Daikin R22, Refrigerant Piping Design Manual, Page: 27 / 78

www.DaikinApplied.com 27 AG 31-011 • REFRIGERANT PIPING DESIGN
How to Size a Discharge Line (continued)
Step 4 – Calculate the Actual Pressure Drop
The top of Table 7 shows the pressure drop for 1°F (0.56°C)
saturation temperature change with a 100 ft equivalent length
is 3.05 PSI.
A 4-1/8" pipe has 0.86°F temperature drop and a 2.61 PSI
pressure drop which is acceptable for discharge pipe.
Step 5 – Confirm Oil Return At Minimum Load In Riser
Next we evaluate whether the riser size will provide acceptable
oil return at minimum load.
Minimum Capacity = Actual Unit Capacity × Turn Down
Minimum Capacity = 250 Tons × 0.33 = 82.5 Tons
(Minimum Capacity = 879 kW × 0.33 = 290 kW)
The actual discharge refrigerant temperature and condensing
temperature are given as 140°F and 110°F respectively.
The actual SST and superheat are given as 20°F and 15°F
respectively.
Using
Table 15 on page 48 with the above given conditions,
the minimum allowable capacity is 62 tons (218 kW). Since
the minimum system capacity (82.5 tons) is greater than the
minimum riser capacity (62 tons) the riser is acceptable as
designed.
Had the riser been too large for the minimum system capacity,
the discharge riser should have been decreased one pipe size
and Step 5 repeated until an acceptable size was found.
∆ T
Actual
= ∆ T
Table
Actual Length
Table Length
Actual Capacity
Table Capacity
1.8
∆ T
Actual
= 1°F
∆ T
Actual
= 0.56°C
= 0.86°F
110.0 ft
100.0 ft
250.0 Tons
287.0 Tons
1.8
= 0.48°C
35.5 m
30.5 m
879 kW
1009 kW
1.8
Discharge Line — Step 3
Pressure Drop
Actual
= Pressure Drop
Table
∆ T
Actual
∆ T
Table
Pressure Drop
Actual
= 3.05 PSI
Pressure Drop
Actual
= 21.03 kPa
= 2.62 PSI
0.86°F
1°F
= 18.03 kPa
0.48°C
0.56°C
Liquid Line — Step 4