10
ACZ 010A through 039A
IOMM ACZ1
Add b and c above to obtain the total equivalent feet. Use the ASHRAE table for R22. Suction line
selections are based upon the pressure equivalent of a 2ºF loss per 100 equivalent feet.
Select a line size that displays an equal or slightly larger tons then that determined in a) above.
To determine the actual line loss:
1.
Modify the table tons by the value for the design condensing temperature.
2.
Use the formula in the notes to calculate the line loss in terms of the saturation temperature.
3.
Convert the saturation temperature loss calculated to a pressure drop equivalent using the (Delta)
listed in the table for the comparable delta temperature.
Caution: Excessive pressure drop is undesirable because:
•
It reduces available compressor capacity.
•
It increases power consumed for the net tons realized.
•
It can affect the performance of both the evaporator and the expansion valve previously selected
for the application.
The line loss calculated, expressed in temperature, or PSID pressure drop will be used to establish the
temperature required at the evaporator to produce the required cooling, as well as, the suction
pressure that the compressor must operate at to deliver the required capacity.
Having selected the suction line size, based upon total equivalent length and maximum tons, verify
the line size selected will maintain entrainment of the lubricating oil up any vertical risers at the
minimum tons for the circuit. See d) above, and ASHRAE Tables.
If the line size selected will not maintain satisfactory oil return in a suction riser, the following options
are available:
The vertical length can be sized smaller to accommodate the lower circuit tons at reduced load.
Hot gas bypass can be introduced at the distributor to the evaporator, increasing the volume of gas
available in the suction line to entrain the oil.
An oil separator can be installed in the discharge line.
Note:
In horizontal refrigerant gas lines, oil return to compressors is provided by sizing lines at a
velocity above the minimum recommended and pitching the lines in the direction of refrigerant flow.
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.