liquid directly into the suction line inside the condensing unit.
180
Define saturation temperature.
The temperature at which a gas begins to turn into liquid.
181
What is a sight glass?
A glass window type device placed in a liquid line for visual inspection of the liquid.
182
What is sil-phos?
Brazing material composed of silver, phosphorous, and copper used for brazing joints of copper pipe.
183
What is a slug in refrigeration?
A column of liquid refrigerant returned to the compressor in the suction line.
184
What is the function of a solenoid valve?
An electromechanical valve used to shut-off refrigerant flow.
185
What does split-coil mean?
A single evaporator or condenser coil plumbed to serve two or more independent refrigeration circuits.
186
Define subcooling.
Cooling of refrigerant liquid below its saturated temperature while holding it at saturated pressure.
187
What is superheat?
Heating of refrigerant gas above its saturated temperature while holding it at saturated pressure.
188
What is a thermometer well?
A device located in the liquid line that allows a thermometer to be inserted for accurate temperature measurement.
189
What is a thermostatic expansion valve (TXV)?
An extremely precise type of expansion device that regulates refrigerant flow into the evaporator based on superheat.
190
What does 'unload' refer to in refrigeration?
See Capacity Reduction.
191
What is a vapor line?
The discharge hot gas line in heating mode and the suction line in cooling mode.
192
Define variable capacity.
See Capacity Reduction.
193
What does velocity measure in refrigeration systems?
The speed at which refrigerant travels through a pipe, usually expressed in feet per minute.
194
What is wrought copper?
Hammered refrigeration grade copper used in refrigerant fittings.
