A
CU MANUAL
IOM-14
22 of 46
Feb 06 R4
3.
Selections are based on Equivalent length. Equivalent length is the actual length plus the additional
losses in feet due to fittings. See Table 1 for pressure losses due to fittings.
(If number of fittings is unknown an equivalent length estimate can be made by multiplying the actual
piping run by a complexity factor of 1.5 to 2 times the actual length. 1.5 times for a simple system or
long runs and 2 times for a close coupled system or one with a lot of fittings.)
4.
For compressors or circuits with unloading (Tandem compressors included). Always check tubing sizes
for oil return at the unloaded conditions. Determine the unloaded capacity in tons and verify that the
selected tubing is not larger than maximum riser size at the unloaded capacity.
5.
Selection Criteria to develop table.
Suction line
- PD less than 2°F temperature penalty.
Discharge line - PD less than 2.5°F temperature penalty.
Liquid line
- PD less than 2°F temperature penalty, + (velocity less than 350fpm for liquid hammer).
Condensate line (condenser to receiver if equipped) … velocity less than 115 fpm. (two phase flow)
Maximum riser sizes are the largest recommended tubing sizes for oil return. Sizes are based on 75%
capacity to allow for low load conditions.
For detailed evaluation of piping systems, guidelines and pressure losses consult ASHRAE handbooks.
Refrigeration Table 3
Approximate effect of gas line pressure drop
on compressor capacity and power (ASHRAE
REFRGERATION 2.3)
Line Loss
Capacity
Required Power
Suction
%
%
0°F
100
100
2°F
96.4
104.8
4°F
92.9
108.1
Discharge
%
%
0°F
100
100
2°F
99.1
103.0
4°F
98.2
106.3
Refrigeration Table 4
Weight of refrigerant in liquid lines per 100ft of tubing (100°F)
Liquid
Line
R134a
Lbs (kg)
R407c
Lbs (kg)
R410a
Lbs (kg)
3/8”
3.9 (1.8)
3.6 (1.6)
3.4 (1.5)
1/2”
7.3 (3.3)
6.8 (3.0)
6.2 (2.8)
5/8”
12 (5)
11 (2.3)
10 (4.5)
7/8”
24 (11)
23 (10.4)
21 (9.5)
1 1/8”
41 (19)
39 (18)
36 (16)
1 3/8”
63 (29)
59 (27)
54 (24)
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