McQuay ACZ 010A, Инструкция по установке, эксплуатации и обслуживанию, Страница: 11 / 48

IOMM ACZ1 ACZ 010A through 039A 11
Figure 6, DX Coil Piping
Condensing Unit Above Coil Condensing Unit Below Coil
EXPANSION VALVE
CONTROL BULB
STRAP TO LINE
AND INSULATE
SUCTION TRAP
SHORT AS
FITTINGS PERMIT
LIQUID TO
COIL
SU
CT
IO
N
PIT
CH
TO
CO
MP
RE
SS
OR
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.