Daikin R22 Guide

AG 31-011
Refrigerant Piping Design Guide
TX valve
in vertical pipe
Sight
Glass
Solenoid
Valve
Liquid
Line
Filter-
Drier
Distributor
External
Equalization
Line
Suction
Line
Bulb

AG 31-011 • REFRIGERANT PIPING DESIGN 2 www.DaikinApplied.com
The information contained within this guide represents the opinions and suggestions of Daikin Applied. Equipment, and the application of the equipment and system
suggestions are o󰀨ered by Daikin Applied as suggestions and guidelines only, and Daikin Applied does not assume responsibility for the performance of any system as a
result of these suggestions. The system engineer is responsible for system design and performance.
Introduction..................................3
Audience ...................................3
Using This Guide.............................3
How to Determine Equivalent Length ..........3
Refrigerant Piping ............................4
Refrigerant Piping Design Check List .............5
Product Information .........................5
Jobsite Information..........................5
Typical Refrigerant Piping Layouts ..............6
Piping Design Basics..........................9
Pressure Drop and Temperature Change ........9
Liquid Lines ................................10
Suction Lines...............................11
Suction Line Piping Details ..................11
Discharge Lines ............................13
Discharge Line Piping Details ................14
Multiple Refrigeration Circuits ..................15
Sizing Refrigerant Lines ......................16
Refrigerant Capacity Tables ...................16
Equivalent Length for Refrigerant Lines ..........17
How to Determine Equivalent Length .........17
How to Size Liquid Lines ..................18
Refrigerant Oil ..............................20
Suction Line Sizing ..........................20
Oil Return in Suction and Discharge Risers .......21
How to Size Suction Lines ................23
How to Size a Suction Line Double Riser ....25
Discharge Line Sizing ........................26
How to Size a Discharge Line...............26
Thermal Expansion Valves ....................28
Hot Gas Bypass ............................29
Hot Gas Bypass Line Sizing .................30
Hot Gas Bypass Valves.......................30
How to Size a Hot Gas Bypass Line..........32
Installation Details ...........................33
Pump Down................................33
Piping Insulation ............................33
Refrigerant Line Installation ...................33
Low Ambient Operation .......................34
Fan Cycling and Fan Speed Control ............34
Condenser Flood Back Design .................34
Safety and the Environment ...................36
Appendix 1 — Glossary .......................37
Appendix 2 – Refrigerant Piping Tables
(Inch/Pound) ................................40
Appendix 3 – Refrigerant Piping Tables (SI) ......59

www.DaikinApplied.com 3 AG 31-011 • REFRIGERANT PIPING DESIGN
Introduction
Audience
This Application Guide was created for design engineers and
service technicians to demonstrate how to size refrigerant
piping.
Using This Guide
This Guide covers R-22, R-407C, R-410A, and R-134a used
in commercial air conditioning systems. It does not apply to
industrial refrigeration and/or Variable RefrigerantVolume
(VRV) systems. Illustrations and gures are not to scale.
Examples showing how to perform an analysis appear under
shaded headlines as seen below.
How to Determine Equivalent Length
Calculate the equivalent length of the liquid line for the
following condensing unit with DX air-handling unit.
The liquid line is composed of the following elements:
• 30 ft (9.14 m) of 1-3/8 inch (35 mm) piping
• 4 long radius elbows
• 1 lter-drier
• 1 sight glass
• 1 globe type isolating valve
To determine the equivalent length for the refrigerant
accessories use Table 5 and Table 6 on page 41.
Item Quantity Dimension, ft (m) Total, ft (m)
Long radius elbow 4 2.3 (0.7 m) 9.2 (2.8 m)
Filter-drier 1 35 (10.7 m) 35 (10.7 m)
Sight glass 1 2.5 (0.76 m) 2.5 (0.76 m)
Globe valve 1 38 (11.6 m) 38 (11.6 m)
Piping 1 30 (9.1 m) 30 (9.1 m)
Total 117.7 (34.96 m)

AG 31-011 • REFRIGERANT PIPING DESIGN 4 www.DaikinApplied.com
Refrigerant Piping
Several HVAC systems require eld refrigeration piping to be
designed and installed on-site.
Examples include:
• Condensing units
• Direct expansion (DX) coil in air handlers
• Remote evaporators with air-cooled chillers (Figure 1)
• Chiller with a remote air-cooled condensers
The information contained in this Application Guide is based
on Chapter 2 of ASHRAE’s Refrigeration Handbook and Daikin
Applied’s experience with this type of equipment. A properly
designed and installed refrigerant piping system should:
• Provide adequate refrigerant ow to the evaporators, using
practical refrigerant line sizes that limit pressure drop
• Avoid trapping excessive oil so that the compressor has
enough oil to operate properly at all times
• Avoid liquid refrigerant slugging
• Be clean and dry
Figure 1: Typical Field Piping Application

www.DaikinApplied.com 5 AG 31-011 • REFRIGERANT PIPING DESIGN
Refrigerant Piping Design Check List
The rst step in refrigerant piping design is to gather product
and jobsite information. A checklist for each is provided below.
How this information is used will be explained throughout the
rest of this guide.
Product Information
• Model number of unit components (condensing section,
evaporator, etc.)
• Maximum capacity per refrigeration circuit
• Minimum capacity per refrigeration circuit
• Unit operating charge
• Unit pump down capacity
• Refrigerant type
• Unit options (Hot Gas Bypass, etc.)
• Does equipment include isolation valves and charging ports
• Does the unit have pump down?
Jobsite Information
• Sketch of how piping will be run, including:
—Distances
—Elevation changes
—Equipment layout
—Fittings
—Specic details for evaporator piping connections
• Ambient conditions where piping will be run
• Ambient operating range (will the system operate during
the winter?)
• Type of cooling load (comfort or process)
• Unit isolation (spring isolators, rubber-in-shear, etc.)
Tip: Use this list to gather the information required to design your refrigerant piping system

AG 31-011 • REFRIGERANT PIPING DESIGN 6 www.DaikinApplied.com
Typical Refrigerant Piping Layouts
This section shows several typical refrigerant piping layouts for
commercial air conditioning. They will be used throughout this
guide to illustrate piping design requirements.
Figure 2 shows a condensing unit mounted on grade connected
to a DX coilinstalled in a roof-mounted air-handling unit.
1. A liquid line supplies liquid refrigerant from the condenser
to a thermal expansion (TX) valve adjacent to the coil.
2. A suction line provides refrigerant gas tothe suction
connection of the compressor.
Figure 2: Condensing Unit with DX Air Handling Unit
DX
Air Handling
Unit
TX
Valve
Sight
Glass
Solenoid
Valve
Filter-
Drier
Liquid
Line
Suction
Line
Air Cooled
Condensing
Unit
Suction riser
inverted trap
not required
with pumpdown

www.DaikinApplied.com 7 AG 31-011 • REFRIGERANT PIPING DESIGN
Figure 3 shows a roof-mounted air-cooled chiller with a remote
evaporator inside the building.
1. There are two refrigeration circuits, each with a liquid
line supplying liquid refrigerant from the condenser to
a TX valve adjacent to the evaporator, and a suction
line returning refrigerant gas from the evaporator to the
suction connections of the compressor.
2. There is a double suction riser on one of the circuits.
Double suction risers are covered inmore detail in the “Oil
Return in Suction and Discharge Risers” on page 21.
Figure 3: Air-Cooled Chiller with Remote Evaporator
Remote
Evaporator
Air Cooled
Chiller with
Remote
Evaporator
Sight
Glass
TX
Valve
Solenoid
Valve
Filter-
Drier
Liquid
Line
Liquid
Line
Riser
Suction Line
Riser
Double
Suction
Line
Riser

AG 31-011 • REFRIGERANT PIPING DESIGN 8 www.DaikinApplied.com
Figure 4 shows an indoor chiller with a remote air-cooled
condenser on the roof.
1. The discharge gas line runs from the discharge side of
the compressor to the inlet of the condenser.
2. The liquid line connects the outlet of the condenser to a
TX valve at the evaporator.
3. The hot gas bypass line on the circuit runs from the
discharge line of the compressor to the liquid line
connection at the evaporator.
Figure 4: Indoor Chiller with Remote Air-cooled Condenser
Air Cooled
Condenser
Discharge line
inverted trap
(can be replaced
with a check valve)
Discharge
Line
Liquid
Line
Riser
Discharge
riser trap
only at base
Hot gas bypass
top connection
to avoid refrigerant
collection
Sight
Glass
TX
Valve
Solenoid
Valve
Filter-
Drier
Chiller

www.DaikinApplied.com 9 AG 31-011 • REFRIGERANT PIPING DESIGN
Piping Design Basics
Good piping design results in a balance between the initial
cost, pressure drop, and system reliability. The initial cost
is impacted by the diameter and layout of the piping.The
pressure drop in the piping must be minimized to avoid
adversely a󰀨ecting performance and capacity. Because almost
all eld-piped systems have compressor oil passing through
the refrigeration circuit and back to the compressor, a minimum
velocity must be maintained in the piping so that su󰀩cient
oil is returned to the compressor sump at full and part load
conditions. A good rule of thumb is a minimum of:
• 500 feet per minute (fpm) or 2.54 meters per second
(mps) for horizontal suction and hot gas lines
• 1000 fpm (5.08 mps) for suction and hot gas risers
• Less than 300 fpm (1.54 mps) to avoid liquid hammering
from occurring when the solenoid closes on liquid lines
Hard drawn copper tubing is used for halocarbon refrigeration
systems. Types L and K are approved for air conditioning and
refrigeration (ACR) applications. Type M is not used because
the wall is too thin. The nominal size is based on the outside
diameter (OD). Typical sizes include 5/8 inch, 7/8 inch, 1-1/8
inch, etc.
Figure 5: Refrigerant Grade Copper Tubing
Copper tubing intended for ACR applications is dehydrated,
charged with nitrogen, and plugged by the manufacturer (see
Figure 5).
Formed ttings, such as elbows and tees, are used with the
hard drawn copper tubing. All joints are brazed with oxy-
acetylene torches by a qualied technician.
As mentioned before, refrigerant line sizes are selected to
balance pressure drop with initial cost, in this case of the
copper tubing while also maintaining enough refrigerant
velocity to carry oil back to the compressor.
Pressure drops are calculated by adding the length of tubing
required to the equivalent feet (meters) of all ttings in the line.
This is then converted to PSI (kPa).
Pressure Drop and Temperature Change
As refrigerant ows through pipes the pressure drops and
changes the refrigerant saturation temperature. Decreases
in both pressure and saturation temperature adversely a󰀨ect
compressor performance. Proper refrigeration system design
attempts to minimize this change to less than 2°F (1.1°C) per
line. Therefore, it is common to hear pressure drop referred to
as “2°F” versus PSI (kPa) when matching refrigeration system
components. For example, a condensing unit may produce
25 tons (87.9 kW) of cooling at 45°F (7.2°C) saturated suction
temperature. Assuming a 2°F (1.1°C) line loss, the evaporator
would have to be sized to deliver 25 tons (87.9 kW) cooling at
47°F (7.2°C) saturated suction temperature.
Table 1 compares pressure drops in temperatures and
pressures for several common refrigerants. Note that the
refrigerants have di󰀨erent pressure drops for the same
change in temperature. For example, many documents refer
to acceptable pressure drop being 2°F (1.1°C) or about 3 PSI
(20.7 kPa) for R-22. The same 3 PSI change in R-410A, results
in a 1.2°F (0.7°C) change in temperature.
Table 1: Temperature versus Pressure Drop
Refrigerant Suction Pressure Drop Discharge Pressure Drop Liquid Pressure Drop
°F (°C) PSI (kPa) °F (°C) PSI (kPa °F (°C) PSI (kPa)
R-22 2 (1.1) 2.91 (20.1) 1 (0.56) 3.05 (21.0) 1 (0.56) 3.05 (21.0)
R-407C 2 (1.1) 2.92 (20.1) 1 (0.56) 3.3 (22.8) 1 (0.56) 3.5 (24.1)
R-410A 2 (1.1) 4.5 (31.0) 1 (0.56) 4.75 (32.8) 1 (0.56) 4.75 (32.8)
R-134a 2 (1.1) 1.93 (13.3) 1 (0.56) 2.2 (15.2) 1 (0.56) 2.2 (15.2)
NOTE: Suction and discharge pressure drops based on 100 equivalent feet (30.5 m) and 40°F (4.4°C) saturated temperature.

AG 31-011 • REFRIGERANT PIPING DESIGN 10 www.DaikinApplied.com
Liquid Lines
Liquid lines connect the condenser to the evaporator and
carry liquid refrigerant to the TX valve. If the refrigerant in
the liquid line ashes to a gas because the pressure drops
too low or because of an increase in elevation, then the
refrigeration system will operate poorly. Liquid sub-cooling is
the only method that prevents refrigerant ashing to gas due to
pressure drops in the line.
The actual line size should provide no more than a 2 to 3°F
(1.1 to 1.7°C) pressure drop. The actual pressure drop in PSI
(kPa) will depend on the refrigerant.
Oversizing liquid lines is discouraged because it will
signicantly increase the system refrigerant charge. This, in
turn, a󰀨ects the oil charge.
Figure 2 on page 6 shows the condenser below the
evaporator. As the liquid refrigerant is lifted from the condenser
to the evaporator, the refrigerant pressure is lowered. Di󰀨erent
refrigerants will have di󰀨erent pressure changes based on
elevation. Refer Table 2 to for specic refrigerants. The total
pressure drop in the liquid line is the sum of the friction loss,
plus the weight of the liquid refrigerant column in the riser.
Table 2: Pressure Drop in Liquid Lines by Refrigerant
Refrigerant Pressure Drop PSI/ft (kPa/m) Riser
R-22 0.5 (11.31)
R-407C 0.47 (10.63)
R-410A 0.43 (9.73)
R-134a 0.5 (11.31)
Based on saturated liquid refrigerant at 100°F (37.7°C)
Only sub-cooled liquid refrigerant will avoid ashing at the TX
valve in this situation.If the condenser had been installed above
the evaporator, the pressure increase from the weight of the
liquid refrigerant in the line would have prevented the refrigerant
from ashing in a properly sized line without sub-cooling.
It is important to have some sub-cooling at the TX valve so
that the valve will operate properly and not fail prematurely.
Follow the manufacturer’s recommendations. If none are
available, then provide 4 to 6°F (2.2 to 3.3°C) of sub-cooling
at the TX valve.
Liquid lines require several refrigerant line components and/
or accessories to be eld selected and installed (Figure 6).
Isolation valves and charging ports are required. Generally,
it is desirable to have isolation valves for servicing the basic
system components, such as a condensing unit or condenser.
In many cases, manufacturers supply isolating valves with their
product, so be sure to check what is included. Isolating valves
come in several types and shapes.
Figure 6: Refrigerant Accessories
Photos courtesy of Sporlan Division – Parker Hannin Corporation
Referring to Figure 2 on page 6:
1. Working from the condenser, there is a liquid line
lter-drier.The lter drier removes debris from the liquid
refrigerant and contains a desiccant to absorb moisture
in the system. Filter driers are either disposable or a
permanent with replaceable cores.
2. Next there is a sight glass that allows technicians to view
the condition of the refrigerant in the liquid line. Many
sight glasses include a moisture indicator that changes
color if moisture is present in the refrigerant.
3. Following the sight glass is the TX valve. (More
information about TX valves is available under ”Thermal
Expansion Valves” on page 28.)
Aux SideConnector
Distributor
Sight Glass
Solenoid Valve
TX Valve
Filter-Drier

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Possible accessories for this system include:
• A hot gas bypass port. This is a specialty tting that
integrates with the distributor – an auxiliary side
connector (ASC).
• A pump down solenoid valve. If a pump down is utilized,
the solenoid valve will be located just before the TX valve,
as close to the evaporator as possible.
• Receivers in the liquid line. These are used to store
excess refrigerant for either pump down or service (if the
condenser has inadequate volume to hold the system
charge), or as part of a ooded low ambient control
approach (More information about ooded low ambient
control approach is available under “Condenser Flood
Back Design” on page 34).
Receivers are usually avoided because they remove sub-
cooling from the condenser, increase the initial cost, and
increase the refrigerant charge.
Liquid lines should be sloped 1/8 inch per foot (10.4 mm/m) in
the direction of refrigerant ow. Trapping is unnecessary.
Suction Lines
Suction gas lines allow refrigerant gas from the evaporator to
ow into the inlet of the compressor. Undersizing the suction
line reduces compressor capacity by forcing it to operate at
a lower suction pressure to maintain the desired evaporator
temperature. Oversizing the suction line increases initial project
costs and may result in insu󰀩cient refrigerant gas velocity
to move oil from the evaporator to the compressor. This is
particularly important when vertical suction risers are used.
(More information about designing vertical suction risers is
covered in more detail in “Suction Line Sizing” on page 20)
Suction lines should be sized for a maximum of 2 to 3°F (1.1 to
1.7°C) pressure loss. The actual pressure drop in PSI (kPa) will
depend on the refrigerant.
Suction Line Piping Details
While operating, the suction line is lled with superheated
refrigerant vapor and oil. The oil ows on the bottom of the
pipe and is moved along by the refrigerant gas owing above
it. When the system stops, the refrigerant may condense in the
pipe depending on the ambient conditions. This may result in
slugging if the liquid refrigerant is drawn into the compressor
when the system restarts.
To promote good oil return, suction lines should be pitched
1/8 inch per foot (10.4 mm/m) in the direction of refrigerant
ow. Evaporator connections require special care because
the evaporator has the potential to contain a large volume of
condensed refrigerant during o󰀨 cycles. To minimize slugging
of condensed refrigerant, the evaporators should be isolated
from the suction line with an inverted trap as shown in Figure 7
and Figure 8 on page 12.
The trap should extend above the top of the evaporator before
leading to the compressor.
1. With multiple evaporators, the suction piping should be
designed so that the pressure drops are equal and the
refrigerant and oil from one coil cannot ow into another
coil.
2. Traps may be used at the bottom of risers to catch
condensed refrigerant before it ows to the compressor.
Intermediate traps are unnecessary in a properly sized
riser as they contribute to pressure drop.
3. Usually with commercially produced air conditioning
equipment, the compressors are “pre-piped” to a
common connection on the side of the unit.
4. Suction line lter-driers are available to help clean the
refrigerant before it enters the compressor. Because
they represent a signicant pressure drop, they should
only be added if circumstances require them, such as
after compressor burnout. In this instance, the suction
lter drier is often removed after the break-in period for
the replacement compressor. Suction lter-driers catch
signicant amounts of oil, so they should be installed per
the manufacturer’s specications to promote oil drainage.

AG 31-011 • REFRIGERANT PIPING DESIGN 12 www.DaikinApplied.com
Figure 7: Remote Evaporator Piping Detail
Figure 8: Suction Piping Details
Inverted trap
only required if
there are
evaporators
upstream
Trap to protect
TX valve
from liquid line
Slope in
direction of the
refrigerant flow
Slope in
direction of
refrigerant flow
Trap to protect
TX valve bulb
from liquid
refrigerant
Compressor Above Coil
Slope in
direction of
refrigerant flow
Trap above
coil height not
required with
pumpdown
systems
Compressor Below Coil
Slope in
direction of
refrigerant flow
No inverted trap
required if
properly sloped
Trap to protect
TX valve bulb
from liquid
refrigerant
Compressor Above Coil

www.DaikinApplied.com 13 AG 31-011 • REFRIGERANT PIPING DESIGN
Discharge Lines
Discharge gas lines (often referred to as hot gas lines) allow
refrigerant to ow from the discharge of the compressor to the
inlet of the condenser. Undersizing discharge lines will reduce
compressor capacity and increase compressor work. Over
sizing discharge lines increases the initial cost of the project
and may result in insu󰀩cient refrigerant gas velocity to carry oil
back to the compressor.
Discharge lines should be sized for no more than 2 to 3°F (1.1
to 1.7°C) pressure loss. The actual pressure drop in PSI will
depend upon the refrigerant. Figure 9 illustrates how capacity
and power consumption are a󰀨ected by increasing pressure
drop for both discharge and suction lines. Although these
curves are based on an R-22 system, similar a󰀨ects occur with
other refrigerants.
Figure 9: Capacity and Performances versus Pressure Drop
Approx. E󰀨ect of Gas Line Pressure Drops on R-22 Compressor Capacity & Power – Suction Line
Approx. E󰀨ect of Gas Line Pressure Drops on R-22 Compressor Capacity & Power – Discharge Line
Approx. Effect of Gas Line Pressure Drops on R-22 Compressor Capacity & Power – Suction Line
92
94
96
98
100
102
104
106
108
110
00.5 11.5 22.5 33.5 4
Line Loss, oF
%
Power
Capacity
Approx. Effect of Gas Line Pressure Drops on R-22 Compressor Capacity & Power – Discharge Line
96
98
100
102
104
106
108
00.5 11.5 22.5 33.5 4
Line Loss, oF
%
Power
Capacity

AG 31-011 • REFRIGERANT PIPING DESIGN 14 www.DaikinApplied.com
Discharge Line Piping Details
Discharge lines carry both refrigerant vapor and oil. Since
refrigerant may condense during the OFF cycle, the piping
should be designed to avoid liquid refrigerant and oil from
owing back into the compressor. Traps can be added to the
bottom of risers to catch oil and condensed refrigerant during
OFF cycles, before it ows backward into the compressor.
Intermediate traps in the risers are unnecessary in a properly
sized riser as they increase the pressure drop. Discharge lines
should be pitched 1/8 inch per foot (10.4 mm/m) in the direction
of refrigerant ow towards the condenser (Figure 10).
Whenever a condenser is located above the compressor,
an inverted trap or check valve should be installed at the
condenser inlet to prevent liquid refrigerant from owing
backwards into the compressor during OFF cycles. In some
cases (i.e. with reciprocating compressors), a discharge mu󰀪er
is installed in the discharge line to minimize pulsations (that
cause vibration). Oil is easily trapped in a discharge mu󰀪er, so
it should be placed in the horizontal or downow portion of the
piping, as close to the compressor as possible.
Figure 10: Discharge Line Piping Details
Slope in
direction of
refrigerant flow
Keep trap at
bottom of riser
as small
as possible

www.DaikinApplied.com 15 AG 31-011 • REFRIGERANT PIPING DESIGN
Multiple Refrigeration Circuits
For control and redundancy, many refrigeration systems
include two or more refrigeration circuits. Each circuit must
be kept separate and designed as if it were a single system.
In some cases, a single refrigeration circuit serves multiple
evaporators, but multiple refrigeration circuits should never
be connected to a single evaporator. A common mistake is
to install a two circuit condensing units with a single circuit
evaporator coil.
Figure 11 shows common DX coils that include multiple
circuits. Interlaced is the most common. It is possible to have
individual coils, each with a single circuit, installed in the same
system and connected to a dedicated refrigeration circuit.
While most common air conditioning applications have one
evaporator for each circuit, it is possible to connect multiple
evaporators to a single refrigeration circuit.
Figure 12 shows a single refrigeration circuit serving two
DX coils. Note that each coil has its own solenoid and
thermal expansion valve. There should be one TX valve for
each distributor. Individual solenoids should be used if the
evaporators will be operated independently (i.e. for capacity
control). If both evaporators will operate at the same time, then
a single solenoid valve in a common pipe may be used.
If the two evaporators serve a common airstream, then one
solenoid valve serving both evaporators is su󰀩ciant at point
“X” in Figure 12.
Figure 11: DX Coils with Multiple Circuits
Figure 12: Two Evaporators on a Common Refrigeration
Circuit
Refrigerant
(In)
Refrigerant
(In)
Refrigerant
(In)
Refrigerant
(Out)
Face Control Row Control Interlaced
Refrigerant
(Out)
Refrigerant
(Out)
TX
Valve
Solenoid
Valve
Filter-
Drier
Sight
Glass
Suction
Line
Liquid
Line
External
Equalization
Line
Bulb mounted
on horizontal pipe,
close to coil to
avoid mounting
in traps
Slope in direction
of refrigerant flow
Trap to protect
TX Valve bulb
from liquid
refrigerant
X

AG 31-011 • REFRIGERANT PIPING DESIGN 16 www.DaikinApplied.com
Sizing Refrigerant Lines
Refrigerant Capacity Tables
Appendix 2 (page 40) and Appendix 3 (page 59) provide
refrigerant line sizes for commonly used refrigerants. There
is data for suction, discharge, and liquid lines. Suction and
discharge lines have data for 0.5, 1, and 2°F (0.28, 0.56,
and 1.7°C) changes in saturated suction temperature (SST).
Liquid lines are based on 1°F (0.56°C) changes in saturation
temperature.
The data is based on 105°F (40.6°C) condensing temperature
(common for water-cooled equipment) and must be corrected
for other condensing temperatures (air-cooled equipment is
typically 120 to 125°F [48.9 to 51.7°C]). The tables are also
based on 100 feet (30.5 m) of equivalent length. The actual
pressure drop is estimated based on the actual equivalent
length of the application using equations in the footnotes of the
refrigerant capacity tables.
Tip: Saturated suction temperature is based upon the pressure leaving the evaporator and represents
the refrigerant temperature as a gas without superheat. The actual refrigerant temperature leaving the
evaporator will be higher than this. The dierence between the two temperatures is called superheat.

www.DaikinApplied.com 17 AG 31-011 • REFRIGERANT PIPING DESIGN
Equivalent Length for Refrigerant Lines
Table 5 and Table 6 on page 41 in Appendix 2 (page 40)
provide information for estimating equivalent lengths. The
actual equivalent length is estimated by calculating the path
length in feet (meters) that the piping will follow and adding
the pressure drops of the ttings and/or accessories along that
length. The tables provide pressure drops in equivalent feet of
straight pipe for ttings and accessories.
For example, in Table 5, we see that a 7/8-inch (22 mm) long
radius elbow has a pressure drop equivalent to 1.4 feet (0.43
m) of straight copper pipe.
How to Determine Equivalent Length
Calculate the equivalent length of the liquid line for the
following condensing unit with DX air-handling unit:
The liquid line is composed of the following elements:
• 22 ft (6.7 m) of 1-3/8 inch (35 mm) piping
• 7 long radius elbows
• 1 lter drier
• 1 sight glass
• 1 globe type isolating valve
To determine the equivalent length for the refrigerant
accessories use Table 5 and Table 6).
Item Quantity Dimension, ft (m) Total, ft (m)
Long radius elbow 7 2.3 (0.70 m) 16.1 (4.90 m)
Filter-drier 1 35 (10.70 m) 35 (10.70 m)
Sight glass 1 2.5 (0.76 m) 2.5 (0.76 m)
Globe valve 1 38 (11.58 m) 38 (11.58 m)
Piping 1 22 (6.70 m) 22 (6.70 m)
Total 113.6 (34.64 m)
Liquid
Line

AG 31-011 • REFRIGERANT PIPING DESIGN 18 www.DaikinApplied.com
How to Size Liquid Lines
Size the refrigerant liquid lines and determine the sub-cooling
required to avoid ashing at the TX valve for the condensing
unit with DX air-handling unit shown in the previous example.
The system:
• Uses R-410A
• Has copper pipes
• Evaporator operates at 40°F (4.4°C)
• Condenser operates at 120°F (48.9°C)
• Capacity is 60 tons (211 kW)
• Liquid line equivalent is 113.6 ft (34.64 m)
• Has a 20 ft (6.1 m) riser with the evaporator above the
condenser
Step 1 – Estimate Pipe Size
To determine the liquid line pipe size for a 60 ton unit, use
Table 9 in Appendix 2. According to the table, a 1-3/8 inch (35
mm) pipe will work for a 79.7 ton (280 kW) unit. Note, the table
conditions (equivalent length and condensing temperature) are
di󰀨erent than the design conditions.
Step 2 – Calculate Actual ∆T
Using Note #5 in the table, we can calculate the saturation
temperature di󰀨erence based upon the design conditions:
Step 3 – Calculate Actual Piping Pressure Drop
According to Table 9, the pressure drop for 1°F (0.56°C)
saturation temperature drop with a 100 ft equivalent length is
4.75 PSI (32.75 kPa).
The actual piping pressure drop is determined using the
equation:
Step 4 – Calculate Total Pressure Drop
Next to determine the Total pressure drop, we use Table 2 on
page 10, and recall that the riser is 20 ft. For R-410A the
pressure drop is 0.43 PSI per ft (9.73 kPa/m).
Total Pressure Drop = Actual Pressure Drop + Riser Pressure Drop
Total Pressure Drop = 3.23 PSI + 8.6 PSI = 11.83 PSI
(Total Pressure Drop = 59.35 kPa + 22.81 kPa = 82.16 kPa
Step 5 – Determine the Saturated Pressure of R-410A at
the TX Valve
Using refrigerant property tables which can be found in
Appendix 2 of Daikin Applied’s Refrigerant Application Guide
(AG 31-007, see www.DaikinApplied.com) the saturated
pressure for R-410A at 120°F is 433 PSIA (absolute) (2985
kPaA). To calculate the saturation pressure at the TX valve, we
take the saturated pressure of R-410A at 120°F and subtract
the total pressure drop.
Saturated PressureTX Valve = Saturated Pressure120°F – Total
Pressure Drop
Saturated PressureTX Valve = 433.0 PSIA – 11.83 PSIA = 421.17 PSIA
(Saturated PressureTX Valve = 2985.0 kPa – 82.15 lPa = 2902.85 kPa)
Step 6 – Determine the Saturation Temperature at the TX
Valve
Referring back to the Refrigeration property tables in
Application Guide 31-007, the saturation temperature at the
TX valve can be interpolated using the saturation pressure at
the TX valve (421 PSIA). The saturation temperature at the TX
valve is found to be 117.8°F
∆TActual = ∆TTable
Actual Length
Table Length
Actual Capacity
Table Capacity
1.8
∆TActual = 1°F
∆TActual = 0.56°C
= 0.68°F
113.6 ft
100.0 ft
60.0 Tons
79.7 Tons
1.8
= 0.39°C
34.64 m
30.48 m
211 kW
280 kW
1.8
Liquid Line — Step 2
Pressure DropActual = Pressure DropTable
∆TActual
∆TTable
Pressure DropActual = 4.75 PSI
Pressure DropActual = 32.75 kPa
= 3.23 PSI
0.68°F
1°F
= 22.81 kPa
0.39°C
0.56°C
Liquid Line — Step 3
Pressure Drop from the Riser = Pressure Drop ×
Total Pressure Drop = Actual Pressure Drop + Riser Pressure Drop
Total Pressure Drop = 3.23 PSI + 8.6 PSI = 11.83 PSI
(Total Pressure Drop = 59.35 kPa + 22.81 kPa = 82.16 kPa)
Saturated PressureTX Valve = Saturated Pressure120°F – Total Pressure Drop
Saturated PressureTX Valve = 433.0 PSIA + 11.83 PSIA = 421.17 PSIA
(Saturated PressureTX Valve = 2985.0 kPa + 82.15 kPa = 2902.85 kPa)
Refrigerant Pressure Drop
ft
Pressure Drop from the Riser = 20.0 ft ×
Pressure Drop from the Riser = 6.1 m ×
= 8.6 PSI
0.43 PSI
ft
= 259.35 kPa
9.73 kPa
m
Liquid Line — Step 4
Liquid Line — Step 5
Subcooling = Actual Saturation Temperature – Saturation TemperatureTX Valve
Subcooling = 120.0°F – 117.8°F = 2.2°F
Liquid Line — Step 7
Subcooling Requirement = TX Valve Temperature + Minimum System Temperature
Subcooling Requirement = 2.2°F + 4.0°F = 6.2°F
Liquid Line — Step 8
∆TActual = ∆TTable
Actual Length
Table Length
Actual Capacity
Table Capacity
1.8
∆TActual = 1°F
∆TActual = 0.56°C
= 0.68°F
113.6 ft
100.0 ft
60.0 Tons
79.7 Tons
1.8
= 0.39°C
34.64 m
30.48 m
211 kW
280 kW
1.8
Liquid Line — Step 2
Pressure DropActual = Pressure DropTable
∆TActual
∆TTable
Pressure DropActual = 4.75 PSI
Pressure DropActual = 32.75 kPa
= 3.23 PSI
0.68°F
1°F
= 22.81 kPa
0.39°C
0.56°C
Liquid Line — Step 3
Pressure Drop from the Riser = Pressure Drop ×
Total Pressure Drop = Actual Pressure Drop + Riser Pressure Drop
Total Pressure Drop = 3.23 PSI + 8.6 PSI = 11.83 PSI
(Total Pressure Drop = 59.35 kPa + 22.81 kPa = 82.16 kPa)
Saturated PressureTX Valve = Saturated Pressure120°F – Total Pressure Drop
Saturated PressureTX Valve = 433.0 PSIA + 11.83 PSIA = 421.17 PSIA
(Saturated PressureTX Valve = 2985.0 kPa + 82.15 kPa = 2902.85 kPa)
Refrigerant Pressure Drop
ft
Pressure Drop from the Riser = 20.0 ft ×
Pressure Drop from the Riser = 6.1 m ×
= 8.6 PSI
0.43 PSI
ft
= 259.35 kPa
9.73 kPa
m
Liquid Line — Step 4
Liquid Line — Step 5
Subcooling = Actual Saturation Temperature – Saturation TemperatureTX Valve
Subcooling = 120.0°F – 117.8°F = 2.2°F
Liquid Line — Step 7
Subcooling Requirement = TX Valve Temperature + Minimum System Temperature
Subcooling Requirement = 2.2°F + 4.0°F = 6.2°F
Liquid Line — Step 8
∆TActual = ∆TTable
Actual Length
Table Length
Actual Capacity
Table Capacity
1.8
∆TActual = 1°F
∆TActual = 0.56°C
= 0.68°F
113.6 ft
100.0 ft
60.0 Tons
79.7 Tons
1.8
= 0.39°C
34.64 m
30.48 m
211 kW
280 kW
1.8
Liquid Line — Step 2
Pressure DropActual = Pressure DropTable
∆TActual
∆TTable
Pressure DropActual = 4.75 PSI
Pressure DropActual = 32.75 kPa
= 3.23 PSI
0.68°F
1°F
= 22.81 kPa
0.39°C
0.56°C
Liquid Line — Step 3
Pressure Drop from the Riser = Pressure Drop ×
Total Pressure Drop = Actual Pressure Drop + Riser Pressure Drop
Total Pressure Drop = 3.23 PSI + 8.6 PSI = 11.83 PSI
(Total Pressure Drop = 59.35 kPa + 22.81 kPa = 82.16 kPa)
Saturated PressureTX Valve = Saturated Pressure120°F – Total Pressure Drop
Saturated PressureTX Valve = 433.0 PSIA + 11.83 PSIA = 421.17 PSIA
(Saturated PressureTX Valve = 2985.0 kPa + 82.15 kPa = 2902.85 kPa)
Refrigerant Pressure Drop
ft
Pressure Drop from the Riser = 20.0 ft ×
Pressure Drop from the Riser = 6.1 m ×
= 8.6 PSI
0.43 PSI
ft
= 259.35 kPa
9.73 kPa
m
Liquid Line — Step 4
Liquid Line — Step 5
Subcooling = Actual Saturation Temperature – Saturation TemperatureTX Valve
Subcooling = 120.0°F – 117.8°F = 2.2°F
Liquid Line — Step 7
Subcooling Requirement = TX Valve Temperature + Minimum System Temperature
Subcooling Requirement = 2.2°F + 4.0°F = 6.2°F
Liquid Line — Step 8

www.DaikinApplied.com 19 AG 31-011 • REFRIGERANT PIPING DESIGN
How to Size Liquid Lines (continued)
Step 7- Determine The Sub-cooling Required for Saturated
Liquid at the TX Valve
The sub-cooling require to have saturated liquid at the TX
valve can be found by:
Subcooling = Actual Saturation Temperature – Saturation
TemperatureTX Valve
Subcooling = 120.0°F – 117.8°F = 2.2°F
Step 8- Determine the Required Sub-cooling for Proper
Operation
2.2°F is the amount of sub-cooling required to have saturated
liquid refrigerant at the TX valve. Anything less, and the
refrigerant will start to ash and the TX valve will not operate
properly. For TX valves to operate properly and avoid
diaphragm uttering, there should be an additional 4°F of sub-
cooling at the TX Valve.
Subcooling Requirement = TX Valve Temperature + Minimum
System Temperature
Subcooling Requirement = 2.2°F + 4.0°F = 6.2°F

AG 31-011 • REFRIGERANT PIPING DESIGN 20 www.DaikinApplied.com
Refrigerant Oil
In the DX refrigeration systems covered by this guide, some
amount of compressor lubricating oil travels with the refrigerant
throughout the piping system. The system design must
promote oil return or the compressor sump will run dry and
damage the compressor.
Recall, refrigerant piping should be pitched to promote
adequate oil return. Fittings and piping layout that traps and
retains oil must be avoided. Compressor capacity reduction
contributes to the challenge of designing the system.
For example, a screw compressor may reduce refrigerant
ow (unload) down to 25%. At this reduced refrigerant ow
rate, the refrigerant velocity is reduced to the point that the oil
may not be pushed through the piping system and back to the
compressor.
Examples of compressors that unload include:
• Scroll compressors often have multiple compressors on a
common refrigeration circuit. The circuit can unload to the
smallest compressor size. For example, 4 equally sized
compressors can unload down to 25%.
• Individual reciprocating compressors unload down to as
low as 33%. There can be multiple compressors on a
common circuit allowing even more unloading.
• Screw compressors may unload down to 25%.
Always check the manufacturer’s information to determine
circuit unloading.
More piping typically requires more oil. This is particularly
true for long liquid lines. Residential split systems are often
pre-charged at the factory with enough oil and refrigerant for
a specied line distance. When that distance is exceeded,
additional refrigerant and oil will be required. For commercial
split systems, the equipment may come pre-charged or it may
be provided with either nitrogen or a small holding charge. The
refrigerant and oil charge is then provided in the eld.
To conrm if more oil is required, the system refrigerant charge
must be calculated. Table 19 on page 50 through Table 22
on page 50 provide the charge per 100 feet(30.5 m) length
for various refrigerants. Generally, the oil charge should be 2
to 3% of the liquid line charge. Consult the manufacturer for
the correct volume of oil in the system and the amount of oil
shipped in the compressor sump. The required oil that needs
to be added is the calculated total oil requirement less the oil
shipped in the equipment.
Required oil = Total oil required – oil shipped in equipment
HFC refrigerants use synthetic POE oils. These oils cannot
be mixed with mineral oils. Refer to the manufacturer’s
instructions for the correct type of oil to use.
Suction Line Sizing
Suction lines contain gaseous refrigerant that moves oil along
the piping and back tothe compressor. Over-sizing suction
pipes increases the initial costs and may reduce the refrigerant
gas velocity to the point where oil is not returned to the
compressor. Recall, under-sizing suction pipes reduces system
capacity. Oil movement is also impacted negatively by risers,
because gravity prevents oil from returning to the compressor.