AAON M1-011 - Manual (Page 21)

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the liquid lines, the overall efficiency is reduced, and
the system may malfunction.
A pressure loss of 3 psi in the liquid line results in a
1
°F loss of sub-cooling temperature with R-22.
Table 5.1, R-22 Liquid Line Capacity w/ 3 PSI (1 °F)
Pressure Loss per 100 Feet at 100 °F Liquid
Line Size (In.) Max. Tons
1/2 4.0
5/8 7.6
7/8 19.1
Note: The equivalent feet for a piping system must include the
equivalent length of straight tubing for all the fittings, and any valves
that are added to the system.
Suction Line Piping
Suction lines are more critical than liquid lines and
discharge lines from a design and construction
standpoint. The proper return of oil to the
compressor(s) is critical, and depends on maintaining
sufficient velocity in the suction lines to carry the oil
along with the refrigerant gas. Simultaneously, high
refrigerant velocities in the suction line bring high-
pressure losses that reduce capacity.
Suction lines should be sized to:
1. Provide minimum pressure drop at full load,
and
2. return oil from the evaporator to the
compressor under minimum load conditions,
and
3. prevent oil from draining from an active
evaporator into an idle one.
Over sizing of suction lines results in poor oil return to
the compressor. Therefore, minimum suction gas
velocity of 750 fpm in horizontal runs, and 1500 fpm in
vertical runs is necessary.
A pressure drop in the suction line reduces a system’s
capacity because it forces the compressor to operate
at a lower suction pressure to maintain a desired
evaporating temperature in the coil. The suction line is
normally sized to have a pressure drop from friction no
greater than the equivalent of an approximate 2°F
change in saturation temperature.
If oil is entrained up vertical risers at partial loads, and
pipe size must be reduced to provide sufficient gas
velocity, then greater pressure drops are imposed at
full load. These pressure drops can usually be
compensated for by over sizing the horizontal and
down-run lines, and components. As shown in Figure
5.1, a double suction riser may be required in order to
return oil at partial load.
Figure 5.1, Double Suction Riser Example
All vertical suction risers should be checked to confirm
that oil will be returned to the compressor. Use the
tables in this section for pipe sizing information.
Table 5.2, Minimum Tons of Capacity to Carry Oil Up a
Suction Riser at 40
°F Saturated Suction
Line Size (In.) Min. Tons
5/8 .3
7/8 .8
1 1/8 1.6
1 3/8 2.8
1 5/8 4.4
All suction lines must be pitched in the direction of flow
and supported to maintain their position. Full
insulation must be used between the evaporator and
condensing unit.
Suction accumulators are not included with AAON
equipment (except with air source heat pumps), and
must be field furnished and installed if required by job
conditions.
Table 5.3, R-22 Suction Line Capacity w/ 3 PSI (2 °F)
Pressure Loss per 100 Feet at 40 °F Saturated Suction
Line Size (In.) Max. Tons
5/8 1.1
7/8 2.7
1 1/8 5.5
1 3/8 9.3
1 5/8 14.9
Discharge Lines
Discharge (hot-gas) lines should be designed to:
Evaporator
Suction Line to
Compressor