21
General Installation Guidelines
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Under normal operating conditions, the vapor pipe temperature of a
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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 mounted in the horizontal
plane. When expansion loops are placed in a vertical riser, the loop
is to be formed in a horizontal fashion resulting in a torsional move-
ment during expansion and contraction. 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 12, find the row corresponding with the actual length
of the straight pipe segment.
2. Estimate the minimum and maximum temperature of the pipe
typical pipe temperature change range: High Pressure Vapor:
ambient temperature to 215°F; Low Pressure Vapor: ambient to
35°F; Liquid pipe: ambient, 80°F, 110°F. Choose the two most
extreme. 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.
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there is a 260 feet straight segment of tubing between a Y-branch
and an indoor unit. The system operates 24 hours per day. In heat-
ing, 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 calculate the difference.
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Transporting Hot Vapor: 260 ft. pipe at 120°F = 3.64 in.
Transporting Suction Vapor: 260 ft. pipe at 40°F = 1.04 in.
Anticipated Change in Length: 3.64 in. – 1.04 in. = 2.60 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 depth 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 13. 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
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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.)
Copper Expansion and Contraction
Piping Preparation
GENERAL INSTALLATION GUIDELINES
