Product manual

IOMM ACR/AGR-1 15
Underground Refrigerant Lines
McQuay does not recommend the installation of suction lines underground. If job conditions require
that they be located below ground, a suitable sized suction accumulator must be installed ahead of the
compressor to interrupt liquid refrigerant slugs at start-up.
Long Vertical Riser Installation
Where job conditions require refrigerant gas lifts of more than 25 feet, McQuay recommends the
installation of a short trap half-way up the riser or at not more than 20 feet intervals. These traps are
required to capture and hold small quantities of oil during off cycles.
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 may 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.
4. Liquid line solenoid valves should be located adjacent to the expansion valve with possibly only
a sight glass interposing the two.
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. As the line becomes
heated the pressure will increase so the check valve should include a pressure relief device to relieve
pressure 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.
CAUTION
The liquid line should not include a check valve unless the line also includes an
automatic resetting pressure relief device.
CAUTION
If the relief device being used is relieving from the line to the condenser side of the
check valve, the maximum desirable pressure differential with R-22 refrigerant
is 180 psi, with 134a, 100 psi.
If liquid lines are short, they may be of smaller diameter than the size indicated in the ASHRAE
Refrigerant Handbook, 1998 Edition, Chapter 2, Tables 3 or 4. 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 ten degrees F of subcooling. Each degree represents 3.05 psi with R-22
(or 2.2. psi with R-134a). The liquid line and its refrigerant specialties may have pressure losses