Daikin RoofPak RPS Series Installation And Maintenance Manual page 37

RFS/RCS Permanent Split Systems
Piping Recommendations
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
buildup. Insulate the liquid line, where located in areas above
ambient temperature, to prevent loss of subcooling and
consequent liquid flashing.
The recommended source for refrigerant piping techniques and
sizing is the Daikin AG31-011 Refrigerant Piping Design Guide.
Although conflicting piping recommendations can be found in
different sources, Daikin 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.
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 lines underground.
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Procedure
1. Use type K or L clean copper tubing. Thoroughly clean or
braze all joints with high temperature solder. Make sure
nitrogen is flowing through the tubes while brazing to
minimize the formation of oxide contaminants.
2. Base piping sizes on temperature/pressure limitations
as recommended in the following paragraphs. Under no
circumstances should pipe size be based strictly upon
coil or condensing unit piping connection size.
3. To determine the minimum tonnage required to carry
oil up suction risers of various sizes, check the vertical
suction risers using
4. Size the liquid line for a pressure drop not to exceed
the pressure equivalent of 2°F (1°C), 6 psi (41.4 kPa)
saturated temperature. The RFS unit includes a factory
installed filter-drier, solenoid valve, and sightglass in each
liquid line, upstream of the thermostatic expansion valve.
Table 10: Minimum Tonnage (R-22 or R-407C) to Carry Oil
Up Suction Riser at 40°F Saturated Suction
Line size O .D .
1-1/8ʺ
1-3/8ʺ
1-5/8ʺ
2-1/8ʺ
2-5/8ʺ
3-1/8ʺ
3-5/8ʺ
4-1/8ʺ
37 IM 926-3 • ROOFPAK APPLIED SYSTEMS
Mechanical Installation
Table 10.
Minimum tonnage
1.5
2.5
3.8
7.6
13.10
20.4
29.7
41.3