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6/21 57-02611 / 101628 ©2021, Refrigerated Solutions Group™. All rights reserved. 15
SUCTION AND LIQUID LINE SIZES
Liquid Lines
Liquid lines should be sized for a minimum pressure drop to prevent “flashing.” Flashing in the liquid lines
would create additional pressure drop and poor expansion valve operation. If a system requires long liquid
lines from the receiver to the evaporator or if the liquid must rise vertically upward any distance, the losses
should be calculated to determine whether or not a heat exchanger is required. The use of a suction to
liquid heat exchanger may be used to subcool the liquid to prevent flashing. This method of subcooling
will normally provide no more than 20
°
F subcooling on high pressure systems. The amount of subcooling
will depend on the design and size of the heat exchanger and on the operating suction and discharge
pressures. An additional benefit from the use of the suction to liquid type heat exchanger is that it can help
raise the superheat in the suction line to prevent liquid returning to the compressor via the suction line.
Generally, heat exchangers are not recommended on R-22 low temperature systems. However, they have
proved necessary on short, well insulated suction line runs to provide superheat at the compressor.
Refrigerant Piping
Install all refrigerant components in accordance with applicable local and national codes and in
accordance with good practice for proper system operation. The thermostatic expansion valve must be
the externally equalized type. It can be mounted inside the unit end compartment. Mount the
expansion valve bulb on a horizontal run of suction line as close as possible to the suction header. Use
the clamps provided with the valve to fasten the bulb securely so there is a tight line-to-line contact
between the bulb and the suction line. Note postion of bulb. Suction and hot gas connections are made
on outside of unit.
Suction lines should be sloped towards the compressor at the rate of one ½-inch per 10 feet for good oil
return. Vertical risers of more than four (4) feet should be trapped at the bottom with a P-trap. If a P-trap
is used, the expansion valve bulb should be installed between the unit and the trap
Unit Cooler Piping
Pipe size example:
Given: -10°F Freezer with one system having (2) evaporators
• One condensing unit rated at 24,000 BTUH’s @ -20°F SST R404A refrigerant.
• Two evaporators each rated at 12,000 BTUH’s @ 10°F TD.
• 100 feet of actual line run between condensing unit to first evaporator and 20 feet of actual line
run between the first evaporator and the second evaporator (see figure below).
Evaporator 1
Evaporator 2
Lines for multi-evaporator
systems should be as
equidistant as possible
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