Multi F Outdoor Unit Engineering Manual

Copper is the only approved refrigerant pipe material for use with LG
Multi F air conditioning products, and LG recommends hard-drawn
rigid type “K” or “L”, or annealed-tempered, copper pipe.
•Drawn temper (rigid) ACR copper tubing is available in sizes 3/8
through 2-1/8 inches (ASTM B 280, clean, dry, and capped).
•Annealed temper (soft) ACR copper tubing is available in sizes 1/4
through 2-1/8 inches (ASTM B 280, clean, dry, and capped).
Tube wall thickness should meet local code requirements and be
approved for an operating pressure of 551 psi. If local code does
not specify wall thickness, LG suggests using tube thickness per the
table below. When bending tubing, use the largest radii possible
to reduce the equivalent length of installed pipe; also, bending radii
greater than ten (10) pipe diameters can minimize pressure drop. Be
sure no traps or sags are present when rolling out soft copper tubing
coils.
OD (in)
1/4 3/8 1/2 5/8 3/4
Material
Rigid Type “K” or “L” -
Soft ACR Acceptable
Rigid Type “K” or “L” Only
Min. Bend
Radius (in)
.563 .9375 1.5 2.25 3.0
Min. Wall
Thickness (in)
.031 .031 .031 .039 .039
Table 173: ACR Copper Tubing Material.
Type
Seamless Phosphorous Deoxidized
Class
UNS C12200 DHP
Straight Lengths
H58 Temper
Coils
O60 Temper
Table 174: Piping Tube Thicknesses.
Under normal operating conditions, the vapor pipe temperature of a
Multi F system can vary as much as 280°F. With this large
variance in pipe temperature, the designer must consider pipe
expansion and contraction to avoid pipe and fitting fatigue failures.
Refrigerant pipe, along with the insulation jacket, form a cohesive
unit that expands and contracts together. During system operation,
thermal heat transfer occurs between the pipe and the surrounding
insulation.
If the pipe is mounted in free air space, no natural restriction to
movement is present if mounting clamps are properly spaced and
installed. When the refrigerant pipe is mounted underground in a
utility duct stacked among other pipes, natural restriction to linear
movement is present. In extreme cases, the restrictive force of
surface friction between insulating jackets could become so great
that natural expansion ceases and the pipe is “fixed” in place. In this
situation, opposing force caused by change in refrigerant fluid/vapor
temperature can lead to pipe/fitting stress failure.
The refrigerant pipe support system must be engineered to allow
free expansion to occur. When a segment of pipe is mounted
between two fixed points, provisions must be provided to allow pipe
expansion to naturally occur. The most common method is the
inclusion of expansion Loop or U-bends. See Figure 55 on page
205. Each segment of pipe has a natural fixed point where no
movement occurs. This fixed point is located at the center point
of the segment assuming the entire pipe is insulated in a similar
fashion. The natural fixed point of the pipe segment is typically
where the expansion Loop or U-bend should be. Linear pipe
expansion can be calculated using the following formula:
1. From Table 175, find the row corresponding with the actual length
of the straight pipe segment.
2. Estimate the minimum and maximum temperature of the pipe.
In the column showing the minimum pipe temperature, look up the
anticipated expansion distance. Do the same for the maximum
pipe temperature.
3. Calculate the difference in the two expansion distance values.
The result will be the anticipated change in pipe length.
Example:
A Multi F MAX system is installed and the design shows that there
is a 100 foot straight segment of tubing between a Y-branch and
a branch distribution unit. In heating, this pipe transports hot gas
vapor to the indoor units at 120°F. In cooling, the same tube is a
suction line returning refrigerant vapor to the outdoor unit at 40°F.
Look up the copper tubing expansion at each temperature and calcu-
late the difference.
Vapor Line
Transporting Hot Vapor: 100 ft. pipe at 120°F = 1.40 in.
Transporting Suction Vapor: 100 ft. pipe at 40°F = 0.40 in.
AnticipatedChangeinLength:1.40in.–0.40in.=1.00in.
Liquid Line
The liquid temperature remains the same temperature; only the
direction of flow will reverse. Therefore, no significant change in
length of the liquid line is anticipated.
When creating an expansion joint, the joint height should be a
minimum of two times the joint width. Although different types of
expansion arrangements are available, the data for correctly sizing
an Expansion Loop is provided in Table 176. Use soft copper with
long radius bends on longer runs or long radius elbows for shorter
pipe segments. Using the anticipated linear expansion (LE) distance
calculated, look up the Expansion Loop or U-bend minimum design
dimensions. If other types of expansion joints are chosen, design
per ASTM B-88 Standards.
LE = C x L x (T
r
–T
a
) x 12
LE = Anticipated linear tubing expansion (in.)
C = Constant (For copper = 9.2 x 10
-6
in./in.°F)
L = Length of pipe (ft.)
T
R
= Refrigerant pipe temperature (°F)
T
a
= Ambient air temperature (°F)
12 = Inches to feet conversion (12 in./ft.)
Selecting Field-Supplied Copper Tubing
Copper Expansion and Contraction
REFRIGERANT PIPING DESIGN
Due to our policy of continuous product innovation, some specications may change without notication.
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204 | DESIGN & PRACTICES
Multi F and Multi F MAX Heat Pump System Engineering Manual
MULTI
F
MAX
MULTI
F