Screw Compressor Central Chiller
Chapter 3: Installation
27
Refrigerant Charge Determination
The approximate amount of refrigerant charge required by the system varies based on the
total length of the refrigerant lines and the size of the chiller. Referring to Figure 6,
determine the amount of charge based on discharge and liquid line sizes and lengths. Add
these four numbers together to find the total operating charge.
Figure 6: Refrigerant Charge Determination (per circuit)
Chiller Charge
Air Cooled Condenser
Charge
Field Installed Piping Charge
Horsepower
Lbs. of R134a
Horsepower
Lbs. of R134a
Pipe O.D.
Inches
Discharge
Line
R134a (Lbs.)
Liquid Line
R134a
(Lbs.)
35
20
35
19
7/8”
1.0
24.3
40
25
40
24
1 1/8”
1.7
41.4
50
30
50
29
1 3/8”
2.6
63.0
60
35
60
29
1 5/8”
3.6
89.2
70
40
70
36
2 1/8”
6.3
155.1
80
50
80
43
2 5/8”
9.7
239.2
90
55
90
50
3 1/8”
13.9
341.4
110
65
110
58
3 5/8”
18.8
461.8
4 1/8”
24.4
600.2
Based on 100 feet of pipe, 100°F Liquid, 100°F
Discharge
Verify Correct Charge
The final operating charge must be verified by running the system and checking the liquid
line sight glass as well as the sub-cooling.
The system should have at least enough load to run one compressor fully loaded in order to
properly verify operating charge.
Typical condensing pressure with a full load and 95°F ambient air over the condenser will be
170 PSI or HFC 134a. Each circuit should be charged to maintain 10°F sub-cooling under
these conditions.
