Unit installation

12 ACZ 010A through 039A IOMM ACZ1-2
Liquid Lines
Liquid lines are generally sized for 1 to 2 degree F line losses or their equivalent in pressure
drop. Actual selection can vary based upon the pressure drop expected from refrigerant
specialties such as solenoids, refrigerant driers, valves, etc. piping lifts or risers and the
amount of condenser sub-cooling expected.
The principal concern in sizing and routing liquid lines is assurance that liquid is present in
the line at start-up of the compressor, and that liquid and not vapor is available at the inlet
to the expansion valve during system operation.
Liquid can not be available in a liquid line at start-up if:
1. The solenoid valve is located adjacent to the condenser or condensing unit, remote
from the expansion valve.
2. An excessive length of liquid line is located in a heated ambient and the application
permits migration of the refrigerant to a cold air-cooled condenser.
3. Liquid refrigerant is permitted to gravitate from the liquid line to the condenser because
of the relative location of components.
In the event 2) or 3) above are possible, the application should include a check valve at the
condenser end of the liquid line. The check valve should be a low-pressure drop valve.
The line between the check valve and the solenoid valve can be comparable to a pressure
vessel and as the line becomes heated refrigerant trapped in the confined space will
increase in pressure. The check valve should include a pressure relief devise, relieving
from the line side to the condenser side of the circuit. The relief can be sized for a pressure
differential from 80 to 180 psi, but not more than 180 psi, and should be auto-resetting as
the pressure is relieved.
Liquid line solenoid valves should be located adjacent to the expansion valve with possibly
only a sight glass interposing the two.
If liquid lines are short, they may be of smaller diameter than the size indicated in the
current ASHRAE Refrigerant Handbook. As indicated above, the designer must size the
liquid line to assure that pure liquid will reach the inlet of the expansion valve. If the
condenser is sized to produce 10ºF of subcooling, and each degree represents 3.05 psi with
R-22, the liquid line and its refrigerant specialties can have pressure losses totaling 10 x
3.05 psi (or 10 x 2.2) and still satisfy the objective of delivering pure liquid to the
expansion valve.
In calculating the pressure losses, or gains, note that each foot of rise in a liquid line results
in an approximate 0.5 psi loss. Thus a 10 foot rise represent 5 pounds per square inch loss
in refrigerant pressure, or the equivalent of 1.6ºF subcooling with R-22. Total line losses
will include values for line friction, equivalents for valves and elbows and pressure losses
from manufacturers’ catalogs for driers, solenoids, sight glasses, etc.
When calculating condenser subcooling, note that saturated condensing pressure should be
read at the same point in the system where the liquid refrigerant temperature is obtained.