Operating instructions

Refrigerant Piping
All field piping, wiring, and procedures must be performed in accordance with ASHRAE, EPA, and
industry standards. Proper refrigerant piping can make the difference between a reliable system and
an inefficient, problematic system.
The primary concerns related to piping are refrigerant pressure drop, a solid liquid feed to the
expansion valves, continuous oil return and properly sized refrigerant specialties.
Insulate the suction line to reduce excessive superheat build-up. Insulate the liquid line, where
located in areas above ambient temperature, to prevent loss of subcooling and consequent liquid
flashing.
A holding charge of R-22 is provided for the evaporator (AGZ-BM) and the outdoor section. The
installer must properly evacuate the piping system and provide the operating charge of R22. Refer to
the piping schematic drawing on page
22 for additional details.
The recommended source for refrigerant piping techniques and sizing is the ASHRAE 2002
Refrigeration Handbook, chapter 2.
Although conflicting piping recommendations can be found in different sources, McQuay offers the
following recommendations for these controversial issues.
The use of double risers for vertical gas risers is generally not required and should be used only as a
last resort to maintain the minimum refrigerant flow to carry oil up the vertical risers. Slightly
downsizing the vertical riser is a preferable option to providing double risers.
Slope the refrigerant lines 1” per 10 feet of horizontal run in the direction of refrigerant flow to assist
oil return.
Resist using hot gas bypass for applications when operation in ambient temperature below 40
degrees is expected. This recommendation helps to maintain adequate condensing pressures and
liquid refrigerant at the expansion valve when condenser capacities are at their maximum.
Pressure drops in the refrigerant lines should be maintained at or below the ASHRAE
recommendations and line lengths should be made as short as possible. Exceeding these
recommendations will decrease performance and could impact reliability.
Small traps should be provided at the base of each major vertical gas riser to assist in the collection
of oil. If vertical risers exceed more than 25 feet, install a small trap at the midpoint and at a
maximum of 20 foot intervals.
Use caution in sizing the liquid line in applications where the evaporator is above the outdoor
section. The weight of the liquid refrigerant in the vertical column will decrease the pressure at the
top of the riser (approximately 0.5 psi per foot of vertical rise) allowing some of the refrigerant to
flash to a gas. Adequate refrigerant subcooling is needed at the outdoor section to prevent large
volumes of refrigerant gas at the expansion valve.
The piping systems should always extend above the highest component in the refrigeration system
before dropping down to make the final refrigerant connections to components. This practice will
hinder the draining of condensed refrigerant to the lower component when normal shutdown
procedures do not occur (such as a power failure).
NOTE: Do not run refrigerant piping underground.
Pumpdown
The pumpdown capacity of ACZ/AGZ units is given in the Physical Data Tables. Care should be
exercised to include all equipment and lines when calculating the system charge relative to the unit’s
pumpdown capacity. The AGZ-BM remote evaporators have an insignificant operating charge.
IMM ACZ/AGZ-4 ACZ / AGZ-BM 23